I have had one eye looking larger than the other for years. What causes this and what procedure is needed? (Photo)

Eyelid symmetry depends upon the lid height, surrounding soft tissues, and brow height. It appears you have some asymmetric ptosis of the lids. This can be fixed with surgery. You really need an in person consultation. Best to see an eyelid expert.

It is not unusual that people have different looking eyes. In your case, based on these photos, one can think of droopy eyelids, ptosis, as one of contributing factors. Only on the basis of in person evaluation a board certified plastic or Oculoplastic surgeon can give you more information about your condition. Good luck.

All people have facial asymmetry. Nobody has a symmetrical face.
During embryological development, the two sides of the face develop independently from each other and eventually fuse in the midline.
Not only our peoples faces asymmetrical, but the entire body is as symmetrical.
Internal organs are typically placed in an asymmetrical fashion. People are either right, handed or left-handed. There’s simply nothing symmetrical about the human body.
If you look at computer generated images of perfectly symmetrical faces, you’ll notice they have an odd unfamiliar appearance. The human brain is accustomed to seeing a symmetry as normal. For that reason, when we see a computer generated symmetrical face, it has an unfamiliar appearance.
Great artists throughout history having incorporated facial asymmetry into classic works of art because they understood that the human form is not based on symmetry.
Your face looks normal without any need or indication for surgical intervention.
Best,
Mats Hagstrom, MD