OPTIC-NERVE HEAD ANALYZER AND HEIDELBERG RETINA TOMOGRAPH - RELATIVE ERROR AND REPRODUCIBILITY OF TOPOGRAPHIC MEASUREMENTS IN A MODEL EYE WITH SIMULATED

Background: We measured the relative error and reproducibility of the optic nerve head analyzer (ONHA) and the Heidelberg retina tomograph ( HRT) in a model eye with a cataract that was simulated by Bangerter fo ils. Methods: There were two artificial discs and one retinal elevatio n (the latter could not be analyzed by the ONHA) that could be inserte d into the model eye. The relative error of the parameter 'cup area' ( 'cup volume') of the ONHA for the measurement of artificial disc no. 1 changed from 1.1% (5.4%) without Bangerter foil to 7.9% (7.6%) with B angerter foil 0.6. The standard deviation of the ONHA increased from 0 .059 mm(2) (0.1 mm(3)) without Bangerter foil to 0.142 mm(2) (0.121 mm (3)) with Bangerter foil 0.6. With the smaller artificial disc no. 2, no measurements with Bangerter foils were obtained. Results: Relative error and reproducibility of the parameter 'volume below (above) surfa ce' of the HRT did not show any consistent change with increasing inte nsity of the simulated cataract. With artificial disc no. 1, the relat ive error without Bangerter foil was 14.6%, while the worst relative e rror with one of the Bangerter foils 0.8 to 0.4 was 16.4%. The corresp onding values for the standard deviation were 0.019 mm(3) and 0.033 mm (3). With the smaller artificial disc no. 2, the relative error withou t Bangerter foil was 6.3%, while the worst relative error with one of the Bangerter foils 0.8 to 0.2 was 18.3%. The corresponding values for the standard deviation were 0.016 mm(3) and 0.017 mm(3). The relative error in measuring a retinal elevation without a Bangerter foil was 6 .3%, with a Bangerter foil 11.2-18.0%. The standard deviation was 0.06 8 mm(3) without Bangerter foil and 0.013-0.023 mm(3) with Bangerter fo ils. Conclusion: Our data support the assumption that the HRT is able to measure fundus structures even in the case of opaque optical media. The HRT is superior to the ONHA in this regard.