In a healthy eye, light rays enter the eye through the cornea and are focused with the help of a “crystalline lens” behind the pupil at a point directly on the retina (the light-sensitive nerve tissue at the back of the eyeball). However, only about four in 10 people have normal visual acuity. For the other 60 percent, clear vision may be achieved by refocusing light rays with the use of corrective lenses.
One aspect of a healthy eye is one that remains moist due to the presence of a three-layer tear film. The outermost layer is an oily layer, the middle layer is water and the tear layer closest to the cornea is mucus. In order for the eyes to remain healthy, there has to be a continuous fresh layer of tears being produced.
- Dry eye occurs when the eye does not produce enough tears or produces tears that do not have the proper chemical composition causing an irregularity of the tear film.
Some common causes of dry eye include:
- Environmental factors, such as dry air from heating or air conditioning
- Reduced blinking and eye strain from close-up work, such as on a computer
- Prescription drugs, especially antihistamines, diuretics and anti-anxiety pills
With contact lens use, there has to be a continuous fresh layer of tears evenly spread across the ocular surface creating a “comfortable cushion” between the contact lens and eye surface. Discomfort, especially dryness, remains the most common complaint from contact lens wearers, with 2.2 million contact lens wearers dropping out of the category each year.