[The electroretinogram and the visual evoked potential in normal and glaucomatous eyes (author's transl)]

Abstract

The functional changes of the intraocular nerve structures caused by glaucoma were examined electro-ophthalmologically. The OPs, the photopic and scotopic ERG to examine the receptor and bipolar layers, as well as the EPs, elicited by luminance and pattern-reversal stimuli, for evaluation of the signal conduction in the optic nerve, were recorded. The problem was approached by way of three investigations: first was the question of which nerve structures are affected by glaucoma and exactly how the loss of visual field due to glaucoma can be determined. For this reason, 55 glaucomatous eyes with regulated intraocular pressure and different visual field losses were examined. The results show a functional diminution of all intraocular nerve structures in which the prelaminary part of the optic nerve is most affected. Differences in the visual field loss of both eyes can be well determined by the EPs. Second, the electro-ophthalmologic behavior in seven normal and eight pressure-regulated glaucomatous eyes was studied by gradually elevated intraocular pressure in order to obtain better insight into the functional pathology of glaucoma. The elevation of intraocular pressure was performed with a Müller spring dynamometer in five steps, depending on the ophthalmic blood pressure. The pressure behavior of the ERG components and the EPs is different. The amplitudes of the ERG components show a gradual decrease in normal as well as in glaucomatous eyes when intraocular pressure is increased, and are maintained when intraocular pressure reaches ophthalmic blood pressure. On the other hand, the EPs show a strong decrease in amplitude when intraocular pressure exceeds the mean ophthalmic blood pressure, particularly in the case of glaucomatous eyes. This behavior can be explained by a high pressure sensitivity of the preliminary part of the optic nerve, even greater in glaucomatous eyes. Third, the influence of pressure decrease on the electrical response was examined in glaucomatous eyes with chronic and acute pressure increase before and after pressure regulation. A mean pressure decrease of 37-13.6 mm Hg in ten eyes with chronic pressure increase led to no change in electrical responses other than a phase shift on the pattern-reversal EPs. In five cases with acute pressure increase, an amplitude increase on the luminance EPs was noticed after pressure regulation, with unchanged systemic blood pressure and almost unchanged ERG components. However, in one case an amplitude decrease on luminance EPs and ERG components was found with simultaneous blood pressure decrease. The increase of the amplitudes of the luminance EPs and the phase shifts of the pattern-reversal EPs can be explained as the functional improvement of the prelaminary part of the optic nerve caused by pressure decrease due to improved blood circulation in the prelaminary part of the optic nerve...