Keratoconus association with axial myopia: a prospective biometric study

To determine if the axial length and its components are significantly different between a keratoconic eye and an emmetropic eye and also to determine if the degree of corneal ectasia is associated with axial myopia in a keratoconic eye.

A prospective observational study was conducted with keratoconic patients and emmetropic controls. All subjects underwent corneal topography analysis and axial length measurement by immersion-ultrasound biometry. Statistical methods were employed to compare the two groups and to ascertain whether any associations exist.

The axial length, anterior chamber depth, and posterior segment length were all significantly longer in the keratoconic group (n=41) than in the emmetropic control group (n=33) in a statistically significant fashion. The mean keratoconic axial length was 24.40 vs. 23.24 mm for the emmetropic group (P=0.001). The mean keratometry for the keratoconic group correlated with spherical equivalence and visual acuity in statistically significant manners but not with axial length.

Keratoconic eyes have on average longer axial lengths that are primarily because of longer posterior segment lengths than emmetropic eyes. This finding should be considered in keratoconic patients undergoing keratoplasty because it relates to postkeratoplasty refractive outcomes.