What are the signs/issues of muscle/nerve damage after having an Upper Blepharoplasty operation?

Muscle and nerve injury after upper lid blepharoplasty is rare.  If it were to happen usually it is injury to the superior oblique muscle when it is entraped by a suture or injured from cautery.  Symptoms would include diplopia (seeing double) or uneven closure of the lids.   This can happen when fat is being removed from the retroseptal or preaponeurotic space.  More commonly are complications related to excessive fat removal or scar asymmetry.  A skin only blepharoplasty is thus safer, however some fat removal is usually necessary in a blepharoplasty. 

This problem is almost unheard of but without knowing what you are concerned about, its difficult to speculate.  Most complications from from bleeding or transecting muscles the lead to double vision, or taking too much skin leaving your lids unable to close completely.  Skin only blepharoplasties are not expected to result in any motor or sensory deficits.