Unilateral keratoconus and mirror image in a pair of monozygotic twins

We report the first observation to our knowledge of mirror unilateral keratoconus in monozygotic twins. The observation focuses on monozygotic twins, followed for 5 years. The progression of the refraction, the clinical examination, the video-topographic data, and the Orbscan elevation curves of the twins were collected and analyzed. For each twin, there was slightly progressive unilateral keratoconus during that time, located on the right for the first twin and on the left for the second one. Within the current limits of our diagnostic means, it appears to be the first case of mirror unilateral keratoconus in monozygotic twins. Several cases of mirror pathologies have been described, mainly concerning the renal and dental organs. The appearance of such mirror pathologies may be the consequence of the rise of a genetic or environmental factor during the acquisition of the symmetry of the zygote, occurring before its split into two monozygotic embryos.