Better eyesight also improves their quality of life, the researchers said.
"These preliminary results indicate that improved vision can have a variety of benefits for people with dementia and their loved ones, both visual and non-visual," said Dr. Alan Lerner, of Case Western Reserve University and University Hospitals Case Medical Center, in Ohio.
Cataract surgery involves removing the eye's cloudy natural lens and replacing it with a clear artificial lens.
The study included 20 dementia patients who had cataract surgery and a control group of eight patients who did not have the procedure.
Six months after the surgery, the patients in the surgery group had significantly improved vision and quality of life, slower decline in memory and thinking, and greater improvements in behavior than those in the control group, the researchers found.
Improved quality of life was also reported by caregivers of the patients who had cataract surgery, according to the study. The report was scheduled for presentation Sunday at the Alzheimer's Association's annual meeting in Copenhagen, Denmark.
"Our findings need to be verified in a larger study, but they suggest the need to aggressively address dementia co-morbidities such as vision-impairing cataracts, while balancing safety and medical risks," Lerner added in an association news release.
"If the results hold up, it will significantly affect how we treat cataracts in individuals with dementia. Other interventions to offset sensory loss -- including vision and hearing -- may help improve quality of life for people with dementia and their caregivers," Lerner said.
An Alzheimer's Association spokeswoman said the study supports the organization's view that people with dementia benefit from full healthcare treatment.
"Too-common attitudes such as, 'There's no need for extra care' or 'Why put them through all of that,' are not justified and are bad medical practice," said Maria Carrillo, the association's vice president of medical and scientific relations.
"Appropriate thoughtfulness and restraint are necessary when considering surgery or other procedures for people with Alzheimer's or another dementia," Carrillo said. "However, we should not assume that medical procedures cannot be pursued or are too risky."
These results show that improving sensory abilities can provide benefits in a variety of ways -- for people with Alzheimer's and also for their caregivers, she added.
Data and conclusions presented at meetings are typically considered preliminary until published in a peer-reviewed medical journal.