What could be causing bad eyesight?

It could be congenital or it could also be due to poor practices like reading with insufficient light or washing your eyes right after you watching TV for a long time or staying in front of the computer for a long time. Vitamin A insufficiency can also cause poor eyesight. And also wearing graded eyeglasses when you're not supposed to, will definitely make your eyesight poor.

Staring at the computer screen for long period of time without letting your eye rest. Reading on moving vehicle. Reading under insufficient light. lying down and read. sitting less than 1 metre from television screen. Staring at bright light source.