Will the sensation in my nipples be affected by top surgery?

This depends very much on the technique that is used for the operation, and whether the nipple needs to be completely removed and repositioned. If nipple sensation is very important to you (e.g. in your romantic life), then be sure to make this known. Your surgeon may use a different technique to reduce the risk of nipple sensation loss, but that may in turn increase the need for a revision. Talk it through.