Corneal Ectasia

Lasik surgery weakens the corneal stroma, leading to progressive corneal thinning and protrusionSubclinical keratoconus and pellucid marginal degeneration greatly increase the risk of progressive ectasia after lasikA residual stromal bed thickness less than 250um likely weakens the cornea

excessively and increases the risk of ectasiaA residual stromal bed thickness of less than 50% of the original corneal thickness may also excessively weaken the cornea and predispose to ectasia PreventionReview the preoperative corneal topography to exclude mild keratoconus and pellucid marginal degeneration Make sure the expected residual bed thickness for each patient is >250um and >50% of the original corneal thickness Consider measuring the flap thickness intraoperatively to be sure there is adequate residual stromal bed thickness for the planned ablationConsider a surface ablation procedure if the residual stromal bed thickness is <250um>