<unk>  is caused by inflammation due to the activation of immune cells, including lymphocytes and macrophages. Most of the time, the cause of<unk>  is never determined (idiopathic). An identifiable cause is discovered in about one third of cases. Several diseases are associated with<unk> , including systemic vasculitis (polyarteritis nodosa, granulomatosis with polyangiitis, Behçet's disease), connective tissue diseases (rheumatoid arthritis, relapsing polychondritis, systemic lupus erythematosus), psoriatic arthritis, ankylosing spondylitis, Cogan syndrome, rosacea, gout, atopy, Crohn's disease, and ulcerative colitis. 59 percent of patients with relapsing polychondritis have either<unk>  or scleritis. Rarely,<unk>  may be caused by scleritis. Very rarely,<unk>  is associated with infections, including Lyme disease, tuberculosis, syphilis, and herpes zoster. The redness in the eye associated with<unk>  is due to engorgement of the large episcleral blood vessels, which run in a radial direction from the limbus. Typically, there is no uveitis, or thickening of the sclera.
Episcleritis
Scleritis
Retinal vasculitis
Hypertensive retinopathy
Diabetic retinopathy
Corneal neovascularization
Interstitial keratitis
Corneal hydrops