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*

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

We studied the relationship between the prevalence of lattice degeneration and the axial length in patients with myopia who had undergone photorefractive keratectomy(PRK). 355 eyes of 186 myopic patients with axial length of 22.99mm~30.67mm were evaluated by using A-scan axial length measurements and fundus examination. The myopic patients with posterior staphyloma did not undergo PRK.Eyes were classified into three groups on the basis of axial length:mild(<26mm), moderate(26~28 mm)and severe(>28mm)axial myopia.The prevalence of lattice degeneration was then studied according to axial length group. The highest prevalence of lattice degeneration(13 of 35 eyes, 37.1%)was found among eyes of axial length 28 mmor greater;the lowest prevalence of lattice degeneration(10 of 174 eyes, 5.7%)was found among eyes of axial length under 26 mm. We could find statistically significant association between the prevalence of lattice degeneration and axial length(X2 27.356 P-value<0.005). Unless the axial myopia is related to posterior staphyloma, this may explain the observation that lattice degeneration has been noted more commonly among patients with severe than mild or moderate axial myopia. As lattice degeneration is recognized as a frequent cause of retinal detachment, we recommend peripheral fundus examination be done carefully before PRK or LASIK.
Humans ; Keratomileusis, Laser In Situ ; Myopia ; Photorefractive Keratectomy ; Prevalence ; Retinal Detachment

PURPOSE: To report a new method for measuring corneal refractive power after photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) using the Orbscan(R) and autorefractokeratometer. METHODS: This study involved 12 cases that had undergone cataract surgery after corneal refractive surgery. Five cases had PRK and seven had LASIK. Keratometric values were evaluated with three different methods. The first, defined as RK, used an autorefractokeratometer (AK) (n=1.3375). The second, defined as K1, added the posterior surface diopter using AK and anterior surface diopter using an Orbscan. The last, defined as K2, added the posterior surface diopter and the anterior surface diopter using an Orbscan. Low K was a lower value between K1 and K2. RK, K1, K2 and Low K were compared with the back-calculated K value (Real K) 2 months after cataract surgery. RESULTS: The mean differences between RK, K1, K2, Low K and Real K were 3.08 +/- 0.98D, 0.41 +/- 0.66D, 0.27 +/- 0.77D, and -0.02 +/- 0.53D, respectively. In 9 of the 12 patients the difference was within 1D (75%) when either K1 or K2 was selected and in all patients, the difference between Low K and Real K was within 1D. CONCLUSIONS: The method of IOL calculation using Low K showed more accurate and predictable results in patients who had had cataract surgery after corneal refractive surgery.
Cataract ; Humans ; Keratomileusis, Laser In Situ ; Photorefractive Keratectomy ; Refractive Surgical Procedures*

PURPOSE: To evaluate the accuracy of the surgeon-selected ablation center in active eye-tracker-assisted ASA-PRK and to identify factors influencing the ablation center. METHODS: This retrospective study included 109 eyes of 62 patients who underwent active eye-tracker-assisted ASA-PRK (VISX STARTM S4 with ActiveTrakTM System). The location the surgeon-selected ablation center and its distance from the center of the entrance pupil were analyzed by corneal topography (EyeSys Corneal Analysis SystemTM with pupil finding software). The factors influencing centration were investigated. RESULTS: The mean decentration was 0.24+/-0.13 mm (range 0.04 to 0.83 mm). One-hundred and five eyes (96%) were within 0.5 mm of the pupillary center. Supero-nasal displacement of the ablation center occurred most frequently in 44 eyes (40%) after ASA-PRK. The decentration amount was not dependant on factors related to the patient, the surgeon, or the surgery. There was no significant correlation between the amount of decentration and the vertical scale bar of the ActiveTrakTM icon on the screen representing the distance from the pupil center determined by the tracking system, to the surgeon-selected ablation center. CONCLUSIONS: This method of tracking the ablation center, which was selected by the surgeon according to each patient's specific pupil decentration with the active eye tracking system, was highly accurate and effective in avoiding severe decentration in ASA-PRK.
Corneal Topography ; Humans ; Photorefractive Keratectomy ; Pupil ; Retrospective Studies