Comparison between tomographic scanning evaluation and photographic measurement of the neuroretinal rim

To compare laser tomographic scanning evaluation with photographic measurement of size and shape of the neuroretinal rim.

For 25 normal eyes and 32 glaucomatous eyes, the optic disks were examined with the Heidelberg Retina Tomograph (software version 1.11) for confocal laser tomographic scanning evaluation, and color stereoscopic optic disk photographs for planimetric measurements. Area and width of the neuroretinal rim were determined as percentages of the disk area and diameter, respectively.

For the normal and glaucomatous eyes, the tomographic results compared with the photographic measurements disclosed significantly larger values for the relative width and relative area of the neuroretinal rim. The differences between both methods were most marked in the nasal part of the optic disk and least marked in the temporal disk region. The relative differences increased significantly (P < .05) with increasing degree of glaucomatous optic nerve damage.

In normal and glaucomatous eyes, the Heidelberg Retina Tomograph determines the neuroretinal rim, expressed as percentage of optic disk measurements, to be significantly larger than when the rim is evaluated on optic disk photographs. Because parts of the central retinal vessel trunk are defined as neuroretinal rim in the algorithm of the Heidelberg Retina Tomograph, the differences between Heidelberg Retina Tomograph measurements and photographic determinations of the rim are largest in the nasal disk region and smallest in the temporal disk area. The neuroretinal rim shape and neuroretinal rim area differ appreciably between the two methods. These differences increase with increasing degree of glaucomatous optic nerve damage.