Why are my eyes uneven and one eye smaller than the other? (Photo)

Many different situations can lead to uneven eyelids. Some of these can be treated non-surgically and conservatively, even using some very advanced injection techniques with filler or very precise placement of Botox. Other is true we do require surgery to resolve. 
It is important that you seek a consultation with an eyelid expert to delineate the exact cause and treatment options.

Unfortunately, the photo image is too small for us to adequately evaluate your concern. As others mentioned, asymmetry can be related to the eyeball size, eyeball position in the eye socket, or just the eyelid position, both upper and/or lower.  Asymmetry is extremely common, but if you notice a definite change, then you need to see an oculofacial/orbital surgeon. The Casey Eye Center in Oregon is a good place to start. Good luck.

Eye asymmetry is very common, to varing degrees. The causes of eye asymmetry are many. Personal consultation is needed to determine your situation. See following video.

It is very difficult to tell from the photograph,  however everyone has  some degree of eyelid asymmetry.  As long as there is no ptosis present, we address this issue at the time of the cosmetic blepharoplasty procedure.  For many examples of cosmetic blepharoplasty in patients with asymmetrical  eyelids, please see the link and the video below

Hello Wrinkle Toes,It is hard tell from the picture but it could be that your eyelid might be a little lower or that your eyeball could be protruding on the right a little. Being that you have had this all you life, I don't think it's anything to worry about. Whatever the cause, it's very subtle and might be best to leave it alone. My suggestions is to see an Oculoplastic surgeon to have a detailed discussion and modes of treatment.Cheers