Alzheimer’s is a disease of the brain, usually diagnosed through MRI scans and a battery of other tests. 

Researchers, however, have found that the human eye can show early signals of this common form of dementia long before symptoms become apparent.

Researchers at Cedars-Sinai Medical Center in Los Angeles, California, led the study, which was published in the journal Acta Neuropathologica last month.

The researchers analyzed human eyes and brain tissue from 86 deceased patients who had been diagnosed with either Alzheimer’s disease or mild cognitive impairment before they died.

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The researchers also compared samples from people who had normal cognitive function to those who had early-stage symptoms and to those who had late-stage Alzheimer’s.

The retinas of the patients with mild cognitive impairment and Alzheimer’s disease, the researchers found, had an excess amount of amyloid beta 42, a protein that forms the "plaques" that build up in the brains of people with Alzheimer’s. 

Additionally, the retinas contained cells called microglia, which are also associated with progression of the disease.

"We discovered the accumulation of highly toxic proteins in the retinas of patients with Alzheimer’s disease and mild cognitive impairment, causing severe degeneration of cells," said Dr. Yosef Koronyo, research associate in the Cedars-Sinai Department of Neurosurgery and first author of the study, in a statement on the Cedars-Sinai website.

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The changes were also detected in patients who did not display any cognitive decline or had only very mild signs, indicating that retinal tests could help enable early diagnosis.

This study is the most comprehensive analysis of the human retina in terms of how it relates to the brains and cognitive functions of Alzheimer’s patients.

That's according to Maya Koronyo-Hamaoui, PhD, professor of neurosurgery, neurology and biomedical sciences at Cedars-Sinai, in a statement.

"These findings may eventually lead to the development of imaging techniques that allow us to diagnose Alzheimer’s disease earlier and more accurately, and monitor its progression non-invasively by looking through the eye," said Koronyo-Hamaoui, senior author of the study.

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More than six million Americans currently have Alzheimer’s, according to the Alzheimer’s Association. 

The disease is expected to affect 12.7 million people by 2050 as the population ages.

"The population of people age 65 and older is expected to grow from 58 million in 2021 to 88 million in 2050," Nicole Purcell, DO, general neurologist and senior director of clinical practice at the Alzheimer's Association in Chicago, Illinois, told Fox News Digital in an earlier interview.

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Fox News Digital reached out to the authors of the new study for comment.

A car was swept away and two passengers drowned early Friday in Missouri during torrential rains that were part of a severe weather system roaring across parts of the Midwest and South.

The accident happened just after midnight in a sparsely populated area of southwestern Missouri. Authorities said six young adults were in the vehicle that was swept away as the car tried to cross a bridge over a flooded creek in the town of Grovespring.

Four of the six made it out of the water. The body of Devon Holt, 20, of Grovespring, was found at 3:30 a.m., and the body of Alexander Roman-Ranelli, 19, of Springfield, was recovered about six hours later, Missouri State Highway Patrol Sgt. Thomas Young said.

PERSON MISSING AFTER FLASH FLOODING IN SOUTHWESTERN MISSOURI

The driver told authorities that the rain made it difficult to see that water from a creek had covered the bridge, Young said.

Meanwhile, the search continued in another southwestern Missouri county for a woman who was missing after flash flooding from a small river washed a car off the road. The Logan Rogersville Fire Protection District said the victim's dog was found safe, but there was no sign of the woman. Two others who were in the car were rescued. Crews planned to use boats and have searchers walking along the riverbank.

Some parts of southern Missouri saw nearly 3 inches of rain Thursday night and into Friday morning as severe weather hit other areas. A suspected tornado touched down early Friday in north Texas as a volatile storm system threatened to spawn tornadoes in several Southern states.

Matt Elliott, warning coordination meteorologist at the National Oceanic and Atmospheric Administration’s Storm Prediction Center in Norman, Oklahoma, said severe weather is expected across several states.

"We’re talking several tornadoes, including some that might be strong and intense," Elliott said.

The Storm Prediction Center warned the greatest threat of tornadoes would come Friday afternoon and evening in portions of Arkansas, Louisiana, Mississippi and Tennessee. Storms with damaging winds and hail were forecast from eastern Texas and southeastern Oklahoma into parts of southeastern Missouri and southern Illinois.

"Now is the time to start checking batteries on your weather radios and making sure you have multiple ways to receive weather warnings, but also having a plan so that if storms start approaching your area and warnings are issued you’re able to get yourself and your family to a place that’s safe," Elliott said.

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Louisiana Gov. John Bel Edwards warned of potential tornados reaching the state overnight and urged residents to prepare for severe weather, including damaging winds and hail. The risk of personal vulnerability increases with overnight severe weather as residents are less likely to receive warnings because they are asleep and tornadoes are more difficult to spot, according to the National Weather Service.

In Texas, a suspected tornado struck about 5 a.m. in the southwest corner of Wise County, damaging homes and downing trees and power lines, said Cody Powell, the county's emergency management coordinator. Powell said he had no reports of injuries.

The weather service had not confirmed a tornado, but damage to homes was also reported in neighboring Parker County, said meteorologist Matt Stalley. Investigators likely will go to the area later Friday to make that determination.

The two areas are about 10 miles apart on the western edge of the Dallas-Fort Worth metroplex, and Stalley said the storm system was expected to move east of the region by early Friday afternoon.