The members of our group did not use anything except warm compresses after uncomplicated strabismus surgery performed on an eye for the first time. A review of over 40,000 surgical charts following correction of strabismus showed only one case of endophthalmitis. This was in a case that gut suture was used back in the late '60's.
About two years ago, I was attending John Simon and Jack Baker's course on complications following strabismus surgery. A show of about 80% of hands in reply to this question made me take the position that if I was brought to litigation, and one of the audience was queried about the standard of care, and I did not use a drop, I might be in trouble fighting a case related to loss of an eye to endophthalmitis.
I now use drops. Tobradex, QID for 3-4 days.