Exotropia
 

. A patient with alternating exotropia a Left secondary exotropia from ROP Exotropia correctable with minus lenses. The minus  lens stimulate accommodation and hence convergence.

Exotropia is less common than esotropia in the ocular motility examination. However, it is commonly seen in patients with  poor vision from varied causes such as chronic retinal detachment or optic neuropathy. Most cases seen in the examination will either be intermittent exotropia or consecutive exotropia from over-correction of esotropia. In intermittent exotropia, three types may be seen. 1) Divergence excess On cover/uncover test for near fixation, the eye is orthophoric but on alternating cover test, there is a large exophoria which recovers slowly. With distant fixation, the eye shows exotropia which becomes straight after one or two blinks. The exotropia increases on alternating cover test. 2) Convergence weakness In this condition, the exotropia is worse with near fixation. 3) Basic The magnitude of the exotropia is the same for near and distant fixation.   Other examination: mention that you would like to perform ocular motility. Patients usually has a V pattern ie. the exotropia increases  on upgaze if the patient has constant exotropia mention that you would like to test the visual acuity. The exotropia may be  secondary to poor vision in patients with evidence of DVD (dissociated vertical deviation) during the cover/uncover test consider the  possibility of consecutive exotropia and examine the eye for previous squint surgery (conjunctival scar).

Questions:

1. How would you manage a patient with intermittent exotropia?

answer
Conservative treatment:
orthoptic exercises with anti-suppression exercises
optical treatment with concave lenses to stimulate convergence or prisms to compensate the strabismus and tinted glasses to prevent bright light from causing dissociation of the eyes
Surgery

2. What is meant by secondary exotropia and how would you manage the patient?

answer
Secondary exotropia occurs secondary to poor vision and is commonly seen in adult (in children with poor vision, the eye usually shows secondary esotropia).
It is important to look for any underlying treatable cause of poor vision such as cataract. In patients whose vision cannot be improved and in whom the ocular deviation presents a cosmetic problem, surgery may be considered. However, this should also be performed when the strabismus has remained constant. It is also important to assess the patient carefully before the operation for the risk of post-operative diplopia. The patient should also be told about the high chance of recurrence due to the lack of binocular vision. Alternatively treatment may be botulinum toxin to the lateral rectus of the affected eye.

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