Background: There is increasing evidence that diabetic retinopathy is caused by the action of free radicals. Radical scavengers like vitamin C and superoxide dismutase (SOD) may influence the outcome and progression of diabetic retinopathy, but no systematic review of the literature has been published to examine this hypothesis.
Objectives: The aim of the current research was to review the literature in a standard systematic way in order to assess the effects of vitamin C and superoxide dismutase on diabetic retinopathy in methodologically robust trials.
Search strategy: We tried to obtain studies from computerised searches of MEDLINE, EMBASE, CINAHL, Web of Science and The Cochrane Library.
Selection criteria: Only randomized clinical trials (RCTs) that evaluated the effect of vitamin C, superoxide dismutase or both in the treatment of diabetic retinopathy were considered.
Data collection and analysis: Two authors independently read all abstracts, titles or both and wanted to assess risk of bias and to perform data extraction. Discrepancies were planned to be resolved by consensus or by the judgement of a third author.
Main results: A total of 241 publications were identified by the electronic searches. Of these, 28 were identified as potentially containing information about the treatment of patients with diabetic retinopathy using vitamin C or SOD and were read in full. No trial evaluated the treatment of diabetic retinopathy with vitamin C or SOD.
Authors' conclusions: No research to date has adequately examined the treatment of diabetic retinopathy with vitamin C or SOD in such a way as to indicate whether this form of intervention has a significant impact on the progress of this clinical condition. The potential role of these substances in the treatment of diabetic retinopathy remains open to debate, and it is suggested that future research focusing on patient-oriented outcomes should address this important issue.