Imagine waking up one morning. You walk into the dining hall, picking up the Times on your way to the Lucky Charms. Glancing down, you notice that the paper looks odd. The letters appear squiggly and foreign — are they Cyrillic? No, they aren’t quite anything recognizable. You realize, suddenly, chillingly, that you cannot read.

This is just what happens to Howard, a real-life novelist and one of the patients of celebrated neurologist and author Oliver Sacks in “The Mind’s Eye.” Sacks (who spoke with first-years at Amherst in 2004) has become known for his deft blend of deep medical knowledge and empathetic storytelling, although he has also faced criticism for turning his patients into characters for profit in his previous books, including “The Man Who Mistook His Wife for a Hat.” Clearly, Sacks retains his professional reputation, since most of the patients in this book, including Howard, seem to have sought him out for answers to their baffling neurological complaints.

In his usual style, Sacks presents his patients’ stories as a series of case studies. There’s Lillian, a concert pianist who slowly loses her ability to recognize objects; she confuses an umbrella with a snake and is unable to relocate a plate that she has set out on the table. After a stroke, Pat suffers from aphasia, an inability to understand or even recognize language. Formerly a popular and sociable woman, she becomes completely isolated from her family and friends. But the patient who receives the most attention is Sacks himself. After experiencing a sudden and frightening distortion of vision in a darkened theater, Sacks is diagnosed with melanoma of the eye, the destructive effects of which he chronicles in a series of personal journal entries.

Here, in the penultimate part of the book, Sacks exposes his own weakness and fragility; unfortunately, the writing is weaker here, too. What makes Sacks such a good read (and, I suspect, such a good doctor) is his ability to mitigate the clinical detachment necessary to diagnose and treat with palpable care for his patients. He sees them not only as miswired brains, but as real people with a diversity of interests and passions, all of whom deserve sensitivity. “Her piano-playing always added a transcendent note to my visits, and it recalled her, no less crucially, to her identity as an artist,” Sacks writes of Lillian, the musician with visual agnosia. “It showed the joy she could still get and give, whatever other problems were now closing in on her.”

This kind of informed sensitivity dissolves when Sacks turns inward. He remains perfectly cheerful and self-aware when discussing his sometimes amusing experiences with prosopagnosia (an inability to recognize faces: Sacks records an episode when he mistook a man behind a window as his own reflection). But in his melanoma journals, Sacks loses perspective and panics; he throws aside the screen of science and withdraws into a confined space of self-pity and terror. In other words, he does exactly what any of us would do, when faced with an unpredictable and dangerous disease. It’s understandable, but it doesn’t make for good writing, uncharitable as it may seem to criticize such honest confessions as: “I know that, with [my doctor], I am in the best possible hands, but I feel a terrified child, a child screaming for help inside me.” This is a book about the incredible resilience of the human mind, its ability to compensate for massive injury and disorder with efficiency and grace. Sacks’ own candid but unliterary reflections remind us of the limits of this mental power.

It’s a relief when Sacks returns, too briefly, in his customary benevolent-doctor form at the end of the book. The last few pages attempt, mostly successfully, to connect Sacks’ experience with the stories of his patients, and with the history of neurological research, which turns out to be more than mildly interesting. The book as a whole, in fact, is remarkably unified, threaded together not only by footnotes that are genuinely readable in their own right, but also by the patients’ ingenious ways of coping with extraordinary losses. One does not get the sense that Sacks sought out patients who would fit a premeditated theme, but rather that he collected stories over decades of practice, and then mulled them over for a while until he had an idea of their significance beyond the mere medical. This isn’t a textbook, but it’s not a memoir either. “The Mind’s Eye” is able to shift from the anatomical to the emotional and back, to keep in focus both small personal triumphs and groundbreaking scientific achievements. It’s flexible and complex, like the brain that is its subject.