E-news Exclusive

Vision Prescription Often Differs Between Eyes

Follow-up in older adults shows a high rate of anisometropia, or differing levels of visual abnormalities between their eyes, according to a study in Optometry and Vision Science.

“Uncorrected anisometropia is likely to lead to disturbances in binocular vision and stereopsis, which in turn may contribute to falls in the elderly,” concludes the new research, led by Gunilla Haegerstrom-Portnoy, OD, PhD, FAAO, of the University of California, Berkeley. Researchers emphasize the importance of appropriate vision correction in both eyes for older adults, especially at more advanced ages.

The researchers analyzed vision examination results in 118 older adults followed for more than 12 years, from an average age of 67 to 79 at the end of the study. The study focused on the development of anisometropia, defined as a significant difference (one diopter or more) in prescription (refractive error) between the two eyes in one of four components.

During the study period, the prevalence of anisometropia increased significantly. For each of the four prescription components, the prevalence of anisometropia approximately doubled. As the participants approached the age of 80, 32% met the study definition of anisometropia.

The differences in prescription components provided some clues to the causes of aging-related anisometropia. Most cases were related to differing degrees of farsightedness (hyperopia) between eyes. Others were caused by early but unequal blurring of the lens of the eye, even though none of the older adults in the study had eye lenses that met the usual clinical definition of cataracts.

Within the age range studied, differences between eyes could begin to occur any time, with no particular preference for any one age. In a few patients, anisometropia actually decreased during the study.

Both Eyes Require Proper Correction
Previous studies, based on cross-sectional (one-time) measurements, have suggested that the rate of anisometropia increases exponentially with aging. However, these studies provide no information on how the visual mismatch develops over time nor the specific refractive error components involved.

The researchers cited previous studies showing that the prevalence of anisometropia in children is only 2% to 4%. “Whatever the cause of the increase in anisometropia with aging, the fact that significant anisometropia is at least 10 times more common in those over 75 years of age than in children needs to be clearly emphasized to clinicians,” the researchers wrote.

“For older people, a lack of correction of this prescription difference between the eyes may contribute to the increased frequency of falls that, in turn, can have a severe impact on health and even life expectancy,” says Anthony Adams, OD, PhD, editor-in-chief of Optometry and Vision Science.

Under current American Academy of Optometry guidelines, people over the age of 65 are considered a high-risk group for whom visual examination and screening are recommended at least every two years.

Adams raises special concern over older adults’ frequent use of “over-the-counter drugstore reading glasses. These ‘dime-store readers’ are made to be generic, with identical focusing or magnification power in each eye—certainly not an ideal solution for at least 30% of the over-age-75 population who have differing visual requirements between eyes.”

— Source: American Academy of Optometry