Thinner RNFL and GCL were associated with lower Full Scale IQ in childhood and at age 45 years, while thinner RNFL in middle age was associated with greater decline in processing speed.
New research observed the thickness of the retinal nerve fiber layer (RNFL) and the ganglion cell layer (GCL) was associated with cognitive performance in both childhood and adulthood, while thinner RNFL was linked to a decline in processing speed between childhood and adulthood.
Study authors Ashleigh Barrett-Young, PhD and Richie Poulton, PhD, Dunedin Multidisciplinary Health and Development Research Unit, Department of Psychology, University of Otago, noted further longitudinal studies are necessary to determine whether retinal thinning precedes cognitive decline.
“RNFL thinning could be a useful biomarker in identifying those experiencing the early stages of cognitive decline, before global cognitive decline becomes apparent,” investigators wrote.
As potential biomarkers for Alzheimer disease, the study examined whether RNFL and GCL thickness was associated with global cognitive performance in middle age and in childhood and with a decline in cognitive performance from childhood to adulthood and if thickness was associated with declines in specific cognitive domains.
Study participants in the longitudinal cohort study were members of the Dunedin Multidisciplinary Health and Development Study representative birth cohort. A total of 1037 births were included from participants born between April 1972 - March 1973 in New Zealand. They were followed up for 45 years, with 94% of the living cohort (n = 997) continuing to participate.
Investigators took optical coherence tomography measurements at age 45 years. The measurements included were mean RNFL thickness and thickness of 4 quadrants (superior, temporal, inferior, and nasal) and mean thickness of ganglion cell-inner plexiform layer (GCL) and thickness of 6 segments (temporal-superior, superior, nasal-superior, nasal-inferior, inferior, and temporal-inferior).
Additionally, cognitive function was assessed at ages 7, 9, and 11 years old and in adulthood at age 45 years, including Full Scale IQ (FSIQ), processing speed, perceptual reasoning, and verbal comprehension. Data were analyzed between August 2020 - April 2021.
The data set consisted of study members with RNFL data available (n = 865; 50.2% male). Participants with OCT data excluded at age 45 years due to issues with the scan or diseases affecting the retina had slightly lower childhood FSIQ (OCT included: mean FSIQ, 101.3; OCT excluded: mean FSIQ, 95.7, P = .04).
Investigators observed lower FSIQ was associated with thinner mean RNFL thickness (B = 0.202, P < .001) and thinner nasal quadrant (B = 0.118, P = .01), and inferior quadrant (B = 0.115, P = .001) at age 45 years.
Additionally, lower FSIQ at age 45 years was associated with thinner mean GCL thickness (B = 0.178, P = .04) and thinner temporal-superior segment (B = 0.216, P = .01), inferior segment (B = 0.187, P = .02), and temporal-inferior segment (B = 0.224, P = .008).
Furthermore, lower childhood FSIQ was associated with thinner mean RNFL at age 45 years (B = 0.213, P <.001) and thinner mean GCL thickness (B = 0.247, P = .003).
A reduction in processing speed was associated with thinner mean RNFL thickness (B = 0.292, P = .04) and thinner RNFL in the temporal (B = 0.403, P = .01) and inferior quadrants (B = 0.590, P = .02).
“Our findings suggest that RNFL could be an indicator of overall brain health and that IQ may reflect a healthy and well-functioning brain,” investigators concluded.
The study, “Associations Between Retinal Nerve Fiber Layer and Ganglion Cell Layer in Middle Age and Cognition From Childhood to Adulthood,” was published in JAMA Ophthalmology.