Visual Impairment Linked to Cognitive Function Decline

In an invited commentary, a trio of authors called the concept of improving or protecting visual function as a viable intervention to prevent or control cognitive decline overall both “plausible and attractive.”

Diane Zheng, MS, PhD-C

Credit: University of Miami

Visual impairment, measured at a distance, has been linked to declining cognitive function over time, both longitudinally and cross-sectionally. Ultimately, declines in vision had a stronger association to cognitive function than the reverse.

According to the authors of the study, part of the Salisbury Eye Evaluation, this new data reveals that maintaining vision may have an impact on the mitigation of age-related declines in cognitive function.

Led by Diane Zheng, MS, a second-year PhD student of epidemiology at the Department of Public Health Sciences at the University of Miami Miller School of Medicine, the data consisted of 2520 residents of the greater Salisbury area of Maryland aged 65 to 84 years. They were assessed in 4 rounds: At baseline between September 1993 and August 1995, and then 2, 6, and 8 years later. Patients were assessed by visual acuity (VA), as measured by the Early Treatment Diabetic Retinopathy Study (ETDRS) chart scores, and cognitive status, as measured by the Mini-Mental State Examination (MMSE).

A trio of Paul J. Foster, PhD, FRCS (Ed); Sharon Y. L. Chua, PhD; and Axel Petzold, MD, PhD, wrote in an invited commentary that “the tacit assumption is that improving (or protecting) visual function may be a viable intervention to prevent or control cognitive decline in older age. To put this concept into perspective, the onset of clinically ‘definite’ Alzheimer disease is preceded by a mean (SD) loss of 3.1 (2) points on MMSE about 5 years earlier. Importantly, changes in the MMSE are anticipated by other variables and protein biomarkers for neurodegeneration are anticipated another 10 to 15 years earlier.”

The mean age of patients was 73.5 years (standard deviation [SD], 5.1 years), 58% were women (n = 1458), and 26% were black (n = 666). Each round saw some drop off, more than half of the loss due to death, with round 2 including 2240 patients (89%), round 3 including 1504 patients (61%), and round 4 including 1250 patients (50%).

Both VA and MMSE scores deteriorated over time, with the average biannual decline of MMSE being —0.59 (95% CI, –0.64 to −0.54) and the average decline of VA being 0.022 logMAR (95% CI, 0.018 to 0.026), translating to roughly 1 line over 8 years (P <.001 for both). There was an association between worse baseline VA and worse baseline MMSE score (r = —0.226; 95% CI, −0.291 to −0.16; P <.001).

The rate at which VA worsened was linked with the rate of decline for MMSE score (r = −0.139; 95% CI, −0.261 to −0.017; P = .03). The authors noted that cross-sectional models revealed that VA from the preceding round was associated with MMSE score in the following round (β = −0.995, P <.001). Meanwhile, MMSE score from the earlier round was linked to VA in the subsequent round (β = −0.003, P <.001).

Despite that, Zheng and colleagues noted that the standardized effect size of VA on MMSE score (β = −0.074; SE, 0.015; P <.001) was found to be greater relative to the reverse effect (β = −0.038; SE, 0.013; P <.001), thus indicating that VA is most probable to be the main influence in those associations.

Foster, Chua, and Petzold noted that additional research in this area should contemplate recording low-contrast visual acuities as well as the more widely used high-contrast visual acuities, as retinal imaging could provide a “more complete characterization of ocular anatomy and visual function with the aim of earlier recognition of impending cognitive decline.”

“However, with the principles described by Wilson and Jungner in mind, early recognition should only be pursued widely if there is a viable intervention to alter the trajectory of the condition,” they wrote. “Zheng et al raise this possibility of optimizing visual function to reduce cognitive decline. Overall this is a plausible and attractive concept.”

The study, “Longitudinal Associations Between Visual Impairment and Cognitive Functioning,” was published in JAMA Ophthalmology.