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Value of vision

Visual value
Comparison with other conditions
Comment

These days it's all about cost. That's what many people think about modern medicine. Others, and most health economists and purchasers would say, au contraire, it's all about value. The most expensive medicine, they would say, is the one that doesn't work. Yet others, perhaps those giving a tad more deep thought, would point out that no medicine works in every patient, and perhaps if we could discover which patients would benefit from which medicine we might do rather better for all of them.

While the argument rages, or mumbles, on, we are stuck with a definition of good value that works out, for a quality-adjusted year of life (QALY) of about £30,000 or $50,000 or less. These are not easily calculated, and lead into some very convoluted paths, as the example of age-related macular degeneration (ARMD) demonstrates [1].

Visual value

We measure vision most commonly by visual acuity, a quantitative measure of the ability to identify black symbols on a white background at a standardized distance as the size of the symbols changes. Visual acuity is the smallest size that can be reliably identified. The well-known phrase '20-20 vision' refers to the distance in feet that objects separated by an angle of 1 arc minute can be distinguished as separate objects. The metric equivalent is 6-6 vision.

20/20 means one can see small letters, 20/40 moderate letters only but not small ones, while 20/100 means that only the very largest letters can be distinguished at 20 feet, but that someone with normal vision would be able to distinguish these letters at a distance of 100 feet. As the second number increases, then, visual acuity gets worse.

A review [1] brings together some aspects of the way we value vision. For instance, Figure 1 shows the time trade-off utility values for different levels of visual acuity, where a value of 1 is normal health and zero death. Here people are asked how many years of remaining life they would trade for permanent normal health. People with a moderate reduction in acuity to 20/40 say they would be willing to trade four of 20 remaining years of life for a return to normal visual acuity (1.0 minus {4/20}).



Figure 1: Time-trade utility values for different levels of visual acuity





Clearly, impaired vision impacts significantly on health utility, but the degree by which vision is valued is under appreciated by the public, clinicians in general, and ophthalmologists in particular (Table 1). Ophthalmologists, for instance, considered that patients would be prepared to lose 2% of available life years to return to 20/20 vision from 20/40, which is what a utility value of 0.98 says in Table 1. By contrast, patients were prepared to lose 17% of their remaining time of life (utility = 0.83).



Table 1: Time-trade utility values given by patients and others for different levels of age-related macular degeneration severity



Utility values
ARMD severity
Patients with ARMD
(n=82)
Community
(n=142)
Clinicians
(n=62)
Ophthalmologists
(n=46)
Mild (20/20 to 20/40)
0.83
0.96
0.93
0.98
Moderate (20/50 to 20/100)
0.68
0.92
0.88
0.89
Severe (20/200 or worse)
0.47
0.86
0.82
0.73
Very severe (<20/800)
0.39
not available
not available
0.67


Comparison with other conditions

Visual acuity of <20/200 in the better eye (severe ARMD) has utility values similar to severe stroke, or advanced prostate cancer with uncontrollable pain. Moderate ARMD (20/50 to 20/100) has similar utility values to moderate stroke or a hip fracture. Mild ARMD has similar utility values to vertebral fractures or symptomatic HIV.

When value gains are compared between some interventions for macular degeneration and interventions for other conditions (Table 2), it is clear that they compare well in terms of quality or length of life.



Table 2: Value gain in quality or length of life for interventions in age-related macular degeneration and other conditions



Intervention
Value gain
(%)
Interventions for macular degeneration
Laser photocoagulation; subfoveal classic
4.4
Laser photocoagulation; extrafoveal classic
8.1
Photodynamic therapy
8.1
Intravitreal pegaptanib
5.9
Intravitreal ranibizumab
> 15
Interventions for other conditions
Bisphosphonates for osteoporosis
1.1
Alpha-blockers for BPH
1 - 2
Statins for hyperlipidaemia
3.9
Beta-blockers for hypertension
6 - 9
PPI for reflux
11


Comment

This particular paper [1] is not one that Bandolier would normally consider for its pages. It is not a systematic review, and though it does look at quality of evidence, there are some deficiencies in the amount of evidence available. But it does make one think, and for that reason alone is worth a quick read. For those engaged in the difficult decisions around value and cost for different interventions, it is probably worth a more detailed read, especially with some effective but perhaps costly therapies coming our way.

Reference:

  1. MM Brown et al. Value-based medicine and interventions for macular degeneration. Current Opinion in Ophthalmology 2007 18: 194-200.

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