system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 why sometimes when we wake up in the middle of the night, our vision can get "fuzzy" or "grainy"
gpt
Nursing student here ~

You have 2 receptors in your eyes, rods and cones. When it's dark, only the rods - the cells that detect light - are active. Problem is, they're not the best with detail.

Cones, which are responsible for color detection, are FANTASTIC at gathering sharp, clear and vivid details of your vision, but they don't work when there's not enough light hitting them.

(Additionally, there is ALWAYS fuzz in your vision if you choose to focus on it, but your brain is typically both so stimulated by color/detail, and so used to seeing it, that it tunes out that visual "grainy" texture.)