Flap folds, or striae, are a potential cause of decreased visual quality or acuity after LASIK. When present, most (56%) flap folds are noted on the first postoperative day, and 95% are noted within the first week. Risk factors for development of folds include excessive irrigation under the flap during LASIK, thin flaps, and deep ablations with mismatch of the flap to the new bed. Recognition of visually significant folds is important. Early intervention is often crucial in treating folds that cause loss of BCVA or visual distortion.
The first step in evaluating a patient with corneal folds is determining the BCVA. Folds are not treated if the BCVA and the subjective visual acuity are good. Folds are examined with a slit lamp using direct illumination, retroillumination, and fluorescein staining. Circumferential folds may be associated with high myopia and typically resolve with time. Folds that are parallel and emanate from the flap hinge grouped in the same direction indicate flap slippage, which requires prompt intervention. Corneal topography is usually not helpful in diagnosing folds.
Folds are often categorized as either macrostriae or microstriae, although there is significant overlap between these types (Table 6-1). Macrostriae represent full-thickness, undulating stromal folds. These folds invariably occur because of initial flap malposition or postoperative flap slippage (Fig 6-11A). Current approaches to smoothing the flap and avoiding striae at the end of the LASIK procedure vary widely. No matter which technique is used, however, the surgeon must carefully examine for the presence of striae once the flap is repositioned. The surgeon can apply momentary medical grade compressed air and instruct the patient to not overly squeeze the eyelids upon removal of the speculum. Coaxial and oblique illumination should be used at the operating microscope to examine for striae. Macrostriae may occur as patients attempt to squeeze their eyelids shut when the speculum and drape are removed. Accordingly, before removing the speculum, the surgeon should instruct the patient to actively suppress the otherwise natural reflex to squeeze the eyelids at this stage. Checking the patient in the early postoperative period is important to detect flap slippage. A protective plastic shield is often used for the first 24 hours to discourage the patient from touching the eyelids and inadvertently disrupting the flap.
Flap dislocation has been reported to occur in up to 1.4% of eyes. Careful examination will disclose a wider gutter on the side where the folds are most prominent. Flap slippage should be rectified as soon as it is recognized because the folds rapidly become fixed. Under the operating microscope or at the slit lamp, an eyelid speculum is placed, the flap is lifted and repositioned, copious irrigation with sterile balanced salt solution is used in the interface, and the flap is repeatedly stroked perpendicular to the fold until the striae resolve or improve. Using hypotonic saline or sterile distilled water as the interface-irrigating solution swells the flap and may initially reduce the striae, but swelling also reduces the flap diameter, which widens the gutter, delays flap adhesion because of prolonged endothelial dehydration time, and may worsen the striae after the flap dehydrates. If the macrostriae have been present for more than 24 hours, reactive epithelial hyperplasia in the valleys and hypoplasia over the elevations of the macrostriae tend to fix the folds into position. In such a case, in addition to refloating of the flap, the central 6 mm of the flap over the macrostriae may be de-epithelialized to remove this impediment to smoothing the wrinkles. A bandage contact lens should be used to stabilize the flap and to protect the surface until full reepithelialization occurs. In cases of intractable macrostriae, a tight 360° antitorque running suture or multiple interrupted sutures using 10-0 nylon may be placed and retained for several weeks, but irregular astigmatism may still be present after suture removal.
Table 6-1 Differentiation Between Macrostriae and Microstriae in LASIK Flaps
Figure 6-11 Post-LASIK striae. A, Retroillumination of multiple horizontal parallel macrostriae in the visual axis from mild flap dislocation. B, Numerous randomly directed microstriae on fluorescein staining. These striae resemble dried, cracked mud, are apparent on the first postoperative day after LASIK, and usually resolve without intervention.
(Part A courtesy of Parag Majmudar, MD; part B courtesy of Steven C. Schallhorn, MD.)
Microstriae are fine, hairlike optical irregularities that are best viewed on red reflex illumination or by light reflected off the iris (Fig 6-11). They are very small folds in the Bowman layer, and this anterior location accounts for the disruption of BCVA in some eyes. Computer topographic color maps do not usually show these subtle irregularities. However, disruption of the surface contour may result in irregularity of the Placido disk image. In addition, application of dilute fluorescein often reveals so-called negative staining, in which the elevated striae disrupt the tear film and fluorescence is lost over them.
If optically significant microstriae persist, the flap may be sutured in an attempt to reduce the striae by means of tension. As with macrostriae, however, suturing has the potential to induce new irregular astigmatism. An alternative procedure is PTK. Pulses from a broad-beam laser, set to a maximal diameter of 6.5 mm, are initially applied to penetrate the epithelium in about 200 pulses. The epithelium acts as a masking agent, exposing the elevated striae before the valleys between the striae. After the transepithelial ablation, additional pulses are applied, and a thin film of medium-viscosity artificial tears is administered every 5–10 pulses, up to a maximum of 100 additional pulses. If these suggestions are followed, little to no haze results, and an average hyperopic shift of less than +1.00 D occurs as a result of the minimal tissue removal.
Ashrafzadeh A, Steinert RF. Results of phototherapeutic keratectomy in the management of flap striae after LASIK before and after developing a standardized protocol: long-term follow-up of an expanded patient population. Ophthalmology. 2007;114(6):1118–1123.
Jackson DW, Hamill MB, Koch DD. Laser in situ keratomileusis flap suturing to treat recalcitrant flap striae. J Cataract Refract Surg. 2003;29(2):264–269.
Excerpted from BCSC 2020-2021 series: Section 13 - Refractive Surgery. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.