The corneo-limbal ring in normal and keratoconic eyes

The corneo-limbal ring (CLR) is defined here as the best fitting ellipse within the limbal region and characterized by the horizontal diameter (Dh), the vertical diameter (Dv), the eccentricity (e), and the circumference (O). The shape of CLR is expressed by e. The larger the e the more oval is CLR. Based on photoslit-lamp examination the parameters of CLR were estimated in 29 normal and 27 keratoconic eyes. Pooled values of the normal eyes demonstrated means +/- SD of Dh, Dv, e, and O to be 11.86 +/- 0.53, 11.47 +/- 0.68, 0.25 +/- 0.11 and 36.65 +/- 1.83 mm, respectively. No significant differences could be demonstrated between normal and keratoconic eyes with respect to the CLR parameters. From photokeratoscopic examinations the corneal astigmatism (delta Kmm) was determined in the two groups. In the normal, but not in the keratoconic group delta K was positively correlated to the difference between Dh and Dv. In conclusion, the equal shape and size of CLR in normal and keratoconic eyes indicate a mainly corneal alteration in keratoconus.