Over the next three decades the number of US adults with cataracts is expected to double from 25 to 50 million. It’s the reason one in five lose their sight and one in seven suffer moderate to severe vision impairment.
This is a needless tragedy because cataract removal is one of the most routine, safe and effective types of surgery performed.
Bad as it is to go blind, here’s something even worse:
Sight loss and vision impairment strike more than the eyes alone. They’re also linked with cognitive decline and dementia. In theory, recovering the gift of sight should slow down or stop this process. But does it work in practice?
Common Cause or Cascade?
Scientists don’t know the reason for the eyesight-cognition link, but they’ve put forward a few theories.
The first suggests it’s an indirect association. Aging factors, such as central nervous system degeneration, affect both at the same time. This is called the common cause hypothesis.
The cascade hypothesis proposes that declining vision lowers belief in one’s own abilities, increases isolation from other people, causes depression, and often leads to less physical activity. These in turn increase the risk of cognitive loss. Depression, lack of exercise and social isolation are all known to be risk factors for dementia.
Whatever the true explanation, there’s little doubt the association is real.
The strong link between poor vision and dementia was highlighted in a 2010 study from researchers at the University of Michigan. They followed 625 cognitively healthy men and women over 70 for an average of ten years.
Those with very good or excellent vision were found to have a much lower risk of dementia – 63% lower, in this study. People with untreated poor vision had a five-fold increased risk of cognitive impairment and – alarmingly – a nearly ten-times-higher risk of Alzheimer’s disease.
If the common cause theory is correct, redressing poor eyesight won’t alter cognitive abilities. But if the cascade hypothesis holds true, correcting visual impairment should help restore the mind.
Several research groups have attempted to find the answer.
Slows Cognitive Decline by 50%
In Japan, a study compared 20 cognitively impaired patients with an average age of 82 who had cataract surgery with 20 similar patients who did not have surgery. The surgical group saw a significant improvement in cognition.
Cognitive improvements after cataract surgery were also seen in a UK study of 112 participants over the age of 75.
In the first large scale study, taking into account many factors that influence cognition, researchers in Japan found that cataract surgery reduced the risk of cognitive impairment by 34%.
That’s equivalent to a miracle drug for cognitive loss.
The most robust study to date was published in PLOS One in October.
A research group from the University of Manchester in the UK compared 2,068 people aged 50 or more who underwent cataract surgery at some point during a 12-year period with 3,636 who did not have surgery. All participants underwent memory tests.
The authors took into account many risk factors for cognitive decline, such as education, marital status, wealth, physical activity and medical history.
Their findings supported the cascade theory, because those who accepted surgery had half the rate of cognitive decline compared to those who did not undergo surgery.
Dr. Asri Maharani, who led the research, said he was excited by the prospect of slowing down or even preventing some cases of dementia by this intervention.
Caroline Abrahams from the charity Age UK explained that correcting sensory disturbances “can open up a world that was previously closed off and reduce some of the isolation and loneliness that these problems can bring.”