Debris under the flap after LASIK

Plastic particles at the LASIK interface
Ivarsen A, Thogersen J, Keiding SR, Hjortdal JO, Moller-Pedersen T. 2004
Ophthalmology. Jan;111(1):18-23.

PURPOSE: To investigate the origin, composition, and persistence of the interface particles that frequently are observed after LASIK.

DESIGN: Small case series and experimental animal study.

METHODS: Four patients received LASIK using a Schwind Supratome (Schwind, Kleinostheim, Germany) and a MEL 70 G-Scan excimer laser (Asclepion, Jena, Germany) and were examined over the course of 1 year using slit-lamp and in vivo confocal microscopy. Four rabbits received a monocular microkeratome incision and were examined immediately after surgery without lifting the flap. After monthly evaluation for 4 months using in vivo confocal microscopy, 2 corneas were processed for histologic analysis and were sectioned serially. To measure the iron content, atomic absorption spectrometry was performed on 2 operated and 2 unoperated rabbit corneas. The chemical composition of the metal and plastic parts of the microkeratome blade was identified using energy dispersive x-ray fluorescence (metal part), and Raman and infrared spectroscopy (plastic part). Before and after oscillation in air, the microkeratome blade and motor-head were examined using light and fluorescence microscopy. In serial sections, interface particles were identified by fluorescence microscopy and their chemical composition was determined using Coherent Antistokes Raman Scattering microscopy.

RESULTS: In LASIK patients, thousands of brightly reflecting particles (up to 30 micro m) were observed throughout the interface. The highest particle density was detected where the microkeratome blade had first entered the cornea. Both in the center and at the flap edge, the morphologic features, distribution, and density of these particles remained unaltered throughout the 1-year observation period. In rabbit corneas, interface particles were observed immediately after the microkeratome incision, even though the flap had not been lifted. These particles were similar to those observed in humans and persisted unaltered throughout the study. The operated and unoperated rabbit corneas had comparable iron content, demonstrating that the particles were not fragments of the uncoated steel blade. Only a few particles were observed on the unused microkeratome motor head and blade, whereas numerous fluorescent particles were detected after oscillation in air, the amount of particles increasing with oscillation time. Interestingly, the only fluorescent part of the microkeratome was the plastic segment of the blade. This plastic (polyetherimide) emitted fluorescence identical to that of the observed particles, whereas all metal parts of the microkeratome blade and motor head were nonfluorescent. In serial sections, interface particles showed fluorescent properties equivalent to polyetherimide and exhibited molecular resonance at 1780 and 3100 cm(-1), in accordance with the Raman spectrum of polyetherimide.

CONCLUSIONS: Numerous plastic particles are generated during microkeratome oscillation and are deposited at the interface during LASIK. The particles persist unaltered for at least 1 year.

Slitlamp, Specular, and Light Microscopic Findings of Human Donor Corneas After Laser-assisted In Situ Keratomileusis
V. Vinod Mootha, MD; Dan Dawson, MD; Amit Kumar, MD; Joel Gleiser, MD; Clifford Qualls, PhD; Daniel M. Albert, MD
Arch Ophthalmol. 2004;122:686-692.

Highly reflective particles were seen by specular microscopy in the stroma of 23 (88%) of 26 LASIK donor corneas

Conclusions: Detection of a flap edge by slitlamp examination may detect at least half of the donor corneas that may have undergone LASIK. The detection of highly reflective stromal particles may form an effective basis for screening for LASIK donor corneas using specular microscopy and requires further study.

Confocal microscopic evaluation of particles at the corneal flap interface after myopic laser in situ keratomileusis.
J Cataract Refract Surg. 2003 Jul;29(7):1373-7.
Perez-Gomez I, Efron N.

Department of Optometry and Neuroscience, UMIST, Manchester, United Kingdom. i.perez-gomez@umist.ac.uk

PURPOSE: To investigate the appearance and origin of interface particles in the cornea after myopic laser in situ keratomileusis (LASIK) using the confocal microscope.

SETTING: Department of Optometry and Neuroscience, UMIST, Manchester, United Kingdom.

METHODS: An in vivo slit-scanning, real-time confocal microscope (Tomey ConfoScan P4) fitted with an Achroplan(R) 40X/0.75 NA immersion objective (Zeiss) was used to examine the morphology of the central cornea in 6 patients (12 eyes) at the initial visit (before surgery) and 1 week and 1, 3, and 6 months after LASIK for myopia.

RESULTS: In all eyes, several interspersed particles of variable size and brightness were observed 1 week after surgery at the flap interface. The overall density of these particles decreased with time (F = 14.34, P =.01). For analysis, the particles were divided by density into high brightness and low brightness. The low-brightness particles significantly decreased with time (F = 13.26, P =.02). The high-brightness particles remained constant in density at all postoperative visits (F = 1.3, P =.15).

CONCLUSIOINS: The particles of low reflectivity may represent 1 or more types of remains. It is unclear whether the low-reflectivity particles will eventually disappear. The high-reflectivity particles may represent fine metallic debris arising from the mechanical drive mechanism and/or the disposable knife of the microkeratome. If they are metallic and magnetic, they could be cleared during surgery (immediately before flap replacement) using a specially adapted magnet.

Large interface particles from LASIK surgery.
Clin Exp Optom. 2006 Jul;89(4):253-6.
Eisemann J, Carkeet A, Swann PG.
School of Optometry, Queensland University of Technology, Brisbane, Queensland, Australia.

The presence of interface debris is commonly reported in patients having undergone LASIK refractive surgery. The patient described here had numerous large particles believed to be plastic and metal artefacts from the surgery at the level of the stroma/flap interface, along with a corneal scar consistent with a foreign body injury. The aetiology and possible sequelae of the particles and scar are discussed.

Ex vivo confocal microscopy of human LASIK corneas with histologic and ultrastructural correlation.
Ophthalmology. 2005 Apr;112(4):634-44.
Dawson DG, Holley GP, Geroski DH, Waring GO 3rd, Grossniklaus HE, Edelhauser HF.

"Clinical human studies that use in vivo confocal microscopy have demonstrated that the 2 most prevalent permanent findings in the central portion of LASIK corneas are interface particles (100% of cases) of variable size (≤25 μm2), number (20–683 particles per square millimeter), and reflectivity (low to high) and microfolds in Bowman's layer (92%–97% of cases)."

Corneal stromal changes induced by myopic LASIK.
Invest Ophthalmol Vis Sci. 2000 Feb;41(2):369-76.
Vesaluoma M, Perez-Santonja J, Petroll WM, Linna T, Alio J, Tervo T.
Department of Ophthalmology, Helsinki University Central Hospital, Finland. minna.vesaluoma@huch.fi

PURPOSE. Despite the rapidly growing popularity of laser in situ keratomileusis (LASIK) in correction of myopia, the tissue responses have not been thoroughly investigated. The aim was to characterize morphologic changes induced by myopic LASIK in human corneal stroma.

METHODS: Sixty-two myopic eyes were examined once at 3 days to 2 years after LASIK using in vivo confocal microscopy for measurement of flap thickness, keratocyte response zones, and objective grading of haze.

RESULTS: Confocal microscopy revealed corneal flap interface particles in 100% of eyes and microfolds at the Bowman's layer in 96.8%. The flaps were thinner (112 +/- 25 microm) than intended (160 microm). The keratocyte activation in the stromal bed was greatest on the third postoperative day. Patients with increased interface reflectivity due to abnormal extracellular matrix or activated keratocytes at > or = 1 month (n = 9) had significantly thinner flaps than patients with normal interface reflectivity (n = 18; 114 +/- 12 versus 132 +/- 22 microm, P = 0.027). After 6 months the mean density of the most anterior layer of flap keratocytes was decreased.

CONCLUSIONS: Keratocyte activation induced by LASIK was of short duration compared with that reported after photorefractive keratectomy. The flaps were thinner than expected, and microfolds and interface particles were common complications. The new findings such as increased interface reflectivity associated with thin flaps and the apparent loss of keratocytes in the most anterior flap 6 months to 2 years after surgery may have important clinical relevance.

Confocal Microscopy Comparison of IntraLase Femtosecond Laser and Moria M2 Microkeratome in LASIK
Journal of Refractive Surgery Vol. 23 No. 2 February 2007
Jaime Javaloy, MD, PhD; María T. Vidal, MD, PhD; Ayman M. Abdelrahman, MD, MSc; Alberto Artola, MD, PhD; Jorge L. Alió, MD, PhD

From the article:
A different etiology has been suggested for the particles that constantly appear at the interface in eyes operated by LASIK. We found a lower density of these particles at the interfaces of the eyes operated with the femtosecond laser as we expected perhaps due to the absence of a metallic blade and a smaller degree of manipulation of the anterior corneal stroma at this level. The progressive disappearance of the particles could be explained by their predominantly organic (non-metallic or plastic) nature. A qualitative analysis by confocal microscopy of corneas operated by LASIK using the IntraLase femtosecond laser was reported by Sonigo et al. The authors found particles at the interface of the operated eyes, supporting the idea that the nature of the particles seen after LASIK is not only metallic.

Confocal Microscopy Changes in Epithelial and Stromal Thickness up to 7 Years After LASIK and Photorefractive Keratectomy for Myopia
Journal of Refractive Surgery Vol. 23 No. 4 April 2007
Sanjay V. Patel, MD; Jay C. Erie, MD; Jay W. McLaren, PhD; William M. Bourne, MD

From the article:
Profiles generated from corneas after LASIK also showed a peak corresponding to the lamellar interface, and this typically was confirmed by the presence of interface debris in the corresponding video image.

Particles at the laser in situ keratomileusis flap interface
Volume 30, Issue 9, Page 2021 (September 2004)
J Cataract Refract Surg
Inma Perez-Gomez, MSc, PhD, Ian Cameron, BSc (Hons), Nathan Efron, PhD, DSc

From the article:
In a recent issue, we reported the presence of particles at the corneal flap interface following myopic laser in situ keratomileusis (LASIK) up to 6 months postoperatively.1 We report here observations in 4 patients (8 eyes) between 3 and 4 years after LASIK. The materials and methods in the present study were similar to those in the previous paper except the present observations were made with the newer ConfoScan 3 Corneal Confocal Microscope (Nidek Technologies).

The results in this study show that some particles of low reflectivity (PLR) are seen up to 4 years after LASIK and the density of these PLR is comparable to that of particles of high reflectivity. In our original paper, we presumed that PLR, which had significantly decreased 6 months after LASIK and were thought to have degraded, were of cellular origin.1 It now appears some PLR remain in the cornea long term. Since the particles are of low reflectivity, it is unlikely they are metallic; however, since they are permanent, they may be composed of some nondegradable substance.

It is possible that these nondegradable PLR are metallic but for some reason show low reflectivity. Perhaps these particles reflect light diffusely rather than specularly because of surface roughness. The density of PLR seen in this study is much higher than that reported in similar studies. This may be from the apparently superior resolution and image-capture characteristics of the ConfoScan 3, which was released at the end of 2002. Previous studies1, 2, 3 were performed using earlier generation instruments.

The long-term effects of these particles are not known; undetected subclinical changes in corneal structure/function may be occurring. However, since the particles have been present since 1999 without obvious clinical repercussions in our patients, it would seem they are relatively inert. Although the particles are of metallic origin, siderosis or a similar response is not possible since the metal is surgical steel and, as such, is inert.

Since the particles observed in this report have remained in the stroma for at least 3 years, they may represent a nondegradable material such as metal or plastic. Based on energy dispersive X-ray fluorescence and infrared and Raman spectroscopy of particles retrieved from rabbit eyes after LASIK using a Schwind Supratome and MEL 70 excimer laser (different instruments than those used in our studies), Ivarsen et al.4 suggest that the particles are plastic. Like us, these authors postulate that the particles are generated during microkeratome oscillation. Notwithstanding their apparently benign clinical presentation, it would seem prudent to strive to minimize or, preferably, eliminate the formation of these particles during LASIK.