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Notes: Summary To establish the diagnosis in cases of an acute affection of the optic nerve, the investigator must rely on functional examinations such as determination of visual acuity and of the visual field. Only when the process is localized at the optic disc abnormalities become apparent with the aid of the ophthalmoscope. Affections of longer standing may lead to atrophy of nerve fibres, and this may become visible in the fundus in that the disc is pale of appearance. However, not in all cases is the so-called disc atrophy associated with poor visual acuity: in these cases the functional findings seem to contradict the fundoscopic findings. Another example is the choked disc, which produces highly pathological fundoscopic features even though visual acuity and visual field are quite intact. The opposite situation is that of the acute stage of retrobulbar neuritis, in which the optic disc may present an entirely normal appearance whereas visual acuity and visual field are severely disturbed. Findings such as the above mentioned evoke the wish for an extended examination which includes methods supplying some information on the manner in which, under pathological circumstances, the optic nerve does or does not conduct. Recording visually evoked responses provides a possibility in this respect. Visually evoked responses are known to be largely determined by photic stimulation of the central retina (Vav Hof1960; Copenhaver & Perry 1964). However, stimulation of the peripheral retina likewise makes a contribution be it much smaller - in illiciting the VER. This means that intactness of the central fovea, the maculopapillary fibre bundle in the optic nerve, and the projection of the fovea in the optic cortex, is a prerequisite for recording VERs. On the other hand, the development of sophisticated recording techniques (e.g. with the aid of the computer) which make it possible to identify the VER amidst the ever-present background activity (the EEG), has enabled the investigator to record an ERG from a very small retinal area, e.g. the local photopic ERG of the central fovea (FERG). Simultaneous recording of FERG and VER makes it possible to examine the function of, exclusively, that part of the optic system that encompasses the fovea, the maculopapillary fibre bundle and the projection of the fovea in the optic cortex. Visual acuity is determined by this part of the optic system. It is the diminished visual acuity (and a central scotoma in the visual field) that, in many cases, characterizes an affection of the optic nerve. If, under these pathological conditions, one can nevertheless record VERs after local (foveal) stimulation, and recognize pathological changes in the recordings, then it should be ascertained that these VERs have indeed been obtained by stimulation of the fovea. This can be achieved by recording the FERG, for which normal values are given in chapter VI. Chapters II and III discuss the development of methods to record VER and FERG. The method used in our study is described in detail in chapter IV. Chapter V presents a description of the protocol of examination to which our patients were submitted, and lists the number of patients examined. Chapter VII describes the electro-ophthalmological findings obtained in patients with optic neuritis. In the acute stage of optic neuritis (diminished visual acuity and a central scotoma in the visual field), no VER can be recorded after local (foveal) stimulation of the retina. The impairment of conduction, thus objectively demonstrated, may result from the development of an inflammatory-like oedema which impairs the capillary blood circulation in the optic nerve; one of the consequences of this situation is a pathological metabolism of the nerve tissue and release of toxins (e.g. Bonamour 1968). If in such cases it is possible to identify a VER in the recordings after full field stimulation of the retina, then we are dealing, we believe, with the contribution of the peripheral retina to the generation of the VER. In this context it is to be noted that, in the acute stage of optic neuritis, it is often surprising to see how well the patient can fix the (small) photic stimulus in spite of the poor visual acuity and the central scotoma in the visual field. If visual acuity and visual field fail to recover after the acute stage, then the VER after local (foveal) stimulation remains absent. This is a result of demyelination and atrophy of nerve fibres, particularly those of the maculopapillary bundle. In this stage examination does become more difficult because the patient's ability to fix the stimulus diminishes as poor visual acuity is of longer standing. Upon partial recovery from optic neuritis (e.g. visual acuity 0.6–0.7 and a relative central scotoma in the visual field), we have observed that the VER after local (foveal) stimulation can nevertheless remain absent. We believe that in these cases there has been demyelination of the fibres in the maculopapillary bundle, but that yet the majority of these fibres does still conduct, even over the segment of demyelination. The mode of conduction in the demyelinated segment differs from normal and may well resemble that in naturally unmyelinated fibres in the peripheral nervous system. A consequence of this might be that the conduction velocity diminishes. As a result, the conduction time of the nerve fibres can come to show interdifferences due to which depolarization of the projection of the fovea in the optic cortex takes place only gradually so that at no time a potential occurs of sufficient amplitude to permit our apparatus to record it. In the case of complete recovery from optic neuritis, one can observe a return of the VER after local (foveal) stimulation to the extent that there is no longer a significant difference between the VER recorded after stimulation of the one (unaffected) eye and that recorded after stimulation of the other (affected) eye. We believe that electro-ophthalmological examination demonstrates in these cases that no demyelination as a result of the optic neuritis has occurred, or that, as a result of remyelination, a restitutio ad integrim has occurred. Chapter VIII presents the results of an examination of twelve patients with Leber's hereditary optic atrophy. The majority had regained fair-to-good visual acuity in at least one eye. In only one patient of this group were VERs identifiable in the responses after local (foveal) stimulation. We observed that in a few cases of Leber's optic atrophy a visual acuity of 1.0 could be attained. In these cases a central scotoma in the visual field had in its exact centre an intact sparing corresponding to ≤ 1 ° subtended visual angle. The absence of the VER after local (foveal) stimulation is ascribed to the fact that only a small number of fibres in the maculopapillary bundle is still intact; impulses conducted by these few fibres, effect depolarization of so small a part of the projection of the central fovea in the optic cortex that a potential of sufficient amplitude to be recorded, is never produced. In patients with traumatic optic atrophy, it was difficult to record ERG and VER after local (foveal) stimulation because all were examined long after the accident, so that visual acuity had long been poor. However, in one case (visual acuity 0.6 in the eye, of which the optic nerve was affected) a disturbance of conduction in the maculopapillary bundle could be demonstrated because the VER after local (foveal) stimulation of this eye was absent (chapter IX). Simple glaucoma (chapter X) was not systematically studied. Two patients are discussed. The results of their examinations do not warrant the expectation that a more comprehensive examination by the techniques we used will reveal many new points of view on the disturbance of conduction of the nerve fibres in this condition. A patient with toxic opticoneuropathy due to ethambutol medication and one with juxtapapillary retinitis (J