Binocular Diplopia Following Vision Restoration in Patients with Keratoconus and Sensory Strabismus

Spectrum of Binocular Vision Anomalies in Keratoconus Subjects

Keratoconus (KC) is typically a bilateral asymmetric corneal condition associated with anisometropia. A detailed evaluation of binocular vision function is therefore a critical component of ocular examination in these patients for early detection and treatment of binocular vision anomalies.

PURPOSE

The purposes of this study were to measure the various parameters of binocular vision (BV) in patients with KC and to identify the factors that possibly influence them.

METHODS

This was a prospective, observational study of BV in patients with KC and with best-corrected visual acuity ≤0.4 logMAR in each eye. Age-matched, nonstrabismic normal patients served as controls. Binocular vision examination included motor assessment, accommodation parameters, and fusional vergence.

RESULTS

Binocular vision parameters of 84 KC patients were compared with those of 71 normal controls. The KC group showed statistically significant differences between fellow eyes in refractive cylinder (0.44 ± 2.1 D, P = .03), best-corrected visual acuity (0.06 ± 0.09 logMAR, P = .001), and maximum keratometry (6.64 ± 8.2D, P = .005). The control group showed no significant difference in any refractive or keratometric parameter between fellow eyes. Sixty-six (78.6%) of 84 KC patients had various combinations of BV anomalies: 48.8% had impaired stereopsis, 44% had abnormal fusional vergence, and 39.3% had accommodative infacility. Among individual parameters, all except accommodative amplitudes and negative distance fusional vergence showed statistically significant impairment compared with controls (P < .001). Median (interquartile range) stereoacuity was 70 (50 to 550) arc sec in the KC group and 40 (30 to 50) arc sec in control (P < .0001). There was a statistically significant but weak correlation between stereoacuity and positive fusional vergence for near (P = .008; Spearman coefficient, -0.28) and weak but significant negative correlation between phoria status and negative fusional vergence for near (P = .03; Spearman coefficient, -0.24).

CONCLUSIONS

A large proportion of KC patients have BV anomalies. Assessment of BV function should be included in the clinical examination of all KC patients.

A Teenager with Vernal Keratoconjunctivitis and Pellucid Marginal Degeneration, Presenting with Exotropia

Background

Vernal keratoconjunctivitis (VKC), an allergic disease, has a known association with ectatic disorders of the cornea. Pellucid marginal degeneration (PMD) is a bilateral, asymmetrical, ectatic disorder of the cornea characterized by inferior corneal thinning. We report a case of sensory exotropia due to PMD in association with VKC.

Case Details

A 19-year old boy with a history of VKC presented with exotropia of the right eye of 3 years’ duration. His unaided vision in his right eye was 1/60 and in his left eye it was 6/36. On examination, both eyes had high against the rule astigmatism, which was more in the right eye. There was exotropia of 15º (40 prism diopter base in) in the right eye with suppression (Worth four dot test). Corneal examination in both eyes showed inferior band thinning, 2 mm above the inferior limbus, extending from 4 to 8 clock hours, with bulging of the cornea just above the thinning. The clinical features were suggestive of PMD, which was supported by his corneal scans – Atlas, Pentacam, and Optovue. Although he was undergoing treatment for VKC, the onset of PMD and decrease in vision went unnoticed. The asymmetric error which was not corrected during the sensitive period of visual development led to sensory exotropia.

Conclusion

A child with VKC should undergo regular refraction so as not to miss any ectatic changes occurring in the cornea. A delay in diagnosing corneal ectasia may negate the possibility of collagen cross-linking which prevents progression of ectasia. If visual rehabilitation is delayed beyond the age of visual maturation, it can lead to strabismus, suppression, and loss of binocular function.

Sensory exotropia due to keratoconus and review of the literature

This case report describes a 17-year-old boy with sensory strabismus due to keratoconus and an ipsilateral nodular lesion of the bulbar conjunctiva. The aligned eye was the right eye and keratoconus in this eye was of late onset. Vision in the left eye was poor and keratoconus was advanced in this eye. Due to the longstanding nature of the keratoconus and its occurrence in a developmentally sensitive period, sensory exotropia had developed in the left eye. There was a nodular lesion of the bulbar conjunctiva in the ipsilateral eye. If keratoconus occurs before the age of 7 years and the prolonged visual loss is not corrected, sensory strabismus can develop, as in this patient.