The analysis of corneal topography for keratoconus

Objective To investigate th e refraction and videokeratographic characteristics of keratoconus. Me thods 262 eyes of 147 patients with keratoconus were examined using autorefractor and computerized corneal topography, which generated the quantita tive descriptors including refraction, keratometry, corneal astigmatism, the sur face regularity index (SRI) , the surface asymmetry index (SAI), and morphologic description. Results All patients were classified into four groups: suspect, mild, moderate and advanced group. The topographical conf igurations of the lesions were divided into bow-tie pattern subdivided into sym metric and asymmetric pattern, and non-bow-tie pattern including nipple, oval, global and anomalistic pattern. The bow-tie pattern mostly appeared symmetric al and occurred in suspect and mild cases. The nipple and oval pattern mostly o ccurred in mild and moderate ones located in the central or inferior paracentral cornea. The global pattern mostly occurred in moderate and advanced ones locat ed in the central cornea. The anomalistic pattern occurred in advanced ones. B ilateral topography showed symmetrical in majority of patients with bilateral ke ratoconus. There was no correlation between the diameter of lesion and the refr action power of corneal apex (r=0.208, P=0.092). There was negative c orrelation between the distance from corneal center to the apex of lesion and th e refraction power of corneal apex (r=-0.400, P=0.001). Conclusions Corneal topography is a sensitive method to detect the keratoconus earlier,which helps eye doctors to take appropriate measures to imp rove patients vision and avoid patients from undergoing excimer laser keratore fractive surgery. In addition, it can show the configuration of the lesion, whi ch guide the fitting of hard contact lens. (Chin J Ophthalmol, 2006,42: 231-235)