Scar Wars: Managing Dry Eye Associated With LASIK

BY SHACHAR TAUBER, M.D.

In the 16 years since it was first tested preclinically, LASIK has rapidly become a widespread procedure that has improved the lives of countless patients.¹ Despite its popularity, LASIK is not free from the possibility of complications. Some complications surgeons may face intraoperatively include minor corneal bleeding and a thin flap (seen in 3% and 1% of cases, respectively), while postoperative effects are more common — 5% of patients exhibit minor epithelial defects after surgery and 6% exhibit punctate epithelial keratopathy.²

Dry Eye Following LASIK Surgery

In light of the impact LASIK can have on the ocular epithelium, it should come as little surprise that one of the most commonly noted issues following surgery is dry eye. Punctate keratitis is a standard clinical sign for dry eye. Keratitis is best assessed using various methods of vital dye staining, primarily fluorescein, which stains between dried and shriveled epithelial cells, and lissamine green, which stains the dying cells themselves.³

Although it is minimally invasive, LASIK can affect corneal innervation and epithelial cells in a manner that leads to dry eye. Research indicates that 20% or more of LASIK procedures result in chronic dry eye, as defined by both signs and symptoms that may persist at least 6 months postop.⁴

In dry eye, a tear film containing unhealthy or insufficient lipids, aqueous or mucins can become unstable, forcing it to frequently disperse before the eye has a chance to replenish it with a blink. This rapid tear film breakup time (TFBUT) results in inadequate ocular surface protection as measured by the ocular protection index (OPI).³

The resulting exposure of the surface of the eye causes desiccation and damage to the corneal and conjunctival epithelium, making it less likely that the tear film will adhere to the damaged surface. The dry eye cycle can cause quality-of-life-altering discomfort for patients, with commonly reported symptoms including burning, stinging, grittiness, photophobia, general dryness and blurry vision. The condition is often managed with artificial tears, though concomitant treatments can include punctal occlusion, "pulse" steroid regimens and cyclosporine A (Restasis, Allergan) treatment.

Possible Damage Caused by LASIK

The cornea is the most densely innervated surface on the human body and intact innervation is believed to be important for maintaining lacrimal function. The sensory nerves in the cornea send information directly to the central nervous system, which in turn stimulates sympathetic and parasympathetic nerves in the accessory lacrimal glands, the goblet cells and the meibomian glands. Interruption or hindrance of this neural loop can, in theory, affect aqueous, mucin or lipid production.⁵ It has been demonstrated that the number of nerves in the sub-basal and superficial layers of the corneal stroma can be decreased by 90% following a LASIK procedure.⁶

The damage to the sub-basal nerve plexus caused by LASIK as a result of the corneal flap that is made during the surgery (PRK can similarly damage the nerve plexus), though not irreversible, does take some time to heal. During this re-innervation process, the ocular surface does not have the sensations it normally would, which can lead to extended periods between blinks.⁷ This in turn affects OPI — the longer time between blinks suggests there is a greater interval during which the ocular surface could be exposed. Exposure is especially likely if neural loop interference has altered the secretion of any tear film components, thereby destabilizing it.

Additionally, even minor epithelial damage in the eye resulting from the surgery can make it more difficult for surface cells to retain the tear film. It is through some combination of altered blink rate, tear film destabilization and ocular surface damage that post-LASIK dry eye is thought to come about.

Figure. Tear film break-up in a dry eye patient. Break-up time drops below the 5 second threshold in over 90% of patients post-LASIK.

Despite the partial denervation that is often caused by LASIK, patients are bound to feel dry eye symptoms almost immediately. In one study, 15.6% of patients reported some dry eye symptoms prior to undergoing LASIK surgery. One day after the procedure, an overwhelming 94.8% reported dry eye symptoms, and though this slowly fell to 85.4% after 1 week, and 59.4% after a month, the results remained significant.⁸

It is evident that LASIK does not just exacerbate pre-existent symptomatology, but can actually bring about dry eye symptoms in otherwise healthy eyes. This is supported by recent data showing that in 20% of 190 eyes that were asymptomatic prior to surgery, dry eye symptoms were reported 1, 3 and even 6 months after the LASIK procedure.⁴ In addition to these symptomatic influences, LASIK can worsen the various clinical signs associated with dry eye.

Tear Film Breakup Time

In a study investigating the effects of LASIK on dry eye, preoperative mean TFBUT was determined to be 5.32 seconds, a value not associated with dry eye. A day after surgery, this value had dropped to 4.14 seconds (suggesting a state of dry eye) and remained at a low 4.49 seconds a week after the procedure. Not until a month after LASIK did mean breakup time return to a level that was considered healthy (5.09 seconds).⁸

A more recent study yielded significant decreases in TFBUT that lasted until 6 months after surgery.⁴ These changes could be attributable to inadequacies with any of the three major components of the tear film: the aqueous, lipids or mucins. In a study investigating clinical signs at an average of 14 weeks post-LASIK, lipid layer thickness was found to be significantly decreased (P=.032), suggesting insufficient lipid secretion by the meibomian glands.⁹ A separate study evaluating factors at 2 weeks, 1, 3, 6 and 12 months after surgery determined that goblet cell density was decreased after LASIK.¹⁰ Fewer goblet cells suggest that mucin production will be reduced, and sufficient mucin is important both for lubrication and for adherence of the tear film to the ocular surface.

Measuring Tear Production

Aqueous production can also become inadequate in the wake of LASIK surgery. As measured by Schirmer I testing, significant reductions in tear production have been seen at 1 week and 1 month post-surgery. Basal tear secretion dropped from 8.49 mm pre-LASIK to 6.80 mm a day after, 5.97 mm a week after and 5.89 mm a month after the procedure, all statistically significant reductions. It seems that the body's ability to produce any or all of the three tear film components may be reduced following a LASIK operation, possibly due to interference with the neural feedback loop. The result is a loss of tear film stability consistent with dry eye.

Dry Eye Treatment

Tear film and ocular surface must be taken into account when performing LASIK. Research suggests cyclosporine A to be a useful therapy pre- and postop for some LASIK patients. In a 2006 study, eyes that were pretreated for 1 month with cyclosporine and continued dosing for a year after surgery, had significantly increased tear production and refractive stability at 1 week, 1 month and 6 months post-procedure.¹¹

A separate study looked specifically at the effects of cyclosporine on visual function in patients recovering from LASIK. Blurry vision is one of the more commonly reported symptoms of post-LASIK patients, because even if they cannot fully feel ocular discomfort due to denervation, they do experience the loss of visual acuity that occurs when the tear film, which has refractive qualities, disperses too rapidly. It was found that in 102 patients, b.i.d. cyclosporine use postop yielded 20/20 vision or better in 76.9% of patients at 3 months, whereas only 48.0% of controls achieved 20/20 or better.¹² As the only currently marketed prescription therapy indicated for dry eye, cyclosporine has seen its effects enhanced when an artificial tear is used concomitantly.

Artificial tear use in general can help maintain the ocular surface and minimize dry eye symptomatology. The tear substitute that has seen the best results clinically when used simultaneously with Restasis is Systane (Alcon), a drop that incorporates the lubricants propylene glycol and polyethylene glycol 400 with the gelling agent hydroxypropyl-guar. After 6 months of treatment the combination treatment of Restasis and Systane increased breakup times significantly longer than did Restasis used concomitantly with another artificial tear (Refresh Tears, Allergan), yielding a mean TFBUT of over 6 seconds in what were formerly dry eye patients.¹³ Any benefits conferred by treatment for ocular dryness may benefit a patient not only after LASIK, but also leading up to the procedure.

It is recommended that a clinic offering LASIK have a standard protocol in place for pre- and post-procedure. A patient entering surgery with an unstable tear film or ocular surface damage is not only more likely to experience worse dry eye signs and symptoms after LASIK, but is also more at risk for epithelial defects during surgery. The patient should begin an artificial tear regimen prior to surgery, and if the patient can be diagnosed with aqueous deficiency, cyclosporine may be added as well. All agents and devices known to facilitate ocular drying should be discontinued more than 1 week prior to surgery — this includes contact lenses and the use of systemic antihistamines. For patients experiencing allergies with an ocular component, topical antihistamines provide a good alternative. Clinical data suggest they do not cause drying as their systemic counterparts do.¹⁴ Maintaining a healthy ocular surface and tear film prior to LASIK minimizes the risk for peri- or postop problems relating to these areas.

Postop Measures

In the aftermath of surgery, the goal is to return the ocular surface and tear film to their healthy symbiotic state, and by so doing, to restore visual function as quickly and completely as possible. Medications with drying effects should still be avoided, if possible, and contact lenses should no longer be necessary. Artificial tear use should continue, and cyclosporine therapy may begin if signs or symptoms of dry eye are present. Collagen plugs are recommended at the time of surgery for patients at high risk of developing dry eye, and if a patient exhibits relatively severe dry eye after LASIK, longer-term punctal occlusion may be considered. At the clinician's or patient's discretion, natural supplements may be added to the treatment regimen — Omega 3 fatty acids have demonstrated some promise for alleviating ocular dryness.¹⁵ Finally, in order to help maintain visual function early on, patients should receive instruction about blink rate. When blink rate is decreased as a result of denervation, ocular surface exposure and blurring of the vision can follow. If patients can be made consciously aware of their blinking, they can limit the impact of these factors.

LASIK has become a reliable and widely performed procedure. Nevertheless, its side effects, though generally not severe, have prompted the search for new alternative refractive surgeries. Although alternatives do exist, such as PRK and laser subepithelial keratomileusis (LASEK), few or none can offer the relatively smooth postop recovery that LASIK does for qualified patients. And so it is up to us, for the time being, to make the best of what we have and minimize the side effects of LASIK surgery as much as possible. Through patient education and an attentiveness to tear film stability and ocular surface health before, during and after a LASIK procedure, a clinician can best help patients avoid the discomfort and vision problems that are associated with post-LASIK dry eye.OM

Shachar Tauber, M.D. is the Director of Ophthalmology Research at St. John's Hospital and Clinics in Springfield, Missouri. Dr. Tauber serves on the Speakers Alliance for Alcon.