Background: To determine the prevalence of Orbscan II-derived keratoconus traits in relations of individuals with keratoconus and a control group and to apply these to a pedigree analysis.
Methods: In a controlled, prospective, observational case series, four Orbscan II-derived corneal parameters were examined in relations of individuals with keratoconus and a control group of low myopes (<2.5 D). The four parameters and thresholds for abnormality (derived from a literature review) were as follows: average keratometry (> or =47.2 D), I-S value (> or =1.2 D), posterior float apex (> or =42 microm) and thinnest pachymetry (< or =463 microm).
Results: Forty-four unrelated controls (88 eyes) and eight families with 90 members without known (178 eyes) and 11 members with keratoconus (19 eyes) were analysed. One of 88 (1.14%) control eyes had a single keratoconus trait, and none had more than one trait. Of 178 eyes from relatives of patients with keratoconus, 45 (25.3%) had one or more keratoconus traits. Relatives of patients with keratoconus had an elevated risk of possessing a keratoconus trait (relative risk 14.67, CI 2.07-104.07, P < 0.001) compared with controls. Approximately 53.3% of relatives with a keratoconus trait were evident on either pachymetric or posterior elevation indices alone. Six of eight families suggested dominant inheritance.
Conclusions: Keratoconus traits are common in relatives of patients with keratoconus. There prevalence may have been previously underestimated by using placido image-based topography alone where corneal pachymetry and posterior elevation are not assessed. This study suggests an autosomal dominant pattern of inheritance with variable expressivity in some families.