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Elias Flockerzi, Theresia Nzau, Ulrike Klühspies, Loic Hamon, Timo Eppig, Achim Langenbucher, Berthold Seitz; Age-dependent Characteristics of Belin’s ABCD Grading System in 1.000 Patients of the Homburg Keratoconus Center (HKC). Invest. Ophthalmol. Vis. Sci. 2019;60(9):4778.
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Keratoconus is a corneal ectasia of unknown etiology, usually affecting both eyes with progressive thinning of the cornea. Belin and Duncan  proposed a new keratoconus grading system based on the analyses of the anterior (A) and posterior (B) curvature of the cornea, the thinnest pachymetry (C) and visual acuity (D) including stages 0 to 4 for each parameter (Tab.1).
1.917 eyes of 1.000 patients of the HKC were allocated to nine groups by the age of the patients (Tab.2), classified according to Belin’s grading system and, subsequently, put into relation to age.
Seventythree percent (n=728) of the patients were males, 27% (n=272) were females, and the highest prevalence of keratoconus occurred in the age range of 21 to 30 years (n=585 eyes, 294 patients). With regard to the anterior (A) and posterior (B) curvature, the proportion of A was significantly higher than B in all age groups for the stages 0, 1 and 2 (A0>B0, p<0.03; A1>B1, p<0.03; A2>B2, p<0,005; calculated as mean±SD by paired t-test). For stage 3, there was no difference between A and B, whereas analysis of stage 4 revealed B being significantly higher than A in all age groups (B4>A4, p<0.02). Comparing the curvatures (A, B) shows that 99.5% (mean, SD 0.76) of patients with stage A4 also were classified as B4 (83.9% A3/B3, mean, SD 34.3). As to the thinnest pachymetry (C), the proportion of patients in all age groups was significantly higher in C0 than C1 (p<0.05). The same applied to the other stages (C1>C2, p<0.03; C2>C3, p<0.02; C3>C4, p<0.04; calculated as mean±SD by paired t-test). Early stages of corneal curvature (62% of patients in A0, B0 and B1) have a normal corneal thickness (C0), which decreases in later stages. For the distance visual acuity (D), a significantly higher number of patients were classified as stage D1 compared to D0 (p<0.03; D0>D2, p<0.05; D2>D3, p<0.02; D3>D4, p<0.02; calculated as mean±SD by paired t-test).
The stage distributions in all age groups were comparable. There were significantly more patients at stage B4 than stage A4 in all age groups. Thus, keratoconus remains a disease of all ages which might originate from the posterior part of the cornea. Belin MW, Duncan JK. Keratoconus: The ABCD Grading System. Klin Monbl Augenheilkd 2016;223(6): 701-7.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
Tab. 1: Keratoconus Grading System taken from .
Tab. 2: Patients in the HKC according to age.
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