Structural retinal and choroidal changes in keratoconus: A cross-sectional OCT study stratified by ABCD grading

To evaluate posterior segment structural changes in patients with keratoconus (KC), and to assess their association with anterior segment parameters across disease severity stages using the ABCD classification system.

This cross-sectional observational study graded staged KC severity I-IV based on the ABCD grading system. All participants underwent comprehensive ophthalmic evaluation, including corneal tomography (Pentacam HR), optical coherence tomography with enhanced depth imaging (Spectralis EDI-OCT), and ocular biometry. Posterior segment parameters were compared across KC stages and with controls. Correlation analyses were performed to assess associations between anterior and posterior segment metrics.

The study included 124 eyes from 124 patients with keratoconus and 32 right eyes from healthy control individuals. RNFL thickness was significantly reduced in KC eyes compared to controls (103.7 ± 11.6 μm vs. 110.0 ± 12.0 μm; P = 0.008), with a progressive decline observed from stage I to IV. Central foveal retinal thickness showed a mild, non-significant reduction in stages III and IV (234.6 ± 20.9 μm and 232.8 ± 19.7 μm, respectively) compared to earlier stages and controls (P = 0.066). SFCT remained relatively unchanged across all KC stages and between KC and control groups (416.6 ± 85.4 μm vs. 420.3 ± 70.2 μm; P = 0.824). Correlation analyses revealed no significant associations between anterior segment parameters (e.g., apex pachymetry, thinnest corneal thickness) and posterior segment measurements (P > 0.05 for all).

KC is associated with significant RNFL thinning, particularly in advanced stages, suggesting posterior segment involvement. However, retinal and choroidal thicknesses remain largely unaffected.