A SIMPLE CLINICAL METHOD TO MEASURE THE OPTIC DISC SIZE IN GLAUCOMA

Purpose: The cup-to-disc ratio is a widely used clinical measure of op tic nerve damage in the management of glaucoma patients and those susp ected of having glaucoma. Knowledge of the optic disc size allows for a better assessment of the clinical significance of the cup-to-disc ra tio. In this study, two optical methods -slit-lamp biomicroscopy and c onfocal scanning laser ophthalmoscopy -were used to measure the vertic al disc diameter as an indirect measure of optic disc size. The aim wa s to provide a simple and clinically useful examination technique in t he management of glaucoma. Methods: The vertical optic disc diameter w as measured with aspheric lenses (Volk 60, 78, and 90 D, and Nikon 60 and 90 D) using slit-lamp biomicroscopy in 25 emmetropic normal volunt eers. The average of three readings was determined for each of the len ses and the measurements were correlated with the magnification-correc ted diameter measured with the Heidelberg Retina Tomograph. Results: T he mean vertical disc diameter of the group, as measured with the Heid elberg Retina Tomograph, was 1.81 +/- 0.18 mm. Results obtained with t he lower-power lenses correlated best with the Heidelberg Retina Tomog raph measurements (for example, Volk 60 D: r = 0.80, p = 0.0001, 95% c onfidence interval 1.76-1.85 mm), whereas the 90-D correlation was the weakest (for example, Volk 90 D: r = 0.59, p = 0.002, 95% confidence interval 1.75-1.87 mm). With the Volk 60-D lens, the ''best fit'' equa tion for estimating disc diameter, in millimetres, is Y = 0.85X + 0.06 , where Y is the Heidelberg Retina Tomograph value and X is the slit-l amp biomicroscopy measurement. Conclusion: Using these formulae, the c linician is able to estimate the optic disc diameter with sufficient a ccuracy to allow clinical decisions to be made in the evaluation of pa tients with glaucoma, without recourse to expensive technology.