The prevalence of nonrefractive visual impairment in the United States has increased significantly in recent years, which may be partly related to a higher prevalence of diabetes, an associated risk factor, according to a study in the December 12 issue of the Journal of the American Medical Association.
It is estimated that more than 14 million individuals in the United States aged 12 years and older are visually impaired (<20/40). Of these cases, 11 million are attributable to refractive error. In the United States, the most common causes of nonrefractive visual impairment are age-related macular degeneration, cataract, diabetic retinopathy glaucoma and other retinal disorders, according to the article. Previous studies have shown that visual impairment is common in persons with diabetes. “The prevalence of diagnosed diabetes has increased among adults in recent years, rising from 4.9 percent in 1990 to 6.5 percent in 1998, 7.9 percent in 2001, 10.7 percent in 2007 and 11.3 percent in 2010,” the authors write.
Fang Ko, MD, of the Johns Hopkins University School of Medicine, and colleagues conducted a study to assess the prevalence of nonrefractive visual impairment and factors associated with risk of visual impairment. The study included data from the National Health and Nutrition Examination Survey (NHANES), a representative sample of the U.S. population. In 1999 to 2002 and 2005 to 2008, 9,471 and 10,480 participants 20 years of age or older received questionnaires, laboratory tests and physical examinations. Visual acuity of less than 20/40 aided by autorefractor was classified as nonrefractive visual impairment.
The researchers found that prevalence of nonrefractive visual impairment increased 21 percent, from 1.4 percent in 1999 to 2002 to 1.7 percent in 2005 to 2008; and increased 40 percent among non-Hispanic whites 20 to 39 years of age, from 0.5 percent to 0.7 percent. In analysis among all participants, factors associated with nonrefractive visual impairment included older age, poverty, lower education level and diabetes diagnosed 10 or more years ago. Among these risk factors, only the latter has increased in prevalence between the two time periods considered. Prevalence of diabetes with 10 or more years since diagnosis increased 22 percent overall from 2.8 percent to 3.6 percent; and 133 percent among non-Hispanic whites 20 to 39 years of age, from 0.3 percent to 0.7 percent.
“We report a previously unrecognized increase of visual impairment among U.S. adults that cannot be attributed to refractive error,” the authors write. “If the current finding becomes a persisting trend, it could result in increasing rates of disability in the U.S. population, including greater numbers of patients with end-organ diabetic damage who would require ophthalmic care. These results have important implications for resource allocation in the debate of distribution of limited medical services and funding. Continued monitoring of visual disability and diabetes, as well as additional research addressing causes, prevention and treatment, is warranted.”
Glaucoma Testing Lags In Hispanics
The odds of individuals with open-angle glaucoma undergoing visual field testing decreased for all racial/ethnic groups from 2001 through 2009, but the odds decreased the most for Hispanic men and women in a study of enrollees in a large U.S. managed-care network, according to a report published in the December issue of Archives of Ophthalmology.
Open-angle glaucoma is more prevalent in racial minorities compared with whites, and racial minorities are more likely to experience vision loss and blindness from OAG, according to the study background.
Joshua D. Stein, MD, MS, and colleagues at the University of Michigan, Ann Arbor, examined whether racial disparities exist in the use of ancillary testing to evaluate individuals with open-angle glaucoma. The researchers identified all enrollees age 40 years and older in a large managed care network who had retinal or optic nerve conditions that could warrant ancillary testing.
Among the 797,879 eligible enrollees, 149,018 individuals had open-angle glaucoma. The researchers performed statistical analyses to determine the odds and probabilities each year of undergoing visual field testing and other procedures for black (n=15,905), white (n=118,062), Hispanic (N=9,376) and Asian-American (n=4,350) men and women and then compared the groups, according to the study.
The odds of undergoing visual field testing decreased for all groups from 2001 through 2009, decreasing most for Hispanic men and women (63 percent and 57 percent, respectively) and least (36 percent) for Asian-American men. By comparison, the odds of undergoing other ocular imaging increased for all groups from 2001 through 2009, increasing most (173 percent) for black men and women and least (77 percent) for Hispanic women, according to the study results.
“While it is encouraging that black individuals are receiving similar or greater levels of monitoring of OAG relative to white individuals, it is disconcerting that there are significant disparities in glaucoma testing among the Hispanic population, the fastest growing racial minority in the United States,” the authors comment.
The authors note that further research should focus on reducing racial disparities.
“Although increases in glaucoma testing have been noted in recent years among Hispanic men and women for some types of ancillary tests, efforts should be made to better understand and overcome some of the persistent barriers to monitoring for glaucoma in this group,” they conclude.
New Technique to Deliver Stem Cells to the Cornea
In research published in the journal Acta Biomaterialia, researchers from the University of Sheffield, South Yorkshire, England, describe a new method for producing membranes to help in the grafting of stem cells onto the eye, mimicking structural features of the eye itself. The technology has been designed to treat damage to the cornea, which is one of the major causes of blindness in the world.
Using a combination of techniques known as microstereolithography and electrospinning, the researchers are able to make a disc of biodegradable material that can be fixed over the cornea. The disc is loaded with stem cells which then multiply, allowing the body to heal the eye naturally.
“The disc has an outer ring containing pockets into which stem cells taken from the patient’s healthy eye can be placed,” says EPSRC Fellow, Ílida Ortega Asencio, from Sheffield’s Faculty of Engineering. “The material across the center of the disc is thinner than the ring, so it will biodegrade more quickly allowing the stem cells to proliferate across the surface of the eye to repair the cornea.”
A key feature of the disc is that it contains niches or pockets to house and protect the stem cells, mirroring niches found around the rim of a healthy cornea. Standard treatments for corneal blindness are corneal transplants or grafting stem cells onto the eye using donor human amniotic membrane as a temporary carrier to deliver these cells to the eye. For some patients, the treatment can fail after a few years as the repaired eyes do not retain these stem cells, which are required to carry out on-going repair of the cornea. Without this constant repair, thick white scar tissue forms across the cornea causing partial or complete sight loss. The researchers have designed the small pockets they have built into the membrane to help cells to group together and act as a useful reservoir of daughter cells so that a healthy population of stem cells can be retained in the eye.
“Laboratory tests have shown that the membranes will support cell growth, so the next stage is to trial this in patients in India, working with our colleagues in the LV Prasad Eye Institute in Hyderabad,” says Professor Sheila MacNeil. “One advantage of our design is that we have made the disc from materials already in use as biodegradable sutures in the eye so we know they won’t cause a problem in the body. This means that, subject to the necessary safety studies and approval from Indian Regulatory Authorities, we should be able to move to early stage clinical trials fairly quickly.”
Glaucoma Study Could Inspire E-Reader Apps
Adults with glaucoma read slower when reading silently for long periods of time and are more likely to have their reading speed decrease over time, possibly a result of reading fatigue, according to a new study in Investigative Ophthalmology & Visual Science.
Technological solutions such as e-readers and apps could help. “Right now, so many products are available for presenting reading material in a variety of formats,” says author Pradeep Ramulu MD, PhD, of the Wilmer Eye Institute, Johns Hopkins Hospital. “If the optimal format for reading in the context of glaucoma could be determined, it would be easy to create an application to present text in this manner as part of a commercial device such as an iPad or Kindle.”
The article reports that the sustained silent reading speed for glaucoma patients with bilateral visual field loss is significantly less than the speed associated with out-loud reading.
The study was conducted with two groups from the Wilmer Eye Institute: patients with bilateral VF loss from glaucoma and the control group made up of glaucoma suspect patients. Both groups were evaluated using two out-loud reading tests (IReST and MNRead), a sustained silent reading test over a 30-minute period and a comprehension evaluation corresponding to the sustained silent reading material. On the IReST evaluation, those with glaucoma read 147 vs. the control group 163 words per minute; on the MNRead, those with glaucoma read 172 vs. the control group 186 wpm; and on the sustained silent reading test, those with glaucoma read 179 vs. the control group 218 wpm—a 16 percent slower reading speed.
The results also showed that reading comprehension was lower in the glaucoma group than the control group. Though this finding fell just outside the cutoff for statistical significance, the research team suggests further studies be conducted to investigate whether visual defects or coexisting cognitive defects are the cause.
“The ultimate goal is to be able to rehabilitate individuals with reading difficulties due to glaucoma,” says Dr. Ramulu. “Our group and others are exploring possible reasons behind these impairments, including disruption of the tear film and aberrant eye movements. Understanding why people with glaucoma read slower and show reading fatigue will pave the way for solving these reading difficulties.” REVIEW