How Abnormal Is the Noncorneal Biometry of Keratoconic Eyes?

Purpose:To determine whether the noncorneal biometry in keratoconic eyes deviates from that in healthy eyes.Methods:The right eyes of 200 healthy subjects and 76 patients with keratoconus were measured with an autorefractometer, a Scheimpflug tomographer, and an optical biometer. The analysis consisted of a general linear model (GLM), correcting for age and gender effects, comparing keratoconic eyes with healthy eyes, and emmetropic eyes. Next, 20 patients with mild keratoconus in one eye and moderate keratoconus in the fellow eye were analyzed to assess the effect of disease stage.Results:As expected the keratoconic group differed significantly from both the healthy and the emmetropic groups for most refractive, corneal, and anterior chamber parameters (GLM, P < 0.001). For the vitreous depth V and the axial length L, the keratoconic group showed significantly larger values than the emmetropic group (V: +0.68 0.19 mm, P = 0.001; L: +0.63 +/- 0.14 mm, P < 0.001), but not larger than the healthy group (V: +0.18 +/- 0.20 mm, P = 0.364; L: +0.09 +/- 0.14 mm, P = 0.519). Besides the corneal parameters, the stage of the disease led to a significantly deeper aqueous depth (+0.07 +/- 0.02 mm; Wilcoxon signed rank, P = 0.002), but no significant difference in axial length (P = 0.940).Conclusions:Current analysis does not confirm the previously suggested association between keratoconus and higher amounts of axial myopia, which may have been the result of selection bias by using emmetropic eyes as a healthy control group.