Subclinical keratoconus detection with three-dimensional (3-D) morphogeometric and volumetric analysis

Abstract

Purpose: To assess the efficacy of morphogeometric and volumetric characterization of the cornea based on three-dimensional (3-D) modelling in diagnosis of subclinical keratoconus (KC). Methods: Cross-sectional study. Ninety-three eyes with subclinical KC with a best spectacle-corrected distance visual acuity ≥20/20 (grade zero KC according to the RETICS classification) and 109 control eyes were included. Computer-based 3-D corneal morphogeometric model was generated using raw topographic data. Distance-, area- and volume-based parameters were used for statistical analysis. Distance parameters included deviation of anterior (Dapexant)/posterior (Dapexpost) apices and minimum thickness points (Dmctant, Dmctpost) from corneal vertex, and Dapexant-Dapexpost difference. Areal variables were derived from anterior (Aant) and posterior (Apost) corneal surfaces, sagittal plane passing through corneal apices (Aapexant, Aapexpost) and thinnest point (Amctant, Amctpost). Total corneal volume (Vtotal) and volumetric distribution (with 0.1mm steps) centred to thinnest corneal point (VOLmct) and anterior (VOLaap)/posterior (VOLpap) apices comprised the volume-based parameters. Results: In the subclinical KC group, all D values, Dapexant-Dapexpost difference, Aant, Apost and Aapexant values were higher (p < 0.001), while Aapexpost, Amctpost, Vtotal, VOLmct, VOLaap and VOLpap values were lower when compared to the control group (p < 0.001). Regression analysis-based formula correctly classified 96.8% of the eyes with subclinical KC and 94.5% of the normal ones (p < 0.0001). Conclusions: Eyes with subclinical KC seem to represent asymmetrically displaced anterior and posterior corneal apex, corneal thinning and volume loss. 3-D morphogeometric and volumetric parameters and differentiation formula can be incorporated into topography software to detect subclinical KC with high sensitivity and specificity in clinical practice.