A Conversation with Study Co-Authors, Abraham D. Flaxman, PhD and David B. Rein, PhD
Prevent Blindness is first and foremost a public health organization, and quantitative empirical epidemiology is essential to our work. As a member of the International Agency for the Prevention of Blindness (IAPB) with interest in contributing to international eye health, we are pleased to see recent advancements in vision epidemiology on the global level – the World Health Organization’s World Report on Vision, the Lancet Global Health Commission on Global Eye Health, and of course the IAPB Vision Atlas.
As an organization with a primary national aim of providing equitable access to eye care for all residents of the United States of America, we are particularly drawn to research with a U.S. focus, such as that found in the study Prevalence of Visual Acuity Loss or Blindness in the U.S., recently published in JAMA Ophthalmology. Its authors found that more than 7 million people in the United States live with uncorrectable vision loss, including more than 1 million Americans with Blindness. This estimate is nearly 70% higher than previously found.
Such research inevitably draws comparisons across studies. I couldn’t help noticing the significant differences between these new U.S. estimates and the numbers previously reported by the Vision Loss Expert Group (VLEG) in the IAPB Vision Atlas. I wanted to take this opportunity to ask two of the co-authors of the JAMA Ophthalmology study, Abraham D. Flaxman, PhD, Association Professor of Health Metrics Sciences at the University of Washington School of Medicine, and David B. Rein, PhD, Program Area Director for NORC at the University of Chicago’s Public Health Analytics Program to discuss the differences and place their estimates in context.
Jeff Todd (JT): How do you explain the differences between the U.S. numbers you found and those shared in the IAPB Vision Atlas? For example, a key finding of your work is that more than 7 million people in the U.S. are living with uncorrectable vision loss, including more than 1 million who are living with blindness. And yet, the Vision Atlas suggests that in 2020 there were an estimated 16 million people with vision loss, of whom 640,000 were blind.
Dr. Abraham Flaxman (AF): That’s a good question, and one that we had an eye on as we developed the results in our new paper. Our work is aimed at a U.S. audience, and since the Vision Atlas is global this has led to some apples-and-oranges comparisons. For example, in the Atlas, the definition of blindness is based on a visual acuity threshold in meters of 3/60, while in our work, we used a threshold in feet of 20/200. This means that many individuals who were considered to be “living with blindness” in our study would not have met the international threshold. Another difference is that, in our study, we restricted our estimates to uncorrectable visual acuity, while the Vision Atlas used “presenting” visual acuity, which means that they included individuals with correctable vision loss in their estimate. This is an important population to measure, but one that fell outside of the scope of our project, which focused on eye health and did not investigate coverage of eye care.
JT: This study speaks to uncorrectable vision loss and blindness. Does this mean the results do not include those with refractive errors?
David Rein (DR): As Dr. Flaxman noted, our study’s focus was uncorrectable or permanent vision loss or blindness. Distinguishing between presenting and uncorrectable visual impairment is important for understanding different aspects of vision related health problems, and the clinical and preventive policy solutions differ for uncorrectable as compared to presenting acuity problems. Historically, our estimate can be considered an update to a landmark paper published by the Eye Disease Prevalence Research Group in 2004 which estimated the prevalence of uncorrectable low vision using a meta-analysis of population-based studies among adults ages 40 and older.
JT: This work also addresses those living in group quarters, such as nursing homes or jails/prisons. Any unique findings among that data?
AF: One thing that was really challenging and exciting in the methods we deployed for this project was using data from a massive survey run by the U.S. Census Bureau, called the American Community Survey, or “ACS” for short. This survey includes a representative sample of individuals living in what Census Bureau calls “institutional group quarters”, which is jargon for places like skilled nursing facilities, jails, and prisons. In many population health surveys, these populations are simply excluded, but we knew from reading previously published research that there might be much higher rates of vision loss and blindness in nursing homes. What we found was that over 10% of people living with blindness are living in institutional group quarters, which means there is a lot of the burden of vision loss in this population.
JT: Most previous U.S. studies have focused on populations ages 40 and above. Yours brings in younger ages as well. What are some of your findings among the 0-40 age group?
DR: Using multiple data sources, we estimated that 22.9% of uncorrectable visual acuity loss or blindness occurs among people younger than age 40. This means that 1.62 million people in the United States who are younger than age 40 have permanent vision loss. We know from other studies that poor visual acuity can impact a range of life outcomes, including employment opportunities, productivity, and general quality of life and happiness, so I think it’s important and significant that we were able to include younger adults in our estimate to help direct attention to this group. In the past, including in some of my own studies, researchers would overlook vision problems among younger people in order to focus on what we perceived to be the larger problem of vision loss among older adults. In our new paper, we tried to address this oversight, by incorporating previously unused information such as information from the American Community Survey and the National Survey of Children’s Health to develop a solid estimate for people younger than 40.
JT: Can you discuss some of the differences your study found? For example did you find differences by age group, race/ethnicity, or between males and females?
AF: We found huge differences by age group, which we expected, but I was surprised to learn that 1.6 million people under the age of 40 are living with vision loss. We also found that the prevalence of vision loss and blindness both appear to be higher among non-Hispanic Blacks than other racial and ethnic groups, and that the prevalence estimates appear to be higher among females than males. I say “appear” because our estimates all have substantial uncertainty, which we worked hard to quantify. That means we know that this study is not able to really confidently confirm or refute these differences—I hope that our findings will help propel future work into these sorts of health disparities, especially inquiries into why racial disparities persist, and what countermeasures can reduce them.
JT: Can you describe the Centers for Disease Control’s (CDC) Vision and Eye Health Surveillance System (VEHSS) and how it fits into this study? How was CDC involved in this study?
DR: This project was funded under an umbrella grant mechanism from CDC’s Vision Health Initiative, which supports the development of the Vision and Eye Health Surveillance System (VEHSS) as well as research activities to use data compiled in that system to create composite estimates of the prevalence of important vision conditions. As recently as 2015, the United States had no centralized data or surveillance system to monitor and track changes in vision health-related outcomes. The Director of CDC’s Vision Health Initiative, Dr. Jinan Saaddine, has been an advocate for science-based public health approaches to visual health since 2003 and has made enormous contributions to the field. Before a lot of people were aware of so-called big-data solutions, Dr. Saaddine conceptualized and funded a grant-based effort to develop vision surveillance tools based on secondary data sources. Those efforts resulted in the Vision and Eye Health Surveillance System, a publicly accessible data system which organizes and provides public access to vision health information ranging from national surveys, to Medicare and Medicaid claims, to county level composite estimates of visual acuity loss and blindness. It is not at all an understatement to say that this study would not have been possible without the support and contributions of CDC’s Vision Health Initiative, and the paper includes two coauthors, Dr. Saaddine and Dr. Elizabeth Lundeen, from that group.
JT: Do you envision ways that this U.S.-based study may be informative for our partners working across the globe?
AF: Oh, thanks for asking. I hope so! The thing that we did here, which I am trying to convince my colleagues in global health metrics to also try out, is to use what we call “respondent reported” data on vision loss. In survey research, it is straightforward to ask a question like “do you have trouble seeing, even with glasses?” but it has been a challenge to know what to do with the results. Through this work, I have come to believe that individuals can report on their own vision reliably enough to be a valuable addition to our evidence base. This has not been the dominant view in the past, however, especially in a global context.
JT: Who do you think will utilize this work? And how do you hope this study will inform new interventions for the prevention and care of vision and eye problems?
DR: I think the work provides an opportunity to understand the problems of uncorrectable visual acuity loss in some new ways. For example, we have been able to provide estimates for adults younger than 40 that were not previously available, and we have also been able to provide estimates of geographic variation in prevalence. In the paper, we’ve provided this variation by state, and on the VEHSS website we’ve extended the model to produce estimates by U.S. County. Ultimately, I see this paper as a surveillance product, and surveillance is usually understood as a tool to meet public health objectives. Our hope is that these estimates can help public health professionals better assess the extent of potential vision problems at the local level and guide the development of programs to mitigate the societal impacts of vision loss in the future.
JT: What are the next steps? Will you be continuing your research in this area?
AF: Our next step is to look into the vision and eye health conditions that are causing vision loss and blindness, and we plan to use the VEHSS databases to produce synthesis estimates of some of these conditions, like age-related macular degeneration and diabetic retinopathy.
The JAMA Ophthalmology study discussed here – Prevalence of Visual Acuity Loss or Blindness in the U.S. – can be found at https://jamanetwork.com/journals/jamaophthalmology/fullarticle/2779910.
Additional resources to support this work are housed on the Prevent Blindness website at https://preventblindness.org/prevalence-visual-acuity-loss-blindness-us/.
The Vision and Eye Health Surveillance System (VEHSS) can be further explored at https://www.cdc.gov/visionhealth/vehss/.
Prevent Blindness, a primary stakeholder in the study, serves as an engagement and communication channel for the VEHSS, working directly with NORC, CDC, and other partners.