The Effect of Photographic Light Exposure on Cup to Disc Ratio Grading

Background: Digital optic disc images are integral in remote telehealthcare, yet no quality control standards exist for the exposure setting of the images. This study evaluated the relationship between exposure setting and cup/disc ratio (c/d) grading among glaucoma specialists. Methods: : Color disc photos were taken of 50 eyes of pediatric patients under anesthesia at 3 light exposure settings: dark, medium, and bright. 9 glaucoma specialists evaluated the c/d of the imaged discs in random order. The relationships between the exposure levels and the c/d estimates as well as between c/d size and variability were evaluated. Results: : A total of 150 photos of 50 optic discs were graded. The c/d estimates were significantly larger among bright when compared to photos taken at the medium exposure setting(0.53 vs 0.48, P < 0.001) as well as the dark exposure setting (0.47, P < 0.001). In addition, images with larger mean c/d did not show more variability amongst readers (P = 0.59). Conclusion: Image exposure affects c/d grading of nonstereoscopic disc images. The brighter exposure is associated with larger c/d grading. Exposure consistency is key in longitudinal care.