TORONTO - Researchers at McMaster University, The Hospital for Sick Children (HSC) and University of Toronto have unravelled the mystery of what causes the vision of human babies to improve so rapidly after birth. Vision scientists were previously unclear as to whether the five-fold visual improvement that babies experience within the first six months of life was built into the developing brain or depended on the babies actually using their eyes. The research is reported in the October 1 issue of the journal Science.
"By studying a group of infants with dense cataracts, we were able to determine that it's visual stimulation, not intrinsic brain development, that is responsible for the rapid improvement in vision," explains one of the study's authors Dr. Terri Lewis, a professor of Psychology at McMaster University, a vision scientist in Ophthalmology at The Hospital for Sick Children, and an adjunct professor of Ophthalmology with the University of Toronto.
"In our study, we assessed the vision of 28 babies at The Hospital for Sick Children, which has the largest program in North America for the treatment of cataracts in children," explains McMaster University vision scientist Dr. Daphne Maurer. "All of the babies, who ranged in age from 1 week to nine months old, had dense cataracts (in one or both eyes) that were surgically removed. The babies were then fitted with contact lenses. Immediately following contact lens fitting, the babies' vision was measured using a special eye chart."
The researchers discovered that once the cataracts were removed and the contact lenses were in place, the babies' vision was still like that of newborns but the brain was ready to learn to see. The babies began to develop the ability to see more clearly after only one hour of using their eyes. Over the next month, their vision continued to improve more rapidly than normal, so that the size of their visual impairment was reduced.
"Cataracts are a loss of transparency that develops in the natural lens of the eye," explains HSC staff ophthalmologist Dr. Alex Levin, assistant professor of Paediatrics, Genetics and Ophthalmology at the University of Toronto and co-director of the HSC Eye Genetics team, who performed the surgery on the babies. "When the cataracts are dense it's like looking through waxed paper, or worse: light can be perceived but not definite shapes. To remove the cataract, we must remove the entire lens of the eye which leaves the eye with no means to focus the light that can now enter. The contact lenses, which are very strong, take the place of the natural lens."
The treatment implications of this study are critically important for the approximately one in 1,000 to 4,000 babies born with cataracts. If surgery is done too late then the brain may not learn to use the vision in that eye. With successful early intervention, even in the first week of life if possible, some children can develop vision as good as 20/20 and go on to lead relatively normal lives.
Media contacts:
Andrea Farquhar, Public Relations
McMaster University
(905) 525-9140 ext. 23658
farquhar@mcmaster.ca
Joanne Kehoe, Public Relations
McMaster University
(905) 525-9140 ext. 22959
kehoej@mcmaster.ca
Liz Leake, Public Affairs
The Hospital for Sick Children
(416) 813-5046
liz.leake@sickkids.on.ca
Journal
Science