ELIZABETH A. DAVIS, MD
The loose epithelium in both flaps and the buttonhole in the left eye suggest the presence of anterior basement membrane dystrophy (ABMD) that was either subclinical or overlooked. In ABMD, the aberrant basement membrane and abnormal hemidesmosomal attachments lead to loose epithelium that can be abraded readily by a microkeratome and even an applanation cone. The thickened basement membrane (seen as a small linear shadow) can interfere with the transmission of femtosecond laser energy and hence preclude the formation of a cleavage plane.
At this point in the surgery, the patient’s right eye can be treated with the excimer laser beneath the flap, and a bandage contact lens may be placed over the eye after the flap’s replacement. The surgeon must be vigilant, however, for the development of localized diffuse lamellar keratitis in the area of abraded epithelium as well as a greater risk for epithelial ingrowth there.
The patient’s left eye cannot be treated beneath the flap, because it cannot be lifted due to the buttonhole. The surgeon’s options are (1) to replace the flap, place a bandage lens, and later perform PRK or (2) to immediately proceed with PRK. In either case, I would recommend the adjunctive use of mitomycin C (MMC) at the end of the ablation. Again, because of the loose epithelium, diffuse lamellar keratitis and epithelial ingrowth are possible.
All patients seeking laser vision correction should be screened for ABMD. A history of recurrent corneal erosions or fluctuating vision can sometimes be elicited. Because ABMD can cause irregular astigmatism, the BCVA may be less than expected for what appears to be an otherwise healthy eye. Keratometry may display irregular mires, and irregular astigmatism may be present on corneal topography. The presence of ABMD on slit-lamp examination is best discerned with retroillumination and a widely dilated pupil. In this case, the cysts, dots, and fingerlike maps are readily visible. In severe ABMD, a phototherapeutic keratectomy should be performed first in order to treat the irregular astigmatism and obtain a reliable refraction, WaveScan (Abbott Medical Optics Inc.), and topography. After 3 to 6 months of stability, PRK could be performed. In mild cases where BCVA is not affected and irregularity is minimal, the surgeon can proceed directly to PRK.
CLAYTON FALKNOR, MD,
AND TERRY KIM, MD
A long-feared complication of LASIK is an abnormal flap (eg, a partial flap, a free cap, or a buttonhole). The literature contains many reports of such cases involving a mechanical microkeratome. As the use of a femtosecond laser to create the LASIK flap has become more popular, the incidence of abnormal flaps has decreased significantly; to our knowledge, there are no published reports of buttonhole flaps caused by a femtosecond laser. That is not to say, however, that no complications occur. Although rare, they include vertical gas breakthrough (subepithelial or transepithelial) with a loss of suction,1 air bubbles in the anterior chamber,2 macular hemorrhage,3 peripheral sterile corneal infiltrates,4 and transient light sensitivity syndrome.5
In the case presented, the linear shadow seen under the applanation plane likely represented an area of folded, loose epithelium. As a result, the femtosecond laser pulse was unable to penetrate to the appropriate stromal depth with the expected laser energy during the raster phase in the one isolated area. Dissection was therefore incomplete in the plane of the flap at the superonasal quadrant.
We recently had a similar case. After using the 60-Hz Intralase FS laser to create the LASIK flaps in both of a patient’s eyes, we noticed a 2.5 X 1.0-mm paracentral buttonhole in the second eye. The flap was not lifted and was allowed to heal. Several months later, we performed a transepithelial PRK using laser scraping, with the application of MMC 0.02%, in lieu of attempting to re-create the flap with the femtosecond laser. Three weeks after surgery, the patient was doing very well.
In 2003, Tekwani and Huang reported a 9.7% incidence of intraoperative epithelial defects in eyes undergoing LASIK using a Hansatome microkeratome (Bausch + Lomb, Rochester, NY).6 The risk factors were increased age, greater preoperative corneal thickness, treatment of the second eye, and maintenance of the suction ring’s vacuum during the microkeratome’s reverse pass. At the ASCRS convention this year, Andrew Holzman, MD, reported that “every 10 years’ increase in age is associated with a twofold increase in the risk of epithelial disruption.”7
The patient described in the case presented had none of the aforementioned findings. Given the loose epithelium in both eyes intraoperatively, however, we have to wonder if the slit-lamp examination might have revealed an epithelial basement membrane dystrophy. This finding might have steered the surgeon toward performing PRK instead of LASIK.
WILLIAM B. TRATTLER, MD
When speaking with patients about LASIK, I believe it is important to mention that, rarely, problems with the flap may require the completion of the procedure on a different day. In this case, where the flap cannot be lifted safely, I would replace it and advise the patient that we will need to return on another day to complete the surgery.
Approximately 6 weeks later, I would perform an alcohol-assisted surface ablation procedure with MMC 0.02% applied for 12 seconds. A few days prior to the treatment, I would have the patient return for a final examination to confirm refractive stability. My final target refraction for a 34-year-old is typically +0.30 D. An additional consideration is that, when using MMC intraoperatively, I have found that I need to reduce my treatment by 10%. In this case, I would therefore target plano and expect the patient’s postoperative refraction to be approximately +0.30 D.
Because the patient would undergo surface ablation rather than LASIK in her second eye, I would reset her expectations in regard to speed of visual recovery and postoperative discomfort. Overall, I would expect her to achieve a highly satisfactory visual result.
Editor’s note: this article discusses the off-label use of MMC.
Section editor Stephen Coleman, MD, is the director of Coleman Vision in Albuquerque, New Mexico. Parag A. Majmudar, MD, is an associate professor, Cornea Service, Rush University Medical Center, Chicago Cornea Consultants, Ltd. Karl G. Stonecipher, MD, is the director of refractive surgery at TLC in Greensboro, North Carolina. Dr. Majmudar may be reached at (847) 882-5900; email@example.com.
Clayton Falknor, MD, is a cornea and refractive surgery subspecialist at the Eye Clinic of Austin in Texas. He acknowledged no financial interest in the products or companies he mentioned. Dr. Falknor may be reached at (512) 427-1100; firstname.lastname@example.org.
Terry Kim, MD, is an associate professor of ophthalmology, cornea, and refractive surgery at the Duke Eye Center in Durham, North Carolina. He acknowledged no financial interest in the products or companies he mentioned. Dr. Kim may be reached at (919) 681- 3568; email@example.com.
William B. Trattler, MD, is the director of cornea at the Center for Excellence in Eye Care in Miami and the chief medical editor of Eyetube.net. Dr. Trattler may be reached at (305) 598-2020; firstname.lastname@example.org.
- Srinivasan S,Herzig S.Sub-epithelial gas breakthrough during femtosecond laser flap creation for LASIK.Br J Ophthalmol.2007;91(10):1373.
- Srinivasan S,Rootman DS.Anterior chamber gas bubble formation during femtosecond laser flap creation for LASIK.J Refract Surg.2007;23(8):828-830.
- Principe AH,Lin DY,Small KW,Aldave AJ.Macular hemorrhage after laser in situ keratomileusis (LASIK) with femtosecond laser flap creation.Am J Ophthalmol.2004;138(4):657-659.
- Lefshitz T,Levy J,Mahler O,Levinger S.Peripheral sterile corneal infiltrates after refractive surgery.J Cataract Refract Surg.2005;31(7):1392-1395.
- Muñoz G,Albarrán-Diego C,Sakla HF,et al.Transient light-sensitivity syndrome after laser in situ keratomileusis with the femtosecond laser incidence and prevention.J Cataract Refract Surg.2006;32(12):2075-2079.
- Tekwani NH,Huang D.Risk factors for intraoperative epithelial defect in laser in-situ keratomileusis.Am J Ophthalmol.2003;136(2):393-394.
- Holzman AE.Evaluation of preoperative hyperosmotics on risk for corneal epithelial disruption during femtosecond LASIK.Paper presented at:The ASCRS Symposium on Cataract,IOL and Refractive Surgery;April 11,2010;Boston,MA.