There are many conditions that might constitute "bad eyesight." Myopia (nearsightedness), Hyperopia (farsightedness), and Astigmatism (irregular curvature of the cornea) are all eye conditions that are carried to our offspring through our genes. The genes that cause them are dominant.
I'm a 5th generation sufferer of both Myopia and Astigmatism! In fact, of all my brothers and sisters (14 in all), over half of us have had to have some sort of vision correction. And, it didn't stop there! My husband had 20/20 vision when we got married, but of our eight children, half of them inherited my nearsightedness. I already have one grandson in glasses and fully expect to see more grandchildren needing them in the future. Who knows when the cycle will end, or if it ever will.
There is some speculation that our diets can halt or even reverse the tendency to pass along the bad sight, but that remains to be seen in the future. For now, we just have to live with it and expect that if our parents wear glasses, we may someday, too!