Ординатура / Офтальмология / Английские материалы / Fixing My Gaze_Barry, Sacks_2010

show at the end of the school year. My mother didn’t sew, so she couldn’t help me, and my grandmother, who still used a manual sewing machine with a foot pedal, saw no reason for me to learn to use an electric model. Finally, my father, an artist, seeing my distress and total incompetence, did my sewing projects for me. After getting through sewing class, I never touched a sewing machine again, and when I got married, I told my husband that he would have to hem his own pants.

To read you need to pinpoint the location of letters on a page, to sew you need to position the needle on the cloth, but to get around you need to know where your own body is in space. My favorite way of getting around was on my own two feet—by walking or running. I felt very unsteady on a bicycle, and during the first year after learning to ride, I walked the bike down hills. I did not want to learn to drive. When I first got behind the wheel, the oncoming traffic petrified me, and I thought that good driving basically involved avoiding head-on collisions. Since I concentrated on looking straight ahead and paid little attention to my peripheral vision, cars and pedestrians seemed to appear suddenly out of nowhere. It was hard to maintain a steady gaze while looking down a long straight road. The distant scene seemed to grain out like static building up on a TV screen. I would shake my head to get back a clear view. Not surprisingly, I got my driver’s license a year after most of my peers. On my first solo outing, a three-mile trip to my boyfriend’s house, I scraped the side of the car on a stone

wall on one side of his driveway. My parents said nothing but offered to drive me anywhere I needed to go.

Indeed, I was always just a step behind everybody else. In college, I wanted to join an athletic team but was not good enough to participate in softball or tennis. Since I loved the water, I joined the women’s crew team and rowed in an eight-person shell. In a crew boat, the rowers sit in a line facing backward and match the rhythm of their strokes with that of the person sitting in the stern. I was not particularly surprised when my coach told me that my pace was just a little slower than everyone else’s. Happily for me, she didn’t drop me from the team. Instead, she put me in the bow of the boat so that my slightly delayed stroke wouldn’t confuse another rower sitting behind me.

Obviously, I wasn’t going to become a star athlete, but I did enjoy my science classes and liked being out of doors. So, in college, I thought I would study animal behavior and follow my keen interest in birds. One of my professors was a great birder. Like many naturalists, he had uncanny powers of observation. “Driving and birding are my two great loves,” he would say as he accelerated the car to dangerous speeds on our way to prime birding sites. I thought his two great passions made for a strange combination until I realized that his driving style was matched only by his quickness in observing the natural world. He had sharp eyes and ears and would spot birds in the foliage long before anyone else. Despite my intense interest in ornithology, I soon noticed that I was always the

last in the group to see the birds. On one trip to Hawk Mountain in Pennsylvania, I was supposed to help spot and catalog the migrating hawks. I wasn’t much help to the other birders, often missing the majestic birds entirely. On that trip, I decided that I would not make a very good ornithologist. I would always enjoy watching birds, but I didn’t see quickly enough to make important, new observations.

Even if I was poor at observing animals in nature, I could study the neurons that help them sense and move through the world. So, I took my first class in neurophysiology and in that class made my first recordings of nerve cells. When neurons fire, they generate electrical signals that resemble the waveforms seen in an electrocardiogram. I loved watching these signals; it was like listening to the mysterious language of nerve cells. I wanted to learn more about this language, but to do so, I realized, I would have to overcome a new visual challenge.

To record the electrical activity of individual neurons, I had to use a stereomicroscope to see and then position a tiny glass needle through the thin outer envelope of a nerve cell. The stereomicroscope, with its two eyepieces, was designed to help people see the needle and nerve cells in three dimensions, but by this point I knew that I didn’t have stereovision. I decided not to tell my teachers initially about my visual deficit lest they discourage me from pursuing my interests. Instead, I developed my own strategy to reconstruct the three dimensions. I continually adjusted the

fine-focus knob on the microscope, which brought my view of the electrode and nerve cell in and out of focus. By looking at the changing focus, I could gauge the depth. My lack of stereovision was less of a problem when using stereomicroscopes than it was when driving cars or watching birds because I didn’t have to see things as they sped by. Instead, I could take my time and move deliberately. I used this microscope technique all through college and graduate school and throughout much of my career as a neurobiology researcher and professor.

However, as often happens with people with childhood strabismus, my vision began to trouble me more in my late thirties. By this time, I was married with children and working as a professor at Mount Holyoke College. When I was forty years old, I went to see a local, well-respected ophthalmologist. My lack of stereovision was not what concerned me. I had long ago accepted that I would never gain stereopsis. Instead, I told the doctor that the world appeared jittery, especially when I looked in the distance. I had trouble reading road signs when driving because I couldn’t keep my eyes on the words. I would slow the car to a crawl in order to read them, unnerved by the honks from angry drivers behind me. If I had to go someplace new, I would head out the day before at the least-trafficked time and drive to the new location so that I wouldn’t get lost on the following day. What’s more, I told the doctor, I could not see clearly from the middle of my children’s school auditorium. The faces of the children on-stage were all a

blur.

The ophthalmologist checked my right eye and then my left and told me that I was very lucky. Without glasses, my right eye saw 20/50 while my left eye saw 20/60, and my glasses totally corrected for these small flaws. “Why, then, am I having trouble seeing?” I asked him. He dismissed my concerns. “There’s nothing wrong with your vision,” he insisted, adding that if the world appeared unstable to me, it was probably because I’d been traumatized by my childhood surgeries and, as a result, “dreamed up” my vision problems. Perhaps, he said, I needed to see a psychiatrist.

I left his office as soon as possible after grudgingly paying the bill. I felt angry and tearful, but I told myself that, in the end, the news was really good. The doctor didn’t say something like, “Your complaints indicate that you have an incurable brain tumor.” He told me that my eyesight was fine. I had no vision problems. If I was simply less anxious, these troubles would surely go away.

4

KNOWING WHERE TO LOOK

You never really understand a person until you consider things

from his point of view.

—Atticus Finch in To Kill a Mockingbird, by Harper Lee

In his thoughtful and moving memoir, Touching the Rock, John Hull recounts what it is like to be blind. He describes sitting on a park bench while listening to the sounds around him. He hears children shouting, people running, balls bouncing, wind blowing, birds calling, and traffic rumbling. It is “an astonishingly varied and rich panorama of music, movement and information,” he notes, and yet he adds that things that are beyond his reach and make no noise simply do not exist. Only when his children shout to him from a paddleboat floating on a nearby pond does he know that they are there.

John Hull can get up from the park bench and discover more about his surroundings by using his cane and sense

of touch. Yet, most of us can find out where we are in the world much more quickly; we simply look around. Vision allows us to be active participants in our world, continually moving through it and molding it to our needs and our desires.

Indeed, our ability to move confidently and accurately is intimately tied to our ability to see. If we didn’t have legs and arms for climbing trees and fingers for manipulating objects, we would never have needed such a complicated visual system or brain. Similarly, our marine cousins, the tunicates (Figure 4.1), have eyes when they are young larvae in order to swim about and find a good place to settle down. Once they come across a suitable rock on the sea floor, they attach themselves to it and transform from active swimmers into stationary filter feeders. At this point, their eyes and brain degenerate as they have little need for a good visual system and brain if they are not moving.

FIGURE 4.1: The tunicate as a sessile adult (left) and swimming larva (right). (© Margaret C. Nelson)

To move accurately, we must first move our eyes. Imagine that you are driving down a treacherous mountain road. You gaze directly at the curve a second or two before rounding the bend, then turn your head in the direction of your gaze and masterfully steer the car around the curve. On a more pedestrian level, when you walk down the street and turn the corner, the rotation of your body follows the direction of your gaze. You reach for an object first by directing your eyes, then your head, and finally your arm toward the target. The movement of your eyes anticipates and then directs the movement of your head, body, and limbs.

We move our eyes before our body because we must look directly at objects to see them clearly and in detail. If you try to read this book by holding it to the right or left of center while looking straight ahead, you will still be able to see that there are letters on the page, but you won’t be able to identify them. You do not have to move the book very far from your direct gaze before you can no longer read it.

We must look directly at the words because our sharpest, most acute vision is located in the central part of the retina. This region, called the fovea, receives input from about the central 2º of the visual field, an area about equal to the size of a quarter as seen from arm’s length. If you try to read this book while moving it away from your central

gaze, you will begin to have trouble recognizing the words when the letters move out of foveal range. Since the fovea sees such a small part of the visual field, we move our eyes constantly to see one part of a scene and then another in sharp detail.

To pick up an object or move around it, however, not only must you see it clearly, but you must also know where it is in space. To do that, you need to know the direction in which your eyes are pointing. If we had only one eye, this would be simple. Assuming that your head was oriented straight forward, you could determine the location of an object by where your eye was aiming. But with two eyes, the situation is much more complex.

While holding this book about fourteen inches from your face, look at the large X below while thinking about the position of your eyes.

X

If the X is directly in front of you, your right and left eye have each turned in to the same degree but in opposite directions, as in the picture of the two eyes shown in Figure 4.2.

Your sensed visual direction—the direction in which you are looking—is not the direction in which either eye is pointing but one that seems to emanate from the center of your forehead. Since our eyes are both aimed at the target,