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

experiments really serve as a good model for the most common forms of amblyopia in people? These animal experiments mimic the effects of a cataract present in one eye of a child at birth, but this condition, called deprivation amblyopia, is very rare, affecting only 0.03 percent of children. Much more common are forms of amblyopia that develop from strabismus or a condition called anisometropia.

Amblyopia can be caused by strabismus when only one eye does the looking. If a young child looks through only one and the same eye at all times and turns in the other, then vision is reduced in the turned eye. This is what happened to Caitlin Ronayne and also to Cyndi Monter, the woman whose first stereo view was of her lunchtime salad. Strabismus is not present at birth but occurs at about two to three months of age, and amblyopia, which is an adaptation to the strabismus, develops sometime after that. S o , unlike the animals in the monocular deprivation experiments, children with strabismic amblyopia have not been deprived of all vision in one eye since the first days of life.

If one eye is considerably more farsighted (hyperopic) than the other, then the weaker eye may be continually out of focus. Under these conditions, a condition called anisometropic amblyopia may develop in the more farsighted eye. Since humans do not have sharp vision at birth but develop 20/20 eyesight over their first three to five years, it is unlikely that this form of amblyopia is present in

very early life.

Several scientists recognized that the monocular deprivation experiments were not a good model for most cases of human amblyopia. Anthony Movshon, Lynne Kiorpes, and their colleagues at New York University induced amblyopia in monkeys by less drastic means, such as putting a lens over one eye to reduce, but not completely eliminate, vision in that eye. Not surprisingly, these investigators found that the changes in circuitry in the visual cortex were not as severe as in the cortex of the monocularly deprived animals. For example, more connections survived between the compromised eye and the brain. Combined, these studies teach us that animal experiments are critical to understanding how the brain is wired, but we must be careful in generalizing from animal experiments to the human condition.

The most common approach to amblyopia is to treat only young children by patching the nonamblyopic eye. This treatment was used as early as 1743 by Georges-Louis Leclerc, the Comte de Buffon. Patching, or occlusion, of the “good” eye may strengthen connections between the amblyopic eye and the brain. This treatment is somewhat analogous to Hubel and Wiesel’s experiments in which they closed one eye, then reopened it, and, at the same time, closed the other. With these manipulations, the input onto cortical neurons changed as well. Pharmacological treatments such as the use of atropine to blur vision in the “good” eye force the child to use the amblyopic eye and

may produce effects similar to those resulting from patching. One drawback of occlusion therapies is that the open eye may improve its acuity at the expense of the occluded, or “good,” eye. One eye gets better as the other gets worse.

What’s more, patching may have adverse effects on binocularity and stereovision. Indeed, in his address upon winning the Nobel Prize for his research on vision, Torsten Wiesel expressed these concerns. A recent study by the federally funded Pediatric Eye Disease Investigator Group found that one-quarter of patients successfully treated with a patching regimen lost the acuity gains in the amblyopic eye one year after the patching regimen ended. The loss in eyesight may result because the patients still did not use their two eyes together. Something more or different was needed.

When Caitlin’s mother was told that Caitlin would always have poor vision in her turned eye, she, like mothers everywhere, did not give up. She found Dr. Ruggiero instead. An amblyopic eye, Dr. Ruggiero told Caitlin and her mother, is amblyopic in all ways. Scientific studies have revealed that the amblyopic eye not only has reduced acuity but provides a distorted sense of space, tracks objects less accurately, and is the poorer eye for directing hand movements. To reduce amblyopia, you must train the eye and brain in many different tasks. So, Caitlin practiced many exercises first with her amblyopic eye, then with her nonamblyopic eye, then with her amblyopic eye again. The

number of tasks that a vision therapist can design to counter amblyopia are limited only by her imagination. For example, Caitlin practiced using one eye to pick up rice with tweezers, sort piles of colored rice into the different colors, or play number games like Yahtzee with miniature dice.

In 2007, Robert Hess and his colleagues at McGill University published a study demonstrating that people with amblyopia do not discount all information from the amblyopic eye. Instead, the amblyopic eye provides such weak input that it makes little contribution overall to what is seen. They suggested that therapy for amblyopia should include procedures in which the good eye is not patched but is put at a disadvantage. In this way, the input from the two eyes will be better balanced, and the patient may learn to use them more equally. In fact, this general strategy has been used by developmental/behavioral optometrists for the past forty years. They have developed a class of procedures called “monocular fixation in a binocular field” (MFBF). Dr. Ruggiero gave Caitlin several MFBF procedures to practice.

In MFBF procedures, both eyes are open, but only the amblyopic eye can be used for the difficult tasks. For example, Caitlin played the “wall game,” a task I described in chapter 5. In this game, Caitlin looked at a set of red lights on a board. One light was illuminated at a time, and she had to find that light, hit it, then find the next illuminated light, hit it, and so on. Caitlin played this game while

wearing red/green glasses. With the red lens over her amblyopic eye, only her amblyopic eye could see the illuminated light. So, Caitlin had to use her weak eye to find and hit the illuminated target, while the “good” eye, the eye behind the green lens, did not see the light but did see the general surroundings. This reversed the way Caitlin habitually saw since her amblyopic eye normally took a backseat to the better-seeing eye. Procedures like this helped Caitlin to balance and integrate the input from her two eyes. Once Caitlin had mastered these tasks, she was ready to practice binocular procedures, such as those described in earlier chapters.

Caitlin graduated from vision therapy after five months. It has been ten years, and Caitlin still maintains good vision in both eyes and has stereopsis. Her eyes are straight.

“How did you know,” I asked Caitlin’s mother, “if she was seeing differently after the vision therapy?”

Her mother told me that Caitlin stopped having trouble looking first at the words in her schoolbooks and then up at the blackboard. Caitlin used to grow restless with arts and crafts, but after vision therapy, she protested if she had to stop coloring and go to bed. She volunteered to do the reading when she and her mother read aloud to each other. She no longer tilted her head to go upstairs. The head tilt had been a strategy to judge the height of the steps, a habit she no longer needed once her stereovision improved. Best of all, Caitlin’s confidence increased, especially with

dancing, her favorite activity.

“She is a child in motion,” her mother said, “and now her motions are more fluid.”

Caitlin was only six years old when she began vision therapy. Are the same treatments effective in older children and adults? When a person has amblyopia, do the connections from the amblyopic eye to the brain die out, or are these connections masked by input from the “good” eye? In chapter 4, I described the case of Red Greene, an amblyope who lost vision in his good eye in his fifties. When this happened, eyesight in his amblyopic eye improved to 20/20. His case is not unique. In one published study, one-third of the 203 amblyopes examined, many of whom were older adults, experienced significantly improved eyesight in their amblyopic eye after vision was lost in the fellow eye. Obviously, loss of the “good” eye is not a treatment for amblyopia. However, Red’s story and this and other studies indicate that connections from the amblyopic eye to the brain may survive throughout life long after the close of the critical period. These connections, however, may be weak and suppressed.

Evidence lurking in the scientific literature for at least the last half century indicates that amblyopia can be treated in adulthood. As early as 1957, Carl Kupfer published a study in which he showed dramatic improvements in adult amblyopes after a four-week period of patching combined with vision therapy. In a 1977 study, Martin Birnbaum and

his colleagues reviewed twenty-three published studies on amblyopia and reported that improvements in eyesight were found for all ages. Sadly, these and other studies continue to be overlooked. Many doctors still believe that amblyopia can be treated only in young children.

This is what Dr. Joan Lester, an anisometropic amblyope since early childhood, was repeatedly told. When she was sixty-five years old, however, a friend suggested that she consult a developmental optometrist. Dr. Lester saw Dr. Julie Kim, an associate at the office of Drs. Carole Hong and Kristina Stasko. Dr. Kim prescribed for Dr. Lester a program of optometric vision therapy that taught her how to use her long-neglected amblyopic left eye as an equal partner with her right. After six therapy sessions, Dr. Lester was ready to be fitted with a contact lens in the left eye. She described her first experience with the contact lens in this way: “Suddenly, the world sparkled. I felt an unaccountable joy explode. ‘Oh my god,’ I shrieked. . . . I felt unmoored, floating above the ground, dizzy.” Dr. Lester described how each morning, when she slid the contact lens into the amblyopic eye, she experienced the same sudden “inexplicable joy.” She felt like shouting, as if newly in love. Her friends say that Dr. Lester is now a changed person, more curious and eager for new adventure. At age sixtyseven, she has no plans to retire.

Scientific investigations, performed largely in the twentyfirst century, give great credence to Dr. Lester’s case. They suggest that the mature visual system is more plastic than

once thought. For example, exposing adult rats to enriched environments reverses the amblyopia produced by monocular deprivation occurring in infancy. Placing adult rats in the dark for three to ten days can also reverse the effects of monocular deprivation. Studies of “perceptual learning” in human amblyopes pioneered by Dennis Levi and Uri Polat in the mid-1990s demonstrate improvements in eyesight in the amblyopic eye even in adult patients. These studies and others demonstrate that visual acuity can be improved in the amblyopic eye of adults by training the participants to detect, for example, small discontinuities in a straight line or to discern faint lines against a slightly lighter background. In contrast to the results with patching, but similar to the results with vision therapy, eyesight improved in the amblyopic eye without a loss of vision in the “good” eye.

While the best approach may vary from patient to patient, one basic principle needs to change. The brain may be more plastic, more responsive to treatments in infancy, but this period of high malleability does not exclude the possibility that improvements can occur later in life. If an effective treatment—be it surgery, eyeglasses, occlusion, or optometric vision therapy—is available, it should be applied at the youngest age possible. For example, surgery for infantile strabismus may be most effective if it

straightens the eyes in a stable manner within three months of the initial eye misalignment. But a period of three months from strabismus onset to surgery is a very short window, and many patients will miss this period.

Only 20 percent of patients with infantile strabismus who have surgery after the age of two years develop stereopsis. In contrast, 38 to 50 percent of patients with infantile strabismus and 70 percent of patients whose strabismus develops after the first year acquire stereopsis through optometric vision therapy. Treatments should not be denied to older children and adults solely on the basis of age.

I had lectured in the classroom for seventeen years on early critical periods in visual development before I discovered that I was not permanently stereoblind. When I first went to see Dr. Ruggiero, I did not believe I could gain stereovision but was hoping instead to find a way to stabilize my gaze. No wonder gaining stereopsis was one of the most powerful and liberating experiences of my life. But now I had a new and important question. What specific conditions facilitate changes in the adult brain? Could my experience apply to rehabilitation in general?

9

VISION AND REVISION

Time for you and time for me,

And time yet for a hundred indecisions, And for a hundred visions and revisions, Before the taking of a toast and tea.

—From “The Love Song of J. Alfred Prufrock,” by T. S. Eliot

Four years after I learned to see in stereo, I visited Dr. Ruggiero for my annual exam. I had graduated from weekly vision therapy sessions three years earlier, although I still practiced some vision therapy techniques at home every day. At the time of this yearly checkup, I was caring for my ill father. Since I had no idea that my mental state could influence how I used my eyes, I didn’t mention my personal difficulties to Dr. Ruggiero. She picked up her occluder and moved it in front of my eyes in order to complete a quick test of eye alignment. With the sight of the occluder, I felt myself slip back in time, back to being the little cross-eyed girl in my eye surgeon’s office. The doctor was waving the occluder in front of my face and asking me to focus at a