Can you use PRP under the eyes if you already have filler under the eyes?

You can have PRP under the eyes if you've already have filler but the question is what are you looking to achieve?  PRP for under-eyes may offer some slight temporary improvement in skin quality and texture but there are generally much better options for this. I suggest you consult with an oculoplastic surgeon for your full range of well-vetted options. 

PRP can be beneficial when injected deep around the eyes. Stem cell injections, with or without fat grafting; and with or without PRP can be even a better choice for eyelid rejuvenation. 

The answer is yes, you can inject PRP under the eye even if you had filler there. I am not sure why you want PRP, but PRP injection under the eye has the potential to improve the skin integrity/thickness thereby improving the appearance of dark discoloration, and potentially improve the appearance of mild eye bag. Severe eye bag may need surgery. As far as mild nasolabial fold, PPR injection may help as well.

PRP, botox and fillers are often used in conjunction with one another and do offer different benefits. I would not recommend PRP around the eyes and filler at the same time. It can take up to two weeks for fillers to fully settle, so it would not be wise to mess with that process. Regarding nasolabial folds, PRP injections can soften the look of these areas by building new collagen and the best part is that it looks very natural. If the creases are very prominent and deep, filler would probably be the best option.