The Correlation between Corneal Findings and Disease Severity in Keratoconus per Scheimpflug Corneal Tomography

Abstract

Purpose. This study aims to correlate the clinical signs of keratoconus (KC) which include superficial apical scarring, Fleischer rings, and Vogt striae with best spectacle-corrected visual acuity (BSCVA) and corneal tomography findings. Patients and methods. A retrospective observational study. 72 consecutive KC patients seen by the senior author over the course of one year were included in this case series. Eyes with pellucid marginal degeneration, postrefractive ectasia, history of a corneal graft, prior corneal collagen cross-linking, intracorneal ring segments or hydrops were excluded from analysis. Subsequently, the final analysis included only treatment-naïve KC eyes with varying degrees of disease severity. Results. BSCVA with manifest refraction was 0.5 logMAR higher in eyes with apical scarring (p<0.001). Eyes with apical scarring had worse vision than eyes with Fleischer rings alone (0.43 logMAR higher in the former, p<0.009). Eyes with apical scarring had higher keratometry readings (K2 = 64.56 ± 12.89 D versus 49.07 ± 6.61 D, p<0.001); this was also true for eyes with Fleischer rings compared with ring-free eyes (K2 = 56.23 ± 11.52 D versus 48.91 ± 7.79 D, p<0.001) and eyes with Vogt striae (K2 = 56.19 ± 10.27 D versus 50.68 ± 9.21 D, p=0.01). Atopic disease was a risk factor for scarring: odds ratio (OR) = 2.87 (p=0.03). The OR of observing Fleischer rings in KC eyes was 12% per year (p=0.001). Additionally, each mm of corneal apex displacement from the pupillary center led to a 0.76 logMAR increase in visual acuity (p=0.001). Conclusion. The presence of apical scarring and Fleischer rings on biomicroscopy can aid the clinician in making the distinction between severe or long-standing disease (respectively). Apical scarring is a sign of advanced disease and is associated with worse BSCVA and tomography findings. Fleischer rings are markers of intermediate disease and their presence correlates with disease duration.