Changes in corneal topography asymmetry indices after corneal collagen cross-linking in keratoconus

Abstract

Purpose The aim of this study was to evaluate the changes in corneal topography asymmetry indices after corneal collagen cross-linking (CXL) in patients with keratoconus and to analyze their correlation with visual acuity changes and preoperative average keratometric (K) value. Setting and design This is a prospective interventional noncomparative nonrandomized study that was conducted at the Outpatient Clinic of the Ophthalmology Department of Tanta University Hospital. Patients and methods CXL was conducted in 30 eyes of 15 patients with keratoconus. Quantitative descriptors of corneal topography were measured with corneal tomography using a rotating Scheimpflug camera (Pentacam-Oculus). They included seven indices: index of surface variance (ISV), center of keratoconus index (CKI), index of height asymmetry (IHA), index of vertical asymmetry (IVA), keratoconus index (KI), index of height decentration (IHD), and minimum radius of curvature (Rmin). Follow-up of cases was done for 6 months. Results There was a statistically significant improvement in ISV (P<0.001), IVA (P<0.001), KI (P<0.001), CKI (P=0.007), IHD (P<0.001), and Rmin (P=0.001). However, there was no statistically significant difference in IHA (P=0.082). The improvement in postoperative indices was not correlated with the changes in corrected distance visual acuity. The preoperative average K value was statistically significantly positively correlated with the improvement in KI (r=0.589, P=0.001), ISV (r=0.495, P=0.005), preoperative IHD (r=0.422, P=0.020), and preoperative CKI (r=0.663, P=0.001), with a statistically significant negative correlation with the preoperative Rmin (r=-0,916, P>0.001). However, the preoperative average K value was not significantly correlated with the improvements in IHA (r=-0,078, P=0.681) and IVA (r=0.204, P=0.280). Conclusion There was a significant improvement in six of the seven topography indices 6 months after CXL. Improvement in these indices was not correlated with corrected distance visual acuity changes. The preoperative average K value was significantly correlated with the improvement in KI, ISV, preoperative IHD, preoperative CKI, and preoperative Rmin.