Conventional Photorefractive Keratectomy Research Articles

Astigmatism: Risk factor for postoperative corneal haze in conventional myopic photorefractive keratectomy

Astigmatism: Risk factor for postoperative corneal haze in conventional myopic photorefractive keratectomy

Astigmatism: Risk factor for postoperative corneal haze in conventional myopic photorefractive keratectomy

To retrospectively assess risk factors other than high myopia for corneal haze in patients who had conventional photorefractive keratectomy (PRK) without mitomycin-C (MMC). Department of Ophthalmology, Naval Hospital Camp Pendleton, California, USA. This retrospective study comprised 362 eyes of 193 military members who had conventional PRK with the Star excimer laser system from 2004 to 2006. Study inclusion criteria were myopia less than -6.0 diopters (D) spherical equivalent with or without astigmatism, no MMC applied, and at least 3 months of postoperative data available. Nine eyes had grade 2 corneal haze or greater. Of these eyes, 5 had greater than 2.0 D of astigmatism and 4 had no identifiable risk factors. Clinically significant postoperative corneal haze was associated with the level of preoperative astigmatism (P<.001). Preoperative astigmatism was significantly associated with the development of corneal haze after conventional PRK without MMC. Based on these data, surgeons should consider prophylactic MMC use during conventional PRK procedures for patients with moderate to high levels of astigmatism (approximately >or=1.25 D).

Management of Irregular Astigmatism Following Rotationally Disoriented Free Cap After LASIK

To illustrate the challenges associated with a misaligned free flap (cap) and to report the outcome of applying wavefront-guided customized photorefractive keratectomy (PRK) followed by conventional PRK ablation to correct residual refractive error and aberrations after LASIK free cap complications. The clinical course and surgical interventions of two patients with free cap complications from LASIK surgery were reviewed. The first patient underwent a total of six interventions after the initial LASIK procedure, and the second patient underwent a total of five interventions. Interventions included cap lift, cap rotation, custom PRK, and conventional PRK enhancement with prophylactic topical mitomycin C (MMC). Customized PRK treatment and subsequent enhancements with prophylactic topical MMC led to the recovery of best spectacle-corrected visual acuity (BSCVA), neutralization of higher and lower order aberrations, and astigmatic neutrality. Symptoms related to higher order aberrations resolved in both patients. Wavefront-guided custom PRK for higher order aberrations followed by conventional PRK enhancement for residual lower order aberrations, both with topical MMC application, represents an efficacious strategy for treating patients with loss of BSCVA and visual symptoms due to LASIK free cap complications.

Biomechanical and Wound Healing Characteristics of Corneas After Excimer Laser Keratorefractive Surgery

To describe the biomechanical and wound healing characteristics of corneas after excimer laser keratorefractive surgery. Histologic, ultrastructural, and cohesive tensile strength evaluations were performed on 25 normal human corneal specimens, 206 uncomplicated LASIK specimens, 17 uncomplicated sub-Bowman's keratomileusis (SBK) specimens, 4 uncomplicated photorefractive keratectomy (PRK) specimens, 2 uncomplicated advanced surface ablation (ASA) specimens, 5 keratoconus specimens, 12 postoperative LASIK ectasia specimens, and 1 postoperative PRK ectasia specimen and compared to previously published studies. Histologic and ultrastructural studies of normal corneas showed significant differences in the direction of collagen fibrils and/or the degree of lamellar interweaving in Bowman's layer, the anterior third of the corneal stroma, the posterior two-thirds of the corneal stroma, and Descemet's membrane. Cohesive tensile strength testing directly supported these morphologic findings as the stronger, more rigid regions of the cornea were located anteriorly and peripherally. This suggests that PRK and ASA, and secondarily SBK, should be biomechanically safer than conventional LASIK with regard to risk for causing keratectasia after surgery. Because adult human corneal stromal wounds heal slowly and incompletely, all excimer laser keratorefractive surgical techniques still have some distinct disadvantages due to inadequate reparative wound healing. Despite reducing some of the risk for corneal haze compared to conventional PRK, ASA cases still can develop corneal haze or breakthrough haze from the hypercellular fibrotic stromal scarring. In contrast, similar to conventional LASIK, SBK still has the short- and long-term potential for interface wound complications from the hypocellular primitive stromal scar. Ophthalmic pathology and basic science research show that SBK and ASA are improvements in excimer laser keratorefractive surgery compared to conventional LASIK or PRK, particularly with regard to maintaining corneal biomechanics and perhaps moderately reducing the risk of corneal haze. However, most of the disadvantages caused by wound healing issues remain.

Randomized Prospective Comparison of Visian Toric Implantable Collamer Lens and Conventional Photorefractive Keratectomy for Moderate to High Myopic Astigmatism

To compare the Visian Toric Implantable Collamer Lens (TICL), a toric phakic intraocular lens (IOL), and photorefractive keratectomy (PRK) in the correction of moderate to high myopic astigmatism. This prospective, randomized study consisted of 43 eyes implanted with the TICL (20 bilateral cases) and 45 eyes receiving PRK with mitomycin C (22 bilateral cases) with moderate to high myopia (-6.00 to -20.00 diopters [D] sphere) measured at the spectacle plane and 1.00 to 4.00 D of astigmatism. All patient treatment and follow-up occurred at the Naval Medical Center San Diego. Study follow-up was 1 day, 1 week, 1, 3, 6, and 12 months postoperative. Mean best spectacle-corrected visual acuity (BSCVA), change in BSCVA, proportion of cases with improvement of 1 or more lines of BSCVA, proportion of cases with BSCVA and uncorrected visual acuity (UCVA) 20/12.5 or better, proportion of cases with BSCVA and UCVA 20/16 or better (6 months, 88% vs 54%, P=.002), and predictability +/-1.00 D (6 months, 100% vs 67%, P<.001) were all significantly better in the TICL group than the PRK group at all time periods studied postoperatively. Similarly, contrast sensitivity, tested at both the 5% photopic level and the 25% mesopic level, was significantly better at all postoperative time points in the TICL group. Mean spherical equivalent refraction was closer to emmetropia (0.28+/-0.41 vs 0.76+/-0.86, P=.005), and predictability +/-0.50 D and stability of manifest refraction (+/-0.50 D and +/-1.00 D) were significantly better in the TICL group at all postoperative visits through 6 months. Mean astigmatism correction at 6 months was not significantly different between the two groups (0.52+/-0.33 vs 0.46+/-0.35, P=.450). The TICL performed better than PRK in all measures of safety (BSCVA), efficacy (UCVA), predictability, and stability in this comparison, supporting the TICL as a viable alternative to existing refractive surgical treatments.

Changes in Higher Order Aberrations after Wavefront-Guided Prk for Correction of Low to Moderate Myopia and Myopic Astigmatism: Two-Year Follow-Up

To assess efficacy, safety, and changes in higher order aberrations after wavefront-guided photorefractive keratectomy (PRK) in comparison with conventional PRK for low to moderate myopia with myopic astigmatism using a WASCA Workstation with the MEL 70 G-Scan excimer laser. A total of 126 myopic or myopic-astigmatic eyes of 112 patients were included in this retrospective study. Patients were divided into two groups: Group 1, the study group; and Group 2, the control group. Group 1 consisted of 78 eyes treated with wavefront-guided PRK. Group 2 consisted of 48 eyes treated with spherocylindrical conventional PRK. Two years postoperatively, in Group 1, 5% of eyes achieved an uncorrected visual acuity (UCVA) of 0.05; 69% achieved a UCVA of 0.00; 18% of eyes experienced enhanced visual acuity of -0.18 and 8% of -0.30. In Group 2, 8% of eyes achieved a UCVA of 0.1; 25% achieved a UCVA of 0.05; and 67% achieved a UCVA of 0.00 according to logMAR calculation method. Total higher-order root-mean square increased by a factor 1.18 for Group 1 and 1.6 for Group 2. There was a significant increase of coma by a factor 1.74 in Group 2 and spherical aberration by a factor 2.09 in Group 1 and 3.56 in Group 2. The data support the safety and effectiveness of the wavefront-guided PRK using a WASCA Workstation for correction of low to moderate refractive errors. This method reduced the number of higher order aberrations induced by excimer laser surgery and improved uncorrected and spectacle-corrected visual acuity when compared to conventional PRK.

Photorefractive keratectomy with aspheric profile of ablation versus conventional photorefractive keratectomy for myopia correction

To analyze ocular wavefront error and corneal asphericity (Q) in patients treated with aspheric profile photorefractive keratectomy (PRK) compared with patients having conventional PRK to correct myopia and myopic astigmatism and to evaluate the effect of postoperative corneal shape on visual performance. Eye Clinic, University G. d'Annunzio, Chieti-Pescara, Italy. Fifty eyes were treated with aspheric profile PRK using the MEL 80 flying-spot excimer laser, and 24 eyes were treated with standard PRK using the MEL 70 flying-spot excimer laser. Postoperative wavefront error increased in both groups. Six months after surgery, there was a smaller increase in root mean square (RMS) of total higher-order aberrations and spherical aberration (59% and 106%, respectively) in the aspheric profile PRK group than in the conventional PRK group (94% and 136%, respectively) (P<.01). The aspheric profile PRK group showed more prolate corneal asphericities (mean Q of 0.15 +/- 0.26) than the conventional group (mean Q of 0.45 +/- 0.26) (P<.001), with increasing oblateness for higher attempted corrections. A higher percentage of patients with better low-contrast uncorrected visual acuity and best corrected visual acuity was observed in the aspheric PRK group than in the conventional PRK group (P<.05). Aspheric profile and conventional PRK were safe and efficient for the correction of myopia and myopic astigmatism. Moreover, aspheric profile PRK induced a smaller increment of total wavefront error, was related to a smaller increase in spherical aberration, and better maintained the physiology of the corneal surface than conventional treatment.

Epithelial healing and clinical outcomes in excimer laser photorefractive surgery following three epithelial removal techniques: Mechanical, alcohol, and excimer laser

To evaluate epithelial healing, postoperative pain, and visual and refractive outcomes after photorefractive keratectomy (PRK) using three epithelial removal techniques. Prospective, nonrandomized, comparative trial. Department of Ophthalmology, Yonsei University College of Medicine and Balgensesang Ophthalmology Clinic, Seoul, Korea. For the PRK procedure, the corneal epithelium was removed in one of three ways: mechanically (conventional PRK [PRK]) in 88 eyes of 44 patients; using excimer laser (transepithelial PRK [tPRK]) in 106 eyes of 53 patients; or using 20% diluted alcohol, laser-assisted subepithelial keratomileusis (LASEK) in 106 eyes of 53 patients. Epithelial healing, postoperative pain, uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), and remaining refractive error. The mean postoperative pain scores were 4.84 +/- 1.45 for PRK, 4.71 +/- 1.62 for tPRK, and 4.63 +/- 1.52 for LASEK (P = .125). The mean epithelial healing rates were 12.3 +/- 4.6 for PRK, 15.2 +/- 4.9 for tPRK, and 18.1 +/- 5.2 mm2/day for LASEK (P < .001). The postoperative 6-month remaining mean spherical equivalents (diopters) were -0.46 +/- 1.01 for PRK, 0.18 +/- 0.91 for tPRK, and -0.82 +/- 1.18 for LASEK (P = .01). The LASEK group showed less favorable UCVA than other groups. There was no significant difference in BSCVA between the groups. Postoperative pain, subepithelial opacity and BSCVA were similar regardless of the epithelial removal procedure. A faster epithelial healing rate did not result in better visual or refractive outcomes. Using the same nomogram, tPRK resulted in a slight overcorrection, and LASEK resulted in a slight undercorrection.

Prospective Randomized Comparison of Wavefront-guided and Conventional Photorefractive Keratectomy for Myopia With the Meditec MEL 70 Laser

To study refractive results and aberrometric changes in myopic patients treated with wavefront-guided photorefractive keratectomy (PRK) in comparison with standard PRK. Sixty eyes of 60 patients with myopic astigmatism were randomly divided into two groups. Group 1 included 30 eyes (mean spherical equivalent refraction -4.39 +/- 1.31 D; range -2.50 to -6.50 D) treated with wavefront-guided PRK using the WASCA workstation and the Asclepion Meditec flying spot MEL 70 excimer laser. Group 2 had 30 eyes (mean spherical equivalent refraction -4.33 +/- 1.22 D; range -2.50 to -6.50 D) that underwent conventional PRK using the same laser, and served as the control group. Wavefront analysis of high order aberrations was performed before and 6 months after surgery. Postoperatively, wavefront error increased in both groups (5.0-mm wavefront aperture diameter). Six months after surgery, the eyes that received the WASCA ablation had a smaller increase in root-mean-square (RMS; 70% of increment) compared to the conventional PRK group (139% of increment) (P<.001). In the standard PRK group, all aberrations notably increased; in the wavefront-guided PRK group there was a smaller increase of trefoil and spherical aberrations (P<.001) and a decrease of coma aberrations (P<.001). The smaller increase of wavefront error in the wavefront-guided PRK group compared to the standard PRK group was more evident when preoperative RMS values were higher than 0.4 microm (P<.01). The visual parameters (spherical equivalent refraction, uncorrected and best spectacle-corrected visual acuity) did not show significant differences between the two groups. Wavefront-guided PRK induced a smaller increase of postoperative wavefront-error compared to conventional PRK, particularly in patients with higher preoperative higher order aberrations.

Comparison of laser subepithelial keratomileusis and photorefractive keratectomy for the correction of myopia

To compare the effectiveness and difference between laser subepithelial keratomileusis (LASEK) and conventional photorefractive keratectomy (PRK) for the treatment of myopia up to -8.00 diopter. In this prospective study, 46 patients with a manifest refactiion of -1.75 to -8.00 diopters were treated and followed up for 6 months. In each case, PRK was performed in one eye and LASEK in the other eye. The first eye treated and surgical method used in the first eye was randomized. Epithelial healing time, postoperative pain, uncorrected visual acuity (UCVA), manifest refraction, corneal HAZE were followed and compared in PRK and LASEK treated eyes. LASEK eyes took a mean time of 3.49 days to heal the epithelium, whereas PRK eyes took 2.45 days, which is statistically significant (P <0.05). Postoperative pain index was 2.04 and 2.45 in LASEK eyes and PRK eyes respectively (P <0.05). There were no significant differences between eyes in UCVA and manifest refraction during the follow time (P >0.05). However, LASEK-treated eyes showed less corneal haze than PRK eyes. LASEK can effectively and safely treat myopia up to -8.00 diopters as PRK did, and can diminish early pain after surgery and prevent corneal Haze from happening.

Laser-assisted subepithelial keratectomy for myopia: two-year follow-up

The authors conducted a prospective comparative study to assess and compare the clinical results (efficacy, safety, stability, and postoperative pain or discomfort) of laser-assisted subepithelial keratectomy (LASEK) and conventional photorefractive keratectomy (PRK) for the correction of low to moderate myopia. Laser-assisted subepithelial keratectomy was performed in one eye and PRK was performed in one eye in 92 patients who underwent bilateral treatment. Both procedures were performed with the Nidek EC-5000 excimer laser using the same parameters and nomogram, with the first eye being randomized. The preoperative mean spherical equivalent was −4.65 diopters (D) ± 3.14 D standard deviation (range, −1.75 D to −7.50 D). The mean pain level was significantly lower on days 1 to 3 in the LASEK eyes (P < .05). The mean uncorrected visual acuity was significantly better in LASEK (0.87) than PRK eyes (0.64) at 1 week (P < .05) but virtually identical at 1 month (0.89 vs 0.78), 1 year (0.91 vs 0.88), and 2 years (0.94 vs 0.92). The mean corneal haze was significantly lower in LASEK eyes (0.21) than in PRK eyes (0.43) (P < .05). The mean spherical equivalent at 2 years was −0.23 ± 0.46 D for LASEK eyes, and −0.18 ± 0.53 D for PRK eyes (not significant). There were no statistically significant differences between LASEK and PRK eyes in safety and efficacy indices. Overall, 86% of patients preferred LASEK over PRK. The authors conclude that LASEK provides significantly quicker visual recovery, less postoperative pain, and results in less subepithelial haze than PRK, although the long- term visual and refractive outcomes are virtually identical with the two procedures.—Michael D. Wagoner

Laser-assisted subepithelial keratectomy for myopia: two-year follow-up

Purpose To assess and compare the clinical results (efficacy, safety, stability, and postoperative pain or discomfort) of laser-assisted subepithelial keratectomy (LASEK) and conventional photorefractive keratectomy (PRK) for the correction of low to moderate myopia. Setting Department of Ophthalmology, Masaryk University Hospital, Brno, Czech Republic. Methods A prospective comparative study was performed in 184 eyes of 92 patients who had surface excimer ablation for the correction of myopia. The preoperative mean spherical equivalent (MSE) was −4.65 diopters (D) ± 3.14 (SD) (range −1.75 to −7.50 D). In each patient, LASEK was performed in 1 eye and PRK in the fellow eye by the same surgeon. The first eye treated and the surgical method used in the first eye were randomized. Both procedures were performed with the Nidek EC-5000 excimer laser using the same parameters and nomogram. The postoperative pain level, visual recovery, complications (haze), uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), and refractive outcome were evaluated and compared. All eyes completed a 24-month follow-up. Results The postoperative MSE was −0.18 ± 0.53 D in the PRK eyes and −0.33 ± 0.46 D in the LASEK eyes. At 1 week, the mean UCVA was 0.64 ± 0.21 and 0.87 ± 0.23, respectively. No LASEK eye lost a line of BSCVA. There were no statistically significant differences between PRK and LASEK eyes in the safety and efficacy indices at 2 years. The mean pain level was significantly lower on days 1 to 3 in the LASEK eyes ( P < .05). The mean corneal haze level was lower in the LASEK eyes (0.21) than in the PRK eyes (0.43) ( P < .05). Seventy-nine patients preferred LASEK to PRK. Conclusions Laser-assisted subepithelial keratectomy provided significantly quicker visual recovery, eliminated post-PRK pain, and reduced the haze level in eyes with low to moderate myopia compared with conventional PRK. It provided good visual and refractive outcomes. There were no serious complications.

Laser subepithelial keratomileusis: electron microscopy and visual outcomes of flap photorefractive keratectomy.

Laser epithelial keratomileusis (LASEK) is a surgical technique that may be performed in patients with low myopia who are considering conventional photorefractive keratectomy (PRK), in patients with thin corneas, and in patients with professions or lifestyles that predispose them to trauma. Ethanol (18%) is applied for 25 seconds and a hinged epithelial flap is created. After laser ablation, the flap is repositioned over the ablated stroma. Our data showed that epithelial defects occurred in 63% eyes on Day 1. Postoperative pain was absent in 47%. Uncorrected visual acuity of 20/40 or better was achieved in all patients at 1 week. Data from several studies suggest that LASEK may reduce postoperative pain and corneal haze associated with PRK. LASEK offers the potential advantage of avoiding flap-related complications associated with laser in situ keratomileusis and decreasing postoperative pain and corneal scarring associated with PRK. Long-term studies are needed to confirm these potential advantages and to determine the safety, efficacy, and predictability of this surgical technique.

Comparison of laser epithelial keratomileusis and photorefractive keratectomy for low to moderate myopia

Purpose To compare the effectiveness, safety, and stability of laser epithelial keratomileusis (LASEK), a modified photorefractive keratectomy (PRK) technique, with those of conventional PRK for low to moderate myopia. Setting Department of Ophthalmology, Yonsei University School of Medicine, Seoul, Korea. Methods In this prospective study, 27 patients with a manifest refraction of –3.00 to –6.50 diopters were treated and followed for 3 months. In each case, PRK was performed in 1 eye and LASEK in the other eye. The first eye treated and the surgical method used in the first eye were randomized. Postoperative pain, epithelial healing time, uncorrected visual acuity (UCVA), manifest refraction, corneal haze, and surgical preference were examined in PRK- and LASEK-treated eyes. Results During the 3 month follow-up, there were no significant between-eye differences in epithelial healing time, UCVA, or refractive error. However, LASEK-treated eyes had lower postoperative pain scores ( P = .047) and corneal haze scores (1 month; P = .02) than PRK-treated eyes. Seventeen patients (63%) preferred the LASEK procedure. Conclusions Laser epithelial keratomileusis safely and effectively treated eyes with low to moderate myopia. It reduced the incidence of significant postoperative pain and corneal haze and may prevent the flap- and interface-related problems of laser in situ keratomileusis.

Cooling effect on excimer laser photorefractive keratectomy

Purpose To evaluate the effect of cooling on pain, corneal haze, and refractive outcome after excimer laser photorefractive keratectomy (PRK). Setting Tokyo Medical and Dental University Hospital, Tokyo, Japan. Methods The corneal surface was cooled before, during, and after laser ablation using a method called cooling PRK. Thirty-eight highly myopic eyes of 38 patients whose spherical errors ranged from −8.00 to −18.75 diopters (D) were randomized into 2 groups: 16 eyes with conventional PRK and 22 eyes with cooling PRK. Postoperative pain was measured using the Visual Analogue Scale (VAS). Refraction, visual acuity, and complications were followed for up to 2 years. All data were analyzed and compared between groups to evaluate the cooling effect on PRK. Results One day postoperatively, patients in the cooling PRK group had significantly less pain ( P < .01). At 3 months, the haze score in the cooling PRK group was significantly less than in the conventional PRK group ( P < .01). The residual refractive error was not significantly different between the 2 groups until 2 years, when it was greater in the conventional PRK (mean −5.09 D ± 2.11 [SD]) than the cooling PRK group (−4.64 ± 2.27 D). Ten eyes (62.5%) in the conventional PRK group and 15 eyes (68.2%) in the cooling PRK group were within ±1.00 D of the intended refraction. There were no serious complications in the cooling PRK group. Two eyes in the conventional PRK group had severe corneal haze and lost 2 Snellen lines of best corrected visual acuity. Conclusion Corneal cooling on PRK effectively reduced postoperative pain, corneal haze, and myopic regression.