Scientists have established a relationship between clearness of vision and cognitive function in older individuals; they seem to rise or fall together. But does one cause the other? In an attempt to answer that question, a trio of researchers introduced time into the analysis, exploring the relationship between clarity of vision at time 1 and cognitive function at time 2, and vice versa, repeatedly over an 8-year period. The study does find a relationship but, given the large number of participants in the study (more than 2500), it is a modest one. Alas, that does not deter either sources in the story or the headline writer, who opt into causal statements that are far stronger than the data warrant.
Maintaining cognitive capacity is a major goal for aging individuals, so anything that contributes to that objective is worth attention. If eye health indeed proves to be a substantial contributor, that will ramp up attention to diagnostic and treatment options. But such behavior awaits more robust studies, and stories about this link need to tread cautiously.
Maintaining visual capabilities does not come cheaply in the United States, given the need for diagnostic visits, eyewear that can run into the hundreds of dollars, and expensive medical procedures to manage a litany of age-related problems, such as cataracts and macular degeneration. Although the story mentions these options, their related costs are missing in action.
The story describes a relationship between vision and cognition, but we never get a feel for how strong that link might be.
Although the debits of traditional eye exams are minor, more substantive “fixes” of vision problems mentioned in the story (such as cataract surgery) do bring with them possible risks.
While the story does provide some details about the study, such as the number of individuals (more than 2,500) and the length (8 years), its brief description of the study design leaves some key details unexplored. This was a cross-lagged analysis in which a measure of eyesight at time 1 was associated with a cognitive test at time 2. That kind of analysis can make a stab at establishing cause-and-effect if it also examines the opposite relationship (cognitive test at time 1 to visual test at time 2) and finds it to be nonexistent. The analysis actually did this and determined that the visual-to-cognitive test was a stronger relationship than its opposite. But while that fuller explanation would have made the story more complete, it would still omit an important caution: The correlations running in both directions are quite modest. Thus, there is evidence in this study that vision could be a factor in cognitive health, but it seems to play only a minor role. And its impact, if any, would still need to be tested in a clinical trial to be proven conclusively.
Both cognitive decline and vision loss accompany aging. Neither is necessarily lethal, but seeking to learn if they are related would be beneficial. An invited commentary that accompanied the report of this research in the Journal of the American Medical Association Ophthalmology describes a number of studies exploring this relationship in recent years,
The study was funded by the National Eye Institute and the Jane Kroger Fund. It would have been beneficial to include the funding sources in the story. However, omitting the name of a government or non-profit funder does not merit a Not Satisfactory rating.
The story mentions several approaches to maintaining eyesight. Mentioning other possible approaches to preventing cognitive decline (diet, exercise, etc.) would’ve been a bonus.
The story implies that the vision treatments mentioned (“a new eyeglass prescription or surgery to remove cataracts”) are available in the marketplace, which is accurate.
Although the commentary in the JAMA Ophthalmology issue where the research appears makes the point that this study’s effort to introduce causality into the vision/cognition relationship is a “new dimension,” that novel element is not made clear in the story.
It’s clear there was some original reporting done, and the story didn’t rely excessively on any news release.