The brighter the light, the better your vision. I've noticed this effect. In bright sunlight, the aperture opening of my iris is so small that I can see pretty clearly without my glasses.
It is the pinhole camera effect.
That is interesting.
Speaking of pinhole cameras... I recall reading that Alfred Hitchcock used all sorts of fancy mechanical and optical stuff for the stairway shot in Vertigo to keep the zoom in sync with the camera motion. If he'd built a bellows pinhole camera, it would seem he could have saved himself a lot of work (exposure times would be quite long, but if you're trying to get a second of film who cares it it takes 24 5-second exposures?