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Letters

Visual impairment is not enough to assess need for treatment

BMJ 1998; 317 doi: https://doi.org/10.1136/bmj.317.7168.1319a (Published 07 November 1998) Cite this as: BMJ 1998;317:1319
  1. Alan Mordue, Consultant in public health medicine.,
  2. David W Parkin, Senior lecturer in health economics.
  1. Borders Health Board, Melrose, Roxburghshire TD6 9DB
  2. Department of Epidemiology and Public Health, University of Newcastle upon Tyne, Newcastle upon Tyne NE2 4HH

    EDITOR-Reidy et al found that 6% (92 of 1547) of an elderly population had serious and potentially remediable visual impairment (<6/60) and far higher numbers had less serious impairment.1 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 caution is needed in drawing conclusions for service provision. Case definitions are critical in epidemiological investigations. The authors chose a visual acuity threshold of <6/12 in the worst affected eye as part of their case definition, giving rise to high prevalences. However, this choice needs to be justified because it may critically affect the implications of the study. Firstly, it is not the level of visual acuity that is important but the impact of visual impairment on a person's life-in other words the degree of visual handicap. 2 3 A level of 6/18 or even 6/24 may not interfere with some people's lifestyles, particularly if vision in the other eye is better. In the absence of a standard measure of visual handicap it would have been helpful to present a range of prevalence ratios depending on the visual acuity threshold adopted for treatment. Using a treatment threshold of 6/24, as has been applied elsewhere, would have suggested far lower levels of unmet need.4 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 within ophthalmology services, it would therefore 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 specialties. Finally, it would be easier to judge the generalisability of the study's findings, particularly in terms of the apparent unmet need, if the currently available services in the area had been described-for example, the adequacy of primary care services and recent cararact surgery rates.

    References

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