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Makassar, Indonesia — Orbis Flying Eye Hospital Program— May 2014 Asivha, 3, presented at screening day with bilateral congenital esotropia (strabismus).

When someone has a strabismus there are many different factors to consider when determining the course of treatment. Treatment and management are individualized for each person specific to their needs, and the type of strabismus. Decisions regarding the course of treatment can depend on the person’s: concerns, desired outcome, symptoms, level of visual discomfort, visual demands, age when they developed the strabismus, age at the time of assessment, general health, and expected level of ability to participate in the treatment protocol. It will also depend on the nature of the strabismus such as: how often the person turns their eye, whether they turn it in (esotropia) or out (exotropia), how far they turn it, and whether they also have amblyopia (reduced eyesight)

It is important for parents who have children with strabismus to learn about the condition, and to understand the risks of developing amblyopia and having reduced three-dimensional depth perception. If someone suddenly develops a strabismus with no immediate identifiable cause, they need to also be seen by a health care professional that can further test for changes in overall health, or for other neurological disease.

The strategies of strabismus treatment are focused on optimising the person’s ability to develop the use of both eyes together binocularly. Goals of treatment are specific to each person and can include: being able to see equally clear out of each eye, developing the ability to fuse the images from both eyes into a single image, having three dimensional depth perception, and having eyes that are straight and aligned. The importance of having properly aligned eyes in developing a positive self-image and allowing interpersonal eye contact cannot be overstated. After the age of 5, is when other children will start to recognize something different about a child with a turned eye.

The starting point for all treatment and management begins with a prescription for the best lenses, either glasses or contact lenses, to allow each eye to see clearly and promote the ability of the brain to use both eyes together. It is critical to the success of any treatment program that the person uses the lenses as prescribed. The amount of strength that is prescribed in the lenses can vary depending on many factors. More or less strength may be used to: create a specific change in the nature or amount of the eye turn, achieve three-dimensional depth perception, allow for ease of use or getting used to the glasses, and to promote normalization of the person’s visual status. Prisms (a special type of lens), may be incorporated into the prescription to relieve eyestrain, help the eyes lock in together, and reduce double vision. When a prism is expected to be a temporary part of the prescription, or if it is a large amount, it can be applied to glasses as a stick-on lens called a Fresnel prism.

Accommodative esotropia, is a type of inward eye turn associated with focusing effort. Glasses can be used to hold the eye straight or partially straight. This type of turn is usually associated with being farsighted and also tends to occur more when looking at something close up. The amount of lens power prescribed depends at least in part on the amount that will keep the eyes the straightest. Often these types of lenses are bifocal when a stronger power is needed for looking close up compared with distance. Changes in lenses may be needed throughout the course of treatment. Nonaccommodative esotropia is an inward eye turn that is not associated with focusing effort. If there is coexisting farsightedness, compensating lenses won’t significantly decrease the eye turn. When someone turns their eye out, as in exotropia, glasses don’t usually have a straightening effect on the eye, except in certain specific circumstances.

Vision therapy is a non-surgical method of treatment that we can use to develop skill in using both eyes together binocularly. Usually this requires intensive office based treatment. Glasses often are combined in the therapeutic process. In the case of esotropia, occluding the inner portion of the lenses (for example: binasal occlusion) can assist the person in straightening their eyes. Therapy involves active training procedures that improve: fixation ability, eye movement control, focusing control, as well as eye re-positioning ability and ranges for moving the eyes in and out together. This helps to eliminate amblyopia, improve eye alignment and three-dimensional depth perception. Vision therapy procedures are adapted to the individual and modified as binocular vision is achieved. This therapy is successful in treating many forms of strabismus. This includes people who have an intermittent or a constant strabismus, whether it is of recent onset or longstanding, whether the eye turn is inward or outward, whether the amount of turn is small or larger, whether the turn resulted after an acquired brain injury, or people with eye turns that recur after having strabismus surgery treatment.

The time required for therapy depends on the individual. A course of therapy is anticipated to vary in length from 24 to 75 hours of treatment in office. This is usually divided into 30 or 60 minute sessions once or twice a week in the office. In addition, home therapy may also be prescribed, requiring 20-60 minutes per day. During office visits, the optometrist reviews home treatment and prescribes appropriate changes as the patient shows progress with therapy.

Botulinum toxin is sometimes used as an alternative non-surgical intervention for strabismus. When injected into the eye muscle, the toxin prevents the nerve from activating the eye muscle. This causes a temporary paralysis of the eye muscle, which can have a lasting change in the eye’s position. The procedure is more likely to have long term results if the person has the necessary meaningful visual experiences during the temporary paralysis. Up to half of people treated this way will require additional injections.

All aspects of nonsurgical treatment of strabismus should be considered before surgery. People who may prefer surgery tend to have a primary concern with the cosmetic appearance of the turned eye. Or they may not be interested in, or able to commit to a course of vision therapy. Surgery can also be considered if non-surgical therapies are not resulting in a favourable response. Surgery is not performed for small eye turns. There has to be a sizable amount of eye turn to be enough for surgery. Strabismus surgery can restore the ocular alignment closer to normal. The surgeon will consider the surgery a success even if the patient has a small residual eye turn. This amount of residual eye turn is enough to interfere with development of optimum three-dimensional depth perception. Some rudimentary binocular vision might be gained if the residual eye turn is small enough. Multiple surgical procedures are frequently recommended in such cases. Preoperative and/or postoperative vision therapy should be considered to enhance functional vision outcomes.

For infantile esotropia, most surgeons prefer to intervene before the age of 2 years, and some as early as 6 months. However, general anesthesia in young children does have risks.  It is commonly upheld from the research that a child has a better chance of developing rudimentary binocular vision with limited three-dimensional depth perception if the surgery is done at an early age. There are, however, no randomized clinical trials available to indicate an age to suggest surgical intervention for infantile esotropia. Surgery is rarely performed in a child under 4 years of age with exotropia, because of the risk of causing an esotropia with amblyopia. There is also a high recurrence rate of exotropia after surgery, and a second surgery is often needed to straighten the eye.

Complications of surgery can include double vision, scar tissue, inflammation, and overcorrection (resulting in the eye turning the opposite direction) or undercorrection (the full amount of the turn is not eliminated). For infantile esotropia, there is a lack of consensus regarding what surgical method is most effective to perform as well. There is also a lack of randomized clinical trials in this area, which is needed to improve the evidence base for the management of infantile esotropia. Reported success rates of VT and surgery for infantile esotropia are mixed in the scientific literature. The success depends on many factors. There are no double blind studies for surgical treatment or vision therapy to give high quality evidence either way. With the retrospective studies that exist, the success of vision therapy is as good or better than surgery.

Read Part 1 What is strabismus and VT for strabismus and amblyopia.

Learn about strabismus surgery outcomes

The beautiful photo of Asivha was taken by Orbis and posted to Flickr.  It is being used under a Creative Commons license  and has not been altered.

 

References

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