For how long will it last? 

Only a tiny portion is needed for a single application. A daily application should last you three months making this the best under eye cream for you. Using a little will go a long way. A single purchase will yield noticeable results for the best under eye cream.

Should I use eye cream as part of my skin care routine?

It's important to first understand how the eye works. We have very thin skin under our eyes. Compared to the rest of the face, the eye area contains less collagen and elastin, and combined with the amount of time we spend blinking or squinting and applying multiple products and make-up, our skin near our eyes are prone to wrinkles.
There is a tendency for dark circles to appear under the lower eyelids. No matter how much sleep we get, we can sometimes look tired because of bags and puffiness. Dark circles can be caused by a number of factors and not just lack of sleep.
Although fatigue may seem like the most well-known cause, there are other factors such as genetics and hormonal imbalances that can contribute to drowsy looks. In such cases, there is a need for under eye cream for dark circles.

What are some good ingredients for under eye cream for dark circles?

Usually, products with retinol as the active ingredient will do great things for eye areas. WishCare Under Eye Cream is the best under eye cream made with a natural and stable form of Vitamins making it suitable for all skin types including sensitive skin. It also contains Hyaluronic Acid(Hydration), Retinol(Anti-Aging), and Caffeine (De-Puffing) making it the best under eye cream for your tired eyes.