1. Local

 A. Aging
 B. Hypothermia
 C. Sympathetic irritation
 D. Vasodilator drugs that are applied locally

2. Systemic or hyperviscosity with increase in serum proteins

 A. Cryoglobulinemia
 B. Hyperglobulinemia
 C. Hypertension
 D. Macroglobulinemia (Waldenström syndrome)
 *E. Multiple myeloma (Kahler disease)
 *F. Sickle cell disease (Herrick syndrome)

Lu LM, et al. Sjögren's syndrome and benign hyperglobulinemic purpura of Waldenström. Ann Ophthalmol 1981; 13: 1285-1287.

Maisel JM, et al. Multiple myeloma presenting with ocular inflammation. Ann Ophthalmol 1987; 19:170-174.

Roy FH. Ocular syndromes and systemic diseases, 3rd ed. Philadelphia: Lippincott Williams & Wilkins, 2002.