Vision Disorders - Other Refractive Errors

While the above refractive errors may be congenital (originating at birth) or occur gradually, fast changes in the eyes' focusing ability should be investigated immediately by an ophthalmologist. Some causes may be senile cataracts (described below); diabetes mellitus—in which fluctuating blood sugar levels cause corresponding fluctuations in focus; external pressure from lumps or cysts on the eyelids distorting the shape of the cornea; subluxation (partial dislocation) of the crystalline lens, causing hyperopia when it moves backward and myopia when it moves forward; and keratoconus, the thinning of the cornea allowing irregular curvature of the eyeball.