Cytokine Expression in Keratoconus and its Corneal Microenvironment: A Systematic Review.

Keratoconus (KC) is a progressive corneal ecstasia characterized by thinning and weakening of the cornea that leads to a cone-like appearance, scarring, and decreased vision. Despite the well-described clinical signs, the cause of KC is unknown. Nevertheless, various genes, proteinases, and environmental factors (eye-rubbing, contact lens wear, tear film composition) have been implicated in its etiology. Although classically defined as a predominantly degenerative disease, with mechanically induced trauma accelerating its course, accumulating evidence suggests a pivotal role for inflammation in the pathophysiology of KC. Several reports have linked various inflammatory mediators (cytokines) with KC, but with contradictory findings. The methods and materials used in these studies vary considerably and warrant critical evaluation to decipher the role of inflammatory mediators in KC. We performed a systematic review of current literature on cytokine expression studies in KC and discuss critical soluble and cellular inflammatory mediators that are implicated in its pathogenesis.