According to WebMd, the best treatment for the bruising that accompanies a black eye is to apply an ice pack for 10 minutes and then remove the ice for 10 minutes to prevent damaging the surrounding skin. The cold compress stops the bleeding under the skin and limits the amount of bruising. For convenience, a bag of frozen vegetables can be used in place of an ice pack.
WebMD recommends consulting an eye specialist if vision is affected or if there is obvious damage to the eyeball. Avoid putting pressure on the eye by attempting to force it open, and use nonprescription pain relievers if necessary.
HowStuffWorks indicates that the bruising associated with a black eye normally lasts one to two weeks, even with the application of ice. However, ice helps in relieving pain. When applying ice to a black eye or any other part of the body, wrapping the cold pack in a washcloth prevents direct contact with the skin and reduces the chance of causing further injury by leaving the ice in place too long. If the trauma that caused the black eye also broke the skin, it's important to clean the cuts gently, using soap and water to reduce the chances of infection.