Determination of optic cup depth by confocal scanning laser tomography

PURPOSE: To assess whether confocal scanning laser tomography of the optic disc and clinical ophthalmoscopy using stereoscopic optic disc photographs, agree in the evaluation of the deepest part of the optic cup. PATIENTS AND METHODS: The study included 33 eyes of patients with focal normal-pressure glaucoma. Using 15 degrees color stereoscopic optic disc photographs and dividing the optic disc into an upper and a lower half, two trained observers independently established the location of the deepest part of the cup. By selection, the two observers had made congruent judgements for all eyes in the study. All patients also underwent confocal scanning laser tomography of the optic disc using the Heidelberg Retina Tomograph (HRT). The location of the deepest "mean cup depth" was noted. RESULTS: The deepest optic cup region based on stereoscopic evaluation of photographs and on scanning laser tomography did not correlate significantly with each other (p=0.18; chi-square test, linear-by-linear association). According to the scanning laser tomography data, the maximal optic cup depths were not correlated with the corresponding locations of maximal visual field defect (p=0.80). Using the stereo photographic data, the locations of maximal optic cup depth and maximal visual field defect were correlated (p=0.006). CONCLUSIONS: In some glaucomatous eyes, confocal scanning laser tomographic assessment of the location of the deepest optic cup region does not agree with clinical judgement and, in contrast to clinical examination, does not correlate with the location of the maximal visual field defect.