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Michael A. Page, David L. Davis-Boozer, Jeff Holiman, Winston Chamberlain; Femtosecond Laser Assisted Keratoplasty: Wound Burst Pressure and Effects on Endothelium. Invest. Ophthalmol. Vis. Sci. 2011;52(14):3378.
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To evaluate wound strength properties and effects on corneal endothelium when partial- and full-thickness femtosecond laser-assisted keratoplasty (FLAK) wounds are made in cadaveric corneas.
18 cadaveric human corneoscleral rims were mounted on an anterior chamber maintainer and cut with the femtosecond laser programmed to one of six possible wound patterns. 3 corneas each were assigned to one of the following 6 groups: A1 (full-thickness "zig-zag"), A2 (partial-thickness "zig-zag" with intact posterior 70uM tissue bridge), B1 (full "mushroom"), B2 (partial "mushroom"), C1 (full "top hat"), and C2 (partial "top hat"). The intracameral pressure required to produce leakage from the corneal wound was then measured in each case. In a separate experiment, 6 cadaveric corneas were cut with the "zig-zag" pattern: 3 full-thickness wounds and 3 partial-thickness wounds with the same 70uM posterior bridge. The full-thickness corneal buttons were floated in optisol and shipped to a remote site per eye bank protocol for tissue distribution of pre-cut donor FLAK tissue. The buttons were then returned and analyzed for endothelial cell loss with vital dye staining and digital image analysis. The partially-cut corneas were analyzed for endothelial cell loss from laser effect alone.
Mean leakage pressure in mm Hg for group A1 was 110 (SD 94); group A2, 1180 (SD 468); group B1, 978 (SD 445); group B2, 987 (SD 576); group C1, 710 (SD 474); group C2, 1290 (SD 231). There was a borderline statistically significant difference in leakage pressure between groups A1 and A2, p=0.05; between group A1 and B1 (p=0.05), and between group A1 and C1 (p=0.05). Mean endothelial cell loss in the three full-thickness FLAK buttons that underwent shipping in optisol was 17.25% (SD 3.65). Mean cell loss in the partial thickness FLAK incision group was 8.48% (SD 4.99, p=0.05) for the full limbus-to-limbus area, and 5.87% (SD 4.60, p=0.05) for the central 8mm.
Partial-thickness FLAK wounds with a 70uM posterior tissue bridge demonstrate excellent resistance to rupture by direct intracameral pressurization, for a variety of programmed wound patterns. Full-thickness "mushroom" and "top hat" wounds demonstrate surprising burst resistance. Full-thickness laser trephination and current eye bank handling protocol for donor FLAK buttons leads to moderate peripheral endothelial cell loss in donor tissue. Partial-thickness FLAK incisions down to -70uM produce a ring effect of mild to moderate endothelial cell loss, corresponding spatially with the laser pattern.
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