Keratoconus: classification scheme based on videokeratography and clinical signs

Abstract

Purpose: To determine in a longitudinal study whether there is correlation between videokeratography and clinical signs of keratoconus that might be useful to practicing clinicians.

Setting: Cornea-Genetic Eye Institute, Cedars-Sinai Medical Center, Los Angeles, California, USA.

Methods: Eyes grouped as keratoconus, early keratoconus, keratoconus suspect, or normal based on clinical signs and videokeratography were examined at baseline and followed for 1 to 8 years. Differences in quantitative videokeratography indices and the progression rate were evaluated. The quantitative indices were central keratometry (K), the inferior-superior (I-S) value, and the keratoconus percentage index (KISA). Discriminant analysis was used to estimate the classification rate using the indices.

Results: There were significant differences at baseline between the normal, keratoconus-suspect, and early keratoconus groups in all indices; the respective means were central K: 44.17 D, 45.13 D, and 45.97 D; I-S: 0.57, 1.20, and 4.44; log(KISA): 2.49, 2.94, and 5.71 (all P<.001 after adjusting for covariates). Over a median follow-up of 4.1 years, approximately 28% in the keratoconus-suspect group progressed to early keratoconus or keratoconus and 75% in the early keratoconus group progressed to keratoconus. Using all 3 indices and age, 86.9% in the normal group, 75.3% in the early keratoconus group, and 44.6% in the keratoconus-suspect group could be classified, yielding a total classification rate of 68.9%.

Conclusions: Cross-sectional and longitudinal data showed significant differences between groups in the 3 indices. Use of this classification scheme might form a basis for detecting subclinical keratoconus.

Figures

Figure 1

Normality plot of central K, I–S, and logKISA values (blue = normal group; orange = keratoconus-suspect group; red = early keratoconus group) (I–S = inferior–superior; K = keratometry; Log(KISA) = logarithm transformation of keratoconus percentage index).

Figure 2

Scatterplot of canonical discriminant analysis (blue = normal group; orange = keratoconus-suspect group; red = early keratoconus group).