Objective Versus Subjective Evaluation of the Optic Disc Using a Novel Digital Stereoscopic Assessment Method

Abstract

Abstract: : Purpose: To quantify the difference between subjective and objective methods for the clinical evaluation of the optic disc using a novel digital stereoscopic assessment system. Methods: 186 consecutive patients were selected from a database of glaucoma referrals to the eye clinic. Cup-disc ratios were estimated clinically by the referring optometrists and compared to those made by the optometrist in the screening clinic. Three additional observers, experienced in optic disc analysis determine the vertical CDR of the same images using a digital stereoscopic viewing system (Z screen) to provide a gold standard assessment. These values were compared with the subjective assessment made by the referring optometrists and screening optometrists. Results: Data was obtained from 310 eyes from 186 patients. The three observers showed near perfect agreement in their measurements of vertical cup-disc ratios (Intraclass correlation coefficient = 0.91) using the Z screen. Comparison with the referring and screening optometrists indicated a systematic difference in the estimation of CDR. With a referred CDR of 0.1, the 3 observers measured cup-disc ratios of 0.15 – 0.55 (mean 0.45). With a referred CDR of 0.9, the 3 observers measured cup-disc ratios of 0.7-0.9 (mean 0.8). This trend was similar, but less marked, between the screening optometrists and 3 observers. These differences can be modeled by linear regression as: Objective CDR = 0.55 * (Referring optometrist’s CDR value) + 0.4 Objective CDR = 0.45 * (Screening optometrist’s CDR value) + 0.3 Conclusions: Our data indicate systematic differences in the clinical and objective assessment of stereoscopic optic nerve head images, when digital stereoscopic assessment is taken as the gold standard and may provide a basis for the correction of subjective assessment to derive an accurate measure of the neuroretinal rim in clinical practice. The high level of agreement between observers with the digital analysis system suggests that it may have a useful clinical role in the detection of glaucomatous optic neuropathy.

Keywords: optic disc • imaging/image analysis: clinical • clinical (human) or epidemiologic studies: sys