Tuesday morning my Dad had a stroke.

A stroke is a failure of the circulatory system to deliver blood to a section of the brain, either because of a clot or a burst blood vessel. In this case, the section of my Dad’s brain that was affected was the vision center — he lost much of the right side of his field of vision. There’s a chance that some of his field of vision will return, but if it doesn’t happen in the next 24 hours, the loss will probably be permanent. Because my Dad is subject to migraines with aura, which (like mine) manifest as a temporary loss of vision, he initially thought the stroke was just of those, and didn’t consider getting treatment until the critical first hour was already past.

We’re very grateful that things weren’t worse. Stroke can cause motor impairment, mental problems, memory loss, and difficulties with speech. I was relieved when I got to my Dad’s house to see that he was otherwise in good condition, moving around without difficulty, speaking lucidly, and maintaining a sense of humor about the whole experience. While vision loss is a wretched thing to have to live with, it’s the stroke symptom to which sufferers can most readily adjust.

We checked Dad into the hospital for the night so that they could keep a good eye on him, but it appears that he’ll probably be discharged today after they run an MRI on him to determine whether the cause was a clot or a burst blood vessel. (The treatments for these are different: blood clots can be prevented with blood thinning agents, which would be counterproductive if the brain was already hemorrhaging.)

I’ll provide an update when I know more. In the meantime, you can learn about how to recognize stroke at the American Stroke Organization.