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)

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