Scleritis is very rare (I’ve never seen a case)! The sclera is the white, leathery shell that keeps the eyeball together (see Diagram — Anatomy of the Eye). It can get inflamed; half the time it’s due to diseases like rheumatoid arthritis, half it’s “idiopathic” (“nobody knows why”). Scleritis can destroy the eye.
Symptoms are mainly a deep, digging pain, that’s worse with eye movements. At first glance, the eye looks red because the conjunctiva are inflamed; but on closer inspection, we may see the normally-white color of the sclera has turned a subtle dusky purplish. Treatment requires anti-inflammatory medications. Anybody with bad eye pain needs to see an ophthalmologist ASAP.