Purpose: We aimed to explore a new classification system based on the change of focal corneal curvatures and corneal thickness in Terrien's corneal degeneration with optical coherence tomography.
Methods: This was a cross-sectional study. Ninety eyes of 59 patients with Terrien's degeneration were examined with slit lamp biomicroscopy, Orbscan II corneal tomography and the Visante OCT system, and were staged according to Süveges's classification.
Results: The ratio of female to male patients was 1.57:1. The ratio of bilateral to unilateral lesions was 1.27:1. The occurrence of bilateral lesion was higher in males than in females (x(2) = 7.791, p = 0.005). There was no difference in the mean age between female and male patients (t = 1.859, p = 0.068), or between patients with bilateral and unilateral lesions (t = 1.797, p = 0.078).The minimum corneal thickness at the thinnest point (MinCT) and anterior curvature of the peripheral cornea were almost normal in the initial stages of disease. The anterior curvature was flattened when MinCT became less than 0.56 mm, returned to normal when MinCT was no more than 0.24 mm, and bowed forward when MinCT was no more than 0.13 mm. The posterior corneal curvatures were bowed forward from their normal curvatures in 42 of 90 eyes when MinCT was no more than 0.41 mm. These eyes' MinCT ranged from 0 to 0.41 mm. There was a strong correlation between change of corneal curvatures and MinCT (r = -0.943, p < 0.01). A new classification of six stages based on corneal curvatures is proposed for evaluating the development of Terrien's degeneration. Statistically, there was a moderate correlation between either the Süveges staging or the new staging and the width and circumference of corneal lesions, visual acuity, and simulated keratometric value (all r < 0.6). The correlation of MinCT with the new classification based on corneal curvatures was higher than that with Süveges's classification (r 1 vs. r 2 , -0.943 vs. -0.801).
Conclusion: The proposed new classification based on focal corneal curvatures is closely associated with corneal thinning, is valuable for evaluating the development of Terrien's degeneration and may enhance surgical planning.
Keywords: Classification of development; Corneal curvature; Corneal thinning; Optical coherence tomography; Terrien’s degeneration.