The cornea forms the anterior portion of the outer tunic of the eye and its transparency plays a vital role in the eye's refractive system. This transparency is achieved by a combination of physiological and anatomical adaptations, including a non-keratinized surface epithelium, its relative acellularity, lack of pigment, lymphatic vessels and blood vessels and the presence of non-myelinated corneal nerves. Any process that alters the cornea's epithelial or stromal architecture, increases corneal pigmentation, contributes to blood vessel migration, or predisposes to corneal edema, impairs transparency and is indicative of corneal disease. Infection and inflammation as well as traumatic or surgery-induced lesions of the cornea are common causes of such a loss of transparency. There are numerous ways to classify corneal diseases, and the color of their presenting lesions may be helpful for the clinician in determining the underlying cause and therefore give direction regarding the appropriate treatment selection.
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