Left eye appearing smaller than the right eye is a common form of facial asymmetry. This can occur due to several reasons:

1. Natural facial asymmetry: It's normal for faces to have some degree of asymmetry, and slight differences in eye size or position are common3.

2. Ptosis: A drooping upper eyelid (ptosis) in one eye can make it appear smaller than the other. This condition can be congenital or develop with age14.

3. Enophthalmos: If one eyeball is more sunken than the other, it can create the illusion of a smaller eye. This can be caused by genetics, prior orbital fractures, or other conditions1.

4. Eyelid retraction: If the right eye's upper eyelid is higher than normal, it may make the left eye appear comparatively smaller1.

5. Orbital asymmetry: Differences in the positioning of the eye sockets within the skull can lead to one eye appearing smaller1.

6. Medical conditions: In some cases, conditions like thyroid eye disease or neurological issues can cause eye asymmetry26.

Treatment options depend on the underlying cause and can include:

1. Non-surgical methods: For mild asymmetry, specialized eyewear or cosmetic techniques may help balance the appearance3.

2. Ptosis surgery: If drooping eyelids are the cause, surgical correction (blepharoplasty) may be recommended45.

3. Orbital surgery: In cases of significant orbital asymmetry, complex surgical procedures might be considered1.

4. Treatment of underlying conditions: If a medical condition is causing the asymmetry, addressing that condition may help resolve the issue2.

It's important to consult an ophthalmologist or oculoplastic surgeon for a proper evaluation. They can determine the cause of the asymmetry and recommend appropriate treatment options. In many cases, mild asymmetry is considered normal and doesn't require intervention unless it affects vision or causes significant cosmetic concerns36.