I received a surgery on my eye muscles a year ago because I had a lazy eye, but the site of cut is still red. Should I be worried?

No. A suture can cause a "pyogenic granuloma" or sometimes there may be exuberant scarring response that can appear red if vascular. These can be removed usually without problems.
Probably not. Stitches are used in strabismus surgery. Sometimes, these take quite a while to dissolve with some redness. Occasionally, a small non-infectious lesion called a granuloma can form around the stitch and sometimes needs to be removed.