<unk>  causes may be congenital in nature, such as with Aniridia, or acquired. Frequently, inflammatory, infectious, degenerative, traumatic or iatrogenic (e.g. contact lenses) conditions can be responsible for acquired<unk> . Some major acquired inflammatory conditions include graft rejection following keratoplasty, graft or host diseases of the new tissue, atopic conjunctivitis, rosacea, ocular pemphigoid, Lyell's syndrome, and Steven's Johnson syndrome. Infections responsible for<unk>  range from bacterial (chlamydia, syphilis, pseduomonas), viral (herpes simplex & herpes zoster viruses), fungal (candida, asperigillus, fusarium), to parasitic (onchocerca volvolus) infection. Degenerative diseases such as pterygiums and terrien's marginal degeneration may also be responsible. Traumatic causes of<unk>  include ulceration, alkali burns, and stem cell deficiency. One of the most common causes of<unk>  is iatrogenic pathology from extended contact lens wear. This is especially likely with lenses made with older hydrogel materials such as HEMA (2-hydroxyethyl methacrylate) for both daily and extended wear. Such older hydrogel materials have a relatively low oxygen transmissibility so the cornea becomes starved of oxygen; this leads to the ingress of blood capillaries into the clear cornea, in an attempt to provide more oxygen to the affected area. Older estimates cite 128,000 to 470,000 cases of lens-induced<unk>  each year, but this may be decreasing due to the increasing popularity of daily disposable lenses. The risk for<unk>  is elevated in certain instances for patients following penetrating keratoplasty without active inflammation or epithelial defects. For example, the condition is more likely to occur in those with active blepharitis, those who receive sutured knots in their host stromas, and those with a large recipient area.
Corneal neovascularization
Macular corneal dystrophy
Granular corneal dystrophy
Corneal hydrops
Macular edema
Macular scarring
Lattice corneal dystrophy
Interstitial keratitis