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Correlation found between retinal changes, Alzheimer’s disease
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A systematic review and meta-analysis of published literature showed a significant association between retinal measurements by SD-OCT and Alzheimer’s disease, confirming the role of OCT as a tool for studying neurodegenerative changes.
Thirty studies that complied with the criteria established by the authors and used the latest SD-OCT technology were included. Correlation with retinal parameters was investigated for Alzheimer’s disease (AD) and mild cognitive impairment (MCI) in comparison with controls.
Patients with AD had significantly lower average macular ganglion cell-inner plexiform layer thickness, which corresponded with an absolute decrease of 3.66 µm. Thinning occurred in most sub-sectors of the macula except the superotemporal sector.
Macular ganglion cell complex thickness was also significantly lower in patients with AD, with an absolute decrease of 7.04 µm. Macular volume was smaller in patients with AD, and macular thickness was significantly reduced in all sectors, with the inner inferior sector exhibiting the greatest magnitude. Retinal nerve fiber layer thickness was significantly reduced in patients with AD, with an absolute decrease of 5.99 µm.
The same parameters applied to MCI showed a similar trend, although in most cases differences did not reach statistical significance.
“There are two possible mechanisms that may explain the differences of SD-OCT measurements in AD. The first proposed that the cerebral pathology of AD may affect the visual pathway and cause retrograde degeneration of the optic nerve,” the authors wrote. “Alternatively, it is also possible that AD pathology occurs simultaneously both in the brain and retina, leading to thinning of the retinal neuronal layers.”
Whatever the mechanism, the retina can be used as a “window” for early diagnosis of AD, and SD-OCT has the potential to be used to study neurodegenerative processes of AD and to be integrated with other clinical imaging techniques such as brain MRI, the authors said. – by Michela Cimberle
Disclosure: The authors reported no relevant financial disclosures.
Perspective
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Brad Sutton, OD, FAAO
Alzheimer’s disease has devastating consequences, both on affected individuals and on society. At the current time, effective treatment options remain somewhat limited. It is true, however, that early detection facilitates an improved potential for meaningful intervention. Unfortunately, the financial burden associated with current testing modalities, including MRI and PET scanning, is substantial. In an effort to decrease that sizeable burden, might considerably less expensive OCT technology play a role?
The authors performed a very thorough meta-analysis of 30 published articles addressing this topic. Their conclusion was that Alzheimer’s disease is clearly associated with significant thinning of the retinal nerve fiber layer, ganglion cell complex, ganglion cell complex-inner plexiform layer, macula and choroid. Given that GCC and RNFL thinning can also accompany neurodegenerative conditions such as multiple sclerosis and stroke, this is not surprising.
So, what do we do with this information? Ganglion cell and nerve fiber layer thinning can be the result of many, many things, and, conversely, some patients with Alzheimer’s disease will not exhibit retinal changes. Clearly, we can’t use OCT findings alone to definitely diagnose someone with Alzheimer’s disease or to say that they don’t have it, but, utilized in conjunction with other test results and clinical findings, OCT has the potential to be a valuable tool.
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