1: Invest Ophthalmol Vis Sci. 2006 Feb;47(2):599-604.

A femtosecond laser creates a stronger flap than a mechanical microkeratome.

Kim JY, Kim MJ, Kim TI, Choi HJ, Pak JH, Tchah H.

Department of Ophthalmology and Asan Institute for Life Sciences, University of
Ulsan College of Medicine, Asan Medical Center, Seoul, Korea.

PURPOSE: To compare corneal flaps made with a femtosecond (FS) laser with those
made with a mechanical microkeratome (MM) in rabbits, measuring early
postoperative inflammation and apoptosis and late postoperative adhesion
strength. METHODS: Study 1 involved four treatment groups: one with flaps made
only with the FS laser (FS group), one with flaps made with the FS laser followed
by excimer laser ablation (FS+LASIK), one with flaps made with the MM, and one
with flaps made with the MM followed by excimer laser ablation (MM+LASIK). The
eyes were analyzed by histology and TUNEL staining for apoptosis at 4 and 24
hours. Study 2 involved two reference groups: an FS group and an MM group.
Adhesion strength was measured with a tension meter 1 and 3 months later.
RESULTS: Study 1: Inflammatory cell infiltration in the central cornea was
significantly greater in the FS group than in the MM group at 4 and 24 hours (P <
0.05) and was significantly greater in the FS+LASIK group than in the MM+LASIK
group at 24 hours (P < 0.05). Infiltration at the peripheral interface was
significantly greater in the FS group than in the MM group and was significantly
greater in the FS+LASIK group than in the MM+LASIK group at 24 hours (P < 0.05).
Study 2: At 1 and 3 months, 126.7 and 191.3 grams of force (gf) were needed to
detach the flaps in the FS group, compared with 65 and 127.5 gf in the MM group,
respectively. The grams of force needed was significantly higher in the FS group
than in the MM group at 3 months (P < 0.05). CONCLUSIONS: The FS laser produces
greater corneal stromal inflammation than the MM early postoperatively without
any increase in apoptosis and stronger flap adhesion late postoperatively.
Therefore, it may require stronger anti-inflammatory drugs to be administered.

PMID: 16431956 [PubMed - indexed for MEDLINE]

1: J Cataract Refract Surg. 2006 Jun;32(6):1046-51.

Stability of the laser in situ keratomileusis corneal flap in rabbit eyes.

Laurent JM, Schallhorn SC, Spigelmire JR, Tanzer DJ.

U.S. Naval Hospital, Okinawa, Japan.

PURPOSE: To quantify the force required to dislodge a laser in situ
keratomileusis (LASIK) corneal flap in rabbits and correlate that force with
sources of injury to LASIK corneal flaps in humans. SETTING: Animal Vivarium and
Department of Ophthalmology, Naval Medical Center, San Diego, California, USA.
METHODS: Corneal flaps were cut in 56 eyes of 30 rabbits. A -8.00 diopter excimer
ablation was also performed in 32 of the eyes. Injury testing, using a burst of
CO2 from a modified paintball gun, was conducted from 1 to 9 days
postoperatively. Impact force was compared to that generated by mechanical trauma
(fingers and a small tree branch) striking a force gauge. RESULTS: Of 43 eyes
tested for injury, flaps could not be dislocated in 11 eyes (26%). There was no
significant difference between eyes treated with flap only and those that also
had ablation. When flaps were dislodged, the required force generally resulted in
extensive intraocular injury. There was no significant difference between the
force required for flap dislocation on postoperative days 1 and 9. CONCLUSIONS:
In rabbits, LASIK corneal flaps were very resistant to high-speed wind trauma as
early as 24 hours postoperatively. Flap stability was robust prior to the
formation of collagen scar tissue, probably due to epithelial bridging at the
edge of the flap and an osmotic gradient across the flap-stromal bed interface.
Although this study used a rabbit model, it seems likely that both these flap
adhesion mechanisms would also provide stability to the LASIK flap in humans.

PMID: 16814069 [PubMed - indexed for MEDLINE]

Untersuchung der kohäsiven Zugbelastbarkeit menschlicher LASIK Wunden mit histlogischen, ultrastrukturellen und klinischen Korrelationen

Ergebnis: Das menschliche Hornhautstroma heilt nach einer LASIK typischerweise in begrenzter und inkompletter Weise. Daraus resultiert eine schwache, zentral und parazentral zellarme primitive stromale Narbe die durchschnittlich nur 2.4 % der Stärke des normalen Hornhautstromas erreicht. Umgekehrt heilt der LASIK Flap Wundrand mit einer 10-fach stärkeren, peripher zellreichen bindegewebigen stromalen Narbe welche durchschnittlich 28.1 % der Stärke des normalen Hornhautstromas erreicht. Diese periphere Narbe des Wundrandes zeigt eine merkliche Variabilität.

Hier das Abstract:
1: J Refract Surg. 2005 Sep-Oct;21(5):433-45.

Cohesive tensile strength of human LASIK wounds with histologic, ultrastructural,
and clinical correlations.

Schmack I, Dawson DG, McCarey BE, Waring GO, Grossniklaus HE, Edelhauser HF.

Emory Eye Center, Emory University School of Medicine, Atlanta, GA 30322, USA.

PURPOSE: To measure the cohesive tensile strength of human LASIK corneal wounds.
METHODS: Twenty-five human eye bank corneas from 13 donors that had LASIK were
cut into 4-mm corneoscleral strips and dissected to expose the interface wound.
Using a motorized pulling device, the force required to separate the wound was
recorded. Intact and separated specimens were processed for light and electron
microscopy. Five normal human eye bank corneas from 5 donors served as controls.
A retrospective clinical study was done on 144 eyes that had LASIK flap-lift
retreatments, providing clinical correlation. RESULTS: The mean tensile strength
of the central and paracentral LASIK wounds showed minimal change in strength
over time after surgery, averaging 2.4% (0.72 +/- 0.33 g/mm) of controls (30.06
+/- 2.93 g/mm). In contrast, the mean peak tensile strength of the flap wound
margin gradually increased over time after surgery, reaching maximum values by
3.5 years when the average was 28.1% (8.46 +/- 4.56 g/mm) of controls. Histologic
and ultrastructural correlative studies found that the plane of separation always
occurred in the lamellar wound, which consisted of a hypocellular primitive
stromal scar centrally and paracentrally and a hypercellular fibrotic stromal
scar at the flap wound margin. The pathologic correlations demonstrated that the
strongest wound margin scars had no epithelial cell ingrowth-the strongest
typically being wider or more peripherally located. In contrast, the weakest
wound margin scars had epithelial cell ingrowth. The clinical series demonstrated
the ability to lift LASIK flaps without complications during retreatments up to
8.4 years after initial surgery, correlating well with the laboratory results.
CONCLUSIONS: The human comeal stroma typically heals after LASIK in a limited and
incomplete fashion; this results in a weak, central and paracentral hypocellular
primitive stromal scar that averages 2.4% as strong as normal comeal stroma.
Conversely, the LASIK flap wound margin heals by producing a 10-fold stronger,
peripheral hypercellular fibrotic stromal scar that averages 28.1% as strong as
normal comeal stromal, but displays marked variability.

Publication Types:
Research Support, N.I.H., Extramural
Research Support, Non-U.S. Gov't
Research Support, U.S. Gov't, P.H.S.

PMID: 16209440 [PubMed - indexed for MEDLINE]


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VG, Ron