Optic disc classification by the Heidelberg Retina Tomograph and by physicians with varying experience of glaucoma

Abstract

Purpose: To compare the diagnostic accuracy of the Heidelberg Retina Tomograph's (HRT) Moorfields regression analysis (MRA) and glaucoma probability score (GPS) with that of subjective grading of optic disc photographs performed by ophthalmologists with varying experience of glaucoma and by ophthalmology residents.

Methods: Digitized disc photographs and HRT images from 97 glaucoma patients with visual field defects and 138 healthy individuals were classified as either within normal limits (WNL), borderline (BL), or outside normal limits (ONL). Sensitivity and specificity were compared for MRA, GPS, and the physicians. Analyses were also made according to disc size and for advanced visual field loss.

Results: Forty-five physicians participated. When BL results were regarded as normal, sensitivity was significantly higher (P<5%) for both MRA and GPS compared with the average physician, 87%, 79%, and 62%, respectively. Specificity ranged from 86% for MRA to 97% for general ophthalmologists, but the differences were not significant. In eyes with small discs, sensitivity was 75% for MRA, 60% for the average doctor, and 25% for GPS; in eyes with large discs, sensitivity was 100% for both GPS and MRA, but only 68% for physicians.

Conclusion: Our results suggest that sensitivity of MRA is superior to that of the average physician, but not that of glaucoma experts. MRA correctly classified all eyes with advanced glaucoma and showed the best sensitivity in eyes with small optic discs.

Figure 1

Sensitivity and false positives (1-specificity) obtained with MRA, the GPS, and subjective classification by the average physician. The letters in the coloured circles represent disc size: ‘L', large; ‘M', medium; ‘S', small. (a) Analysis using the more specific approach considering ‘BL' as healthy, GPS had 100% sensitivity and low specificity in eyes with large discs, and low sensitivity but perfect specificity in eyes with small discs. For MRA, sensitivity was 100% in eye with large discs, and 75% in small discs; corresponding values for assessement by the average physician were 68% and 60%, respectively. In large discs, specificity was low for both MRA and GPS. (b) Using the more sensitive approach considering ‘BL' as glaucoma. GPS had high sensitivity in large discs, but only 50% in eyes with small discs. MRA had similar sensitivity in large discs, but better sensitivity in small discs, as compared with GPS. The average doctor reached 86% sensitivty in large and 77% in small discs. Specificity was low for both MRA (25%) and GPS (38%) in large discs. ^*Eight optic discs in healthy subjects were incompatible with the GPS database (four small and four medium sized discs) and were thus excluded from the calculation of specificity.