If a person with 20/20 vision hits a golf ball, how far along the ball’s flight path can they see and track the ball before it disappears?

It can be challenging to demonstrate to someone how you actually see without your glasses. You can’t just give them your glasses to try on since their eye will automatically try to clear them up (and possibly kick start a headache). But it turns out pretty much every smartphone has built in feature that does an excellent job in truly capturing how bad you see when your glasses are off.

Can an eagle see better than a hawk? How about an owl? And how much better can each see than the average human?

There is an old joke about people living out in the prairies being able to watch their dog run away for days.  Well if this is true (it isn't), then people living near the longest sightline on earth would be able to watch their dog run away for years.

Pinhole glasses operate on an optics principle that has been known for centuries.  By decreasing the aperture size, the depth of field increases (i.e. the distance between the maximum and the minimum an object appears clear).  It's the same reason people squint when they try to see better.  So glasses based on this principle do work, but there are some drawbacks that keep them from being replacements to regular glasses, although in desperate situations they can be very handy.

Why do nearsighted people hold things very close to read? Why do farsighted people complain of eyestrain? Why do people need reading glasses as the get older?

What could be of enough importance in 1962 that if it was lost, a regular season NHL game would halt mid-play and the players would drop down on their hands and knees and look for it?

Of all the things you've seen in your life, I promise you none of them were of the reddish-green colour.  Nor were any of them of the blueish-yellow hue.  Some scientists refer to these two colours as the forbidden colours.  But why cant we see them?

Every so often I come across a patient who has vision loss as the result of a parasitic infection.  The parasite in question is usually Toxoplasmosis gondii, and it can cause significant damage to the human retina.  But that may not even be the most terrifying trait of the parasite that is nicknamed "The Zombie Parasite".