Dry Eyes After Laser in situ Keratomileusis (LASIK)
Dry Eye Syndrome after Laser in situ keratomileusis (LASIK) is the most common side effect encountered by cornea-refractive surgeons since femtosecond technology has nearly eliminated flap related complications. Unfortunately, despite the continuing advances in LASIK technology and visual results, the cure for LASIK-associated dry eye has yet to be elucidated.
Approximately 4% of LASIK patients develop dry eye syndrome , however this has been reported to be as high as 60-70% . Varying degrees of dryness usually last from 3-6 months; however it can persist for months to years. This is especially true for those that had dry eye symptoms before surgery and were inadequately treated. Dryness after LASIK has been linked to numerous possible etiologies to include, but not limited to, dryness before surgery, female gender  and mean spherical equivalent treatment. The most common etiology described is secondary to the transection of corneal nerves and loss of superficial corneal innervation   . These sensory nerves originate from the ophthalmic division of cranial nerve V, the trigeminal nerve. Classically during flap creation, a superior hinge is created resulting in the greatest transection of corneal nerves since a large proportion of nerves enter from the radial aspects of the cornea. These radial fibers run radially in the middle third of the stroma, divide to form a dense subepithelial plexus and then run perpendicularly to penetrate Bowmans layer and supply the epithelium . Alternating the hinge to the nasal or temporal aspect has been shown to reduce the amount of dryness and lost corneal sensation up to 6 months postoperatively (p < 0.0001) . However, beyond that time point there are no differences. The relative risk for dryness per diopter of myopia was found to be 0.88 which correlated approximately with the laser-calculated depth of ablation and combined ablation depth and flap creation (RR 1.01/µm). In order to possibly decrease dryness caused by flap creation, reducing the flap thickness has been shown to have less of an effect on corneal sensation and tear function tests . The alternative is to perform surface ablation or small incision lenticule extraction (SMILE), as these patients typically experience less dry eye symptoms because only superficial nerves are altered versus the deeper stromal nerve plexus .
Despite controlling the above etiologies/risk factors, dryness continues to occur. Given the advent of femtosecond technology, the microkeratome versus the femtosecond laser was evaluated for differences in the mechanism of flap creation. In a randomized clinical trial of 51 patients, one eye was performed with a mechanical keratome and the fellow eye with a femtosecond laser keratome. There was no statistically significant difference in self-reported dry eye symptoms between the 2 eyes. These findings were irrespective of the central ablation depth, flap thickness and age . However, another study presented the opposite results and postulated that the femtosecond laser may transect peripheral corneal nerve fibers after they have undergone more branching or lost their nerve sheath. This was thought to be related to the ability of the femtosecond laser to create a more uniform flap .
One special consideration is the hyperopic population. This group was evaluated retrospectively and dryness was found to occur mainly in females. Interestingly enough, the same group was also found to undergo regression in 32% of individuals 12 months after surgery . Whether or not the regression is secondary to the dryness or the inherent effects of the hyperopic ablation has yet to be elucidated.
For the vast majority of patients, dry eye poses little concern, especially since symptoms typically abate within 3 to 6 months. The most common symptom associated with dry eye after LASIK is fluctuation in vision, especially within the first 6 weeks. Other symptoms can vary dramatically and include but are not limited to, irritation, pain, redness, foreign body sensation, slow healing, regression, and worsening astigmatism .
Dry eye symptoms, although mild for some, can be the number one reason for dissatisfaction with LASIK, despite having excellent visual acuity results . Therefore, in order to maximize surgical outcomes, it is imperative to optimize the ocular surface before performing any refractive surgical procedure.
The most important step in the prevention or reduction of dry eyes after LASIK is a detailed pre-operative screening. However, for those that do develop dry eyes after LASIK, the Preferred Practice Patterns from the American Academy of Ophthalmology provides a great outline for treatment. Patients with mild dry eye symptoms should be treated with conservative measures. These include artificial tears/ointments, warm compresses and environmental modification. A preserved or non-preserved tear can significantly reduce, if not eliminate, all symptoms. Evening ointments should not be used during the initial postoperative period, in order to avoid possible migration under the flap . In extreme weather (hot or cold), air conditioning and heating systems, dry out the air within a home or office. Simply humidifying the environment can help dramatically. Another conservative measure that should always be performed upon initial presentation is a thorough check into medications that may exacerbate dry eye. Common medications include antihistamines, allergy medications, hormone replacement therapy, and over the counter “common cold” remedies .
For moderate symptoms that are unresponsive to the above therapeutic measures, cyclosporine A 0.05%, punctual plugs and omega-3 fatty acid supplements should be used. Previous studies have reported that the use of cyclosporine A 0.05% not only improves dryness and neurotrophic epitheliopathy, but also reduces the time needed for faster visual recovery after LASIK . Per the Food and Drug Administration (FDA) this is the only medication approved for the treatment of chronic dry eye (there are other medications currently undergoing FDA trials, in various phases). Omega-3 fatty acids are a nutritional supplement that has been shown to reduce the viscosity of meibomian oils and the inflammation within . (Note: A complete listing of therapeutic options, can be found within the Preferred Practice Patterns for Dry Eye Syndrome).
Dry eye syndrome is the most common side effect encountered after LASIK. All of the above therapeutic options and more have been shown to help control symptoms. Even without treatment, dry eye will usually resolve without sequela in 3-6 months. However, in order to improve patient outcomes and satisfaction, it is imperative to optimize the ocular surface before performing any refractive surgical procedures.
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