OPTIC-NERVE HEAD ANALYZER AND HEIDELBERG RETINA TOMOGRAPH - ACCURACY AND REPRODUCIBILITY OF TOPOGRAPHIC MEASUREMENTS IN A MODEL EYE AND IN VOLUNTEERS

The accuracy and reproducibility of the optic nerve head analyser (ONH A) and the Heidelberg retina tomograph (HRT) were compared and the per formance of the HRT in measuring fundus elevations was evaluated. The coefficient of variation of three repeated measurements in a model eye and in volunteers and the relative error in a model eye was calculate d. With ONHA measurements the pooled coefficient of variation in volun teers was 9.3% in measuring cup areas and 8.4% in measuring the cup vo lume. In a model eye the pooled coefficient of variation was 7.6% for the parameter 'cup area' and 9.9% for the parameter 'cup volume'. The pooled relative error in the model eye was 6.6% for the parameter 'cup area' and 5.1% for the parameter 'cup volume'. With HRT measurements in volunteers the pooled coefficient of variation of both the paramete rs 'volume below contour' and 'volume below surface' was 6.9%. In the model eye the pooled coefficient of variation was 2.4% for the 'volume below contour' and 4.1% for the parameter 'volume below surface'. The pooled relative error in the model eye was 11.3% for the 'volume belo w contour' and 11% for the 'volume below surface'. The pooled relative error in measuring retinal elevations in the model eye was 3.8%. The coefficient of variation was 3.5%. The accuracies of the HRT and ONHA were similar. However, as the ONHA 'cup volume' is unreliable in patie nts because of the design of the ONHA whereas the HRT volume parameter s are reliable it seems reasonable to assume that the HRT is superior to the ONHA. Only the HRT is capable of quantifying retinal elevations .