system
Given the following post, respond as if you're commenting on Reddit:
human
What happens do your photoreceptors when you pass out?

When having a vasovagal reaction, vision starts to fade as your BP drops. What exactly is occurring with your photoreceptors as everything turns dark? Is it the same mechanism as you fall asleep?
gpt
It's mostly in the cortex, not the retina, just the effects of anoxia on the visual part of the brain. Loss of BP often causes "tunnel vision" that closes inward from the edges, sometimes with pinwheels or kaleidoscopic effects.

The photoreceptors aren't really relevant. When you do choke off photoreceptor circulation alone (knuckle your eyes too long) you can see kaleidoscopic effects but these are the brain circuits with gain full up and filters turned off, searching for a signal that has disappeared.