Changes to the eyes might help diagnose the onset of the second most common form of dementia, according to new research.
The findings show that a loss of cells in the retina is one of the earliest signs of frontotemporal dementia (FTD) in people with a genetic risk for the disorder - even before any changes appear in their behaviour.
The researchers from the University of Alabama at Birmingham, Gladstone Institutes and the University of California, San Francisco, studied a group of individuals who had a certain genetic mutation that is known to result in FTD.
They discovered that, before any cognitive signs of dementia were present, these individuals showed a significant thinning of the retina compared with people who did not have the gene mutation.
"This finding suggests that the retina acts as a type of window to the brain," said Erik Roberson, associate professor in the Department of Neurology at UAB and a study co-author.
"Retinal degeneration was detectable in mutation carriers prior to the onset of cognitive symptoms, establishing retinal thinning as one of the earliest observable signs of familial FTD," Li Gan, from Gladstone said.
"This means that retinal thinning could be an easily measured outcome for clinical trials," said Gan.
Although it is located in the eye, the retina is made up of neurons with direct connections to the brain. This means that studying the retina is one of the easiest and most accessible ways to examine and track changes in neurons.
Using a process called ERG, or electroretinogram, Roberson and Timothy Kraft, associate professor in the UAB Department of Vision Sciences, showed that the retinas in mice with FTD had a loss of ganglion cell function; these cells are responsible for transmitting signals from eye to brain.
"We have a more complete understanding about how the retina functions as opposed to the operations of the complex brain," said Kraft.
"That makes it much easier to use the retina as a tool for better understanding FTD," said Kraft.
The researchers also discovered new mechanisms by which cell death occurs in FTD. As with most complex neurological disorders, there are several changes in the brain that contribute to the development of FTD.
"The results of this study have shown that we can use the thinning of retinal cells as a marker for this type of dementia," said Roberson.
The finding was published in the Journal of Experimental Medicine.