As scientists continue to try understand Alzheimer's and how it might be cured, new research has uncovered an intriguing link between the condition and some degenerative eye diseases, including glaucoma.

While it's much too early to say Alzheimer's causes eye defects (or vice versa), the research might open up new avenues for spotting the brain disease earlier – if someone checks in at the doctor's with an eye complaint, for example.

The new study took place across five years, covering 3,877 patients aged 65 and over, and found that those with specific degenerative eye diseases were 40-50 percent more likely to develop Alzheimer's too. That's a correlation that's well worth investigating further.

"We don't mean people with these eye conditions will get Alzheimer's disease," says lead researcher Cecilia Lee, from the University of Washington School of Medicine.

"The main message from this study is that ophthalmologists should be more aware of the risks of developing dementia for people with these eye conditions, and primary care doctors seeing patients with these eye conditions might be more careful on checking on possible dementia or memory loss."

Could the eyes give us a window into what's happening in the brain? It's a possibility. Eye checkups could be used to screen people with a greater risk of Alzheimer's perhaps – and while there's no cure yet, appropriate care could be provided earlier.

Age-related macular degeneration, diabetic retinopathy, and glaucoma were the three eye conditions that showed a strong link with Alzheimer's. All three affect vision to varying degrees, but have different combinations of risk factors, including age, existing conditions, genetics, and lifestyle choices.

Cataracts meanwhile, most commonly caused by ageing, didn't seem to have the same relationship with Alzheimer's.

The statistics were controlled for several factors, including for age, sex, education level, and smoking, as well as the APOE genotype linked to Alzheimer's disease.

Exactly how Alzheimer's and the subsequent dementia starts has been the topic of much research in recent years, with clumping, abnormal proteins in the brain thought to be responsible for breaking key neural connections.

However, that hypothesis has been challenged in recent studies, while other research has pointed to a link between viruses and Alzheimer's.

It's possible that this new correlation with eye diseases could give us more insight into the origins of Alzheimer's, perhaps joining up the dots for some of what's happening in the nervous system.

While scientists continue to try and figure out causes the disease and how we might treat it, what's definitely clear is the scale of the problem: close to 50 million people are thought to be living with Alzheimer's worldwide, a figure that could more than double by 2050.

The more we know about Alzheimer's, the better the chances of preventing it and maybe one day reversing its effects – and this could be a key step forward.

"What we found was not subtle," says one of the researchers, Paul Crane from the University of Washington School of Medicine. "This study solidifies that there are mechanistic things we can learn from the brain by looking at the eye."

The research has been published in Alzheimer's & Dementia.