The common ectatic disorders of the cornea include keratoconus, keratoglobus and pellucid marginal degeneration (PMD). All these disorders are described in this chapter with its background, epidemiology, clinical signs, diagnosis and topography which may help in surgical treatment plans. Topography is a clinical tool used for assessment of corneal anatomy and identification of subtle changes in corneal curvature. Elevation-based topographic devices, pachymetric mapping, placido topography and corneal rigidity measurements are commonly used for assessment of the cornea during preoperative refractive evaluation. Keratoconus is considered a bilateral condition and is associated with numerous ocular and systemic diseases such as eye rubbing, atopy, Down’s syndrome, retinitis pigmentosa, etc. PMD is progressive, noninflammatory corneal, ectatic disorder involving thinning of the inferior cornea in a crescentic pattern. Keratoglobus is a rare, noninflammatory ectatic disorder characterized by bilateral corneal thinning with diffuse globular protrusion.