Fillers to Make Upper Eyelids Fuller?

Fat graft the upper lid?  No.  Add fat to the brow-upper lid junction?  Absolutely. This is an excellent question, and I think the wide range of answers is in part an issue of terminology. In before and after fat grafting around the eye galleries on the websites of plastic surgeons, you will ideally see people weeks and years after fat grafting to the eye area including the upper eyelid area. 
The upper eyelid is a thin structure that normally does not contain any significant amount of subcutaneous fat.  So fat grafting of the upper eyelid itself would not produce an aesthetically pleasing result, and would in fact be quite dangerous to attempt. The area between the brow and the upper eyelid crease, on the other hand, is full of subcutaneous fat in most young people, and that fullness looks youthful.  I refer to this area as the ‘brow-upper lid junction’, and I add fat to make it fuller in the majority of patients for who I perform eye-area rejuvenation surgery.
Take a look at the eyes of fashion models in advertisements: in most cases you actually see little to none of the upper lid.  What you see is a youthful soft tissue fullness that extends from the brow to the upper lid lashes. As we age, this fatty fullness atrophies and the brow-upper lid junction gradually becomes hollow.  The outline of the bony structures below the brow (the superior orbital rim) becomes visible, and one begins to look older, sometimes even ill, and in advanced stages even skeletal.  In some patients that I treat this appearance is inherited and they have a hollow look at their brow-upper lid junction at a young age.  It is also an appearance that some people have following an overly aggressive upper blepharoplasty, where the surgeon inappropriately removes fat from the brow-upper lid junction.
Unfortunately, this is a result that quite a few patients get from upper blepharoplasty, and I treat a significant number of these patients who need that fatty fullness restored between their brow and upper lid. Whether hollowness at the brow-upper lid junction is something that was always present, something that has developed with aging, or something that resulted from an overly-aggressive upper blepharoplasty, fat grafting of the brow-upper lid junction can rejuvenate the eye area in a manner that is simply impossible by means of standard blepharoplasty techniques.  It does not look like ‘surgery’, and patients for whom I perform this procedure return to say that their friends and acquaintances think they look great, but they can’t quite put their finger on why.
A word of caution: this is a delicate surgery that requires a significant amount of experience with fat grafting, careful preoperative evaluation, and meticulous surgical technique.  In experienced hands a youthful and aesthetically ideal brow-upper lid contour can be achieved.  Make sure your surgeon can show you numerous photographic examples of brow-upper lid junction fat grafting. .

Upper eyelid fullness is often the sign of youth.  Yes, fillers can be injected into the upper eyelid. Some people use hyaluronic acids. Some also use autologous fat.