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By Michael Smith, North American Correspondent, MedPage Today Reviewed by Robert Jasmer, MD; Associate Clinical Professor of Medicine, University of California, San Francisco and Dorothy Caputo, MA, BSN, RN, Nurse PlannerVisual impairment, correctable or not, is associated with poor balance.Note that the findings might partly explain why people with visual impairments have been observed to have a greater risk of falling.Visual impairment -- correctable or not -- is associated with poor balance, researchers reported.
In a large cross-sectional study, people with visual impairment or uncorrected refractive errors (such as near- or farsightedness) were more likely to lose their balance in a standard test, according to Pradeep Ramulu, MD, PhD, of the Johns Hopkins University School of Medicine, and colleagues.
Self-reported problems with falling were also associated with worse visual impairment, although not with worse uncorrected refractive errors, Ramulu and colleagues reported online in JAMA Ophthalmology.
The findings might partly explain why people with visual impairments have been observed to have a greater risk of falling, Ramulu and colleagues concluded.
"One putative link between vision and falls is poor balance," they noted, but studies evaluating the issue have largely been done in clinic-based samples, where a bias exists because participants have already sought care.
To overcome that issue, they turned to the National Health and Nutrition Examination Surveys for 2001-2002 and 2003-2004, which reflect a representative sample of the U.S. civilian, non-institutionalized population.
In those years, participants underwent visual acuity testing, objective balance testing, and assessment of peripheral neuropathy, the researchers noted, while interviews yielded self-reported medical history and demographic data.
To test balance, participants stood with feet together on a firm or soft foam surface with eyes open or closed. The eyes-closed test on the foam surface, Ramulu and colleagues reported, minimized visual and proprioceptive inputs in order to assess vestibular balance.
The main outcome measure was how long it took for balance to fail in each of the four tests, which were taken in order -- eyes open and then closed, first on a firm surface and then on the soft foam.
Participants also reported any difficulties with falling during the previous year.
Of the 6,785 participants who were 40 or older, 4,590 had complete data on vision, balance, and peripheral neuropathy, including 4,201 with normal vision, 248 with an uncorrected refractive error, and 141 with visual impairment.
On the firm surface, Ramulu and colleagues reported, there was little difference among the groups with eyes closed or open.
However, multivariable analysis found higher rates of balance loss on the foam surface with eyes closed: Among people with vision loss linked to visual impairment. The hazard ratio was 1.7 per unit change in the logarithm of the minimum angle of resolution (logMAR), and was significant at P=0.02.Among those with vision loss associated with an uncorrected refractive error. The hazard ratio was also 1.7 per unit change in the logMAR, but was significant at P=0.04.
Self-reported difficulties with falling were associated with worse visual impairment; the odds ratio was 3.7 per logMAR unit change, which was significant at P=0.03. The odds ratio for falling problems, given an uncorrected refractive error, was similar, but did not reach statistical significance.
The finding that worse balance was associated with poor vision during the eyes-closed foam test was "surprising given that eye closure would be expected to neutralize the effect of decreased vision on balance," Ramulu and colleagues commented.
One possible explanation, they noted, is that reduced input from the eyes weakens the vestibulo-ocular reflex, which maintains the effectiveness of vestibular balance. On the other hand, they added, common degenerative pathways or lower physical activity levels might affect balance and be especially severe among those with visual impairment.
They cautioned that about a third of the NHANES participants did not complete the tests in the study and in general those who did not complete balance testing were older and sicker than those who did, which might underestimate the effects.
The researchers did not report external support for the study. The journal said they made no financial disclosures.
Michael Smith
North American Correspondent
North American Correspondent for MedPage Today, is a three-time winner of the Science and Society Journalism Award of the Canadian Science Writers' Association. After working for newspapers in several parts of Canada, he was the science writer for the Toronto Star before becoming a freelancer in 1994. His byline has appeared in New Scientist, Science, the Globe and Mail, United Press International, Toronto Life, Canadian Business, the Toronto Star, Marketing Computers, and many others. He is based in Toronto, and when not transforming dense science into compelling prose he can usually be found sailing.
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