Objective: To evaluate the effect of age, duration of diabetes, cataract, and pupil size on the image quality in digital photographic screening.
Research design and methods: Randomized groups of 3,650 patients had one-field, non-mydriatic, 45 degrees digital retinal imaging photography before mydriatic two-field photography. A total of 1,549 patients were then examined by an experienced ophthalmologist. Outcome measures were ungradable image rates, age, duration of diabetes, detection of referable diabetic retinopathy, presence of early or obvious central cataract, pupil diameter, and iris color.
Results: The ungradable image rate for non-mydriatic photography was 19.7% (95% CI 18.4-21.0) and for mydriatic photography was 3.7% (3.1-4.3). The odds of having one eye ungradable increased by 2.6% (1.6-3.7) for each extra year since diagnosis for nonmydriatic, by 4.1% (2.7-5.7) for mydriatic photography irrespective of age, by 5.8% (5.0-6.7) for non-mydriatic, and by 8.4% (6.5-10.4) for mydriatic photography for every extra year of age, irrespective of years since diagnosis. Obvious central cataract was present in 57% of ungradable mydriatic photographs, early cataract in 21%, no cataract in 9%, and 13% had other pathologies. The pupil diameter in the ungradable eyes showed a significant trend (P < 0.001) in the three groups (obvious cataract 4.434, early cataract 3.379, and no cataract 2.750).
Conclusions: The strongest predictor of ungradable image rates, both for non-mydriatic and mydriatic digital photography, is the age of the person with diabetes. The most common cause of ungradable images was obvious central cataract.