Comparison between laser scanning tomography and computerised image analysis of the optic disc.

AIMS To study the interchangeability of the measurements of the optic disc topography obtained by one computerised image analyser and one confocal laser tomographic scanner. METHODS One eye of 28 patients with glaucoma or glaucoma suspects was studied. All cases had simultaneous stereoscopic disc photographs taken with the fundus camera Topcon TRC-SS and optic disc examination with the Heidelberg retina tomograph (HRT) during the same visit. The optic disc photographs were digitised and analysed with the Topcon ImageNet (TI) system. Three variables of the optic disc topography provided by the TI and the HRT were compared--cup volume (CV), rim area (RA), and cup area to disc area ratio (CA/DA). RESULTS The mean values of CV and RA provided by the TI (0.52 (SD 0.32) mm3 and 1.58 (0.39) mm2, respectively) were greater (p < 0.01) than the mean values of CV and RA determined by the HRT (0.32 (0.25) mm3, and 1.33 (0.47) mm2, respectively). The mean value of CA/DA provided by the TI (0.42 (0.14)) and the HRT (0.42 (0.18)) was similar (p = 0.93). Correlation coefficients between measurements obtained by the two methods ranged from 0.53 to 0.73. CONCLUSION There was a significant discrepancy in the measurements of rim area and cup volume of the optic disc obtained by a computerised image analyser and a laser scanning tomograph.