system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: On what do our eyes focus in pitch dark?

Like if it is pitch dark, do the eyes focus on the dark "wall" directly in front of them? Or are they just indefinitely trying to focus on something? Or are they idling because it is dark? :) Thanks!
gpt
Optometry student here. Your eyes have several stages of accommodation including tonic and proximal accommodation. 

When your eyes have nothing to focus on they will relax to tonic accommodation which is the point where muscles rest with minimal nervous innervation.

If you suddenly hit a wall, your eyes will accommodate to the proximal distance of that wall based on previous life experience.

Edit: Accommodation is where the lens in your eye (imagine a magnifying glass) changes power to help bring a near image into focus.

Edit2: A few of you are curious about relaxing your eyes and accommodation to relieve eye strain. You can use the 20/20/20 rule: every 20 minutes stare at something 20 feet away for 20 seconds. 

Edit3: Accommodation is fully relaxed at 20 feet (6 meters) which is why you're tested at this distance when at the optometrist's office.