Keratoconus is a progressive, dystrophic, most often bilateral disease of the cornea that leads to refractive errors (myopia and irregular astigmatism) and resultantly impairment of visual acuity and conical corneal protrusion. The main condition responsible for corneal ectasia is the progressive thinning of the stroma. Adolescents at puberty and young adults until the fourth decade of life with aged between approximately 12 and 35 years are the most affected by this disease, a period in which the disease can progress or spontaneously arrest. As such, an early diagnosis of fruste and clinical keratoconus is very important in order to prevent progression of the illness by performing a corneal crosslinking riboflavin UVA procedure.

The genetic component of this disease has been supported by evidence of familial inheritance and the high correlation among monozygotic compared to dizygotic twins. This is also supported by its association with multiple systemic and ocular disorders such as Down syndrome, Leber congenital amaurosis, and Ehler-Danlos syndrome. Thus, an association between environmental and genetic factors is likely responsible for the development of the disease. Among the exogenous environmental factors that induce mechanical changes are contact lens wearing and eye rubbing, causing corneal epithelial microtraumas that stimulate the expression of cellular inflammatory mediators. Atopy has also been shown to correlate with keratoconus, although it is still uncertain whether the atopic ground itself or its effect (eye rubbing) is the one responsible for the effects on the cornea, as it has been shown that eye rubbing releases inflammatory mediators such as interleukin-6 (IL-6) and growth factors. The stromal degradation and its thinning are the most important aspects and many hypotheses have been raised in order to explain it. Some studies relate the thinning to increased levels of proteolytic enzymes on the one hand and decreased levels of their inhibitors on the other hand. The abnormal collagenolytic activity of the cells and the accelerated apoptosis of keratocytes induce a loss of extracellular matrix and redistribution of collagen fibrils. Thus, stromal thinning and possible breaks in Bowman’s layer with subsequent scarring occur.

The aim of this Special Issue is to collate original research and review articles describing advances in this field.

Potential topics include but are not limited to the following:

• The influence of interleukin 6 (IL-6) and growth factors on the progression of keratoconus
• Inflammation as a factor for the appearance and progression of keratoconus
• The genetic component responsible for the appearance and progression of keratoconus
• Familial inheritance of keratoconus
• The role of eye rubbing in the expression of cellular inflammatory mediators
• Contact lenses as a trigger for the release of cellular inflammatory mediators
• The correlation between atopy and keratoconus