With improvement in the techniques and instruments used in LASIK, the incidence of complications has decreased. Clinical outcome, safety, and patient satisfaction from modern LASIK with advanced technology have been found to be significantly better than when LASIK was first introduced about 30 years ago.
Although the outcomes have improved dramatically, we should continue doing our best to prevent and quickly treat even minor complications of refractive surgery such as LASIK.
Therefore, we need to understand the nature of post-LASIK dry eye and devise strategies for its management. In the past, we have encountered many LASIK patients who complain of dry eye-like symptoms, such as discomfort, ocular fatigue, dryness, and red eye, in the early postoperative period; however, these symptoms disappeared over time.
Subsequently, we reported in a retrospective study that dry eye symptoms and tear functions worsened for at least 1 month after LASIK, and we defined this condition as post-LASIK dry eye. The symptoms of post-LASIK dry eye include typical dry eye symptoms, such as dryness, irritation, ocular fatigue, and red eye. We believe that decreased visual acuity is more pronounced in post-LASIK patients than in other patients with dry eye, possibly because patients who have undergone LASIK treatment are more attentive to their visual performance than others with dry eye.
It should be noted that decreased visual acuity or residual refractive errors may be caused by post-LASIK dry eye, and could be corrected by treating the dry eye symptoms rather than by LASIK enhancement. The typical signs of post-LASIK dry eye are positive vital staining of the ocular surface, especially the corneal flap, by fluorescein, rose bengal, and lissamine green.
Tear breakup time TBUT is shortened in almost all cases within 1 week after surgery, and this continues for 3 months on average. Basic tear secretion was determined by the Schirmer test with anesthesia, and was found to significantly decrease postoperatively over 6 months.
Color maps of corneal topography reveal that irregular astigmatism is induced in patients with very short TBUT or superficial punctate keratitis SPK; Figs.
These patients often experience decreased quality of vision. Figure 1. View Original Download Slide. SPK can be observed. B Color map of topography showing that irregular corneal surface is detected in the same area that shows SPK.
C After insertion of punctal plugs into both puncta, SPK disappeared. D Uncorrected visual acuity was improved along with the improvement in the color map. If post-LASIK dry eye lasts long, refractive regression may be caused by epithelial hyperplasia and stromal remodeling. Although the contribution of post-LASIK dry eye to refractive regression is not conclusively established, the evidence reported by Albietz et al.
Although conventional visual acuity is not affected, functional visual acuity may be impaired in dry eye patients. If patients keep their eyes open for a longer time than the TBUT, their visual function may deteriorate due to induced irregular astigmatism with tear film instability, resulting in induced higher order aberrations of the cornea. This may occur during various activities, such as driving, working on a computer, and reading. After full refractive correction, the visual acuity of patients is tested by determining the smallest Landolt ring that can be recognized by them.
During the experiment, the monitor continuously displays various Landolt rings, and patients register their responses using a joystick.
If a patient answers correctly, the next ring shown will be the same size as the previous one; however, if a patient answers incorrectly or fails to answer in 2 seconds, the next ring shown will be larger Fig.
Figure 2. Functional visual acuity test. During the experiment, the monitor continuously displays different Landolt rings, and patients register their responses using a joystick. If a patient answers correctly, the next ring shown will be of the same size as the previous one; however, if a patient answers incorrectly or fails to answer for 2 seconds, the next ring shown is of a larger size.
The functional visual acuity was defined as the visual acuity measured 10 seconds after eye opening. VA, visual acuity; FVA, functional visual acuity. Figure 2 Functional visual acuity test. Tear function and dry eye symptoms improve to preoperative levels thereafter. However, a small number of patients still experience chronic dry eye symptoms more than 1 year after LASIK.
Previous studies and our clinical impressions suggest that preoperative or intraoperative risk factors for developing post-LASIK dry eye include preexisting dry eye, 18 Asian race, 19 female sex, higher refractive correction, deeper ablation depth, 9 , 10 thicker flap, 9 superior flap hinge, 20 and narrow flap hinge. Although the mechanisms involved in post-LASIK dry eye are not completely understood, temporary denervation of the cornea caused by flap creation, and the resulting decreased corneal sensitivity, may be associated with the condition.
We hypothesize that decreased corneal sensitivity may affect the corneal-lacrimal gland and corneal-blinking reflex loops, which in turn may decrease tear secretion and blinking. Ablamowicz et al. Song et al. Figure 3. Although post-LASIK dry eye is a temporary complication, as corneal sensitivity measured with a Cochet-Bonnet esthesiometer appears to return to preoperative values by 6 months after LASIK, a small number of patients complain of dry eye symptoms longer.
Recently, another refractive surgical option, small incision lenticule extraction SMILE , has emerged. The vertical cut of the cornea is much shorter that the length of a LASIK flap, and preserves the corneal nerves. Li et al. The reductions for the two groups were not significantly different at 6 months. Although corneal sensitivity significantly decreased postoperatively in both groups, the reduction was significantly greater in FS-LASIK-treated groups at 1 week, 1, 3, and 6 months.
However, mechanisms other than corneal denervation may also be involved in the development of post-LASIK dry eye. This fact is not consistent with a neurotrophic effect functioning as the only mechanism for post-LASIK dry eye. One possible explanation is that changes in corneal curvature and smoothness may alter the friction between the cornea and lid, resulting in tear film instability.
Dry eye-like symptoms after LASIK, especially long-lasting chronic symptoms, may not be a single entity. Previous studies indicated there are at least two entities, chronic post-LASIK tear dysfunction and neuropathic pain.
The latter is thought to be a pathological postoperative pain state, caused by abnormal reinnervation and neural sensitization leading to dysesthetic cornea after corneal nerve injury. LASIK-induced corneal nerve damage causes neurogenic inflammation, which contributes to peripheral sensitization of sensory nerves and resulting in a relative hyperesthesia. The number of sodium ion channels in the nociceptor membrane increases in response to persistent stimulation of nociceptors, which in turn decreases the threshold for activation.
As a result, patients suffer from persistent pain. This state falls in the same category as the persistent post-surgical pain that can occur after a variety of surgical interventions, such as C-section, knee replacement, inguinal hernia repair, and mastectomy. Post-LASIK ocular surface pain is not associated with tear dysfunction and cannot be treated with conventional dry eye management.
The mechanism for development of post-LASIK ocular surface pain is unknown, but is suspected to involve an interaction between genetic disposition and environmental factors. Further research is needed to understand the mechanisms, treatments, and prevention of this rare but devastating condition.
If post-LASIK dry eye is caused only by the loss of neurotrophic effects, it should recur after enhancement by flap-lifting. We have retrospectively examined symptoms and tear functions after enhancement. We concluded that post-enhancement dry eye is absent or considerably milder than dry eye after initial LASIK, in which tear secretion and TBUT decreased postoperatively.
Certain medications. If you take antihistamines for your allergies, or if you take blood pressure medication or antidepressants, you may be at increased risk of developing dry eye after LASIK.
Dry weather or environment. Air conditioning and indoor heating cause many people to develop dry eye, as do dry climates such as the desert. To learn more about causes, treatments, risk factors and other factors pertaining to dry eye, schedule an appointment with you eye doctor today.
Mark R. Mandel is a board-certified ophthalmologist who has performed more than 90, surgical procedures, including 60, LASIK surgeries. He is a cornea sub-specialist and LASIK surgeon well-trusted for his experience, expertise, surgical precision and integrity.
He has advanced training in corneal transplant surgery and external eye conditions, and currently teaches at the University of California, Berkeley, the University of California, San Francisco, and the California Pacific Medical Center in San Francisco, in addition to leading the team at Optima Ophthalmic Medical Associates, Inc. Dry-eye pretreatment could be a game changer. Again, cases of dry eye lasting longer than a couple of weeks are extremely rare, and even then, the condition is generally manageable.
LASIK requires the creation of a flap in the outermost layer of the cornea, the clear, protective covering at the front of the eye.
While we use the latest technologies to ensure the highest levels of safety and precision in creating corneal flaps, some temporary damage to the corneal nerves is inevitable.
This damage causes the normal nerve impulses that control tear production to be interrupted. As the cornea heals after surgery, the nerves also heal, resulting in the resumption of the normal function of the nerves in most patients. Flap complications are extremely rare among patients who follow the post-operative instructions provided to them closely; however, when they do occur, they can be addressed by our eye surgeons.
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