Many prospective Lasik surgery patients wear contact lenses. When they’ve come to the point of considering Lasik surgery, they may have tired of the inconvenience of contacts or perhaps they may have problems tolerating contacts for long periods. With all patients that undergo evaluations for Lasik, I ask them to discontinue their contacts for at least 2 weeks prior to the exam. Although 2 weeks may seem like a somewhat long time to be without contacts, it is extremely important to the outcome of the Lasik, so we insist on it.
An optical system like glasses is much closer to perfect compared to an eye because it can be ground and shaped in a laboratory. The eye, on the other hand, is made of human tissue and it is naturally imperfect, so we expect a certain amount of lumps, bumps, and warping to be present. These human imperfections of the eye are as unique to the individual as their fingerprints. Modern Lasik technology is capable of registering these little imperfections and accounting for them in the laser treatment. Because of the sensitivity of this equipment, it is particularly important that the corneal surface is allowed to reach its most relaxed, natural optical state. Modern lasers usually incorporate a wave scan system which allows the computer to measure optical refractions and aberrations in an ultra-sensitive manner. In simplest terms, a wave scan system sends light into your eye and is very accurately able to measure the light that reflects back to it. By mathematically analyzing this returning light, the computer can derive an incredible amount of optical information about your eye. This optical information can in turn be used by the laser during a Lasik treatment to render very accurate treatments. With these systems, optical aberrations that may be unique to your eye can be analyzed and treated in ways that older laser technology could not.
Contact lenses sit directly on the outer corneal surface of the eye. They are a relatively firm “plastic” material and essentially a foreign body to the eye itself. So although they improve your vision while you wear them, they are directly rubbing on the outer eye surface and have been shown to create significant surface changes when they are worn. These surfaces changes are generally not permanent so when the contact is discontinued the eye returns to it native state. The outer corneal surface is composed of a very rapidly growing and renewing cell layer called the corneal epithelium. This cell layer rapidly regrows and rejuvenates so over time the surface returns to its normal physical and optical condition. In years past, we allowed patients to be out of their contacts for just 3 days prior to their Lasik evaluations and we felt this time was adequate for the measurements that we required. However, when the more advanced technologies were developed, particularly the highly sensitive wave scan analyzers, it became important that even very subtle corneal surface changes be allowed to resolve over a greater length of time. Currently a minimum of 2 weeks is considered standard for patients that wear soft contact lenses. Longer periods of over a month or more may be needed for patients who wear hard or gas permeable lenses.
Soft lenses probably only alter the outer corneal epithelium by direct contact or perhaps by affecting the amount of oxygen available to the cells. These effects can definitely create measurable warping that can be detected on corneal mapping (topography) and could alter the wave scan measurements as well. In a small number of cases, changes in the epithelium could create topographical changes in the cornea that mimic pathological problems in the eye such as keratoconus, a potentially progressive weakening and warping of the cornea. Only by stopping contact lens wear and observing the measurements after an adequate recovery period can we be sure if the cornea is healthy and stable.
Hard or gas permeable (GP) contact lenses can alter the epithelium similarly. However, these lenses are known to also flatten or compress the entire body (stroma) of the cornea in a way that may change the exact amount of nearsightedness of the patient. In this case, wearing the hard or GP contact can actually change the apparent amount of nearsightedness of the patient to a falsely lower level. If the patient discontinues the contact for several weeks, the cornea will relax and resume its natural curvature and the patient’s full nearsightedness will reveal itself. Because of the falsely lower nearsightedness readings for hard and GP contact wearers, proceeding with Lasik without an extended period out of the contact can lead to a higher chance of under correction and subsequent need for additional treatment at a later date.
In summary, contact lens patients considering Lasik should discontinue wearing their contacts for at least 2 weeks (longer for hard and GP contacts) prior to their preoperative exam and surgery. This precaution will allow for the most accurate measurement of the patient’s prescription as well as higher order optical aberrations. Getting the most stable measurements which are free of contact related distortions allows for the most accurate Lasik treatments, the best potential visual outcomes, and the lowest chance of requiring a second Lasik treatment.
Dr. John Suson MD is an ophthalmologist and a clinical instructor at the Medical College of Wisconsin. Currently, Dr. Suson is in private practice with his sister at their “Suson Eye Specialists” clinic. Dr. Suson offers a free consumer guide to laser eye surgery at our site.