CASE PRESENTATION
A 24-year-old white male presented for a LASIK consultation. He desired freedom from his spectacles and contact lenses and had no history of ophthalmologic or medical problems.
The preoperative examination revealed a UCVA of 20/400 OU. The patients' manifest refractions were -4.50 +1.00 X 175 OD and -4.50 +0.75 X 005 OS, both yielding a BCVA of 20/20. Cycloplegic refraction produced nearly identical results. The central pachymetry readings were 565 µm OU, and the external examination was normal. The patient's pupils measured 3.0 and 5.5 mm OU under photopic and scotopic conditions, respectively. The slit lamp examination was normal with a good tear film, and his fundi were unremarkable. Keratometry measurements were 43.00/44.00 D OD and 43.75/44.25 D OS. Tomey readings (Tomey Corp., Nagoya, Japan) were unremarkable with no hint of keratoconus or other contraindications to LASIK. The patient was scheduled for bilateral LASIK.
I set the NIDEK-MK-2000 System (Nidek Inc., Fremont, CA) for a 160-µm flap, a setting that, with my practice's machines and in my experience, yields a 130- to 140-µm flap. The LASIK procedure on the patient's right eye was uneventful. I used the same microkeratome blade for the patient's left eye. The case was routine until the microkeratome blade stopped in the middle of the cornea, at or just slightly past the visual axis (Figure 1). Initially, I thought the problem was suction loss, but suction was, in fact, present at all times. There were no obstructions. I left the microkeratome in place for 20 to 25 seconds in hopes it would resume function. When it did not, I deliberately broke suction and gently withdrew the device. Leaving the keratome in place longer would have posed a threat to the patient's central retinal and ophthalmic arteries.
The hinge itself was not far enough away from the visual axis. I could not lift the flap away in order to perform a treatment centered on the visual axis.
HOW WOULD YOU PROCEED?1. Would you reposition the flap and attempt LASIK again a few months later?
2. Reposition the flap and perform PRK a few months later?
3. Perform PRK with manual, mechanical, or laser epithelial removal over the replaced LASIK flap during the same surgical session?
SURGICAL COURSE
The most commonly recommended course for incomplete, thin, or irregular flaps is simply repositioning the flap, applying no laser treatment, and reattempting LASIK after at least 3 months have passed. An alternative method is to perform PRK over the replaced LASIK flap during the same surgical session. I have found that this technique can quicken patients' rehabilitation and decrease possible complications from fibrosis during flap healing.
In this case, the incomplete flap seemed quite symmetrical and regular. I informed the patient that his second flap was incomplete and that the case would be converted to PRK mode. After I had placed the PTK card into the STAR S3 excimer laser (VISX, Inc., Santa Clara, CA), I programmed 200 laser shots for a 6.5-mm stromal bed (a discussion of this decision appears later in the article). I centered the laser with the reticule over the central pupil (the location of the subjective visual axis) and applied the laser pulses. Next, I inserted the refractive PRK laser card into the STAR S3 and applied the planned laser correction in the PRK mode.
I placed a bandage contact lens on the PRK eye and provided the patient and his family with appropriate instructions for post-PRK care. I prescribed a fluoroquinolone and steroid for use q.i.d. OU.OUTCOME
On the first postoperative day, the patient's UCVA was 20/25+2 OD and 20/100 OS, and the left eye had completely re-epithelialized on the following day. His UCVA was 20/50+3 OS at 1 week. At 2 weeks, his UCVAs were 20/15-2 OD and 20/20 OS. The patient continued the fluoroquinolone and steroid regimen for another 2 weeks (4 weeks total) OS, and his UCVA remained 20/20 OS. There was very mild haze in that eye at the 2-week follow-up visit that eventually disappeared. The patient's UCVA has remained 20/20 OS, and his cornea has been free of haze for 2 years.
DISCUSSION
Performing immediate PRK surgery over a LASIK flap remains a controversial procedure. Many surgeons maintain that there is a much higher risk of severe haze following PRK performed at any time over a pre-existing LASIK flap. This has not been my experience in four cases of PRK performed over an unsatisfactory LASIK flap immediately following its creation.1 According to our conversation in March 1998, neither was it the experience of Thomas Abell, Jr, MD, of Lexington, Kentucky, in his series of seven such cases. To my knowledge, Dr. Abell was the first to describe the concept for this technique.2 My decision to apply 200 laser pulses is based on Dr. Abell's success with this procedure using between 180 and 200 pulses with the Summit Apex Plus laser on PTK mode to remove epithelium with the laser, rather than with a manual or mechanical technique.
The theory behind this technique is that, after the creation of an irregular LASIK flap, the mirror image of that irregularity exists on the bed. Without laser intervention on the bed, the surfaces of the bed and the underside of the flap should fit back together perfectly. This same theory underlies the current conventional wisdom that the preferred procedure in cases of small, thin, or irregular flaps is to perform no laser treatment, carefully reposition the flap on the bed, and attempt another LASIK flap after a set number of months.3 The conventional course is not without potential pitfalls and complications. It is arguable that variable flap healing will introduce some imprecision into the case. There are also significant risks involved with subsequently cutting into a flap area, which appears to be well healed but in fact is not.4,5
Performing immediate PRK surgery over an unsatisfactory LASIK flap avoids these complications. The technique is not recommended for grossly irregular or mangled flaps, but it is appropriate in cases of small, thin, or irregular flaps. Dr. Abell's and my combined 11 cases resulted in no clinically significant haze. Our success may be due to our use of transepithelial PRK, which relies upon the laser's PTK mode instead of other means of epithelial removal, which would be contraindicated with fresh LASIK flaps.
Better-engineered microkeratomes and superior flap-making technologies may reduce the occurrence of flap complications, but it is unrealistic to expect them to disappear completely.6,7 At my laser center, we have incorporated the immediate-PRK concept into our informed consent process and documents.
William I. Bond, MD, is Director of Bond Eye Associates in Pekin, Illinois. He does not hold a financial interest in any of the companies or products mentioned herein. Dr. Bond may be reached at (309) 353-6660; bondeye@bondeye.com.1. Bond W. PRK over incomplete LASIK flap. J Refract Surg. 2000;16:483.
2. Jain V, Abell T, Bond W, Stevens G. Immediate transepithelial photorefractive keratectomy for treatment of laser in situ keratomileusis flap complications. J Refract Surg. 2002;18:109-112.
3. Wilson S. LASIK: Management of common complications. Laser in situ keratomileusis. Cornea. 1998;17:459-467. Review.
4. Talamo JH, Krueger RR. The Excimer Manual. A Clinician's Guide to Excimer Laser Surgery. Thorofare NJ: SLACK, Inc; 1997:10:232-240.
5. Wu H, Thompson V, Steinert R, Slade S, Hersh P. Refractive Surgery. New York, NY: Thieme; 1999:265-266,270,299.
6. Tham VM, Maloney RK. Microkeratome complications of laser in situ keratomileuis. Ophthalmology. 2000;107:920-924.
7. Gimbel H, Iskander N, Peters T, Penno E. Prevention and management of microkeratome-related laser in situ keratomileusis complications. J Refract Surg. 2000;16 (suppl):S226-S229.
