To achieve the goals, we measured the levels of thirteen complement proteins/fragments, including 4 proteins in the CP (C1q, C2, C4, and C4b), 4 factors in the AP (CFB, CFD, CFI, and CFH), 1 protein in the MBL pathway (MBL), and 4 proteins involved in the common pathway (C3, C3b/iC3b, C5, and C5a) in the plasma and the aqueous humour of 20 RVO and 20 cataract patients. The gene discussed is C4A; the disease is cataract.