Several methods have been described to both evaluate and document progression in keratoconus and to show efficacy of cross-linking, however, there are no consistent generally accepted parameters. Modern corneal tomography, including both anterior and posterior elevation and pachymetric data can be used to screen for ectatic progression, be employed to detect earlier change and additionally to show efficacy of new treatment modalities, such as crosslinking.To describe specific quantitative values that can be used as progression and efficacy determinants, the normal noise measurements of the three parameters used in the ABCD keratoconus classification (corneal thickness at the thinnest point, anterior and posterior radius of curvature taken from the 3.0 mm optical zone centered on the thinnest point), were determined. Values were obtained from both a normal population and a known keratoconic population. The 80 and 95% one-sided confidence intervals for all three parameters were surprisingly small, suggesting that they may perform well as progression and efficacy determinants.

Purpose: To incorporate advanced corneal imaging into a new keratoconus classification system that utilizes posterior curvature, thinnest pachymetry, and best-corrected distance vision (CDVA) in addition to standard anterior parameters. Materials and methods:A total of 672 eyes of 336 normal patients were imaged with the Oculus Pentacam HR. Anterior and posterior radius of curvature measurements were taken using a 3.0 mm zone centered on the thinnest area and corneal thickness was measured at the thinnest point. Mean and standard deviations were recorded and anterior data were compared to the existing Amsler-Krumeich (AK) classification. Results:A total of 672 eyes of 336 patients were analyzed. Anterior and posterior values were 7.65 ± 0.236 mm / 6.26 ± 0.214 mm respectively and thinnest pachymetry values were 534.2 ± 30.36 um. Comparing anterior curvature values to AK staging yielded 2.63, 5.47, 6.44 standard deviations for stages 1, 2, and 3 respectively. Posterior staging uses the same standard deviation gates. Comparative pachymetric values yielded 4.42, and 7.72 standard deviations for stages 2 and 3 respectively. Conclusion:A new keratoconus staging system incorporates posterior curvature, thinnest pachymetric values, and distance visual acuity in addition to the standard anterior curvature and consists of stages 0 to 4 (5 stages), closely matches the existing AK classification stages 1 to 4 on anterior curvature. The new classification system by incorporating curvature and thickness measurements based on the thinnest point, as opposed to apical, better reflects the anatomic changes in keratoconus.