An observational study of exotropia with the application of the Classification of Eye Movement Abnormalities and Strabismus

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Exotropia is a cosmetically distressing strabismus with lasting negative psychosocial impact on the patient. Aim: The purpose of our study was to apply the Classification of Eye Movement Abnormalities and Strabismus (CEMAS) to the patients of exotropia (XT) in our study, identify the common types and causes of this cosmetically and psychosocially distressing strabismus, and to determine if any of these causes are preventable. Materials and Methods: A prospective, cross-sectional study was carried out in patients aged 6 months and more with exotropia attending the ophthalmology outpatient department of a tertiary care hospital from December 2016 to July 2018. Complete strabismus evaluation of the patients was done, the exotropia seen in the patients was categorized in types according to the CEMAS classification and possible causes of exotropia were studied. Results: Of the total 120 patients, 110 had comitant XT, whereas 10 had incomitant. Of the 110 comitant cases, intermittent XT was maximum – 54 (45%). A significant number of patients had XT due to sensory or neurological causes 46 (38.8%). The etiology of XT due to sensory or neurological causes included amblyopia due to uncorrected refractive errors, trauma, media opacities in cornea and lens, and posterior segment diseases. Other causes included developmental delay, congenital fibrosis of the extraocular muscles, isolated 3rd N palsy, and basic XT. Conclusions: Our study shows that although majority of the patients had intermittent exotropia, a significant number of patients had exotropia due to visual or neurological causes, which may be preventable in many cases. Diagnosis of the cause of XT at the appropriate time may prevent unnecessary visual loss and reduce the negative psychosocial impact of squint.