PROJECT SUMMARY Diabetic retinopathy is a significant cause of vision impairment worldwide. Patients with diabetes should be screened for diabetic retinopathy since the retinal findings can be detected before the patient is symptomatic and because there are effective treatments to prevent progression of disease. Patients are most often screened with an indirect ophthalmologic examination by an ophthalmologist, or by a retinal photograph. In telemedicine programs, a non-ophthalmologist technician can perform the photography, and then a grading center can grade the images. Optical coherence tomography (OCT) is a newer technology for imaging the retina. OCT provides cross-sectional views through the retinal tissue, and thus provides better information on retinal swelling, which can be more difficult to assess on photography. Moreover, OCT is better than photography for assessing features of other screenable eye diseases, such as glaucoma and age-related macular degeneration. Thus, OCT could offer a simpler screening test for multiple eye diseases at once. However, OCT has not been fully validated for use specifically as a screening test for diabetic retinopathy. In this supplemental study, we add an ancillary study to an existing randomized trial called the Village- Integrated Eye Workers II (VIEW II) trial. In VIEW II, communities in Nepal are randomized either to enhanced eye disease screening with OCT, or no enhanced screening. Participants with abnormal OCT findings are referred to the local eye hospital for a comprehensive eye examination. In this supplemental study, the use of OCT as a screening test will be validated against fundus photography. A series of participants with diabetes will undergo both OCT and fundus photography, and the images will be graded for diabetic retinopathy. The diagnostic accuracy of each test (i.e., OCT and photography) will be judged relative to an ophthalmologist examination. The hypothesis of the study is that the accuracy of OCT for diagnosing diabetic retinopathy will not be inferior to that of photography. The supplemental study will be performed in two populations: first, patients being seen in the retina clinic, and second, patients referred in from the VIEW II screening visit. This supplemental study will provide additional validation of the OCT intervention for the existing clinical trial, and will also be useful for telemedicine programs throughout the world.