[Intermittent Exotropia]

Abstract

Intermittent exotropia (IXT) is a congenital form of divergent strabismus. Its incidence is estimated to be 32 per 100 000. Most often, IXT is first noted in early childhood when intermittently manifest outward deviation of the eyes is seen. Patients with IXT can control the deviation and keep the eyes aligned; this ability can be measured with "control scores". Complications such as amblyopia and loss of binocular functions are rare but should be looked for and need to be avoided. IXT can have a negative impact on quality of life. Conservative treatment includes the correction of refractive errors, (alternating) occlusion, over-minus lenses and orthoptic exercises. By injecting an extraocular muscle with botulinum toxin (to weaken its function) or with bupivacaine (to strengthen its function), IXT can be treated pharmacologically. Diagnostic occlusion and prism adaptation are strategies to uncover the true (largest) angle. Eye muscle surgery aims at eliminating the condition, but recurrences are common. The literature on large, randomized prospective trials for IXT is scarce. However, there are trials underway in the United Kingdom and in North America to better understand the natural course of IXT and to determine the most appropriate therapeutic approach.