Lasik And The Dry Eye Revisited

The many benefits of LASIK are obvious, vision without glasses, however several side affects must always be considered prior to surgery. One of the most significant, and bothersome is Dry Eyes. Most individuals that undergo the procedure will experience at least some dryness, yet others will be greatly affected.

There has been a great deal of research, and clinical trials performed in an effort to determine the exact cause of the post operative dry eye, but the specific etiology has yet to be determined. One such theory is the Neural Feedback Loop Theory. This theory suggests that the disruption in the corneal nerve fibers; as a result of the flap creation and stoma layer ablation decreases corneal sensitivity. Consequently there is a decreased blink rate leading to an increase in tear film evaporation; thus the eyes become dryer. Clinical trials have shown that this anomaly corrects itself in most, but not all individuals.

The second theory is Goblet Cell Damage. Goblet cells manufacture the mucin layer in tears preventing tear film evaporation. Microkeratome pressure on the cornea during flap creation can damage conjunctiva Goblet cells resulting in an unstable tear mucin layer. An unstable tear mucin layer will cause the tears to evaporate quick and leave the exposed cornea dry.

Next theory is the Change in Corneal Curvature. Changing the corneal curvature is required to alter one’s prescription, but also affects how the tear film overlays the cornea. This change causes an iron stained epithelium, resulting in a very dry eye.

In all cases, osmolarity changes because of the decreased blink rate results in damage to the cornea called Keratopathy. These are the most widely accepted theories on why eyes become dry following LASIK. It should be noted that dryness rates are much lower for PRK because there is no flap creation and many of these factors do not exist with that procedure.

Extensive dry eye testing should be performed prior to LASIK to determine if there is an underlying dry eye condition. Some routine tests that must be done are Tear film evaluation, Schirmer test, Lissamine green staining, tear meniscus height measurement, Phenol red thread testing and Fluorescein staining. While all of these need not be done, some must be performed because the surgeon must know not only if there is a dry eye condition, but how bad it is.

In cases where there is an existing dry eye, preoperative treatment can be done. The use of artificial tears, and in more serious cases, Cyclosporin commonly known as Restasis can be prescribed prior to surgery. In addition, topical steroids can also be employed to help re-mediate the condition.

During the procedure the surgeon can also lessen the dry eye affect by creating the flap with a nasal hinge instead of a superior one. This appears to cause less dryness since only one side of the nerve is severed, while with the superior hinge both sides are cut; this affects corneal sensitivity. Some studies have not supported this theory while others do. The method of flap creation is a much greater factor. The microkeratome definitely creates more damage to the corneal nerves and thus dryer eyes. The better alte
ative is flap creation with the femtosecond laser commonly called Intralase. Corneal tissue disruption is much less and corneal sensation returns much faster.

Post operative dryness can be dealt with most commonly with artificial tears. The best of which is Celluvisc. Restasis is also often employed, but must be used for at least 3-6 months to be affective. Inserting a collagen plug in the area of the lid where tears drain is also used in extreme cases to retain tear volume in the eyes.

In summation, extreme dry eye patients should carefully consider, and discuss with their surgeon whether LASIK is appropriate, and all refractive surgery patients must be prepared to suffer from dry eyes post operatively for at least several months and perhaps even longer.