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The flexible standard reference plane allows for automatic determination of intrapapillary variables once a disc border contour line is interactively defined. In contrast to a fixed offset reference plane (e.g. 320 microm below the mean retina height), the interindividual variability of optic disc topography (oblique insertion, glaucomatous surface flattening) is respected at the cost of the need for an accurate optic disc border outline.

To evaluate the effects of the presence of glaucomatous visual field defects and of intraocular pressure elevations on optic nerve head topography, we analyzed 148 left optic nerve heads of 148 patients using laser scanning tomography. The optic discs are classified according to computerized static perimetry and documented IOP readings: 101 discs show normal visual fields (36 normal discs, 22 ocular hypertensives, 28 normotensive glaucoma suspects and 15 ocular hypertensive glaucoma suspects), 47 discs (34 high-pressure glaucoma discs, 13 normal-tension glaucoma discs) demonstrate glaucomatous visual field damage. A two-way analysis of variance discloses significant differences (P < 0.01) between the groups of optic discs classified according to perimetry for most topometric parameters evaluated except for disc area. Classification according to documented IOP (cut off at 21 mmHg) results in larger disc areas in normotensive discs compared to hypertensive optic nerve heads in the study population. Results suggest that large discs may be susceptible to glaucomatous visual field damage at statistically normal IOP readings.

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Laser scanning tomography (LST) and computed stereophotogrammetry (CSP) are sophisticated diagnostic tools for the three-dimensional analysis of optic nerve head topography. The two methods are based on different physical principles. To compare the information about the shape of the cup of an optic nerve head obtained by LST and CSP, we evaluated the volume profile (VP; i.e., the cross-sectional area of the cup from top to bottom) in 36 discs of 36 patients (20 control group discs C, 16 glaucoma discs G). The Spearman correlation coefficient between the photogrammetric and the laser scanning VP-slope measurements was rs = 0.931; P < 0.001 (rs = 0.935 G, P < 0.001; rs = 0.910 C, P < 0.001). The results suggest that confocal laser scanning provides readings of the shape of the optic disc cup that are similar to the measurements of computed stereophotogrammetry.

The reproducibility of optic disc cup measurements was analyzed in 24 eyes of 24 patients [8 normals, 8 glaucoma patients, 8 glaucoma suspects] using the Laser Tomographic Scanner. The mean coefficient of variation in triple measurements was 5.0% for the cup area, 5.4% for the rim area, 7.0% for the cup volume, 4.0% for the mean cup depth, and 4.3% for the maximum cup depth. Mean reliability between two of the three measurements performed in each eye was better than 0.988 for the cup area, 0.995 for the cup volume and 0.996 for the mean cup depth readings. These results suggest that laser scanning tomography allows highly reproducible measurements in living eyes and adds an important tool to the ophthalmologist's armamentarium for the diagnosis and follow-up of glaucoma patients.