Newsletter, Summer 2003
As you know, we are collaborating with ophthalmologists at The Hospital for Sick Children to study visual development after treatment for cataract. It has been an exciting year! We would like to update you on some of our findings and thank you for your contribution to our research.
Our eye chart for babies uses stripes that start out thick—like the big letters at the top of the eye chart at your doctor's office—and then become skinnier and skinnier. Babies "tell" us that they can see the thick stripes by looking toward the left when the stripes are on the left of the card and toward the right when the stripes are there. When the stripes get skinnier, babies stop showing this preference, presumably because they cannot make out stripes and just see grey everywhere on the card.
We use our stripe test to measure babies' acuity as soon as they can first see—on the day they get their first contact lenses after surgery. The results indicate that their vision is like that of newborns, even though they were as old as nine months at the time of the test. In one sense, this is good news because it means that vision doesn't deteriorate before the surgery; on the other hand, it also indicates that patients have a lot of catching up to do. Amazingly, after just one hour of practice seeing—after the first waking hour with the contact lens in place, vision improves as much as it usually does in the first six weeks of life! Patients' vision continues to improve faster-than-normal over the next month. Their brains seem ready to make up for lost time.
Yet so far none of our adult patients have ended up with perfect 20/20 vision. Many have vision in the treated eyes that is quite good—good enough to read normal newsprint or even drive a car. Patients with the best acuity are the ones who wore their contact lenses regularly and, in unilateral cases, those whose parents followed the recommended patching regimen throughout early childhood. It is worth all the effort we know parents put in! To find out why the final outcome is not perfect, we are now measuring patients' acuity at regular intervals after treatment to determine what limits the catching up.
In our acuity studies, we are investigating how well patients see fine detail—like the small print in books. In other studies, we are measuring how well patients can put together the details to see a whole object—like your face—or to see what the object is doing—like where you are looking or which way you are moving. Our easiest task asks babies if they can tell the difference between a drawing that looks like a face and a drawing that we distorted by putting the features in the wrong place. Babies without eye problems look longer at realistic drawings of faces than at distortions—and between birth and 12 weeks of age, they get pickier about how realistic the drawing has to be. We are testing patients on the day they can first see. So far the babies have performed like newborns rather than like age-mates without eye problems. They'll still be fascinated by your face—but not yet realize how much more interesting it is than a mobile. These results tell us that the development of face perception, like acuity, depends on visual input and again underscores the value of early treatment.
Other studies in our lab indicate that when patients are older, they are essentially normal in their ability to see faces—providing they can use information in the shape of large features like the eyes, mouth or chin. When that information is available, they will be as good as children without eye problems in recognizing your face, reading your lips, perceiving whether you look happy, surprised or disgusted, and decoding where you are looking. However, our tests indicate that if they have to rely on spacing among internal features—how far apart your eyes are—they have trouble. They mistake two faces as being the same despite big differences in the distance between the eyes. Normally this doesn't matter—it's easy to recognize Bill Clinton from his distinctive chin—but patients will have more trouble than children without eye problems when it's hard to see the large features because a head is turned sideways, or the lighting is poor, or the person is far away. The pattern of results indicates that the limitation in seeing the spacing of features is probably in the right hemisphere. Some patients have told us about special strategies they use to recognize their friends—an example of how well humans adapt to their special circumstances. At Sunnybrook Hospital, we are beginning to use imaging techniques to measure where in the brain those adaptations occur so that we can develop new approaches to rehabilitation, which harness that plasticity.
We have also been testing the ability of older patients to see whether something is moving, which direction it is going in, and how fast it is moving. The results so far indicate that they are almost as good as children without eye problems in seeing which way, and how fast, an object is going if the object is moving quickly, but that they have more trouble if it is moving slowly. Children without eye problems can see that an object has started to move at a very slow speed. For children treated for cataract, the object seems stationary until it gets going at twice that speed.
Fortunately, we are talking about very slow speeds here that rarely matter in the real world—traffic goes at speeds the patients have no trouble seeing.
Our work during the past 20+ years with patients treated for cataract has resulted in over 30 publications in scientific journals or books, in over 100 presentations at scientific meetings, and in world-wide media attention. For example, in the fall of 2001, we were featured in a special series produced by the Public Broadcasting System on the Secret Life of the Brain. You can check out highlights of the series on the web at www.pbs.org/wnet/brain/. If you would like copies of any of our scientific papers, or have any questions, feel free to contact us.
Once again, thank you for your valuable help in furthering our knowledge about visual development and the optimal treatment for children with cataracts. We have exciting new studies in progress and hope that, if we call upon you again, you will be able to participate.