Bilberry are very similar to blueberries, they are native to Europe so often referred to as European blueberries. They are one of the richest sources of naturally occurring anthocyanosides. Anthocyanosides are chemicals found in some plants that provide the plant with their dark purple/blue pigment and gives it its high antioxidant status. Bilberries also contain numerous other phytochemical providing it with a powerhouse of all the antioxidants needed to fight off free radicals in the body. It also contains iron chelators which can help remove heavy metals from the body.
There are many benefits from including them in your diet or taking them in supplement form, but below are my top 3.
Circulation - Research shows that supplementing with bilberries can help improve circulation (CVI chronic venous insufficiency) varicose veins and decreased blood flow to the veins.
Eye health - Studies have shown that bilberry might improve vision and help with eye fatigue and heaviness.
Blood Sugar - Bilberries may help improve blood sugar levels in those with type 2 diabetes by reducing the glucose response after meals. Bilberry tea leaves have been used to control blood sugar levels for many years. 
*Always speak to your Doctor first before adding a new supplement to your existing medication. Bilberry can effect you if you are on blood thinners as it can thin your blood too. It can also interfere with diabetic medication as it lowers blood sugar levels.