Prevalence of serious eye disease and visual impairment in a north London population: population based, cross sectional study

EDITOR - Reidy et al. found that 6% (92 of 1547) of an elderly population have serious and potentially remediable visual impairment (<6/60) and far higher numbers with impairment of a lower order1. Since many of these people were not in touch with eye services, it would be easy to conclude that, for example, the volume of cataract surgery should be substantially increased. The findings are important, but need to be interpreted with caution before drawing conclusions for service provision.

Case definitions are critical in epidemiological investigations. The authors chose a visual acuity threshold of Secondly, the additional health benefits from expanding current treatment may be lower than the average benefits now being realised. Unless the additional costs are also lower, cost-effectiveness, in terms of the extra benefits per pound spent, will diminish. Cataract surgery at 6/36 which restores vision to 6/6 is likely to generate greater health improvement than surgery at 6/18, but costs the same. For priority setting purposes within ophthalmology services, it would therefore again be valuable to have information on different base levels of need. More generally, such data would assist Health Boards and Authorities in decisions about the costs and benefits of different levels of service provision, since they must compare the health improvements which would be generated by treating more patients at 6/18 with those from investing resources in other ophthalmological treatments or in other speciality areas.

Finally, it would be easier to judge the generalisability of the study findings, particularly in terms of the apparent unmet need, if currently available services in the locality were outlined, for example the adequacy of primary care services and recent cararact surgery rates.

Alan Mordue Consultant in public health medicine
Borders Health Board, Melrose, Roxburghshire
TD 6 9DB
(Tel. 01896 825560, Fax. 01896 823401)

David W Parkin Senior lecturer in health economics
Department of Epidemiology and Public Health,
University of Newcastle upon Tyne, Newcastle upon Tyne
NE2 4HH
( Tel. 0191 222 7375, Fax. 0191 222 6746)

1 Reidy A et al.. Prevalence of serious eye diseases and visual impairment in a north London population: population based, cross sectional study. BMJ 1998;316:1643-6.
2 Royal College of Ophthalmologists. Guidelines for cataract surgery, 1995.
3 World Health organisation. International classification of impairments, disabilities and handicaps. WHO, Geneva, 1980.
4 Mordue A, Parkin DW, Baxter C, Fawcett G, Stewart M. Thresholds for treatment in cataract surgery. J Public Health Med 1994;16:393-8.