A number of conditions may cause a corneal ring.
Infectious causes include:
(1) Acanthamoebic keratitis
(2) Capnocytophaga ochracea
(3) ring abscess
Immunologic conditions include:
(1) rheumatoid arthritis
(2) Sjogren's syndrome
(3) Wegener's granulomatosis (granulomatosis with polyangiitis)
(4) allergic keratitis (double ring formation)
Corneal disorders:
(1) marginal dystrophy
(2) marginal ulcer or ring ulcer
(3) Mooren ulcer (corneal melting)
(4) Terrien marginal degeneration
(5) furrow dystrophy (after steroid use)
