When you view 'distance' with your normal vision, you are viewing at Infinity distance.
But when you view 'Infinity' on the SLR focus screen your eyes are really focused [somewhere between 30" away up to 1 meter] away!
Most camera viewfinders, depending upon brand, have eyepieces that place the focusing screen and any in-viewfinder text/symbols at a virtual distance of 30" to 1m. So young eyes can adjust themselves to see well both at Infinity and 8" away, while eyes older than 45 years typically can see well (with or without glasses) at Infinity yet cause difficulty for more folks 'at reading distance'...why drugstores so often sell reading glassess, as a very affordable way to give folks the ability to see more clearly at very close distances!
Bifocal lenses or trifocal lenses came about due to the desire to correct for BOTH distance and reading in a single lens.
Camera viewfinders with adjustable diopter viewfinders are a way to allow the photographer to see at distance, with the nake eye yet not have to don a pair or reading glasses to focus and set the camera using the in-viewfinder text/symbology.