When it is just the left eye that gets tired and red, it relates to congestion of the thoracic duct, the main lymphatic duct responsible for draining about 90% of the body's acidic metabolic waste products and 30 billion cells that the body needs to turnover each day. This includes the dead, turned-over yes cells and the acidic waste eye-cells produce each and every day. When the thoracic duct is unable to take up all this waste, some of stays in the eyes and begins to accumulate. This causes irritation and eventually inflammation of eye tissue and the blood vessels that supply it with nutrients. The result is reddening, eye-fatgue and poor eye sight. The best approach is to remove the lymph congesiton where it it begins - the lymph vessels around the intestinal area. I have described this in detail in my book The Amazing Liver and Gallbladder Flush and Timeless Secrets of Health & Rejuvenation. To focus should be on improving digestive functions through cleansing the liver and colon, and dietary/lifestyle changes that support proper lymph drainage and blood circulation.