Optic disc measurement: a comparison of indirect ophthalmoscopic methods.

Abstract

Two methods of indirect ophthalmoscopic estimation of optic disc size, the 78 dioptre lens and optic disc biometer were evaluated. Twenty nine eyes of 29 patients were measured by both methods and compared with optic disc size calculated using the three planimetric corrections described by Bengtsson and Krakau. The closest agreement with the clinical measurements was found using correction 3. There was a significant difference between both the 78 D lens (p < 0.0001) and the biometer (p = 0.0027) and the planimetric results. There was also a significant difference between the two clinical methods (p < 0.0001). Both methods showed acceptable intraobserver variation (CoV 2.45% and 3.13% respectively). Overall, both methods give larger measurements than planimetry; the 78 D lens by 0.41 mm and the biometer by 0.15 mm. Neither method gives a satisfactory estimation of optic disc size when compared with planimetry.