Among the possible postoperative complications of laser-assisted in situ keratomileusis (LASIK), flap striae are relatively uncommon. However, they are important for us to address because of their potential effects on our patients' quality of vision. In some cases, striae can reduce visual quality without an accompanying loss of Snellen best-corrected visual acuity (BCVA).

Striae are preventable and treatable. Improved microkeratomes, which allow for superior-hinged flaps, have helped to decrease the incidence of this complication, but we must also understand risk factors, prevention, appearance and treatment of striae in order to further reduce the incidence and impact on visual outcome.

We have closely tracked post-LASIK striae at the Gimbel Eye Centre and have made a concerted effort to eliminate it. (See "Tracking our Progress,") In this article, we will explain how we diagnose, manage and prevent striae and how our efforts have lowered our incidence to 0.14%.

Risk factors and diagnosis

Symptoms of striae may include glare, ghosting, image doubling and blurring. Striae in the periphery or just off the visual axis may not effect BCVA or quality of vision but may result in astigmatism. However, when the striae cross the visual axis, significant reduction in the quality of vision or the BCVA results.

We always consider striae as we differentially diagnose decreased quality of vision or BCVA post-LASIK. Once the possible diagnosis is in the differential, we can more easily identify it on routine slit-lamp exam via retroillumination through a dilated pupil.

Risk factors for the development of striae include a thin flap and high myopia due to the "tenting effect" of the corneal flap over the ablated stromal bed. The greater depth of ablation in high myopes may lead to an alteration in the relationship between the underside of the flap and the stromal bed.

Loose epithelium at the time of surgery may lead to stromal hydration, causing the flap to not fit well at the edge. In these cases, it may be difficult to put the flap into position because the loose epithelium makes it impossible to maneuver the flap and to stretch it out again using a dry sponge on the surface. Prolonged surgery time using excess irrigation may also cause stromal hydration and decreased adhesion of the flap. Exophthalmos and lagophthalmos are other risk factors that can lead to flap displacement and wrinkles because of poor tear film distribution.

Successful management

Some lasers have a slit beam capability, which allows visualization and management of the flap striae intraoperatively. Postoperatively, when striae are not in the visual axis and are not impairing vision in any way, we leave them alone. And if wrinkles are localized in only one peripheral area, we lift and refloat only that portion of the flap.

However, removal of striae in the visual axis mandates relifting and refloating the entire flap. Early recognition and treatment produce the best results. We treat these wrinkles the same as wrinkles from displaced flaps even if the flap is in place. We start by raising the flap with a modified Sinskey hook and clearing the epithelium from the edge of the flap and the stromal bed edge with a Paton spatula. This is essential for preventing possible epithelial ingrowth.

We then float the flap into position with balanced salt solution through a mid-shaft opening cannula. Using very wet sponges and a feather-light touch, we express the fluid and approximate the edge of the flap to the stromal bed. You can use dry sponges to stretch the flap after it begins to adhere to the stromal bed, ensuring that the gutter is as small as possible. Avoid overhydration of tissue to minimize the risk of stromal swelling and poor adherence. Though the stromal striae can be smoothed out, epithelial striae will still be evident for up to 12 hours. On careful inspection with the laser slit beam or slit lamp, one cannot distinguish epithelial striae from stromal striae.

Some surgeons advocate use of pressure patches after refloating the flap to avoid additional striae. We have found that refloating the flap and using dry sponges to stretch the flap into position to be the most effective means of management. A flap can be lifted and stretched for up to 6 months and possibly 1 year.

If relifting and repositioning the flap fails to improve the quality of vision, transepithelial phototherapeutic keratectomy (PTK) may be useful in smoothing subtle irregularities in Bowman's membrane that contribute to image distortion and doubling, even when they're not detected by corneal topography. When striae have persisted for several months, suturing the flap after relifting may be required. (See "Case Studies," )

Of course, the ultimate goal of our efforts when dealing with any type of complication is prevention. Striae can form intraoperatively or postoperatively. We avoid intraoperative striae by making sure the flap or stromal bed does not overly hydrate or dry out. We advocate laying the flap in a cupped fashion on a wet Gimbel-Chayet sponge during the ablation. Once the ablation is done, we refloat the flap into position with only brief, gentle irrigation, avoiding overhydration of the flap or stromal bed. If we see debris near the edge of a flap, we irrigate only that area of the flap using a bent 30-gauge cannula. Irrigation should always be minimal. Once the flap is floated into position, we stroke it with very wet sponges and a feather-light touch and remove any excess fluid from underneath. Any pressure may create striae. Metal instruments cause too much friction for this step.

If a large gutter remains after the flap is positioned, we use dry sponges to stretch the flap after it has adhered to the stromal bed for 1 to 2 minutes. We wait at least 2 minutes for the flap to adhere to the stromal bed before we remove the speculum. To prevent patients from squeezing their eyes, we ask them to focus at a point on the ceiling, and we support the lids with thumb and forefinger while removing the speculum. We also hold the eyelids open while taking off the sticky drapes.

Postoperatively, we use moisture chamber shields to prevent excessive surface drying and flap dislodgement from eyelid adherence to the flap in our low humidity climate. The moisture chambers are recommended for the first 24 hours and then nightly for the first week. We instruct patients to avoid eye rubbing and excess eye squeezing to prevent flap shifting postoperatively.

Remain diligent

LASIK presents us with the possibility of unique complications because we're using a microkeratome and creating a corneal flap. But we can significantly reduce the incidence of striae by following the protocols described above and continually honing our surgical skills. Surgeons transitioning to LASIK may pursue fellowship training and mentoring opportunities. We all can benefit from sharing our experiences and comparing our techniques and results.

Tracking Our Progress

Following the first 73 LASIK procedures performed at Gimbel Eye Center, seven patients experienced peripheral striae, and one patient experienced visually significant straie, an incidence of 10%. In a subsequent analysis of 1,000 LASIK patients, we found 11 cases of striae, an incidence of 1.1%. Currently, our incidence is 0.14%, 5 cases out of 3,695.

* Cumulative to August 2000

** Most recent 3,695 patients

RISK FACTORS

Risk factors for striae include:

�         high myopic correction

�         thin flaps

�         loose epithelium

�         excess irrigation

�         prolonged surgical time

�         displaced flap.

Case Studies

The following cases illustrate our approach to and experiences managing striae:

Case 1 -  One week after uncomplicated LASIK OU (nasal-based flap), a 57-year-old woman presented with acuities of 20/60 OD and 20/70 OS. Her best-corrected vision OU was 20/40 OD with a manifest refraction of +0.75 -1.50 x 110 and 20/40 OS with a manifest refraction of +1.00 -1.25 x 120. No striae were mentioned at that time. Three months postoperatively, the refraction had not changed. With contact lenses she was correctable to 20/25 OU. Surface irregularities were evident OU. Microstriae were noted centrally OS.

Four months postoperatively, the flap OS was relifted for an enhancement to treat hyperopic astigmatism and to reposition the flap to eliminate striae. Three months post-enhancement OS, acuity was 20/40 OD and 20/400 OS. Best-corrected vision was 20/40 OD with a manifest refraction of +0.75 -1.25 x 127 and 20/50 OS with a manifest refraction of -1.75 -1.25 x 168. With RGP contact lenses she was correctable to 20/25 OD and 20/20 OS, but she complained of poor fit and distortion OS.

On examination, she was noted to have epithelial keratitis OS with persistent striae. At that time she underwent epithelial debridement OS, which was to be followed, if necessary, by relifting the flap at a later time. Two months after debridement OS, the acuity OS was 20/400 with best-corrected vision of 20/80 and a manifest refraction of -1.00-0.75 x 20. We performed transepithelial PTK rather than relifting and stretching the flap because of persistent epithelial keratitis, wrinkles seen during the debridement, and the hope for a hyperopic shift to help her myopia.

Transepithelial PTK addressed the keratitis, surface irregularity, striae and myopia. Two months post-PTK OS, the patient's acuity was 20/40 OS, identical to baseline BCVA correctable to 20/25 -2 with a manifest refraction of -0.50 -0.75 x 170. The patient noted that the central distortion had diminished. Earlier management may have been more effective and prevented the keratitis.

Case 2 -  A 41-year-old man, who was slightly exophthalmic, underwent LASIK OU (nasal-based flap) without complications. On the third postoperative day, visual acuity was 20/25-2 OD with a manifest refraction of -0.75 -0.50 x 105 for best-corrected vision of 20/20-1. Vision OS was 20/125 with a manifest refraction of -2.00 -1.00 x 60 for best-corrected vision of 20/100. The flap OD was in good position. The flap OS had central wrinkling and had shifted inferior-temporally.

The patient was returned to the operating room. Since the flap edge had curled under, the epithelium on the flap and on the stromal bed had to be removed. The flap was refloated into position and then secured with 10-0 nylon interupted sutures. A bandage contact lens was placed. Three days later the sutures were removed. Striae reappeared, so the flap was resutured with 10-0 nylon.

One week postoperatively, acuity was 20/30-2 with a manifest refraction of -0.75 -0.50 x 150 for best-corrected vision of 20/20-3 OS. At that time no striae were evident. Sutures were removed 6 weeks postoperatively. Visual acuity was 20/25-3 with a manifest refraction of -0.75 -0.25 x 5 for best corrected vision 20/15-3 OS. Suture removal too early may allow flap slippage and reappearance of wrinkles.

 Case 3 -  A 39-year-old woman was referred to our center 6 months post-LASIK (superior-based flap) for evaluation of her reduced quality of vision OU. Her symptoms included decreased night vision, loss of contrast sensitivity, halos and ghosting, worse in OD than OS. She described her vision as "looking though an aquarium." Acuity was 20/40 OD and 20/25 OS. BCVA was 20/20-3 OD with a manifest of 0.00 -0.75 x 97 and 20/20 OS with a manifest of 0.50 -0.25 x 65. Although she was correctable to 20/20, she complained of persistent halos and ghosting. Her pupils measured 6.5 mm OU in dim light with a treatment zone of 6.25 mm OU. Corneal topography using Technomed and Orbscan showed no irregularity OU. On dilated exam with retroillumination, striae were noted centrally OD and temporally in the papillary area OS. Our recommendation was to lift and refloat the flap to smooth out the striae and to consider a surface PTK to improve her quality of vision if relifting the flap is not effective. This patient is currently considering retreatment.

Prevention of Striae

To minimize the risk of striae:

�         reduce the time that the stromal bed is exposed to fluid

�         immediately remove fluid from interface

�         avoid using metal on the flap; it causes too much friction

�         use a very moist sponge with a feather-light touch

�         prevent flap from drying out

�         discourage eye squeezing or rubbing

�         use moisture chambers post-op.

For More Information

Gimbel HV. Flap Complications of Lamellar Refractive Surgery. American Journal of Ophthalmology 1999, 127:202-204.

Iskander NG, Peters NT, Penno EEA, Gimbel HV: Postoperative Complications in laser in situ keratomileusis. Current Opinion in Ophthalmology 2000, 11:273-279.

Gimbel HV, Basti S, Kaye G, Ferensowicz M: Experience during the learning curve of laser in situ keratomileusis. J Cataract Refractive Surgery 1996, 22:542-550.

Gimbel HV, Penno EEA, Van Westenbrugge JA, et al.: Incidence and management of intra and early postoperative complications in 1000 consecutive LASIK cases. Ophthalmology 1998, 105:1839-1848.

Probst LE, Machat J: Removal of flap striae following laser in situ keratomileusis. J Cataract Refractive Surgery 1998, 24: 153-155.

Gimbel HV, Penno EEA. LASIK Complications Prevention and Management. Thorofare, NJ: Slack Incorporated; 1999.

Kronemeyer B. LASIK Flap Management entails mark and moisten technique. Ocular Surgery News 2000, 18: 30-31.

Dr. Gimbel, world renowned for his commitment to education, is the founder, medical director and senior surgeon of Gimbel Eye Centre in Calgary, Alberta, Canada. He is a professor and the chairman of the ophthalmology department at Loma Linda University in Loma Linda, Calif.

Dr. Keamy is a refractive surgery fellow at Gimbel Eye Centre. She studied medicine at the State University New York Health Science Center in Brooklyn and completed an ophthalmology residency at New England Eye Center, Tufts University School of Medicine in Boston.

Dr. Penno is the Corporate Director of Research at Gimbel Eye Centre. She has an extensive research background, which includes work at the Mayo Clinic and the University of Minnesota. She also provides clinical and surgical care to cataract and refractive patients.