Binocular Visual Function Changes After Corneal Collagen Cross-linking in Patients With Keratoconus

High-order aberrations (HOAs) have been demonstrated to profoundly affect both visual acuity and stereoacuity in patients with keratoconus. Corneal collagen cross-linking (CXL) has been proven to significantly lower HOAs in keratoconus. Yet, to the present date, no evaluation of the effect of the procedure on stereopsis has been performed. The purpose of the study was to assess differences in binocular visual performance in patients with keratoconus before and after CXL.Patients with keratoconus undergoing standard Dresden protocol epi-off CXL in the ophthalmology department of Policlinico Universitario Agostino Gemelli Hospital received slitlamp examination, uncorrected distance visual acuity and corrected distance visual acuity assessment, corneal tomography, Lang stereotest, TNO stereoacuity assessment, distance and near cover test, and Irvine test before surgery and 6 months after CXL. Stereopsis tests were performed with spectacle correction.The analysis included 30 patients (mean age 24.63 ± 3.49 years). The Lang test improved after treatment (P 0.027), with 6 of 30 patients (20%) showing a positive Lang test before CXL compared with 16 of 30 patients (53.3%) after treatment. Moreover, TNO stereoacuity increased after treatment (P 0.043), and 14 of 30 patients (46.7%) manifested an improvement of at least 250″ at the TNO test after CXL. In this subgroup of patients, total root mean square values decreased after treatment (P0.001), whereas patients who did not manifest a clinically significant improvement in stereoacuity did not show a reduction in total root mean square values after CXL (P = 0.11). The results of cover test and Irvine test did not vary after CXL.Patients with keratoconus showing a reduction of HOAs after CXL also manifest a significant improvement in stereoacuity after the treatment.