As we age, there is a slow reduction of tear formation. Also, prolonged use of contact lens may lead to dry eyes, making contact lens wearers intolerant to their contact lenses. Many contact lens users seek LASIK treatment because they want freedom from their spectacles, but can no longer use contact lenses because of their dry eyes. In addition, the frequent use of eyedrops with preservatives have a tendency to make the eye much more sensitive with concomitant reduction of tear production. Should long-term artificial tears be needed as supplements, it is recommended that preservative-free eyedrops be used.
After LASIK, most patients may develop some dry eye. Fortunately for the vast majority, this is a temporary situation, which can be rectified in a few days to a few weeks after surgery with preservative-free eyedrops and oral supplements such as flaxseed oil. In addition, persistent dry eye can be managed by plugging the drainage ducts to retain tears produced in the eye. For patients with very severe dry eyes, moisture chambers can be used at night to help ease this problem. One factor which would affect a patient’s development of dry eye as a result of LASIK treatment would be the direction in which a flap is cut. The cornea can become desensitised when the flap is being made, as corneal nerves are severed during surgery. The lowered sensitivity of the cornea results in less stimulation of tear production. This leads to dry eyes. Fortunately, this sensitivity recovers after a period of 1 to 3 months post-surgery.
Flaps cut in a down-up (vertical) direction cause slightly more anaesthesia of the cornea. Most corneal nerves enter the cornea from the sides, and in creating vertical flaps, nerves on both sides are cut. Whereas in lateral-to-medial (horizontal) corneal flaps, corneal nerves on one side are preserved. Horizontal flaps reduce the development of post-LASIK dry eye.
The thickness of the flap is also another factor in the development of dry eye. Thinner flaps mean less corneal desensitisation for a shorter period of time. The corneal nerves have a shorter distance to grow to reinnervate and resensitise the cornea.