Accuracy of digital images for assessing diabetic retinopathy

To determine the accuracy of diabetic retinopathy status assessments with and without pupil dilation using digital fundus photographs acquired by a clinic staff person and interpreted remotely by ophthalmologists.

Using early treatment diabetic retinopathy study (EDTRS) grading criteria, diabetic retinopathy status assessments were made by an experienced (nonphysician) retinal grader (NPG) based on seven standard field 35-mm stereoscopic slides acquired by an experienced ophthalmic photographer. These assessments were compared with those of the same eyes made by two ophthalmologists and the NPG using digital photographs acquired by a clinic staff person using a high-resolution (800 x 600) digital color camera system.

Based on 35-mm slides, 38% of 244 diabetic patients had ETDRS > or =35 in at least one eye and 5% had vision-threatening diabetic retinopathy (ETDRS > or =53 or macular edema). The proportion of ungradable images was significantly greater for nonmydriatic than mydriatic assessments (30% versus 10% ungradable as determined by the NPG). For ETDRS level > or =35, specificity ranged from moderate to high (0.70 to 0.96) for the three graders, while sensitivity was poor to moderate (0.38 to 0.71), and the area under the receiver-operating characteristic curves was less than satisfactory (0.67 to 0.71).

The low sensitivity of the digital assessments indicates a significant proportion of patients in need of referral would not have been referred. These findings suggest that implementation of a simplified screening system using nonphotographer clinic staff acquiring nonmydriatic images, with interpretation by an ophthalmologist, should take place with an understanding of potential limitations.