The Sun generally does not hurt our retina because it is so bright that we do not stare at it very long. If we do, our pupils contract to get very tiny as well. But when the Solar Eclipse darkens the day to night and it is easy to look, infra red light can make you blind permanently.
If you look at the Eclipse with even regular sunglasses, that infra red, which you cannot see, is going into your very wide open pupils and overwhelming your photoreceptor cells. Pushing them very hard and damaging them. It is the near infra red light. The Sun emits a lot of this energy, you feel how it heats up your parked car, even in Winter?
You need to watch a projection of the Eclipse through a card with a pinhole in it, or use a real lens, camera lens even, and let it project an image on another white card.
You can also buy glasses made to watch the sun directly. They are so dark that you cannot even see bright fluorescent lights though them. They will also be marked to match an approved ISO standard set in 2015.
You can learn and see more from my interview on Detroit Chanel 7 News, using the link below.
If you would like to make a simple solar eclipse viewer based on design provided by NASA, then you can download the PDF instructions I made found at the following google drive link:
or you can download from a Dropbox link here:
All you need is a cereal box, a piece of white paper, tape, pencil, scissors and aluminum foil. And one pin to make a pinhole in the foil.
Download my free PDF
Kenneth P. Mitton, PhD FARVO
Eye Research Institute