Association of Serum Complement C3 with Primary Open Angle Glaucoma and its Severity

Abstract Background: Primary open angle glaucoma (POAG) is the most common type of glaucoma, which may lead to irreversible blindness. Identifying risk factors for its development can aid disability prevention. While elevated intra-ocular pressure (IOP) is a key risk, some patients still experience vision loss despite IOP reduction. Evidence shows that low serum complement C3 is linked to early nerve damage and retinal ganglion cell (RGC) loss, implying C3’s protective role against early glaucomatous damage. Aims: To assess the association of serum complement C3 level with POAG and its severity. Methods: This cross-sectional comparative study was conducted in a tertiary ophthalmic care centre in Dhaka, Bangladesh, during January, 2022 to August, 2023. A total of 40 diagnosed cases of POAG were the study population, and 40 patients were selected considering a similar age group as a comparison group without glaucoma. Complete clinical evaluation was done. Visual field analysis, colour fundus photography (CFP), optical coherence tomography (OCT), and retinal nerve fibre layers (RNFL) were done in the Ophthalmology department, and serum complement C3 level was measured using an immuno-nephelometry system in the Department of Microbiology, BSMMU. Statistical analyses of the results were obtained by using Statistical Packages for Social Sciences (SPSS-26). Results: The mean serum complement C3 level was 1.02 ± 0.12 (g/l) in the POAG group and 1.09 ± 0.15 (g/l) in the control group. The difference was statistically significant ( P < 0.05) between groups. Most of the patients (47.5%) had severe glaucomatous damage, 27.5% mild, and 25.0% moderate glaucomatous damage on the basis of mean deviation (MD) of visual field. The mean serum complement C3 level was 1.07 ± 0.12 (g/l) in mild glaucomatous damage, 1.03 ± 0.14 (g/l) in moderate glaucomatous damage, and 0.99 ± 0.99 (g/l) in severe glaucomatous damage. The mean serum complement C3 was not statistically significant ( P > 0.05) in different gradings of severity of POAG patients. Conclusion: The majority of patients displayed pronounced signs of severe glaucomatous damage. Furthermore, the analysis revealed reduced serum concentrations of C3 in individuals diagnosed with POAG compared to the comparison group. However, there was no correlation between serum complement C3 levels and the severity of POAG.