Effect of topographic cone location on outcomes of corneal collagen cross-linking for keratoconus and corneal ectasia.

PURPOSE To assess the effect of preoperative topographic cone location on 1-year outcomes of corneal collagen cross-linking (CXL). METHODS In this prospective, randomized, controlled clinical trial, 99 eyes (66 keratoconus, 33 ectasia) from 76 patients underwent CXL. Cone location was defined by the coordinates of preoperative maximum keratometry (maximum K) using the anterior sagittal curvature topography map (Pentacam, Oculus Optikgeräte GmbH). Patients were divided into three groups: those with a maximum K located within the central 3-mm (central cone group), 3- to 5-mm (paracentral cone group), and outside the 5-mm (peripheral cone group) optical zones. Topography and visual acuity data were obtained preoperatively and at 1 year. RESULTS In the combined cohort, maximum K and uncorrected and corrected distance visual acuity significantly improved by -1.60±3.40 diopters (D) (P<.001), -0.08±0.25 logMAR (P=.001), and -0.10±0.18 log-MAR (P<.001), respectively. Comparing cone groups, maximum K decreased by 2.60±4.50 D (P<.001) in the central cone group, 1.10±2.50 D (P=.02) in the paracentral cone group, and 0.40±1.20 D (P=.08) in the peripheral cone group. Differences among groups were statistically significant (P<.001). Uncorrected distance visual acuity improved by -0.07±0.3 logMAR (P=.1) (central cone group), -0.1±0.17 logMAR (P=.004) (paracentral cone group), and -0.1±0.25 logMAR (P=.04) (peripheral cone group). Corrected distance visual acuity improved by -0.14±0.21 logMAR (P<.001) (central cone group), -0.08±0.17 logMAR (P=.01) (paracentral cone group), and -0.08±0.12 logMAR (P=.002) (peripheral cone group). For both UDVA and CDVA outcomes, these differences among groups were not statistically significant. CONCLUSIONS After CXL, more topographic flattening occurs in eyes with centrally located cones and the least flattening effect occurs when the cone is located peripherally. This cone-location effect is found in eyes with both keratoconus and ectasia.