I also fought not to be angry and afraid, a struggle familiar to anyone with a significant illness or disability. The fear arose less from what I’d already lost than from what I might lose still. Over the next five years, there’s a roughly 20 percent chance that what happened to my right eye could also happen to my left. I could go blind.

The odds are on my side. But the stakes are enormous. So how am I supposed to process this? Where on the spectrum of optimism to resignation — of hope to dread — do I position myself?

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On that first morning, several hours passed before I accepted that something was seriously wrong. I figured that I was just groggier than usual. Maybe I needed more coffee.

As I sat at my computer transcribing a long interview that I’d just done, I repeatedly took off my eyeglasses to clean them, convinced that the smudginess of my vision was some streakiness on the lenses. When I finally gave up on that, I rinsed my eyes with water — to no avail. It was as if someone had deposited a blob of petroleum jelly in my right eye and nothing would dislodge it.

The next morning I visited my ophthalmologist, who for many years had kept tabs on my run-of-the-mill astigmatism and fine-tuned my prescription so that I saw 20-20 with each eye. He said that in this case I needed a neuro-ophthalmologist. (I didn’t know that such a specialty existed.) I found one, Golnaz Moazami, who could squeeze me in a few days later, and after three tedious hours of staring at or into charts and colored patterns and sophisticated machines, she told me this, in a rat-tat-tat fashion:

I had almost certainly experienced what is colloquially called “a stroke of the eye,” whereby the optic nerve is ravaged by a brief reduction of blood flow and thus oxygen. The name for this condition is nonarteritic anterior ischemic optic neuropathy (N.A.I.O.N.), and it afflicts perhaps one in 10,000 Americans. But I’d need extensive blood work and tests to rule out other possibilities.