Spectrum of Binocular Vision Anomalies in Keratoconus Subjects

Abstract

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.