Many people suffer from cataracts in old age, an increasing clouding of the lens in the eye. If left untreated, the disease can lead to blindness. A study now shows that eye surgery not only restores their eyesight, but is also associated with a lower risk of developing dementia in the following years. The results suggest that a lack of visual input could play a role in the development of dementia.
Almost 50 million people worldwide are affected by dementia. The mechanisms of the disease are only partially understood and there is no treatment. In addition to the search for drugs, research focuses on finding effective preventive measures. Previous studies have indicated that impaired sensory perception – such as hearing loss and poor eyesight – are linked to an increased risk of dementia. The eye disease cataracts plays an important role in this context. The lens becomes increasingly cloudy, which can lead to blindness. Around 35 million people worldwide are affected by cataracts and 20 million go blind as a result. But eyesight can be restored by removing the natural lens and replacing it with an artificial one.
Eye surgery against dementia?
“Since both sensory impairment and dementia are strongly linked to aging, more knowledge about the relationship between sensory impairment and dementia could have important implications for individual and global public health, especially if measures to improve sensory function reduce the risk of dementia,” writes a team led by Cecilia Lee from the University of Washington in Seattle. The researchers therefore investigated to what extent restoring eyesight through eye surgery affects the risk of dementia.
To do this, the researchers used data from a long-term study that has been regularly examining volunteers aged 65 and over for dementia since 1994 and collecting additional health data. Lee and her colleagues focused on participants who developed cataracts or glaucoma and either underwent surgery or not. Of 3,038 people with cataracts, 853 developed dementia during the observation period. 1,382 people had their cataracts operated on.
Not every operation helps
“The risk of developing dementia was significantly lower in participants who underwent cataract extraction than in people who did not undergo cataract surgery,” the researchers report. The people with restored eyesight had a 30 percent lower risk of developing dementia in the years that followed, compared to the slowly blind people. In order to rule out bias – for example, because healthier people with a lower risk of dementia are more likely to opt for an operation – the researchers adjusted their data to include factors such as age, weight, blood pressure, diet, exercise and education.
As a comparison, they also looked at how glaucoma surgery affects the risk of dementia. In glaucoma, the optic nerve is damaged by increased intraocular pressure. Unlike cataracts, surgery cannot restore vision, it can only prevent it from deteriorating. 105 of 728 glaucoma patients decided to have an operation during the observation period. However, glaucoma surgery had no effect on the risk of dementia.
Possible mechanisms
From the point of view of the researchers, this indicates that people who opt for an eye operation do not generally have a lower risk of dementia, but that it is really about restoring their eyesight. Although the study can only establish an association rather than a causal relationship, the results suggest that it is actually cataract removal that reduces the risk of dementia. “No other medical procedure has shown such a strong association with reducing the risk of dementia in the elderly,” says Lee.
According to the researchers, several factors are possible mechanisms behind the connection. “Cataract-related visual impairments can decrease neural input, potentially accelerating neurodegeneration or exacerbating the effects of neurodegeneration,” they explain. “It has already been proven that the visual cortex undergoes structural changes as a result of the loss of vision.” Social factors can also play a role: “Sensory impairments can contribute to social isolation and reduced cognitive stimulation, which can increase the risk of dementia,” say the researchers .
Source: Cecilia Lee (University of Washington) et al., JAMA Internal Medicine, doi: 10.1001 / jamainternmed.2021.6990