Just last week, I have just seen two keratoconus patients that only need scleral lens for one eye. So does unilateral keratoconus exist? Well, both of them have bilateral keratoconus, but it is just that the other eye is at a very mild stage. Their visual acuities are almost 20/20 for the better eye. Lucky for them right? Visual acuity is sometimes spared if the cone is located not directly on the visual axis (as seen in my attached corneal topography). You will note there that the steepest portion of the cone is located slightly lower than the center. Although their other eye has nearly perfect vision, the eye with moderate to advanced keratoconus may cause headaches due to very poor and even double vision. Thus the need of managing the more affected eye. Now back to the question....so does unilateral keratoconus exist? In a study by Wei RH et al*, the incidence of unilateral keratoconus is only about 4.5%. It was also indicated in the study that the fellow eye would u