Role of electroretinography in investigation of impaired visual function in childhood.

Visual function is difficult to assess in young children because their limited ability to understand and communicate determines the necessity of adopting, to a large extent, objective methods of examination and investigation (Harcourt and Wybar, 1966). This also applies sometimes to older children who are not sufficiently co-operative in their subjective responses. The afferent visual system is a complex mechanism (Fig. 1), and a dysfunction of any of its components may cause a profound visual defect. When a clinical examination of a young child suggests that the vision is defective the site of the impairment may be obvious (as in some disorder of the ocular media, like a cataract), but sometimes it is not apparent because of an absence of any objective clinical evidence of an ocular disorder. There are several reasons for this difficulty. In some cases there may be a gross functional abnormality of the retinal elements without any obvious ophthalmoscopic evidence of retinal disease, and in others there may be an optic atrophy difficult to distinguish from the physiological pallor of the optic discs commonly seen in normal young children. Furthermore, there may be a dysfunction of the optic radiation or visual cortex which is not reflected in any changes in the pupillary light reflexes or the optic discs because of the suprageniculate nature of the lesion, or the child may show little or no interest in visual stimuli simply because of a gross degree of mental retardation. Finally, an older child's inability to give a correct response in subjective visual tests may be due to a state of hysteria. In these conditions in early childhood the normal clinical methods of examination are often inadequate for the assessment of visual function and for the localization of the visual defect so that additional forms of investigation are necessary; these include electrodiagnostic methods which are applied to the visual apparatus-electroretinography, electro-