What is the best filler for hollow sub brow, sunken eyes and how long does it last? Will it look as natural as fat?

The best treatment for under eye hollows really depends on your bone structure, skin quality etc.  That being said, in general, most surgeons have gotten away from using fat around the eyes because there are now excellent long lasting fillers that are usually more predictable and safe, for most patients and in most doctors hands then fat.  There is nothing "natural" about injecting fat from one area of the body into another so the issue really is how to get a smooth contour which looks natural, is safe and predictable as well as cost effective and with minimal downtime.  I generally use a thicker filler such as Voluma or Radiesse in the mid cheek for support and Restylane (with added lidocaine to customize it to the patient) around the eyes, if needed.  These are all off label treatments, however, and it's important that you seek out a board certified experienced injector because complications are not uncommon in this delicate region with inexperienced injectors.  The doctor can explain which filler or treatment they prefer in your case and why so you can make an informed decision.  I have seen too many problems with patients having fat injections around the eyes at other practices and discontinued performing those treatments years ago when the current fillers became available.I hope that helps and best of luck!

Hyaluronic acid fillers (juvederm, restylane fillers) are useful in restoring volume to the brow (to soften boney orbital rim and give a brow lift).  A hyaluronic acid that does not absorb a lot of fluid (like restylane fine line) works well in reducing the tear troughs providing a rejuvenated appearance to the eye.  These products can last over a year when injected deep in these sites.  The result is very natural as long as it is not overdone.  Fat survival is variable.  If you are prone to weight gain the transplanted fat can increase in size and may produce eyelid bags.