Obscan II topography sensitive indices to aid in screening for early keratoconus

Objective To evaluate the characteristic and search the sensitive index for diagnosis of early keratoconus in corneal topography.Methods A prospective study using Orbscan was performed in early keratoconus,media /high myopia with/without a history of corneal contact lens of similar age and diopter as control.We evaluated the results and carried out discriminant analysis.Results In this study,there is no statistically significance among the three groups in ages,degree of myopia and astigmatism (all P 0.05).we discover that there are statistically significance in the Im-Sm、I-S、central keratometry、the thin-nest thickness of cornea、anterior elevation、posterior elevation、SimK's Astig、SimK's Max、3.0mm Zone Irreg、3.0mm Zone Mean Pwr、3.0mm Zone Astig Pwr and 5.0mm Zone Irreg between the early keratoconus and control (all P0.05).There are not statistically significance in the CTI、5.0mm Zone Mean Pwr and 5.0mm Zone Astig Pwr between the early keratoconus and control (all P0.05).The Im-Sm,central corneal keratometry,Thinnest corneal thickness,3.0mm Zone Irreg and 3.0mm Zone Astig PWr are sensitive index in the diagnosis of early keratoconus according to discriminant analysis.Canonical discriminant function formula are as follow:D=-6.560+0.274X1+0.177X2-0.005X3+0.182X4+0.224X5 (X1= Im-Sm;X2= central keratometry;X3=thinnest corneal thickness ;X4=3.0mm Zone Irreg;X5=3.0mm Zone Astig Pwr).We got the discriminant rate of 90.1%.Conclusions All Im-Sm,central keratometry,thinnest corneal thickness,3.0mm Zone Irreg and 3.0mm Zone Astig PWr appear to be sensitive and specific for diagnosing early keratoconus.These indices may prove to be clinically useful parameters for distinguishing early keratoconus from myopia with /without a history of corneal contact lens.