Corneal surface disease topology

The study of surface corneal disease often neglects the analysis of the num erous subtle factors that determine the morphology and distribution of dise ase. For example, surface corneal anatomy is both aspherical and asymmetric al. The adnexa and their position create microenvironments for adjacent and distant areas of the cornea. The corneal limbus creates a different physio logy and biochemistry in the peripheral cornea as compared to the central c ornea and creates an "edge" effect. The superficial cornea has many feature s that influence corneal disease, including tear-film distribution and prox imity to other structures, yet we seldom consider corneal disease within th e context of these influences. Generally, we divide disease into our own ex ternal and more artificial classification (i.e., infectious, inflammatory m etabolic, congenital, neoplastic, iatrogenic, traumatic, and degenerative). However, this scheme does not allow us to predict the cause of surface dis ease as we might on the basis of simply its morphology and location on the corneal surface. The study of the morphology and physical location of surface disease leads to an understanding of the diverse influences that create the disease envir onment. However, this understanding finds our old classification to be insu fficient. For example, blepharitis is not merely infectious. Blepharitis is due to a combination of a bacterial agent (infectious classification), hos t susceptibility (congenital), and a host response (inflammatory), that lea ds to a cellular change (degenerative), with neovascularization (possibly n eoplastic) and corneal metabolic changes (metabolic); and often the disease is overtreated by the physician (iatrogenic). The diagnosis blepharitis de scribes a diverse group of eyelid diseases that encompass the anterior and posterior lamella and cannot be described in terms of one physical and morp ological. appearance. This example demonstrates the importance of definitio ns in improving our understanding of corneal disease and the inability of o lder classification systems to help us to understand the disease process.