A novel insight into keratoconus: mechanical fatigue of the cornea.

An integrated model for keratectasia risk assessment has received much attention over many years. The objective of this article is to propose a more complete, conceptual model by which high risk individuals can be screened, even with no topographic irregularity or corneal thinning. In this model, corneal ectasia results from the fatigue effect of cyclic shear stress and tensile stress, caused by eye rubbing and fluctuating intraocular pressure (IOP), respectively, on corneal microstructures. The model clarifies the importance of the magnitude of shearing force applied by eye rubbing, the amplitude of IOP fluctuations, the frequency of eye rubbing and IOP fluctuations, the geometry of the cornea, the temperature of the cornea, and the effects of oxidative stress on the cornea in keratectasia development. Therefore, preoperative screening strategies based on these concepts can be designed to assess the risk of keratectasia at an early stage, and select the best candidates who can benefit from keratorefractive surgeries.