Ectasia of the cornea is a risk when performing LASIK on a cornea that has pellucid marginal degeneration. Ectasia is a condition wherein the cornea is weakened to the point that it fails to maintain its normal shape and bows forward like a bulge on an auto tire. There are many conditions that weaken the strength of the cornea and its ability to resist this ectasia. Pellucid degeneration is one of these conditions. Pellucid degeneration and several other cornea-weakening conditions may be difficult to observe during a routine eye examination, although they are easily observed through a routine pre-operative test called corneal topography.