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 las er tomographic scanner. Methods-One eye of 28 patients with glaucoma or glaucoma suspects was studi ed. 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 w ere digitised and analysed with the Topcon ImageNet (TI) system. Three vari ables of the optic disc topography provided by the TI and the HRT were comp ared-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) mm( 3) and 1.58 (0.39) mm(2), respectively) were greater (p<0.01) than the mean values of CV and RA determined by the HRT (0.32 (0.25) mm(3), and 1.33 (0. 47) mm(2), 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 coeffic ients 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 a rea and cup volume of the optic disc obtained by a computerised image analy ser and a laser scanning tomograph.