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 foils.
Methods: There were two artificial discs and one retinal elevation (the latter could not be analyzed by the ONHA) that could be inserted 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 Bangerter foil 0.6. The standard deviation of the ONHA increased from 0.059 mm2 (0.1 mm3) without Bangerter foil to 0.142 mm2 (0.121 mm3) 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) surface' of the HRT did not show any consistent change with increasing intensity of the simulated cataract. With artificial disc no. 1, the relative error without Bangerter foil was 14.6%, while the worst relative error with one of the Bangerter foils 0.8 to 0.4 was 16.4%. The corresponding values for the standard deviation were 0.019 mm3 and 0.033 mm3. With the smaller artificial disc no. 2, the relative error without 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 mm3 and 0.017 mm3. The relative error in measuring a retinal elevation without a Bangerter foil was 2.3%, with a Bangerter foil 11.2-18.0%. The standard deviation was 0.068 mm3 without Bangerter foil and 0.013-0.023 mm3 with Bangerter foils.
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.