Thinning of tissue in an uncontrolled, progressive, or unanticipated fashion. Corneal ectasia can have adverse optical consequences, as abnormally thin tissue can be biomechanically and optically unstable. Keratoconus (see below) is a type of corneal ectasia, characterized by thinning and steepening of the central or paracentral cornea. A much rarer condition, called keratoglobus, is characterized by ectasia of the peripheral cornea. Ectasia is thought to be aggravated by eye-rubbing in some, but not all cases. Ectasia is rarely associated with laser sculpting surgery, but when it occurs can cause untoward visual consequences and may be difficult to treat.
