Loss of vision in the ageing eye

Age and Ageing, March, 1997 by A.J. Bron

The purpose of this multidisciplinary workshop was to set out the present state of knowledge of the common causes of visual loss in elderly people and their management, and to explore the best lines for future research. The meeting, convened by Research into Ageing, and held under the chairmanship of Professor A. J. Bron, Professor of Ophthalmology in the University of Oxford, was hosted by British Telecom.

Ageing and visual function

Professor R. Weale (Honorary Senior Research Fellow, Age Concern Institute of Gerontology, King's College London) indicated that many or most measurable ocular functions, anatomical, biochemical and visual, decline linearly with age, but the rate of decline is such that the function [e.g. melanin in the retinal pigment epithelium (RPE) or photoreceptor pigment concentration] would not reach the threshold for affecting vision until extreme old age, nor reach 0 until the age of 120 years on average. Since 120 years is thought to be the maximum human life span, the implications are that the visual system is built to last, and that ocular senescence keeps in step with the senescence of the body as a whole.

One exception is presbyopia, one of the best-known age-related eye disorders, but its development can be traced to events which start in infancy, and reach their conclusion halfway through the lifespan, before most other ocular functions have begun their decline. Thus the accommodative process may have lagged behind in the course of evolution and failed to keep up with our social needs.

There is evidence that climatic conditions may increase the rate at which yellowing and fluorescence of the lens develop. The former process alters the spectral quality of the light reaching the retina, and the tatter may affect vision in some lighting conditions by producing haze [1, 2].

In discussion, the question of reduction in the prevalence of age-related macular degeneration (ARMD) by yellowing of the lens was raised. Professor Weale felt that, although there was some evidence for this, the answer was still uncertain.

The epidemiology of visual loss

Professor Ralph Rosenthal (Professor of Ophthalmology, University of Leicester) felt that Blind Registration statistics in the UK were the best anywhere, although inevitably not totally accurate. The register showed that visual loss was age-related, the great majority of registrations being over the age of 65, with a sharp increase with advancing age. In three studies (in the West of Scotland, Nottingham and Leicester), ARMD accounted for 39-47% of registrations, glaucoma for 12-13%, cataract for 11-20%, diabetic retinopathy for 2-8% and other causes for 19-26%. In Leicester between 1965 and 1985, there had been an increase in registrations for blindness due to ARMD from 71 to 110/[10.sup.5] and for glaucoma of 17 to 29/[10.sup.5]; there had also been an increase in registration for partial sightedness.

In a study of 529 people over the age of 75 in Melton Mowbray, half had a visual acuity (VA) of 6/9 or more in the better eye. Fifteen people were registered blind (5%) and 11 (2%) partial sighted, but seven women (all over 80) had visual loss qualifying for registration as blind, and were not registered.

Of those living in institutions in the USA, 40% were visually impaired, as against 12% of the same age in the ambulant population of the same age [3-5].

In the discussion, it was remarked that the proportion of those registrable as blind who were not registered (30%) has not fallen in the past 25 years. Both this and the high proportion of visual impairment among older residents of institutions had implications for those caring for elderly people. In the future, there might be much more visual loss caused by diabetic eye disease in older people who were ethnically from the Indian subcontinent, who had not had the opportunity of close supervision in the past.

Chronic simple glaucoma

Mr John Salmon (Consultant Ophthalmologist, Oxford Eye Hospital) discussed primary open-angle glaucoma (POAG), the commonest form of glaucoma in old age, with a prevalence of 10% at age 80. It is the cause of one in eight registrations for blindness. This is a chronic and insidious condition in which raised intra-ocular pressure (IOP) leads to progressive damage to the optic nerve, particularly in its upper and lower parts, with a resulting characteristic pattern of visual field loss, superiorly, inferiorly and nasally. with eventual tunnel vision.

In most cases progression can be prevented by lowering the IOP, but in as many as one in six subjects, IOP is never raised above normal, and other mechanisms may play a part in damage to the optic nerve. A factor in the pathogenesis of this condition is a nocturnal fall in blood pressure, which causes a reduction in optic nerve head perfusion.

Clinical recognition is often late, with one eye showing major field loss at presentation Diagnosis is based on detection of raised IOP, demonstration of pathological cupping of the disc, and of characteristic field loss. Optometrists are well equipped to detect the disorder at an early stage, though those individuals with field loss and glaucomatous cupping of the discs, but persistently normal IOP, can be difficult to detect. A high index of suspicion is needed, particularly in those over 70 or with a family history of glaucoma.