We compared postoperative visual outcome and corneal refractive power depending on preoperative corneal topographic pattern and the predictibility of corneal topographic measurement compared with keratometric measurement after PRK. The subjects were 91 eyes divided into two goups composed of 44 eyes, symmetric bow tie type(SB) and 47 eyes, asymmetric bow tie type (aSB). The visual acuity, central power, and topographic pattern were measured before operation, postoperative 1 week, 1, 2 and 6 month in two groups, but no statistical difference(p>0.05). The averages of uncorrected visual acuity at 6 month were improved to 0.80(SB) and 0.85(aSB) from 0.09(SB) and 0.11(aSB) before operation. Topographic central refractive powers of +42.98D (SB), +43.32D(aSB) before operation were changed to +37.68D(SB), 37.56D(aSB) at 6month. The pattern of the region affected by the excimer laser was classified by key hole type 38%(SB) , 34%(aSB) , uniform roud type 41%(SB), 43%(aSB), semicircular type 21%(SB), 23%(aSB). The proportion of the difference less than one diopter between PRK setting and the change of the corneal refractive power at 6month was 36% and 76% in keratometric and topographic measurement. Above results show that the asymmetricity of bow tie type did not influence the visual outcome. The topographic measurement was better than keratometric measurement in evaluating the corneal refractory change after PRK.
Lasers, Excimer* ; Visual Acuity

Corneal haze and myopic regression are not uncommon complications following photorefractive keratectomy(PRK). To avoid these problems, multipass multizone technique has been introduced. However, it is quite difficult to coincide the center of the each ablation zone during the procedure and needs to take longer operation time. Single-pass multizone software was replaced by Summit technology(USA). The current study evaluates the clinical results of single-pass multizone PRK for high myopia. We performed PRK using single-pass multizone technique on 48 eyes of 44 patients for the treatment of high myopia. Preoperative spherical equivalent refractions ranged from -8.00 diopters((D) to -16.00 D (mean+/-SD, -11.01 +/- 1.84 D). Mean postoperative refraction was +1.12 +/- 1.20 D at one month, -0.42 +/- 1.24 D at six months, and -0.92 +/- 1.09 D at one year. The percentage of patients achieving correction within +/-2.0 D was 79.2% at one month, 85.4% at six months, and 88.2% at one year postoperatively. There was no serious complications after surgery. This study provides evidence that single-pass multizone PRK is a safe, simple and fairly predictable method for high myopic correction. But further studies are needed to confirm the longer-term stability.
Humans ; Lasers, Excimer* ; Myopia*

Corneal haze and myopic regression are not uncommon complications following photorefractive keratectomy(PRK). To avoid these problems, multipass multizone technique has been introduced. However, it is quite difficult to coincide the center of the each ablation zone during the procedure and needs to take longer operation time. Single-pass multizone software was replaced by Summit technology(USA). The current study evaluates the clinical results of single-pass multizone PRK for high myopia. We performed PRK using single-pass multizone technique on 48 eyes of 44 patients for the treatment of high myopia. Preoperative spherical equivalent refractions ranged from -8.00 diopters((D) to -16.00 D (mean+/-SD, -11.01 +/- 1.84 D). Mean postoperative refraction was +1.12 +/- 1.20 D at one month, -0.42 +/- 1.24 D at six months, and -0.92 +/- 1.09 D at one year. The percentage of patients achieving correction within +/-2.0 D was 79.2% at one month, 85.4% at six months, and 88.2% at one year postoperatively. There was no serious complications after surgery. This study provides evidence that single-pass multizone PRK is a safe, simple and fairly predictable method for high myopic correction. But further studies are needed to confirm the longer-term stability.
Humans ; Lasers, Excimer* ; Myopia*

We evaluated the safety and efficacy of photo-astigmatic refractive keratectomy(PARK) with Schwind excimer laser for one year. We performed PARK procedures on 28 eyes with compound myopic astigmatism. Twenty eight eyes were divided into two groups according to their astigmatism: low(up to -1.5D, 15 eyes), high(over -1.5, 13 eyes). Mean preoperative astigmatism was 1.17+/-0.28 in low astigmatism group and 2.67+/-0.90 in high astigmatism group. Mean one year postoperative astigmatism was 0.40+/-0.39 in low astigmatism group and 0.48+/-0.56 in high astigmatism group. Correction rate of astigmatism was 62.3% in low astigmatism group and 79.4% in high astigmatism group. Complications were loss of best corrected visual acuity 2 line or more(2 eyes), temporary increased intraocular pressure(4 eyes), over 0.25mm eccentric ablation(2 eyes). We concluded that the Schwind excimer laser PARK appeared to be a safe and relatively accurate proceudre to correct myopic astigmatism, especially predictability of astigmatism correction was very satisfactory.
Astigmatism ; Lasers, Excimer ; Visual Acuity

In order to evaluate the effect of topical prostaglanduin synthesis inhibitor(Diclod) and therapeutic contact lens(T-lens) on pain control and epithelial wound healing following excimer laser photorefractive keratectomy(PRK) we examined the score of subjective pain & the degree of corneal epithelial defect on 40 consecutive patients with or without above treatment. The patients were subdivided into 4 groups : 10 patients treated with only pressure patch(Group 1), 10 patients with pressure patch & Diclod(Group 2), 10 patients with only T-lens(Group 3), and 10 patients with T-lens & Diclod(Group 4). Diclod(Group 2&4) was effective on pain control during three days after excimer laser PRK, while T-lens treatment was not effective. Subjective pain score between the patient with Diclod(Group 2&4) and those without Diclod(Group 1&3) was significantly different(p< 0.05). In the point of epithelial wound healing after excimer laser PRK, 95% of patients treated with T-lens(Group 3&4) revealed no epithelial defect three days after excimer laser PRK, while only 65% of the patients treated with pressure patch revealed that. The difference was statistially significant(p< 0.05). Diclod, however, did not influence the epithelial wound healing in both pressure group and T-lens group. In this study we could find that the combination of Diclod & T-lens was a recommendable method to decrease the pain & to increase the epithelial wound healing after excimer laser PRK.
Humans ; Lasers, Excimer* ; Wound Healing

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

No abstract available.
Angioplasty ; Angioscopy ; Lasers, Excimer ; Stents

Objective: To compare the predictability of flap thickness, visual and refractive outcomes, and higher order aberrations in eyes that underwent myopic LASIK using either a Technolas femtosecond laser or a Zyoptix XP mechanical microkeratome for flap creation. Methods: The study involved a total of 44 eyes of 22 patients who underwent LASIK. Flap creation was randomized to using the Technolas femtosecond laser in one eye and Zyoptix XP microkeratome in the contralateral eye. Flap thickness was measured intraoperatively using ultrasonic pachymetry and postoperatively using the Visante ASOCT. Refractive outcome, visual acuity (VA), higher order aberrations, and contrast sensitivity were compared between the two groups. Results: Twenty-two patients had LASIK for myopia or myopic astigmatism. Using ultrasonic pachymetry intraoperatively, the mean flap thickness was 134 (±10) um and 124 (±23) um in the femtosecond (FS) and microkeratome (MK) groups respectively. Comparing the deviation of the actual from the intended flap thickness, the FS group had statistically lower standard deviation compared to the MK group (p=0.04). Using the AS-OCT, the mean flap thickness at 3 months postoperatively was 119 (±10.82) um and 123 (±15.77) um in the FS and MK groups respectively. The difference in standard deviation between the two groups did not reach statistical significance (p=0.19). The mean spherical equivalent at 3 months was -0.45D (±0.42) and -0.13D (±0.16) respectively. Eightynine percent (89%) of eyes had uncorrected VA of 20/20 or better in both groups. All eyes attained best corrected VA of 20/20 or better in both groups. Differences in total higher order aberrations (p=0.09) and contrast sensitivity scores (p=0.47) were not statistically different between the two groups. Conclusion Flap thickness predictability was better using the Technolas femtosecond laser compared to the XP microkeratome blade. Visual and refractive outcomes, higher order aberrations, and contrast sensitivity were comparable between the 2 groups.
Keratomileusis, Laser In Situ ; Lasers, Excimer

To investigate the effect of deep excimer laser ablation on the corneal endothelium, excimer laser photo refractive keratectomy(PRK) with different ablation depths were performed to obtain various residual corneal thickness(range: 90-250 micrometer) in white rabbit corneas(N=50). Corneal endothelium was stained with Alizarin red S(pH 4.2) for 2 minutes three days after excimer laser ablation and was analyzed morphometrically using digitizer the morphometric parameters according to residual corneal thickness. In the corneas of residual corneal thickness(RT) over 200 micrometer and untreated controls(N=6), endothelial damages were rarely seen. With the decrease of residual corneal thickness, hexagonality and shape factor decreased, and coefficient of variation of the cell area(CV) increased(p<0.01). In corneas of RT less than 200 micrometer, endothelial damages were found and become more severe in corneas of RT between 90~149 micrometer. Hexagonal shaped cells were rarely observed, and the shapes of most cells were changed. Deep excimer laser PRK might affect corneal endothelial cells if the RT is less than 200 micrometer, and these findings suggest that care is recommended when doing deep excimer laser corneal ablation, especially excimer laser assisted in situ keratomileusis.
Cornea ; Endothelial Cells ; Endothelium, Corneal ; Lasers, Excimer*

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