The human eye is capable of adjusting to wide variations in light intensity by altering the pupil size and the sensitivity of the retina to light. Falls are one of the commonest problems of old age, and the causes are multifactorial. As falls often occur at night, this study was designed to compare dark adaptation in groups of elderly fallers and non-fallers. Twenty-two female patients in a geriatric assessment ward were included in the study and classified as 'fallers' or 'non-fallers'. A full ophthalmic examination was performed on each subject, and dark adaptation measured, in a single-blind fashion, using the Friedmann visual field analyser; following initial bleaching of the retinal photoreceptors, the room was placed in total darkness and retinal sensitivity measured every minute for 20 min. The values, expressed as log filter density, were plotted against duration of time in the dark. The mean values at 5 min were 0.9 in the fallers and 1.4 in the non-fallers (p < 0.02 unpaired t test) and at 20 min 2.2 and 3.2, respectively (p < 0.04). These results indicate reduced retinal sensitivity and hence impaired dark adaptation in the falling group. Lighting levels in the homes of many old people have been shown to be inadequate. Impaired dark adaptation may leave an elder person virtually blind for a minute or more on moving from a bright room to a darker area. The provision of night lights in the homes of recurrent fallers may offset the influence of impaired dark adaptation.
- Dark adaptation