Vision loss in Australia

To the Editor: The timely report of Taylor and colleagues of large numbers of Australians suffering visual impairment caused by refractive error raises some important questions.1

Firstly, is it reasonable to assume that visual acuity of less than 6/12 is disabling and demands intervention? The correlation of visual acuity and visual disability is tenuous.2-4 This is not surprising. Visual acuity measures a narrow domain of visual function. Different abnormalities differentially impact across wide domains of visual function. Everyday sight-dependent functions will be affected differently. For example, people with cataracts may experience reduced contrast sensitivity and colour discrimination, while those with advanced glaucoma will lose visual field, but those losses will affect a person’s life independent of visual acuity. Conversely, myopia acquired in old age may reduce visual acuity to less than 6/12 but may also provide spectacle-free near vision adequate for reading and other daily tasks. This may not cause any disability for an elderly person whose life is spent predominantly indoors.

Therefore, it seems inappropriate to assume that the 62% of people with visual impairment caused by refractive error suffer visual disability to the extent of those with glaucoma or age-related macular degeneration. A better approach to measuring visual impairment would be to use patient-centred measures, which consider the impact of eye disease on visual performance, rather than the convenient but narrow measure of visual acuity. If visual acuity is to be used, its limitations as an indicator of visual disability should be considered, and inferences about visual impairment should remain constrained by these limitations.

The second question which follows from the report that uncorrected refractive error is responsible for 62% of visual loss below 6/12 is: why do people so affected not wear spectacles? Perhaps there are barriers to acquiring spectacles, such as access. However, this seems unlikely as there is an optometrist in every major shopping centre. Certainly, cost may be a barrier, and a study from our Centre has shown that spectacle correction may reduce quality of life in the domains of wellbeing, convenience, and economic concerns.5 Therefore, it seems likely that the cost–benefit balance is such that these people are not sufficiently dis-abled by their vision to go to the inconveni-ence and expense of acquiring spectacles.

The authors have raised important issues which require clarification. Is it that visual acuity overestimates the impact of refractive error on visual disability, or is the system for supplying spectacles to Australians failing?