system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 - Why do our eyes become bloodshot when we're tired?
gpt
The whites of our eyes are filled with blood vessels that swell up and become noticeable when the surrounding cornea and eye tissue are lacking in oxygen. If you have a lack of sleep you're body is in need of rest, especially your eyes. Sleeping also protects the eyes from becoming dry and irritated which will result in redness as well. Additionally, being awake for long periods of time means there is more time that you are actively using your eyes, generally the more strain put on your eyes means more pressure resulting in the inflammation of the blood vessels in the eye.