To the Editor: Taylor and colleagues have provided an excellent analysis of the prevalence and causes of vision loss in Australia.1 However, their conclusion that vision loss in Australia is a much bigger problem than is usually recognised and requires “save your sight” public promotion bears some discussion.

The main outcome measure used was impairment in visual acuity. Impairment does not necessarily equate with disability. Disability has been defined as an alteration of an individual’s capacity to meet personal, social or occupational demands, or statutary or regulatory requirements, because of an impairment.2 An impaired person is not necessarily disabled.

The study of Taylor et al did not use measures of visual disability, such as the VF-14 (Visual Function Index). Participants were asked to complete a questionnaire that included information about “symptoms of eye disease”, but it is not clear that the questionnaire explored self-perceived problems with vision. Nor does the study seem to have looked at the level of cognitive impairment within this aged population. Tielsch et al, in a similar study,3 made the point that whether people who have both a treatable loss of vision and cognitive impairment should receive ophthalmological intervention depends on the cause and severity of the cognitive deficit.

Further, Taylor and colleagues stated that, after undercorrected refractive error, cataract is the most common cause of low vision and is also comparatively easily treated, but they did not objectively evaluate the relative risks and benefits of such interventions.

The study provides interesting data on the extent of visual impairment in Australia, but the authors are presupposing that the uncovered prevalence of visual impairment necessarily constitutes a social problem requiring “save your sight” public health measures. Reference should be made to patient goals and needs, and an objective cost–benefit analysis, before such a conclusion can be reached.

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?

In reply: Boffa and Pesudovs and Coster all correctly point out that a reduction in visual acuity does not always lead to dis-ability, and that not all people with impaired vision are disabled or report impaired quality of life. Large Australian and American population-based studies have shown that visual acuity below a critical level of 6/12 is associated with disability and affects participation in chosen activities and quality of life.1 When compared with people with normal vision (≥ 6/12), those with impaired vision have an increased risk of falls and hip fractures, depression, difficulties with activities of daily living and social functioning.1

Not all people with reduced visual acuity are affected in the same way at any vision threshold, even if there is a demonstrated statistically significant association between poor vision and visual function and quality of life. For example, not all people with severe visual impairment (visual acuity < 6/60) report an impact on their own visual functioning or quality of life. The impact of poor vision on functional ability is similar for conditions such as cataract or acute macular degeneration as for refractive error. The impact has been shown with both correctable and uncorrectable vision impairment.2

The VF-14 (Visual Function Index) can be used as a measure of visual disability, as suggested by Boffa. It was used in the Melbourne Visual Impairment Project and confirmed the functional implications of vision impairment (visual acuity < 6/12).3 Studies show unequivocally that vision impairment is a social3 and economic4 problem, and suggest the need for health promotion campaigns.

Pesudovs and Coster ask why, in a country such as Australia, with optometrists “in every major shopping centre”, do people with refractive error not have the correct spectacles? They suggest some barriers of access to care. The Brotherhood of St Laurence has shown that affordability of glasses and rural disadvantage are barriers to access and equity of use of eye care services.5

Our report highlighted the fact that catar-act is an important cause of vision loss that is highly amenable to surgical intervention.6 We did not discuss the relative risks and outcomes of cataract surgery, which is well documented to be highly successful, with low complication rates (< 2% for most complications),7 and very high cost-effectiveness.