New low vision research could make clinicians 'Double-Happy'
By BILL WINTER
Dr. Barry S. Kran peered through a peephole into the eyes of a 15-year-old boy.
The boy was blind. He was also deaf. He had cerebral palsy and cognitive disabilities. He had very limited ability to communicate.
As the Optometric Director at the New England Eye Low Vision Clinic at Perkins, it was Kran's job to help figure out whether the boy had any usable vision.
But a traditional vision test won't work for a patient who is unable to describe what he can and can't see. And who can't respond to questions.
So Kran peered through a peephole in the center of a large, rectangular card he held directly in front of the boy's face. He watched the boy's eyes.
Kran was using Teller Acuity Cards™, a test of acuity for lines. On each card, there are vertical lines on one half; the other half is blank. The lines range from very wide to extremely fine. This test works on a principle optometrists call "preferential looking." That's their technical way of saying that a person would rather look at something rather than at nothing.
If the boy had any vision at all, Kran would see his eyes focus on the widest lines.
They didn't. The boy's eyes danced wildly, focusing on nothing. Normally, that would answer the question: the boy was completely blind.
But it wasn't that simple, said Darick Wright, the clinic's coordinator.
"His classroom teacher swore she witnessed him seeing things," he said. The boy attended Perkins' Deafblind Program, and his teacher said he sometimes appeared to react to visual stimuli.
So the team working with the boy—Dr. Kran, Wright and the boy's teacher—decided to test his contrast sensitivity.
The other half of the vision equation
Contrast sensitivity is the other half of the vision equation. The first half is acuity—the ability to see detail in small or distant objects. The classic eye chart in your optometrist's office measures acuity. The smaller row of letters you can read, the higher your visual acuity. At the Low Vision Clinic, the smaller the lines patients can detect on the Teller Cards, the higher their acuity.
Meanwhile, contrast sensitivity is your ability to distinguish an object from its background. The more subtle distinctions in colors or shades you can observe, the higher your contrast sensitivity.
However, at the time the clinic's team tested the boy, no good contrast sensitivity tests existed for patients with multiple disabilities. They were forced to improvise.
So they placed Cheerios on a tray in front of the boy. Some of the tasty cereal snacks were put on a high-contrast background. Some were on a low-contrast background.
The boy didn't hesitate. He quickly snatched up the Cheerios that stood out sharply against the darker, high-contrast background. He completely ignored the others.
The team tried several different arrangements. Without fail, the boy eagerly ate only the high-contrast Cheerios.
Mystery solved. The boy could see—but only when the contrast was high enough. Armed with that knowledge, the boy's teacher was able to tailor his educational environment to his specific visual abilities.
"The boy's teacher went back to her classroom and modified factors to reflect higher contrast in the environment," Wright said. For example, the teacher placed yellow classroom items on a black background. "Immediately the boy's performance improved," he said.
The clinic's challenge
That 15-year-old boy is a perfect example of the challenge the clinic's experts face every day—trying to determine subtle gradations of almost non-existent eyesight in individuals with multiple disabilities that make it difficult for them to communicate.
"Our tenet is that it's never the patient's fault if we can't get the information we need," Wright said. "We just need to figure out how to observe the patient. We need to consult the patient's support team. And we need to set the environment to allow that person to tell us what we need to know about their vision."
Located on Perkins' campus in Watertown, Mass., the New England Eye Low Vision Clinic is a collaborative effort between The New England Eye Institute and Perkins. It's the only clinic in the region specializing in vision assessment for patients with multiple disabilities.
The clinic's team offers a unique blend of educational and clinical expertise. While the clinic does see adults with visual impairments and physical or cognitive disabilities, a majority of its patients are pre-school and school-age children.
"The teachers and parents of our students want to know how healthy their eyes are and how clearly they can see, but we can't measure those things as easily," said Donna Bent, Perkins Deafblind teacher and Orientation and Mobility specialist. "Maybe the student isn't able to express what they can see or maybe they can't match symbols or read a chart."
The clinic also does original research. Inspired by the 15-year-old boy and similar patients, the clinic is developing new ways to more precisely measure contrast sensitivity.
At the forefront of this work is Dr. Luisa Mayer, Ph.D., an internationally known expert in visual fields and a practicing clinician at the clinic.
"Contrast sensitivity is the new frontier for low vision," she said.
Poor contrast sensitivity can be dangerous
That's because contrast sensitivity is more difficult to measure than acuity—but can profoundly impact a low-vision child's ability to successfully function in life or thrive in school.
"We were getting patients who scored very high on visual acuity tests," Wright said. "But when they got home they were still bumping into things, tripping over door thresholds, for instance, that were similar in color to the floor."
If you're walking down the stairs, reduced contrast sensitivity can be dangerous, he said. "If [the steps are] all the same color and the lighting isn't that good, the contrast is reduced. If your eyes don't process that fine difference in contrast, you may fall down the stairs."
Contrast also plays an important role in the classroom.
For students with poor contrast sensitivity, all lessons must be presented with contrast in mind. For example, text on a computer screen may need to be enlarged and shown in bright white text against a black background. If a teacher writes on a white board, it needs to be done with a dark blue or black marker. During meals or snacks, food must be served on high-contrast plates.
Currently, there are no established methods to precisely quantify a multiply disabled patient's contrast sensitivity.
That's less than ideal, Mayer said, when "we're trying to get the finest estimate of a person's vision."
So, drawing on 40 years of vision field expertise, Mayer is developing a new test to measure contrast sensitivity in children with multiple disabilities.
She calls it the "Double-Happy Face" test.
Symmetrical Smiley Faces
In the test, patients are shown a series of cards featuring a graphic image that resembles two smiley faces on top of one another. As with the Teller Acuity Cards, the patient's eyes are observed through a peephole in the card.
Mayer selected the happy face design to make the test more useful for babies and children with limited cognitive abilities, because early developmental psychologists have shown that the human face is a natural point of interest for infants.
On each card, the Double-Happy Face remains exactly the same in terms of size and shape. However, in subsequent cards, the image gradually fades from a dark black to a pale grey.
In other words, the acuity remains the same. Only the contrast changes. So if a low-vision patient focuses on one card but not the next, it's probably because the image on the latter card dropped below his or her contrast sensitivity.
"It's measuring what's called a threshold," Mayer said. "We're trying to get a measure that represents the real world in some way. That's part of the science and part of the art of designing a test like this. You don't want to make treatment decisions based on unreliable measures."
Mayer's Double-Happy Face cards are still in the early stages of testing. She will first test populations who can respond verbally to the cards, she said. If those tests show consistent and reliable results, she will gradually expand into populations with multiple disabilities.
If the Double-Happy Face test is successful, it could be a major breakthrough in measuring precise contrast sensitivity levels. And that could give teachers useful information that might lead to significantly better educational opportunities for children who struggle not only with blindness, but with additional disabilities.
As they continue to develop the test, Mayer and her colleagues at the New England Eye Low Vision Clinic will continue to peer though the peephole—into the eyes of children who need their unique expertise, and into the future of low-vision research.