Retinal Thinning Correlates with Pace of Cognitive Decline
The central nervous system is inconveniently situated for those who wish to examine it in detail in living people, but one tiny portion is at least readily available for visual inspection - the retina at the back of the eye. To the degree that the retina is subject to the same mechanisms of aging as the brain, one might expect to be able to use retinal imagery as a measure of brain aging. A number of studies have done just that, and a number of different aging clocks have been derived from standard forms of retinal imagery. Here, researchers look at just one aspect of retinal structure as a measure of age-related degeneration, the thickness of its different layers.
The retina, an extension of the central nervous system, reflects neurodegenerative changes. Optical coherence tomography (OCT) is a non-invasive tool for assessing retinal health and has shown promise in predicting cognitive decline. However, prior studies produced mixed results. This study investigated a large cohort (n = 490) of Asian individuals attending memory clinics. Participants underwent comprehensive neuropsychological testing annually for five years. Retinal thickness was measured by OCT at baseline. We assessed the association between baseline retinal thickness and subsequent cognitive decline.
Participants with a significantly thinner macular ganglion cell-inner plexiform layer (GCIPL) at baseline (≤ 79 μm) had a 38% greater risk of cognitive decline compared to those who did not (≥ 88 μm). In a multivariable model accounting for age, education, cerebrovascular disease status, hypertension, hyperlipidemia, diabetes and smoking, thinner GCIPL was associated with an increased risk of cognitive decline (hazard ratio = 1.14). Retinal nerve fiber layer (RNFL) thickness was not associated with cognitive decline.
Retinal thinning is corelated with other things, such as the shape of the eye.
For example, very nearsighted people often have eyeballs that are shaped like footballs rather than basketballs. The "point" of the ball puts additional strains on the retina and stretches it, increasing the likelihood of a tear. This is why nearsighted individuals are at higher risk of detached retinas and why extra care has to be taken when they have cataract surgery..
If the researchers did not account for this factor, the correlation between retinal thinning and aging is overstated.
It would be interesting to limit the study sample to persons with normal vision and see if the same correlation appears.