ELECTROPHYSIOLOGY AND PSYCHOPHYSICS IN OCULAR HYPERTENSION AND GLAUCOMA - EVIDENCE FOR DIFFERENT PATHOMECHANISMS IN EARLY GLAUCOMA

It is not clear whether glaucomatous optic nerve damage is the end res ult of one pathological process or whether there are several mechanism s by which the final disease is manifest. The use of electrophysiologi cal and psychophysical tests which measure the function of specific su bdivisions of the visual pathways have been shown to be of use in the early diagnosis of glaucoma. In addition these results may help to elu cidate the mechanisms of loss of visual function in patients with earl y glaucoma. One hundred and ninety-three patients with ocular hyperten sion (intraocular pressure >24 mmHg, with normal visual fields and opt ic discs), 30 with glaucoma and 35 controls underwent pattern electror etinogram (PERG), peripheral colour contrast thresholds, motion detect ion thresholds (MDT) and Humphrey automated visual fields at the same visit. For each test there was a significant proportion of patients wi th abnormal results as has been found in previous studies of these tec hniques. However, there was a significant lack of correlation between the groups with only a small number of patients having abnormalities o n more than one test. Of the patients demonstrating abnormal PERGs, 36 % had abnormal colour contrast and 32% abonormal MDT, but only 15% wer e abnormal on both tests. Early glaucomatous damage may be focal or di ffuse in nature. Similarly there may be preferential damage to ganglio n cells subserving different visual functions or damage at different r etinal layers. The results lend support to these hypotheses and give f urther evidence that more than one pathomechanism may be involved earl y in the glaucomatous process.