Tear trough hollows vary quite a bit. The amount of filler need also varies. Most patients need significant volume under the eyes. In a study I recently completed looking at 400 consecutive under eye Restylane treatments, the average volume was 1 ml under each eye.
However, I have some patients who needed less and others who needed much more. Generally I would recommend a consultation with an experienced injector to be assessed regarding what you need. This is a great treatment option.