Is this a normal amount of difference or is another revision required? (Photos)

Dear Jen232,
I understand your concern. However, without a proper assessment, it would be difficult to determine what went wrong. It is best that you visit your plastic surgeon for further assessment or ask for a second opinion. Only after a thorough examination, you can get proper recommendations and advice.
Daniel Barrett, MDCertified, American Board of Plastic SurgeryMember, American Society of Plastic SurgeryMember, American Society of Aesthetic Plastic Surgery

A lot depends on your appearance before surgery.

You have more skin laxity in your right breast and the implant sits lower and your upper pole fullness has decreased. I will usually accept 1 to 2cm of difference here, but a lot also depends on what we see in the mirror.

Its likely that over time the implant stretched out the pocket. The solution may be to add some mesh or even switch to a textured implant which I feel can remain higher for longer.

An examination is needed to be certain, but your right implant pocket appears to have stretched more to the outside and inferior area. A revision with an internal bra of mesh would be helpful. You might want to consider going down in size so there is less weight on your always stretchy breast tissue.

If your breasts look symmetrical in clothes, leave them alone. It appears that one upper medial pocket is more open than the other.