Which eyelid is normal? My eyes don't look the same, but I don't know which eye is normal. (photo)

Your left eyelid is lower than the right, a condition doctors called ptosis.  The muscles that control the eyelid position can be tightened to give you more symmetry.  Please seek a experienced surgeon for a consultation.

Thank you for the question and photo.  It does appear that your left upper eyelid is drooping.  However, before a definitive statement can be made it would be helpful to examine you in person and review some old photographs.

Thank you for your picture. Your right upper eyelid is the normal eyelid. Your left upper eyelid suffers from ptosis. This is a drooping of the eyelid can be due to laxity or disruption of the muscle that holds your eyelid in good position and and helps an eyelid closure

You have bilateral upper eyelid ptosis.  The left is the more ptotic of the two upper eyelids.  However, the right side is also ptotic.  In a detailed consultation the I suspect one will find that ptosis surgery is needed on both upper eyelids.  Both eyebrows are being raised to compensate for the upper eyelid heaviness.  Just performing surgery on the heavier of the two eyelids, often causes the lest heavy eyelids to fall after surgery.  That is because once one of the eyelids is corrected surgical, there is less of a need for the muscles to strain to open both eyes.  The result is that when only one eyelid is surgically address, the other side tends to fall after surgery.  The solution is to anticipate this before surgery and perform bilateral ptosis repair.

Thanks for your question. While both eyes are variations of normal, I think what you are likely referring to as 'abnormal' is the extra fold of skin at the nasal side of your left eyelid. This is known as an epicanthal fold and if it bothers you it is relatively easily corrected during a blepharoplasty.

Each aesthetic orbital unit has differences in them. Complete symmetry is NEVER possible. Best to be seen in person... 

The left upper eyelid has ptosis.  This is evident by the high ridding supratarsal crease.  See a plastic surgeon who is experienced in ptosis repair for correction of this problem.  Most likely you will need a correction of both sides if you want to achieve anything close to symmetry.