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Case of the week 128  ( August 2013 )
Intermittent exotropia


This girl has been noted by her parents and her friends to have an eye that wanders out when she is tired or when she is ‘day dreaming’. She habitually closes one in bright sunlight. The girl has no awareness of this unless it is called to her attention. She is symptom free.


 See video of this patient
 


Intermittent exotropia is a common form of strabismus where Patients demonstrate a duality of behavior in that they seem to be completely normal during orthotropic intervales and totally ‘turned off’ during periods of manifest exodeviation.In contrast to the exophoria, patients with intermittent exotropia demonstrate a manifest deviation part of the time.
 Intermittent exotropia in the preschool years has 2 common characteristics, first there are increasing likelihood of tropia when the child is fatigued, day-dreaming, or inattentive and second is the closing of one eye in bright sunlight.
These patients are classified into four types on the basis of in what field or distance of gaze the deviation is greater :

I. Basic type : The exodeviation is the same at distance and at near.

II. Divergence excess type : The distance exodeviation is greater than the near deviation by 15 prism diopters.

III. Convergence insufficiency type : The near exotropia is greater than the far deviation by 15 prism diopters.

IV. Simulated divergence excess type

The surgical treatment of intermittent exotropia presents some philosophical problems. These patients have a lot going for them before anything is done. Vision is usually equal and normal in each eye, sensory fusion with stereopsis and motor fusion amplitudes are present, and versions and ductions are intact. In other words, the ‘good’ intermittent exotropia patient has no problems, if there is any, it always starts after surgical interference !!

This girl represents a straightforward case of intermittent exotropia basic type since the far fixation is only 10 PD larger than the near fixation. There is no urgent need for surgery, but on the other hand it could be done at any time. A bilateral lateral rectus recession of 7.0 mm would be sufficient. In case of surgery is not done at this time, regular follow up at 6 month intervals is recommended.


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