Effect of Unilateral Intravitreal Bevacizumab on Contralateral Eye and Associated Factors in Patients with Diabetic Macular Edema at Kilimanjaro Christian Medical Centre

Background: Diabetic macular edema being a foremost cause of visual loss in the diabetic population, is typically managed with intra-vitreal anti-VEGF therapy. The unilateral intra-vitreal bevacizumab (IVB) injections are standard, but the possible bilateral effect on the un-injected eye remains unclear, specifically in the African population. Aims: This study intended to evaluate the anatomical and visual outcomes in the un-injected eye after a single dose intra-vitreal bevacizumab injection and to identify systemic and ocular factors associated with these outcomes in patients with Diabetic Macular edema (DME). Study Design: A hospital-based prospective cohort study. Place and Duration of Study: Department of Ophthalmology, Kilimanjaro Christian Medical Centre (KCMC), between Jun 2024 and July 2025. Methodology: We included 105 patients (53 male, 52 female, mean age 64.1(±9.06) years) with diabetic macular edema (DME). Each patient received a single intra-vitreal bevacizumab injection in the eye with worse baseline Central Subfield Macular Thickness (CSMT). The un-injected eye was assessed for changes in CSMT and Best Corrected Visual Acuity (BCVA) after 4 weeks post injection. Paired t-tests and Wilcoxon signed-rank tests were applied for within-eye assessments. Pearson and Spearman correlations evaluated inter-eye associations. Generalized linear models (GLM) with a gamma distribution and log link were used to identify factors associated with anatomical and visual outcomes. Results: The mean CSMT of un-injected eye changed from (300.9 ± 31.5 μm) to 304.7 ± 36.9 μm), p = 0.1472, and median BCVA remained unchanged (LogMAR 0.3 at baseline and follow-up), p = 0.1154). Nevertheless, significant associations were observed between increased CSMT and systemic hypertension (ARR = 1.07; p = 0.021), elevated serum creatinine (ARR = 1.002; p = 0.038), and history of prior bevacizumab use (ARR = 1.09; p = 0.001). The history of PRP was associated with decrease in mean CSMT (ARR = 0.94; p = 0.021). Conclusion: A single unilateral IVB injection did not produce significant anatomical or visual improvements in the contralateral eye after 4 weeks. Though, systemic comorbidities such as hypertension and good renal function significantly influenced anatomical outcome, highlighting the need for integrated systemic and ocular management in DME treatment.