Healthy eye vision guide:

Practice Distance seeing (more than 20 feet’s away): The human eye was not designed by creation for extended use in close-work (reading, computers, factory work, sewing etc). Gazing into the distance is the natural position of the eye (20 or more feet away). Eye muscles RELAX when distance seeing. So it is always good for your eye and vision, if you regularly practice distance viewing or gazing.
Don't do Close Work during and immediately after Meals: During digestion, blood are drawn to the stomach for digestion purpose, so close work during or after digestion has shortage of nutrition to eyes, thus this lack of nutrients to the eyes, weak eye muscles and thus cloudy vision.
Avoid reading when tired or sick: Weak bodily energy weakens the entire system. Reading during illness or fatigue weakens the focusing eye muscles.
Should not read more than thirty minutes at a time: Thirty minutes is about maximum time the eyes can handle without strain or fatigue. So practice some eye relaxation exercises in between to avoid eye strains.
Sunshine(Rising or falling) is Food for the Eyes: It is nourished and healed by its warm radiating energy. So it is always best to expose yourself and particularly your eye to the sunlight to nourish it.
Eye massages and Eye exercises: Eye exercise and or massages gives some physical exercise, better blood flow and thus high nutrients to our eye muscles thus they regain its lost elasticity.

Source : http://www.e-healtharticles.com/Detailed/6163.html