Dear Dr. Johnson: I have noticed in the last year that I have a harder time seeing at night when I`m driving. It was very scary, especially since I used to have very good vision. In one case, specifically, I could not see the road signs even though they were well illuminated by my headlights. I had to pull off the road and try to figure out where I was.
Ever since then I noticed that I consistently have trouble with distant vision at night, whether it is to see road signs or features along the road that are far (but directly) ahead. Does this mean that I am developing night blindness?
Night blindness is technically defined as a disorder of the back of the eye, the retina, that is caused by a deficiency of vitamin A. It can usually be improved with adequate vitamin A intake.
I think it is much more likely, however, that you are developing a condition usually known as night myopia, which is really a variation of problems we all develop with distant vision as we grow older.
The reason distant vision becomes worse at night is that the hole in the center of the eye opens wider to let in as much available light as possible. This widened state makes it more difficult for the lens to change its shape to focus on distant objects.