Corneal Physiology: Corneal Form and Function

Abstract

The cornea forms the anterior meniscus-shaped transparent portion of the ocular globe; it serves as the principal refractive element in the eye, while maintaining a highly impermeable barrier between the eye and the environment. The cornea is avascular, meeting its oxygen requirements largely from the atmosphere by diffusion across the tear film and epithelium; conversely, it derives most of its additional nutritional requirements from the aqueous humor arising from across the corneal endothelium. The epithelium of the cornea provides the major barrier to tear-borne pathogens, while the corneal endothelium is principally responsible for maintaining the hydration and clarity of the corneal stroma. As the highest refractive power in the optics of the eye, subtle variations in corneal curvature lead to higher order aberrations that can be assessed with corneal topography. Measured with instruments that analyze reflected patterns from the tear film, variations of the Placido disk permit the most sensitive assessments of corneal optical properties. These data form the basis for the color-coded contour map display of corneal curvature, permitting clinical diagnosis of a wide variety of corneal pathologies as well as evaluation and development of refractive surgical procedures. Adjunct slit-based methodologies provide tomographic curvature data of both corneal surfaces and three-dimensional corneal pachymetry. Several artificial intelligence-based approaches have used topography and tomography variables for the automatic detection and interpretation of corneal shape anomalies.