Quality Adjusted Life Years (QALYs)
In addition to DALY losses, we also estimate loss of well-being by calculating the quality adjusted life years (QALYs) cost due to prevalent low vision. QALYs are a summary outcome measure in which years of life are adjusted to account for patient utility and are the most commonly cited measure of patient well-being in U.S. based economic studies. In the 2007 PBA vision problem burden estimate, Frick, et al. (2007) estimated QALY losses directly from MEPS data based on self-reported quality of life among respondents reporting low vision. This approach is not feasible for the younger than age 40 populations due to MEPS’ structure and we found co-linearity between quality of life measures and self-reported overall health, which was one of the independent variables in the regression.
Table 14.3. Literature Values of Utility Costs of Visual Loss
We used an alternative methodology in which we multiply utility loss estimates from the literature by population background utility levels and apply these utility rates to the affected population to estimate total QALYs. We identified 13 studies in the literature reporting utility losses from low vision or vision disorders (Table 14.3). [13, 48-58] However, the wide range of results, differences in methodology, inclusion of other impacts of disease, and limitations in reporting resulted in a wide range of utility values and an inability to distinguish between mild and moderate impairment.
Although these values are based only on utility valuation studies conducted on adults, we also apply this function to children due to the lack of empirical evidence on utility losses from visual impairment among children. Chadha et al. estimate that visual loss results in a 35.6% decrease in quality of life among children aged 3 to 16 with acuity of 20/40 or worse. The values we identified among adults do not find this level of utility loss even for U.S. defined legal blindness. Given that 92% of children with visual loss had only mild impairment of 20/80 or better, the adult-based utility values predict much lower and therefore more conservative levels of utility loss among children than the overall utility loss value reported by Chadha et al. We also estimate the monetary value of loss of well-being based on $50,000 per QALY, a commonly cited although largely baseless value.
We elected to use utility values reported by Brown et al 2003, as this paper included a table synthesized from multiple analyses from the same authors that were conducted in comparable manners to produce utility values for a range of acuity in the better-seeing eye (Table 14.4).[57, 62]
Table 14.4. Utility Losses by Better-seeing Eye Acuity used in Analysis, Brown et al 2003
Table 14.5 reports the quality-adjusted life years (QALYs) and monetary value of QALYs lost due to low vision. We estimated the impact of low vision on personal well-being based on QALY losses. We adjusted the utility values based on age-specific background utilities. We then multiplied the adjusted utility values by the prevalent visually impaired and blind population and calculated QALY losses based on the reduction from normal vision utilities.