Preoperative mapping benefits
Epithelial thickness mapping can help us identify early keratoconus while screening patients for corneal refractive surgery. Although keratoconus can also be identified with topography, epithelial thickness mapping provides additional supporting evidence in the diagnosis, which allows us to offer alternative treatment options.
Kanellopoulos et al found that overall epithelial thickness appears increased in ectatic corneas. They suggested that overall average increased epithelial thickness may be a reliable early biological marker of loss of biomechanical corneal stability.
Their results indicated that, firstly, highly irregular epithelium is often an indicator for a thicker and ectatic cornea; secondly, the epithelium is thinner over the keratoconic protrusion, often by up to 30 μm; and thirdly, on average, there is a thicker epithelium in keratoconic corneas.1
They further noted that nonprogressive and nonectatic conditions, such as contact lens warpage, can give similar topographic appearances, making clinical decision-making difficult. They examined the relationship between epithelial thickness and corneal topography maps in patients with keratoconus or contact lens warpage and determined that there was focal epithelial thickening associated with the areas of corneal steepening in contact lens warpage, which was in contrast with the focal epithelial thinning associated with the areas of corneal steepening in keratoconus.
In conclusion, careful preoperative examination of epithelial thickness and its distribution may be a useful tool for detection of early keratoconus.2