Bilberry jam is made from a little blue berry that is related to blueberries and cranberries. Bilberry grows in the mountainous areas of Poland and is related to the American blueberry.   This jam is a perfect sweetener for bilberry tea (item 983789) instead of sugar.

During World War II, British Pilots ate bilberry jam before going out on night flights. They claimed it improved their vision. It is believed that the bilberry herb helps the eyes to adjust to changes in light quickly.
Source: http://ezinearticles.com/?The-Health-Benefits-of-Bilberry&id=386416