This handout largely refers to the intermittent exotropia that is seen in children and adolescents. In these patients, there is an underlying tendency for the eyes to diverge outwards (probably because of the anatomical arrangement of the muscles and other orbital tissues). This is controlled to varying degrees by the patient. One way the brain responds to this intermittent misalignment is to shut down certain parts of the visual field when the eyes are divergent.

Symptoms

The symptoms that are noticed are an outswing of one or both eye(s), intermittent tendency to close the out-turning eye (squinting) and intermittent double vision.

The normal expectations vary. Many cases gradually deteriorate with time. The duration of each episode of out-turning increases and then the frequency of these episodes increases. Eventually the angle of out-turning increases. Not all cases get worse and a small number of cases may spontaneously get better (especially very young children) as the orbital tissues grow and change.

Sometimes glasses are needed if there is poor focussing.

Treatment

Treatment depends on the severity of the condition and on the age of the patient. The severity of the condition is determined by a combination of what I find in the office, and what you report happens at home.

Up to the age of 4, a treatment that sometimes works is to patch the eye that is usually straight for one or two hours a day (or use a blurring eye drop one or two days a week).

From age 4 to 7 giving glasses that are similar to the glasses we would give to a child who is short-sighted often helps. The glasses are not used to improve vision (the usual purpose of glasses) but are used to change the aim of the eyes by modifying the focus. Glasses can be a useful delaying technique that allows us to defer surgery until the age of 6 or 7 (there are some small theoretical advantages to delaying surgery).

Surgery

In general, the most reliable treatment is surgery. The threshold for contemplating surgery should include one or more of the following:

1. I think my child often looks a bit weird because of the eye condition.

2. Others notice that my child often looks a bit weird.

3. My child has bothersome double vision.

Once the decision has been made to consider surgery, the patient needs a separate visit for a pre-operative examination using techniques (e.g. wearing a patch for 30-60 minutes) that try and simulate the "maximum" degree of outward deviation present. At this pre-operative assessment, we are able to show that 1 in 10 children may require bifocals at some stage.

In the first week or two after surgery intermittent cross-eyedness with intermittent double vision is frequent. Of patients who have surgery, approximately 80% have a good result at 12 months and there is a low "deterioration" rate beyond that.

Repeat surgeries are needed in about 10% of patients in the first year after surgery and about another 20% before adulthood. Those who have measurable stereopsis (depth perception) are probably at lower risk of needing repeat surgery - it's like having brain "glue" assisting the mechanical effect of the muscles in holding the left eye and right eye visual systems together.

MOST children with intermittent exotropia become myopic (short-sighted), probably independent of any treatment they do or do not receive.