Astigmatic changes have been shown to occur after ptosis repair due to the altered vector forces on the underlying cornea from the repositioned upper eyelid. The astigmatic change is usually transient, but it may affect a patient’s vision for at least the first few months after surgery. The authors present a case of a patient who underwent ptosis repair and subsequently developed postoperative decline in best-corrected visual acuity due to previously undiagnosed keratoconus. The patient’s irregular astigmatism seems to have been masked by the ptotic upper eyelid, which we postulate to have acted similar to a stenopaic slit. Correction of the upper eyelid ptosis unveiled previously asymptomatic irregular astigmatism including vertical coma, leading to alteration in the optical wavefront and resultant image degradation.