I went for an eye exam yesterday. Among other things, the optometrist dilated my pupils so that she could check out my retinas. In order to see inside, she shone a very bright light in my eyes for what seemed like forever, because the brightness was actually painful.
I asked her why it was that she could shine THAT light in my eyes for at least 10-15 seconds at a time (multiple times) when we are constantly warned not to stare at bright light sources such as the sun. She had no idea what the difference was, and could only offer the thought that shining the exam light in my eyes for too long might eventually cause some damage as well.
Anyone got any ideas about this? I thought that perhaps the wavelength of the exam light might have something to do with it - it seemed a bit greenish to me. But as I said, the doctor herself didn’t know whether that might be the case.
It’s because her exam light was less intense than other light sources. So the energy is less and has less chance of harming your retina. The light just seemed brighter because more of its light was being admitted to your eyes because of the dialation.
(You can look at headlight in the daytime with little problem because the ambient light makes your pupils small. But at night, your pupils are enlarges, so the same light [being reflected to your face by your rear-view mirror] is irritating, even painful.)
Staring at the sun is just like using a magnifying lens on a defenseless bug. The energy is so intense (even through such a small opening as your pupil) that focusing it will definately start to burn.
Yes, it is the wavelength that is important. The light the doctor was putting in your eye was mostly just visible light. The light that comes from the sun also contains ultraviolet wavelengths. The UV wavelengths are the ones that burn your skin when you get a sunburn. Your skin is able to defend itself some from UV wavelengths, but your retina has very little protection. They don’t tell you not to look at the sun because it is visibly bright (although if this visible brightness were all that were involved, it still probably wouldn’t be a good idea to look directly at the sun because your eye acts as a lens that will focus the light ). They tell you not to look at the sun because of the concentration of UV rays that will hit your retina.