Journal of Cataract & Refractive Surgery
Volume 34, Issue 1 , Pages 28-31, January 2008

Incidence of diffuse lamellar keratitis after laser in situ keratomileusis associated with the IntraLase 15 kHz femtosecond laser and Moria M2 microkeratome

From Vissum Madrid (Gil-Cazorla, Teus, de Benito-Llopis, Fuentes), E.U. Óptica Universidad Complutense de Madrid (Gil-Cazorla), and Universidad de Alcalá (Teus), Madrid, Spain

Accepted 6 August 2007.

Article Outline

Purpose

To analyze the incidence of diffuse lamellar keratitis (DLK) after laser in situ keratomileusis (LASIK) performed with an IntraLase 15 kHz femtosecond laser (IntraLase, Corp.) or a Moria M2 mechanical microkeratome (Moria SA).

Setting

Vissum Madrid, Madrid, Spain.

Methods

This retrospective study compared the incidence of DLK in consecutive LASIK procedures performed with the IntraLase 15 kHz femtosecond laser (study group) or the Moria M2 microkeratome (control group). Two surgeons performed both types of surgeries (femtosecond laser and microkeratome) using the same excimer laser (Technolas 217, Bausch & Lomb). During the first week postoperatively, topical dexamethasone drops were applied 8 times daily in the femtosecond group and 4 times daily in the mechanical microkeratome group.

Results

A total of 2000 consecutive eyes were analyzed (1000 eyes in each group). Diffuse lamellar keratitis stage 2 developed in 1 patient in each group; DLK stage 3 developed in 4 patients in the study group and in no patient in the control group (P = .03).

Conclusion

Despite more intense postoperative steroid treatment, DLK seemed to occur more frequently after LASIK performed with the IntraLase 15 kHz femtosecond laser than after LASIK performed with the Moria M2 microkeratome.

 

Diffuse lamellar keratitis (DLK), also known as sands of Sahara syndrome or interface keratitis, is a noninfectious condition in which white blood cells infiltrate the space between the flap and the stromal bed shortly after laser in situ keratomileusis (LASIK).1 This complication can also appear months or even years after LASIK associated with trauma,2, 3 epithelial abrasions,4, 5, 6, 7, 8 or iritis.9 Diffuse lamellar keratitis is typically associated with moderate foreign-body sensation and decreased visual acuity, and it usually resolves without sequelae with appropriate treatment.

Since Smith and Maloney1 first described DLK in 1998, additional sporadic and epidemic cases of DLK have been reported.10 The etiology of DLK is most likely multifactorial. The possible causes of DLK include povidone–iodine solutions,1 meibomian gland secretions,11 hemoglobin,12 microkeratome oil,13 carboxymethylcellulose drops,14 bacterial endotoxins,15, 16, 17 and epithelial defects at the time of surgery.4, 5, 8, 18

The IntraLase femtosecond laser (IntraLase Corp.) is a relatively new device for lamellar corneal cutting that delivers thousands of microphotodisruptive pulses focused on a precise plane of the cornea to obtain a smooth cut and create a stromal flap with parallel anterior and posterior surfaces.19

The development of DLK after LASIK performed with a mechanical microkeratome is well recognized and reported in the literature.18, 20, 21 In contrast, the incidence of DLK after LASIK performed with the IntraLase femtosecond laser has been reported in only 2 pilot studies,22, 23 in which the incidence of DLK was 19.4%22 and 17%.23 Thus, we designed a study to compare the incidences of DLK after LASIK performed with the IntraLase 15 kHz femtosecond laser and after LASIK performed with the Moria M2 microkeratome (Moria SA).

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Patients and methods 

The medical records of the first 1000 consecutive eyes that had LASIK performed with the IntraLase 15 kHz femtosecond laser and the last consecutive 1000 eyes that had LASIK performed with the Moria M2 microkeratome at Vissum Madrid were retrospectively reviewed. All procedures were performed in 2006. When evaluated for surgery, patients were excluded for unstable refraction, previous ocular surgery (refractive or other surgical procedures), suspicion of keratoconus, ocular disease, and systemic disease that could alter the wound-healing process such as diabetes and connective tissue disorders. The decision to use the femtosecond laser instead of the mechanical microkeratome was based on keratometry that was too high or too low to allow a safe LASIK procedure with the mechanical microkeratome or on patient preferences after the patient was fully informed about the advantages and disadvantages of both methods. All patients signed an informed consent before the surgery.

In all cases, a full ophthalmologic examination was performed preoperatively. It included measurement of uncorrected visual acuity (UCVA); best spectacle-corrected visual acuity (BSCVA), including manifest and cycloplegic refractions; keratometry and corneal topography (EyeSys, EyeSys Premier); ultrasound pachymetry (DGH 5100, Technology Inc.); slitlamp biomicroscopy; mesopic pupil measurement (Colvard pupillometer, Oasis Medical Inc.); tonometry; and fundoscopy.

Surgical Technique 

All IntraLase 15 kHz femtosecond laser and M2 microkeratome LASIK procedures were performed by 1 of 2 surgeons (MAT, LBL); both surgeons performed both types of surgeries using the same excimer laser (Technolas 217, Bausch & Lomb).

A 5% povidone–iodine solution was applied to the skin and conjunctiva, and a sterile surgical drape and a rigid eyelid speculum were positioned. Surgery was performed using topical anesthesia of lidocaine 2%; 2 drops were applied with a 5-minute interval between drops.

In the mechanical microkeratome group, all cutting heads were used according to the manufacturer's nomogram. The same cut parameters and the same blade were used for the second eye unless a flap complication occurred in the first eye.

The femtosecond laser had 15 kHz software with the following parameters: a raster pattern using an energy level of 1.70 mJ, a side-cut energy of 1.90 mJ, a 60-degree side cut (following the manufacturer's instructions), and an attempted flap depth of 120 μm. The laser was programmed to achieve a hinge length of 50 degrees, corresponding to a hinge length of 3.8 mm, and a flap diameter of 9.0 mm.

In both groups, once the flap was created with either method, it was raised with a spatula. The stromal bed was dried with a sponge, and the eye tracker was placed in the center of the pupil. After ablation with the Technolas 217C excimer laser, the stroma was washed with 3 mL balanced salt solution (BSS) and the flap was gently put back in place with a cannula. Ofloxacin 3 mg/mL and ketorolac tromethamine 5 mg/mL were applied.

Postoperative Follow-up 

Postoperatively, all patients used preservative-free artificial tears as needed and were instructed to apply ofloxacin 3 mg/mL drops 4 times daily for 1 week. Dexamethasone 1 mg/mL drops were used 4 times daily in the mechanical microkeratome group and 8 times daily in the femtosecond laser group during the first postoperative week. The difference in treatment between groups was based on the expected higher risk for DLK after femtosecond laser surgery reported in the literature.22

Routine clinical examinations were performed 1 day, 1 week, and 1 and 3 months postoperatively and included measurement of UCVA and slitlamp biomicroscopy. At the last examination, measurement of the BSCVA, manifest and cycloplegic refractions, corneal topography, and ultrasound pachymetry were also performed.

The occurrence and severity of DLK was recorded according to the DLK classification system of Linebarger et al.,24 the most widely accepted grading classification. In this classification system, stage 1 DLK begins with a faint sterile infiltration of inflammatory cells at the flap edge within the interface that commonly progresses to a more central and diffuse pattern (stage 2) (Figure 1). If the inflammation worsens, aggregation of the inflammatory cells within the visual axis can occur, often associated with a subjective decline in visual quality (stage 3). In rare instances, collagenase release and stromal melting with subsequent loss of BSCVA can develop (stage 4).

A standardized protocol is used if DLK stage 2 or greater is diagnosed. Patients are followed every 24 hours until the DLK begins to regress. Once regression is observed, follow-up is performed weekly until the DLK resolves. Patients with a stage 2 DLK are instructed to increase the frequency of application of topical steroids (prednisolone acetate 10 mg/mL) to every 1 to 2 hours. If the DLK progresses to stage 3, oral prednisone is prescribed at a dose ranging from 40 to 80 mg a day, depending on the patient's weight. Oral prednisone is reduced to 20 to 30 mg/day once regression of the DLK is detected. Then, topical and oral corticosteroids are slowly tapered depending on the clinical response. If topical and oral corticoid treatment fails to control the DLK, the flap is lifted and the interface copiously rinsed with BSS.

Statistical Analysis 

Statistical analysis was performed using Statview SE+Graphics (Abacus Concepts, Inc.) software on a Macintosh PowerBook 1,400 cs/117 (Apple Computer, Inc.) personal computer. The chi-square test was used for comparisons between groups. A P value of 0.05 or less was considered statistically significant.

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Results 

Of the 2000 consecutive eyes evaluated, 1000 had LASIK with the IntraLase 15 kHz femtosecond laser and 1000 with the Moria M2 microkeratome. The mean patient age was 31 years ± 6 (SD) in both groups.

One eye (0.1%) in the IntraLase group and 1 eye (0.1%) in the mechanical microkeratome group developed DLK stage 2. Four eyes (0.4%) in the IntraLase group and no eye in the Moria M2 microkeratome group developed stage 3 DLK. No eye required flap lifting and interface irrigation. All cases had uneventful surgery without sharing an apparent predisposing factor (eg, sex, surgeon, age). All DLK cases resolved without serious corneal scarring or other sequelae.

The overall incidence of significant DLK was 0.5% in the IntraLase group and 0.1% in the Moria M2 microkeratome group (P = .03).

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Discussion 

In our study, we found a higher incidence of DLK in the femtosecond laser group than in the mechanical microkeratome group despite a more frequent postoperative topical corticoid regimen in the femtosecond laser group. Nevertheless, the incidence of the complication was low and led to no significant visual loss.

Diffuse lamellar keratitis has been described as a serious sight-threatening condition requiring aggressive treatment to prevent the development of permanent visual sequelae due to stromal tissue loss, corneal scarring, irregular astigmatism, hyperopic shift, and loss of BSCVA.24

Numerous cases of DLK after LASIK using mechanical microkeratomes have been reported in the literature.18, 20, 21 Our results show a lower incidence of DLK after LASIK performed with an automated microkeratome than the incidence reported in previously published retrospective reviews. A 4% incidence of DLK was reported in an analysis of 1000 consecutive LASIK procedures performed at a private eye clinic in Eugene, Oregon,18 while a review of 2711 LASIK procedures performed over a 3-year period (September 1996 to September 1999) at a university-affiliated center in Boston reported a 1.3% incidence of DLK.20 Bigham et al.21 reviewed 72360 LASIK procedures performed from 2000 to 2002 and found an incidence of 0.67%. The lower DLK incidence in the current study represents an actual lower incidence rate that may be the result of better sterilization and instrument cleaning or a more meticulous surgical protocol.

To our knowledge, only 2 previous studies have reported the incidence of DLK after LASIK performed with the IntraLase femtosecond laser. Binder22 reported moderate DLK in the first 20 eyes in a series of 103 eyes operated on with the IntraLase 6 kHz femtosecond laser (19.4%). Javaloy et al.23 found mild to moderate DLK (stages 1 to 3) in 17 of 100 eyes (17%) using a 15 kHz femtosecond laser. The lower incidence of DLK in the IntraLase group in the current study may be explained by the more intense antiinflammatory therapy (8 times daily in the femtosecond group instead of 4 times daily) during the first postoperative week.

In the current study, all procedures were performed in the same operating room after the same sterilization method and by the same surgeons, which suggests the increased incidence of DLK in procedures performed with the IntraLase femtosecond laser compared with the Moria M2 mechanical microkeratome was due to the different technology used to cut the flap. The higher incidence of DLK associated with the femtosecond laser could have resulted from gas accumulation, more antigenic material present in the interface of these eyes, or a more easily infiltrated space under the flap. These factors might stimulate mild inflammatory responses in individuals more susceptible to developing DLK and might explain the higher incidence of DLK in the study group.

In the 2 studies reporting the incidence of DLK after IntraLase surgery,22, 23 the authors suggest that a decrease in the energy parameters for cutting the flap seemed to reduce the incidence of postoperative DLK. The new software (30 and 60 kHz) of the femtosecond laser not only allows for much faster treatment, it also permits decreasing the energy use for cutting the flap. No study has reported the incidence of DLK after the use of these new versions of the IntraLase femtosecond laser.

In conclusion, DLK seems to appear more frequently after LASIK performed with the IntraLase femtosecond laser than after LASIK performed with the Moria M2 mechanical microkeratome. More studies are needed to elucidate the possible causes of the increased incidence of DLK with the IntraLase femtosecond laser and to determine whether the use of the new versions (30 and 60 kHz software) decrease the incidence of DLK after this procedure.

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References 

  1. Smith RJ, Maloney RK. Diffuse lamellar keratitis; a new syndrome in lamellar refractive surgery. Ophthalmology. 1998;105:1721–1726
  2. Schwartz GS, Park DH, Schloff S, Lane SS. Traumatic flap displacement and subsequent diffuse lamellar keratitis after laser in situ keratomileusis. J Cataract Refract Surg. 2001;27:781–783
  3. Weisenthal RW. Diffuse lamellar keratitis induced by trauma 6 months after laser in situ keratomileusis. J Refract Surg. 2000;16:749–751
  4. Haw WW, Manche EE. Late onset diffuse lamellar keratitis associated with an epithelial defect in six eyes. J Refract Surg. 2000;16:744–748
  5. Shah MN, Misra M, Wilhelmus KR, Koch DD. Diffuse lamellar keratitis associated with epithelial defects after laser in situ keratomileusis. J Cataract Refract Surg. 2000;26:1312–1318
  6. Chang-Godinich A, Steinert RF, Wu HK. Late occurrence of diffuse lamellar keratitis after laser in situ keratomileusis. Arch Ophthalmol. 2001;119:1074–1076
  7. Yeoh J, Moshegov CN. Delayed diffuse lamellar keratitis after laser in situ keratomileusis. Clin Exp Ophthalmol. 2001;29:435–437
  8. Harrison DA, Periman LM. Diffuse lamellar keratitis associated with recurrent corneal erosions after laser in situ keratomileusis. J Refract Surg. 2001;17:463–465
  9. Keszei VA. Diffuse lamellar keratitis associated with iritis 10 months after laser in situ keratomileusis. J Cataract Refract Surg. 2001;27:1126–1127
  10. Wilson SE, Ambrósio R. Sporadic diffuse lamellar keratitis (DLK) after LASIK. Cornea. 2002;21:560–563
  11. Fogla R, Rao SK, Padmanabhan P. Diffuse lamellar keratitis: are meibomian glands responsible?. [letter] J Cataract Refract Surg. 2001;27:493–495
  12. MacRae S, Macaluso DC, Rich LF. Sterile interface keratitis associated with micropannnus hemorrhage after laser in situ keratomileusis. J Cataract Refract Surg. 1999;25:1679–1681
  13. Kaufman SC, Maitchouk D, Chiou AGY, Beuerman RW. Interface inflammation after laser in situ keratomileusis; sands of the Sahara syndrome. J Cataract Refract Surg. 1998;24:1589–1593
  14. Samuel MA, Kaufman SA, Ahee JA, et al. Diffuse lamellar keratitis associated with carboxymethylcellulose sodium 1% after laser in situ keratomileusis. J Cataract Refract Surg. 2002;28:1409–1411
  15. Holland SP, Mathias RG, Morck DW, et al. Diffuse lamellar keratitis related to endotoxins released from sterilizer reservoir biofilms. Ophthalmology. 2000;107:1227–1233discussion by EJ Holland, 1233–1234
  16. Peters NT, Iskander NG, Anderson Penno EE, et al. Diffuse lamellar keratitis: isolation of endotoxin and demonstration of the inflammatory potential in a rabbit laser in situ keratomileusis model. J Cataract Refract Surg. 2001;27:917–923
  17. Yuhan KR, Nguyen L. Boxer Wachler BS. Role of instrument cleaning and maintenance in the development of diffuse lamellar keratitis. Ophthalmology. 2002;109:400–403discussion by SN Rao, RJ Epstein, 403–404
  18. Johnson JD, Harissi-Dagher M, Pineda R, et al. Diffuse lamellar keratitis: incidence, associations, outcomes, and a new classification system. J Cataract Refract Surg. 2001;27:1560–1566
  19. Ratkay-Traub I, Ferincz IE, Juhasz T, et al. First clinical results with the femtosecond neodynium-glass laser in refractive surgery. J Refract Surg. 2003;19:94–103
  20. Melki SA, Azar DT. LASIK complications: etiology, management, and prevention. Surv Ophthalmol. 2001;46:95–116
  21. Bigham M, Enns CL, Holland SP, et al. Diffuse lamellar keratitis complicating laser in situ keratomileusis; post-marketing surveillance of an emerging disease in British Columbia, Canada, 2000–2002. J Cataract Refract Surg. 2005;31:2340–2344
  22. Binder PS. Flap dimensions created with the IntraLase FS laser. J Cataract Refract Surg. 2004;30:26–32
  23. Javaloy J, Vidal MT, Abdelrahman AM, et al. Confocal microscopy comparison of IntraLase femtosecond laser and Moria M2 microkeratome in LASIK. J Refract Surg. 2007;23:178–187
  24. Linebarger EJ, Hardten DR, Lindstrom RL. Diffuse lamellar keratitis: diagnosis and management. J Cataract Refract Surg. 2000;26:1072–1077
biography

First author

Raquel Gil-Cazorla, DOO

Vissum Madrid and E.U. Óptica Universidad Complutense de Madrid, Madrid, Spain

 No author has a financial or proprietary interest in any material or method mentioned.

PII: S0886-3350(07)01678-1

doi:10.1016/j.jcrs.2007.08.025

Journal of Cataract & Refractive Surgery
Volume 34, Issue 1 , Pages 28-31, January 2008

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