Value-Based Medicine

Evaluating the Utility of Vision

By Melissa M. Brown, MD, MN, MBA

It may seem obvious, but the first building block of Value-Based Medicine is simply our evidence. The best evidence — with low errors of measurement, high significance and validity — lays out the initial scientific data. Evaluating that evidence in light of quality of life (QOL) is the next important step in converting evidence-based medicine to Value-Based Medicine.

Measurement of the objective improvement in QOL, as well as any lengthening of life, conferred by our medical interventions, is a critical step in valuing our care. Many methods are used to measure QOL improvement. I find that time-tradeoff utility assessment is one that is all-encompassing, sensitive to small changes in health, reliable, valid, applicable across medical specialties and understandable by patients — all important needs of a QOL assessment methodology.

As discussed in previous columns, patients who have experienced the health state in question are the most appropriate respondents for utility assessment, since even physicians often fail to appreciate the QOL associated with a disease or health state (one or more diseases). Obtaining the information from patients is best accomplished by direct interview, since they often have questions regarding assessment methodology. Such data obtained in a standardized fashion become the framework for QOL databases, which are needed to determine the value (improvement in length-of-life and/or quality-of-life) gained from our medical interventions.

Recall that utility ranges from 0.0, representing death, to 1.0, which reflects permanent, perfect health. The closer the utility to 1.0, the better the QOL associated with a health state, while the closer it is to 0.0, the poorer the associated QOL. Also, remember that a time tradeoff utility is calculated by subtracting from 1.0 the theoretical proportion of remaining time of life a patient is willing to trade to be free from his or her health state during what is left of their time.

The Value Placed on Good Vision

Let's look at the mean utilities for different visual acuities obtained from many individuals who have a visual problem ranging from refractive errors to blindness. A listing of time trade-off utilities seen with different visual acuity levels is shown above. While 1.0 is the theoretical value for guaranteed, permanent perfect vision, the utility of persons with ocular diseases and good bilateral vision is only 0.97, most commonly due to apprehension and anxiety regarding the possibility of visual loss at some time in the future.

The importance of this information is quickly appreciated. One can see the relative linearity of these numbers, with decreasing utilities corresponding with decreasing visual acuity in the better-seeing eye. Of particular, note is the fact that the change in utility from NLP to 20/200 is greater than that from 20/200 to 20/20. This reminds us that low vision patients very much appreciate their capabilities. Attention to even small changes in vision at the lower end of the spectrum are appreciated greatly, just as much if not more than changes that improve vision at the upper end of the scale.

Ophthalmic utilities have been shown to be relatively unaffected by gender or level of education. They appear to be consistent at different ages, but this has been noted to drop in the years following age 85. Utilities appear to be related more to the degree of vision loss than to the underlying disease process causing the visual impairment. The effect of length of time of visual loss upon utilities is less clear. It appears that patients with visual changes due to AMD of less than one year's duration have lower utility scores, and thus poorer QOL, than those of with the same visual changes experienced for greater than one year. Also, practitioners often appreciate the better QOL and adaptation to lesser visual levels in persons with visual loss since childhood. Further study is needed in this area.

Next month, we will compare these utilities with health states in other fields of medicine and see just how our care stacks up against that given in other specialties. OM

Value-Based Medicine is a registered trademark of the Center for Value-Based Medicine.

Melissa M. Brown, MD, MN, MBA, is president and CEO of the Center for Value-Based Medicine in Philadelphia, She can be reached via e-mail at mbrown@valuebasedmedicine.com