Strabismus

Description

Strabismus is an eye condition where both eyes do not align properly and point in different directions. One eye may look straight ahead while the other may turn inward, outward, upward or downward. The eye turn may be intermittent or consistent. Strabismus most commonly affects children, and to compensate for double vision the brain naturally ignores the visual input from the misaligned eye which quite often leads to amblyopia (lazy eye) in that eye.

Symptoms

The primary sign of strabismus is the obvious misalignment of one eye either outward, inward, upward, or downward. When the misalignment of the eye is largely obvious, the strabismus is called “large-angle”. This refers to the angle of deviation between then line of the straight eye and that of the misaligned eye. Less obvious turns are called “small-angle” strabismus. Large-angle strabismus does not often result in eye strain or headaches. This is largely due to the brain making no attempt to correct the vision of the misaligned eye. This usually causes severe amblyopia in the turned eye. Less noticeable cases of small-angle strabismus are often accompanied by headache, eye strain, fatigue when reading, and unstable vision. This is due to the small-angle strabismus being more likely to cause disruptive visual symptoms, this is especially true if the strabismus is intermittent or alternates between eyes. It is common for both large and small-angle strabismus to affect self-esteem of children and adults with the condition as it may interfere with making normal eye contact when speaking to others.

Causes

The human eye has six external muscles that control eye position and movement. In order for normal binocular vision (normal vision in both eyes), the position, neurological control and functioning of these muscles for both eyes must be perfectly coordinated. Strabismus occurs when there are neurological or anatomical problems that interfere with the control and function of the external muscles. The problem may be associated with the muscles themselves, or in the nerves or vision centres in the brain that control vision. There may be a genetic element associated with strabismus. If both parents have strabismus, children have a greater risk of developing the condition. For more information on genetic inheritance please visit our Genetic Inheritance section.

Diagnosis

Strabismus can be diagnosed during a routine eye exam. It is recommended that all children by the age of three have their vision tested by their eye doctor each year. The earlier strabismus is diagnosed the greater the chance of successful treatment. A number of routine eye tests are used to help diagnose strabismus and to assess the level of vision. The types of tests performed depend on the age of the patient but may include some of the following: • Doctors may use an ophthalmoscope (a magnifying glass type device with a large light connected to it) to see in to the eye and test overall eye health • Children may be asked to match letters and pictures • Patients may be asked to read letters off a chart (Snellen chart-used to determine the clarity of distance vision • And following visual targets A refractor may also be used to measure the exact refractive error (level of near-sightedness in this case) of the eyes. This will help to determine the correct glasses prescription to correct the visual impairment.

Treatment

Multiple treatment options are available for strabismus, these include glasses, eye patch, botulinum toxin (Botox) injection, and surgery. Glasses Glasses are the first port of call for the treatment of strabismus. They are used to correct the visual problems associated with strabismus which may include myopia (short sightedness), hyperopia (longsightedness), or astigmatism (unevenly curved corneas). Eye Patch If the strabismus has resulted in amblyopia (lazy eye), an eye patch is used to cover the “good” eye and to encourage the misaligned eye to work harder. Overall this does not correct the strabismus but it may help to improve the vision in the lazy eye. Eye patches are most effective if work before the age of 8 and should be work for several hours a day, several days a week. Botox Injections Strabismus may be caused by the external muscles of the eye pulling to tightly in one direction. Botox is a toxin that in very small doses can be effective in the treatment of a number of health conditions. Botox can be injected in to one of the muscles of the affected eye. Botox weakens the injected muscle and allows both eyes to realign. Effects of botox wear off after several months, the eyes may remain realigned or one may move again and require further treatment. Surgery Surgery is often only used to treat strabismus is the preceding treatments have no effect. Surgical intervention can be used to realign the eyes or to help the eyes to work better together. Corrective strabismus surgery requires the movement of the external muscles of the eye to a new position. It may be necessary to operate on both eye even if only one is affected. This allows for the optimal positioning of both eyes to aid in improving vision. Eye drops are often prescribed following a surgical procedure to promote healing and ward off infection. No matter what level of vision a person may have, it is important to look after the eyes. To find out more about what can be done to take care of the eyes on a daily basis, please visit our Tips for Good Eye Health. For further information, please contact the Research Department on 01 6789004 or email research@fightingblindness.ie.

Research

Researchers and clinicians are continually seeking to improve interventions and outcomes of treatment of strabismus. Research areas regarding strabismus are focusing on optimising imaging and measuring techniques to accurately diagnose large or small-angle strabismus. Post-surgical effects and aftercare are also being re-evaluated. Information about other clinical trials that are on-going and completed can be found on the clinical trials website and can be searched by both condition and location.

Support

Receiving a diagnosis can be overwhelming for anyone, but this is not a journey that you have to make alone. There are many groups and resources available to provide support for people living with Stargardt Disease. Fighting Blindness offers a free and confidential counselling service (Insight Counselling). For further information please contact insight@fightingblindness.ie or call 01 6746496. We also offer support groups for people with a visual impairment to share their feelings and experiences with others facing the same challenges. Please consult the support groups section of our website here to access the latest timings and days for the various support groups we offer. For further information please contact insightgroups@fightingblindness.ie or call 01 6746496.

Resources

Féach provides support for parents of children living with sight loss in Ireland. ChildVision is the national education centre for children with sight loss in Ireland. Vision Ireland, formerly NCBI (National Council for the Blind in Ireland) provides support and services for people living with sight loss in Ireland. Irish Guide Dogs for the blind helps individuals and their families to achieve improved mobility and independence.