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 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 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*

We have studied the overcorrection, undercorrection, astigmatic change and its incidence on time sequence after the excimer laser photorefractive keratectomy, and its relation with the degree of preoperative myopia, sex, and age. The study has been done with 429 eyes which we could assess for 6 months or more after excimer laser photorefractive keratectomy of myopia from July 1993 to march 1997. Overcorrection of more than -1D was common during the early postoperative periods and then gradually decreased with time. Overcorrection has been seen in 261 eyes(60.84%) after 1 month, but only 33 eyes(13.47%) after 1 year, and 13 eyes(11.02%) after 2 years. Undercorrection has been seen in 2 eyes(0.47%) after 1 month, but 25 eyes(10.20%) after 1 year, and 20 eyes(16.95%) after 2 years. Surgically induced astigmatism increased to 0.54+/-0.84D after 10 days and then decreased 0.19+/-0.75D after 12 months. Also, surgical induced astigmatism developed 1.13+/-1.10D in 247 eyes (57.58%) after 1 month, but decreased 0.89+/-0.45D in 107 eyes(43.67%) after 12 months. The occurrence of overcorrection and undercorrection was related to the severity of preoperative myopia(p<0.05), but with sex and age, it had no statistical correlation(p>0.05). The amount of postoperative astigmatism was related to preoperative astigmatism(p<0.05), but it had no statistical correlation with the degree of preoperative myopia, age, sex, and development and increase of surgically induced astigmatism(p>0.05).
Astigmatism ; Incidence ; Lasers, Excimer* ; Myopia* ; Photorefractive Keratectomy* ; Postoperative Period

In order to prevent the development of central island after excimer laser photorefractive keratectomy(PRK), 547 eyes which had undergone PRK were studied to evaluate the incidence, width and height of central island retrospectively. Based on this result, PRK was performed on 63 eyes under conventional protocol(software version 3.20, VISX Twenty/twenty Inc, Santa Clara, CA) and then additional laser ablation with a correction amount of 2.5D and adiameter of 3mm was performed whether the incidence has been decreased and additional complications have occurred. As a result of conventional protocol, central island had occurred in 121 eyes out of 547(22.1%) and the width was 2.94+/-0.22mm and the height was 2.64+/-0.89D. In case of 63 eyes which underwent additional laser ablation, central island occurred in 4 eyes (6.34%) and overcorrection occurred only in 3 eyes(4.76%) at one month after PRK. From the standpoint of the above results, we reached the conclusion that the additional ablation for 2.5D by a 3mm in diameter after PRK under conventional protocol is effective. By using this method, we could reduce the incidence of central island without the aid of the upgraded version that contains the anti-central island program.
Incidence ; Laser Therapy ; Lasers, Excimer* ; Myopia* ; Photorefractive Keratectomy* ; Retrospective Studies

PURPOSE: To determine whether the refractive change obtained using the Orbscan-derived power maps is in concordance with the manifest refractive change produced after photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK). METHODS: Forty eyes of 21 PRK patients and 40 of 21 LASIK patients were included in the study. Orbscan topographical analysis and manifest refraction were performed preoperatively and 1 month postoperatively. This study evaluated the concordance between the change in manifest refraction (corrected to the corneal plane) and the change measured by Orbscan power maps before and after PRK and LASIK. We also compared the concordance of the change in manifest refraction (corrected to the corneal plane) with the change calculated using the Gaussian optics formula, radius of anterior and posterior corneal surface , and corneal thickness measured by ultrasound pachymetry. RESULTS: The 3.0-mm zone axial power anterior map gave the best correlation between manifest refractive change, and Orbscan-measured corneal power change in PRK (r =0.733, P<0.001). The 4.0-mm zone of calculated refractive change using Gaussian optic formula map gave the best correlation with manifest refractive change in LASIK (r =0.531 , P<0.001). The change of anterior corneal surface maps in PRK and the change of total power maps in LASIK represented the best correlation with the change in manifest refraction, but they did not reliably represent the changes in manifest refraction due to high standard deviation value. CONCLUSIONS: The 3.0-mm zone axial power anterior map gave the best correlation between manifest refractive change, and Orbscan-measured corneal power change in PRK. The 4.0-mm zone of calculated refractive change using Gaussian optic formula map gave the best correlation with manifest refractive change in LASIK. Nevertheless, these maps did not reliably represent the changes in manifest refraction because of the high standard deviation value.
Humans ; Keratomileusis, Laser In Situ* ; Photorefractive Keratectomy* ; Radius ; Ultrasonography

PURPOSE: To compare the corneal power (K) measured by different methods in the patients who underwent photorefractive keratectomy (PRK) or laser in situ keratomilieusis (LASIK) METHODS: Fifty-four patients who had undergone PRK or LASIK from December 1999 to December 2000 and followed for 3 months or longer were selected for this study. The corneal power was measured by five different methods in 35 eyes(18 patients) of PRK group and in 70 eyes (36 patients) of LASIK group: calculation method (C-K), hard contact lens method (H-K), autorefractokeratometer (A-K), manual keratometer (M-K) and topography (T-K). RESULTS: Preoperative mean corneal power was 43.41+/-1.06 D in PRK group and 43.75+/-1.03 D in LASIK group. Postoperative corneal power in PRK group showed following Results: C-K, 40.94+/-1.51 D; H-K, 41.04+/-1.23 D; A-K, 41.18+/-1.29 D; M-K, 41.38+/-1.33 D; T-K, 41.67+/-1.26 D. In LASIK group, the results were: C-K, 38.64+/-2.25 D; H-K, 39.29+/-1.66 D; A-K, 39.53+/-1.61 D; M-K, 39.85+/-1.54 D; T-K, 40.36+/-1.26 D. The corneal power of calculation method was lowest in both groups. Each corneal power was not different statistically from the others in PRK group(p=0.16). However, C-K was significantly lower than A-K (p=0.02), M-K (p=0.00) or T-K (p=0.00) in LASIK group. Also, H-K or AK was lower than T-K statistically in LASIK group (p=0.00, p=0.02). CONCLUSIONS: The corneal power was lowest when measured by calculation method after refractive surgery. In LASIK group, there were statistical differences among the corneal powers by each method.
Humans ; Keratomileusis, Laser In Situ ; Photorefractive Keratectomy ; Refractive Surgical Procedures*