Table 1. Proposed ABCD keratoconus grading system. Stages (0 to IV) are based on anterior and posterior radius of curvature (ARC, PRC), thinnest pachymetry, corrected distance visual acuity (CDVA) (mm- millimeter, μm- micrometer, D – diopter)).
| ABCD criteria | A | B | C | D |
|---|---|---|---|---|
| ARC (3 mm Zone) | PRC (3 mm Zone) | Thinnest pach μm | CDVA | |
| Stage 0 | > 7.25 mm (< 46.5 D) | > 5.90 mm | > 490 μm | ≥ 20/20 (≥ 1.0) |
| Stage I | > 7.05 mm (< 48.0 D) | > 5.70 mm | > 450 μm | < 20/20 (< 1.0) |
| Stage II | > 6.35 mm (< 53.0 D) | > 5.15 mm | > 400 μm | < 20/40 (< 0.5) |
| Stage III | > 6.15 mm (< 55.0 D) | > 4.95 mm | > 300 μm | < 20/100 (< 0.2) |
| Stage IV | < 6.15 mm (> 55.0 D) | < 4.95 mm | ≤ 300 μm | < 20/400(< 0.05) |