Arch Dis Child: first published as 10.1136/adc.43.232.658 on 1 December 1968. Downloaded from Arch. Dis. Childh., 1968, 43, 658. Role of Electroretinography in Investigation of Impaired Visual Function in Childhood KENNETH WYBAR and BRIAN HARCOURT From The Hospitalfor Sick Children, Great Ormond Street, London Visual function is difficult to assess in young oculography, and visually evoked cortical responses. children because their limited ability to understand In this paper only electroretinography is discussed. and communicate determines the necessity of When the healthy retina is stimulated by a bright adopting, to a large extent, objective methods of flash of light a complex series of changes is induced examination and investigation (Harcourt and Wybar, in the electrical potential of the retinal elements. 1966). This also applies sometimes to older children The sum of these changes may be detected by who are not sufficiently co-operative in their placing an active electrode on the cornea by means subjective responses. of a contact lens, and also earth and reference The afferent visual system is a complex mechanism electrodes on the skin of the face (Fig. 2). When (Fig. 1), and a dysfunction of any of its components amplified and recorded these changes are summated may cause a profound visual defect. When a clinical to form the electroretinogram (ERG) which has examination of a young child suggests that the two principal features (Karpe, 1945): an initial vision is defective the site of the impairment may a-wave of negative potential and a subsequent be obvious (as in some disorder of the ocular media, b-wave of positive potential (Fig. 3). These electrical by copyright. like a cataract), but sometimes it is not apparent changes represent a mass response from all the because of an absence of any objective clinical elements in the outer retinal layers. The experi- evidence of an ocular disorder. There are several mental investigation of the alterations which occur reasons for this difficulty. In some cases there may in the wave-form of this response under the be a gross functional abnormality of the retinal influence of selective retinotoxic drugs suggests elements without any obvious ophthalmoscopic that the a-wave is due principally to changes evidence of retinal disease, and in others there may occurring in the electrical potential of the outer be an optic atrophy difficult to distinguish from the segments of the retinal receptors as the result physiological pallor of the optic discs commonly of light stimulation, and the b-wave is due princi- seen in normal young children. Furthermore, pally to changes in the bipolar cells (Noell, 1959). http://adc.bmj.com/ there may be a dysfunction of the optic radiation The changes in potential which occur in the gang- or visual cortex which is not reflected in any lion cells of the retina and in the optic nerve changes in the pupillary light reflexes or the optic fibres after stimulation of the retina by light form discs because of the suprageniculate nature of the no significant part of the ERG response, so that lesion, or the child may show little or no interest it is normal in cases of optic atrophy despite a in visual stimuli simply because of a gross degree profound loss of vision. The amplitude of the re- an of mental retardation. Finally, older child's sponse is proportional to the total number of on September 28, 2021 by guest. Protected inability to give a correct response in subjective retinal elements stimulated, and because of the visual tests may be due to a state of hysteria. preponderance of the rods over the cones the total In these conditions in early childhood the normal response is due principally to rod activity; this is clinical methods ofexamination are often inadequate illustrated by the increase in the amplitude of the for the assessment of visual function and for the response which follows a progressive dark adapta- localization of the visual defect so that additional tion because this enhances the light sensitivity forms of investigation are necessary; these include and the electrical activity of the rods. electrodiagnostic methods which are applied to The amplitude and wave-form of the ERG re- the visual apparatus-electroretinography, electro- sponse may be abnormal in several different ways; it may be inverted if only the negative a-wave is present, subnormal ifboth the a-wave and the b-wave Received May 20, 1968. are diminished in amplitude, or absent. At birth 658 Arch Dis Child: first published as 10.1136/adc.43.232.658 on 1 December 1968. Downloaded from Eilectroretinography in Investigation of Impaired Visual Function in Childhood 659 FIG. 1. A diagrammatic representation of the affer- ent pathway, demonstrating 20 the three orders of sensory neurones involved in the >< >--< relay of information be- tween the retinal receptors (rods and cones) and the visuo-sensory cortex. (1) The retinal receptors; (2) the bipolar cells (first order neurones); (3) the optic nerve fibres, passing without delay into the optic chiasma and the optic tract (second LGB order neurones); (4) The optic radiation (third order -l neurones). L.G.B. = the lateral geniculate body; V.S.C. = the visuo-sensory cortex. by copyright. http://adc.bmj.com/ on September 28, 2021 by guest. Protected FIG. 2. Electroretinography in a young child. The contact lens bearing the active electrode and the reference and earth electrodes have been applied under general anaesthesia. Arch Dis Child: first published as 10.1136/adc.43.232.658 on 1 December 1968. Downloaded from 660 Wybar and Harcourt in adults and in older children by a voluntary O.4 effort to keep the eyes steady or by the maintenance of a steady fixation of a dim source of light by the 0-3 - eye which is not under examination, but this is seldom possible in young children because of their natural apprehension and because of the Miilivoits slight discomfort which is caused by the insertion of the contact lens. It follows that the investigation requires general anaesthesia in children under the o-20 age of 6 years, and sometimes in older children .+. who are nervous or mentally retarded. The investi- :V: a gation under general anaesthesia can be combined ..v with a thorough examination of the ocular media and fundi, and with a photographic recording - ^-e.S .I.. A I '. of any abnormal appearances. Preliminary dilatation 0-1 .. .. .. of the pupils with cyclopentolate 1% drops is .I carried out and the ERG response in the light- Light flash; A. adapted state is recorded. The increase in the amplitude of the response which occurs during FIG. 3. A diagrammatic representation* oz.-of <the ..clinical... dark adaptation is then studied, and this creates ERG response in a normal subject showing the short additional problems in the anaesthetized child latent period following the light flash,Secsand -the -- --amplitude : s it is not for the anaesthetist to and wave-form of the a- and b-waves. because possible observe the child adequately in darkness. This difficulty cannot be overcome by simply padding the amplitude of the normal response is extremely the eyes to exclude the light because the pressure small, so that it can be detected only when the of the padding is likely to disturb the position by copyright. light stimulus is intense (Winkelman and Horsten, of the corneal contact lens, and we have, therefore, 1962). It increases gradually during the first six adopted a technique of surrounding the child's months of life, and thereafter it rapidly approaches head with a cage covered with an opaque black adult levels. After that age an inverted, subnormal, material so that all light is excluded from the eyes or absent ERG response implies a widespread without affecting the illumination of the examina- dysfunction of the outer retinal layers, because the tion room and of the rest of the child's body. mass nature of the response means that there is Repeated recordings may then be made using a little or no reduction in its amplitude until about light flash source incorporated within the cage half the retina is functioning abnormally. This (Fig. 4). implies that a dysfunction of the macular area The value of the ERG is illustrated in an assess- http://adc.bmj.com/ alone, while sufficient to cause a profound defect ment of the hereditary tapeto-retinal degenerations. of the central vision, causes no impairment of the These disorders are readily diagnosed on ophthal- ERG. Furthermore, provided the light stimulus moscopic examination when they present with the is sufficiently intense a normal ERG response typical features of a retinitis pigmentosa-bone is obtained in the presence of a healthy retina corpuscle retinal pigmentation, attenuated retinal when there is an opacity of the ocular media that arteries, and pale optic discs. Sometimes, however, is sufficiently dense to make an ophthalmoscopic in the congenital form, the so-called Leber's on September 28, 2021 by guest. Protected examination of the fundus impossible, and to give congenital amaurosis (Leber, 1869), or in the juven- rise to a marked visual defect. ile form, there may be little or no abnormality The practical technique of this investigation of the fundi in the early stages despite a gross requires the insertion of a flush-fitting contact visual impairment or even blindness. These forms lens bearing an electrode over the cornea and the of tapeto-retinal degeneration occur more frequently placing of skin electrodes on the face. It is essential than is generally recognized, and the ERG is of for the eye to remain steady during the recording critical importance in establishing the diagnosis of the ERG, otherwise artefacts appear in the because the diminution or extinction of the ERG tracing because of changes in the orientation of response reflects the widespread retinal dysfunc- the standing potential of the eye and because tion.