Laser In Situ Keratomileusis Group Research Articles

Laser in situ keratomileusis versus laser-assisted subepithelial keratectomy for the correction of high myopia

Purpose: To compare the visual and refractive outcomes of laser in situ keratomileusis (LASIK) and laser-assisted subepithelial keratectomy (LASEK) in the treatment of high myopia. Setting: Institute of Vision Research, Department of Ophthalmology, College of Medicine, Yonsei University, and Balgeunsesang Ophthalmology Clinic, Seoul, South Korea. Methods : Four hundred seventy eyes of 240 patients with manifest refraction spherical components greater than –6.00 diopters (D) were assigned to 2 groups: 324 eyes (167 patients) were treated with LASIK and 146 eyes (73 patients), with LASEK. Uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), remaining refractive error, corneal haze, and complications were followed in both groups for 12 months. Results: At 12 months, the mean spherical equivalent (SE) was within ±0.50 D of emmetropia in 205 eyes (63.3%) in the LASIK group and 81 eyes (55.5%) in the LASEK group and within ±1.00 D in 261 eyes (80.6%) and 104 eyes (71.2%), respectively. The UCVA was 20/25 or better in 269 LASIK eyes (83.0%) and 111 LASEK eyes (76.0%). There was more than a 1-line loss of BSCVA in 4 LASIK eyes (1.2%) and 21 LASEK eyes (14.3%). The between-group differences in SE, magnitude of cylinder, UCVA, and haze were statistically significant ( P<.05). Conclusions: Both LASIK and LASEK were safe and effectively treated eyes with high myopia. Laser in situ keratomileusis provided superior results in visual predictability and corneal opacity.

Fourier analysis of induced irregular astigmatism: photorefractive keratectomy versus laser in situ keratomileusis in a bilateral cohort of hyperopic patients

Purpose To analyze corneal topographic data by Fourier analysis to determine differences in irregular astigmatism following spherical hyperopic correction by photorefractive keratectomy (PRK) or laser in situ keratomileusis (LASIK). Setting Department of Ophthalmology, St. Thomas’ Hospital, London, United Kingdom. Methods Thirty-six eyes of 18 patients with moderate hyperopia had LASIK in 1 eye and PRK in the other eye. The flap was cut on a nasal hinge with a Moria LSK One microkeratome. The laser was a Summit SVS Apex Plus® with an optical zone of 6.5 mm and a blending zone of 1.5 mm. Corneal topographic data were acquired with a TMS-1 topographer (Computed Anatomy Inc.) preoperatively and 1, 3, 6, and 12 months postoperatively. The ASCII files containing the dioptric power values were extracted and analyzed with custom-written software to extract the Fourier harmonics. Results The irregular astigmatism increased in both groups postoperatively, peaking at 3 months and then decreasing over the next 9 months. There was no statistically significant difference between the 2 groups at any time point ( P<.05). The change in the topographically derived equivalent sphere showed undercorrection in both groups at all time points. Regular astigmatism showed a marginal statistically significant increase in the LASIK group at 12 months ( P = .049). Conclusion Irregular astigmatism, equivalent sphere, and regular astigmatism were not significantly different in the PRK and LASIK groups during the follow-up. Based on the corneal topography, the 2 procedures induced an equal amount of irregular astigmatism.

Photorefractive keratectomy or laser in situ keratomileusis for residual refractive error after phakic intraocular lens implantation

Purpose To evaluate the results of combining phakic posterior chamber intraocular lens (IOL) implantation and excimer corneal surgery to treat high myopia or myopia with astigmatism. Setting Service d’Ophtalmologie, Hôpital Purpan, University of Toulouse, Toulouse, France. Methods Thirty-two eyes of 28 patients with extreme myopia or myopia combined with astigmatism were treated by implantation of a phakic posterior chamber IOL. Residual refractive errors were treated no earlier than 6 weeks after IOL implantation by photorefractive keratectomy (PRK) in eyes with low refractive errors or by laser in situ keratomileusis (LASIK) in eyes with higher residual refractive errors. Results The mean preoperative spherical equivalent (SE) refraction was −18.7 diopters (D). The refractive astigmatism ranged from 0 to 3.5 D. After excimer laser treatment, the SE refraction ranged from −0.5 to −2.5 D and the refractive astigmatism, from 0 to 1.5 D in the PRK group. In the LASIK group, spherical ametropia ranged from −1.5 to +1.5 D and astigmatism, from 0 to 1.0 D. After excimer laser treatment, the uncorrected visual acuity improved in all eyes but a loss of 1 line of the corrected vision after IOL implantation occurred in 22.2% of PRK-treated eyes and in 13.6% of LASIK-treated eyes. Conclusion Bioptic treatment of extreme myopia and myopia associated with astigmatism appears to be safer and more predictable than other methods of treatment.

Treatment of simple hyperopia: comparison of laser in situ keratomileusis and laser thermal keratoplasty

Purpose To evaluate and compare the efficacy, stability, and safety of laser in situ keratomileusis (LASIK) and laser thermal keratoplasty (LTK) for the treatment of simple hyperopia. Setting John Hill Eye and Laser Centre, Cape Town, South Africa. Methods This retrospective study comprised consecutive patients having primary treatment of simple hyperopia of up to 3.0 diopters (D) with astigmatism of 0.5 D or less. Treatment methods were as follows: Group 1 (81 eyes), LASIK with the Nidek EC-5000 excimer laser; Group 2 (69 eyes), LASIK with the LaserSight LSX® excimer laser; and Group 3 (84 eyes), LTK with the Sunrise holmium:YAG laser. Results The hyperopia decreased in all 3 groups. Both LASIK groups were stable by 1 month; there was continued regression in the LTK group for up to 18 months. The percentage of eyes achieving uncorrected visual acuities of 20/20 and 20/40 at 3 months were Nidek, 41% and 92%, respectively; LaserSight, 50% and 90%, respectively; and LTK, 21% and 89%, respectively. No eye lost more than 2 lines of best spectacle-corrected visual acuity. Surgically induced astigmatism (SIA) was evident in all 3 groups; it was highest in the LTK group. The mean posttreatment astigmatism was –0.47 D ± 0.40 (SD) (range 0 to −1.50 D) in the Nidek group, –0.45 ± 0.40 D (range 0 to −1.25 D) in the LaserSight group, and –0.81 ± 0.51 D (range 0 to −2.25 D) in the LTK group. The enhancement rates were 16.75%, 22.57%, and 38.30%, respectively. Because of the SIA, 61% of the LTK enhancements were corrected with LASIK. Conclusions All 3 treatment methods corrected hyperopia, but stability was achieved early in both LASIK groups, allowing early enhancement when necessary. Because LTK cannot currently correct astigmatism, many of the LTK repeat treatments required LASIK procedures. For these reasons, LASIK remains my preferred method to treat simple hyperopia up to +3.0 D.

Recovery of corneal sensation after myopic correction by laser in situ keratomileusis with a nasal or superior hinge

Purpose To measure corneal sensitivity after laser in situ keratomileusis (LASIK) to determine the time required for recovery of this parameter. Setting Ohshima Hospital of Ophthalmology, Fukuoka, Japan. Methods Corneal sensation was measured with a Cochet-Bonnet-type esthesiometer in 75 patients before and 1, 3, 6, and 12 months after correction of myopia by photorefractive keratectomy (n = 21) or LASIK (n = 54). Results Photorefractive keratectomy did not affect corneal sensation. In the LASIK group, a large and significant decrease in corneal sensitivity was apparent at 1 month ( P<.05). Although corneal sensitivity appeared to have recovered slightly at 3 months, it remained significantly decreased ( P<.05). By 6 or 12 months, the corneal sensitivity in LASIK patients was not statistically different from the preoperative values in the study patients. A significantly greater decrease in corneal sensitivity was apparent in the LASIK patients with a nasal hinge than in those with a superior hinge (F = 7.54, P<.01). Corneal sensitivity was in the normal range in 31.5% of LASIK patients at 3 months and in 57.4% and 82.1% at 6 and 12 months, respectively. Conclusion Recovery of corneal sensation had begun 3 months after LASIK and appeared complete after 12 months.

Reliability of pachymetric measurements using orbscan after excimer refractive surgery

Purpose To assess the accuracy of pachymetric measurements using Orbscan (Bausch & Lomb, Rochester, NY) after laser in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK). Design Prospective instrument validation study. Participants Seventy-nine nonoperated normal eyes, 84 eyes after LASIK, and 50 eyes after PRK. Intervention Laser in situ keratomileusis or PRK. Methods Central corneal thickness 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. Main outcome measures Central corneal thickness as measured by Orbscan and ultrasound pachymeter. Results Using the adjusted AF, which was 0.946, the mean difference between Orbscan and ultrasonic pachymetric measurements was 0 ± 17, 16 ± 28, and 68 ± 39 μm in the normal, LASIK, and PRK groups, respectively. The difference between all groups was statistically significant ( P < 0.0001). Conclusions Orbscan pachymetric values may be underestimated and less accurate after LASIK and PRK.

Effect of Photorefractive Keratectomy and Laser in situ Keratomileusis in High Myopia on logMAR Visual Acuity and Contrast Sensitivity

To compare effect of photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) on contrast sensitivity (CS) and best corrected visual acuity (BCVA) in high myopia. 38 myopes (PRK) and 31 patients (LASIK) were examined before and 1, 3, 6, and 12 months postoperatively. Mean preoperative spherical equivalent was -8.0 +/- 1.7D (PRK) and -9.2 +/- 2.1D (LASIK). CS was tested on a computerized system of the Contrast Sensitivity 8010 Type at 6 spatial frequencies (0.74 and 29.55 c/deg), BCVA was measured on logMAR charts. At 12 months postoperatively, mean spherical equivalent was -0.6 +/- 1.0D (PRK) and -1.0 +/- 0.8D (LASIK). Postoperative values of CS were significantly higher in the PRK group, except for spatial frequencies of 3.69 and 7.39 c/deg up to 3 months postoperatively. The initial significant decrease of BCVA lasted up to 6 months after PRK. In the LASIK group BCVA was not significantly different from its preoperative level at the 3-months follow-up. The significant improvement of CS after PRK suggest that PRK can improve quality of vision in eyes with high myopia. Although recovery of BCVA after LASIK was faster than after PRK, there may be a persistent decrease in CS.

Induced irregular astigmatism in hypermetropic PRK and LASIK: a bilateral cohort study

Purpose: To determine if there was a difference in irregular astigmatism following hypermetropic correction with Photorefractive Keratectomy (PRK) and Laser In Situ Keratomileusis (LASIK) by Fourier analysis of corneal topographical data.Methods: Thirty‐six eyes of 18 patients affected by hypermetropia were enrolled as part of a prospective study in which one eye was treated with PRK and the other with LASIK. In the eyes that underwent LASIK the flap was cut on a nasal hinge with a LSK one microkeratome. The laser system was a Summit SVS Apex Plus with an optical zone of 6.5 mm and a blending zone of 1.5 mm. Corneal topographical data was acquired with a TMS‐1 pre‐operatively and at 1, 3, 6 and 12 months post‐operatively. The dioptric files for each time point were converted into ASCII format and subsequently analysed with purpose written software to extract the Fourier harmonics. This permitted the objective analysis of the irregular astigmatism, equivalent spherical component and regular astigmatism.Results: The irregular astigmatism increased in both groups post‐operatively, reached a peak at 3 months and then reduced over the next 9 months. There was no statistically significant difference between the two groups at any time point (p &lt; 0.05 all cases). At 12 months the irregular astigmatism values for both groups remained above their pre‐operative levels.Conclusion: The irregular astigmatism analysed in this study showed no statistically significant difference between the PRK and the LASIK group throughout the follow‐up period. It appears that, from a corneal topographical point of view, the two procedures induce an equal amount of irregular astigmatism.

Refractive change in response to acute hyperbaric stress in refractive surgery patients

Purpose To determine whether acute hyperbaric stress affects visual acuity or refractive power after keratorefractive surgery. Setting Clinical multiplace hyperbaric chamber and ophthalmology clinic, University of California, San Diego, California, USA. Methods This prospective convenience sample study included 3 groups: 3 patients who had had bilateral myopic radial keratotomy (RK); 2 who had had bilateral myopic laser in situ keratomileusis (LASIK); and 4 control subjects who had no previous corneal refractive surgery or ocular pathology but had a myopic refractive error (−1.25 to −8.38 diopters [D]) similar to that in the treated patients before refractive surgery. One additional patient had had unilateral LASIK only and was included in the LASIK and control groups. Best spectacle-corrected visual acuity (BSCVA), manifest spherocylindrical refractive error, and intraocular pressure were measured at baseline, at 4 atmospheres absolute (atm abs), and on return to ambient pressure. Corneal pachymetry and keratometry were measured at baseline and on return to ambient pressure. Results The mean BSCVA changed from 0.06 logMAR (20/25 Snellen equivalent) at baseline to 0.10 logMAR (20/25) at 4 atm abs in the RK group and from 0.00 logMAR (20/20) to −0.06 logMAR (20/15) in the LASIK group; it did not change in the control group. The mean refractive error changed from 0.25 D at baseline to 0.50 D at 4 atm abs in the RK group, from −0.90 to −1.02 D in the LASIK group, and from −4.58 to −4.53 D in the control group. Conclusion Acute hyperbaric stress did not appear to alter refractive power after corneal surgery.

Comparison of iris-fixed Artisan lens implantation with excimer laser in situ keratomileusis in correcting myopia between −9.00 and −19.50 diopters: A randomized study

Objective To compare Artisan lens implantation with laser in situ keratomileusis (LASIK) for the correction of myopia between −9.00 and −19.50 diopters. Design Prospective randomized clinical trial. Participants Ninety eyes of 61 consecutive patients were enrolled in the study. Intervention Forty-five eyes (50%) received Artisan lens, and 45 eyes (50%) received LASIK; the procedure assigned to each eye was randomized. Eighteen patients (29.5%) received Artisan lens in one eye and LASIK in the other. Main outcome measures Slit-lamp microscopy, manifest refraction, uncorrected and spectacle-corrected visual acuity, contrast sensitivity, and specular microscopy were performed before surgery, and 1, 3, 6, and 12 months after surgery. Patient satisfaction and preference were assessed by a subjective questionnaire. Results At 1 year, 43 eyes (95.6%) from the Artisan group and 41 eyes (91.1%) from the LASIK group were examined, the mean spherical equivalent refraction was −0.64 ± 0.8 diopter in the Artisan eyes and −0.87 ± 0.8 in the LASIK eyes. The uncorrected visual acuity was 20/20 or better in 9 Artisan eyes (20.9%) and 5 LASIK eyes (12.2%) and 20/40 or better in 38 Artisan eyes (88.4%) and 24 LASIK eyes (58.5%); no Artisan eyes and 5 LASIK eyes (12.2%) lost 2 or more Snellen lines of spectacle-corrected visual acuity. One Artisan eye (2.3%) and six LASIK eyes (14.6%) reported severe night glare; the Artisan lens was exchanged with a larger optic diameter lens. Mean endothelial cell loss at 1 year was 0.7 ± 1.1 cells/mm 2 in the Artisan eyes and 0.3 ± 0.9 cells/mm 2 in the LASIK eyes. Contrast sensitivity curve decreased by 2 or more lines in two Artisan (4.7%) and six LASIK eyes (14.6%). Of the 18 patients who received both surgeries, one in each eye, 13 patients (72.2%) preferred the Artisan procedure because of the better quality of vision. Conclusions In this study, Artisan lens implantation and LASIK were found to be similarly effective, stable, and reasonably safe for the correction of myopia between −9.00 and −19.50 diopters. Better uncorrected and spectacle-corrected visual acuity and contrast sensitivity, a lower enhancement rate, and exchangeability are the main advantages of Artisan lens implantation. Thirteen (72.2%) of the 18 patients who received the Artisan lens in one eye and LASIK in the other preferred the Artisan lens to the LASIK, mainly because of the better quality of vision.

Astigmatic changes after excimer laser refractive surgery

Purpose To compare the astigmatic changes induced by spherical and elliptical excimer laser in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK). Setting University-based refractive surgery practice. Methods Three-month refractive data from 317 eyes of consecutive patients having spherical PRK, astigmatic PRK (A-PRK), spherical LASIK, and astigmatic LASIK (A-LASIK) by a single surgeon (J.S.P.) using VISX 2020B and Star lasers over 2 years were studied for astigmatic changes resulting from the surgical procedure. Results At 3 months, the mean change in absolute astigmatism was +0.15 diopter (D) and −0.07 D in the spherical PRK and LASIK groups, respectively. Photorefractive keratectomy tended to induce with-the-rule (WTR) astigmatism, while LASIK was astigmatically neutral. As expected, the eyes treated with A-PRK and A-LASIK achieved a greater reduction in absolute astigmatism (−1.02 D and −1.28 D, respectively) than those treated with spherical PRK and LASIK. The qualitative nature of the astigmatic change was different between flap-based and PRK-based procedures. Conclusions Spherical PRK is more likely than spherical LASIK to induce astigmatism, with a tendency toward WTR astigmatism. The eyes treated with spherical LASIK had no preponderant change in the direction of astigmatic magnitude or axis. Astigmatic PRK and LASIK effectively reduced astigmatism along the preoperative axis; A-LASIK tended to induce a random resultant axis in most patients.

Photorefractive keratectomy versus laser in situ keratomileusis: Comparison of optical side effects

Objective This report presents patient-reported optical symptoms after photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK). Design Preoperative and postoperative patient surveys in a prospective, multicenter, randomized clinical trial. Participants Two hundred twenty eyes of 220 patients entered the study; 105 were randomized to PRK and 115 were randomized to LASIK. Intervention All patients received a one-pass, multizone excimer laser ablation as part of either a PRK or LASIK procedure. Attempted corrections ranged from 6.00 to 15.00 diopters (D). Main outcome measures Glare, halo, and monocular diplopia symptoms as reported by patients on questionnaires before surgery and at the 6-month follow-up. Comparison was made between symptoms when using optical correction before surgery and symptoms without correction after surgery. Results For both the PRK and LASIK groups analyzed individually, the difference in average glare index before surgery and after surgery was not statistically significant ( P = 0.54 for PRK; P = 0.15 for LASIK; t test). Twenty-four PRK patients (41.4%) reported worsening of glare symptoms from baseline compared with 11 LASIK patients (21.6%); however, the difference between the two groups was not statistically significant ( P = 0.086, chi-square test). Within the PRK group, the difference in average halo index before and after surgery was statistically significant ( P = 0.0003, t test); in the LASIK group, it was not statistically significant ( P = 0.11, t test). Thirty-four PRK patients (58.6%) reported worsening of halo symptoms from baseline compared with 26 LASIK patients (50.0%); this difference was not statistically significant ( P = 0.086, chi-square test). For both the PRK and LASIK groups, the difference in average diplopia index before and after surgery was statistically significant ( P < 0.0001 for PRK; 0.047 for LASIK; t test). Twenty-six PRK patients (44.8%) reported a worsening of monocular diplopia symptoms from baseline compared with 19 LASIK patients (35.8%); this difference was not statistically significant ( P = 0.39, chi-square test). When changes in glare and halo from before surgery to after surgery were pooled as a glare–halo index, however, the PRK group did show a significantly greater likelihood of demonstrating an increase in symptoms compared with the LASIK group ( P = 0.048, chi-square test). Conclusions Optical sequelae of glare, halo, and monocular diplopia may occur in some patients after either both PRK or LASIK for moderate to high myopia; in contradistinction, many other patients’ preoperative symptoms improve after surgery. On average, PRK patients show an increase in halo and diplopia symptoms, but not glare, after surgery, and LASIK patients show an increase in diplopia, but not glare and halo symptoms. There is a suggestion of a somewhat lesser tendency toward postoperative optical symptoms in LASIK compared with PRK treated eyes.

Surgical outcomes of photorefractive keratectomy and laser in situ keratomileusis by inexperienced surgeons

Purpose To investigate the results of photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) procedures performed by novice ophthalmologists and compare the results with those of experienced refractive surgeons. Setting Doheny Eye Institute, University of Southern California, Los Angeles, and Department of Ophthalmology, University of California, Irvine, California, USA. Methods In this retrospective case series, data were examined from the first PRK procedures by 33 consecutive ophthalmologists and the first LASIK procedures by 19 consecutive ophthalmologists. Preoperative and postoperative uncorrected visual acuity (UCVA) and best spectacle-corrected visual acuity (BSCVA), as well as intraoperative and early postoperative complications, were recorded. Results In the PRK group, 33.3% of eyes achieved a UCVA of 20/20 and 87.8%, 20/40 or better; 54.5% were within ±0.5 diopter (D) of emmetropia and 87.8%, within ±1.0 D. Two eyes with a preoperative spherical equivalent of greater than –11.0 D lost 2 lines of BSCVA. If eyes with low myopia (≤ –6.5 D) only were included, 40.7% achieved a UCVA of 20/20 and 96.3%, 20/40 or better. In the LASIK group, 52.6% achieved a UCVA of 20/20 and 84.2%, 20/40 or better; 78.9% were within ±0.5 D of emmetropia and 89.5%, ±1.0 D. No eye in the LASIK group lost 2 or more lines of BSCVA. Conclusions Photorefractive keratectomy and LASIK are reasonably safe procedures that can be learned quickly by ophthalmic surgeons. Our data suggest that results achieved by beginning surgeons are comparable to those reported by experienced surgeons.

Topical intrastromal steroid during laser in situ keratomileusis to retard interface keratitis

PurposeTo evaluate the effect of an intraoperative topical intrastromal steroid on the incidence and severity of nonspecific diffuse intralamellar keratitis (NSDIK). SettingT.L.C. The Laser Center, Brea, California, USA. MethodsThis prospective study included 2 cohort groups, each consisting of 105 consecutive eyes treated with laser in situ keratomileusis (LASIK) for myopia and astigmatism. Group A received the standard LASIK medication protocol and Group B, an additional drop of prednisolone sodium phosphate 1% solution on the undersurface of the cap immediately after it was reflected, prior to initiating the laser treatment. After the laser treatment was completed, the flap was repositioned; 1 minute after the steroid application, the interface was irrigated. All patients were examined postoperatively and placed in 1 of 4 categories: no interface keratitis, grade 1 (mild), grade 2 (moderate with decreased vision), or grade 3 (severe with decreased vision). ResultsThe incidence of NSDIK in Group A was 17.1% (18 eyes); 14 eyes (78.0%) were grade 1 and 4 (22.0%), grade 2. The incidence in Group B was 6.7% (7 eyes); all eyes were grade 1. Topical intrastromal steroid application significantly reduced the incidence and severity of NSDIK (P < .01). ConclusionWe propose that intraoperative intrastromal steroid application is a safe and effective way to reduce the incidence and severity of NSDIK.

Initial results of photorefractive keratectomy and laser in situ keratomileusis performed by a single surgeon

Purpose To determine the safety and efficacy of photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) early in a surgeon’s experience. Setting Ophthalmology Department, John A. Moran Eye Center, Salt Lake City, Utah, USA. Methods Between October 1995 and April 1997, a retrospective analysis was performed of 200 eyes in 128 patients who had PRK or LASIK with a follow-up of at least 3 months. The mean age was 38.1 years ± 10.4 (SD) in the PRK group and 42.3 ± 10.1 years in the LASIK group. There were 36 women and 30 men in the former and 32 women and 30 men in the latter. Photorefractive keratectomy, PRK/astigmatic keratotomy (AK), LASIK, or LASIK/AK was performed with the Summit Omnimed excimer laser. Preoperative evaluation included uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), cycloplegic refraction, tonometry, and computerized videokeratography. At 1, 3, and 6 months, UCVA, BSCVA, mean spherical equivalent (SE), astigmatism, corneal haze, subjective vision (day, night, glare, and halo), and complications were measured. Results Mean SE was 0.16 ± 0.82 diopter (D) in the PRK group and −0.09 ± 0.63 D in the LASIK group at 1 month ( P < .05), −0.18 ± 0.66 D and −0.16 ± 0.58 D, respectively, at 3 months, and −0.33 ± 0.73 D and −0.09 ± 0.62 D, respectively, at 6 months. Achieved correction was similar in the 2 groups. Mean BSCVA was 22.8 ± 6.0 in the PRK group and 22.2 ± 5.3 in the LASIK group at 1 month, 21.1 ± 6.0 and 21.1 ± 3.1, respectively, at 3 months, and 19.8 ± 3.5 and 22.9 ± 5.2, respectively, at 6 months ( P < .005). Mean surface regularity index was 0.68 ± 0.40 in the PRK group and 0.86 ± 0.41 in the LASIK group at 1 month, 0.54 ± 0.26 and 0.72 ± 0.37, respectively, at 3 months ( P < .05), and 0.49 ± 0.27 and 0.84 ± 0.42, respectively, at 6 months. Mean surface asymmetry index was 0.71 ± 0.43 in the PRK group and 0.55 ± 0.21 in the LASIK group at 1 month ( P < .05), 0.53 ± 0.24 and 0.51 ± 0.23, respectively, at 3 months, and 0.46 ± 0.19 and 0.64 ± 0.54, respectively, at 6 months. The subjective parameters between the groups were significantly different only at 6 months; patients in the PRK group reported better day and night vision. Conclusion With careful preparation and proper training, PRK and LASIK appear to be safe and efficacious even during the surgeon’s early learning phases.

Comparison of wound healing after photorefractive keratectomy and laser in situ keratomileusis in rabbits

Purpose To evaluate and compare the corneal wound-healing process after photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK). Setting Kangnam St. Mary’s Hospital, Seoul, Korea. Methods Two surgical procedures, PRK with the VISX Star excimer laser and LASIK with a MicroTech microkeratome, were performed in 24 rabbit eyes. In the PRK group (n=12 eyes), the rabbit cornea was treated with a 20 μm ablation. In the LASIK group (n=12 eyes), a 20 μm laser ablation was performed after a 150 μm thick hinged corneal flap had been made. During both procedures, dichlorotriazinyl aminofluorescien (DTAF) dye was applied to the ablated stromal bed; in the LASIK group, the stromal side of the corneal flap was also stained with DTAF to differentiate regenerated collagen from normal stromal tissue. Corneal wound healing was evaluated postoperatively at 1, 4, 8, and 12 weeks using light, electron, and fluorescence microscopy. The amount of regenerated stromal tissue and the number of keratocytes were analyzed by an image-analysis system. Results In the PRK group, epithelial migration and regeneration were observed in the ablated area without any stromal regeneration 1 week postoperatively. However, newly regenerated, irregularly arranged stromal collagen, with epithelial hyperplasia in the ablated area, was observed 4 to 12 weeks postoperatively by light and fluorescence microscopy. The number of keratocytes in the surgical area was also increased. In ultrastructural observation using an electron microscope, the shape of keratocytes in the ablated area was changed, and the number of rough and smooth endoplasmic reticuli, ribosomes, mitochondria, and electron-dense vesicles in the cytoplasm were increased, suggesting that the cells were activated. In the LASIK group, there was no observed regenerated collagen between the corneal flap and the ablated stromal bed except in the wound margin. Lamellated, parallel collagen fibers in the cornealstroma were not disturbed. However, in the wound margin, corneal epithelial ingrowth between the flap and the stromal bed was observed, as was some regenerated stromal tissue. The amount of regenerated stromal tissue and the number of keratocytes in the wound area were statistically smaller than those in the PRK group ( P < .05). Observation by electron microscopy showed no activated keratocytes, unlike in the PRK group. The collagen fibers in the wound area were parallel. Conclusion Stromal wound healing in the LASIK group was minimal compared with that in the PRK group, except in the wound margin. These results may support the clinical findings of less corneal haze in the human cornea after LASIK.

Surgically induced astigmatism after photorefractive keratectomy and laser in situ keratomileusis

Purpose: To compare the axis and magnitude of surgically induced astigmatism inphotorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK). Setting: Multicenter clinical trial. Methods: In this prospective, randomized trial, 220 eyes of 220 patients entered the study cohort; 105 randomized to PRK and 115 to LASIK. All patients received a single-pass, multizone excimer laser ablation as part of a PRK or LASIK procedure. Attempted corrections ranged from −6.00 to −15.00 diopters (D). The LASIK procedures were performed with nasal hinges. Absolute changes in astigmatism and axis and magnitude of surgically induced astigmatism were analyzed. Patients were followed for up to 6 months. Results: In the PRK group, the mean change in absolute astigmatism was +0.14,+0.16, and +0.32 D at 1, 3, and 6 months, respectively; in the LASIK group, the mean change was −0.15, −0.08, and −0.03 D, respectively. At all time points, a greater proportion of PRK than LASIK eyes had an increase in absolute magnitude of astigmatism. In the PRK group, the axis of vectoral-induced astigmatism was significantly different from random at 3 and 6 months ( P = .01, P < .001, respectively) with a tendency for induced with-the-rule shifts postoperatively. In the LASIK group, the axis of vectoral-induced astigmatism was significantly different from random at only 1 month ( P = .04), and there was no preponderant direction of axis shift. Despite these findings, other analyses ,showed no statistically significant between-group differences in vectoral axis or magnitude of surgically induced astigmatism. Conclusions: Induced astigmatism was generally less and more random in axis in LASIK than in PRK; a general trend for induced with-the-rule astigmatism in PRK. was not seen in LASIK. Hypothetically, the lamellar corneal flap in LASIK may counteract the tendency toward steepening at 90 degrees seen in PRK by retracting toward the hinge, by masking underlying induced astigmatism in, the ablation zone, or by its mitigating influence on postoperative corneal healing.

Gelatinase B and A expression after laser in situ keratomileusis and photorefractive keratectomy.

To compare the expression of gelatinases in the corneal epithelium and stroma after laser in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK). Rabbit eyes were treated with LASIK (n=11), PRK (n=12), or corneal flap construction (n=12); 4 eyes served as unwounded controls. Zymography was performed on the central epithelium and the stroma 1, 3, and 7 days after surgery to determine the expression of gelatinases. Epithelial expression of gelatinase B in the LASIK group (0%-25%) was lower than that in the PRK group at all time points (50%-100%) and was identical to the corneal flap group. Stromal expression of gelatinases A and B was similar after LASIK and PRK, but was minimal after corneal flap construction at all time points. Epithelial expression of gelatinase A was similar for the first 3 days after LASIK and PRK but not thereafter. Gelatinase B epithelial expression was up-regulated after PRK but not after LASIK. Gelatinase B stromal expression was up-regulated after both procedures. Differences in wound healing and subepithelial scarring after these 2 procedures may be related to gelatinase B.

Corneal light scattering with stromal reformation after laser in situ keratomileusis and photorefractive keratectomy

Objective: To correlate corneal light scattering with keratocyte and extracellular matrix reformation after laser in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK).Setting: Wilmer Ophthalmological Institute, Johns Hopkins University, Baltimore, Maryland, USA.Methods: Sixteen pigmented rabbit eyes were randomly divided Into 2 groups. Group 1 (n=8) had a 5.0 mm, -10.0 diopter (D) LASIK treatment and Group 2 (n=8), a 6.0 mm, -10.0 D surface PRK treatment after mechanical epithelial debridement. The stromal surface exposed at surgery was stained with dichlorotriazinylaminofluQrescein (DTAF) solution. Slitlamp biomicroscopic and objective measurement of corneal light scattering using a scatterometer were performed 1 and 2 days and 1, 2, 3, 4, 8, and 12 weeks after surgery. In each group, 2 corneas were harvested at 1 week and 1 month and 4 corneas were harvested at 12 weeks. Tissue sections were examined by light and fluorescence microscopy. The percentage of newly formed stromal tissue was calculated and correlated with the scatterometry index.Results: In Group 1, corneas remained clear and healed without significant scarring throughout the study. In Group 2, subepithelial scarring was noted. Extracellular matrix reformation peaked at 1 month and showed a slight regression thereafter. The percentage of extracellular matrix reformation was strongly correlated with the scatterometry index (r = .86, P < .001).Conclusions: In this study, significant subepithelial stromal tissue reformation followed PRK. The percentage of extracellular matrix reformation correlated well with the objective corneal light scattering measurements.

Corneal topography of photorefractive keratectomy versus laser in situ keratomileusis

Objective This study aimed to compare qualitative patterns of corneal topography early in the postoperative course after excimer laser photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) when used for the treatment of myopia of 6.0 to 15.0 diopters. Design The study design was a prospective, multicenter, randomized clinical trial. Participants A total of 64 eyes were treated with PRK and 54 eyes were treated with LASIK. Intervention Using the Summit Apex excimer laser, patients received either PRK or LASIK using a single pass, multizone excimer laser ablation. Computer-assisted videokeratography was performed at designated postoperative examinations. Main outcome measures Videokeratography maps at 1 and 3 months after surgery were classified using a standard classification scheme. The association of topography patterns to loss of spectacle-corrected visual acuity was tested. Results At 1 month, for the PRK (n = 60) and LASIK (n = 51) groups, respectively, 63.3% and 19.6% of eyes fell into one of the four optically irregular groups (central island, keyhole, semicircular, or irregularly irregular; P < 0.001). At 3 months, for the PRK (n = 49) and LASIK (n = 39) groups, respectively, 36.7% and 10.3% of eyes fell into one of the optically irregular groups ( P = 0.004). Comparing the 1- and 3-month examination results in the PRK and LASIK groups, respectively, 19 (42%) of 45 eyes and 11 (31%) of 36 eyes had a change in topography, generally to an optically smoother pattern. The irregular groups, taken together, were associated with a greater tendency toward loss of spectacle-corrected visual acuity of two or more Snellen lines ( P = 0.01). There also was greater tendency toward loss of spectacle-corrected visual acuity in the PRK group that diminished with time ( P < 0.01 at 1 month, P = 0.05 at 3 months). Conclusions After treatment for moderate-to-high myopia, LASIK topography patterns generally are more regular than are PRK patterns. This may be a result either of masking of underlying topography perturbations by the lamellar corneal flap, thus mitigating induced topography changes, or differences in surface wound healing. This study suggests that more rapid return of spectacle-corrected visual acuity found in patients treated with LASIK may be a result of more regular topography patterns early in the postoperative course.