Variation in the Best Fit Sphere Radius of Curvature as a Test to Detect Keratoconus Progression on a Scheimpflug-Based Corneal Tomographer.

PURPOSE

To evaluate the variation in the best fit sphere radius (BFSR) of curvature on a Scheimpflug corneal tomographer as a test to detect keratoconus progression.

METHODS

In this retrospective, comparative, case-control study, two groups of eyes with stable or progressive keratoconus were identified based on keratometric, refractive, and visual acuity criteria. Two sequential scans were used to assess the variation in topometric variables. Receiver operating characteristic analysis was conducted for anterior and posterior BFSR values.

RESULTS

A total of 94 eyes of 62 patients were included in the study; 43 eyes were included in the progressive group and 51 eyes in the stable group. In the progressive group, these differences were found to be statistically significant in sequential scans for the analyzed variables: steepest axis keratometry value (K2) = 1.94 ± 1.70 D (P < .001), maximum keratometry value (Kmax) = 2.62 ± 3.08 D (P ≤ .001), apex pachymetry = 12.233 ± 13.728 µm (P ≤ .001), anterior BFSR = 0.116 ± 0.107 mm (P ≤ .001) and posterior BFSR = 0.082 ± 0.075 mm (P ≤ .001). In the stable group, changes in K2, Kmax, apex pachymetry, anterior BFSR, and posterior BFSR were not found to be statistically significant. Analysis of the area under the receiver operating characteristic curve (AUROC) showed that the best tests for discriminating between progressive and stable groups were the variation in the anterior BFSR and variation in K2 (AUROC = 0.940, 95% confidence interval [CI] = 0.884 to 0.996 and AUROC = 0.935, 95% CI = 0.881 to 0.990, respectively). Variation in the posterior BFSR had an AUROC of 0.863 with a 95% CI of 0.775 to 0.950.

CONCLUSIONS

Steepening of the BFSR of anterior and posterior surface elevation maps could be used as indices for keratoconous progression. [J Refract Surg. 2018;34(4):260-263.].