Intermittent exotropia is a common form of strabismus that presents a diagnostic challenge and requires considerable therapeutic tenacity. Patients with this type of strabismus demonstrate a duality of behavior in that they seem to be completely normal during orthotropic interludes and totally ‘turned off’ during periods of manifest exodeviation.

It is a common misconception that monocular eye closure in bright sunlight with intermittent exotropes is triggered by diplopia. Although the real cause of photophobia in intermittent exotropes  remains elusive at this time, theories  have been made in the literature to explain photophobia with intermittent exotropes, :

1.    It has been assumed that when a patient is outdoors and looking at infinity, there are no near clues to stimulate fusional convergence.

2.    Bright sunlight dazzles the retinas so that fusion is disrupted causing the deviation to become manifest.

3.    Intermittent exotrope shuts one eye in bright light to avoid the many perceptual visual field changes which in turn may trigger the ‘‘hemiretinal suppression mechanism ".

4.    Bright light causes exophoria to become manifest and this explains  the use of photochromatic lenses to relieve symptoms in such patients.

5.    Enlargement of the field in intermittent exotropes leads to more dazzling on exposure to bright sunlight.

To obtain an accurate distance measurement of the deviation some prefer to measure while a patient fixates on a far distant object at ‘infinity.’ To do this, the patient may be asked to look out of a window at a distant object while prism and cover testing is carried out to detect the maximum distance exodeviation.