The front neck shaping is worked with decreases and increases (see photo below and page 2 of pattern). Sweater has optional crochet edging around neck, cuffs and hem. This sweater is a wardrobe staple worth having in more than one color, and it is a fast knit! (from pattern description) Also available on Craftsy.
In general, if the ptosis is caused by a systemic muscle weakness, other muscles in the face, head, or body may be affected. A drooping eyelid can also be a symptom of a brain tumor or stroke, especially if it comes on within a few days or a few hours or if just one eye is involved.
I am sorry to hear that your left eyelid seems to be drooping, and that it is bothering you. Ptosis (the medical term for drooping of the eyelid) can be caused by many different things. Some of them serious, some of them benign.