Photoastigmatic Refractive Keratectomy Research Articles

Analysis of photoastigmatic keratectomy with the cross-cylinder ablation

Aim:The aim was to evaluate the safety and efficacy of the “cross-cylinder” technique in the correction of astigmatism.Setting and Design:A prospective interventional study from a university eye department was conducted.Material and Methods:The photoastigmatic refractive keratectomy (PARK) using the “cross-cylinder” technique was performed in 102 eyes of 84 patients with at least 0.75 D of astigmatism. The study population was divided into two groups: in the first group the preoperative astigmatic power ranged from –0.75 D to –3.00 D (group 1), in the second group it ranged from –3.25 D to –6.00 D (group 2). Group 1 included 82 eyes of 67 patients (29 males and 38 females) with a mean cylinder power of –1.90 ± 0.63 D, group 2 included 20 eyes of 17 patients (13 males and 4 females) with a mean cylinder power of -4.28 ± 0.76 D. All eyes were targeted for emmetropia. The results were evaluated using Calossi's vector analysis method. Six-month postoperative outcomes are presented.Results:Six months after PARK the mean sphere for the entire cohort was +0.28 ± 0.75 D (range +2.5 to –2 D), the mean cylindrical power was +0.33 ± 0.51 D (range +2.5 to –1.25 D) and the mean spherical equivalent refraction was +0.73 ± 0.81 D (range +1.75 to –2 D).Conclusions:The cross-cylinder technique may be safely used with predictable results for the correction of astigmatism.

Clinical Outcomes of Photoastigmatic Refractive Keratectomy for the Correction of Residual Refractive Errors Following Cataract Surgery

To assess the clinical outcomes of photoastigmatic refractive keratectomy (PARK) for the correction of residual refractive errors after cataract surgery. This study evaluated 88 eyes of 66 consecutive patients with mean spherical equivalent refraction of -3.16±1.71 diopters (D) who underwent PARK to correct refractive errors after phacoemulsification with intraocular lens (IOL) implantation. Patient age at the time of surgery was 65.2±12.7 years. Safety, efficacy, predictability, stability, and adverse events of the surgery were assessed 1, 3, 6, and 12 months postoperatively. At 1 year postoperatively, uncorrected distance visual acuity and corrected distance visual acuity were 0.08±0.16 logMAR (Snellen 20/25) and -0.08±0.11 logMAR (Snellen 20/16), respectively. Safety and efficacy indices were 1.08±0.25 and 0.76±0.28, respectively. At 1 year, 68% of eyes were within ±0.50 D and 88% were within ±1.00 D of targeted correction. Manifest refraction changes of -0.06±1.06 D occurred from 1 week to 1 year. No vision-threatening complications occurred during the observation period. Photoastigmatic refractive keratectomy is safe and moderately effective in the correction of residual refractive errors in pseudophakic eyes, suggesting its viability as a surgical option for the treatment of such eyes.

Postoperative follow up by dynamic light scattering: Detection of inflammatory molecular changes in the cornea, the vitreous and the lens

To detect post-op molecular changes and inflammatory processes by dynamic light scattering (DLS) in eye segments. To develop DLS parameters which are appropriate for the control of post-op course after ophthalmologic surgery. METHODS, DESIGN: Three new DLS devices were tested in different post-op clinical settings such as pseudoexfoliation syndrome (PEX), cataract surgery and retinal surgery. In a second step DLS was used to detect molecular changes in the cornea of 6 patients after photo refractive keratectomy (PRK) and 16 patients after photo astigmatic refractive keratectomy (PARK). In PEX-patients cataract surgery changed the DLS signals of the anterior chamber and the lens in a specific way compared to the pre-op situation. Cataract patients without PEX had more scattering particles post-op and retinal surgery modified the DLS signal of the vitreous. Furthermore it was shown that the length of the corneal scattering vector l correlated with the process of the corneal wound healing after PARK. One and three months after surgery the lengths of the scattering vectors had increased significantly but returned to pre-op values twelve months post-op. The post-op transparency of eye segments such as the cornea, the vitreous and the anterior chamber depends primarily on the wound healing mechanisms. DLS seems to be a suitable method to control the corneal recovery after refractive surgery. The length of the scattering vector l correlates well with the wound healing after refractive surgery. However DLS-signals seem to contain information about the molecular composition of tissue too. Therefore further research is needed to refine the interpretation of the DLS signals.

Customized photoastigmatic refractive keratectomy using combined topographic and refractive data for myopia and astigmatism in eyes with forme fruste and mild keratoconus

To examine the outcomes of photoastigmatic refractive keratectomy using corneal and refractive parameters for myopia and astigmatism in eyes with forme fruste and mild keratoconus. Private practice, Melbourne, Australia. Photoastigmatic refractive keratectomy was performed with a Star 1 or Star 2 laser (Visx) in 45 eyes with forme fruste or mild keratoconus using the Alpins vector planning technique. Inclusion requirements were best corrected visual acuity (BCVA) 20/40 or better, no slitlamp signs of keratoconus, mean keratometry less than 50.00 diopters (D), and corneal and refractive stability for at least 2 years. Thirty-two eyes had follow-up of 5 years and 9 eyes, of 10 years. Preoperatively, the mean refractive astigmatism was -1.39 DC +/- 1.08 (SD) (range 0.45 to -5.04 DC) and the mean corneal astigmatism was 1.52 +/- 1.18 D (range 0.35 to 4.75 D) by manual keratometry and 1.70 +/- 1.42 D (range 0.32 to 5.32 D) by topography. Twelve months postoperatively, the mean refractive astigmatism was -0.43 +/- 0.40 D and the mean corneal astigmatism was 1.05 +/- 0.85 D by keratometry and 1.02 +/- 0.83 D by topography. At 12 months, the uncorrected visual acuity was 20/20 or better in 56% of eyes and 20/40 or better in all eyes. The BCVA was 20/20 or better in 89% of eyes and 20/30 or better in all eyes. Seven eyes had a loss of BCVA, and 16 eyes had a gain. There were no cases of keratoconus progression. Photoastigmatic refractive keratectomy in eyes with forme fruste and mild keratoconus was safe and effective for myopia and astigmatism in carefully selected patients with refractive and corneal stability. The incorporation of the corneal astigmatism data into the applied treatment parameters may improve visual and total astigmatism results.

Amniotic Membrane Corrects Surgically Induced Astigmatism

Human amniotic membrane (AM) has been widely used for the reconstruction of ocular surface. We conducted this study to investigate whether AM shows efficacy in maintaining the correction of astigmatism or not. We performed photoastigmatic refractive keratectomy (PARK) on rabbits and grafted AM on the cornea. The effect of AM on the degree of astigmatism was evaluated by topography and cycloplegic refraction. As will be shown, AM did not show any efficacy in maintaining the correction of astigmatism. On the contrary, AM not only eliminated PARK-induced astigmatism but prevented surgically induced astigmatism. We suggest that AM could be a useful tool for controlling the astigmatism induced by laser refractive surgery. Further clinical study is still left to be elucidated.

Corneal astigmatic change after photorefractive keratectomy and photoastigmatic refractive keratectomy

Purpose To evaluate and compare the efficacy, safety, predictability, and surgically induced astigmatism (SIA) of photorefractive keratectomy (PRK) and photoastigmatic refractive keratectomy (PARK). Setting Department of Ophthalmology, National Taiwan University Hospital, Taipei, Taiwan. Methods In this retrospective study, 70 eyes were treated for myopia and 70 eyes were treated for myopic astigmatism. Refraction, corneal topography, slitlamp findings, and visual acuity in the 2 groups at 1, 3, and 6 months were evaluated and compared. Vector analysis was performed to determine the SIA in both groups. Results The mean preoperative spherical equivalent at the glasses plane in the PRK and PARK groups was –6.06 diopters (D) and –7.18 D, respectively. At 6 months, the mean reduction in astigmatism in the PARK group was 61.0%. Predictability was within ±1.0 D in 85.2% of eyes in the PRK group and 62.5% in the PARK group. An uncorrected visual acuity of 20/40 or better was achieved in 91.8% and 83.9% of eyes, respectively. The mean SIA was 0.64 D in the PRK group, with a general with-the-rule axis shift. The results of vector analysis were more favorable when calculated from refractive values than from Sim-K corneal topography values. The mean astigmatism correction index and index of success calculated from refractive data were 0.75 and 0.38 in the PARK group. The mean magnitude and angle of error were 0.22 ± 0.52 D and –2.13 ± 24.41 degrees, respectively. Conclusion Photorefractive keratectomy and PARK were effective and safe procedures for the correction of myopia and myopic astigmatism. However, SIA occurred with spherical myopic treatments. This small SIA may be a confounding factor in low astigmatic treatments.

Corneal interactive programmed topographic ablation customized photorefractive keratectomy for correction of postkeratoplasty astigmatism

Objective This study evaluated the efficacy, predictability, stability, and safety of a software program (Corneal Interactive Programmed Topographic Ablation [CIPTA], LIGI, Taranto, Italy), which, by transferring programmed ablation from the corneal topograph to a flying-spot excimer laser, provides customized laser ablation for correction of postkeratoplasty astigmatism. Design Noncomparative consecutive interventional case series. Participants Ten eyes of 10 patients with a mean age of 41.4 years (range, 26–64) had CIPTA-guided photoastigmatic refractive keratectomy (PARK ) at the Clinica Oculistica of Bari (Italy). Two patients were treated for hyperopic astigmatism and eight for myopic astigmatism. All the patients had irregular astigmatism after penetrating keratoplasty. Operation Topography was acquired by a corneal topograph (Orbscan II, Orbtek, Inc., Salt Lake City, UT). This, together with refractive data, was processed to obtain a customized altimetric ablation profile that was transferred to a flying-spot laser (Laserscan 2000, Lasersight, Orlando, FL). Main outcome measures Data on uncorrected (UCVA) and best-corrected (BCVA) visual acuity, predictability, stability of refraction, and any complications were analyzed. Results Mean follow-up was 8.4 months (range, 6–12; SD 2.4). At the last postoperative examination, seven eyes (70%) had a UCVA superior to 20/40. Three eyes (30%) had a UCVA of 20/20. Five eyes (50%) were within 0.50 diopters (D) of attempted correction in the spherical equivalent, and eight eyes (80%) within 1 D. Index of success of astigmatic correction was 0.19. All the eyes (100%) gained Snellen lines of BCVA. We did not observe any decentration and/or haze after PARK treatment performed in this study. Conclusions The combination of topographic data with computer-controlled flying-spot excimer laser ablation is a suitable solution for correcting irregular astigmatism after penetrating keratoplasty.

Effect of preoperative pupil measurements on glare, halos, and visual function after photoastigmatic refractive keratectomy

Purpose To prospectively assess the effect of preoperative variables such as pupil size on glare, halos, and visual function after photoastigmatic refractive keratectomy (PARK). Setting Department of Ophthalmology, Stanford University School of Medicine, Stanford, California, USA. Methods Ninety-three eyes had PARK for primary compound myopic astigmatism. Preoperative pupil diameters were measured under scotopic and photopic illuminance conditions. Postoperatively, patients were evaluated at 1, 3, 6, 9, 12, 18, and 24 months. A regression model was performed to evaluate the predictive value of assessing preoperative variables such as pupil diameter on the development of glare and halos, contrast sensitivity, and best spectacle-corrected visual acuity (BSCVA) under scotopic, photopic, and glare conditions. Results The greater magnitude loss of BSCVA under scotopic conditions in the early postoperative period as well as the slower recovery to preoperative levels in eyes with larger scotopic pupil diameters were not statistically significant ( P > .05). An increase in symptoms of glare was related more to the attempted level of spherical equivalent (SE) correction than to the pupil size during the first 12 postoperative months ( P < .01). The photoablation dimensions as determined by the attempted level of astigmatic correction may result in decreases in the glare BSCVA up to 12 months after PARK ( P = .03). At the 2 year follow-up, pupil diameter under both scotopic and photopic illuminance conditions was not predictive of any of the measured outcomes variables. Conclusions An assessment of preoperative pupil size and the attempted level of both SE and astigmatic correction may be useful in identifying patients at risk of developing symptoms or declines in visual performance after PARK. However, follow-up studies are indicated to identify variables predictive of poor visual outcomes following excimer laser refractive surgery.

Correlation between ultraviolet radiation level and the incidence of late-onset corneal haze after photorefractive keratectomy

Purpose To investigate the correlation between environmental changes in ultraviolet (UV) radiation levels and the incidence of late-onset cornea haze (LOCH) after photorefractive keratectomy (PRK). Setting SynsLaser Clinic, Tromsø, Norway. Methods The study comprised 404 eyes that had myopic PRK and photoastigmatic refractive keratectomy from February 1996 through July 1998. The high latitude (70° N) of the observation site provided “natural laboratory” conditions to look at the occurrence of LOCH with high and low UV-radiation levels, which occurred during summers and winters, respectively. The diagnostic criterion for LOCH was acute haze of grade ≥2 occurring between 4 and 12 months postoperatively. Results The follow-up ranged from 12 to 41 months. Of the 314 eyes that met the inclusion criteria, 11 developed LOCH when the environmental UV-radiation level was high. No eye developed LOCH when the level was low. The correlation between a high level of environmental UV radiation and the occurrence of LOCH was statistically significant ( P = .001). Conclusion Environments with high UV-radiation levels may increase the risk of LOCH after PRK in eyes with moderate to high myopia. Use of UV-protective eyewear should be encouraged during the first year after PRK.

Outcome of corneal and laser astigmatic axis alignment in photoastigmatic refractive keratectomy

Purpose To compare the refractive results of laser astigmatic treatment in eyes in which the astigmatic axes of the eye and laser are aligned by limbal marking at the 6 o’clock position and in eyes that are not marked. Setting University Hospital and Clinics, Madison, Wisconsin, USA. Methods This retrospective study comprised 143 eyes that had photoastigmatic refractive keratectomy with the VISX Star excimer laser. The eyes were divided into marked (G1) and unmarked (G2) groups. Based on the preoperative astigmatism, each group was subdivided into low astigmatism (≤1.00 diopter [D]) and high astigmatism (≥1.25 D). Early postoperative manifest refractions (1.0 to 2.5 months) were analyzed. The Alpins vector analysis method was used to calculate the target induced astigmatism, surgically induced astigmatism, difference vector (DV), magnitude of error (ME), angle of error (AE), and index of success (IS). Results There was no significant difference between the groups in DV, ME, and IS. When the subgroups were analyzed, the DV and ME were comparable; the IS in the G1 high astigmatism subgroup was significantly better than that in the G2 high astigmatism subgroup (0.22 ± 0.08 and 0.29 ± 0.04, respectively; P < .0001). There was comparable scatter of AE values; 30% and 36% in G1 and G2, respectively, had an AE of 0. Similar scatter was observed in the subgroups. Of the eyes that had an AE of 0, 90% and 43% in the high astigmatism subgroups of G1 and G2, respectively ( P < .05), had full correction of astigmatism. Conclusion Limbal marking and subsequent eye and laser astigmatic axis alignment improved the refractive outcome of laser astigmatic treatment of ≥1.25 D. A preliminary report of an ongoing prospective randomized study of eyes that had laser in situ keratomileusis is included.

Visual performance following photoastigmatic refractive keratectomy: A prospective long-term study

Purpose To prospectively determine the long-term effect of excimer laser photoastigmatic refractive keratectomy (PARK) on visual performance using psychophysical assessments and to identify predictors of poor performance on the psychophysical assessments. Setting University-based hospital, Stanford University, Stanford, California, USA. Methods Ninety-three eyes of 56 patients with a mean of −4.98 diopters ± 1.80 (SD) of primary compound myopic astigmatism had PARK using the Summit Apex Plus excimer laser and an erodible mask system. Patients were prospectively evaluated 1, 3, 6, 9, 12, 18, and 24 months following the procedure. Primary outcome variables included changes in the contrast sensitivity function curve (3.0, 6.0, 12.0, 18.0 cycles per degree) under 2 standard illuminance conditions (scotopic and photopic) and changes in the best spectacle-corrected visual performance under scotopic, photopic, and glare conditions. Results A relative decline in the contrast sensitivity function curve occurred in the early postoperative period under both scotopic and photopic conditions. This was most pronounced under photopic illuminance and at the low spatial frequencies at the 6 month visit. By 1 year, however, the mean contrast sensitivity at all spatial frequencies and all illuminance conditions had returned to the preoperative level. Further improvements beyond the preoperative level may be related to the independent analysis of retreatment eyes beyond 6 months. A higher level of attempted correction of the spherical equivalent was predictive of an elevated scotopic contrast threshold at the extreme spatial frequencies 6 months after PARK ( P < .05). The attempted level of astigmatic correction was predictive of a poor best corrected visual performance under scotopic conditions at 1 month ( P < .05). This effect was only temporary and by postoperative month 3, there was no predictive effect of preoperative astigmatism ( P > .05). Conclusions Psychophysical assessments may be a more sensitive indicator of decreases in visual performance following excimer laser refractive surgery. The attempted level of correction of spherical equivalent and astigmatism may adversely affect early scotopic visual performance. Decreases in visual performance are temporary, return to normal by 12 months, and remain stable 24 months following PARK.

Theoretical analysis of ablation depths and profiles in laser in situ keratomileusis for compound hyperopic and mixed astigmatism

Purpose To compare the theoretical ablation depths and profiles of 4 treatment strategies for compound hyperopic and mixed astigmatism. Setting Theoretical analysis. Methods Corneal contour drawings of theoretical corneal ablation profiles during laser in situ keratomileusis (LASIK) and photoastigmatic refractive keratectomy were made. The depths of tissue ablation in 4 treatment strategies for compound hyperopic astigmatism (Groups 1 to 4) and for mixed astigmatism (Groups 5 to 8) were compared: (1) combined hyperopic spherical and myopic cylindrical treatments (Groups 1 and 5); (2) combined spherical and hyperopic cylindrical treatments (Groups 2 and 6); (3) combined cylindrical treatments (Groups 3 and 7); (4) combined cross-cylinder and spherical equivalent treatments (Groups 4 and 8). Results In compound hyperopic astigmatism, the 4 approaches resulted in identical final curvatures, but the ablation depths were greatest in Group 1 (combined hyperopic spherical and myopic cylindrical treatments). The smallest amount of ablation occurred in Group 2 (combined hyperopic spherical and hyperopic cylindrical treatments) and Group 3 (combined hyperopic cylindrical treatments), which had similar tissue ablation patterns. In mixed astigmatism, the greatest ablation depth was in Group 5, followed by Group 8, and Groups 6 and 7. The tissue ablation depths and profiles were similar in Groups 6 and 7. Conclusion The treatment approaches in Groups 2, 3, 6, and 7 (which avoided the use of minus cylinder) resulted in the smallest degree of stromal ablation. Patients with compound hyperopic or mixed astigmatism may benefit from reduced ablation depths by deferring treatment until hyperopic cylindrical and/or combined cylindrical treatments are available.

One-year evaluation of myopic laser photoastigmatic refractive keratectomy using the Summit Apex Plus : Phase III of a Food and Drug Administration clinical trial

Purpose To prospectively evaluate the safety and efficacy of the Summit Apex Plus excimer laser in the treatment of primary compound myopic astigmatism. Design Prospective noncomparative interventional case series. Participants Patients with primary compound myopic astigmatism: sphere of −1.0 to −7.0 diopters (D) and cylinder −1.0 to −5.0 D. Methods Ninety-three eyes of 56 patients with a mean spherical equivalent of −4.98 ± 1.80 D (−1.75 to −8.5) underwent photoastigmatic refractive keratectomy (PARK) with the Summit Apex Plus excimer laser using erodible mask technology. Prospective follow-up is analyzed at 1-year postoperatively. Main outcome measures Postoperative reduction in myopic sphere, myopic astigmatism, spherical equivalent, angle of error, magnitude of error, difference vector, uncorrected visual acuity, and corneal haze. Results Seventy-one eyes were available at 1-year follow-up. Mean spherical equivalent was reduced 86.5% to a mean residual of −0.65 D ±0.70 D (−2.88–+1.13 D). Astigmatism was reduced 66.2% to a mean residual of −0.76 ± 0.52 D (−2.25–0.00 D); 77.5% were within 1.0 D of attempted correction; 1.4% of eyes experienced an overcorrection >1.0 D of spherical equivalent; 0.27 D of mean myopic regression was demonstrated between 1 and 12 months; 93.0% of eyes achieved an uncorrected visual acuity of 20/40 or better; and 49.3% of eyes achieved an uncorrected visual acuity of 20/20 or better. Conclusions PARK with the Summit Apex Plus excimer laser is effective at reducing compound myopic astigmatism. However, current laser algorithms result in consistent undercorrection of both the compound myopia and the astigmatic component.

Discussion by

The authors have done an excellent job of demonstrating the reasonable safety and efficacy of photoastigmatic refractive keratectomy with the Summit Apex Plus excimer laser. They found a consistent undercorrection in myopia and astigmatism correction, which may well be nomogram-related. The moderately high rate of reoperations, 14%, is consistent with the degree of undercorrection they found.

Photorefractive keratectomy for compound myopic astigmatism

PURPOSE: To evaluate the safety and efficacy of photorefractive keratectomy for the treatment of primary compound myopic astigmatism. METHODS: In a prospective study, 93 eyes from 56 patients with a mean spherical equivalent of −4.98 ± 1.80 diopters (range, −1.75 to −8.5) underwent photoastigmatic refractive keratectomy with the Summit Apex Plus excimer laser using erodible mask technology and were followed for 2 years. Primary outcome measures included an assessment of astigmatic correction through vector analysis, manifest refraction, uncorrected visual acuity, corneal clarity, and the presence of adverse symptoms. RESULTS: Eighty-five eyes (91.4%) were available for analysis at 6 months. Mean spherical equivalent refraction was reduced 85% (mean, −0.75 ± 0.85 diopter) and the target-induced astigmatism was reduced 70% (mean, 0.98 ± 1.88 diopters). Forty-eight eyes (56%) had an uncorrected visual acuity of 20/20 or greater, whereas 70 eyes (82%) had an uncorrected visual acuity of 20/40 or greater. Twenty-four eyes (26% ) required re-treatment because of undercorrection of the spherical equivalent and astigmatic components after the 6-month follow-up. Fifty-nine of the remaining eyes were available at the 24-month visit. Mean spherical equivalent refraction was reduced to −0.39 ± 0.72 diopter (91.8%). The target-induced astigmatism was reduced 64% from 1.74 diopters. Forty-one eyes (81.3%) were within ±1.0 diopter of attempted spherical equivalent correction. Stability within a spherical equivalent of ±0.5 diopter occurred after the first postoperative month. Fifty-six eyes (94.9%) had an uncorrected visual acuity of 20/40 or greater, whereas 34 eyes (57.6 %) demonstrated an uncorrected visual acuity of 20/20 or greater. One eye (1.7%) lost 2 or more lines of best spectacle-corrected visual acuity. CONCLUSION: Photoastigmatic refractive keratectomy with the Summit Apex Plus excimer laser is a safe and effective method of reducing compound myopic astigmatism. However, higher re-treatment rates may result from significant undercorrections because of current laser algorithms and variability in the mean angle of error.

Excimer laser retreatment of residual myopia following photoastigmatic refractive keratectomy for compound myopic astigmatism

Purpose To prospectively evaluate the safety, efficacy, and visual performance of excimer laser enhancement following photoastigmatic refractive keratectomy (PARK) with the Summit Apex Plus®. Setting Stanford University School of Medicine Eye Laser Clinic, Stanford, California, USA. Methods As part of a Food and Drug Administration clinical trial, 93 eyes of 56 patients with a mean spherical equivalent (SE) of −4.98 diopters (D) ± 1.80 (SD) (range −1.75 to −8.50 D) had PARK for compound myopic astigmatism using the Summit Apex Plus excimer laser and a poly(methyl methacrylate) erodible mask. Seventeen eyes with a mean SE of −2.08 ± 0.76 D required excimer laser refractive keratectomy for residual spherical myopia or compound myopic astigmatism. Patients were prospectively followed 1, 3, 6, 9, and 12+ months after the enhancement procedure. Primary outcome variables included uncorrected visual acuity (UCVA), refraction, vector analysis, best spectacle-corrected visual acuity (BSCVA) under standard ambient conditions (photopic, scotopic, and glare), corneal clarity, and contrast sensitivity function curve under photopic and scotopic conditions. Results At the last postoperative visit, the mean sphere had been corrected 82% to a residual of −0.29 ±1.23 D and mean SE had been corrected 65% to a residual of −0.74 ± 1.27 D. Eighty-two percent of eyes were within ±1.0 D of attempted correction. Eighty-eight percent had a UCVA of 20/40 or better. Vector analysis demonstrated a difference vector of within ±1.0 D in 75% of eyes that had PARK retreatment. There was no significant loss in the contrast sensitivity curve. Late regression associated with corneal haze and loss of BSCVA occurred in 2 eyes (11.7%). Conclusions Retreatment following PARK for compound myopic astigmatism results in effective reduction in residual spherical myopia and compound myopic astigmatism. An improvement in UCVA without loss of contrast sensitivity can be expected in most eyes. However, regression, corneal haze, and loss of BSCVA may occur. Further studies are indicated to predict risk factors for these complications.

Photoastigmatic Refractive Keratectomy or Laser in situ Keratomileusis for Moderate and High Myopic Astigmatism

To compare the efficacy and safety of laser in situ keratomileusis (LASIK) and photoastigmatic refractive keratectomy (PARK) to treat moderate and higher myopic astigmatism. A retrospective nonrandomized study of 78 eyes with myopic astigmatism (range, 2.00 to 6.00 D) was undertaken. Thirty-eight eyes were treated with LASDK and 40 eyes were treated with PARK. Groups were similar in terms of baseline sphere and refraction. Photoablation for both LASDX and PARK was performed by single pass for correction of -6.00 D or less spherical equivalent refraction or multi-pass, multi-zone at 4, 5, and 6 mm for corrections greater than -6.00 D. Astigmatism was corrected using a single-pass ablation at 6.0 mm diameter. Visual acuity, manifest refraction, corneal topography, and patient satisfaction were measured preoperatively and postoperatively. Six months postoperatively, uncorrected visual acuity was 20/40 or better in 100% of LASEK eyes and 90.0% of PARK eyes; 20/25 in 86.84% LASEK eyes and 47.5% of PARK eyes; 20/20 in 65.75% of LASEK eyes and 15% of PARK eyes. Postoperative residual cylinder was -0.54 ± 0.32 D in LASEK eyes and -1.28 ± 0.80 D in PARK eyes. Postoperative residual cylinder axis remained stable (within 15° at 1 month postoperatively) in 61.1% of LASEK eyes and 40% of PARK eyes. In 5.3% of the LASEK eyes, corneal haze developed; 95.5% of PARK eyes developed corneal haze. One LASIK eye lost best spectacle-corrected visual acuity and 3 eyes (7.89%) had a cap complication. Three eyes (7.5%) lost 2 lines of spectacle-corrected visual acuity due to severe corneal haze. Among LASEK patients, 92.1% were highly satisfied and 62.5% of PARK patients were highly satisfied. For myopic astigmatism between 2.00 and 6.00 D, LASEK provided better accuracy, fewer complications, and higher patient satisfaction than PARK. PARK may achieve an incomplete cylindrical correction and may have a higher associated rist of loss of best spectacle-corrected visual acuity. [J Refract Surg 2000;16(suppl):S268-S271).

Photoastigmatic Refractive Keratectomy in Myopes

Photoastigmatic refractive keratectomy (PARK) was studied in a multi-center clinical trial. The Nidek EC-5000 excimer laser was evaluated for its effect on refraction, visual acuity, and safety measures as part of a U.S. Food and Drug Administration (FDA) regulated study. Eight U.S. centers enrolled adults with eyes having refractive astigmatism up to 4.00 D and a myopic spherical equivalent refraction up to -8.00 D. Results are reported for 749 eyes of 486 patients with at least 6 months follow-up. The rectangular beam scanning Nidek EC-5000 used a 5.5-mm-diameter treatment zone, a 7.0-mm-diameter peripheral blend zone, and a 40 Hz pulse rate for surface treatment of myopic astigmatism. Nomogram corrections to machine settings were required to achieve the desired results. Preoperative average spherical equivalent refraction of -4.90+/-1.74 D was reduced to -0.02+/-0.79 D at 6 months. Refractive stability was established at 3 months. Over 62% of eyes were within +/-0.50 D of desired correction at 6 months, with over 86% within +/-1.00 D. Uncorrected visual acuity improved by an average of 10 Snellen lines; over 64% of eyes saw 20/20 or better uncorrected and over 93% saw 20/40 or better uncorrected at 6 and 12 months. PARK treatment effectively reduced astigmatism with little average axis error or magnitude error. Corneal haze and safety concerns were minimal. Photoastigmatic refractive keratectomy using the Nidek EC-5000 excimer laser provided significant reduction of myopia and astigmatism, with minimal complications.

Comprehensive method of analyzing the results of photoastigmatic refractive keratectomy for the treatment of post-cataract myopic anisometropia

PurposeTo assess the efficacy, stability, and safety of photoastigmatic refractive keratectomy (PARK) in treating post-cataract myopic anisometropia to restore binocularity and to describe a comprehensive method for analyzing the results of refractive surgery. SettingSt. Paul’s Eye Center, Royal Liverpool Hospital, Liverpool, United Kingdom. MethodsNineteen patients (20 eyes) with post-cataract myopic anisometropia were treated with PARK using a VISX Twenty-Twenty laser and followed for 12 months. Cataract surgery had been performed between 10 and 144 months (mean 43.4 months) previously. A comprehensive method based on Long’s matrix formalism and the vech operator of Harris, in addition to the nearest equivalent sphere and cylinder, was used to analyze the refractive data. ResultsThe mean preoperative refraction in the post-cataract eyes was –4.79 +1.17 x 0.2 and in the fellow eyes, +0.02 +0.31 x 166. Twelve months after PARK, the postoperative refraction in the post-cataract eyes was–0.90 +0.65 x 2, a significant reduction (P = .15). This postoperative refraction was not significantly different from that in the fellow eye (P = . 93). The pretreatment mean uncorrected visual acuity was 0.12. It improved to 0.41 at 12 months, at which time 52% of eyes achieved a visual acuity of 0.5 or better without correction. All patients regained binocularity. At 12 months, 2 eyes (11%) showed clinically unacceptable regression; 1 eye with grade 2 haze lost 1 line of corrected visual acuity. ConclusionsPhotoastigmatic refractive keratectomy reduced post-cataract myopic anisometropia, allowing restoration of binocularity in all patients. Overall, the results in this elderly population with previous ocular surgery, posterior capsule thickening, and macular degeneration are not as satisfactory as those obtained from similar treatment of physiological myopia. Stability and postoperative complications are acceptable.

Comparision of Clinical Results of Excimer Laser Correction of Myopia and Compound Myopic Astigmatism Using VISX 20/20B isionKey™

Purpose: To compare the efficacy, predictability, stability and safety of excimer laser photorefracive keratectomy(PRK) for myopia and photoastigmatic refractive keratectomy(PARK) for compound myopic astigmatism. Methods: Two-hundred and three eyes(l18 eyes -7D spherical equivalent) received excimer laser correction for compound myopic astigmatism and 152 eyes(116 eyes -7D) for simple myopia. A VISX 20/20B excimer laser was used to perform either PARK or PRK. Visual acuity with and without correction, refraction, IOP, corneal haze, and topography were evaluated at 1, 3, 6, and 12 months postoperatively. All patients were followed up for more than 12 months. Results: Postoperative refraction were generally stable after 3 months without significant early overcorrection. At 12 months, 110(94.8%) eyes that underwent PRK and 104(88.1%) eyes that underwent PARK achieved UCVA of 20/30 or better in the group who had lower than -7D correction. For eyes treated with -7D or more, these figures were 31(86.1%) eyes after PRK and 57(67.1%) eyes after PARK. The incidences of within 1D of plano refraction at 1 year follow-up were 97.4% after PRK and 93.2% after PARK in the group who had lower than -7D correction. For eyes treated with -7D or more, these figures were 80.6% after PRK and 70.6% after PARK. Conclusions Myopia with or without astigmatism was successfully treated in most of the eyes using PRK or PARK with VISX 20/20B excimer laser. The predictability and stability of the postoperative refraction during the first 12 months seem to be quite reliable. Further improvement of excimer laser system and software should increase the clinical outcomes and safety of refractive procedures.