From the academic side, watching television should not harm vision in any way. However, there are some considerations.
*TV is a source of light. The human eye is not designed to look directly at a source of light.The distance from the TV matters.
 Ideally, the distance should be 6-7 times the diagonal of the TV for the older CRT televisions and 4-5 times the diagonal for LCD televisions.
*TV should not be viewed in a dark room.
*Wear corrective glasses if you are advised so.
*Do not stare at the TV. Blink your eye often. This refreshes the eyes.
*Do not watch the TV continuously for more than 2 hours at a stretch. Take a break. Your eyes deserve a break.
*Do not eat your meals in front of the TV. A family that eats together stays together and is happy together. Do not let TV eat into your family time.