The effects of visual field changes and ocular hypertension on the visual evoked potential.

The effects of visual field changes and ocular hypertension on visual evoked potentials were investigated by photopic ERG and by luminance and pattern-reversal EPs on 116 glaucomatous and on 7 normal eyes. The problem was approached by way of four investigations: Firstly, which nerve structures are affected by glaucoma and how do visual field defects caused by glaucoma influence the EP? The results show a functional diminution of all intraocular nerve structures in which the prelaminary part of the optic nerve is most affected. The EPs, especially the pattern-reversal EPs, are markedly diminished if the visual field defects extend inside the 10 degree boundary. Differences in the visual field defects of both eyes and the course of the sickness can be well observed by the EPs. Secondly, which preoperative prognosis for visual acuity produced by the EP can be given to patients who have a dense cataract in addition to glaucoma? A postoperative improvement of the visual acuity can be expected if the L-EPs are within the standard deviation. If the EP is distinctly diminished and does not increase with increasing stimulus intensity, then there is no hope for an improvement of the visual acuity after the operation. Thirdly, does a decrease of intraocular pressure in chronic and acute glaucoma influence the EP? In acute glaucoma with pressure levels of 50 mmHg or more, and sometimes in chronic glaucoma with pressure levels of about 30 mmHg, an increase of the amplitude of the EP and an improvement of the visual field could be noticed after pressure regulation. Fourthly, what is the behaviour of the EP in normal and glaucomatous eyes at experimentally elevated intraocular pressure? 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 systolic 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.