I had Restylane for under eye circles but Dr said I had thin skin and couldn't inject all of the vial. Is that normal?

Yes. That's a scenario that's very common. Overcorrection never looks good and it might even give a blue tinge to the folks with thin skin. I have patients return 2 weeks later and add more if needed. Best wishes, Dr. Aldo

In brief it sounds like your physician has taken a careful approach.  Better under filled than over filled and protruding.  It's probably best to return and discuss with your physician whether you should have more filler at this time.. 

It is not the thickness of skin that determines the amount needed for correction but how hollow is the defect. Also you do not want to be overcorrected and end up bulging and with the possible Tyndall effect

Thank you for your question.  Every patient is different, and the exact volume of filler necessary to treat a particular patient depends on a whole host factors, including their specific facial structure and anatomy, the thickness of their skin and the fat the under their skin, and their specific aesthetic goals.  It's impossible to comment on your specific needs without assessing you in-person, or at least reviewing your before an after photos.  That said, there certainly are some patients with mild volume loss and thinner skin who do not require a full syringe of Restylane for optimal correction under the eyes.  If you find you need additional filler in the future, it is much easier to add more filler than it is to remove filler you don't like.  Best of luck!