Reading

When I was kid, people including my parents, used to tell that lot of reading leads to problem to the eyes. But they never specified what problem ?. I did not come across anything which agreed on this belief during optholmology . But my optholmological knowledge is cursory and not indepth. Over the last two decades lot of progress has gone through. Still I have the doubt.
is the belief true or it is a just worng belief?.
If true, how much is the limit, i.e., how many hours a day?.