Can Someone Tell Me Why One of my Eyes Look Smaller in Pics? (photo)

Looking just at this photograph, the most obvious issue is that you have a defined double fold on the left side but the double fold is not defined on the right side in this image.  A personal consultation would be very helpful to get to the bottom of the difference.

Given the limitation of the photograph, the reason your eyes appear different is because your eyelid folds are uneven. This is quite common and can be addressed but other issues like possible droopy eyelid (ptosis) needs to be excluded on examination especially if this is a new change for you in recent times.
The reason when you try to open wider that you end up with "deer in the headlight" look as you try to compensate is because of our wonderful human anatomy- as you open your eyes bigger, your right eye gets more light into it but less compared to your left (the "normal" side) which feeds in to your brain that your right eye needs to open further but your brain can only send out a universal "open your eyes wider" so you end up opening BOTH eyes wider = Deer in the head light.
Provided you are happy with your left eye, your right eye can be "symmetrised" with creation of a fold that better match your left.
Wish you the best in your journey.
Dr Leo Kim, Specialist Plastic Surgeon in Sydney

Although it's difficult to tell, your creases are assymetric as well as your epicanthal folds. It's best to see a qualified surgeon for evaluation in case there's ptosis as well.