Abstract
AIMS: Two methods of indirect ophthalmoscopic estimation of optic disc size, the 78 dioptre lens and optic disc biometer were evaluated. METHODS: 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. RESULTS: 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). CONCLUSION: 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.