Alzheimer’s disease (AD) is the most common form of dementia, which typically affects people over 65 years of age; it accounts for 60 to 80 percent of all types of dementia. It is the sixth leading cause of death in the United States, and the median survival after diagnosing is 10.3 years, but it can range from 2 to 20 years.
The etiology of AD is believed to be the excessive amount of accumulation of amyloid plaques, and neurofibrillary tangle (NFT) due to phosphorylated protein Tau. As a result, neuron death starts from the entorhinal cortex and hippocampus area, and impacts memory.
To diagnose the “definite” Alzheimer’s, an autopsy is required to confirm the amyloid plaques and NFT in sufficient area and characteristic topographic distribution. However, clinical diagnosis of probable AD corrects 90 to 95% of the time vs. autopsy. Clinicians will evaluate the evidence of cognitive decline or impairment, conduct a thorough physical exam, lab work, brain imaging of CT or MRI to rule out other causes such as focal neurological signs, delirium or Parkinson disease dementia.
Often, from the above diagnosing criteria, when patients are diagnosed with AD, they are at least at mild to moderate stage. Science showed that those microscopic changes (accumulation of amyloid plaques and NFT) can begin 10 to 20 years before symptoms appear. Studies have been focusing on brain imaging system such as positron emission tomography (PET) scan or CSF via lumbar puncture to detect amyloid plaques and tauearly at preclinical stage.
More recently, some groups are investigating the retinal imaging system to scan those biomarkers, such as amyloid plaques. The company, NeuroVision Imaging, from Sacramento, California was first to utilize retinal image fluorescence photography to scan the supranucleus region of the retina to detect beta amyloid plaques. Patients need to take curcumin supplement prior to imaging. Curcumin has fluorescent yellow color, and high affinity for beta amyloid. It will bind to amyloid plaque in the retina and become hyperfluorescent.
Their blinded clinical trial is designed to compare retinal amyloid plaque detected by NeuroVision’s imaging test to brain plaque using PET, which is the current standard for clinical trials. Preliminary results showed significant correlation of beta-amyloid levels detected between the retinal imaging test and PET scan. The trial results also showed that the retinal amyloid-imaging test is able to differentiate between Alzheimer’s and non-Alzheimer’s subjects with 100% sensitivity and 80.6% specificity. Additionally, they further demonstrated the potential to monitor the progression of AD using this retinal imaging technique over 3.5 months of trial.
According to Steven Verdooner, the CEO of NeuroVision, the retinal-imaging test could be commercially available as soon as the second half of 2015. This quick retinal imaging screening for Alzheimer’s could potentially change the way AD is diagnosed, and treated. AD could be detected 20 years earlier before symptoms even come up, and begin being monitored closely by this noninvasive, more affordable technique without harmful side effects such as radiation exposure by PET. It allows patients and their loved ones a better chance to benefit from treatment, have more time to plan for the future, and opportunity to participate in decision making of their medical care or life in general.
Future studies to analyze the validity and repeatability, as well as the efficacy and safety of retinal imaging techniques for AD’s biomarkers are needed.
Dr. Hartman’s Notes: Having an accurate way to reach an early diagnosis of Alzheimer’s Disease could change the course of the disease. It’s exciting that testing the eyes can yield this information.
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