Visual Impairment and Blindness in U.S. Adults: 2015-2050
Shifting demographics and aging populations are increasing the number of individuals with visual impairment (VI) and blindness in the United States. Varma et al. sought to determine the demographic and geographic variations in VI and blindness in adults in the U.S. population in 2015 and to estimate the projected prevalence through 2050. They found that despite the high prevalence of VI and blindness in minorities, the largest current and future burden is predicted to be among older non-Hispanic white women.
This was a population-based cross-sectional study in which the researchers pooled data from 6 population-based studies on VI and blindness in the United States that included participants aged 40 years and older. Prevalence of VI and blindness was reported by age, sex, race/ethnicity, and per capita prevalence by state using the U.S. Census projections (Jan. 1, 2015-Dec. 31, 2050).
The results showed that in 2015, a total of 1.02 million people in the United States were blind (defined as best-corrected visual acuity [BCVA] ≤20/200 in the better-seeing eye), and approximately 3.22 million had VI (BCVA <20/40 in the better-seeing eye, excluding blindness); and up to 8.2 million people had VI due to uncorrected refractive error. By 2050, these numbers are projected to double to approximately 2.01 million, 6.95 million, and 16.4 million, respectively. In 2015, the highest numbers of these conditions were among non-Hispanic white individuals (2.28 million), women (1.84 million), and older adults (1.61 million); these groups are predicted to remain the most affected through 2050.
Currently, African American individuals have the highest prevalence of VI and blindness. But by 2050, the highest prevalence of VI among minorities will shift from African Americans (15.2% in 2015; 16.3% in 2050) to Hispanics (9.9% in 2015; 20.3% in 2050). For both 2015 and 2050, the states projected to have the highest per capita prevalence of VI are Florida and Hawaii, while those with the highest per capita prevalence of blindness will be Mississippi and Louisiana.
In conclusion, the researchers said, these findings suggest that vision screening for refractive error and early eye disease could reduce the proportion of individuals who experience unnecessary VI and blindness, decrease societal costs, and contribute to better quality of life. Further, they suggested that education and screening programs targeted toward non-Hispanic white women and minorities will become increasingly important because of the projected growth of these populations.
Association of Football Subconcussive Head Impacts With Near Point of Convergence
Concern is growing that even low-level (subconcussive) head impacts in sports can cause significant brain injury if they occur repeatedly. Kawata et al. investigated whether such repetitive head impacts during preseason football practice cause changes in the ocular near point of convergence (NPC) ocular-motor function. They found that players who had more frequent and stronger subconcussive impacts had greater convergence insufficiency than those with fewer and less severe impacts. However, after 3 weeks of rest, convergence normalized to baseline levels.
This was a prospective observational study that included 29 National Collegiate Athletic Association Division I football players who participated in baseline and preseason practices (1 noncontact and 4 contact). Each participant was fitted with an accelerometer-embedded mouthguard that measured head impact kinematics. Outcome measures, including head impacts, NPC, and a self-reported symptom checklist, were taken at all practices and at postseason follow-up.
A total of 1,193 head impacts were recorded for the whole group of participants. The players were categorized into lower (n = 7) or higher (n = 22) impact groups, based on the sum of head impacts from all 5 practices. The authors found significant differences in head impact kinematics between lower- and higher-impact groups (number of impacts, 6 vs. 41); linear acceleration (99g vs. 1,112g, respectively); and angular acceleration (7,589 radian/s2 vs. 65,016 radian/s2, respectively). The trajectory and cumulative burden of subconcussive impacts on NPC differed significantly between the 2 groups. In the higher-impact group, there was a linear increase in NPC over time (B for linear trend, unstandardized coefficient [SE]: 0.76 [0.12], p < .001) that plateaued and resolved by postseason follow-up (B for quadratic trend [SE]: −0.06 [0.008], p < .001). In the lower-impact group, there was no change in NPC over time. Group differences were initially observed after the first contact practice and remained until the final full-gear practice. No group differences were observed in postseason follow-up. There were no differences in symptom scores between groups over time.
The authors concluded that even though the participants did not report symptoms, these data suggest that repetitive subconcussive head impacts are associated with changes in NPC, which highlights the vulnerability and slow recovery of the ocular-motor system following such impacts. They further noted that NPC may become a useful clinical tool in deciphering brain injury.
Levels of UV-A Light Protection in Automobile Windshields and Side Windows
Given the association between ultraviolet A (UV-A) light and risks of skin cancer and cataract, Boxer Wachler assessed the level of UV-A protection afforded by the front windshields and side windows of automobiles. He found that the average UV-A blockage from windshields was 96%, while blockage from side windows averaged 71%.
The author carried out a cross-sectional study that included 29 automobiles from 15 automobile manufacturers, with model years ranging from 1990 to 2014. For all autos, he measured the outside ambient UV-A radiation and UV-A radiation behind the front windshield and behind the driver’s side windows. All measurements were taken on the same cloudless day (May 4, 2014) in Los Angeles, using a handheld UV-A light meter.
The average percentage of front-windshield UV-A blockage was 96% (range, 95%-98%) and was higher than the average percentage of side-window blockage, which was 71% (range, 44%-96%). A high level of side-window UV-A blockage (>90%) was found in 4 of 29 automobiles (13.8%). The study did not find any correlation between age of the vehicle and percentage of UV-A blockage.
The author commented that these results may in part explain the reported higher rates of cataract in left eyes and left-sided facial skin cancer, and he suggested that automakers consider increasing the degree of UV-A protection in the side windows. In conclusion, the author noted that this study may have relevance beyond autos in raising awareness of UV-A transmission through other types of windows and developing recommendations for UV protection in glass used in residential, commercial, and school buildings.
JAMA Ophthalmology summaries are written by Peggy Denny and edited by Neil M. Bressler, MD.
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American Journal of Ophthalmology