We recently interviewed 7 experts for a fatigue management course, and I thought I'd share a few things from ophthalmologist Dr Simon Dean relating to eyesight because we don't often consider the impact eyesight can have on our fatigue levels, or how fatigue can influence our eyesight.
At night there's less light and it takes longer for our brain to process the images - it's more effort and concentration. 4-5 hours of nighttime driving or machine operation is the same effort as around 8-9 hours in good daylight.
There 2 main types of eye fatigue:

• Discomfort. The tear film on the eye evaporates and leaves salt which stings. Don't point air conditioning towards the eyes as this makes it worse
• Loss of visual function. A tired brain can lead to double vision as the part of the brain that merges images from your left and right eye gets fatigued

You can reverse them both with rest
When fatigued, we don't look around as much - we become fixated, and we need to consciously scan more and blink more frequently
When tired, blinks last over twice the length. At 100km/h, a tired blink sees you travelling 11m with your eyes closed vs about 4m with a regular blink - consider how much further you are down the road before reacting to a developing hazard.
At night, your pupils are bigger to let in more light. This increases aberrations; nighttime vision is more blurry - to mitigate this, wear glasses and clean your windscreen. Older eyes are worse due to developing cataracts, to the point of disability glare (being unable to see at all) when there are oncoming headlights.
You can see more about who the experts are and the content of the course here https://www.drivingtests.co.nz/course/fatigue-management-course/