In the small laboratory study, researchers determined that people with new lenses spent more time in deep sleep and performed better on tests of cognition than healthy age-matched individuals, according to the results published in JAMA Ophthalmology.
“The main take-home message is that cataract lens replacement may be associated with improved circadian rhythms, better cognitive performance and improved sleep,” said the study’s lead author, Dr Sarah Chellappa, of Harvard Medical School in Boston.
“This is one of the first laboratory studies with patients with previous cataracts to show that intraocular lens replacement had beneficial effects on key aspects of physiology and behaviour,” Chellappa noted.
The new study was designed to look at possible advantages of cataract surgery beyond improved sight.
“Patients with cataracts experience not only vision problems, but also sleep disturbances, cognitive impairments, among other issues that can reduce their quality of life,” Chellappa said. “Intraocular lens replacement can help alleviate some of these symptoms and in the long term bring many health benefits to patients with cataracts.”
Chellappa and her colleagues recruited 13 patients, aged 55 to 80, who had cataract surgery two to three weeks prior to the study along with 16 healthy age-matched individuals without cataracts to serve as controls.
Five of the patients who had cataract surgery were given completely clear lenses that block ultraviolet (UV) light to protect the inner eye, while the other eight got slightly amber-tinted lenses that were designed to block blue light as well as UV.
The 29 volunteers were brought into a sleep lab for three weeks of testing. They were all equipped with wristwatch-like sensors called actigraphs that keep track of a person’s activity during the night.
The volunteers arrived at the lab every night at 6 p.m. and then experienced dim light for an hour, then an hour and a half of dark, then two hours of light exposure and finally one half-hour of dim light before turning in to sleep. Each week during the two-hour light-exposure phase of the evening, a different level of light intensity was used.
During slumber, the volunteers’ sleep cycles were monitored to determine how much time was spent in deep sleep. In the morning after they woke up, they were given cognition tests.
When the researchers analysed their data, they found that the cataract patients experienced less of an increase in melatonin, a hormone that rises as night approaches, in response to light exposure compared to the controls. This ‘suppression’ of melatonin in response to light represents a ‘normalised’ reaction, more typical of younger adults, the study team notes.
The cataract patients also spent more time in deep sleep and performed better on cognitive tests than their age-matched peers in the control group. Moreover, cataract patients with clear replacement lenses experienced better sleep and performed better on cognitive tests than those with blue-blocking lenses.
Even in seniors who don’t have cataracts, vision changes with age, Chellappa and her colleagues note. “With ageing, the natural lens of the eye acquires a yellow-brownish discolouration,” they explain. And because of this, “not only is the amount of light reaching the retina dramatically reduced to about one-tenth of that of younger adults, but also the spectrum of the light transmission into the eye is altered.”
While the study is small, its findings are interesting, said Dr Christopher E. Starr, an associate professor of ophthalmology at NewYork-Presbyterian and Weill Cornell Medicine in New York City.
“They found that lenses that let in all light wavelengths were better than the blue-blocking lenses in every category,” Starr said. “So their recommendation is to use clear lenses.”
While the findings should be considered preliminary because of the study size, they could be important, Starr said. “Cataract surgery is the most commonly performed ambulatory surgery in the U.S.,” he noted. “Each year between 3 and 4 million people will get lens replacements.”
Source: Reuters Health