PURPOSE: The purpose of this study was to investigate the clinical efficacy of an optimized prolate ablation procedure for correcting residual refractive errors following laser surgery. METHODS: We analyzed 24 eyes of 15 patients who underwent an optimized prolate ablation procedure for the correction of residual refractive errors following laser in situ keratomileusis, laser-assisted subepithelial keratectomy, or photorefractive keratectomy surgeries. Preoperative ophthalmic examinations were performed, and uncorrected distance visual acuity, corrected distance visual acuity, manifest refraction values (sphere, cylinder, and spherical equivalent), point spread function, modulation transfer function, corneal asphericity (Q value), ocular aberrations, and corneal haze measurements were obtained postoperatively at 1, 3, and 6 months. RESULTS: Uncorrected distance visual acuity improved and refractive errors decreased significantly at 1, 3, and 6 months postoperatively. Total coma aberration increased at 3 and 6 months postoperatively, while changes in all other aberrations were not statistically significant. Similarly, no significant changes in point spread function were detected, but modulation transfer function increased significantly at the postoperative time points measured. CONCLUSIONS: The optimized prolate ablation procedure was effective in terms of improving visual acuity and objective visual performance for the correction of persistent refractive errors following laser surgery.
Coma ; Humans ; Keratectomy, Subepithelial, Laser-Assisted ; Keratomileusis, Laser In Situ ; Laser Therapy* ; Phosmet* ; Photorefractive Keratectomy ; Refractive Errors* ; Refractive Surgical Procedures ; Treatment Outcome ; Visual Acuity

PURPOSE: To analyze the postoperative intraocular pressure (IOP) underestimation measured with non-contact tonometry after corneal refractive surgery. METHODS: The postoperative IOP decrease measured with non-contact tonometry (NCT), regarded as IOP underestimation, was calculated in 253 LASIK patients and 281 LASEK patients. Multiple regression analysis was performed to determine the preoperative factors which affect postoperative IOP underestimation. The right eye results were reported in this paper. RESULTS: The postoperative IOP decrease was affected by age (r = -0.0420, p = 0.03), corneal ablation depth (r = 0.0466, p < 0.01), and operation method (LASIK or LASEK) (r = 0.6006, p < 0.01). For every 100 microm decrease of corneal thickness by LASIK, the IOP decreased 6.29 +/- 2.40 mm Hg in patients under 26 years of age and 6.12 +/- 2.53 mm Hg in patients above 26 years of age (p = 0.05). For every 100 microm decrease of corneal thickness by LASEK, the IOP decreased 5.77 +/- 2.37 mm Hg in patients under 26 years of age and 5.44 +/- 2.62 mm Hg in patients above 26 years of age (p = 0.05). CONCLUSIONS: The postoperative IOP underestimation measured with NCT was more prominent in younger-aged patients after LASIK than LASEK with deeper ablation depth.
Humans ; Intraocular Pressure* ; Keratectomy, Subepithelial, Laser-Assisted ; Keratomileusis, Laser In Situ ; Manometry* ; Refractive Surgical Procedures*

PURPOSE: To assess the accuracy of pachymetric measurement using Orbscan(Bausch and Lomb, USA) after laser in situ keratomileusis(LASIK), photorefractive keratectomy(PRK), and laser epithelial keratomileusis (LASEK). METHODS: Central corneal thickness of 159 nonoperated normal eyes, 55 eyes after LASIK, 12 after PRK, and 17 after LASEK was measured using ultrasound and Orbscan II. The acoustic factor (AF) was adjusted, based on the results obtained in the normal eye group, to minimize the difference between ultrasound and Orbscan pachymetric values. RESULTS: Using the adjusted AF (0.9607), the mean difference between Ultrasonic pachymetric and Orbscan measurement was 0.00 +/- 21.08, 20.44 +/- 24.12, 27.63 +/- 36.87, and 0.56 +/- 17.26 micro meter in the normal, LASIK, PRK, and LASEK groups, respectively. In the LASIK and PRK groups, there was a statistically significant difference between the two methods (both P<0.001). The postoperative ultrasound measurements were consistent with the theoretical residual corneal thickness in the LASIK and PRK groups (-2.96 +/- 18.00 micro meter, -1.00 +/- 13.59 micro meter), while Orbscan measurements were statistically significantly less than the theoretical residual corneal thickness in the LASIK and PRK groups (21.84 +/- 31.06 micro meter, p<0.001; 21.88 +/- 35.91 micro meter, P=0.036). CONCLUSIONS: Orbscan pachymetric values may be underestimated and less accurate after excimer refractive surgery, especially after LASIK and PRK.
Acoustics ; Keratectomy, Subepithelial, Laser-Assisted ; Keratomileusis, Laser In Situ ; Refractive Surgical Procedures* ; Ultrasonics ; Ultrasonography

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 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*

PURPOSE: To compare the degree of pain between photorefractive keratectomy(PRK) and laser in situ epithelial keratomileusis(LASEK) during intraoperative and postoperative period, we used the visual pain analogue scale. METHODS: Forty patients requiring refractive surgery of both eyes were randomized into 2 groups and were studied by double-blind clinical trial prospectively. Each patient had PRK performed on one eye and LASEK on the other on the same day. On half of the patients PRK was performed before LASEK. The other half had LASEK first and then PRK. All surgeries were performed by one surgeon and subjective pain was assessed using analog scale of no pain(0) to worst pain imaginable(10) during the operation, post operatively, and on the first, second, sixth postoperative day. RESULTS: There were no significant carry-over effects in all 5 comparisons(p>0.30) between the two groups of different operation order. There was less discomfort in the PRK group compared with the LASEK group on all days of measurement. The pain felt by the patients was significantly less in the PRK group on the first(mean 3.29 versus 5.46, p<0.0001) and the second(mean 1.39 versus 3.61, p<0.0001) postoperative day. The sum of pain in all measuring days were also significantly less(mean 10.39 versus 16.29, p<0.0001) in the PRK group. CONCLUSION: We concluded that PRK is a more comfortable refractive surgery than LASEK in the aspect of pain.
Humans ; Keratectomy, Subepithelial, Laser-Assisted ; Photorefractive Keratectomy* ; Postoperative Period* ; Prospective Studies ; Refractive Surgical Procedures

PURPOSE: LASEK is a newly developed refractive surgery technique that can make up for the complications from PRK and LASIK. The most unique procedures in LASEK is covering of the cornea with epithelial flap after keratectomy. We examined the effect of corneal epithelial flap on the wound healing of canine cornea. METHODS: Operation was performed in eyes from 12 dogs, and the 12 eyes were recovered with epithelial flap and the remaining 12 eyes were recovered without epithelial flap. Wound healing process was compared using fluorescein staining, light and transmission electron microscopic examination. RESULTS: Fluorescein stained area of the cornea was reduced with time in both groups, and from 9 hours after the operation, it was significantly reduced in the group with epithelial flap compared with those of the group without epithelial flap (p< 0.05). On light microscopic examination of the group with epithelial flap, and normal epithelial structure was found at 24 and 48 hours, respectively. However, in the group without epithelial flap, no complete reepithelialization had occurred on center at 48 hours after the operation. On transmission electron microscopic examination, eyes of the group with epithelial flap showed hemidesmosomes in the area where epithelial flap was closely contacted with the stroma at 24 hours, and they were completely developed at 48 hours. On the other hand, in the group without epithelial flap, hemidesmosomes developed only in the proximal portion but not at the leading edge even at 48 hours. CONCLUSIONS: These results suggest that corneal epithelial flap accelerate the wound healing process of the cornea and the wound healing process depend on the vitality of the epithelial flap.
Animals ; Cornea ; Dogs ; Fluorescein ; Hand ; Hemidesmosomes ; Keratectomy, Subepithelial, Laser-Assisted ; Keratomileusis, Laser In Situ ; Refractive Surgical Procedures ; Wound Healing* ; Wounds and Injuries*

PURPOSE: High myopia is known to be a risk factor for long-term regression after laser refractive surgery. There have been few studies about the correction of moderate myopias that did not need retreatment after long-term follow-up. We evaluated 10 years of change in visual acuity and refractive power in eyes with moderate myopia after laser refractive surgery. METHODS: We included patients that had undergone laser in situ keratomileusis (LASIK) or laser-assisted subepithelial keratectomy (LASEK) to correct their myopia and that had at least 10 years of follow-up. We evaluated the stability of visual acuity in terms of safety, efficacy, and refractive changes at examinations 6 months and 1, 2, 5, 7, and 10 years after surgery. RESULTS: The study evaluated 62 eyes (36 eyes in LASIK patients and 26 eyes in LASEK patients). In both groups, the efficacy index tended to decrease, and it was consistently higher in the LASEK group compared to the LASIK group over the 10 years of follow-up. The safety index improved over 10 years and was always higher than 0.9 in both groups. The difference between the spherical equivalent at 6 months postoperatively and later periods was statistically significant after 5, 7, and 10 years in both groups (LASIK, p = 0.036, p = 0.003, and p < 0.001, respectively; LASEK, p = 0.006, p = 0.002, and p = 0.001, respectively). Ten years after surgery,26 eyes (66.7%) in the LASIK group and 19 eyes (73.1%) in the LASEK group had myopia greater than 1 diopter. In comparison with the thickness at 6 months postoperatively, central corneal thickness was significantly increased after 5, 7, and 10 years in both LASIK and LASEK groups (LASIK, p < 0.001, p < 0.001, and p < 0.001, respectively; LASEK, p = 0.01, p < 0.001, and p < 0.001, respectively). CONCLUSIONS: Moderately myopic eyes showed progressive myopic shifting and corneal thickening after LASIK and LASEK during 10 years of follow-up. We also found that early refractive regression may indicate the long-term refractive outcome.
Follow-Up Studies ; Humans ; Keratectomy, Subepithelial, Laser-Assisted* ; Keratomileusis, Laser In Situ* ; Myopia* ; Refractive Surgical Procedures ; Retreatment ; Risk Factors ; Visual Acuity

PURPOSE: To compare the safety and efficacy in patients of moderate or high myopia undergoing LASIK and LASEK in criteria of residual corneal thickness of 250 micro meter during six months after surgery. METHODS: We retrospectively analyzed data from 56 eyes of 30 patients in the LASIK group and 31 eyes of 18 patients in the LASEK group. All eyes underwent LASIK and LASEK with the Visx Star S2 excimer laser. All patients were evaluated using a standard protocol, then assessed at 1week, 2month, 6month after surgery. The refractive surgery mainly was performed with mainly LASIK, but was performed with LASEK in cases of the residual corneal thickness less than 250 micro meter. The data were analyzed with Student t-test for continuous data and Pearson chi-square analysis for proportion. RESULTS: A statistically significant difference in spherical equivalent was not observed among eyes that operated LASIK and LASEK during 6months. Uncorrected visual acuity(UCVA) was more rapid recovery after LASIK than LASEK at 1 week (LASIK: 0.73+/-0.24 LASEK: 0.59+/-0.25, p<0.05) but UCVA was no significant difference at 2 month and 6month. At 6month, 41.8% of LASIK were within +/-0.50D from emmetropia and 44.4% in LASIK. The UCVA was 0.8 or better in LASIK(67.9%) and LASEK(64.5%) CONCLUSIONS: There was no significant difference in moderate or high myopia between LASIK and LASEK for 6months, except showing a more rapid visual recovery in eyes that underwent LASIK at 1week after surgery. This study suggest that LASEK should be selected in cases of residual corneal thickness less than 250 micro meter in patients of moderate or high myopia.
Emmetropia ; Humans ; Keratectomy, Subepithelial, Laser-Assisted ; Keratomileusis, Laser In Situ* ; Lasers, Excimer ; Myopia* ; Refractive Surgical Procedures ; Retrospective Studies

PURPOSE: To evaluate the influence of central corneal thickness change after LASIK and LASEK to intraocular pressure (IOP) measured by Goldmann applanation tonometer and noncontact tonometer. METHODS: The pre-and post-operative IOP, central corneal thickness were measured in the 94 eyes of 47 patients who underwent refractive surgeries (LASIK and LASEK) from November 2000 to November 2001. Central corneal thickness was measured by ultrasonic pachymeter. IOP was measured by Goldmann applanation and noncontact tonometer. RESULTS: Post-operative IOP after LASIK and LASEK was significantly lower than pre-operative IOP. IOP measured with the noncontact tonometer was higher than that with Goldmann applanation tonometer in the group with thick cornea (>500micro meter in thickness) and lower in the group with thin cornea (< 500micro meter in thickness). Positive relationship between corneal thickness and measured IOP was greater in noncontact tonometer than Goldmann applanation tonometer. In noncontact tonometer, the amount of decreased IOP of LASIK group was greater than that of LASEK group. CONCLUSIONS: There was a close relationship between central corneal thickness and IOP. Measured IOP may be influenced by surgical method and type of tonometer. These findings suggest that we should be cautious when evaluating the IOP of eyes which underwent excimer laser refractive surgery because the measured IOP can be lower than actual IOP.
Cornea ; Humans ; Intraocular Pressure* ; Keratectomy, Subepithelial, Laser-Assisted* ; Keratomileusis, Laser In Situ* ; Lasers, Excimer ; Refractive Surgical Procedures ; Ultrasonics