Doctor advices ate meant to preventvany other furthe complications. Youbre not wrong.  We are only exchanging opinion.  

In my opinion, 
It's true that we can't sit in one place with the same position for a long time because it can give excessive pressure to our spine and that is not good because there are a lots of nerve end around our spine. It may cause compression tonour nerve and other symptom like pain,  numbness and uneasiness will come and the longer the nerve is compressed it will end up with continuously pain. 

About the lifting,  it depends on our job.  Some people can't avoid lifting so I think the only solution is to strengthen the muscles.  It might not be able to stop the condition get worst but it might be able to slow down the process. If could be avoided then it would be much better I guess.

For your condition,  I agree with the doctor. By following his advice you could use your eyes for a longer time.  It is a precaution measure I guess. 

I still believe that the best doctor is our ownself. We know which one are the best for us. Advices are option, we can choose to follow,  refuse or take it as a precaution matters. Though some advices are a must to follow for our own sake. 

Great talking to you.