Hi Tim,
Thank you for your question. I think that the intervention to prevent diabetic retinopathy have many steps.
The first one is the early diagnosis and adequate treatment of diabetes to reduce the risk factors for DR.
Second, to increase the access to eye exams, it could be performing national campaigns of screening for early diagnosis of retinopathy, which could be done with a telemedicine system using mobile units, as the one I previously mentioned.
However, it will continue the gap between diagnosis and treatment, I am not sure which intervention could be done. I think that it requires more studies evaluating the perceived barriers to getting treatment, especially in those with low access to health care services.