Undercorrection occurs when an eye remains somewhat nearsighted after refractive surgery. It is seldom considered a serious complication. Distance vision is better (if not perfect), and near vision is still good. Undercorrection is much more common in people with severe nearsightedness than in people who had nearsightedness of less than 3 diopters.
Slight undercorrection may be considered an advantage. A little mild nearsightedness will delay the onset of presbyopia. And it may offset the effect of progressive farsightedness (hyperopia). Also, the amount of undercorrection may decrease after several years because of a phenomenon called the hyperopic shift. Hyperopic shift is the gradual increase in farsightedness that may occur for some years after radial keratotomy (RK) surgery.
Undercorrection may be successfully corrected with a repeat surgery. But repeat operations tend to be less effective and less predictable than the first surgery.