Scheimpflug tomographic changes across the keratoconus spectrum based on the modified Rabinowitz-McDonnell classification

PURPOSE: To characterize spectrum-dependent changes in Scheimpflug tomographic parameters across normal, keratoconus suspect, and eyes with keratoconus classified using the modified Rabinowitz-McDonnell index. METHODS: This retrospective comparative study included 115 eyes of 115 patients evaluated at a tertiary ophthalmology clinic. Based on the modified Rabinowitz-McDonnell index, eyes were categorized into control (n = 37), keratoconus suspect (n = 51), and keratoconus (n = 27) groups. All eyes underwent Scheimpflug tomography. Anterior and posterior keratometry values, corneal thickness parameters, corneal volume, anterior chamber depth, and pupil diameter were analyzed. RESULTS: Anterior and posterior corneal curvature parameters increased progressively from control group to keratoconus suspect group and were highest in eyes with keratoconus (all p < 0.001). While anterior keratometric parameters and posterior corneal curvature differed significantly between control and keratoconus suspect groups, pachymetric measurements remained comparable, with significant thinning observed only in the keratoconus group (all p < 0.001). Corneal volume was higher in keratoconus suspect group compared with both control and keratoconus groups (p = 0.001). Anterior chamber depth was greater in keratoconus group, while pupil diameter was smaller in keratoconus suspect group (both p < 0.01). CONCLUSION: When keratoconus is classified using central keratometry, Scheimpflug tomography demonstrates a clear, stage-dependent pattern of corneal change. Curvature-related alterations precede measurable thinning, highlighting that curvature-based classification remains clinically relevant and that tomographic parameters can enhance disease characterization across the keratoconus spectrum.