Last modified: Tuesday, February 10, 2004
How well do babies see?
Eye focusing influences infant brain development
NOTE: For information about participating in this research project, call the Infant Vision Laboratory at 812-855-4959 or send e-mail to jbaby@indiana.edu. A free eye examination for the baby is included as part of the study.
BLOOMINGTON, Ind. -- In the first few months of life, a baby sees the world very differently than an adult does. But exactly how well do babies see? More specifically, how well are infants able to control their focusing on different objects? Answering these questions will reveal the nature and quality of the visual information that guides development of a baby's brain and visual system after birth.
Visual information is the input to motor responses such as reaching and grabbing, so poor vision can significantly affect an infant's ability to learn motor tasks and its developing interactions with its environment.
Professor Rowan Candy and her research group at the Indiana University School of Optometry in Bloomington use EEG, optical and behavioral techniques to measure the visual abilities of infants as young as one month. For example, they make measurements of an infant's focusing ability at a rate of 25 times per second, enabling them to track the infant's performance very closely. Their work is supported by a four-year grant of $850,000 from the National Institutes of Health.
"We want to know how clear the image is in a baby's eye, and the image characteristics that are needed to maintain normal development. How much abnormality can be tolerated before problems arise? What are the risk factors?" Candy said.
Newborn infants only respond to very big, bright visual objects. Color vision and depth perception, for example, take months to mature. If the newborn human brain is not equipped to see well, the implication is that newborns will not be sensitive to blur and will not focus their eyes clearly on an object. This results in a blurred image forming on the retina at the back of the eye, and only blurred signals being sent to the baby's developing visual system.
Candy and her group have demonstrated that infants as young as three months can typically hold their focus steadily at a number of different distances, and change their focus within two seconds to a new distance. They are now determining the smallest amount of blur an infant can detect as a function of age. These data are being used to understand the signals available to the infant's developing visual system, and the levels of blur that can be tolerated by infant patients in an eye clinic.
How is it possible to measure vision in babies only one month old?
"We have three ways to do that, working back through the visual system," Candy said. "The first is to measure how well the baby's eyes can focus and how well they can change focus. We have a camera that uses an optical technique similar to the red-eye reflex seen in photographs taken with a flash. We can estimate how well babies focus at different distances using this instrument.
"Next we record an EEG. We put sensors on the back of the baby's head, where the visual part of the brain is located, and present moving images on a computer screen. Then we look for EEG responses from the baby's brain that are correlated with the image movement. When we see the correlation, we know we've got a response to the images on the screen rather than to some unknown background stimulus.
"Then we find out what babies will actually turn their eyes to look at. For example, we can put two targets next to each other and determine whether an infant looks at one of them consistently. If we have a blank patch on one side with narrow stripes on the other side, and the baby always looks at the side with the stripes, we know the baby can tell the difference between the two images and therefore can see the stripes. We can make the stripes narrower and narrower until the infant shows no preference for either side."
This combination of three techniques allows the scientists to track information as it goes through the baby's visual system, first in terms of the optics of the baby's eye, then in terms of the neural information getting to the visual part of the brain, and then in terms of the baby's resulting behavior.
About 5 percent of babies need monitoring in the clinic, Candy said. "Of six-month-olds, 90-95 percent are doing great. By six months their vision should have matured significantly. They should be seeing objects around the room, looking into the distance and making eye contact with parents coming in through the door."
