Optometric Management

LASIK Causes Dry Eye: True or False?
Our panelists tackle this very basic question and explore the various theories that support their final answer.

Paul M. Karpecki, O.D.: Three oft-cited theories link dry eye and laser-assisted in situ keratomileusis (LASIK).

The neurotrophic theory suggests that severing the nerves desensitizes the cornea, interfering with tear production. A second theory states that the suction ring used during LASIK disrupts the high concentration of goblet cells at the limbus, decreasing mucin production. And a third says that altering tear flow as a result of altering the corneal surface may produce short-term dry eye.

Kerry D. Solomon, M.D.: There's no question that LASIK causes dry eye, but it's a complicated issue because some patients -- contact lens wearers, for example -- probably have pre-existing dry eye problems but are unaware of them.

That said, I'm convinced LASIK causes dry eye, if only temporarily. The condition persists until the nerves regenerate, anywhere from 1 day to 9 months, according to some studies.

Even though I believe the dry eye is temporary, I still tell LASIK candidates that the condition is one of the most common side effects of the procedure. Patients need to be aware of dry eye, and we need to be prepared to address it proactively.

Eric D. Donnenfeld, M.D.: I believe all three etiologies Paul mentioned are accurate. To me, however, the neurotrophic component is the most important.


	DRY EYE DISEASE

We know that when you lose innervation of the cornea, the feedback loop to the brain is affected negatively. This creates a cycle in which there's decreased feedback from the cornea to the brain stem to instruct the lacrimal gland to produce tears so the cornea becomes drier and more anesthetic. By maintaining as much sensation as possible, we may be able to decrease the severity of the dry eye.

Milton M. Hom, O.D.: Blinking also is important. When patients have had their nerve architecture severed, they have a decreased blink rate because the feedback mechanism has been altered. Studies have shown a high correlation between poor blinkers and dry eye, which gives credence to the theory that some neurotrophic cause is producing dry eye in LASIK patients.

Paul M. Karpecki, O.D.: Milton, I know you're following some other research on this topic. What have you learned?

Milton M. Hom, O.D.: Another theory relates corneal geometry and LASIK-related dry eye. Dr. Bob Lingua from the University of Southern California Doheny Laser Medical Group in Brea, Calif., suggests a correlation between the amount of myopia reduced and the severity of post-LASIK dry eye. In other words, if you reduce a large amount of myopic refraction, the dry eye will be more severe. If you reduce a smaller amount, the dry eye will be milder.

Paul M. Karpecki, O.D.: Do the drugs used intra- and postoperatively affect dry eye in your patients?

SERIAL TOPOGRAPHIES OF SOFT LENS-INDUCED CORNEAL WARPAGE (TOP, CENTER). THE DIFFERENCE MAP (BOTTOM) SHOWS 7 DIOPTERS OF TOPOGRAPHIC CHANGE.

Reprinted with permission from Milton M. Hom. LASIK: Clinical Co-Management. Boston: Butterworth-Heinemann, 2001:48 5-S

Eric D. Donnenfeld, M.D.: I definitely would add medicamentosa to the dry eye story. As you know, all medicines have a toxic component. LASIK patients are more susceptible to this toxicity because of:

I believe many LASIK patients have had their dry eye problems worsened by intraoperative and postoperative pharmacologic therapies. To minimize toxicity, we should avoid aminoglycosides and use nontoxic antibiotics.

Eric D. Donnenfeld, M.D.: Fluoroquinolones are certainly the least toxic, broadest spectrum antibiotics. Not only are they the best anti-infectives, they're the least toxic.

I also recommend ofloxacin (Ocuflox) over ciprofloxacin (Ciloxan) because ofloxacin has 15% less benzalkonium chloride (0.005%) as compared to ciprofloxacin (0.006%). Also, remember that ciprofloxacin has a second preservative, disodium edetate 0.05%.

If you're going to use nonsteroidal anti-inflammatory drugs, you should use something that doesn't cause toxicity from preservatives. I use non-preserved ketorolac tromethamine (Acular) on all of our patients after LASIK.

J. James Thimons, O.D.: Besides the theories we've already discussed, other more subtle issues can be related to post-LASIK dry eye. We also should consider:

J. James Thimons, O.D.: I'm most concerned about patients who exit their contact lenses after prolonged wear -- 10 to 20 years -- because they've altered their corneal physiology substantially. I think there's a reasonable level of inflammatory cell presence in those eyes, especially if the patient is intolerant to the lenses.

Paul M. Karpecki, O.D.: How long should patients be out of their lenses before they have LASIK?

J. James Thimons, O.D.: I tell patients to stop wearing their lenses for a minimum of 7 days for daily wear soft contact lenses, 2 weeks for extended wear and toric lenses and 1 month for each decade of rigid gas permeable lens wear. I believe this tactic greatly improves long-term outcomes and diminishes symptomatic dry eye.

Milton M. Hom, O.D.: Corneal distortion is definitely an issue with contact lens wearers. You'd think that a patient who wears a soft toric lens or a soft lens on a daily wear basis won't have very much distortion, but he can. I use corneal topography over a period of time to monitor many of my LASIK candidates who are contact lens wearers. If I see that the distortion has gone away, then I'm more comfortable recommending that patient for LASIK. (The serial maps on the previous page illustrate this point.)

Paul M. Karpecki, O.D.: Jim, you also mentioned systemic disease, drug usage and age as factors affecting post-LASIK dry eye.

J. James Thimons, O.D.: Yes. Many patients have underlying systemic immune factors, such as rheumatoid disease. Even though they're good candidates for LASIK, they're more susceptible to dry eye problems.

You'll also find relationships between dry eye and anti-anxiety medications, which have an anticholinergic effect. They can decrease tear production and increase the risk of dry eye long-term. Most of these patients aren't comfortable going off their medications to have the surgery.

And finally, older patients have a higher prevalence of significant postsurgical dry eye than people in their 20s.

Milton M. Hom, O.D.: A study we did several years ago on the prevalence of meibomian gland dysfunction (MGD) found a very high correlation between age and MGD. As patients get older, they're more likely to have MGD, which of course, leads to dry eye problems. So that correlates to the age factor you're describing, Jim, which, of course, leads to dry eye problems.

Does Dry Eye Hinge on the Hinge?

I believe one reason that post-LASIK dry eye has become more prevalent relates to the increased use of superior-hinge flaps. With this type flap, you're transecting the long posterior ciliary nerves, leaving the cornea neurotrophic predominantly inferiorly. That's the area where the patient is most exposed, and the palpebral fissure is open inferiorly on the cornea. That's where you have the least sensation and the driest of eyes.

A nasal-hinge flap lets you preserve one of the arms of the long posterior ciliary nerve so patients have better corneal sensation postoperatively. In addition, the area that's most neurotrophic is under the upper rim, which is the most protected area. It's a nice combination.

You'll also notice that staining usually is opposite the hinge. With superior flaps, you'll see inferior staining; with nasal flaps, you'll see temporal staining.

Eric D. Donnenfeld, M.D.