[Comparison of two laser scanning tomography systems for three-dimensional analysis of the optic papilla]

The Heidelberg retina tomograph (HRT) allows three-dimensional topographic analysis of the optic disc based on the same confocal laser tomographic scanning principle as the laser tomographic scanner (LTS). We evaluated the reproducibility attained with the HRT and compared the data acquired with the two instruments. To determine the reproducibility of the data acquisition with the HRT, we measured 27 glaucomatous discs five times each. The mean standard deviation was 0.075 mm2 for the cup area, 0.035 mm3 for the cup volume and 0.018 mm for the mean cup depth. In addition, 50 eyes were examined with both instruments. Measurements of the optic disc area and cup area demonstrated slightly increased values obtained with the HRT (mean difference 4.1% and 6.6%, respectively), while the values for cup volume and cup depth were 15.5% and 13.9% larger than those obtained with the LTS. The comparison between LTS and HRT demonstrates good agreement of the reproducibility concerning three-dimensional topometric data relating to the optic nerve head. The differences between the measurements may be due to a modified optical pathway enabling direct assessment of the intraocular focus position in the HRT. In conclusion, the improved and simplified method of laser scanning tomography as used in the HRT yields reproducible and reliable measurements of the optic nerve head. In addition, this instrument makes it possible to obtain high-quality images without pupil dilatation with a significantly shorter examination time.