Morphogeometric characterization in keratoconus according to the RETICS grading system

Abstract

Aims/Purpose: Keratoconus progression characterizes by corneal thinning resulting in irregular astigmatism and visual impairment. In the present work a computerized 3D modelling method is used to describe different morphogeometric variables in healthy corneas and keratoconus. RETICS grading system was used to characterize keratoconus with best corrected visual acuity (BCVA) as the major grading parameter. Analyzing morphogeometric variables and its correlation with visual acuity (VA) may help understand structural changes associated with visual decline in keratoconus.Methods: 124 healthy corneas and 257 eyes with keratoconus were included and classified according to the RETICS grading system as grade 1 (n = 94) when VA > 0.9; grade 2 (n = 65) when 0.6 < VA ≤ 0.9; grade 3 (n = 50) when 0.4 < VA ≤ 0.6; grade 4 (n = 31) when 0.2 < VA ≤ 0.4 and grade 5 (n = 17) when VA ≤ 0.2. Computerized 3D modelling was done and morphogeometric variables analysed: anterior surface area (ASA), posterior surface area (PSA), total area (TA), total volume (TV), anterior apex deviation (AAD), posterior apex deviation (PAD), anterior minimum thickness point deviation (AMTPD) and posterior minimum thickness point deviation (PMTPD).Results: All morphogeometric variables showed differences between normal and keratconic eyes (p < 0.001). ASA and PSA present higher values in keratoconus (p < 0.001), while TV shows lower values in the same subjects (p < 0.001). Correlation between BCVA and all variables was calculated showing a positive correlation for the ASA (p = 0.0036) and PSA (p = 0.0172), and a negative correlation for TV (p = 0.1612) and PAD (p = 0.0821).Conclusions: As keratoconus progresses and VA worsens, corneal structural changes include an increase in the PAD, in addition to an increase of both anterior and posterior corneal areas while TV tends to decrease. Morphogeometric variables represent a new parameter to characterize keratoconus and some demonstrate a statistically significant correlation with visual loss.