[The analysis of corneal topography for keratoconus]

To investigate the refraction and videokeratographic characteristics of keratoconus.

262 eyes of 147 patients with keratoconus were examined using autorefractor and computerized corneal topography, which generated the quantitative descriptors including refraction, keratometry, corneal astigmatism, the surface regularity index (SRI), the surface asymmetry index (SAI), and morphologic description.

All patients were classified into four groups: suspect, mild, moderate and advanced group. The topographical configurations of the lesions were divided into bow-tie pattern subdivided into symmetric and asymmetric pattern, and non-bow-tie pattern including nipple, oval, global and anomalistic pattern. The bow-tie pattern mostly appeared symmetrical and occurred in suspect and mild cases. The nipple and oval pattern mostly occurred in mild and moderate ones located in the central or inferior paracentral cornea. The global pattern mostly occurred in moderate and advanced ones located in the central cornea. The anomalistic pattern occurred in advanced ones. Bilateral topography showed symmetrical in majority of patients with bilateral keratoconus. There was no correlation between the diameter of lesion and the refraction power of corneal apex (r = 0.208, P = 0.092). There was negative correlation between the distance from corneal center to the apex of lesion and the refraction power of corneal apex (r = -0.400, P = 0.001).

Corneal topography is a sensitive method to detect the keratoconus earlier, which helps eye doctors to take appropriate measures to improve patients vision and avoid patients from undergoing excimer laser keratorefractive surgery. In addition, it can show the configuration of the lesion, which guide the fitting of hard contact lens.