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Comparing Endothelial Cell Density after Sub-Bowman’s Keratomileusis and Photorefractive Keratectomy for the Treatment o

Comparing Endothelial Cell Density after Sub-Bowman’s Keratomileusis and Photorefractive Keratectomy for the Treatment of Myopia . Ryan T. Smith, MD Daniel S. Durrie, MD George O. Waring IV, MD Priscilla Thomas, MS

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Comparing Endothelial Cell Density after Sub-Bowman’s Keratomileusis and Photorefractive Keratectomy for the Treatment o

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  1. Comparing Endothelial Cell Density after Sub-Bowman’s Keratomileusis and Photorefractive Keratectomy for the Treatment of Myopia Ryan T. Smith, MD Daniel S. Durrie, MD George O. Waring IV, MD Priscilla Thomas, MS Financial Disclosure: Dr. Smith, Dr. Waring and Ms. Thomas have no financial interest in the material presented. Dr. Durrie is a consultant for AMO and Alcon Labs.

  2. Purpose To compare the effect of Sub-Bowman’s Keratomileusis (SBK) and Photorefractive Keratectomy (PRK) on postoperative endothelial cell density (ECD).

  3. Background • 193-nm excimer laser is totally absorbed at the site of exposure and penetrate less than a diameter of a cell. • Theories for endothelial cell damage • Mechanical trauma from shock waves, thermal effects, actinic effects, and metabolic changes • Most human studies show that PRK and LASIK does not effect corneal endothelial cell densities • SBK uses a femtosecond laser to create a thin (90-110µm) corneal flap • Effects of SBK on the corneal endothelium has yet to be reported • Collins M, Carr J. Effects of Laser In Situ Keratomileusis (LASIK) on the Corneal Endothelium 3 Years Postoperatively. Am J Ophthalmol. 2001 Jan;131(1):1-6 • Simaroj P, Kosalprapai K. Effect of Laser in situ Keratomileusis on the Corneal Endothelium. J Refract Surg. 2003 Mar-Apr;19(2 Suppl):S237-40 • Perez-Santonja J, Sakla H. Evaluation of Endothelial Cell Changes 1 Year After Excimer Laser In Situ Keratomileusis. Arch Ophthalmol. 1997 Jul;115(7):841-6. • Nassiri N, Farahangiz S. Corneal endothelial cell injury induced by mitomycin-C in photorefractive keratectomy: Nonrandomized controlled trial. J Cataratc Refract Surg. 2008 Jun;34(6):902-8 • Diakonis V, Pallikaris A. Alterations in Endothelial Cell Density After Photorefractive Keratectomy With Adjuvant Mitomycin. Am J Ophthalmol. 2007 Jul;144(1):99-103. Epub 2007 May 23. • Durrie D, Slade S. Wavefront-guided excimer laser ablation using photorefractive keratectimy and sub-bowman’s keratomileusis: a contralateral eye study. J Refract Surg. 2008;24:S77-S84.

  4. Methods • Fifty eyes of twenty-five patients were compared in a prospective, randomized contralateral, single center study to compare the effects of SBK and PRK on ECD at one and three months postoperatively • SBK • IntraLase (AMO, Santa Ana CA): 8.5mm diameter, raster pattern, superior hinge • Flap thickness = 100µm • PRK • 8.5mm Trephine • 20% Ethanol for 25 sec • Chilled with balanced salt solution • All eyes treated with Custom LADARVision 4000 (Alcon Labs, Ft. Worth TX) excimer laser • PRK eyes were not treated with an antimetabolite such as mytomycin-C • Endothelial cell densities was measured using Nidek Confocal 4 at preop, one, and three months

  5. Results • SBK: The average was 2995±325 which decreased to 2977±358 at one month (p=0.5756) and to 2931±369 at three months (p=0.4106) • PRK: The average ECD was 3011±329 which decreased to 2951±327 at one month (p=0.5736), and to 2982±365 at three months (p=0.6513)

  6. Discussion • Both PRK and LASIK have been shown to be predictable and effective for the correction of refractive errors • This is the first contralateral study evaluating and comparing the effect PRK and SBK have on the corneal ECD. • SBK was designed to be a hybrid procedure between PRK and LASIK by lessening the biomechanical impact of LASIK while preserving the quick visual recovery • Experimental studies have shown endothelial cell damage with ablation depth within 40µm of Descemet’s membrane or ablation of 90% of the stroma • The vast majority of studies agree that routine LASIK/PRK ablation depth do not cause endothelial cell damage • With thinner flaps, ablation depth is reduced offering more endothelial protection when compared to standard LASIK. • Our results suggest that SBK does not damage the corneal endothelium and has post operative ECD nearly identical to PRK Durrie D, Slade S. Wavefront-guided excimer laser ablation using photorefractive keratectimy and sub-bowman’s keratomileusis: a contralateral eye study. J Refract Surg. 2008;24:S77-S84. Collins M, Carr J. Effects of Laser In Situ Keratomileusis (LASIK) on the Corneal Endothelium 3 Years Postoperatively. Am J Ophthalmol. 2001 Jan;131(1):1-6. Simaroj P, Kosalprapai K. Effect of Laser in situ Keratomileusis on the Corneal Endothelium. J Refract Surg. 2003 Mar-Apr;19(2 Suppl):S237-40 . Perez-Santonja J, Sakla H. Evaluation of Endothelial Cell Changes 1 Year After Excimer Laser In Situ Keratomileusis. Arch Ophthalmol. 1997 Jul;115(7):841-6. Jones S, Azar R. Effects of Laser in Situ Keratomileusis (LASIK) on the Corneal Endothelium. Am J Ophthalmol. 1998 Apr;125(4):465-71.

  7. Study Limitations Relatively short follow up period Lack of endothelial cell morphology analysis (coefficient of variation and percentage of hexagonal cells)

  8. Conclusions • There is no statistically significant change in the ECD following SBK or PRK at 3 months • Additionally, no statistically significant difference was found between the effect of SBK and PRK in the postoperative ECD • Future studies with longer follow up and more detailed endothelial analysis are needed to confirm these early conclusions.

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