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What is strabismus?
Strabismus, more commonly known as crossed-eyes, is a vision condition in which a person cannot align both eyes simultaneously under normal conditions. One or both of the eyes may turn in, out, up or down. An eye turn may be constant (when the eye turns all of the time) or intermittent (turning only some of the time, such as, under stressful situations or when ill). Whether constant or intermittent, strabismus always requires appropriate evaluation and treatment.
Who has strabismus?
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).
Types of Strabismus:
This is the most common type of eye turn occurring in approximately 1-2% of the population. Esotropia can be further divided into various categories each requiring a different treatment plan; each having a different prognosis.
For congenital infantile esotropia, treatment after the age of 2 decreases the prognosis for re-establishment of binocular vision. The chance of developing binocular vision with surgery alone diminishes with age. Older children with infantile esotropia need both surgical intervention if the turn is large and vision therapy. Smaller turns may only require vision therapy. Getting the eyes to work together requires a lot of time and effort.
What Is Accommodative Esotropia?
This refers to a crossing of the eyes (esotropia) caused by hyperopia, commonly known as “farsightedness”. Children who are farsighted easily and automatically focus on objects at distance and near through "accommodation". Accommodation refers to the contraction of a small muscle inside the eye to cause the natural lens in the eye to change its shape and allow images to focus properly on the back surface of the eye. As a result, a child who is farsighted usually does not have blurred vision. However in some children who are farsighted, this accommodative effort is associated with a reflex crossing of the eyes.
Accommodative esotropia can begin anywhere from 6 months to 6 years of age. The usual age of onset is between 2 and 3 years of age.
The degree of farsightedness will often increase gradually until about eight years of age. After this age, the farsightedness typically diminishes each year. Many children will be able to maintain straight eyes without glasses in their early teen years. Some children will no longer need their glasses at an earlier age while others will need the proper farsighted glasses or contact lenses to control the esotropia even as adults.
What are the Signs of Accommodative Esotropia?
A noticeable crossing of the eyes is usually the primary sign. This crossing may only be evident when your child intently views an object at near or when your child is tired or not feeling well. Some children will complain of double vision or may be seen squinting or rubbing one of the eyes.
Treatment Options
Full-time use of the appropriate glasses to correct the farsightedness will often control the esotropia. When wearing the glasses, your child will not need to accommodate and hence the associated eye-crossing reflex will disappear. However, after removing the glasses, the crossing will reappear, perhaps even more than before your child began wearing glasses.
Sometimes the glasses will only cause the crossing to disappear when your child looks in the distance. However, when gazing at near objects, crossing may persist despite the use of the glasses. In these circumstances, a bifocal lens is usually prescribed to permit your child to have straight eyes at all viewing distances.
It is not uncommon that children with accommodative esotropia will have decreased vision in one eye (usually the eye that does most or all of the crossing). This is known as "amblyopia" or “lazy eye.” If there is a significant amblyopia present, the optometrist will prescribe an eye patch to be worn over the stronger eye to force your child to use and strengthen the eye with amblyopia. The glasses must also be worn when using the patch.
In some children, the glasses will diminish the crossing only partially or not at all. Some children whose esotropia was previously controlled with glasses may "deteriorate" and have a significant crossing even when wearing the glasses. If a significant crossing is evident despite the proper glasses, eye muscle surgery or vision therapy can then be performed to establish good ocular alignment.
Exotropia is the outward deviation (turn) of an eye. The deviation may occur while fixating (looking at) distance objects, near objects or both. Fortunately, most exotropia is intermittent and this means that the eye deviation or turn occurs only some of the time. As long as the eyes are straight some of the time, the brain will develop some normal functioning of the eyes (stereoscopic depth perception).
Treatment consists of vision therapy, patching, glasses and/or surgery. The most successful form of treatment is vision therapy. Therapy should be directed at the cause. In a comparative study using both Optometric and Ophthalmological journals, vision therapy had an overall success rate of 78% as compared to surgery of 48%. Thus, surgery should be reserved only for the large deviation or when vision therapy is not as successful as expected.
Hypertropia is the upward deviation (turning) of one eye in relation to the other eye. This is often the result of trauma such as a car accident or blow to the head. This form of eye turn is less tolerated than horizontal eye turns and smaller amounts have a bigger impact on an individual’s life and vision. Double vision is a common complaint. Vertical tropias often occur with a horizontal eye turn as well.
Treatment consists of vision therapy, patching, glasses and surgery. Because of the low tolerance for a vertical tropia, a person must usually use glasses. Surgery if often needed to realign the eyes as a complement to a vision therapy program. Vision Therapy will help gain flexibility to a visual system, but surgery will straighten the vertical eye posture.
Adapted from Vision Therapy Manual, Mitchell Sheiman, 1992
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©2002, 2003, 2004 Dr. Nadine Forché, O.D,M.S, F.A.A.O.
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