RNFL, ganglion cell layer thickness related to cognitive performance
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Retinal nerve fiber layer and ganglion cell layer thickness at age 45 years was linked with cognitive performance in childhood and adulthood, with thinner retinal nerve fiber layer tied to a decline in processing speed, according to data.
“These findings suggest that the retina is a biological correlate of cognitive functioning,” Ashleigh Barrett-Young, PhD, of the Dunedin Multidisciplinary Health and Development Research Unit at the University of Otago in New Zealand, and colleagues wrote in JAMA Ophthalmology. “It has been repeatedly observed that people with higher IQs tend to live longer and be healthier than those with lower IQs, but the mechanisms for this association are likely to be multifarious and complex.”
To examine whether retinal nerve fiber layer (RNFL) and ganglion cell layer (GCL) were associated with global cognitive performance and change in IQ at different life stages, Barrett-Young and colleagues analyzed data from the Dunedin Multidisciplinary Health and Development Study, which included 1,037 individuals born between April 1972 and March 1973 who were monitored until age 45 years.
Of 938 participants seen through age 45, 73 were excluded from the study because of complications with OCT scans (n = 63) and diseases affecting the retina (n = 10). The final data set included 865 individuals (50.2% men).
Results showed that lower Full-Scale IQ (FSIQ) at age 45 years (P < .001) was linked with thinner mean RNFL thickness (P < .001), as well as thinner nasal quadrant (P = .01) and inferior quadrant (P = .001). Lower childhood FSIQ was associated with thinner mean RNFL at age 45 years (P < . 001) and thinner RNFL in the nasal and inferior quadrants, respectively (P = .008 and P < .001).
Thinner mean GCL thickness also was associated with lower FSIQ at age 45 years (P = .04), as was thinner temporal-superior (P = .01), inferior (P = .02) and temporal-inferior segments (P = .008). Lower childhood FSIQ was tied to thinner mean GCL thickness (P = .003), and thinner GCL in the temporal-superior (P = .001), superior (P = .01), nasal-superior (P = .03), nasal-inferior (P = .01), inferior (P = .003) and temporal-inferior segments (P = .001).
Researchers further reported that thinner mean RNFL thickness was associated with a decline in processing speed (P = .04).
“Our study used a unique life-course approach to show that RNFL, and to a lesser extent GCL, in middle age may reflect lifelong interindividual differences in global cognition,” Barrett-Young and colleagues concluded. “In addition, RNFL may be particularly sensitive to changes in processing speed by middle age.”
They added, “RNFL thinning could be a useful biomarker in identifying those experiencing the early stages of cognitive decline before global cognitive decline becomes apparent. However, further longitudinal studies are required to elucidate whether retinal thinning predicts Alzheimer’s disease.”
Perspective
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This study contributes to the growing body of evidence that shows that the retina and brain are closely linked. Optometrists love OCT for its ability to image ocular structures in great detail, and the idea that that information can also tell us more about the brain is exciting both for eye care providers and for those who study and care for people with neurological diseases and dementia. However, this research is still in the early stages and is not clinically useful in everyday practice. Reading this article leaves one with more questions than answers about the associations between RNFL/GCC thickness and cognitive function as well as the associations between cognitive function in childhood and middle age with dementia later in life.
Since the Dunedin Multidisciplinary Health and Development Study is an ongoing lifetime cohort study, it will hopefully provide more and more valuable information as participants age and more serial OCTs and cognitive function scores continue to be collected. There may be a day when optometrists screen patients to assess their risk of Alzheimer’s disease and make referrals for early testing and intervention, but much more research is needed to get to that future.
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