Gyulmyungja, or Cassia, is believed to help with your eye health and is also supposed to be good for your kidney and liver, which are related to your eye function. As such it is used in traditional Eastern medicines. Koreans like to drink a tea of gyulmyungja -- it can be fairly strong tasting. You can buy this at either a Korean or Chinese grocery.
2 tsp of cassia seeds (gyulmyungja 결명자)
4 cups of cold water
Wash and dry.
Fry on the medium heat, stirring frequently - when you hear a rapid popping noise, keep it on couple of more min and turn the heat off.
Boil 4 cups of water, add 2 tsp of gyulmyungja and simmer for 4-5 min.
You can reboil the tea and get more out of it. Drink cold or warm.