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Dr. Q
Average Member
USA
27 Posts |
 Posted - 14 March 2002 : 15:09:40
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Many people who choose to have LASIK do so because contact lenses have become too uncomfortable. Often, the discomfort is due to dryness. However, since we do know that LASIK makes the eyes even more dry for several months (and maybe more) after the procedure, it's a good idea to quantify the level of dryness prior to LASIK, as it is possible to have eyes that are "too dry for LASIK".
A number of tests are useful in evaluating dry eyes prior to LASIK. One test is the tear breakup time or TBUT. Here, the doctor simply observes the tear film under the microscope (with the patient avoiding blinking) until tiny dry spots (breaks in the tear film) develop. The longer the amount of time that passes before the tear film breaks up, the more stable the tear film is, and the better it is able to protect the eye from dryness. A good value to look for is more than 10 seconds.
A second test is called the lissamine green test. Here, a tiny amount of a lissamine green dye is placed in the patient's tear film. The green color will make tiny (microscopic) green dots that the doctor can observe under the microscope in areas where the surface of the eye has become too dry. A little "lissamine green staining", as it is called, is usually o.k. when it is over the white part of the eye, but staining on the cornea itself is a yellow flag for LASIK and often must be addressed with an eye lubrication program prior to surgery.
One final test is called the Shirmer test. Here, tiny strips of filter paper are placed in the patient's eyes and five minutes are allowed to pass. There are several variations of this test, but the basic concept is the same: the more wetting found on the paper strips, the higher the natural tear production.
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