Keratoconus: age of onset and natural history.

Keratoconus is a corneal dystrophy that degrades the optical function of the cornea. The onset of the process manifests optical signs: evolving astigmatism, failure of optical correction by spectacles, and distorted images. We report data from 74 keratoconus patients in need of keratoplasty. The variables studied included sex, age of onset, and refractive error. We find that the average age of the appearance of keratoconus is the second decade of life (mean age of onset = 15.39 years, SD = 3.95), with earlier onset occurring in females that in males, although the differences are not statistically significant. The mean corneal astigmatism before keratoplasty was 4.07 D (SD = 1.57). Optometrists should refer patients for surgery when all optical treatment has failed.