Excimer Laser In Situ Keratomileusis to Correct Compound Myopic Astigmatism

Improving the ablation efficiency of excimer laser systems with higher repetition rates through enhanced debris removal and optimized spot pattern

PURPOSE

To evaluate the reasons for the required increased radiant exposure for higher-repetition-rate excimer lasers and determine experimentally possible compensations to achieve equivalent ablation profiles maintaining the same single-pulse energies and radiant exposures for laser repetition rates ranging from 430 to 1000 Hz.

SETTING

Schwind eye-tech-solutions GmbH and Co. KG, Kleinostheim, Germany.

DESIGN

Experimental study.

METHODS

Poly(methyl methacrylate) (PMMA) plates were photoablated. The pulse laser energy was maintained during all experiments; the effects of the flow of the debris removal, the shot pattern for the correction, and precooling the PMMA plates were evaluated in terms of achieved ablation versus repetition rate.

RESULTS

The mean ablation performance ranged from 88% to 100%; the variability between the profile measurements ranged from 1.4% to 6.2%. Increasing the laser repetition rate from 430 Hz to 1000 Hz reduced the mean ablation performance from 98% to 91% and worsened the variability from 1.9% to 4.3%. Increasing the flow of the debris removal, precooling the PMMA plates to -18°C, and adapting the shot pattern for the thermal response of PMMA to excimer ablation helped stabilize the variability. Only adapting the shot pattern for the thermal response of PMMA to excimer ablation helped stabilize the mean ablation performance.

CONCLUSIONS

The ablation performance of higher-repetition-rate excimer lasers on PMMA improved with improvements in the debris removal systems and shot pattern. More powerful debris removal systems and smart shot patterns in terms of thermal response improved the performance of these excimer lasers.

Analytical optimization of the ablation efficiency at normal and non-normal incidence for generic super Gaussian beam profiles

We suggest a general method to determine the optimum laser parameters for maximizing the ablation efficiency for different materials (in particular human cornea) at different incidence angles. The model is comprehensive and incorporates laser beam characteristics and ablative spot properties. The model further provides a method to convert energy fluctuations during ablation to equivalent ablation deviations in the cornea. The proposed model can be used for calibration, verification and validation purposes of laser systems used for ablation processes at relatively low cost and would directly improve the quality of results.

Macular hole after laser in situ keratomileusis in a 26-year-old patient

The purpose of this study is to describe the 26-year-old patient with developed macular hole after bilateral laser in situ keratomileusis (LASIK). A macular hole with sharp margins and irregular surface of surrounding retina appeared in the left eye of the female 26-year-old patient two months after LASIK for correction of myopia (followup of 6 months). Although the best corrected visual acuity (BCVA) after LASIK was 1.0, after the macular hole has developed BCVA became 0.5. After surgery, the final visual acuity recovered to 0.7. Macular hole may develop after LASIK for myopia correction due to unknown changes of vitreoretinal interface. Complete informed consent must be obtained from patients with high myopic eyes before LASIK.

Analysis of the effects of Eye-Tracker performance on the pulse positioning errors during refractive surgery☆

Purpose

To analyze the effects of Eye-Tracker performance on the pulse positioning errors during refractive surgery.

Methods

A comprehensive model, which directly considers eye movements, including saccades, vestibular, optokinetic, vergence, and miniature, as well as, eye-tracker acquisition rate, eye-tracker latency time, scanner positioning time, laser firing rate, and laser trigger delay have been developed.

Results

Eye-tracker acquisition rates below 100 Hz correspond to pulse positioning errors above 1.5 mm. Eye-tracker latency times to about 15 ms correspond to pulse positioning errors of up to 3.5 mm. Scanner positioning times to about 9 ms correspond to pulse positioning errors of up to 2 mm. Laser firing rates faster than eye-tracker acquisition rates basically duplicate pulse-positioning errors. Laser trigger delays to about 300 μs have minor to no impact on pulse-positioning errors.

Conclusions

The proposed model can be used for comparison of laser systems used for ablation processes. Due to the pseudo-random nature of eye movements, positioning errors of single pulses are much larger than observed decentrations in the clinical settings. There is no single parameter that ‘alone’ minimizes the positioning error. It is the optimal combination of the several parameters that minimizes the error. The results of this analysis are important to understand the limitations of correcting very irregular ablation patterns.

Six-month clinical outcomes of customized treatments minimized for depth and time in laser corneal refractive surgery

PURPOSE

Evaluating the application of 2 methods for minimizing the ablated tissue upon objective minimization of depth and time of Zernike-based customized ablations.

SETTING

Muscat Eye Laser Center, Muscat, Sultanate of Oman.

METHODS

Recently developed algorithms for selection of Zernike terms in customized treatments for refractive surgery were used. Clinical outcomes and tissue-saving attributes were evaluated on 2 groups [minimize depth (MD) and minimize volume (MV); 30 eyes each], plus a control group [corneal wavefront (CW); 30 eyes] with conventional customized approach. Clinical outcomes were evaluated in terms of predictability, safety, and contrast sensitivity and tissue-saving attributes in terms of saved depth and time for each condition (in micrometers, seconds, and percentage) and whether minimized depth or time were less than required for equivalent noncustomized treatments.

RESULTS

Ninety-three percent of treatments in the CW group, 93% in the MD group, and 100% in the MV group were within 0.50 diopters of spherical equivalent (SEq) postoperatively. Forty percent of treatments in the CW group, 34% in the MD group, and 47% in the MV group gained at least 1 line of best spectacle-corrected visual acuity postoperatively. Tissue-saving attributes showed an average saved depth of 8 μm (1-20 μm) and a saved time of 6 seconds (1-15 seconds) in the MD group and 6 μm (0-20 μm) and 8 seconds (2-26 seconds) in the MV group. Proposed corrections were always less deep and shorter than full wavefront corrections. In 43% of the MD cases, corrections were less deep, and in 40% of the MV cases, corrections were shorter than equivalent aberration-free treatments.

CONCLUSION

The minimization techniques compared here effectively reduced depth and time needed for ablation (up to a maximum of 50% and by 15% in average) without negatively affecting clinical outcomes postoperatively, yielding results equivalent to those of the full customization group.

Multizone LASIK with peripheral near zone for correction of presbyopia in myopic and hyperopic eyes: 1-year results

PURPOSE

To investigate the refractive outcomes of multifocal LASIK to create a center far, peripheral near zone in presbyopes.

METHODS

This prospective study using LASIK with a center far, peripheral near ablation algorithm comprised 68 eyes of 34 hyperopes and 78 eyes of 39 myopes. Mean patient age was 49 +/- 5.60 years for hyperopes and 46.0 +/- 3.80 years for myopes. Mean baseline manifest refraction spherical equivalent was +1.76 +/- 0.96 diopters (D) in hyperopes and -3.06 +/- 1.73 D in myopes. The mean baseline addition was +1.94 +/- 0.40 D in hyperopes and +1.67 +/- 0.44 D in myopes. One-year postoperative outcomes are reported.

RESULTS

The mean postoperative spherical equivalent refraction was -0.10 +/- 0.55 D in hyperopes and -0.48 +/- 0.51 D in myopes. Two percent of eyes in each group lost two lines of best spectacle-corrected visual acuity. With the distance correction in place, 20/40 or better near uncorrected visual acuity (UCVA) (Sloan acuity) was achieved in 33% of hyperopes and 36% of myopes. A statistically significant difference was noted in postoperative near visual acuity measured by the Sloan and Rosenbaum charts (P < .05). Fifty-four percent of hyperopes and 48% of myopes were satisfied or very satisfied with their postoperative near UCVA.

CONCLUSIONS

Multifocal LASIK to create a center far and peripheral near zone is safe and allows half of the patients to achieve spectacle independence. A peripheral near zone was only created in myopic treatments.

LASIK world literature review: quality of life and patient satisfaction

PURPOSE

To analyze the patient reported outcome of satisfaction after LASIK surgery.

DESIGN

Systematic review.

PARTICIPANTS

Patient data from previously reported studies.

METHODS

A literature search conducted for the years 1988 to 2008 that included pertinent LASIK surgery information from the review of 2915 retrieved citations. All abstracts from these citations were reviewed and 1581 were deemed to be relevant for review. Complete copies of each of these relevant (1581) articles were obtained, and after thorough analysis each was rated based on the strength of the study design and weight of evidence. A level I rating was assigned to properly conducted, well-designed, randomized clinical trials; a level II rating to well-designed cohort and case-control studies; and a level III rating to case series, case reports, and poorly designed prospective and retrospective studies. Level I and II rated, peer-reviewed articles were entered into a database, and level III articles were eliminated. A total of 309 articles were incorporated into this database, representing level I and level II well-controlled studies of primary LASIK surgery.

MAIN OUTCOME MEASURES

Patients' satisfaction rates and factors associated with dissatisfaction.

RESULTS

Nineteen of the 309 database articles (6.1%) reported on both patient quality of life and satisfaction and together encompassed a total of 2198 subjects. The procedures from these 19 articles took place between 1995 and 2003. The overall patient satisfaction rate after primary LASIK surgery was 95.4% (2097 of 2198 subjects; range of patient satisfaction for the 19 articles was 87.2%-100%). The patient satisfaction rate after myopic LASIK was 95.3% (1811 of 1901 patients), and after hyperopic LASIK was 96.3% (286 of 297 subjects).

CONCLUSIONS

Based on this review, worldwide, an average 95.4% of patients were satisfied with their outcome after LASIK surgery. With 16.3 million procedures performed worldwide, and more than a decade of clinical studies and technological innovation, LASIK surgery should be considered among the most successful elective procedures. LASIK surgery compares more favorably with other elective surgical procedures in terms of generally higher satisfaction rates.

Tissue-Saving Zernike Terms Selection in Customized Treatments for Refractive Surgery

Purpose

To study the possibility of performing customized refractive surgery minimising the amount of ablated tissue without compromising visual quality.

Methods

A new algorithm for the selection of an optimized set of Zernike terms in customized treatments for laser corneal refractive surgery was developed. Its tissue saving attributes have been simulated on 100 different wave aberrations at 6mm diameter. Outcomes were evaluated in terms of how much depth and volume was saved for each condition (in micrometers and in percentage), whether the proposed correction consists of either a full wavefront correction or an aberration-free treatment, and whether the proposed depth or volume was less than the one required for the equivalent aberration-free treatment.

Results

Simulated outcomes showed an average saved depth of 5μm (0-16μm), and an average saved volume of 95μl (0-127μl) or 11% saved tissue (0-66% saved tissue). Proposed corrections were always less deep than full wavefront corrections and in 59% of the cases were less deep than equivalent aberration-free treatments.

Conclusions

Even though Zernike modes decomposition is a mathematical description of the aberration, it is not the aberration itself. Not all Zernike modes affect the optical quality in the same way. The eye does not see through Zernike decomposition but with its own aberration pattern. However, it seems feasible to efficiently perform laser corneal refractive surgery in a customized form minimising the amount of ablated tissue without compromising the visual quality. Further clinical evaluations on human eyes are needed to confirm the preliminary simulated results presented herein.

Long-term Study of Artisan Phakic Intraocular Lens Implantation for the Correction of Moderate to High Myopia

PURPOSE

To determine the long-term performance of the Artisan phakic intraocular lens (PIOL) for the correction of myopia.

DESIGN

Long-term (10 years) retrospective follow-up study.

PARTICIPANTS

Eighty-nine eyes of 49 patients who underwent Artisan PIOL implantation for the correction of myopia.

METHODS

Comparisons were made between preoperative clinical data and the clinical data at 1, 6, and 10 years after surgery.

MAIN OUTCOME MEASURES

Refractive stability, refractive predictability, safety, efficacy, best-corrected visual acuity (BCVA), uncorrected visual acuity (UCVA), intraocular pressure, intraoperative problems, corneal endothelial cell density, corneal endothelial cell loss, and glare levels were evaluated.

RESULTS

The mean spherical equivalent (SE) after 10 years was -0.70+/-1.00 diopters (D; range, -4.00 to 2.00 D), with no significant change in mean SE between 1, 6, and 10 years. At 10 years, 68.8% of all eyes were within 1.0 D of the intended correction. At 10 years, 31.2% (n = 24) gained 1 or more Snellen lines of BCVA and 2.6% (n = 2) lost more than 2 Snellen lines of BCVA; 93.3% reached a BCVA of 20/40 or better, and 82.0% reached a UCVA of 20/40 or better. The mean intraocular pressure remained stable and was 15.5+/-3.5 mmHg (range, 7-25 mmHg) at 10 years. The mean endothelial cell loss was -8.86+/-16.01% (range, -51.69% to 34.43%) at 10 years.

CONCLUSIONS

Long-term results demonstrate that the implantation of an Artisan PIOL for the correction of moderate to high myopia is a stable, predictable, and safe method when strict inclusion criteria for surgery are applied. There was no significant loss of corneal endothelial cells and no reports of long-term glare.

Clinical Results With the Medennium Phakic Refractive Lens for the Correction of High Myopia

PURPOSE

To evaluate the predictability, safety, stability, complications, and biocompatibility of the phakic refractive lens (PRL) as a posterior chamber intraocular lens to correct high myopia.

METHODS

Fifty eyes of 31 patients who underwent posterior chamber PRL implantation were evaluated prospectively. Mean preoperative myopia was -12.54 +/- 4.22 diopters (D) (range: -4.50 to -23.50 D) and mean astigmatic refractive power was -1.38 +/- 1.24 D (range: -1.00 to -4.50 D). Surgical implantation was performed through a 3.0- to 4.0-mm clear cornea sutureless incision using parabulbar (sub-Tenon's) anesthesia. Intra- and postoperative complications were recorded.

RESULTS

Three months after surgery, the mean spherical equivalent refraction was -0.21 +/- 0.42 D (range: +1.00 to -1.75 D). At 6 and 12 months, mean spherical equivalent refraction was -0.23 +/- 0.38 D (range: 0 to -1.25 D). At the last examination, uncorrected visual acuity was > or = 20/40 in 41 (82%) eyes and > or = 20/20 in 22 (44%) eyes. Best spectacle-corrected visual acuity (BSCVA) was > or = 20/40 in 42 (84%) eyes and > or = 20/20 in 27 (54%) eyes. Comparison of pre- and postoperative BSCVA at 12 months showed that 12 (36.4%) of 33 eyes gained > or =1 lines of BSCVA and 7 (21.2%) of 33 eyes gained > or =2 lines. One (2%) eye developed anterior subcapsular cataract requiring lens exchange, and 1 (2%) eye developed acute angle closure glaucoma requiring YAG-iridotomy. One (2%) eye developed macular hemorrhage.

CONCLUSIONS

At 6 months and 1 and 2 years, PRL implantation yielded encouraging visual and refractive results with excellent biocompatibility. The efficacy, stability, and short-term safety of this lens was established. Serious complications, such as cataract and acute angle closure glaucoma, may occur, and long-term safety needs to be evaluated.

CHARACTERISTICS OF SIXTY MYOPIC EYES WITH PRE-LASER IN SITU KERATOMILEUSIS RETINAL EXAMINATION AND POST-LASER IN SITU KERATOMILEUSIS RETINAL LESIONS

PURPOSE

A survey of eyes with pre-laser in situ keratomileusis (LASIK) retinal examinations and characteristics of post-LASIK retinal breaks and retinal detachments (RDs).

METHODS

A survey of worldwide vitreoretinal surgeons (424 physicians). Surveyed information included demographics, best-corrected visual acuity, degree of myopia, pre- and post-LASIK retinal findings, follow-up time, and treatment outcome.

RESULTS

Sixty eyes with pre-LASIK retinal examinations developed post-LASIK retinal breaks and RDs. There was an average of 2.3 breaks per eye, yielding a total of 140 breaks in the 60 eyes. Forty eyes also had RDs besides the retinal breaks. Large percentages of eyes had substantial myopia (mean myopia, -9.5 +/- 5.8 diopters [D]) and complex vitreoretinal complications. Forty percent developed vitreoretinal complications within 6 months after LASIK. The 20 eyes that developed more extensive RDs (>3 clock hours) had a significantly higher mean myopia than did the 6 eyes that developed limited RD (< or = 3 clock hours) within 12 months after LASIK (-8.92 +/- 6.82 D versus -3.50 +/- 1.97 D, P = 0.03). There were significant statistical differences in distribution of retinal breaks and tears between the temporal and nasal quadrants (P < 0.001, P < 0.001, respectively, chi2, but not between the superior and inferior quadrants.

CONCLUSION

Distributions of retinal breaks in this study were comparable with results found in non-LASIK eyes in young myopes. Treatment for post-LASIK vitreoretinal complications was highly successful. The vulnerability of such highly myopic eyes for vitreoretinal complications warrants their close monitoring.

Aspheric Ablation With the Nidek EC-5000 CX II With OPD-Scan Objective Analysis

PURPOSE

To analyze the efficacy, predictability, stability, and safety of laser in situ keratomileusis (LASIK) to correct myopia and myopic astigmatism using the Nidek EC-5000 CX II laser and the Customized Aspheric Transition Zone (CATz) profile.

METHODS

We conducted a retrospective analysis of 100 eyes (50 patients) with myopic astigmatism. A CATz profile was used in all eyes (profile 4) with an ablation zone of 5 mm and a transition zone of 9 mm, using Nidek FinalFit software.

RESULTS

Average patient age was 39 years (range 21 to 69 yr). Preoperative mean spherical equivalent refraction was -4.70 +/- 2.53 D (range -11.88 to -0.50 D), mean preoperative sphere was -4.31 +/- 2.53 D (range -11.25 to -0.25 D), and mean preoperative cylinder was -0.78 +/- 0.69 D (range -3.25 to 0). Postoperative mean spherical equivalent refraction at 6 months was 0.12 +/- 0.53 D (range -1.63 to +0.88 D), mean postoperative sphere was 0.02 +/- 0.56 D (range -1.50 to +2.00 D), and mean postoperative cylinder was -0.29 +/- 0.50 D (range 0 to -1.75 D). Uncorrected visual acuity was 6/6 or better in 58% (58 eyes) and better than 6/12 in 93% (93 eyes).

CONCLUSION

LASIK with the Nidek EC-5000 CX II laser and the CATz profile was effective, reasonably predictable, stable, and safe for correction of myopic astigmatism with a spherical component between -0.25 and -11.25 D, and a cylindrical component up to 3.25 D, using the techniques in this study. Astigmatism was undercorrected with the current algorithm.

Higher Order Aberrations With Aspheric Ablations Using the Nidek EC-5000 CX II Laser

PURPOSE

To analyze the change in higher order aberrations in myopic and myopic astigmatic eyes following an aspheric ablation profile for laser in situ keratomileusis (LASIK) using a Nidek EC-5000 CX II excimer laser system.

METHODS

We performed a retrospective audit of 38 eyes (19 patients) with myopia and myopic astigmatism. A customized aspheric transition zone profile (CATz) was used in all eyes (profile 4) with an ablation zone of 5 mm and a transition zone of 9 mm using FinalFit software and a Nidek EC-5000 CX II excimer laser system.

RESULTS

Mean higher order aberrations (RMS) increased from 0.42 microm at baseline to 0.57 microm at 6-month follow-up. Mean spherical aberrations (Z12) increased from 0.02 microm at baseline to 0.33 microm after LASIK. Mean spherical aberration defocus equivalent (DEQ) increased from 0.56 microm at baseline to 1.54 at 6 months after surgery. Mean trefoil (Z6) was -0.11 microm at baseline and -0.14 microm at the 3-month examination. Mean coma (Z7) was -0.09 microm at baseline and -0.10 microm after surgery. Mean coma (Z8) was -0.03 at baseline and 0 at the 3-month examination. Mean trefoil (Z9) was -0.03 at baseline and -0.12 at the 3-month examination.

CONCLUSION

The amount of postoperative higher order aberrations in these myopic eyes was acceptable. However, the clinical significance of these numerical changes in aberrations is not known.

Development of a Questionnaire to Assess Subjective Vision Score in Myopes Seeking Refractive Surgery

PURPOSE

To assess vision in patients with myopia and myopic astigmatism before and after refractive surgery.

METHODS

A prospective controlled study of visual quality amongst myopes and astigmatic myopes. Focus groups, ophthalmic surgeons, and questionnaire experts devised a Subjective Vision Questionnaire (SVQ), modified after a pilot trial. Participants were administered the SVQ before clinical evaluation. Items answered by over 95%, with factor loadings > 0.55 were included. Test-retest reliability was assessed by repeat testing. Factor analysis identified groups of questions measuring particular dimensions of data.

RESULTS

Sixty-seven items were answered by 128 patients and reduced to 24 items in a final questionnaire. Factor analysis identified six types of questions within the questionnaire, the most important of which was related to driving.

CONCLUSION

The simplicity, low cost, and psychometric properties of the Subjective Vision Questionnaire support its use clinically and in research.

Nomogram Considerations With the Technolas 217A for Treatment of Myopia

PURPOSE

To determine whether surgeon-specific nomogram adjustments are useful when using the Technolas 217A excimer laser for treating myopia and myopic astigmatism.

METHODS

We conducted a prospective evaluation of 216 consecutive eyes with 6 months follow-up after treatment of myopia or myopic astigmatism with the Technolas 217A laser. Attempted vs. achieved change in refraction was analyzed with a statistical analysis software program. Factors such as age, corneal thickness (pachymetry), preoperative spherical equivalent refraction, preoperative cylinder, and optical zone were studied to evaluate their role in predicting refractive outcome at 6 months after LASIK.

RESULTS

The mean value of attempted spherical equivalent refraction was -5.32 +/- 2.72 D. The mean achieved refractive correction at 6 months was -5.55 +/- 2.78 D, with a mean spherical equivalent of 0.13 +/- 0.54 D. The percent achieved effect at 1 month was 105%, and at 6 months, 103%. Preoperative spherical equivalent refraction and optical zone size were strong predictors of 6-month LASIK outcome. There was a 9% difference in the percent achieved effect between a 4 and 7-mm optical zone. There was no correlation between age, preoperative cylinder, or surgeon and 6-month outcome.

CONCLUSIONS

Surgeons using the planoscan software on the Technolas 217A may experience a small initial overcorrection. There may be a benefit to reducing the treatment given with larger optical zones and smaller corrections.

Change to Corneal Morphology after Refractive Surgery (Myopic Laser In Situ Keratomileusis) as Viewed with a Confocal Microscope

PURPOSE

This study aimed to look at morphological changes induced by myopic laser in situ keratomileusis (LASIK) in the human cornea using the confocal microscope and to investigate the link between these changes and alterations to corneal sensitivity.

METHODS

An in vivo slit-scanning real-time confocal microscope (Tomey ConfoScan P4, Erlangen, Germany) fitted with an Achroplan 40x/0.75 NA immersion objective and a Cochet-Bonnet esthesiometer were used to examine the morphology and sensitivity of the central corneas of six subjects (12 eyes) at an initial visit (before surgery), and at 1 week, 1 month, 3 months, and 6 months after LASIK for myopia.

RESULTS

Keratocyte density anterior to the flap interface showed differences between visits (p < 0.0001) and was found to be lower than at the initial visit at 1 week, 1 month, 3 months, and 6 months. Microfolds were noted at the level of the anterior limiting membrane in 11 of 12 eyes after surgery at all visits. Highly reflective flap interface particles were seen in all eyes at all visits after surgery. The subepithelial nerve fiber layer was clearly visible before surgery but could not be imaged in any of the eyes after surgery. Short, unconnected nerve fibers were observed 3 months after surgery; these appeared to form anastomosing interconnections after 6 months. Postsurgical corneal sensitivity was reduced during the first 3 months and recovered to presurgical levels after 6 months.

CONCLUSION

LASIK showed a decrease in anterior keratocyte density and microfolds in the anterior limiting membrane, and reflective particles were observed at the flap interface. Corneal sensitivity was depressed during the first 6 months after LASIK surgery; this time course paralleled the appearance of nerve regeneration during this period. Confocal microscopy is capable of providing interesting new insights into the effects of refractive surgery on corneal morphology.

Contact lens fitting following unsuccessful refractive surgery

A retrospective review of case notes of consecutive patients referred to a contact lens clinic after unsuccessful refractive surgery was carried out to determine the success of contact lens fitting. The main outcome variables in determining success were visual improvement, contact lens tolerance, fitting characteristics and wearing time. Thirteen eyes were fitted with conventional rigid gas permeable (CRGP), 10 with soft and 19 with reverse geometry rigid gas permeable contact lenses (RVG). The mean spectacle visual acuity (VA) was 6/9 (20/30) [range: 6/24 (20/80) to 6/5 (20/15)] and the mean VA after contact lens fitting was 6/6 (20/20) [range: 6/18 (20/60) to 6/5 (20/15)]. Of the 42 eyes, the contact lens VA was better than spectacle acuity in 25 (59.5%) eyes, equal in 14 (33.3%) and worse in three (7.1%). A total of 33 (78.6%) eyes were still wearing their lenses at the last visit. Contact lenses can be a valuable method of managing poor VA after refractive surgery.

Laser in situ Keratomileusis for Compound Myopic Astigmatism Using the Meditec MEL 70 G-Scan Excimer Laser

PURPOSE

To determine the safety, efficacy, predictability, and stability of laser in situ keratomileusis (LASIK) in treating patients with myopic astigmatism using the Meditec MEL 70 G-Scan excimer laser.

METHODS

Seventy-four eyes of 42 patients with myopia ranging from -4.50 to -9.88 D and astigmatism ranging from 0.50 to 4.00 D who underwent LASIK with the Meditec MEL 70 G-Scan excimer laser and the Summit Krumeich-Barraquer microkeratome were studied. Patients were followed for 1 year.

RESULTS

Mean baseline spherical equivalent refraction was -7.12 +/- 1.70 D and cylinder was 1.62 +/- 1.72 D. At 12 months, mean postoperative spherical equivalent refraction was -0.49 +/- 0.57 D and mean refractive cylinder was 0.59 +/- 0.32 D. Mean change in spherical equivalent refraction between 1 and 12 months after surgery was -0.09 +/- 0.31 D, toward myopia. At baseline, no eyes had best spectacle-corrected visual acuity (BSCVA) of 20/20 or better, and 65% had 20/40 or better. At 12 months after surgery, 10% of eyes had BSCVA of 20/20 or better and 88% of eyes had 20/40 or better. The unusually low postoperative BSCVA results were thought to be due to amblyopia or existence of a higher percentage of some optical aberrations in this group of eyes. Mean uncorrected visual acuity was -1.38 +/- 0.42 LogMAR units (20/400) at baseline and -0.29 +/- 0.25 LogMAR units (20/40) at the 12-month postoperative examination. No eyes lost two or more lines of spectacle-corrected visual acuity. No vision threatening complications were observed.

CONCLUSIONS

LASIK with the Meditec MEL 70 G-Scan excimer laser appeared to be safe, effective, reasonably predictable, and stable for correction of myopic astigmatism with a spherical component between -4.25 and -8.25 D and a cylindrical component between 0.50 and 4.00 D. However, astigmatism was slightly undercorrected with the algorithm used.

Mathematical model of corneal surface smoothing after laser refractive surgery

PURPOSE

To construct a quantitative model of corneal surface smoothing after laser ablation for refractive correction.

DESIGN

Experimental study, interventional case series, and meta-analysis of literature.

METHODS

A theory of epithelial smoothing in response to corneal contour change is derived from differential equations that describe epithelial migration, growth, and loss. Computer simulations calculate the effects on postoperative epithelial thickness, topography, refraction, and spherical aberration. Model parameter is matched with laser in situ keratomileusis (LASIK) outcome in literature and in a retrospective study of primary spherical myopic (77 eyes) and hyperopic (19 eyes) corrections. Surgically induced refractive change was the main outcome measure.

RESULTS

Simulated epithelial remodeling after myopic ablation produces central epithelial thickening, reduction in achieved correction, and induction of oblate spherical aberration. Simulation of hyperopic ablation shows peripheral epithelial thickening, a larger reduction in correction, and induction of prolate spherical aberration. Simulation using a minus cylinder laser ablation pattern shows decreased astigmatism correction and increased hyperopic shift. In the LASIK series, linear regression of achieved correction vs ablation setting in hyperopic and minus cylinder corrections shows slopes of 0.97, 0.71, and 0.74, respectively. These clinical results match model predictions when the smoothing constant is set at 0.32, 0.63, and 0.55 mm, respectively.

CONCLUSIONS

Epithelial thickness modulations after ablation can be modeled mathematically to explain clinically observed regression and induction of aberration. The cornea appears to smooth over ablated features smaller than approximately 0.5 mm. The model provides an approach for designing ablation patterns that precompensate for the smoothing to improve final outcome.

Socioeconomic aspects of laser in situ keratomileusis, eyeglasses, and contact lenses in mild to moderate myopia

PURPOSE

To compare the societal costs and consequences of 3 strategies to correct mild to moderate myopia: laser in situ keratomileusis (LASIK), eyeglasses, and contact lenses (CLs).

SETTING

Instituto Oftalmológico de Alicante, Alicante, Spain.

METHODS

A Markov model was set up to compare the present value of LASIK, eyeglasses, and CLs. A structured questionnaire was administered to 40 consecutive patients with mild to moderate myopia to collect resource information including direct medical and nonmedical costs as well as indirect costs (transportation, time spent, hotel, eyeglasses, CLs, LASIK, cleaning products, visits to ophthalmologist/optometrist/optical center, and adverse events linked to LASIK and CLs). The time period ranged from 10 to 30 years with a 5% discount rate. The Spanish population was used as the basis for the economic data. Full sensitivity analyses were conducted.

RESULTS

Based on the time period, LASIK saved from 18 to 278 km in distance to care centers compared with eyeglasses and from 405 to 1436 km compared with CLs. The time to care for visual acuity was similar between LASIK and CLs, but up to 1180 additional hours were spent by CL users. Laser in situ keratomileusis saved from 4.69 to 12.07 eyeglasses and from 28 to 84 eyeglass cleaning packs. With LASIK, there were 18 to 50 visits to the optical center compared with 41 to 117 visits with CLs. Laser in situ keratomileusis saved 4.7 to 12.2 visits to correct visual acuity compared with eyeglasses and CLs. It prevented 95 to 295 per 10 000 cases of CL-related keratitis. Contact lenses were always more costly than LASIK, which was always more costly than eyeglasses. The 2 sensitivity parameters were time period and discount rate.

CONCLUSIONS

Laser in situ keratomileusis was less costly than CLs and more expensive than eyeglasses, although the potential nonmonetary benefit of LASIK over eyeglasses was not taken into account.

Laser in situ Keratomileusis for Myopic Astigmatism With the Nidek EC-5000 Laser

PURPOSE

We studied the efficacy, predictability, and safety of laser in situ keratomileusis (LASIK) for moderate to high simple and compound myopic astigmatism.

METHODS

Ninety-two eyes of 46 consecutive patients who had LASIK for myopic astigmatism (64 eyes, astigmatism 3.00 to 9.00 D; myopia 0 to -20.00 D), or simple myopia (28 eyes, myopia -4.00 to -20.00 D; astigmatism 0 to 0.50 D) were retrospectively studied. Mean baseline spherical equivalent refraction (SE) in the myopia group was -8.11 +/- 3.94 D and in the astigmatism group, -8.55 +/- 4.49 D. All eyes underwent LASIK using the Nidek EC-5000 laser by the same surgeon.

RESULTS

At 6 months after LASIK in the myopia group versus the astigmatism group, 24 eyes (85%) vs. 54 eyes (84%) were available for follow-up, 12 eyes (50%) vs. 13 eyes (24%) had uncorrected visual acuity (UCVA) of 20/20, 19 eyes (79%) vs. 44 eyes (81%) had UCVA of 20/40, 8 eyes (33%) vs. 18 eyes (33%) had SE within +/- 0.50 D, 15 eyes (62%) vs. 39 eyes (72%) had SE within +/- 1.00 D, and mean SE was -1.22 +/- 1.17 D vs. -0.74 +/- 1.46 D. Mean astigmatism (vertexed to the corneal plane) in the astigmatism group was 2.77 D at 0 degrees before surgery and 0.32 D at 7 degrees at 6 months. None of the myopic eyes and three of the astigmatic eyes (5%) lost > or = 2 lines of best spectacle-corrected visual acuity.

CONCLUSION

LASIK with the Nidek EC-5000 laser for myopic astigmatism was reasonably effective, predictable, and safe. Astigmatism was under-corrected with the nomogram implemented in this study.

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.

The effect of water content on the 193 nm excimer laser ablation

BACKGROUND

Water content of the corneal stroma may influence excimer laser ablation and may therefore affect residual refractive error following laser in situ keratomileusis. This study reports associations between water content of hydrogel materials and laser ablation depth.

METHODS

Hydrated (n = 4) and dehydrated (n = 4) hydrogel buttons of 38%, 45%, 55% and 69% water content were ablated with the Nidek EC-5000 ArF 193 nm excimer laser, set to deliver a -6.00 DS curvature. Central curvature, optical quality and water content were measured before and after ablation. Hydrated buttons were rehydrated postablation and prior to measurement, to eliminate the effect of water removal during the procedure. The ablation depth per pulse was calculated.

RESULTS

The average ablation rate for fully hydrated buttons was 0.51 +/- 0.17 microm. The ablation rate for hydrated materials (dry component ablation) reduced with increasing water content (P < 0.001). Dry hydrogel materials (0% water content) had an average ablation rate of 0.23 +/- 0.06 microm per pulse.

CONCLUSIONS

For a constant laser energy output, lower water content materials ablated to a greater extent than higher water content materials. This model provides a simple way to assess the effect of water content and dehydration on myopic laser in situ keratomileusis.

Scanning electron microscopic evaluation of the surface characteristics of 4 microkeratome systems in human corneas

PURPOSE

To evaluate the surface characteristics of keratectomy specimens created with 4 microkeratomes by scanning electron microscopy (SEM).

SETTING

Two university institutions.

METHODS

Keratectomies were performed in 10 fresh, unfrozen human eyes with 1 of 4 microkeratomes: the Draeger rotary microkeratome (Storz Instruments), the Universalkeratome (Phoenix), the Automated Corneal Shaper (Bausch & Lomb), or the Hansatome (Bausch & Lomb). The beds and edges of the keratectomy specimens were then examined by SEM. Standardized photographs were taken, and the surface and cut-edge characteristics of the keratectomies were compared.

RESULTS

Irregularities were noted in the cut edges of Bowman's membrane and the surface of the keratectomy beds with all instruments. The irregularities were most prominent in corneas cut with the Draeger instrument and least prominent in those cut with the Universalkeratome. The serrations in Bowman's membrane and the irregularities in the keratectomy bed appeared to be related to the blade movement in oscillating blade instruments.

CONCLUSIONS

All 4 microkeratomes caused some degree of surface irregularity. The Draeger microkeratome, which uses a continuously rotating blade, resulted in the greatest number of Bowman's membrane serrations and irregularities in the keratectomy bed. The tissue irregularities may be related to the development of pressure ridges ahead of the blade. In instruments that use an oscillating blade, chatter marks appear to be related to the reciprocating movement of the blade as it travels across the corneal stroma.

Laser in situ Keratomileusis and Photorefractive Keratectomy for Residual Refractive Error After Phakic Intraocular Lens Implantation

PURPOSE

To determine the visual and refractive outcome of photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) in eyes with prior posterior chamber phakic intraocular lens implantation for high myopia.

METHODS

We studied a series of 37 consecutive eyes of 31 patients who underwent LASIK or PRK for residual refractive error following collamer posterior chamber intraocular lens (IOL) (Staar Surgical Implantable Contact Lens) implantation into a phakic eye. Twenty-eight eyes had LASIK and nine eyes had PRK. Mean follow-up was 8.1 +/- 4.7 months after laser ablation (range, 3 to 18 mo).

RESULTS

The preoperative mean spherical equivalent refraction prior to phakic posterior chamber IOL implantation was -17.74 +/- 4.89 D (range, -9.75 to -28.00 D). Following phakic IOL implantation and prior to LASIK or PRK, mean spherical equivalent refraction was -2.56 +/- 2.34 D (range, -0.25 to -8.75 D). One month following LASIK or PRK, mean spherical equivalent refraction was -0.24 +/- 0.52 D (range, -1.50 to +1.50 D), 3 months following LASIK or PRK, mean spherical equivalent refraction was -0.19 +/- 0.50 D (range, -1.50 to +1.00 D). The refraction was within +/-1.00 D of emmetropia in 36 eyes (97.2%) and within +/-0.50 D in 31 eyes (83.7%). Three eyes developed anterior subcapsular opacities several weeks after laser ablation, one eye developed macular hemorrhage 4 weeks after laser ablation, and one eye had corticosteroid induced ocular hypertension.

CONCLUSIONS

LASIK or PRK can be used to treat the residual refractive error following posterior chamber phakic IOL implantation.

Symptoms of dry eye and recurrent erosion syndrome after refractive surgery

PURPOSE

To determine the incidence and severity of patient complaints typical of dry eye and recurrent erosion syndrome after excimer laser refractive surgery and to compare the incidence of these symptoms after photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK).

SETTING

Outpatient university practice.

METHODS

A questionnaire was mailed to 1731 patients who had had primary myopic PRK or LASIK at least 6 months previously. Questions were designed to determine the incidence and character of ocular dryness and recurrent erosion symptoms and their impact on patient satisfaction and willingness to have surgery again. Responses from PRK and LASIK patients were compared.

RESULTS

Responses from 231 PRK patients and 550 LASIK patients revealed an incidence of dryness symptoms in 43% and 48%, respectively (P >.05). Soreness of the eye to touch was reported by 26.8% and 6.7%, respectively (P <.0001). Sharp pains occurred in 20.4% of PRK patients and 8.0% of LASIK patients (P =.0001). Complaints of the eyelid sticking to the eyeball occurred in 14.7% and 5.6%, respectively (P =.0001). All symptoms occurred predominantly on waking. Frequency of eyelid sticking (P <.0005) and sharp pain (P <.005) symptoms, as well as severity of sharp pain symptoms (P <.0001), were significantly greater in PRK patients than in LASIK patients. On a scale of 0 to 10 (10 high), median overall patient satisfaction with surgery was 9 in both groups. Soreness of the eyelid to touch occurred significantly more frequently among patients with symptoms of sharp pains on waking (P <.001) and the sensation of the eyelid sticking to the eyeball (P <.001). Patients with 1 or more symptoms were twice as likely as asymptomatic patients to have a satisfaction score of less than 8 (P <.001).

CONCLUSIONS

Ocular dryness symptoms occurred commonly after PRK and LASIK. Symptoms suggestive of mild recurrent erosions included sharp pains, the sensation of the eyelid sticking to the eyeball, and soreness of the eyelid to touch, a previously unrecognized symptom of this condition. These symptoms occurred commonly after excimer laser procedures but were significantly more common, more severe, and more prolonged after PRK. The presence of these symptoms had a significant effect on patient satisfaction.

Change in Intraocular Pressure in Myopic Eyes Measured With Contact and Non-contact Tonometers After Laser in situ Keratomileusis

PURPOSE

To study the change in the intraocular pressure (IOP) after laser in situ keratomileusis (LASIK) for correction of myopia.

METHODS

One hundred twenty consecutive myopic eyes (60 patients) were included in a prospective study. All eyes received LASIK with the Nidek EC-5000 excimer laser and the Chiron Automated Corneal Shaper. Baseline refraction, keratometry, pachymetry, ablation depth, and IOP measured by Goldmann applanation tonometry and non-contact air puff tonometry were correlated with the IOP change after surgery. Sixty healthy eyes of 30 subjects served as controls.

RESULTS

At 6 months, 108 eyes (90%) were examined. Compared to preoperative values, IOP decreased in 103 eyes (95.4%) when measured with applanation tonometry; it decreased in all eyes when measured with air puff tonometry. Mean change in IOP was -4.3 +/- 2.1 mmHg (range, -10.0 to +1.0 mmHg) with the applanation and -6.1 +/- 2.3 mmHg (range, -12.0 to -1.0 mmHg) with air puff tonometry. The IOP change measured with either instrument correlated significantly with the baseline IOP (P < .001) and the ablation depth (air puff, P < .001, applanation; P = .006).

CONCLUSION

Intraocular pressure decreased significantly after LASIK when measured with either Goldmann (mean 4.3 mmHg) or air puff (mean 6.1 mmHg) tonometers. This decrease may delay the diagnosis or affect the management of future glaucoma that may develop in a myopic eye that received LASIK.

Clear lens extraction with intraocular lens followed by photorefractive keratectomy or laser in situ keratomileusis

OBJECTIVE

To study photorefractive keratectomy (PRK) or laser in situ keratomileusis (LASIK) after clear lens extraction (CLE) with intraocular lens (IOL) implantation for hyperopia or astigmatism.

DESIGN

Retrospective, noncomparative interventional case series.

PARTICIPANTS

Sixty-five eyes (55 subjects) had CLE with posterior chamber IOL implants for hyperopia up to 12.25 diopters (D); 31 eyes were retreated with PRK, and 34 eyes were retreated with LASIK for residual ametropias.

INTERVENTION

For PRK and LASIK, the refractive surgery was performed with the slit-scanning excimer laser Nidek EC-5000, Nidek Co., Tokyo, Japan.

MAIN OUTCOME MEASURES

Manifest refraction, best-spectacle and uncorrected Snellen visual acuity, haze, and halos were evaluated before surgery and at 1, 3, 6, and 12 months postoperative.

RESULTS

Forty-seven eyes were evaluated at the 12-month postoperative examination: 96% of these eyes had spherical equivalents (SE) within +/-2 D of emmetropia, 79% of eyes had SE within +/-1 D of emmetropia and 51% of eyes had SE within +/-0.50 D of emmetropia. Eighty-five percent of the eyes at 12 months postoperative had uncorrected visual acuity of 20/40 or better, and 46% of eyes had uncorrected visual acuity of 20/20 or better. Eighty-seven percent of the eyes at 12 months postoperative had uncorrected visual acuity within 1 Snellen line of their initial best spectacle-corrected visual acuity (BSCVA) before all treatment. No eye lost 2 Snellen lines of BSCVA at 3, 6, or 12 months after PRK or after LASIK.

CONCLUSIONS

IOL implantation for CLE, although an invasive technique, resulted in better refractive outcomes without laser-related clinical complications after PRK or LASIK adjustment.

Correction of high astigmatism with astigmatic keratotomy combined with laser in situ keratomileusis

PURPOSE

To evaluate the efficacy, predictability, and stability of a combined procedure, arcuate keratotomy and laser in situ keratomileusis (LASIK), for the correction of high astigmatism.

SETTING

Instituto de Microcirugía Ocular (IMO), Barcelona, Spain.

METHODS

Fifteen eyes of 11 patients with naturally occurring astigmatism (NOA) (86. 66%) or surgically induced astigmatism (SIA) (13.34%) between -3.00 and -8.00 diopters (D) who had astigmatic keratotomy were studied. The patients had a secondary procedure, LASIK, to correct the residual refractive error.

RESULTS

Mean baseline spherical equivalent refraction was -2.47 D +/- 3.69 (SD) and mean refractive cylinder, -4.59 +/- 1.66 D. Twelve months after LASIK, mean spherical equivalent was -0.09 +/- 1.50 D and the mean refractive cylinder, -1. 21 +/- 1.07 D. The mean cylindrical correction attempted in the NOA group was -4.05 +/- 1.19 D and in the SIA group, -7.00 +/- 1.41 D. Postoperatively, the values were -1.50 +/- 1.17 D and -1.62 +/- 0.17 D, respectively. Twelve months after LASIK, the uncorrected visual acuity (UCVA) was 0.5 +/- 0.1. The UCVA in the NOA group (0.50 +/- 0. 08) was better than in the SIA group (0.32 +/- 0.10). The efficacy index was 0.96 overall. Best corrected visual acuity deteriorated by 1 Snellen line in 1 case (6.6%) but improved by 1 and 2 Snellen lines in 4 cases (26.6%) and 2 cases (13.3%), respectively. All procedures were completed without adverse reactions intraoperatively or postoperatively.

CONCLUSION

This combined technique was effective in the treatment of high astigmatism, with excellent results compared with the results of each procedure alone. Because of its high predictability, we strongly recommend the technique in cases with astigmatism higher than 3.0 D, particularly in those with astigmatism higher than 5.0 D.

Photorefractive keratectomy versus laser in situ keratomileusis: a control-matched study

OBJECTIVE

Photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) outcomes were compared at 1, 3, 6, and 12 months after surgery.

DESIGN

Retrospective, nonrandomized, comparative study.

PARTICIPANTS

One hundred seven LASIK-treated eyes (58 patients) and 107 PRK-treated eyes (91 patients) having myopia between -1 and -9.50 diopters (D). All LASIK-treated eyes were analyzed retrospectively and matched with PRK-treated eyes having sphere within +/-0.25 D, +/-1 D of cylinder, and +/-7 years of age.

INTERVENTION

For PRK and LASIK, the refractive surgery was performed with the slit-scanning excimer laser Nidek EC-5000, (Nidek Co. Tokyo, Japan)

MAIN OUTCOME MEASURES

Manifest refraction, best-spectacle and uncorrected Snellen visual acuity, haze, halos, and keratometry were evaluated before surgery and up to 12 months after surgery.

RESULTS

Seventy percent of eyes were evaluated at the 12-month postoperative exam. Of these eyes, 83% of LASIK cases and 86% of PRK cases had uncorrected visual acuities of 20/20 or better. Refractions within +/-0.5 D represented 78% of the LASIK eyes and 83% of the PRK eyes at that follow-up. Patients who underwent LASIK reported halos twice as often as patients who underwent PRK using a subjective scale. The odds ratio of high halos for LASIK versus PRK was 3.50 (95% confidence interval, 1.89-6.46; P<0.0001). At 1 month after surgery, 64% of the LASIK eyes were within +/-0.50 D compared with 77% of the PRK eyes. No eye lost 2 Snellen lines of best corrected visual acuity at 6 or 12 months after surgery. Ten PRK eyes (9.3%) and three LASIK eyes (2.8%) were retreated.

CONCLUSIONS

PRK and LASIK achieved equal refractive outcomes at all postoperative follow-ups, but LASIK patients were twice as likely to experience halos.

Comparing predictability between eyes after bilateral laser in situ keratomileusis: a theoretical analysis of simultaneous versus sequential procedures

OBJECTIVE

To compare the predictability of laser in situ keratomileusis (LASIK) between eyes of individuals to determine whether the refractive result of the first eye is useful in improving fellow eye outcomes.

DESIGN

Single-center case series.

PARTICIPANTS

One surgeon and 196 eyes of 98 patients.

INTERVENTION

All patients received sequential bilateral LASIK. The mean time between procedures was 11.6 days. Attempted corrections ranged from 2.30 to 12.00 diopters (D).

MAIN OUTCOME MEASURES

Predictability (achieved minus attempted correction), postoperative manifest refraction, and theoretical postoperative manifest refraction, using a proposed attempted correction on the second eye based on first eye results, were analyzed.

RESULTS

At 1 week, 1 month, and 3 months, predictability of the first operated eye was correlated with predictability of the fellow eye (1 week: mean 1st = 0.33 D, mean 2nd = 0.33 D, Pearson coefficient = 0.46, P < 0.0005; 1 month: mean 1st = 0.028 D, mean 2nd = -0.020 D, Pearson coefficient = 0.43, P < 0.0005; 3 months: mean 1st = -0.22 D, mean 2nd = -0.12 D, Pearson coefficient = 0.52, P < 0.0005). At the 3-month follow-up of the second eye, comparing the actual distance from emmetropia with that calculated using a theoretical proposed attempted correction based on the first eye refraction, distance from emmetropia was closer in the theoretical correction group. This finding was stronger in patients with preoperative myopia less than 5.5 D (P = 0.03). For this group, 93% of patients in the proposed attempted correction group would fall within 1.0 D of emmetropia compared to 80% found in the actual outcomes.

CONCLUSIONS

The refractive predictability between the two eyes of an individual after LASIK is correlated. Theoretically, therefore, one may be able to achieve correction closer to emmetropia in the second eye by applying the refractive predictability results from the first operated eye. In this study, using a theoretical proposed attempted correction in the second eye based on the first eye outcome, we have shown that better outcomes in the second eye are possible, particularly in low myopes. Thus, it may be advantageous to perform bilateral LASIK sequentially rather than simultaneously, using predictability outcomes from the first operated eye in planning fellow eye treatment. Moreover, waiting approximately 1 week was found to be potentially as effective as waiting longer periods of time between treatments. Further studies are necessary to better assess the actual clinical significance of these findings.

Laser in situ keratomileus using the LaserSight 200 laser: results of 950 consecutive cases

PURPOSE

To examine the refractive outcome in 950 consecutive eyes having laser in situ keratomileusis (LASIK) by 1 surgeon with experience in keratomileusis.

SETTING

Outpatient excimer laser surgical facility.

METHODS

This study comprised 950 consecutive eyes of 475 patients having LASIK as a primary procedure with a LaserSight 200 excimer laser (8.51 software). A nasal hinged flap and a Chiron microkeratome were used. Preoperative cycloplegic refraction was done only in patients younger than 25 years and in all hyperopic cases. Subjective preoperative and postoperative manifest refractions were done after autorefractometry in all cases. In cases of hyperopia, the software was modified by adding 30% to the refractive error. Enhancement results are not included.

RESULTS

Of the 950 eyes, 893 (94.00%) were myopic and 57 (6.00%), hyperopic. In the low myopia group (1.00 to 3.99 D) of 223 eyes (24.97%), mean spherical equivalents (SEs) were -2.90 D +/- 0.56 (SD) preoperatively, -0.46 +/- 0.6 D 3 months postoperatively, and -0.41 +/- 0.5 D 6 months postoperatively. In the moderate myopia group (4.00 to 5.99 D) of 205 eyes (22.96%), respective mean SEs were -4.90 +/- 0.7 D, -0.90 D +/- 0.9 D, and -0.67 +/- 0.7 D. In the high myopia group (6.00 to 9.99) of 266 eyes (25.30%), the respective means were -7.70 +/- 1.3 D, -0.76 +/- 0.99 D, and -0.60 +/- 0.8 D. In the extreme myopia group (10.21 to 30.00) of 199 eyes (22.28%), the respective means were -13.30 +/- 2.9 D, -1.30 +/- 1.4 D, and -1.13 +/- 1.3 D. For the entire myopic group, the mean astigmatism was +1.55 +/- 1.38 D, +1.09 +/- 0.92 D, and +0.87 +/- 0.77 D, respectively. The low hyperopia group (1.00 to 2.99 D) of 39 eyes (68.42%) had a mean preoperative SE of +1.80 +/- 0.59 D and mean postoperative SEs of +1.00 +/- 0.76 D at 3 months and +1.16 +/- 0.52 D at 6 months. The respective means in the moderate hyperopia group (3.00 to 6.00) of 18 eyes (31.57%) were +4.62 +/- 1.19 D, +3.71 +/- 1.12 D, and +4.00 +/- 1.07 D.

CONCLUSIONS

Laser in situ keratomileus for myopia using the LaserSight 200 excimer laser was stable with time and safe for the correction of different degrees of myopia. In the hyperopic group, marked regression occurred in a large percentage of patients. Thus, we will not perform LASIK for hyperopia until the software improves.

Randomized bilateral comparison of excimer laser in situ keratomileusis and photorefractive keratectomy for 2.50 to 8.00 diopters of myopia

OBJECTIVE

To compare effectiveness, safety, and stability of excimer laser in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK) for low-to-moderate myopia.

DESIGN

Prospective, randomized, bilateral study.

PARTICIPANTS

Thirty-three patients with a manifest refraction of -2.50 to -8.00 diopters (D) participated.

INTERVENTION

For each patient, one eye received LASIK and the other received PRK. The first eye treated, and surgical method in the first eye, were randomized. Both eyes were treated by the same surgeon during the same operative session with a Summit Omnimed I laser (6-mm-diameter ablation) and a Chiron Automated Corneal Shaper. Follow-up was 90% at 1 and 2 years.

RESULTS

At baseline, mean (+/-standard deviation) spherical equivalent manifest refraction was -4.80 +/- 1.60 D in LASIK-treated eyes and -4.70 +/- 1.50 D in PRK-treated eyes. At 1 day after surgery, 81% of patients (21 eyes) reported no pain in the LASIK-treated eye, whereas no patient (0%) reported being pain-free in the PRK-treated eye. At 3 to 4 days after surgery, 18 (80%) LASIK-treated eyes either improved or remained within 1 line of baseline spectacle-corrected visual acuity; only 10 (45%) PRK-treated eyes achieved this result. At 2 years after surgery, 18 (61%) LASIK- and 10 (36%) PRK-treated eyes achieved an uncorrected visual acuity of 20/20 or better, with no statistically significant difference in refractive outcome between the two techniques. Quantitative videokeratography showed more regularity after LASIK. Complications were similar in the two groups. Patients preferred LASIK by a margin of 2 to 1 at 1 year but showed no preference at 2 years.

CONCLUSIONS

Using a 6-mm-diameter single-pass, large area ablation and an automated microkeratome to treat myopia of -2.50 to -8.00 D with 1.00 D or less astigmatism in 1994, the authors used LASIK to produce a higher percentage of eyes with an uncorrected visual acuity of 20/20 or better, more regular postoperative corneal topography, less postoperative pain, and more rapid recovery of baseline spectacle-corrected visual acuity than PRK. Both LASIK and PRK achieved successful correction of low-to-moderate myopia at 1 and 2 years after surgery.

Comparison of photorefractive keratectomy with excimer laser in situ keratomileusis in correcting low myopia (from -2.00 to -5.50 diopters). A randomized study

OBJECTIVE

To compare laser in situ keratomileusis (LASIK) with photorefractive keratectomy (PRK) in the correction of myopia from -2.00 to -5.50 diopters.

DESIGN

Prospective, randomized, paired clinical trial.

PARTICIPANTS

Fifty-two eyes of 26 myopic patients were enrolled in the study.

INTERVENTION

Each patient received PRK on one eye (PRK eye) and LASIK on the other (LASIK eye); the procedure assigned to each eye, and the sequence of surgeries for each patient was randomized.

MAIN OUTCOME MEASURES

Slit-lamp microscopy, manifest refraction, uncorrected and spectacle-corrected visual acuity, and videokeratography were done before operation, and 2 weeks, 6 weeks, 3 months, 6 months, and 12 months after operation. Patient satisfaction and preference were assessed by a subjective questionnaire.

RESULTS

All LASIK eyes had fast, painless recovery. At 1 year, 24 patients (92.3%) were examined, the mean spherical equivalent refraction was -0.08 +/- 0.38 diopter in the PRK eyes and -0.14 +/- 0.31 diopter in the LASIK eyes, and the uncorrected visual acuity was 20/20 or better in 15 PRK eyes (62.5%) and 19 LASIK eyes (79.2%); no eye lost 2 or more Snellen lines of spectacle-corrected visual acuity. Both procedures were stable throughout the first year. One PRK eye developed dense subepithelial corneal haze. The strongest correlate to spectacle-corrected visual acuity after the two procedures was the coefficient of variation of corneal power over the pupil. Nineteen patients (79.2%) preferred the LASIK procedure because of the fast, painless recovery.

CONCLUSIONS

In the current study, PRK and LASIK were found to be similarly effective, predictable, stable, and reasonably safe for the correction of myopia between -2.00 and -5.50 diopters. Laser in situ keratomileusis has the advantage of fast, painless recovery. Patients prefer LASIK.

Prospective Bilateral Study of Night Glare After Laser in situ Keratomileusis With Single Zone and Transition Zone Ablation

PURPOSE

Evaluation of night glare after excimer laser in situ keratomileusis (LASIK) using two different ablation zone diameters.

METHODS

One hundred and twenty eyes of 60 consecutive myopic patients received LASIK with the Nidek EC-5000 excimer laser. Eyes were randomized so that every patient had a single ablation zone of 5.5 mm on one eye and an ablation zone of 5.5 mm with a transition zone of 1.0 mm diameter larger on the other eye. Night glare was measured by two methods; a spot light test and a subjective questionnaire.

RESULTS

At 6 months, 54 patients (90%) were examined; results of the spot light test showed that 40 patients (74.1%) perceived more glare with the eye with the single ablation zone; the subjective questionnaire indicated that 22 patients (40.7%) had more night glare with the eye with a single ablation zone compared to the other eye. The use of the transition zone increased the required total ablation depth by 20%.

CONCLUSION

The use of a peripheral transition 1.0 mm diameter larger than the ablation zone significantly decreased night glare after LASIK with slight increase in the required central ablation depth.