AIM:To investigate the effect of the percent tissue altered(PTA)on the safety after laser-assisted in situ keratomileusis(LASIK)based on linear creep characteristics.METHODS:The linear creep characteristics of the cor...AIM:To investigate the effect of the percent tissue altered(PTA)on the safety after laser-assisted in situ keratomileusis(LASIK)based on linear creep characteristics.METHODS:The linear creep characteristics of the cornea were characterized by the generalized Kelvin-Voigt constitutive relationship with five parameters.Then,the displacement and stress distribution on the anterior and posterior surfaces of the cornea were analyzed by constructing the eye model with different PTA.RESULTS:When PTA was above 39%,the vertex displacements under physiological intraocular pressure(IOP,15 mm Hg)exceeded that of the preoperative glaucoma under average IOP.That is,an excessively high displacement value was found.In addition,with the increase of PTA,the central cornea was stretched thinner and more obviously due to IOP.When PTA was above 39%,the stress at the center of the anterior surface of the residual stroma was more than 20%larger than that of the normal human eye.The residual stroma was forced to stretch more severely due to excessive stress on the anterior surface.This resulted in deformation of the stroma and induced corneal ectasia.Meanwhile,the postoperative vertex displacement increased with the decrease in viscosity ratio.CONCLUSION:PTA less than 39%is the safe range for LASIK surgery.This study may provide a reliable numerical basis for postoperative corneal dilatation and the outcomes after refractive surgery.展开更多
AIM： To investigate the long term（≥5 y） efficacy, predictability, and safety of laser in situ keratomileusis（LASIK） in eyes with thin corneas [central corneal thickness（CCT） 〈500 μm]. METHODS： A total of 33...AIM： To investigate the long term（≥5 y） efficacy, predictability, and safety of laser in situ keratomileusis（LASIK） in eyes with thin corneas [central corneal thickness（CCT） 〈500 μm]. METHODS： A total of 339 patients met the criteria of this study. Finally, 175 eyes of 89 patients who had thin corneas and underwent LASIK≥5 y ago returned to our clinic and included in this study. Preoperative parameters recorded included uncorrected visual acuity（UCVA）, corrected distance visual acuity（CDVA）, manifest refraction, CCT and corneal topography. At returning visits, in addition to visual acuity and manifest refraction, ultrasound CCT and corneal topography were performed. Optical coherence tomography was used to measure the CCT, LASIK flap thickness, and residual stromal bed thickness（RSBT）. Safety index, efficacy index, percentage of eyes within ±0.5 D and ±1.0 D of refraction, percent tissue altered（PTA）, and percentage stromal bed thickness（PSBT） were calculated. RESULTS： The safety index was 1.09 and efficacy index was 0.99. The percentages of eyes within ±0.5 D and ±1.0 D were 71.2% and 87.7%, respectively. The mean PTA was 40%±6%（range 20% to 55%）; 76 eyes（43.4%） had PTA 〈40% and 99 eyes（56.6%） had PTA≥40%. The mean RSBT was 303±27 μm（range 240 to 390 μm）, and 2 eyes had RSBT〈250 μm. The mean PSBT was 61%±9%（range 51% to 85%）. No eyes developed ectasia. CONCLUSION： In this cohort with the PSBT of 50% or more, LASIK is safe with follow-up for at least 5 y.展开更多
基金Supported by National Natural Science Foundation of China(No.62165010)The National Key Research and Development Program of China(No.2022YFC2404502).
文摘AIM:To investigate the effect of the percent tissue altered(PTA)on the safety after laser-assisted in situ keratomileusis(LASIK)based on linear creep characteristics.METHODS:The linear creep characteristics of the cornea were characterized by the generalized Kelvin-Voigt constitutive relationship with five parameters.Then,the displacement and stress distribution on the anterior and posterior surfaces of the cornea were analyzed by constructing the eye model with different PTA.RESULTS:When PTA was above 39%,the vertex displacements under physiological intraocular pressure(IOP,15 mm Hg)exceeded that of the preoperative glaucoma under average IOP.That is,an excessively high displacement value was found.In addition,with the increase of PTA,the central cornea was stretched thinner and more obviously due to IOP.When PTA was above 39%,the stress at the center of the anterior surface of the residual stroma was more than 20%larger than that of the normal human eye.The residual stroma was forced to stretch more severely due to excessive stress on the anterior surface.This resulted in deformation of the stroma and induced corneal ectasia.Meanwhile,the postoperative vertex displacement increased with the decrease in viscosity ratio.CONCLUSION:PTA less than 39%is the safe range for LASIK surgery.This study may provide a reliable numerical basis for postoperative corneal dilatation and the outcomes after refractive surgery.
基金Supported in part by the National Natural Science Foundation of China(No.11402161)the Programs for Science and Technique Development of Shanxi Province,China(No.20120313025-3)+1 种基金the Science and Technology Research Projects of the Shanxi Provincial Health Department,China(No.201201018)an unrestricted grant from Research to Prevent Blindness,New York,NY,USA
文摘AIM： To investigate the long term（≥5 y） efficacy, predictability, and safety of laser in situ keratomileusis（LASIK） in eyes with thin corneas [central corneal thickness（CCT） 〈500 μm]. METHODS： A total of 339 patients met the criteria of this study. Finally, 175 eyes of 89 patients who had thin corneas and underwent LASIK≥5 y ago returned to our clinic and included in this study. Preoperative parameters recorded included uncorrected visual acuity（UCVA）, corrected distance visual acuity（CDVA）, manifest refraction, CCT and corneal topography. At returning visits, in addition to visual acuity and manifest refraction, ultrasound CCT and corneal topography were performed. Optical coherence tomography was used to measure the CCT, LASIK flap thickness, and residual stromal bed thickness（RSBT）. Safety index, efficacy index, percentage of eyes within ±0.5 D and ±1.0 D of refraction, percent tissue altered（PTA）, and percentage stromal bed thickness（PSBT） were calculated. RESULTS： The safety index was 1.09 and efficacy index was 0.99. The percentages of eyes within ±0.5 D and ±1.0 D were 71.2% and 87.7%, respectively. The mean PTA was 40%±6%（range 20% to 55%）; 76 eyes（43.4%） had PTA 〈40% and 99 eyes（56.6%） had PTA≥40%. The mean RSBT was 303±27 μm（range 240 to 390 μm）, and 2 eyes had RSBT〈250 μm. The mean PSBT was 61%±9%（range 51% to 85%）. No eyes developed ectasia. CONCLUSION： In this cohort with the PSBT of 50% or more, LASIK is safe with follow-up for at least 5 y.
