Observer variability in optic disc assessment: implications for glaucoma shared care.

Demonstrating that optometrists can make valid and reliable assessments of optic disc features is an important prerequisite for establishing schemes for shared care/co-management. Previous studies have estimated observer variability among experts in the assessment of optic disc cupping, but there has been a paucity of information on observer variability amongst optometrists. This paper describes a study to investigate intra- and inter-observer variability for a range of disc features, as graded by both ophthalmologists and optometrists. Five observers (three optometrists and two ophthalmologists) graded 48 stereo-pairs of optic disc photographs from 48 patients on two separate occasions. Each observer graded the following features: vertical and horizontal C/D ratios, narrowest rim width, the presence/absence of a disc haemorrhage, focal pallor of the neuroretinal rim, peri-papillary atrophy, the steepness of the cup-edge and the presence/absence of the cribriform sign. The average intra- and inter-observer standard deviation (SD) of differences are, respectively, 0.11 and 0.19 for the vertical C/D ratios and 0.10 and 0.18 for the horizontal C/D ratios. For the vertical C/D ratio the average weighted kappa (kappa w) is 0.79 within observers and 0.46 between observers. Percentage agreements for the presence/absence of a disc haemorrhage range from 96 to 100% (average kappa = 0.92) within observers and from 90 to 98% (average kappa = 0.77) between observers. For other disc features, average kappa w values range from 0.67 to 0.71 within observers and from 0.23 to 0.46 between observers. Intra- and inter-observer comparisons (within and between different professionals) across all disc features are comparable for the optometrists and ophthalmologists, thus demonstrating that optometrists can make valid assessments of disc features. The implications for shared care are discussed.