Purpose: To describe the prevalence and systemic associations of keratoconus in young adults in Perth, Western Australia.

Design: Cross-sectional study.

Participants: One thousand two hundred fifty-nine participants 20 years of age.

Methods: The Raine Study is a multigenerational, longitudinal cohort study based in Perth, Western Australia. This study represents a cross-sectional analysis of the birth cohort on returning for a 20-year follow-up. Participants underwent a detailed ophthalmic examination, including visual acuity assessment and Scheimpflug imaging using the Pentacam (Oculus, Wetzlar, Germany), and completed a health questionnaire. Keratoconus was defined as a Belin/Ambrόsio enhanced ectasia display score of 2.6 or more in either eye based on Pentacam imaging.

Main outcome measures: Prevalence of keratoconus in this cohort.

Results: Of the 1259 participants, 50.8% were women and 85.7% were White. Fifteen participants had keratoconus in at least 1 eye, giving a prevalence of 1.2% (95% confidence interval, 0.7%-1.9%), or 1 in 84. A significant difference was found in best-corrected visual acuity (0.01 logarithm of the minimum angle of resolution vs. -0.05 logarithm of the minimum angle of resolution; P = 0.007), cylinder (1.25 diopters [D] vs. 0.25 D cylinder; P < 0.001) and spherical equivalent (-1.42 D vs. -0.50 D sphere; P = 0.02) on objective refraction, mean keratometry of the steep meridian (45.19 D vs. 43.76 D; P < 0.001), and mean corneal thickness at the thinnest point (475 μm vs. 536 μm; P < 0.001) between those with and without keratoconus. Keratoconus was associated with regular cigarette smoking (38.5% vs. 14.6%; P = 0.04), but showed no association with gender, race, body mass index, use of spectacles or contact lenses, history of allergic eye disease, or pregnancy.

Conclusions: The prevalence of keratoconus in this Australian population-based study of 20-year-old adults was 1.2% (95% confidence interval, 0.7%-1.9%), or 1 in 84, which is one of the highest reported in the world. This has important implications for screening individuals at a younger age so that treatment can be initiated before disease progression.