Cup-to-disc ratio: ophthalmoscopy versus automated measurement in a general population: The Rotterdam study

Abstract

Objective To determine the correlations between ophthalmoscopic estimations and the measurements with a semiautomated image-analysis device of the vertical cup-to-disc ratio (VCDR) in the human optic disc. Design Population-based, cross-sectional study. Participants All subjects 55 years of age and older from the population-based sample of 6777 ophthalmologically examined subjects from The Rotterdam Study of whom gradable optic disc transparencies of at least 1 eye and ophthalmoscopic data of the same eye were available. Main outcome measures Ophthalmoscopic assessment of the VCDR and semiautomated measurement of the VCDR. Methods Indirect and direct ophthalmoscopy were performed in mydriasis to assess the VCDR. Optic disc transparencies made with a simultaneous stereoscopic telecentric fundus camera were analyzed with a semiautomated measurement system (Topcon Imagenet). Results In 5143 subjects, the mean ophthalmoscopic VCDR was 0.30 (standard error [SE], 0.0021; range, 0.00, 1.00) compared with a semiautomatically measured VCDR of 0.49 (SE, 0.0019; range, 0.04, 0.86; difference, 0.19; P < 0.0001). The overall correlation between both methods was moderate (correlation coefficient, 0.61; SE, 0.11) and lower in small optic discs. Semiautomated optic disc measurements correctly identified 76% of the glaucoma cases (as defined using visual field data and ophthalmoscopic data about the optic disc). Conclusion Semiautomated measurements of the VCDR are larger than the ophthalmoscopic VCDR estimate with a moderate correlation. The interobserver variability using Imagenet was smaller compared with the ophthalmoscopic assessments, and Imagenet was better standardized, which is important for epidemiologic surveys and follow-up studies.