Sight and Smell Are The Key To Early Detection of Alzheimer’s, Study Finds

New studies suggest that a person's eyes and nose hold early signs of Alzheimer's disease.

The studies, which were presented at the Alzheimer's Association International Conference in Toronto on Tuesday, suggest that the worsening ability to identify odors and the thinning of the retinal nerve fiber layer in the eye are indicators of cognitive decline.

The Smell Test

In one study, Seonjoo Lee, assistant professor of clinical biostatistics in Columbia University, studied 397 healthy people at an average age of 80 and followed them for over four years. The participants were given brain scans and a 40-item University of Pennsylvania Smell Identification Test (UPSIT), which involved a scratch-and-sniff test of familiar scents like turpentine, lemon, licorice and bubble gum.

During the study period, 49 people developed Alzheimer's disease and almost one in five participants exhibited signs of mental decline, CNN reports.

The research team found that participants who got the lowest scores on odor tests at the beginning of the study were likely to be among those who showed weakening cognitive functions. Participants whose brain scan showed a thinning in the area associated with memory were more likely to develop Alzheimer's disease.

In a separate study, William Kreisl, assistant professor of neurology in Columbia University, examined the scores from the smell test and brain scans of 84 mentally weak participants and 26 healthy participants.

At six months, researchers found that 67 percent of the participants showed cognitive decline. The researchers said that while signs of plaque in the brain scan or spinal fluid predicted the participants' mental decline, participants who scored less than 35 in the UPSIT were still three times more likely to develop mental decline than participants who scored higher.

"It's not the sensitivity of the nose itself that diminishes," Dr. David Argus, medical contributor for CBS News, commented on an interview.

"Rather, as cognitive impairment develops, the brain is less capable of identifying what those smells are."

Eyes, The Windows to The Brain?

Another indication of early signs of Alzheimer's, as other studies pointed out, is retinal thickness.

In the first study, Fang Ko of the University College London's (UCL) Institute of Ophthalmology conducted eye tests, physical exams and cognitive tests among 33,068 participants, CNN reports.

The research team found that participants who scored low on the cognitive tests had thinner retinal nerve fiber layers.

In another study conducted by Melanie Campbell, professor of physics at the University of Waterloo, the researchers detected amyloid protein deposits in the retinas of animals and people with Alzheimer's, which began to appear in the retina at the onset of the disease.

The research team also found that their "polarization technique," which measures light reflected off amyloid deposits in the eye, could be used as an early, non-invasive test to detect early signs of Alzheimer's.

With the studies presented, health experts are starting to become hopeful of having a good fighting chance against the disease.

"For the first time now, we have drugs in development that are hitting the biologic processes involved in Alzheimer's," Argus said.