No Abstract Available.
Lasers, Excimer* ; Myopia* ; Photorefractive Keratectomy*

Objective: To present the refractive and visual outcomes of refractive surgical treatment options in high myopia. Methods This was a retrospective review of patients diagnosed with high myopia (manifest refractive spherical equivalent [MRSE] ≥-6.00D) who underwent one of the following procedures: laser-in-situ keratomileusis (LASIK), photorefractive keratectomy (PRK), phakic IOL implantation with the Staar Implantable Collamer Lens (ICL), or Alcon Cachet Phakic IOL. Eyes with best corrected distance vision of less than 20/30 due to amblyopia or other eye pathologies were excluded.
Keratomileusis, Laser In Situ ; Photorefractive Keratectomy

PURPOSE: To investigate the preoperative characteristics and postoperative change of the higher-order wavefront aberrations (HOAs) in myopic photorefractive keratectomy (PRK). METHODS: Standard PRK was performed in 39 eyes (spherical equivalent -4.71+/-1.56D) using the VISX(R) STAR S4(TM) excimer laser system. Wavefront analysis was performed preoperatively and 6 months postoperatively using the VISX(R) WaveScan(TM) aberrometer. Statistical analysis was performed to assess the preoperative characteristics of the HOAs and the PRK-induced aberrations. RESULTS: The preoperative root mean square (RMS) value of the total HOAs was 0.291 micrometer: coma 0.159 micrometer, trefoil 0.157 micrometer, spherical aberration 0.093 micrometer. Among the 3 HOAs, only the spherical aberration showed moderate magnitude negative correlation with the spherical equivalent (p=0.012) and sphere (p=0.005). The magnitude of all of the HOAs, except trefoil, were significantly increased at postoperative 6 months: total HOAs 183% (0.533 micrometer, p<0.001), spherical aberration 341% (0.317 micrometer, p<0.001), coma 185% (0.294 micrometer, p<0.001), trefoil 104% (0.163 micrometer, p=0.681). In the postoperative correlation analysis, only the PRK-induced spherical aberration showed the increase of magnitude with increasing preoperative spherical equivalent (p=0.036) and sphere (p=0.019). CONCLUSIONS: The HOAs, especially spherical aberration and coma, were increased after PRK. Among the 3 HOAs, the spherical aberration showed the greatest increase of magnitude and percent change; it also showed a positive correlation with increasing preoperative spherical equivalent and sphere. Further software improvements in the wavefront-guided surface ablations need to have a diminution of PRK-induced spherical aberration.
Coma ; Lasers, Excimer ; Lotus ; Photorefractive Keratectomy

PURPOSE: To investigate the structural changes of anterior chamber after photorefractive keratectomy in myopic eyes, we assessed the changes of anterior chamber(AC) depth, angle and correlations with ablation depth at sixth postoperative month. METHODS: We performed photorefractive keratectomy on 77 eyes of 40 patients and divided them into 3 groups by the degree of preoperative myopia; less than -4.0 diopter, between -4.0 and -6.0 diopter and greater than -6.0 diopter. We assessed the changes of AC depth and angle using Scheimpflug camera(EAS-1000, Nidek, Japan) after 6 months. RESULTS: The average preoperative AC depth and angle were 3.59+/-0.27 mm, 44.20+/-2.58 and 3.53+/-0.27 mm, 43.29+/-1.65 at sixth postoperative month. The reductions in AC depth and AC angle were statistically significant(P<0.05), and there were no differences among three myopia groups(P>0.05). The changes of both AC depth and AC angle were not affected by ablation depth(P>0.05). CONCLUSIONS: Structural changes of anterior chamber were significant 6 months after photorefractive keratectomy and the changes were not affected by degree of myopia nor by ablation depth.
Anterior Chamber* ; Humans ; Myopia ; Photorefractive Keratectomy*

PURPOSE: To investigate the relationship of refraction, geometry of the posterior corneal surface and the residual corneal thickness after excimer laser photorefractive keratectomy. METHODS: Thirty eyes of 15 patients were treated with Star S2 Smooth Scan (VISX, U.S.A.) and followed up for 3 months. The refractive, anteroposterior changes in the posterior corneal surface and residual corneal thickness were measured using slit-scanning topography, Orbscan IIR (Orbtek, Bausch & Lomb) at 1 week preoperatively, and 1 and 3 months postoperatively. RESULTS: Mean forward shift of the posterior cornea surface was 8.83+/-1.34 micrometer, 11.53+/-4.23 micrometer and 14.70+/-3.50 micrometer at 1 week, 1 month, and 3 months respectively. Mean spherical equivalence of posterior cornea was = -7.01+/-0.31 D preoperatively; it changed to -7.17+/-0.47 D, -7.22+/-0.21 D and -7.17+/-0.6 D at 1 week, 1 month and 3 months. The degree of forward shift of posterior corneal surface is correlated with the posterior corneal refractive changes (r=-0.808, P< 0.01). The forward shift of the posterior corneal surface is correlated with the residual corneal thickness (r=-0.483, P< 0.01). CONCLUSIONS: Photorefractive keratectomy significantly influenced the forward shift of the cornea, which is correlated with the residual corneal thickness.
Cornea ; Humans ; Lasers, Excimer ; Photorefractive Keratectomy*

PURPOSE: To assess the refractive outcomes in photorefractive keratectomy (PRK) of two eximer lasers: Broad beam and Flying spot laser. METHODS: We compared the refractive outcomes of 74 eyes (group I) treated with a VISX 20/20(excimer laser (VISX Inc. USA) using broad beam laser with those of 96 eyes (group II) treated with a Technolas 217 C-Lasik(TM) (Bausch and Lomb, USA) using flying spot laser. Each patients had been followed up for more than 6 months after surgery. RESULTS: Corneal astigmatism at preoperation were 1.25 +/- 0.62D in group I and 1.03 +/- 0.51D in group II and at postoperative 6 months, decreased to 1.12 +/- 0.53D in group I and 0.60 +/- 0.83D in group II. Manifest refraction were outside +/- 1D of spherical lens or 0.5 D of cylinder lens in 23.6 % in group I and 13.5% in group II. CONCLUSIONS: We suggests that PRK using flying spot laser effectively more reduces corneal astigmatism and provided more satisfactory predictability in refractive results than that of broad beam laser.
Astigmatism ; Diptera* ; Humans ; Lasers, Excimer* ; Photorefractive Keratectomy*

PURPOSE: To evaluate the correlation between the conventional method and the clinical history method for intraocular lens power calculation for cataract surgery in eyes with previous photorefractive keratectomy in the absence of pre-PRK data. METHODS: The medical records of 38 eyes in 23 patients who had been treated with PRK for myopia and were followed up for more than 1 year were reviewed. The IOL powers by conventional method using post-PRK keratometric value and by clinical history method were compared. RESULTS: The mean values of IOL powers by conventional method, and by clinical history method were +20.58 +/- 1.10D (range, +16.37~+22.80D) and +21.06 +/- 0.85D (range, +18.85~+22.8D), respectively. The following equation describes the regular relationship between the two METHODS: IOLCHM (clinical history method)= 0.683*IOLCM (conventional method) +7.005 (r=0.878, p<.01). When the IOL powers by conventional method were applied to this equation, the mean difference of value between the IOL powers calculated from this equation and those of the clinical history method was?0.01 +/- 0.41D (range, -0.99~+0.76D). CONCLUSIONS: This equation will be helpful to calculate the IOL power for cataract surgery in eyes with previous PRK in the absence of pre-PRK data.
Cataract ; Humans ; Lenses, Intraocular* ; Medical Records ; Myopia ; Photorefractive Keratectomy

We analyzed the topographic findings of central islands following excimer photorefractive keratectomies(VISX Twenty/Twenty, Inc, Santa Clara, CA) for myopia to evaluate whether the size of the central island was significantly different betwaen 1 week and 6months postoperatively and whether central island at postoperative 6months affected the decrease of corrected visual acuity from preoperative level. There were statistically significant differences in the indices related to the size of central island(peak, height, area) between 1 week(40 patients, 41 eyes) and 6 months(55 patients, 64 eyes) follow-up groups. In 64 eyes of 6months follow-up group, we could not find any statistically significant effect of the indices related to the size of central island on the decrease of corrected visual acuity, except SAI.
Follow-Up Studies ; Humans ; Islands ; Myopia ; Photorefractive Keratectomy* ; Visual Acuity

This study was performed to compare the refractive effect and visual outcome of Excimer laser radial keratotomy(RK) with those of central photorefractive keratectomy(PRK) for myopia correction. The myopic eyes were subdivided into mild(-2.75D), moderate(-3.00 ~ -5.75D) and severe(>-6.00) myopia. In 54 eyes treated with RK 3 eyes(5.6%) were mild, 26 eyes(48.1%) were moderate and 25 eyes (46.3%) were severe myopic eyes. In 518 eyes treated with central PRK 10 eyes(1.9%) were mild, 214(41.3%) were moderate and 294(56.8%) were severe myopic eyes. Mean reduction of refractive power measured with skiascope following RK and central PRK in mild, moderate and severe myopia were 1.42 +/- 0.85D and 3.19 +/- 0.84D, 2.07 +/- 1.75D and 4.66 +/- 1.90D, and 2.54 +/- 2.45D and 7.54 +/- 2.81D, respectively. Mean reduction of keratometric diopter following RK and central PRK in mild, moderate and severe myopia were 2.00 +/- 1.05D and 3.66 +/- 1.03D, 1.90 +/- 1.05D and 4.83 +/- 1.99, and 1.52 +/- 2.54D and 5.58 +/- 3.46D, repectively. Uncorrected visual acuity following RK and central PRK in mild. moderate and severe myopia were 0.73 +/- 0.19 and 0.91 +/- 0.26, 0.43 +/- 0.30 +/- and 0.79 +/- 0.24, and 0.20 +/- 0.13 and 0.66 +/- 0.28, respectively. In conclusion, refractive effect and visual outcome of central photorefractive keratectomy was better than the those of radial keratotomy for correction of myopia; especially high myopic eyes.
Keratotomy, Radial* ; Lasers, Excimer* ; Myopia* ; Photorefractive Keratectomy* ; Visual Acuity

PURPOSE: To investigate the effect of surface fluid on the ablation rate and efficacy of 213-nm solid-state laser during photorefractive keratectomy (PRK). METHODS: Twelve rabbits (24 eyes) underwent myopic PRK for the correction of 10 diopters using 213-nm solid-state laser. Photoablation was performed with removal of corneal surface fluid using the Weckcel(R) sponge every 5 seconds in one eye and without removal of corneal surface fluid in the control eye. The mean central corneal thickness (CCT) was evaluated preoperatively, and at 1 week, 4 weeks postoperatively. RESULTS: The mean CCT of group 1 (with removal of corneal surface fluid) were 361.3+/-13.9 micrometer preoperatively and 321.4+/-18.5 micrometer at 4 weeks postoperatively. The mean CCT of group 2 (without removal of surface fluid) were 358.7+/-8.9 micrometer preoperatively and 338.4+/-12.0 micrometer at 4 weeks postoperatively. The mean ablation depths were 39.8+/-7.4 micrometer in group 1 and 20.3+/-5.8 micrometer in group 2 at 4 weeks postoperatively p<0.05). CONCLUSIONS: Induced corneal surface fluid during PRK may influence the ablation efficacy and accuracy of solid-state laser. This result should be considered in clinical trialswith 213-nm solid-state laser, especially in high myopes.
Eye ; Lasers, Solid-State ; Photorefractive Keratectomy ; Porifera ; Rabbits