Findings from a recent study published in the American Journal of Ophthalmology evaluated outer retinal changes in older adults with early and intermediate age-related macular degeneration (AMD) and compared them to brain changes associated with Alzheimer’s disease (AD).
Give me some background.
AD is a significant cause of morbidity and mortality worldwide, with considerable diagnostic challenges, such as detecting and clinically monitoring the disease during earlier stages when neuronal damage is limited.
However: As a developmental extension of the brain uncovered by bone, the retina offers accessibility for direct, affordable, and noninvasive visualization and temporal monitoring of the central nervous system (CNS).
- In fact: Previous studies have demonstrated associations between retinal changes and AMD with AD and related dementias (ADRD).
Now talk about the study.
In this cross-sectional study, investigators recruited 60 adults (aged 70-87 years; 73% women, 88% White) from Callahan Eye Hospital Clinics at the University of Alabama at Birmingham.
The breakdown was as follows:
- Normal eyes (n = 22)
- Early AMD (n = 19)
- Intermediate AMD (n = 19)
And what testing was conducted?
Participants underwent:
- Cognitive testing
- Optical coherence tomography (OCT)
- Magnetic resonance imaging (MRI)
- Researchers scanned the total brain, cortex, cerebral white matter, gray matter, hippocampus volume, occipital cortex thickness, and cortical thickness in ADRD-related brain regions
Connections between retinal layer thickness and brain volume and thickness of specific brain regions were evaluated using multivariable linear regression.
- Note: The beta (β) coefficient listed below represents the estimated change in the dependent variable (i.e., brain changes associated with AD) for a one-unit change in a predictor variable (i.e., outer retinal changes) while all other predictors are held constant.
Findings?
Participants with a thinner outer retina had significantly:
- Lower cortical thickness in ADRD-related brain regions (β = 7.72, P = 0.006)
- Lower occipital cortex regions of interest (occipital ROIs) thickness (β = 5.68, P = 0.020)
- Smaller hippocampus (β = 0.019, P = 0.022)
In addition, subjects with a thinner total retina had significantly lower occipital ROIs (β = 3.19, P = 0.009) and ADRD-related brain region thickness (β = 3.94, P = 0.005).
Anything else?
Decreased retinal thickness in the outer Early Treatment of Diabetic Retinopathy Study (ETDRS) ring was the most frequently reported retinal variable associated with brain atrophy in regions involved in vision, memory, and dementia.
Finally, total gray matter volume showed positive correlations with education (P = 0.022).
Take home.
These findings indicate that a thinner outer retina was associated with atrophy in brain regions primarily involved in vision and cognition in older adults with normal retinal aging as well as early and intermediate AMD, such as:
- Lower hippocampal volume
- Reduced thickness of the occipital ROIs
- Brain regions known to show early structural changes in dementia
Next steps?
“Future research with larger sample sizes and independent replication studies will be crucial to confirm these associations, in which we also suggest exploring other retinal layer thickness variables that are highly correlated with the ‘marker’ identified in this study,” the study authors noted.