The effect of disc size on diagnostic precision with the Heidelberg Retina Tomograph

Purpose. We evaluated the ability of the Heidelberg Retina Tomograph (HRT) to detect glaucomatous visual field loss by using our previously described discriminant formula on a prospectively obtained cohort. The relationship of optic disc size to diagnostic classification was also evaluated. Methods. One eye was chosen randomly from 103 patients. 36 normals had IOP <22 mm Hg and normal visual fields; 67 glaucomatous eyes had IOP > 21 mm Hg and an abnormal visual field. The optic disc status was purposely not used for classification purposes. All patients were examined with the HRT and Humphreys Perimeter, program 30-2. Visual fields were considered abnormal with our previously published criteria.The HRT classification used age adjusted cup shape measure, rim volume, and height variation contour to classify the optic disc as normal or glaucomatous. We then assessed the sensitivity (se), specificity (sp), post test positive and negative predictive value (pppv, pnpv), and negative predictive value (npv) for the entire group and subsets classified by disc area. Results. n se sp pppv pnpv npv All Discs 103 75% 87% 93% 39% 61% DA<2.00mm2 35 68% 71% 90% 64% 36% 2.00<3.00 mm2 55 79% 95% 96% 26% 74% DA >3.00 mm2 13 78% 75% 88% 40% 60% Conclusions. In a prospective cohort of patients, the HRT was capable of detecting glaucomatous visual field loss with good precision. Unusually small and large optic discs continue to present diagnostic difficulties.