Online optical coherence pachymetry to evaluate intraoperative ablation parameters in LASIK

Abstract

Online OCP allowed a clinical evaluation of intraoperative ablation parameters in LASIK. Further studies are needed to assess a possible active control of the excimer laser ablation from these continuous values, which could possibly improve current ablation nomograms.

Online optical coherence pachymetry as a safety measure for laser in situ keratomileusis treatment in 1859 cases

“…7,10,15,18,34,35 Therefore, the noncontact option of OCPonline technology offers practical advantages over ultrasound and has been successfully used for intraoperative pachymetry in the first clinical series by others. 8,[17][18][19][20] In this study, we also measured the reduction in stromal thickness during the ablation process. The true reduction is difficult to measure, and few reports of this are available.…”

“…17,18,20 In short, the device uses 1310 nm wavelength light waves, which allows noncontact measurements. For measurement, the eye is illuminated with low coherent light of a super-luminescence diode.…”

“…9,16,17 Optical coherence tomography (OCT), a noncontact method of measuring corneal thickness, has also been used for intraoperative pachymetry during corneal refractive surgery in small clinical series. 8,[17][18][19][20] Bausch & Lomb recently incorporated an online optical coherence pachymetry (OCP) device (OCPonline, Heidelberg Engineering GmbH) into the 217z100 excimer laser system for pachymetry measurements during LASIK. The purpose of this retrospective interventional case series was to evaluate the role of this new device in improving safety in LASIK procedures.…”

Changes in the refractive index of the human corneal stroma during laser in situ keratomileusis

“…[32][33][34] Furthermore, when online optical coherence pachymetry was used to monitor central corneal thickness during hyperopic LASIK, the central corneal thickness reduced at a rate of 0.27 mm/sec. 7 This change in thickness was observed in a region precluded from photoablation and as such represents the rate of stromal dehydration that is expected during LASIK. By coupling the Fatt and Harris equation with the thickness-hydration relationships for the human cornea and incorporating this rate of change in stromal thickness as 0.27 mm/sec, one could predict an increase in the stromal refractive index of 0.003 after 120 seconds of exposure.…”

“…Water can be lost by passive evaporation, which is possibly accelerated by the photoablative process, leading to a decrease in corneal hydration. [1][2][3][4][5][6][7] The hydration of the corneal stroma has an inverse relationship to the refractive index. [8][9][10][11][12][13][14] To our knowledge, this was first proposed by Maurice,8 who used the Gladstone-Dale law 15 to show that corneal refractive index depends on the cornea's water content.…”