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The postoperative refractive error after otherwise successful perforating keratoplasty (PK), often negatively influents the visual acuity.The authors refer about the results of postoperative ametropia correction by means of the LASIK method. There were 43 eyes of 38 patients in the study group. In 41 eyes, there was myopia with myopic astigmatism, and in two eyes, the hyperopia with hyperopic astigmatism were present. The average age of the group was 35.6 +/- 10.5 years (24-87 years), and the follow-up period was 27.4 +/- 22.9 months (maximum, 95 months). The average spherical refractive error before the LASIK procedure was -2.67 +/- 3.66 D, and preoperative subjective astigmatism -5.14 +/- 2.81 Dcyl. The average astigmatism established by means of corneal topography was 5.16 +/- 2.45. Dcyl. LASIK was performed during one session using the excimer laser Keracor 117 (Chiron) or Technolas 217 (Bausch & Lomb). For the lamellar keratectomy the authors used the mechanical LKS (Moria) and the automatic ACS keratome (Chiron). For the corneal topography examination, the ORBSCAN II (Bausch & Lomb) machine was used. The authors evaluated 1) the development of the postoperative refraction, 2) the change of the axis of the astigmatism induced by LASIK, 3) the development of the uncorrected visual acuity (UCVA), 4) the final uncorrected and best-corrected visual acuity (UCVA and BCVA), 5) the change of the endothelial cells' density after LASIK, and 6) the occurrence of per- and postoperative complications. At the last postoperative control, the average of the spherical refractive error was -0.17 +/- 1.01 D, subjective astigmatism was -1.58 +/- 2.03 Dcyl, and topographical astigmatism was 3.62 +/- 2.06 Dcyl (t-test, p < or = 0.001). We reduced the spherical refractive error by 93.6%, subjective astigmatism by 69.3%, and topographical astigmatism by 29.8% only. In 14 eyes (32.6%) the change of the axis was recorded--so called surgically induced astigmatism--the average value was 30.8 +/- 19.8 degrees (t-test, p > or = 0.05). The final UCVA 0.5 and better was reached by 74.4% of eyes (t-test, p < or = 0.001) and BCVA 0.5 and better in 83.8% of eyes (t-test, p < or = 0.05). The postoperative UCVA improved according to the preoperative one in 95.3% of cases, the BCVA in 37.2% of cases (by means of gain of lines on the Snellen chart). During the follow-up period the authors didn't prove statistically significant decrease of the endothelial cells' density (CD) according to the LASIK procedure (t-test, p > or = 0.05). Peroperatively, the authors noticed small defect of the lamella 4 times, and total lamellar detachment 2 times. Postoperatively, in 6 eyes a slight fibrosis occurred, and in two cases, the late rejection of the corneal transplant was diagnosed. The keratoconus relapsed 12 months after the procedure in 2 eyes and was indicated to rekeratoplasty. LASIK is an effective and relatively safe method for postoperative refractive error correction after perforating keratoplasty.
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PMID:[Long-term results of the postoperative ametropia correction after perforating keratoplasty using the LASIK method]. 1822 92

In this research, we propose to reduce astigmatism and distortion in a progressive addition lens (PAL) by employing a polymer-based graded-index (GRIN) material. We adopted the diffusion copolymerization method for the GRIN-PAL fabrication. The GRIN material was prepared by partial diffusion of methyl methacrylate (MMA) and 2,2,2-trifluoroethyl methacrylate (3FMA) monomers into the cross-linked benzyl methacrylate polymer gel. GRIN-PAL was prepared by polymerization of the GRIN material in a mold of commercially available PAL. As a result, methods to control Deltan, the diffusion length, and the order of the GRIN profile in polymeric GRIN materials were demonstrated. In a combination of the PBzMA gel and the MMA/3FMA diffusion monomer, 50/50 in volume provides the highest Deltan. The diffusion period mainly affects the diffusion length. These two parameters consequently determine the order of the GRIN profile and the focusing power that the GRIN provides. The difference in the ease of diffusion caused by the difference in the cross-linking density provides a method for positional control of the GRIN profile. Furthermore, GRIN-PAL using a polymeric material was successfully fabricated. Improvement in astigmatism and distortion was demonstrated using GRIN. Therefore, the GRIN material is suggested to be applicable for the further modification of the PAL with low astigmatism and distortion.
ACS Appl Mater Interfaces 2009 Apr
PMID:Copolymer-based progressive addition lens with graded index designed for astigmatism and distortion correction. 2035 16