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What is strabismus

Strabismus (also called squint or lazy eye) is a misalignment of the yes often at birth,with extraocular muscle imbalance often associated with uncorrected hypermetropic refractive error.

What causes Strabismus

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What are the symptoms of strabismus

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How is strabismus treated

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What is Strabismus

Strabismus (also called squint or lazy eye) is a misalignment of the yes often at birth,with extraocular muscle imbalance often associated with uncorrected hypermetropic refractive error.

How is vision affected?

If one eye becomes favoured it can become dominant and  suppress the effect of the other eye vision integrating in the brain .To stop confusion, the brain will sometimes ignore part of the image from one eye.

 

Signs and symptoms

Common signs can include closing one eye, clumsiness, an unusual head position,misaligned eyes , double or blurred vision and difficulty reading.

How is the condition diagnosed?

It is normal for a baby’s eyes to look misaligned for short periods of time up to the age of four months but full assesment is required.

What is the treatment?

Treatment aims to improve the alignment of the eyes and to bring back, or protect, normal vision. Treatment can include glasses, patching, eye drops, eye muscle surgery and eye exercises.

 glasses, prisms, patching or blurring of one eye, botulinum toxin injections, or a combination of these treatments. Other times, eye muscle surgery is necessary to straighten the eyes.

In children with some types of constant strabismus, early surgery may be recommended to improve the chance of restoring or promoting normal binocular vision.

In adults, eye alignment surgery is not strictly cosmetic.

In strabismus surgery, one or more of the eye muscles are strengthened, weakened or moved to a different position to improve alignment.  Prisms are used to measure the degree of the strabismus.

 

Adjustable sutures

In standard strabismus surgery, the muscle is weakened, strengthened or moved and a permanent knot is placed. In adults, there is the added advantage that an adjustable suture can be used. Instead of a permanent knot, a temporary knot is placed. After the surgery, with the patient awake, alignment can be reassessed, and if necessary, adjustments can be made before a permanent knot is placed to minimize the chance of an over-correction or under-correction.

 Patching or blurring the strong eye to improve amblyopia is often necessary.

 

• For accommodative esotropia, glasses reduce the focusing effort and often straighten the eyes. Sometimes bifocals are needed for close work. If significant crossing of the eyes persists with the glasses, surgery may be required.

Very young  often have a wide, flat nose and a fold of skin at the inner eyelid that can make eyes appear crossed. This appearance of pseudostrabismus may improve as the child grows. 

• Six eye muscles, controlling eye movement, are attached to the outside of each eye. In each eye, one muscle moves in the eye to the right, and one muscle moves the eye to the left. The other four muscles move it up or down and at an angle.

To line up and focus both eyes on a single target, all of the muscles in each eye must be balanced and working together. In order for the eyes to move together, the muscles in both eyes must be coordinated. The brain controls these muscles.

With normal vision, both eyes aim at the same spot. The brain then combines the two pictures into a single, three-dimensional image. This three-dimensional image gives us depth perception.

 

Adults who develop strabismus often have double vision because their brains have already learned to receive images from both eyes and cannot ignore the image from the turned eye. A child generally does not see double.

Strabismus is especially common among children with disorders that may affect the brain, such as:

o Cerebral palsy;

o Down syndrome;

o Hydrocephalus;

o Brain tumors;

o Prematurity.

 

Good vision develops during childhood when both eyes have normal alignment. Strabismus may cause reduced vision, or amblyopia, in the misaligned eye.

 Strabismic amblyopia occurs in approximately half of the children who have strabismus.

Amblyopia can be treated by patching or blurring the stronger eye to strengthen and improve vision in the weaker eye. If amblyopia is detected in the first few years of life, treatment is usually successful. If treatment is delayed, amblyopia may become permanent. As a rule, the earlier amblyopia is treated, the better the result for vision.

 It may run in families; however, many people with strabismus have no relatives with the problem.

Infantile esotropia, where the eye turns inward, is a common type of strabismus in infants. Young children with esotropia cannot use their eyes together. Accommodative esotropia is the most common form of esotropia that occurs in children usually 2 years or older. In this type of strabismus, when the child focuses the eyes to see clearly, the eyes turn inward. This crossing may occur when focusing at a distance, up close or both.

Exotropia. Notice the outward-

turning eye.

Exotropia, or an outward-turning eye, is another common type of strabismus. This occurs most often when a child is focusing on distant objects. The exotropia may occur only from time to time, particularly when a child is daydreaming, ill or tired. Parents often notice that the child squints one eye in bright sunlight.

 

One eye or both eyes may turn either inward (esotropia), outward (exotropia), upward (hypertropia) or downward (hypotropia). Strabismus may be constant or intermittent.

Strabismus is one of the most common eye conditions in children, affecting up to 5% of the Australian population.

Causes and risk factors

Whilst the causes of strabismus are not completely understood it is known that abnormalities in the muscles and nerves surrounding the eyes are both contributing factors.

 

Early diagnosis is essential in preventing vision loss.

Amblyopia

Amblyopia, commonly known as ‘lazy eye’, is the loss of vision caused by strabismus if left untreated. When a person with a strabismus looks at an object the brain receives two different images and this can confuse the brain. In children, the brain may learn to ignore the double image from the turned eye. This constant ignoring of the image from one eye during a child’s visual development can result in poor vision. Untreated, the vision will remain poor.

In most cases amblyopia can be successfully treated before the age of nine, it is therefore important to diagnose and treat this condition early on.

3D Vision

Strabismus and amblyopia can also interfere with the development of 3D vision (depth perception). Early treatment can improve the likelihood of depth perception developing in a young child.

Symptoms

The symptoms of strabismus may be constant or intermittent, and include;

• crossed eyes,

• double vision,

• uncoordinated eye movements,

• vision loss,

• loss of depth perception.

 

• Inward turning is called esotropia

• Outward turning is called exotropia

• Upward turning is called hypertropia

• Downward turning is called hypotropia.

Other classifications of strabismus include:

• The frequency with which it occurs—either constant or intermittent

• Whether it always involves the same eye—unilateral

• If the turning eye is sometimes the right eye and other times the left eye—alternating.

Treatment for strabismus may include eyeglasses, prisms, vision therapy, or eye muscle surgery. If detected and treated early, strabismus can often be corrected with excellent results.

What causes strabismus?

 

• Family history. People with parents or siblings who have strabismus are more likely to develop it.

• Refractive error. People who have a significant amount of uncorrected farsightedness (hyperopia) may develop strabismus because of the additional eye focusing they must do to keep objects clear.

• Medical conditions. People with conditions such as Down syndrome and cerebral palsy or who have suffered a stroke or head injury are at a higher risk for developing strabismus.

Many types of strabismus can develop in children or adults, but the two most common forms are:

• Accommodative esotropia often occurs because of uncorrected farsightedness (hyperopia). The eye’s focusing system is linked to the system that controls where the eyes point. So people who are farsighted are focusing extra hard to keep images clear. This may cause the eyes to turn inward. Symptoms of accommodative esotropia may include seeing double, closing or covering one eye when doing close work, and tilting or turning the head.

• Intermittent exotropia may develop when a person cannot coordinate both eyes together. The eyes may point beyond the object being viewed. People with intermittent exotropia may experience headaches, difficulty reading and eye strain. They also may close one eye when viewing at distance or in bright sunlight.

 

• Alignment and focusing testing. Your optometrist needs to assess how well your eyes focus, move and work together. In order to obtain a clear, single image of what you are viewing, your eyes must effectively change focus, move and work in unison. This testing will look for problems that keep your eyes from focusing effectively or make it difficult to use both eyes together.

• Examination of eye health. Using various testing procedures, your optometrist will observe the internal and external structures of your eyes to rule out any eye disease that may be contributing to strabismus. This testing will determine how the eyes respond under normal seeing conditions. For patients who can’t respond verbally or when some of the eyes focusing power may be hidden, your optometrist may use eye drops. The eye drops temporarily keep the eyes from changing focus during testing.

Using the information obtained from these tests, along with 

Treatment

Early diagnosis of strabismus is essential in preventing irreversible vision loss later in life. Strabismus treatment aims to improve the alignment of the eyes and to correct the resulting vision loss (amblyopia).

Strabismus and amblyopia can be treated with any one or a combination of glasses, eye patching or surgery.

The Lions Eye Institute understands that every child’s case is different to another, with its own set of unique challenges. Therefore, tailored treatment strategies for each child are established.

The Lions Eye Institute also conducts an array of Clinical Trials. You can view these on our Clinical Trials page.

Strabismus surgery

Surgery involves moving one or more of the eye muscles in order to adjust the position of the eye(s). The procedure is undertaken in an operating room under a general anesthetic. There are no bandages, with only mild discomfort and redness for a few days. Usually, the patient is ready to go home on the same day.

Australian and international references

www.childrenshospital.org

www.aapos.org

www.cera.org.au

www.nlm.nih.gov

www.chp.edu

Strabismus Inheritance Study

Who is conducting the study?

Professor David Mackey from the Lions Eye Institute and Professor Elizabeth Engle at Children’s Hospital Boston, in conjunction with ophthalmologists from across Australia and the USA. The project is being coordinated by the research team at the Centre for Eye Research Australia (CERA).

Purpose of the study

The research team are investigating the possible genes involved in the development of strabismus and associated eye conditions e.g. wearing glasses, poor depth perception. Families with a strong history of strabismus are of particular interest to the research team.

trabismus (‘squint’) is a common childhood disorder that can cause psychosocial distress and permanent functional disability. Early diagnosis is important to maximise visual rehabilitation and reduce the risk of amblyopia. There is currently no national Australian screening program for strabismus, which makes it important for all general practitioners (GPs) to master practical skills for evaluating this condition. GPs should also be aware of red flags in a history and examination that necessitate prompt investigation and management.

Objective/s

This article reviews practical screening tests to identify childhood strabismus, and discusses a framework for timely intervention.

Discussion

A comprehensive history is used to distinguish between primary and acquired strabismus. The four tests used to screen for stra-bismus are the light reflex test, the red reflex test, the cover test and the uncover test. Any child diagnosed with strabismus should be referred to an ophthalmologist for further assessment.

Strabismus is a common disorder of ocular alignment that affects 2–4% of children.1 It is commonly referred to as a ‘squint’ or ‘lazy eye’. The most debilitating consequence of untreated strabismus is the development of amblyopia (permanent loss of best corrected visual acuity in a structurally healthy eye).2,3 This is because abnormal visual experience during critical periods of early neurodevelopment result in downregulation of the neural pathway to the brain’s visual cortex.2 After the age of 9 years, these pathways may never be recovered even if normal visual function is restored.4 Strabismus also significantly affects quality of life, with lifelong cosmetic disability that may result in poor self-esteem, social prejudice and restricted career opportunities.5

Early detection and treatment improves vision outcomes and psychosocial wellbeing for children with strabismus. Nonetheless, many cases of strabismus go unrecognised. As patients with paediatric strabismus usually present before school age (with an average onset at 1–4 years), population-based pre-school screening programs have been advocated as a way to reduce the rate of untreated strabismus and amblyopia.3,6 Nonetheless, the cost–benefit value of these public health programs is the subject of ongoing debate,6 and the lack of a national Australian screening program necessitates that individual assessment of children currently falls into the realms of primary care clinicians, such as general practitioners (GPs), and maternal and child health nurses. For this reason, GPs should be alert to this common problem and be familiar with practical screening tests that may unmask situations requiring specialist referral.

Causes of strabismus

Strabismus can be either primary or secondary (acquired). Common causes of childhood strabismus are listed in Table 1. Recognised risk factors for primary strabismus include a family history of strabismus, premature birth and a low birth weight.7Secondary strabismus is often associated with neurological pathology, such as intracranial tumours, head trauma, infection and autoimmune disorders.1

Table 1. Common causes of strabismus1

Primary causes of strabismus Secondary causes of strabismus

Idiopathic strabismus

Congenital syndromes Cranial nerve palsies (CNIII, IV, VI) 

Orbital fracture

Intracranial bleed

Intracranial/intraorbital/intraocular mass (benign or malignant)

Intracranial infection

Grave’s disease

Myasthenia gravis

Diabetes mellitus

Amblyopia

Toxins and heavy metal poisoning

Post-vaccination

Amblyopia is a recognised consequence of established strabismus (either primary or secondary). However, amblyopia can paradoxically also be a cause of secondary strabismus, as a degraded visual experience in one eye may result in that eye drifting out of correct alignment.3 Uncorrected refractive abnormalities, such as myopia and hyperopia, may also result in secondary strabismus via a similar mechanism.6

Types of strabismus

The most common type of strabismus involves horizontal misalignment of the eyes, although vertical misalignment also occurs.7 Ocular deviation may be manifest (tropia) or latent (phoria). Manifest ocular deviation can be present in all directions of gaze (comitant) or only present in specific directions of gaze (incomitant) (Table 2).

Table 2. Strabismus terminology1

Terminology

eso- = Nasal horizontal deviation (relative to fixing eye)

exo- = Temporal horizontal deviation (relative to fixing eye)

hyper- = Superior vertical deviation (relative to fixing eye)

hypo- = Inferior vertical deviation (relative to fixing eye)

tropia = Manifest disorder of ocular alignment

phoria = Latent disorder of ocular alignment

comitant = Ocular deviation present in all directions of gaze

incomitant = Ocular deviation only present in specific directions of gaze

amblyopia = Clinically defined as a 2-line difference from best corrected visual acuity in a structurally healthy eye

Manifest symptoms may be either constant or intermittent. Intermittent strabismus can follow a fluctuating course, with symptoms often exaggerated by fatigue. Symptoms may also vary over time, and ocular misalignment that seemed well controlled in early childhood may become more apparent and frequent as the patient grows older.7 For this reason, all patients with a known diagnosis of strabismus require ongoing evaluation.

Differential diagnosis

The most common differentials for strabismus in a general practice setting are ocular instability of infancy and pseudostrabismus.

Newborns often present with unsteady ocular alignment, which is referred to as ocular instability of infancy. This may last up to 3 months and usually presents as a lateral ocular deviation of less than 15°. Any ocular deviation greater than 15° or persisting for more than 3 months is considered abnormal.3

Pseudostrabismus is a condition where unusual facial architecture creates the optical illusion of strabismus, such as when telecanthus (a broad nasal bridge) or epicanthal folds obscure the nasal sclera. If in doubt, a GP is advised to refer the patient to a specialist for assessment.

History

The history aims to distinguish between primary and secondary causes of strabismus, and to screen for red flag features suggesting recent trauma or serious intracranial pathology. New strabismus in a school-aged child is uncommon and necessitates further neurological investigations.3

The key areas on history to explore include the obstetric and developmental history. The medical history should include a focus on any history of malignancy or autoimmune conditions, exposures, vaccinations, and whether the child has been generally well or if there has been unexplained illness. Any history of trauma, particularly to the head, orbit or periorbital area should be elicited.

In regards to vision, any previous visual testing and the outcome are relevant. A detailed history of the onset of symptoms, including any associated signs, such as gait disturbance, nystagmus, decreased visual acuity or diplopia is relevant. The pattern of symptoms is important, such as whether the strabismus is constant or intermittent. If intermittent, consider whether the symptoms have been changing in frequency, and whether they are dependent on direction of gaze, or exaggerated by fatigue.

Screening tests

In the general practice setting, screening for strabismus involves four practical tests: the light reflex test, the red reflex test, the cover test and the uncover test.1 The only equipment required is a direct ophthalmoscope and a torchlight.

The light reflex test1

The child is placed on their parent’s lap. The doctor stands at a distance of 1 m in front of the child, holding a small light. The child’s attention is directed to the light. The position of the light’s reflection in each of the child’s eyes is noted and compared. Normal ocular alignment will generate an identical light reflection in each eye. Deflection of the light reflex indicates abnormal ocular alignment, with each 1 mm of deflection equivalent to 15–20 prism diopters deviation (Figure 1).

Figure 1. The light reflex test

The red reflex test1

The doctor stands at a distance of 0.5 m in front of the child, holding a direct ophthalmoscope (set at 0). The child’s attention is directed to the ophthalmoscope and the doctor attempts to visualise the red reflex of both eyes simultaneously. Both red reflexes should be identical. Inequality in size, shape or colour is abnormal (Figure 2).

Figure 2. The red reflex test

The cover test1,8

The doctor stands in front of the child and directs the child’s attention to a target (eg. a light or a toy). The doctor covers one of the child’s eyes and closely observes the uncovered eye for corrective movement. When the fixating normal eye is covered, a manifest abnormal eye must move from its deviated position and take up correct fixation. Accordingly, movement indicates that manifest strabismus is present in the uncovered eye (a tropia). The cover test is repeated on each eye (Figure 3).

Figure 3. The cover test

The uncover test1

The doctor covers one of the child’s eyes for 5 seconds and directs the child’s attention to a target. The cover is then quickly removed. The newly uncovered eye is closely observed for corrective movement. A latent abnormal eye will drift into a deviated position when covered. After it is uncovered, the abnormal eye must then return to correct fixation. Accordingly, movement indicates that latent strabismus is present in the newly uncovered eye (a phoria). The uncover test is repeated on each eye (Figure 4).

Figure 4. The uncover test

Management of strabismus

All paediatric patients with newly diagnosed strabismus require timely referral to an ophthalmologist for a comprehensive assessment of visual function. Any patient with red flags on history or examination should be referred urgently for specialist investigation.

Specific visual rehabilitation programs will depend on a number of factors, including the precise type of ocular deviation involved and whether the strabismus is primary or secondary.3 Non-surgical interventions commonly include refractive error correction with spectacles or contact lenses, and amblyopia therapy with patching or atropine penalisation. Other uncommon interventions include the use of prisms in glasses, behavioural eye exercises and the use of intramuscular botulinum A neurotoxin.3,5 Surgical correction of ocular alignment is commonly recommended and is well tolerated as a day procedure, with minimal post-operative discomfort. Treatment goals are primarily to prevent amblyopia and achieve binocular vision with functional depth perception (stereopsis), and secondarily to achieve better cosmesis.4

Key points for practice

• Patients with strabismus may suffer functional and psychosocial problems related to their condition.

• Early recognition and referral by GPs is important as visual pathways may become permanently impaired if not addressed early.

• All children with strabismus should be referred to an ophthalmologist for further assessment and visual rehabilitation.

• The new onset of strabismus may be a red flag for serious intracranial or intraocular pathology.

Competing interests: None.

Provenance and peer review: Not commissioned; externally peer reviewed.

Acknowledgments

The author wishes to thank Foad Botan for creating all the medical illustrations used in this article.

References

From: Peter D’Arcy <[email protected]

Sent: Friday, 7 June 2019 8:36 PM

To: [email protected]

Subject: trabsimsus

Strabismus is a failure of the two eyes to maintain proper alignment and work together as a team.

If you have strabismus, one eye looks directly at the object you are viewing, while the other eye is misaligned inward (esotropia, “crossed eyes” or “cross-eyed”), outward (exotropia or “wall-eyed”), upward (hypertropia) or downward (hypotropia).

Strabismus can be constant or intermittent. The misalignment also might always affect the same eye (unilateral strabismus), or the two eyes may take turns being misaligned (alternating strabismus).

To prevent double vision from congenital and early childhood strabismus, the brain ignores the visual input from the misaligned eye, which typically leads to amblyopia or “lazy eye” in that eye.

According to the American Association for Pediatric Ophthalmology and Strabismus, approximately 4 percent of the U.S. population has crossed eyes or some other type of strabismus.

Strabismus Symptoms And Signs

The primary sign of strabismus is a visible misalignment of the eyes, with one eye turning in, out, up, down or at an oblique angle.

Corneal light reflex (Hirschberg) test: A screening test for strabismus that evaluates eye alignment based on the location of reflections of light shined at the eyes.

When the misalignment of the eyes is large and obvious, the strabismus is called “large-angle,” referring to the angle of deviation between the line of sight of the straight eye and that of the misaligned eye. Less obvious eye turns are called small-angle strabismus.

Typically, constant large-angle strabismus does not cause symptoms such as eye strain and headaches because there is virtually no attempt by the brain to straighten the eyes. Because of this, large-angle strabismus usually causes severe amblyopia in the turned eye if left untreated.

Less noticeable cases of small-angle strabismus are more likely to cause disruptive visual symptoms, especially if the strabismus is intermittent or alternating. In addition to headaches and eye strain, symptoms may include an inability to read comfortably, fatigue when reading and unstable or “jittery” vision. If small-angle strabismus is constant and unilateral, it can lead to significant amblyopia in the misaligned eye.

Both large-angle and small-angle strabismus can be psychologically damaging and affect the self-esteem of children and adults with the condition, as it interferes with normal eye contact with others, often causing embarrassment and awkwardness.

Newborns often have intermittent crossed eyes due to incomplete vision development, but this frequently disappears as the infant grows and the visual system continues to mature. Most types of strabismus, however, do not disappear as a child grows.

Routine children’s eye exams are the best way to detect strabismus. Generally, the earlier strabismus is detected and treated following a child’s eye exam, the more successful the outcome. Without treatment, your child may develop double vision, amblyopia or visual symptoms that could interfere with reading and classroom learning.

What Causes Strabismus?

Each eye has six external muscles (called the extraocular muscles) that control eye position and movement. For normal binocular vision, the position, neurological control and functioning of these muscles for both eyes must be coordinated perfectly.

Strabismus occurs when there are neurological or anatomical problems that interfere with the control and function of the extraocular muscles. The problem may originate in the muscles themselves, or in the nerves or vision centers in the brain that control binocular vision.

Genetics also may play a role: If you or your spouse has strabismus, your children have a greater risk of developing strabismus as well.

Accommodative Esotropia

Occasionally, when a farsighted child tries to focus to compensate for uncorrected farsightedness, he or she will develop a type of strabismus called accommodative esotropia, where the eyes cross due to excessive focusing effort. This condition usually appears before 2 years of age but also can occur later in childhood. Often, accommodative esotropia can be fully corrected with eyeglasses or contact lenses.

Strabismus Surgery

In most cases, the only effective treatment for a constant eye turn is strabismus surgery. If your general eye doctor finds that your child has strabismus, he or she can refer you to an ophthalmologist who specializes in strabismus surgery.

The success of strabismus surgery depends on many factors, including the direction and magnitude of the eye turn. In some cases, more than one surgery may be required. The strabismus surgeon can give you more information about this during a pre-surgical consultation.

Strabismus surgery also can effectively align the eyes of adults with long-standing strabismus. In many cases of adult strabismus, however, a significant degree of amblyopia may remain even after the affected eye is properly aligned. This is why early treatment of strabismus is so important.

The earlier strabismus is treated surgically, the more likely it is that the affected eye will develop normal visual acuity and the two eyes will function together properly as a team.

Non-Surgical Strabismus Treatment

In some cases of intermittent and small-angle strabismus, it may be possible to improve eye alignment non-surgically with vision therapy.

Esotropia (crossed eyes) needs to be treated early in life to prevent amblyopia.

For example, convergence insufficiency (CI) is a specific type of intermittent exotropia in which the eyes usually align properly when viewing a distant object, but fail to achieve or maintain proper alignment when looking at close object, such as when reading, resulting in one eye drifting outward. Convergence insufficiency can interfere with comfortable reading, causing eye strain, blurred vision, double vision and headaches.

There also is some evidence that suggests CI can cause attention problems and affect academic performance in children. A recent study conducted by Mayo Clinic researchers found that children with exotropia (including convergence insufficiency) at an early age were significantly more likely to develop attention deficit hyperactivity disorder (ADHD), adjustment disorder and learning disabilities by early adulthood.

Certain types of strabismus also have been associated with an increased risk of myopia. Another Mayo Clinic study published in 2010 followed 135 children with intermittent exotropia over a 20-year period and found that more than 90 percent of these children became nearsighted by the time they reached their 20s.

On the bright side, it appears non-surgical vision therapy can be an effective treatment for convergence insufficiency. In a study published in Archives of Ophthalmology, 73 percent of 221 children with symptomatic convergence insufficiency had a successful or improved outcome following a 12-week program of office-based vision therapy combined with eye exercises performed at home.

Sometimes, a strabismus surgeon may recommend a program of vision therapy for a period of time after strabismus surgery to treat amblyopia and minor binocular vision problems that might remain after surgery. In these cases, the term “orthoptics” (“ortho” = straight; “optics” = eyes) rather than “vision therapy” might be used to describe this treatment, which may be provided by an orthoptist

 working closely with the surgeon rather than by an optometrist.

Questions To Ask

When consulting with your eye doctor or strabismus surgeon prior to treatment, here are a few important questions to ask:

• If surgery is recommended, inquire whether one surgery will suffice or if additional procedures are likely to be necessary.

• Ask the eye surgeon about the success rates for the type of strabismus and the surgery he or she is recommending.

• Ask what criteria are used to determine if the treatment is a success. In other words, is “success” defined as reducing the eye turn so the eyes are better aligned and look more natural in appearance, or is success defined as eyes that are perfectly aligned with normal visual acuity, eye teaming and depth perception.

• For optometrists or orthoptists, ask about the success rate, likely duration and costs of vision therapy (or orthoptics).

• Ask what portion of the costs of surgical or non-surgical treatments for strabismus are covered by health insurance or vision insurance.

Remember, children do not “outgrow” strabismus. For best visual outcomes and to prevent developmental delays and other problems, seek treatment for strabismus as soon as possible.

Strabismus

Strabismus (sometimes also called ‘squint’ or ‘lazy eye’) is a condition where the eyes do not line up together. This means that when one eye is looking at something, the other one turns in, out, up or down. It can be present all the time or just every now and then. Strabismus usually appears in early childhood and may present from birth.

What are the causes?

Strabismus affects approximately five in every 100 children. There are a number of causes.

In children who are born with strabismus, it can be due to muscles or nerves not developing correctly, but if it appears in the first few months of life, it is usually due to the brain not controlling eye alignment correctly.

Children who have a problem with the focus of their eyes, especially those who are longsighted, can develop strabismus.

Strabismus can also appear after head injuries or illnesses that cause weakness in eye muscles.

How is vision affected?

When the eyes are not straight and working together, each eye sends a different image to the brain. To stop confusion, the brain will sometimes ignore part of the image from one eye.

If one eye becomes dominant, it can lead to a decrease of vision in the turned eye (amblyopia). When the turned eye swaps from one side to the other frequently, then the vision is usually equal.

Strabismus also affects a child’s ability to judge distance which may result in clumsiness and poor hand-eye coordination

Signs and symptoms

Common signs can include closing one eye, clumsiness, an unusual head position and eyes that look misaligned.

In some children, the strabismus may only be obvious when looking in a particular direction, or when the child is tired or unwell.

However, some symptoms may not be discovered until child is old enough to describe the problem. These can include double or blurred vision and difficulty reading.

How is the condition diagnosed?

It is normal for a baby’s eyes to look misaligned for short periods of time up to the age of four months. Strabismus that is present always, or is becoming increasingly obvious, is not normal and needs to be seen as soon as is practical.

Strabismus can sometimes be a sign of serious eye and health conditions. Early investigation, diagnosis and treatment of strabismus is important in getting the best outcome for the child.

Eye professionals, including ophthalmologists (eye doctors), orthoptists and optometrists, use an assortment of tests to see if a child’s eyes are straight and working together. The eye professional will almost always need to put eye drops into the child’s eyes as part of the complete first examination.

What is the treatment?

Treatment aims to improve the alignment of the eyes and to bring back, or protect, normal vision. Treatment can include glasses, patching, eye drops, eye muscle surgery and eye exercises.

Eye professionals work together to design a treatment plan for each child. In many cases, it will require a combination of treatments.

Contact us

In some cases of strabismus in children and adults, strabismus treatment consists of glasses, prisms, patching or blurring of one eye, botulinum toxin injections, or a combination of these treatments. Other times, eye muscle surgery is necessary to straighten the eyes.

In children with some types of constant strabismus, early surgery may be recommended to improve the chance of restoring or promoting normal binocular vision.

In adults, eye alignment surgery is not strictly cosmetic. Cosmetic surgery is enhancement surgery, such as restoring youthful appearance in a normal aging person. Eye alignment surgery restores normal appearance and is considered reconstructive. There are many other benefits beyond restoring normal appearance: improved depth perception or binocular vision, improved visual fields, eliminating or minimizing double vision and improved social function — as eye contact is hugely important in human communication. It is important to discuss the goals and expectations of the surgery with your ophthalmologist.

During strabismus surgery, one or more of the eye muscles are strengthened, weakened or moved to a different position to improve alignment. Strabismus surgery is usually performed as an outpatient procedure and does not require an overnight hospital stay.

Preoperative tests for strabismus surgery

Before surgery, a specialized examination called a sensorimotor examination will be performed in the ophthalmologist’s office to assess the alignment of the eyes to determine which muscles are contributing to the strabismus and which muscles need to be altered (weakened, strengthened, or moved) to improve the alignment of the eyes. Prisms are used to measure the degree of the strabismus. These preoperative tests help guide the surgeon in determining the surgical plan. Often both eyes require surgery, even if only one is misaligned. Sometimes the exact surgical plan is determined based on findings at the time of the surgery, especially in reoperations.

Medications and strabismus surgery

Strabismus surgery rarely causes significant bleeding. However, some surgeons may suggest that you stop taking blood thinners, aspirin, aspirin-containing products, ibuprofen or certain nutritional supplements that can affect bleeding for a week before the surgery. Withholding these medications should also be discussed with the prescribing doctor to assess the risk of NOT taking the medication. If a pain medication is necessary during this time, acetaminophen (Tylenol) can be used as a substitute.

The strabismus surgery procedure

Strabismus surgery in children requires general anesthesia. Before surgery, a medication is often given to children to alleviate their anxiety of being separated from their parent. In adults, the procedure can be done with general or local anesthesia. Either way, the patient must fast for about eight hours before the procedure. For this reason, pediatric cases are often scheduled in the early morning.

The eye is never removed to perform the surgery. The eyelids are gently held open with a lid speculum. A small opening is made through the conjunctiva (the mucous membrane surface of the eye) to access the muscle. The muscle is then weakened, strengthened or moved to change its action with dissolvable sutures. Most strabismus surgeries are less than one to two hours; however, the patient will be at the surgery center for several hours including pre-operative and post-operative care.

Adjustable sutures

In standard strabismus surgery, the muscle is weakened, strengthened or moved and a permanent knot is placed. In adults, there is the added advantage that an adjustable suture can be used. Instead of a permanent knot, a temporary knot is placed. After the surgery, with the patient awake, alignment can be reassessed, and if necessary, adjustments can be made before a permanent knot is placed to minimize the chance of an over-correction or under-correction. This is typically done the day of or the day after the surgery.

After surgery

Any patient that has surgery, whether under general anesthesia or local anesthesia with sedation, needs to be monitored after surgery. Children can return to school after two days. Adults should not drive the day of surgery or the day after and may need up to a week before returning to work. You may have double vision that can last hours to days or a week or more, rarely longer. Exercise caution with activities like driving if you have double vision.

Pain is minimal and usually over-the-counter medicines, such as ibuprofen (Motrin) or acetaminophen (Tylenol), and cool compresses are adequate. Adults and older children may need prescription pain medicine.

The main restriction after strabismus surgery is not swimming for two weeks.

The eye will be red for one to two weeks, rarely longer, especially if it is a reoperation.

Potential risks of strabismus surgery

The chance of any serious complication from strabismus surgery that could affect the sight or well-being of the eye is exceedingly rare. However, there are risks with any surgery, including:

• Sore eyes;

• Redness;

• Residual misalignment;

• Double vision;

• Infection;

• Bleeding;

• Corneal abrasion;

• Decreased vision;

• Retinal detachment;

• Anesthesia-related complications.

How successful is strabismus surgery?

Strabismus surgery is a common procedure and most patients will see a large improvement in the alignment of their eyes after surgery. In some cases, you may need additional surgery or prism glasses to optimally align the eyes. Each case of strabismus is unique and should be discussed with your ophthalmologist to understand the goals and expectations of surgery.

Treatment for strabismus works to straighten the eyes and restore binocular (two-eyed) vision. In some cases of strabismus, eyeglasses can be prescribed for your child to straighten the eyes. Other treatments may involve surgery to correct the unbalanced eye muscles or to remove a cataract. Patching or blurring the strong eye to improve amblyopia is often necessary.

• Very young children with esotropia usually require surgery to realign the eyes.

• For accommodative esotropia, glasses reduce the focusing effort and often straighten the eyes. Sometimes bifocals are needed for close work. If significant crossing of the eyes persists with the glasses, surgery may be required.

• With exotropia, though glasses, exercises, patching or prisms may reduce or help control outward-turning of the eye in some children, surgery is often needed.

• How is strabismus surgery done?

• The eyeball is never removed from the socket during any kind of surgery. The ophthalmologist makes a small incision in the tissue covering the eye to reach the eye muscles.

• The eye muscles are detached from the wall of the eye and repositioned during the surgery, depending on which direction the eye is turning. It may be necessary to perform surgery on one or both eyes.

• Recovery time is rapid. Children are usually able to resume their normal activities within a few days.

• After surgery, glasses may still be required. In some cases, more than one surgery may be needed to straighten the eyes.

• Strabismus can be diagnosed during an eye exam. It is recommended that all children between 3 and 3½ years of age have their vision checked by their pediatrician, family practitioner or an individual trained in vision assessment of preschool children. Any child who fails this vision screening should then have a complete eye exam by an ophthalmologist.

• If there is a family history of strabismus or amblyopia, or a family history of wearing thick eyeglasses, an ophthalmologist should check vision even earlier than age 3. After a complete eye examination, an ophthalmologist can recommend appropriate treatment.

• Sep. 10, 2012

• The main sign of strabismus is an eye that is not straight. Sometimes children will squint one eye in bright sunlight or tilt their head to use their eyes together.

•  

• Unlike true strabismus (top of

page), note here the

symmetrical light reflection of

pseudostrabismus.

• Pseudostrabismus

The eyes of infants often appear to be crossed, though actually they are not. This condition is called pseudostrabismus. Young children often have a wide, flat nose and a fold of skin at the inner eyelid that can make eyes appear crossed. This appearance of pseudostrabismus may improve as the child grows. A child will not outgrow true strabismus. An ophthalmologist can distinguish true strabismus and pseudostrabismus.

• Six eye muscles, controlling eye movement, are attached to the outside of each eye. In each eye, one muscle moves in the eye to the right, and one muscle moves the eye to the left. The other four muscles move it up or down and at an angle.

To line up and focus both eyes on a single target, all of the muscles in each eye must be balanced and working together. In order for the eyes to move together, the muscles in both eyes must be coordinated. The brain controls these muscles.

With normal vision, both eyes aim at the same spot. The brain then combines the two pictures into a single, three-dimensional image. This three-dimensional image gives us depth perception.

When one eye is out of alignment, two different pictures are sent to the brain. In a young child, the brain learns to ignore the image of the misaligned eye and sees only the image from the straight or better-seeing eye. The child then loses depth perception.

Adults who develop strabismus often have double vision because their brains have already learned to receive images from both eyes and cannot ignore the image from the turned eye. A child generally does not see double.

Strabismus is especially common among children with disorders that may affect the brain, such as:

o Cerebral palsy;

o Down syndrome;

o Hydrocephalus;

o Brain tumors;

o Prematurity.

A cataract or eye injury that affects vision can also cause strabismus. The vast majority of children with strabismus, however, have none of these problems. Many do have a family history of strabismus.

Strabismic amblyopia

Good vision develops during childhood when both eyes have normal alignment. Strabismus may cause reduced vision, or amblyopia, in the misaligned eye.

 The brain will pay attention to the image of the straight eye and ignore the image of the crossed eye. If the same eye is consistently ignored during early childhood, this misaligned eye may fail to develop good vision, or may even lose vision. Strabismic amblyopia occurs in approximately half of the children who have strabismus.

Amblyopia can be treated by patching or blurring the stronger eye to strengthen and improve vision in the weaker eye. If amblyopia is detected in the first few years of life, treatment is usually successful. If treatment is delayed, amblyopia may become permanent. As a rule, the earlier amblyopia is treated, the better the result for vision.

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What Is Strabismus?

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Strabismus Symptoms

• Related Ask an Ophthalmologist Answers

Strabismus is a visual problem in which the eyes are not aligned properly and point in different directions. One eye may look straight ahead, while the other eye turns inward, outward, upward, or downward. The eye turn may be consistent, or it may come and go. Which eye is straight (and which is misaligned) may switch or alternate.

Strabismus is a common condition among children. About 4 percent of all children in the United States have strabismus. It can also occur later in life. It may run in families; however, many people with strabismus have no relatives with the problem.

Infantile esotropia, where the eye turns inward, is a common type of strabismus in infants. Young children with esotropia cannot use their eyes together. Accommodative esotropia is the most common form of esotropia that occurs in children usually 2 years or older. In this type of strabismus, when the child focuses the eyes to see clearly, the eyes turn inward. This crossing may occur when focusing at a distance, up close or both.

Exotropia. Notice the outward-

turning eye.

Exotropia, or an outward-turning eye, is another common type of strabismus. This occurs most often when a child is focusing on distant objects. The exotropia may occur only from time to time, particularly when a child is daydreaming, ill or tired. Parents often notice that the child squints one eye in bright sunlight.

It is estimated that up to 5 percent of all children have some type or degree of strabismus. Children with strabismus may initially have double vision. This occurs because of the misalignment of the two eyes in relation to one another. In an attempt to avoid double vision, the brain will eventually disregard the image of one eye (called suppression). Learn What is StrabismusStrabismus occurs when the eyes are not correctly aligned and point in different directions when looking at an object. It is commonly known as ‘turned’, ‘lazy’ or ‘crossed’ eyes.

One eye or both eyes may turn either inward (esotropia), outward (exotropia), upward (hypertropia) or downward (hypotropia). Strabismus may be constant or intermittent.

Strabismus is one of the most common eye conditions in children, affecting up to 5% of the Australian population.

Causes and risk factors

Whilst the causes of strabismus are not completely understood it is known that abnormalities in the muscles and nerves surrounding the eyes are both contributing factors.

A person can be born with strabismus or develop it during infancy or childhood, or later in life. It can also occur as a result of injury to the eye or head trauma.

Sometimes strabismus can be a sign of a more serious eye disease or other health problem, and should always be thoroughly investigated by an eye specialist as soon as possible.

Early diagnosis is essential in preventing vision loss.

Amblyopia

Amblyopia, commonly known as ‘lazy eye’, is the loss of vision caused by strabismus if left untreated. When a person with a strabismus looks at an object the brain receives two different images and this can confuse the brain. In children, the brain may learn to ignore the double image from the turned eye. This constant ignoring of the image from one eye during a child’s visual development can result in poor vision. Untreated, the vision will remain poor.

In most cases amblyopia can be successfully treated before the age of nine, it is therefore important to diagnose and treat this condition early on.

3D Vision

Strabismus and amblyopia can also interfere with the development of 3D vision (depth perception). Early treatment can improve the likelihood of depth perception developing in a young child.

Symptoms

The symptoms of strabismus may be constant or intermittent, and include;

• crossed eyes,

• double vision,

• uncoordinated eye movements,

• vision loss,

• loss of depth perception.

Strabismus can be difficult to detect in children, particularly if the size of the turn is small and not cosmetically noticeable. If a child is showing any signs of strabismus they should be examined by an eye specialist immediately.

• What causes strabismus?

• How is strabismus diagnosed?

• How is strabismus treated?

Crossed eyes, or strabismus, is a condition in which both eyes do not look at the same place at the same time. It usually occurs in people who have poor eye muscle control or are very farsighted.

Six muscles attach to each eye to control how it moves. The muscles receive signals from the brain that direct their movements. Normally, the eyes work together so they both point at the same place. When problems develop with eye movement control, an eye may turn in, out, up or down. The eye turning may occur all the time or may appear only when the person is tired, ill, or has done a lot of reading or close work. In some cases, the same eye may turn each time. In other cases, the eyes may alternate turning.

Proper eye alignment is important to avoid seeing double, for good depth perception, and to prevent the development of poor vision in the turned eye. When the eyes are misaligned, the brain receives two different images. At first, this may create double vision and confusion. But over time the brain will learn to ignore the image from the turned eye. Untreated eye turning can lead to permanently reduced vision in one eye. This condition is called amblyopia or lazy eye.

Some babies’ eyes may appear to be misaligned, but they are actually both aiming at the same object. This is a condition called pseudostrabismus or false strabismus. The appearance of crossed eyes may be due to extra skin that covers the inner corner of the eyes or a wide bridge of the nose. Usually, the appearance of crossed eyes will go away as the baby’s face begins to grow.

Strabismus usually develops in infants and young children, most often by age 3. But older children and adults can also develop the condition. 

People often believe that a child with strabismus will outgrow the condition. However, this is not true. In fact, strabismus may get worse without treatment. An optometrist should examine any child older than 4 months whose eyes do not appear to be straight all the time.

Strabismus is classified by the direction the eye turns:

• Inward turning is called esotropia

• Outward turning is called exotropia

• Upward turning is called hypertropia

• Downward turning is called hypotropia.

Other classifications of strabismus include:

• The frequency with which it occurs—either constant or intermittent

• Whether it always involves the same eye—unilateral

• If the turning eye is sometimes the right eye and other times the left eye—alternating.

Treatment for strabismus may include eyeglasses, prisms, vision therapy, or eye muscle surgery. If detected and treated early, strabismus can often be corrected with excellent results.

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What causes strabismus?

Strabismus can be caused by problems with the eye muscles, the nerves that transmit information to the muscles, or the control center in the brain that directs eye movements. It can also develop due to other general health conditions or eye injuries.

Risk factors for developing strabismus include:

• Family history. People with parents or siblings who have strabismus are more likely to develop it.

• Refractive error. People who have a significant amount of uncorrected farsightedness (hyperopia) may develop strabismus because of the additional eye focusing they must do to keep objects clear.

• Medical conditions. People with conditions such as Down syndrome and cerebral palsy or who have suffered a stroke or head injury are at a higher risk for developing strabismus.

Many types of strabismus can develop in children or adults, but the two most common forms are:

• Accommodative esotropia often occurs because of uncorrected farsightedness (hyperopia). The eye’s focusing system is linked to the system that controls where the eyes point. So people who are farsighted are focusing extra hard to keep images clear. This may cause the eyes to turn inward. Symptoms of accommodative esotropia may include seeing double, closing or covering one eye when doing close work, and tilting or turning the head.

• Intermittent exotropia may develop when a person cannot coordinate both eyes together. The eyes may point beyond the object being viewed. People with intermittent exotropia may experience headaches, difficulty reading and eye strain. They also may close one eye when viewing at distance or in bright sunlight.

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How is strabismus diagnosed?

An optometrist can diagnose strabismus through a comprehensive eye exam. Testing for strabismus, with special emphasis on how the eyes focus and move, may include: :

• Patient history. An optometrist will ask the patient or parent about any current symptoms. In addition, the optometrist will note any general health problems, medications or environmental factors that may be contributing to the symptoms.

• Visual Acuity. An optometrist will measure visual acuity to assess how much vision is being affected. For the test, you will be asked to read letters on reading charts that are near and at a distance. Visual acuity is written as a fraction, such as 20/40. The top number is the standard distance at which testing is done (20 feet). The bottom number is the smallest letter size you were able to read at the 20-foot distance. A person with 20/40 visual acuity would have to get within 20 feet of a letter that should be seen clearly at 40 feet. “Normal” distance visual acuity is 20/20. Your eye doctor has other methods of measuring vision in young children or patients who cannot speak or comprehend the visual acuity test. 

• Refraction. An optometrist can conduct a refraction to determine the appropriate lens power you need to compensate for any refractive error (nearsightedness, farsightedness or astigmatism). Using an instrument called a phoropter, the optometrist places a series of lenses in front of your eyes and measures how they focus light using a handheld lighted instrument called a retinoscope. Or the doctor may use an automated or handheld instrument that evaluates the refractive power of the eye without the patient needing to answer any questions.

• Alignment and focusing testing. Your optometrist needs to assess how well your eyes focus, move and work together. In order to obtain a clear, single image of what you are viewing, your eyes must effectively change focus, move and work in unison. This testing will look for problems that keep your eyes from focusing effectively or make it difficult to use both eyes together.

• Examination of eye health. Using various testing procedures, your optometrist will observe the internal and external structures of your eyes to rule out any eye disease that may be contributing to strabismus. This testing will determine how the eyes respond under normal seeing conditions. For patients who can’t respond verbally or when some of the eyes focusing power may be hidden, your optometrist may use eye drops. The eye drops temporarily keep the eyes from changing focus during testing.

Using the information obtained from these tests, along with 

Treatment

Early diagnosis of strabismus is essential in preventing irreversible vision loss later in life. Strabismus treatment aims to improve the alignment of the eyes and to correct the resulting vision loss (amblyopia).

Strabismus and amblyopia can be treated with any one or a combination of glasses, eye patching or surgery.

The Lions Eye Institute understands that every child’s case is different to another, with its own set of unique challenges. Therefore, tailored treatment strategies for each child are established.

The Lions Eye Institute also conducts an array of Clinical Trials. You can view these on our Clinical Trials page.

Strabismus surgery

Surgery involves moving one or more of the eye muscles in order to adjust the position of the eye(s). The procedure is undertaken in an operating room under a general anesthetic. There are no bandages, with only mild discomfort and redness for a few days. Usually, the patient is ready to go home on the same day.

Australian and international references

www.childrenshospital.org

www.aapos.org

www.cera.org.au

www.nlm.nih.gov

www.chp.edu

Strabismus Inheritance Study

Who is conducting the study?

Professor David Mackey from the Lions Eye Institute and Professor Elizabeth Engle at Children’s Hospital Boston, in conjunction with ophthalmologists from across Australia and the USA. The project is being coordinated by the research team at the Centre for Eye Research Australia (CERA).

Purpose of the study

The research team are investigating the possible genes involved in the development of strabismus and associated eye conditions e.g. wearing glasses, poor depth perception. Families with a strong history of strabismus are of particular interest to the research team.

trabismus (‘squint’) is a common childhood disorder that can cause psychosocial distress and permanent functional disability. Early diagnosis is important to maximise visual rehabilitation and reduce the risk of amblyopia. There is currently no national Australian screening program for strabismus, which makes it important for all general practitioners (GPs) to master practical skills for evaluating this condition. GPs should also be aware of red flags in a history and examination that necessitate prompt investigation and management.

Objective/s

This article reviews practical screening tests to identify childhood strabismus, and discusses a framework for timely intervention.

Discussion

A comprehensive history is used to distinguish between primary and acquired strabismus. The four tests used to screen for stra-bismus are the light reflex test, the red reflex test, the cover test and the uncover test. Any child diagnosed with strabismus should be referred to an ophthalmologist for further assessment.

Strabismus is a common disorder of ocular alignment that affects 2–4% of children.1 It is commonly referred to as a ‘squint’ or ‘lazy eye’. The most debilitating consequence of untreated strabismus is the development of amblyopia (permanent loss of best corrected visual acuity in a structurally healthy eye).2,3 This is because abnormal visual experience during critical periods of early neurodevelopment result in downregulation of the neural pathway to the brain’s visual cortex.2 After the age of 9 years, these pathways may never be recovered even if normal visual function is restored.4 Strabismus also significantly affects quality of life, with lifelong cosmetic disability that may result in poor self-esteem, social prejudice and restricted career opportunities.5

Early detection and treatment improves vision outcomes and psychosocial wellbeing for children with strabismus. Nonetheless, many cases of strabismus go unrecognised. As patients with paediatric strabismus usually present before school age (with an average onset at 1–4 years), population-based pre-school screening programs have been advocated as a way to reduce the rate of untreated strabismus and amblyopia.3,6 Nonetheless, the cost–benefit value of these public health programs is the subject of ongoing debate,6 and the lack of a national Australian screening program necessitates that individual assessment of children currently falls into the realms of primary care clinicians, such as general practitioners (GPs), and maternal and child health nurses. For this reason, GPs should be alert to this common problem and be familiar with practical screening tests that may unmask situations requiring specialist referral.

Causes of strabismus

Strabismus can be either primary or secondary (acquired). Common causes of childhood strabismus are listed in Table 1. Recognised risk factors for primary strabismus include a family history of strabismus, premature birth and a low birth weight.7Secondary strabismus is often associated with neurological pathology, such as intracranial tumours, head trauma, infection and autoimmune disorders.1

Table 1. Common causes of strabismus1

Primary causes of strabismus Secondary causes of strabismus

Idiopathic strabismus

Congenital syndromes Cranial nerve palsies (CNIII, IV, VI) 

Orbital fracture

Intracranial bleed

Intracranial/intraorbital/intraocular mass (benign or malignant)

Intracranial infection

Grave’s disease

Myasthenia gravis

Diabetes mellitus

Amblyopia

Toxins and heavy metal poisoning

Post-vaccination

Amblyopia is a recognised consequence of established strabismus (either primary or secondary). However, amblyopia can paradoxically also be a cause of secondary strabismus, as a degraded visual experience in one eye may result in that eye drifting out of correct alignment.3 Uncorrected refractive abnormalities, such as myopia and hyperopia, may also result in secondary strabismus via a similar mechanism.6

Types of strabismus

The most common type of strabismus involves horizontal misalignment of the eyes, although vertical misalignment also occurs.7 Ocular deviation may be manifest (tropia) or latent (phoria). Manifest ocular deviation can be present in all directions of gaze (comitant) or only present in specific directions of gaze (incomitant) (Table 2).

Table 2. Strabismus terminology1

Terminology

eso- = Nasal horizontal deviation (relative to fixing eye)

exo- = Temporal horizontal deviation (relative to fixing eye)

hyper- = Superior vertical deviation (relative to fixing eye)

hypo- = Inferior vertical deviation (relative to fixing eye)

tropia = Manifest disorder of ocular alignment

phoria = Latent disorder of ocular alignment

comitant = Ocular deviation present in all directions of gaze

incomitant = Ocular deviation only present in specific directions of gaze

amblyopia = Clinically defined as a 2-line difference from best corrected visual acuity in a structurally healthy eye

Manifest symptoms may be either constant or intermittent. Intermittent strabismus can follow a fluctuating course, with symptoms often exaggerated by fatigue. Symptoms may also vary over time, and ocular misalignment that seemed well controlled in early childhood may become more apparent and frequent as the patient grows older.7 For this reason, all patients with a known diagnosis of strabismus require ongoing evaluation.

Differential diagnosis

The most common differentials for strabismus in a general practice setting are ocular instability of infancy and pseudostrabismus.

Newborns often present with unsteady ocular alignment, which is referred to as ocular instability of infancy. This may last up to 3 months and usually presents as a lateral ocular deviation of less than 15°. Any ocular deviation greater than 15° or persisting for more than 3 months is considered abnormal.3

Pseudostrabismus is a condition where unusual facial architecture creates the optical illusion of strabismus, such as when telecanthus (a broad nasal bridge) or epicanthal folds obscure the nasal sclera. If in doubt, a GP is advised to refer the patient to a specialist for assessment.

History

chool-aged child is uncommon and necessitates further neurological investigations.3

The key areas on history to explore include the obstetric and developmental history. The medical history should include a focus on any history of malignancy or autoimmune conditions, exposures, vaccinations, and whether the child has been generally well or if there has been unexplained illness. Any history of trauma, particularly to the head, orbit or periorbital area should be elicited.

In regards to vision, any previous visual testing and the outcome are relevant. A detailed history of the onset of symptoms, including any associated signs, such as gait disturbance, nystagmus, decreased visual acuity or diplopia is relevant. The pattern of symptoms is important, such as whether the strabismus is constant or intermittent. If intermittent, consider whether the symptoms have been changing in frequency, and whether they are dependent on direction of gaze, or exaggerated by fatigue.

Screening tests

In the general practice setting, screening for strabismus involves four practical tests: the light reflex test, the red reflex test, the cover test and the uncover test.1 The only equipment required is a direct ophthalmoscope and a torchlight.

The light reflex test1

The child is placed on their parent’s lap. The doctor stands at a distance of 1 m in front of the child, holding a small light. The child’s attention is directed to the light. The position of the light’s reflection in each of the child’s eyes is noted and compared. Normal ocular alignment will generate an identical light reflection in each eye. Deflection of the light reflex indicates abnormal ocular alignment, with each 1 mm of deflection equivalent to 15–20 prism diopters deviation (Figure 1).

Figure 1. The light reflex test

The red reflex test1

The doctor stands at a distance of 0.5 m in front of the child, holding a direct ophthalmoscope (set at 0). The child’s attention is directed to the ophthalmoscope and the doctor attempts to visualise the red reflex of both eyes simultaneously. Both red reflexes should be identical. Inequality in size, shape or colour is abnormal (Figure 2).

Figure 2. The red reflex test

The cover test1,8

The doctor stands in front of the child and directs the child’s attention to a target (eg. a light or a toy). The doctor covers one of the child’s eyes and closely observes the uncovered eye for corrective movement. When the fixating normal eye is covered, a manifest abnormal eye must move from its deviated position and take up correct fixation. Accordingly, movement indicates that manifest strabismus is present in the uncovered eye (a tropia). The cover test is repeated on each eye (Figure 3).

Figure 3. The cover test

The uncover test1

The doctor covers one of the child’s eyes for 5 seconds and directs the child’s attention to a target. The cover is then quickly removed. The newly uncovered eye is closely observed for corrective movement. A latent abnormal eye will drift into a deviated position when covered. After it is uncovered, the abnormal eye must then return to correct fixation. Accordingly, movement indicates that latent strabismus is present in the newly uncovered eye (a phoria). The uncover test is repeated on each eye (Figure 4).

Figure 4. The uncover test

Management of strabismus

All paediatric patients with newly diagnosed strabismus require timely referral to an ophthalmologist for a comprehensive assessment of visual function. Any patient with red flags on history or examination should be referred urgently for specialist investigation.

Specific visual rehabilitation programs will depend on a number of factors, including the precise type of ocular deviation involved and whether the strabismus is primary or secondary.3 Non-surgical interventions commonly include refractive error correction with spectacles or contact lenses, and amblyopia therapy with patching or atropine penalisation. Other uncommon interventions include the use of prisms in glasses, behavioural eye exercises and the use of intramuscular botulinum A neurotoxin.3,5 Surgical correction of ocular alignment is commonly recommended and is well tolerated as a day procedure, with minimal post-operative discomfort. Treatment goals are primarily to prevent amblyopia and achieve binocular vision with functional depth perception (stereopsis), and secondarily to achieve better cosmesis.4

 

Strabismus is a failure of the two eyes to maintain proper alignment and work together as a team.

If you have strabismus, one eye looks directly at the object you are viewing, while the other eye is misaligned inward (esotropia, “crossed eyes” or “cross-eyed”), outward (exotropia or “wall-eyed”), upward (hypertropia) or downward (hypotropia).

Strabismus can be constant or intermittent. The misalignment also might always affect the same eye (unilateral strabismus), or the two eyes may take turns being misaligned (alternating strabismus).

To prevent double vision from congenital and early childhood strabismus, the brain ignores the visual input from the misaligned eye, which typically leads to amblyopia or “lazy eye” in that eye.

According to the American Association for Pediatric Ophthalmology and Strabismus, approximately 4 percent of the U.S. population has crossed eyes or some other type of strabismus.

Strabismus Symptoms And Signs

The primary sign of strabismus is a visible misalignment of the eyes, with one eye turning in, out, up, down or at an oblique angle.

Corneal light reflex (Hirschberg) test: A screening test for strabismus that evaluates eye alignment based on the location of reflections of light shined at the eyes.

When the misalignment of the eyes is large and obvious, the strabismus is called “large-angle,” referring to the angle of deviation between the line of sight of the straight eye and that of the misaligned eye. Less obvious eye turns are called small-angle strabismus.

Typically, constant large-angle strabismus does not cause symptoms such as eye strain and headaches because there is virtually no attempt by the brain to straighten the eyes. Because of this, large-angle strabismus usually causes severe amblyopia in the turned eye if left untreated.

Less noticeable cases of small-angle strabismus are more likely to cause disruptive visual symptoms, especially if the strabismus is intermittent or alternating. In addition to headaches and eye strain, symptoms may include an inability to read comfortably, fatigue when reading and unstable or “jittery” vision. If small-angle strabismus is constant and unilateral, it can lead to significant amblyopia in the misaligned eye.

Both large-angle and small-angle strabismus can be psychologically damaging and affect the self-esteem of children and adults with the condition, as it interferes with normal eye contact with others, often causing embarrassment and awkwardness.

Newborns often have intermittent crossed eyes due to incomplete vision development, but this frequently disappears as the infant grows and the visual system continues to mature. Most types of strabismus, however, do not disappear as a child grows.

Routine children’s eye exams are the best way to detect strabismus. Generally, the earlier strabismus is detected and treated following a child’s eye exam, the more successful the outcome. Without treatment, your child may develop double vision, amblyopia or visual symptoms that could interfere with reading and classroom learning.

What Causes Strabismus?

Each eye has six external muscles (called the extraocular muscles) that control eye position and movement. For normal binocular vision, the position, neurological control and functioning of these muscles for both eyes must be coordinated perfectly.

Strabismus occurs when there are neurological or anatomical problems that interfere with the control and function of the extraocular muscles. The problem may originate in the muscles themselves, or in the nerves or vision centers in the brain that control binocular vision.

Genetics also may play a role: If you or your spouse has strabismus, your children have a greater risk of developing strabismus as well.

Accommodative Esotropia

Occasionally, when a farsighted child tries to focus to compensate for uncorrected farsightedness, he or she will develop a type of strabismus called accommodative esotropia, where the eyes cross due to excessive focusing effort. This condition usually appears before 2 years of age but also can occur later in childhood. Often, accommodative esotropia can be fully corrected with eyeglasses or contact lenses.

Strabismus Surgery

In most cases, the only effective treatment for a constant eye turn is strabismus surgery. If your general eye doctor finds that your child has strabismus, he or she can refer you to an ophthalmologist who specializes in strabismus surgery.

The success of strabismus surgery depends on many factors, including the direction and magnitude of the eye turn. In some cases, more than one surgery may be required. The strabismus surgeon can give you more information about this during a pre-surgical consultation.

Strabismus surgery also can effectively align the eyes of adults with long-standing strabismus. In many cases of adult strabismus, however, a significant degree of amblyopia may remain even after the affected eye is properly aligned. This is why early treatment of strabismus is so important.

The earlier strabismus is treated surgically, the more likely it is that the affected eye will develop normal visual acuity and the two eyes will function together properly as a team.

Non-Surgical Strabismus Treatment

In some cases of intermittent and small-angle strabismus, it may be possible to improve eye alignment non-surgically with vision therapy.

Esotropia (crossed eyes) needs to be treated early in life to prevent amblyopia.

For example, convergence insufficiency (CI) is a specific type of intermittent exotropia in which the eyes usually align properly when viewing a distant object, but fail to achieve or maintain proper alignment when looking at close object, such as when reading, resulting in one eye drifting outward. Convergence insufficiency can interfere with comfortable reading, causing eye strain, blurred vision, double vision and headaches.

There also is some evidence that suggests CI can cause attention problems and affect academic performance in children. A recent study conducted by Mayo Clinic researchers found that children with exotropia (including convergence insufficiency) at an early age were significantly more likely to develop attention deficit hyperactivity disorder (ADHD), adjustment disorder and learning disabilities by early adulthood.

Certain types of strabismus also have been associated with an increased risk of myopia. Another Mayo Clinic study published in 2010 followed 135 children with intermittent exotropia over a 20-year period and found that more than 90 percent of these children became nearsighted by the time they reached their 20s.

On the bright side, it appears non-surgical vision therapy can be an effective treatment for convergence insufficiency. In a study published in Archives of Ophthalmology, 73 percent of 221 children with symptomatic convergence insufficiency had a successful or improved outcome following a 12-week program of office-based vision therapy combined with eye exercises performed at home.

Sometimes, a strabismus surgeon may recommend a program of vision therapy for a period of time after strabismus surgery to treat amblyopia and minor binocular vision problems that might remain after surgery. In these cases, the term “orthoptics” (“ortho” = straight; “optics” = eyes) rather than “vision therapy” might be used to describe this treatment, which may be provided by an orthoptist

 working closely with the surgeon rather than by an optometrist.

Questions To Ask

 

Remember, children do not “outgrow” strabismus. For best visual outcomes and to prevent developmental delays and other problems, seek treatment for strabismus as soon as possible.

 If the angle of deviation varies with the direction of gaze, the deviation is said to be incomitant.

When investigating strabismus or heterophoria, the angle of deviation is either constant or varies with the direction of gaze.

Concomitant deviations are relatively common. They are usually associated with hypermetropia or the anomalous placement of one or more of the extraocular muscles. Various treatment options are available including refractive or prismatic management, exercises or surgery.

Incomitant deviations are usually caused by a functional anomaly of one or more of the extra-ocular muscles or their associated neurology. This may be a result of a defective muscle or mechanical interference in the orbit (myogenic), or a consequence of a lesion in the nerves supplying the musclature (neurogenic).

 The presence of diplopia usually suggests that the incomitancy is of recent origin and indicates a disturbance to some component of the oculomotor system. This may have been caused by trauma or may indicate the presence of an intracranial tumour, aneurysm or haemorrhage.

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A detailed analysis of the oculomotor fields can be obtained using  a Hess or Lees screen. 

The patient wears red and blue goggles and is positioned in front of the computer screen at the appropriate distance. 

Results of the plots for the left and right eyes, indicate which eye has a palsied muscle and providing an index for monitoring the progression of an incomitant deviation.

 The Circles are used for routine testing. Butterfly and flower pattern can be used to make the test more appealing for children. The Bars stimulus is used to measure torsion in each direction of gaze.

Motility is tested normally in nine positions of gaze for each eye but can be done in 25 positions of gaze.

The grid can be specified in units of degrees or prism dioptres.A prism dioptre corresponds to a deviation of 1 cm at 1 metre, which is equivalent to 0.573 degrees.

The primary muscles acting in each direction of gaze can be shown.Error lines can also be shown The direction of the deviation is described as exo, eso, hyper or hypo and measurements are

What is binocular vision?
What we see is the result of signals sent from the eyes to the brain. Usually the brain receives signals from both (bi) eyes (ocular) at the same time. The information contained in the signal from each eye is slightly different and with well-functioning binocular vision, the brain is able to use these differences to judge distances and coordinate eye movements.

What causes loss of binocular vision?
Binocular vision anomalies are among the most common visual disorders. They are usually associated with symptoms such as headaches, eye strain, eye pain, blurred vision, and occasionally double vision. There are many reasons binocular vision might become reduced or lost altogether, including:

Reduced vision in one eye
Loss of coordination of movement between the two eyes (strabismus)
Problems with the brain comparing images from both eyes
Why is this important?
One of the main benefits of binocular vision is the ability to judge depth and speed of objects. Children with poor or no binocular vision can have difficulty with these tasks. This may lead to problems with:

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