Flap striae are among the most challenging and frustrating complications of refractive surgery because they can be difficult to resolve and often occur after a perfectly executed LASIK procedure. These folds or irregularities within the stroma of the corneal flap usually occur perpendicular to the flap hinge, and several types of striae have been defined.1 Pseudostriae and peripheral flap striae, which do not affect visual acuity, require no treatment. Striae in the visual axis, however, may cause a loss of BCVA, induce irregular astigmatism,2,3 cause a hyperopic shift in the patient's refraction,3 and lead to a loss of contrast sensitivity.
DIAGNOSIS
Although striae may be seen under direct illumination, they are best viewed either by retroillumination through a dilated pupil or by looking for negative staining with fluorescein at the apices of the striae and pooling in the troughs (Figure 1).4 A refractive surgeon may detect striae at the immediate postoperative examination, but diagnosis usually takes place 24 hours after surgery, once the flap edema has subsided. Most flap striae occur within the first hours following LASIK before the flap has the opportunity to adhere to the stromal bed.
ETIOLOGY OF FLAP STRIAE
Flap striae have multiple etiologies. Causes include the improper placement of the flap onto the corneal bed, as well as a deep photoablation resulting in tenting of the flap in the bed and folds induced by the normal loss of tissue. Moreover, excessive flap manipulation may produce an irregular flap and cause corneal striae. Mechanical trauma after LASIK can dislocate the flap and result in striae. This trauma can be minimal, caused by eye rubbing or eye squeezing. Although dry eye does not cause striae, an epithelial defect resulting from the condition can. Additionally, any change in the flap's size from overhydration or dehydration will prevent it from fitting physiologically back into the corneal bed and thereby induce striae.
Poor flap adherence may cause the flap to slip and produce striae. A breakdown of the surface epithelium can compromise the endothelial pump function of the cornea that holds the flap in place. As the barrier function of the epithelium becomes ineffective, the flap loosens from the bed. For this reason, preserving the epithelium at the time of LASIK surgery is very important to maintaining flap placement and reducing the risk of striae.
Similarly, in individuals with endothelial dysfunction, the flap adheres less strongly to the underlying stroma. Refractive surgeons must therefore carefully monitor patients who have a poor endothelial reserve in order to prevent striae formation.
CORNEAL FLAP STRIAE PROPHYLAXISPatient Risk Factors
There are many steps for reducing the risk of striae, including identifying and monitoring high-risk candidates. Patients exhibiting any type of epithelial problem are at the greatest risk of striae because their corneal flaps are less adherent. For this reason, it is important to preoperatively identify individuals with basement membrane dystrophy, which is a well-known cause of epithelial sloughing during LASIK and a risk factor for corneal striae.5,6 High myopes are also at increased risk for striae and pseudostriae, so surgeons need to monitor them more carefully during the immediate postoperative period.
Toxicity
Avoiding epithelial toxicity during refractive surgery reduces the risk of epithelial breakdown. It is better to use minimal anesthetic and administer it only immediately prior to the case. Also beneficial is selecting antibiotics that are less toxic to the epithelium, for instance, using fluoroquinolones in lieu of aminoglycosides. We suggest considering ofloxacin (Ocuflox; Allergan, Inc., Irvine, CA) because it possesses a more physiologic pH and fewer preservatives than other commercially available antibiotics.
Nonsteroidal anti-inflammatory drops reduce patients' discomfort and uncontrolled blinking after surgery. Using nonpreserved drops during the perioperative period is beneficial, because the preservative has been shown to delay epithelial healing significantly.
Intraoperative Steps
Techniques that help prevent striae include preplacing surgical landmarks across the flap edge to enable the accurate repositioning of the flap, lubricating the cornea prior to the microkeratome's pass, and avoiding flap desiccation by using a moistened Merocel sponge (Medtronic Merocel, Mystic, CT). Generally, thicker flaps are less likely to develop corneal striae. We therefore create a 140- to160-µm flap when possible and carefully position it in the stromal bed. We moisten and lubricate the ocular surface with carboxymethylcellulose 1% (Celluvisc) immediately postoperatively so that (1) the irregular corneal epithelium does not catch the tarsal conjunctiva, thereby inducing flap dislocation, and (2) in order to protect the ocular surface while the blink reflex is suppressed following anesthetic use (Figure 2).7
Postoperative Steps
We believe that eyelid closure is extremely important to striae prevention, so we ask patients to wear protective eyeshields and keep their eyes closed for a minimum of 2 hours postoperatively. At the slit lamp, we evaluate patients immediately postoperatively and again 15 and 30 minutes later, at which time the flap striae are usually much more visible due to flap dehydration.
Timing
Striae never spontaneously resolve, and earlier treatment has a greater chance of success, because flap striae become more difficult to remove later in the postoperative course.8 When we see flap striae in the immediate postoperative period, we treat visually symptomatic patients as soon as possible. The timing of surgical intervention depends on whether the flap is irregular due to surgery or healthy with striae. Physicians should reposition a poorly placed, surgically irregular flap as soon as possible, and they should simply observe a well-positioned, surgically irregular flap as healing continues. Surgeons should always reposition a healthy LASIK flap with striae as soon as possible. The choice of several treatment options for striae depends on their timing and etiology (Table 2).
Flap Refloatation
The conventional treatment of postoperative striae occurring within the first several hours of surgery involves refloating the flap with hypotonic BSS (Alcon Laboratories, Inc., Fort Worth, TX) or sterile water, both of which osmotically force striae to resolve.9-11 Unfortunately, when the cornea dehydrates, the striae will recur unless they are stretched while the cornea is swollen.
This technique has many disadvantages. First is inconvenience; the patient must return to the laser room. Second, the technique provides the surgeon with poorer visualization of the striae and flap position under the laser microscope than does a slit-lamp view. Third, the technique necessitates using additional anesthetic, which is toxic to the epithelium. Fourth, refloating the flap requires more time and a greater delay in treatment than does the slit lamp stretching technique, which is described next. Fifth, it further exposes and dehydrates the ocular surface, and, sixth, the irrigation necessary for flap refloatation results in more stromal edema. All these factors increase the patient's risk of developing epithelial defects or a malpositioned flap, and they predispose eyes to subsequent flap striae and slippage.
Slit Lamp Stretching Technique
The slit lamp stretching technique12 involves observing the flap at the slit lamp and manipulating it through gentle, perpendicular pressure applied with a cotton-tipped applicator. Using this technique (instead of flap refloatation), the surgeon is better able to evaluate the gutters between the flap and the bed, as well as to reposition the flap. This technique reduces the risk of corneal edema because it requires no irrigation under the flap; edema increases the risk of the flap's not fitting well into the stromal bed and of epithelial defects, both of which are associated with striae, flap dislocation, and DLK.
We will relift and stretch the flap if (1) striae are present in the visual axis at the initial postoperative visit or (2) if they become visible after this visit and their position in the visual axis results in a loss of visual acuity, a decrease in contrast sensitivity, or glare. Striae occurring at 1 week or later postoperatively require aggressive stretching and smoothing. They are more densely positioned due to collagen cross-linking, during which the stromal collagen forms bonds that hold the striae in place and makes them more difficult to remove. For striae of 3 weeks' or longer duration, we employ one of the more aggressive management techniques described later in this article.
Recently, we compared the efficacy and safety of treating immediate postoperative flap striae and poor flap positioning by stretching the flap at the slit lamp versus refloating it.12 We determined that, during the immediate postoperative period, the stretching technique simply, safely, and effectively reduced visually significant flap striae. Unlike refloating with BSS, flap stretching at the slit lamp neither requires additional anesthetic, nor does it further expose or dehydrate the ocular surface.
Flap Suturing
The surgeon places either running or interrupted sutures5 and generally removes them after 1 to 2 weeks. To be successful, the physician must possess significant technical expertise. If he fails to apply tension equally and place the sutures radially, this technique may induce striae in the area of the tight sutures. While the sutures are in place, the patient's vision will be diminished, but BCVA returns rapidly following suture removal. We use this technique for regular striae that have been present for 1 month or longer.
Hyperthermic Treatment of the Flap
We have examined the use of this technique13 for striae of greater than 1 month's duration when more conventional options have been ineffective. We based our approach on previous studies that showed that low levels of heat can cause collagen relaxation and the return of flaccidity to the stromal lamellae;14 at higher levels of heat, the collagen lamellae denature and shrink significantly. At lower levels of dry or wet heat, we observed no significant damage, and the collagen relaxed. We removed the central 6 mm of epithelium from affected corneas and elevated the flaps. After heating a striae-removal spatula to 65ºC in sterile water, we used it to mechanically massage both sides of the flaps for 5 to 10 minutes until the striae were visibly reduced (Figure 3). All patients experienced a clinical reduction of striae, and they subjectively noted reduced haze and glare. The treatment did not result in any loss of BCVA, and no serious flap complications occurred.13
Phototherapeutic Keratectomy
Transepithelial phototherapeutic keratectomy (PTK) with a masking agent is another treatment option for long-standing striae. The surgeon uses the epithelium as a masking agent and turns the illumination down as low as possible in order to see the autofluorescence of the epithelium as he ablates it. Once the autofluorescence has completely disappeared, the surgeon may remove the peaks of the striae, without touching the troughs of the folds in the flap. Following the PTK, the surgeon may remove additional residual striae by using the epithelium as a masking agent and Healon5 (Pharmacia Corporation, Peapack, NJ) or carboxymethylcellulose as a second masking agent.
PTK may be associated with epithelial haze, but the technique can be successful. Adjunctive mitomycin C to reduce the epithelial haze after PTK may help decrease stromal scarring and improve visual outcomes.
CONCLUSION
Proper preoperative evaluation and intraoperative management can minimize the incidence of post-LASIK corneal flap striae. When these problems do occur postoperatively, the surgeon should initiate treatment as expeditiously as possible. Striae management is based on their duration. Appropriate treatment may be extremely effective at reducing patients' visual complaints and improving their level of satisfaction.
Eric D. Donnenfeld, MD, is a partner in Ophthalmic Consultants of Long Island and is Co-Chairman of Corneal and External Disease at the Manhattan Eye, Ear, and Throat Hospital in New York. He is a consultant for Allergan, Inc., and performs research for Alcon Laboratories, Inc., Allergan, Inc., and Santen, Inc. He holds no financial interest in any products mentioned herein. Dr. Donnenfeld may be reached at (516) 766-2519; eddoph@aol.com.
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12. Solomon R, Donnenfeld ED, Perry HD, et al. Slit-lamp Stretching of the Corneal Flap After LASIK Reduces Corneal Striae. J Cataract Refract Surg. In press.
13. Donnenfeld ED, Perry HD, Doshi S, et al. Hyperthermic Treatment Of Post-LASIK Corneal Striae. J Cataract Refract Surg. In press.
14. Goldblatt WS, Finger PT, Perry HD, Donnenfeld ED, et al. Hyperthermic treatment of rabbit corneas. Invest Ophthalmol Vis Sci. 1989;30:1778-1783.
