When I look at the Profile Options here at this site, I do not see something that plainly states a preference to this effect: "Send me a notification whenever any of my posts is replied to". Perhaps this idea is conveyed to others based on the terminology used typically in relation to such social interactions, but to me this plainly stated idea is not conveyed at all. If it is there, can someone quote that statement to me so that I can be sure that I have it set in accordance with my preferences. <rolling eyes>
When in a topic look near the upper-right hand side you'll see a white button labeled: Follow this topic
Clicking it will alert you to changes in that particular topic.
Edit:
Then if you wish to delve into this more go into your profile settings, and click on the left: Notification Options
In there you can play around to see what suits you.
Or click on your username, My Settings, Notification Options, Topics and Posts, check Auto follow topics I reply to. I hope the problem with your eyes is quickly resolved.