Corneal ectasia characterises a group of different conditions and/or clinical presentations: keratoconus, pellucid marginal degeneration, keratoglobus, and iatrogenic or post-LASIK ectasia. It is still uncertain whether keratoconus, pellucid marginal degeneration and keratoglobus are different conditions or represent different clinical presentations with the same underlying disease process. The classification currently focuses on the pattern and location of corneal thinning and bulging. Moreover, they can present at different ages.