The clinical situations precluding corneal NV are replete; however, they can be grouped into four categories (Table 10.1 and Figures 10.1–10.3):

	1.	Inflammatory disorders: ocular pemphigoid, atopic keratoconjunctivitis, rosacea, graft rejection, Lyell's syndrome, Stevens–Johnson syndrome, and graft-versus-host disease.
	2.	Infectious diseases: viral keratitis (i.e., herpes simplex keratitis, herpes zoster keratitis), bacterial keratitis (i.e., Pseudomonas infection, syphilis), fungal keratitis (i.e., Candida, Fusarium, Aspergillus), and parasitic infection (i.e., onchocerciasis).
	3.	Degenerative: congenital disorders: pterygium, Terrien marginal degeneration, and aniridia.
	4.	Traumatic: iatrogenic disorders and miscellaneous: contact lens wear, chemical burns, iatrogenic injury, and stem cell deficiency.