Serum C3 levels may serve as a biomarker for primary open-angle glaucoma

This study assessed the association between serum levels of complement component 3 (C3) and primary open-angle glaucoma (POAG) severity.

Study design

Researchers recruited 190 POAG patients and 204 controls from a Chinese hospital during a 3-year period. Participants underwent an array of ophthalmic and systemic testing. Glaucoma patients were divided into subgroups according to age, sex and mean deviation (MD) of visual acuity: mild (MD≤6 dB), moderate (6 dB–12 dB), and severe (MD>12 dB) glaucoma.

Blood samples were collected after an 8 hour fast by standard venipuncture of anteriorelbow veins. Serum C3 concentration was measured by immunoturbidimetry using a commercially available kit.

Outcomes

Serum C3 levels were more than 20% lower in POAG patients compared with controls (95.6 mg/dL vs. 115.7 mg/dL; P<0.001), even after controlling for age and gender. The severe POAG group had the lowest C3 levels compared with the moderate and mild group (85.2 mg/dL vs. 96.6 mg/dL and 110.4 mg/dL, respectively). 

Levels of C3 correlated with vertical cup-disc ratio (P=0.026). Statistical analysis revealed serum C3 associated with disease severity (OR 0.939).

Limitations

The exact role of C3 protein in glaucoma pathogenesis cannot be elucidated and is only theorized in this paper. Furthermore, all study participants were of Chinese descent, which may have impacted the results.

Clinical significance

These findings support a role for complement activation and contribution to the pathology of glaucoma. Reduced serum C3 may prove to be an important biomarker in glaucomatous optic neuropathy.