An analysis of how the retina of the eye scatters light shows promise as an aid for the early diagnosis of Alzheimer's disease.

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Examining how the retina disperses light can provide insight into Alzheimer's disease.

Scientists from the University of Minnesota in Minneapolis came to this conclusion after carrying out a recent study, the findings of which appear in ACS Chemical Neuroscience.

The researchers investigated retinal hyperspectral imaging (HSI) as a potential technique for early Alzheimer's detection in 35 people.

HSI is an emerging imaging method in medicine. As a diagnostic aid, it can provide valuable information about tissue composition and structure.

Scientists can take HSI scans of the retina using a special camera that attaches to a spectral imaging system.

The method, which takes about 10 minutes to administer, is noninvasive and does not require the injection of tracer substances.

Need for biomarkers of early Alzheimer's

Alzheimer's disease is responsible for 60–80% of cases of dementia, an incurable condition that progressively impairs memory and thinking to the point that independent living is no longer possible.

The presence of toxic clumps of beta-amyloid protein in the brain is an established hallmark of Alzheimer's disease.

If there was a way to detect the toxic beta-amyloid clumps in their early stages, this could greatly improve early diagnosis and increase the potential for treatment to delay disease progression.

As the retina is an extension of the brain, it is possible for these toxic protein clumps to form there as well.

This knowledge has spurred scientists to look for Alzheimer's biomarkers in the retina, which is easy to examine noninvasively.

Retinal HSI uses light scattering

Retinal HSI applies the principle of Rayleigh scattering, which is the dispersion of electromagnetic radiation by particles that are much smaller than the wavelength of the radiation.

In their study paper, the authors explain that because of this principle, they would expect retinas with small, early clusters of beta-amyloid to scatter the light in a different way than retinas that either lack the protein clumps or have clumps that are more developed.

The team had already demonstrated the effectiveness of the technique in mouse models of Alzheimer's disease.

The new study "concerns the translation of our [retinal HSI] technique from animal models to human [Alzheimer's disease] subjects," write the authors.

In the new investigation, the team compared retinal HSI results from 19 people at different stages of Alzheimer's with those of 16 controls who did not have the disease and also had no family history of it.

Retinal HSI picks out MCI stage

For each participant, the team took HSI scans from different parts of the retina, including the optic disc, the perifoveal retina, and the central retina.

The results showed that individuals whose retinal light scatter had the "largest spectral deviation from control subjects" were those whose memory tests indicated that they were at the mild cognitive impairment (MCI) stage.

In addition, the researchers found that the amount of spectral deviation correlated with the memory test scores of those at the MCI stage.

They suggest that these results indicate that the technique's sensitivity is higher in the early stages of Alzheimer's disease.

Age and certain eye conditions, such as glaucoma and cataracts, appeared to have little or no effect on the results.

The study's first and corresponding author, Swati S. More, Ph.D., who is an associate professor in the Center for Drug Design at the University of Minnesota, envisages retinal HSI becoming part of annual eye tests that could help identify individuals who might need a further exam or treatment.

"The preliminary results from this study are promising and have laid the foundation for next steps involving rigorous validation of the technique in a clinical setting."

Swati S. More, Ph.D.