Screen time - my Grandmother would love this debate

When I was a but a boy I remember my grandmother telling my to stop reading so much. Constantly having my head in a book was bad for my eyes, she said. My parents' rationale for a two hour per week TV allotment was that any more and I'd go blind and rot my brain.

Has anyone gone blind from too much reading or TV watching? Are there documented cases of rotted brains due to too much ESPN or Nickelodeon?