If it's not a leak why does it look smaller than the other?

The first thing to note here is that it will be next to impossible for us to determine exactly the cause or nature of your specific asymmetry here on this forum.  That is something that your local surgeon is better equipped to do as it requires at the very least a good physical exam of the breasts.  Having said that, there is great value in answering your question here, and I am glad you asked it.  If you have saline implants, then certainly any change or difference in volume or projection can be explained by a leak.  Typically when that happens, however, it is an "all or none" thing, and most if not all of the saline leaks out, so the difference is not subtle.  On the other hand, if you have silicone implants, or if you have saline implants that are intact and not leaking, there are many other reasons why you might see or feel asymmetry.  Most of these have more to do with the tissues around the implants and not the implants themselves.  The silicone implants we are currently using in the US are all a version of a solid type of silicone gel, and as such, they don't "leak" like a true liquid.  That is to say, if there is a rupture in the shell of the implant, the gel usually still stays in one piece and doesn't leak or run out of the breast.  Thus, the implant/breast would not demonstrate a change in size or volume.  Most of the time when a patient reports a difference in what appears to be VOLUME, she is really noticing a difference in PROJECTION.  That is, the fullness or the amount that the breast seems to stick out from the body; said another way, it could be called its "perkiness!"  If we have a capsule contracture or tightness of the tissues surrounding one implant, then it can change the shape and projection of that breast without changing the volume one cc.  The tighter breast look fuller and project more, and especially when viewed from above like most ladies look at their own breasts, it will look "bigger."  But this is not a phenomenon of true volume difference, such as we would expect with a leak where some of the material in the implant actually leaves the implant making it smaller.  It is a difference in "packaging." Another possibility is that the underlying chest wall tissues may project or stick out differently, and thus, the implants may be sitting on different foundations.  Sometimes there are subtle differences in the sternum or rib cage from side to side, and while we try to point these out before surgery so we can set expectations, sometimes they're very subtle and not seen until accentuated by having implants in.  When this happens, one breast can project more, or sit up higher, than the other, and this can give the illusion of more volume, or a bigger breast.  But again, this is not a phenomenon of actual volume difference.Lastly, we can simply get a slightly different position of the implants, usually one is higher on the chest wall than the other, and this can cause the upper pole of that breast to look fuller and project more than the other side.  Again, this will look like a difference in volume to many ladies, especially when they are looking down at their own breasts, but it is not really a difference in volume, just in position of the implants.So, these are a few of the more common reasons why we might see asymmetry of the breasts that don't involve a true difference in volume (and thus a leak) between the breasts, and I would venture to say that these are FAR more common, especially when it comes to silicone implants, than leaks or ruptures.  Each of these has a different solution, and depending upon how far out you are from surgery, that solution may be just to watch things a little longer.  That is why it is very important to be sure you get advice from a board certified plastic surgeon who has experience with breast augmentation and a variety of different types of implants.Stick with your surgeon who can examine you in person, and if you would feel more comfortable, it would not be out of the question to get a second opinion too.  You can either ask your surgeon for a recommendation of a trusted colleague for this purpose, or if that is not comfortable for you, perhaps a friend or relative knows an experienced, board certified plastic surgeon who will take the time to carefully assess your situation and sit down with you for a good explanation of what s/he sees.  Best of luck.

No two breasts match, either before or after surgery. Sometimes one breast is narrower or higher, and sometimes the ribs on one side  are more prominent, giving the illusion that that breast is larger. Since your bra fits normally, there may be other factors contributing to appearance. You're still early in your recovery, so one side may be a little more swollen at the top or has a smaller, tighter skin envelope to settle into, pushing it higher. After your breasts have settled 3 to 6 months after surgery, you should review the size with your plastic surgeon. Looking at the before photos next to after photos can help you see the little asymmetries that most people don't otherwise notice.I agree with your plastic surgeon and the second one you saw. Just watch it for now until you're closer to your final result.All the best.