There are a number of limitations in this analysis. Inherent in all forecasts is the limitation of the uncertainty of future changes which cannot be predicted. Major shifts in medical care or technology, healthcare utilization, access to care, economic conditions, or demographic changes would impact the prevalence and costs of vision problems in ways that cannot be predicted. In addition to the uncertainty of the future, this analysis is limited by uncertainty in the data. The population projections, disease prevalence and costs are all measured with a degree of uncertainty, which we attempt to measure in the sensitivity analyses.
Other limitations include limited availability of data. Comparable nationally representative prevalence data is not available for persons aged younger than 40, and these age groups are therefore not included in the prevalence projections. All underlying data in this analysis groups results among ages 80 or 85 and older. The projections indicate that the growth of the population aged 90 and older is among the most important trends that will occur in the coming decades, yet almost no data is available for this age group. Our methodology of predicting single-age prevalence functions attempts to conservatively predict the high prevalence rates reported at these ages based on small or international samples.
Finally, our prevalence-based projection methodology may not fully account for the future impact of current or recent trends in visual health. For example, some of the underlying studies in the Vision Problems in the U.S. database were first reported more than 10 years ago. Since that time frame, emerging changes have occurred that may not be fully accounted for as their effects were not fully realized in the prevalence data. For example, in this time period AMD has seen many important changes such as possible decreases in incidence, vitamin formulations for early stage AMD, and anti-VEGF treatments for choroidal neovascularization. Whether and to what extent such recent and ongoing developments may impact future prevalence and costs remains subject to high uncertainty.