Purpose: To investigate the hypothesis that the death of retinal ganglion cells in diabetic retinopathy involves excitotoxic effects from elevated concentrations of vitreal glutamate.
Material and methods: Patients with diabetic retinopathy who had not undergone prior vitreous or intraocular surgery were studied. Undiluted vitreous samples from 75 patients with diabetic retinopathy who underwent pars plana vitrectomy were analyzed. Mean levels of vitreal glutamate were determined in this group and they were compared with the levels in a control group. Glutamate and other free amino acids were determined using high-performance liquid chromatography. Patients were divided into two groups: Group A: Patients with proliferative diabetic retinopathy (PDR) and group B: Patients with PDR and macular edema.
Results: The mean level of vitreal glutamate in the diabetic population was 3.9 SD 4.5 mcmol/L which was not significantly different from the concentration in the control group (3.8 SD 5.1 mcmol/L). No statistically significant difference was found in the vitreous concentration of amino acids between the two groups of patients with PDR (p > 0.05).
Conclusions: Vitreal glutamate concentration is not elevated in eyes with diabetic retinopathy. This finding is in contradiction to previous reports that stated that vitreal glutamate increases to toxic levels and probably contributes to diabetic damage of retinal ganglion cells.