Effect of dexamethasone implant on intraocular cytokines in diabetic macular edema

Our primary aim was to evaluate intraocular cytokines (IC) before and after dexamethasone in diabetic macular edema (DME). Our secondary aim was to study the early and late effects of single dexamethasone implant in DME.

This before and after comparative study was conducted at the Department of Ophthalmology and Centre for Nanosciences at a quaternary referral center in Kerala, India, from September 2016 to September 2018. Patients underwent complete ophthalmological examination and cytokine analysis before and after dexamethasone implant. Levels of cytokines at baseline and repeat sample were studied.

Twenty-seven eyes (21 patients) were divided into two groups depending on time from baseline to second injection. Group 1 included patients with <3 months between the two samples - 12 (44.4%). Group 2 included patients with >3 months between the two samples -15 (55.6%). Best corrected visual acuity (BCVA) and central macular thickness (CMT) improved significantly post-dexamethasone in group 1, but not in group 2. Interleukin (IL)-4, IL-6, IL-10, vascular endothelial growth factor (VEGF), IL-1β, interferon-gamma inducible protein-10 (IP-10), monocyte chemoattractant protein-1 (MCP-1), and IL-2 decreased post-injection in group 1. But cytokines increased post-dexamethasone in group 2, except IL-10. When compared to baseline, IL-6 reduced to half in group 1 (P-value 0.814) and it tripled in group 2 ( P-value 0.009). The level of VEGF in the first and second samples was not different in either group.

Our study suggests that dexamethasone acts more on IC than VEGF in DME. This is significant in the first 3 months with a rebound effect on IL-6 after 3 months. Our study also suggests that repeat injection of DEX in DME should be done at 3 months to prevent deterioration of visual acuity (VA) and worsening of CMT.