Induced optical aberrations following formation of a laser in situ keratomileusis flap

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

PURPOSE

To analyze ocular wavefront error and corneal asphericity (Q) in patients treated with aspheric profile photorefractive keratectomy (PRK) compared with patients having conventional PRK to correct myopia and myopic astigmatism and to evaluate the effect of postoperative corneal shape on visual performance.

SETTING

Eye Clinic, University G. d'Annunzio, Chieti-Pescara, Italy.

METHODS

Fifty eyes were treated with aspheric profile PRK using the MEL 80 flying-spot excimer laser, and 24 eyes were treated with standard PRK using the MEL 70 flying-spot excimer laser.

RESULTS

Postoperative wavefront error increased in both groups. Six months after surgery, there was a smaller increase in root mean square (RMS) of total higher-order aberrations and spherical aberration (59% and 106%, respectively) in the aspheric profile PRK group than in the conventional PRK group (94% and 136%, respectively) (P<.01). The aspheric profile PRK group showed more prolate corneal asphericities (mean Q of 0.15 +/- 0.26) than the conventional group (mean Q of 0.45 +/- 0.26) (P<.001), with increasing oblateness for higher attempted corrections. A higher percentage of patients with better low-contrast uncorrected visual acuity and best corrected visual acuity was observed in the aspheric PRK group than in the conventional PRK group (P<.05).

CONCLUSIONS

Aspheric profile and conventional PRK were safe and efficient for the correction of myopia and myopic astigmatism. Moreover, aspheric profile PRK induced a smaller increment of total wavefront error, was related to a smaller increase in spherical aberration, and better maintained the physiology of the corneal surface than conventional treatment.

Aberrations induced in wavefront-guided laser refractive surgery due to shifts between natural and dilated pupil center locations

PURPOSE

To determine the aberrations induced in wavefront-guided laser refractive surgery due to shifts in pupil center location from when aberrations are measured preoperatively (over a dilated pupil) to when they are corrected surgically (over a natural pupil).

SETTING

Center for Visual Science and Department of Ophthalmology, University of Rochester, Rochester, New York, USA.

METHODS

Shifts in pupil center were measured between dilated phenylephrine hydrochloride (Neo-Synephrine [2.5%]) and nonpharmacological mesopic conditions in 65 myopic eyes treated with wavefront-guided laser in situ keratomileusis (Technolas 217z, Bausch & Lomb). Each patient's preoperative and 6-month postoperative wave aberrations were measured over the dilated pupil. Aberrations theoretically induced by decentration of a wavefront-guided ablation were calculated and compared with those measured 6 months postoperatively (6.0 mm pupil).

RESULTS

The mean magnitude of pupil center shift was 0.29 mm +/- 0.141 (SD) and usually occurred in the inferonasal direction as the pupil dilated. Depending on the magnitude of shift, the fraction of the higher-order postoperative root-mean-square wavefront error that could be due theoretically to pupil center decentrations was highly variable (mean 0.26 +/- 0.20 mm). There was little correlation between the calculated and 6-month postoperative wavefronts, most likely because pupil center decentrations are only 1 of several potential sources of postoperative aberrations.

CONCLUSIONS

Measuring aberrations over a Neo-Synephrine-dilated pupil and treating them over an undilated pupil typically resulted in a shift of the wavefront-guided ablation in the superotemporal direction and an induction of higher-order aberrations. Methods referencing the aberration measurement and treatment with respect to a fixed feature on the eye will reduce the potential for inducing aberrations due to shifts in pupil center.

Étude prospective de la sensibilité au contraste et des effets visuels après LASIK

PURPOSE

To evaluate changes in visual effects (contrast sensitivity, halos, and glare) following laser in situ keratomilleusis (LASIK).

PATIENTS AND METHODS

In this prospective study, 72 eyes had LASIK to correct myopia. Contrast sensitivity was tested preoperatively, as well as 6 and 12 months postoperatively. The spatial frequencies tested were 3, 6, 12, and 18 cycles per degree (c/d). There were two groups: group 1 for myopia between -6 D (n=30) and -7.5 D and group 2 for myopia between -7.5 D and -10 D (n=25). There were 17 cases with loss of sight. For each visit, pupil diameter, halos, and glare were measured.

RESULTS

Contrast sensitivity was better in group 1 than in group 2 (p<0.05) (for spatial frequencies of 3, 12, 18, c/d). In group 1, contrast sensitivity decreased 6 months postoperatively for all spatial frequencies (p<0.05); 12 months after surgery the changes were not significant. In group 2, changes were not significant. For halos and glare, pre- and postoperative percentages were not different. There was no correlation with pupil diameter.

CONCLUSIONS

After LASIK to correct myopia, there may be a persistent decrease in contrast sensitivity. Changes are only significant at 6 months postoperatively. Patients should be informed preoperatively of this possible decrease in functional vision.

A Comparison of Higher Order Aberrations Following Implantation of Four Foldable Intraocular Lens Designs

PURPOSE

To determine the higher order aberrations following implantation of four foldable intraocular lens (IOL) designs.

METHODS

One hundred twenty-two eyes were randomly assigned to undergo implantation with one of four foldable IOL designs--Collamer (STAAR Surgical, Monrovia, Calif), plate haptic silicone (STAAR Surgical), AcrySof (Alcon, Ft Worth, Tex), or the Sensar (Advanced Medical Optics, Santa Ana, Calif). All enrolled eyes underwent wavefront assessment using the Tracey Visual Function Analyzer (Tracey Technologies, Houston, Tex).

RESULTS

Preoperatively, no significant differences were noted in higher order aberrations between the four lens groups. No significant differences were noted among the plate haptic silicone, Sensar, or AcrySof lenses at 1 week or 1 month postoperatively, or among the Collamer, plate haptic silicone, or Sensar lenses, with regard to total higher order aberrations, although differences were observed in individual aberration terms. At 1 week and 1 month postoperatively, the Collamer IOL had significantly less higher order aberrations than the AcrySof lens (P < .01). Significantly less third and fourth order aberrations, coma, trefoil, spherical aberration, and tetrafoil were observed postoperatively with the Collamer than the AcrySof IOL. There were no parameters where the AcrySof had significantly less optical aberrations than the Collamer.

CONCLUSIONS

The Collamer IOL design is associated with fewer higher order aberrations than the AcrySof lens.

Reverse Geometry Contact Lens Fitting After Corneal Refractive Surgery

PURPOSE

To describe reverse geometry rigid gas permeable (RGP) contact lens fitting in eyes with irregular surface induced by complications after myopic corneal refractive surgery.

METHODS

Reverse geometry RGP contact lenses were fit in nine eyes that underwent myopic corneal refractive surgery and experienced a reduction in best spectacle-corrected visual acuity (BSCVA) Snellen lines postoperatively.

RESULTS

Comparing the BSCVA with contact lenses, 5 (55.6%) eyes improved > or = 2 lines of BSCVA, 2 (22.2%) eyes improved 1 line, and 2 (22.2%) eyes maintained the same BSCVA as the one eye with spectacles (P < .004). No eye lost lines of BSCVA. All patients reported excellent tolerance and subjective visual quality with the contact lenses. The mean time of contact lens wear was 10.44 +/- 0.88 hours per day (95% confidence interval, 9.76 to 11.12).

CONCLUSIONS

Reverse geometry RGP contact lens fitting is effective in correcting surgically induced irregular surfaces with improved visual acuity and comfortable wear. These lenses may be the best choice in cases in which surgical retreatment is unfeasible or undesirable.

Influence of laser in situ keratomileusis and laser epithelial keratectomy on patients' reading performance

PURPOSE

To evaluate the influence of laser in situ keratomileusis (LASIK) and laser-assisted subepithelial keratectomy (LASEK) on reading performance regarding reading acuity, reading speed based on print size, maximum reading speed, and critical print size.

SETTING

Department of Ophthalmology, University of Vienna, Vienna, and Auge-und-Laser, Medicent Baden, Austria.

METHODS

Fifty-two eyes of 34 patients (26 eyes per group) were studied. Best corrected LogMAR visual acuity (Early Treatment Diabetic Retinopathy Study charts), reading acuity, and reading speed were tested monocularly before LASIK or LASEK and 3 weeks after surgery. Reading acuity (LogRAD) and reading speed were determined with the standardized Radner reading charts.

RESULTS

Preoperatively, the distance visual acuity and reading acuity were comparable between the LASIK and LASEK patients. Reading speed measurements also showed no statistical difference. Three weeks after refractive surgery, no statistically significant differences in the preoperative measures and between the 2 surgical procedures could be found in any tested parameters. The mean distance visual acuity was LogMAR -0.02 +/- 0.06 (SD) (LASIK) and LogMAR -0.05 +/- 0.07 (LASEK). The mean reading acuity was LogRAD 0.00 +/- 0.12 (97.7% of LogMAR) (LASIK) and LogRAD 0.04 +/- 0.16 (93.7% of LogMAR) (LASEK). The mean maximum reading speed was 235 +/- 35 words per minute (LASIK) and 240 +/- 37 words per minute (LASEK), and the mean critical print size was at LogRAD 0.48 +/- 0.19 (LASIK) and 0.49 +/- 0.17 (LASEK).

CONCLUSIONS

In a standardized reading test setting, no significant effects of LASIK and LASEK on individual reading performance could be evaluated. This indicates that patients can expect to retain their normal visual function after refractive surgery with these 2 procedures under full light conditions.

Flap dimensions created with the Hansatome microkeratome: correlation with Orbscan-derived anterior segment data

PURPOSE

To investigate the flap dimensions created by Hansatome microkeratome (Bausch & Lomb Surgical) and their correlation with anterior segment biometric data measured by the Orbscan II (Bausch & Lomb).

SETTING

Cerrahpasa Medical Faculty, Istanbul University, Istanbul, Turkey.

METHODS

Forty-four myopic eyes of 22 patients (mean age 29 years +/- 7 [SD]) that had laser in situ keratomileusis surgery using the Hansatome microkeratome were enrolled in the study. Intraoperative images taken from video recordings of procedures were analyzed with image analysis software to determine flap size and hinge size. White-to-white corneal diameter, corneal curvatures (K(max), K(min)), corneal thickness, and anterior chamber depth were deducted from Orbscan measurement. Correlation analyses between flap dimensions and Orbscan-derived anterior segment biometric data were done.

RESULTS

The mean corneal flap diameter was 9.56 +/- 0.28 mm in the right eye and 9.62 +/- 0.28 mm in the left eye. There was no difference in flap size between the right and left eyes (P=.43). The mean hinge size was 4.98 +/- 0.37 mm in the right eye and 5.07 +/- 0.41 mm in the left eye. There was no difference in hinge size between the right and left eyes (P=.46). There was a significant correlation between flap size and preoperative corneal thickness (P<.001, r=0.487), but there was no correlation between flap size and corneal curvature (P=.40, r=-0.12), white-to-white corneal diameter (P=.11, r=0.47), or anterior chamber depth (P=.52, r=0.09). There was also no correlation between hinge size and preoperative anterior segment biometric data.

CONCLUSION

The Hansatome microkeratome produced a flap whose diameter is close to the intended flap diameter, and preoperative corneal thickness seems to be the important factor in determining flap size.

Wavefront-guided correction of ocular aberrations: are phase plate and refractive surgery solutions equal?

Wavefront-guided laser eye surgery has been recently introduced and holds the promise of correcting not only defocus and astigmatism in patients but also higher-order aberrations. Research is just beginning on the implementation of wavefront-guided methods in optical solutions, such as phase-plate-based spectacles, as alternatives to surgery. We investigate the theoretical differences between the implementation of wavefront-guided surgical and phase plate corrections. The residual aberrations of 43 model eyes are calculated after simulated refractive surgery and also after a phase plate is placed in front of the untreated eye. In each case, the current wavefront-guided paradigm that applies a direct map of the ocular aberrations to the correction zone is used. The simulation results demonstrate that an ablation map that is a Zernike fit of a direct transform of the ocular wavefront phase error is not as efficient in correcting refractive errors of sphere, cylinder, spherical aberration, and coma as when the same Zernike coefficients are applied to a phase plate, with statistically significant improvements from 2% to 6%.

Thin flap laser in situ keratomileusis: analysis of contrast sensitivity, visual, and refractive outcomes

PURPOSE

To analyze refractive, visual, and contrast sensitivity outcomes of laser in situ keratomileusis (LASIK) performed under thin flaps (less than 100 microm), and compare them with those of conventional thicker flaps.

SETTING

Clínica Baviera, Instituto Oftalmológico Europeo, Madrid, Spain.

METHODS

This retrospective study comprised 280 consecutive eyes that had LASIK for myopia using the Moria LSK-One microkeratome and the Technolas 217C excimer laser. Efficacy, predictability, and contrast sensitivity indicators were compared between 3 groups of flap thickness: thin (<100 microm, n = 105), medium (100 to 129 microm, n = 122), and thick (>130 microm, n = 53).

RESULTS

Refractive results were excellent and comparable between the 3 groups; however, visual outcomes-measured as efficacy, postoperative evolution of uncorrected visual acuity, and contrast sensitivity-test were significantly better in the thin flap group. Efficacy results were 92.9%, 91.0%, and 81.0% in the thin, medium, and thick flap groups, respectively (P < .05), and the rate of enhancements was 0%, 2.3%, and 5.6%, respectively. With regard to contrast sensitivity, changes between preoperative and postoperative values at month 3 of follow-up, the thin flap group achieved the preoperative levels at 3 spatial frequencies (3, 6, and 18 cycles per degree), while the thicker flap groups maintained lower than preoperative levels at more than 2 spatial frequencies. When comparing contrast sensitivity values between the 3 groups, the thin flap group also obtained the best results at lower spatial frequencies.

CONCLUSIONS

Thin flap LASIK is a safe technique to correct myopic defects since it blends the advantages of surface and lamellar procedures (minimal debilitation of corneal biomechanical architecture with the rapid and comfortable visual recovery of lamellar approaches). Moreover, it achieves excellent refractive outcomes, a lower rate of enhancements, and a good visual performance with better contrast sensitivity test results.

Flap-induced and Laser-induced Ocular Aberrations in a Two-step LASIK Procedure

PURPOSE

To identify aberrations created by making a laser in situ keratomileusis (LASIK) flap and treating the refractive error with laser ablation at a later date.

METHODS

Twenty-two eyes (11 patients) underwent a two-step LASIK procedure with the Alcon LADAR-Vision laser (Alcon Laboratories, Ft Worth, Tex). In the first step, a flap was created, and 1 month later the flap was lifted and laser ablation performed. Aberrations were measured with the LADARWave wavefront measurement device preoperatively, after making the flap (1 day, 1 week, 1 month) and after laser treatment (1 week and 3 months). Two different microkeratomes were used (Moria M2 [Moria; Antony, France] and SKBM [Alcon]). With the SKBM, all flap hinges were nasal; with the Moria M2, the flap hinge was randomly selected as superior in one eye and nasal in the other.

RESULTS

A slight hyperopic shift was seen in the manifest and wavefront refractions at 1 week and 1 month after flap creation for the Moria M2, but not for the SKBM. Statistically significant change in manifest sphere with the Moria M2 showed a mean shift at 1 month of +0.50 +/- 0.08 diopters (D) whereas the SKBM showed no mean shift, but less reproducibility, +0.06 +/- 0.17 D. Higher order aberrations after flap creation were statistically significantly higher for all except coma with both microkeratomes, but with no predictable trends observed. Although higher in magnitude, post flap aberrations were less than one quarter the increase noted in post laser aberrations, except for "other terms."

CONCLUSIONS

Creating a LASIK flap induces changes in lower and higher order ocular aberrations. The change in lower order terms is microkeratome dependent. Higher order aberrations increase to a much larger degree after laser than after flap, making a two-step procedure unnecessary in conventional LASIK.

Intracorneal Hydrogel Lenses and Corneal Aberrations

PURPOSE

To investigate the optical performance of the cornea based on corneal aberrometry following intracorneal hydrogel lens implantation.

METHODS

A retrospective, nonconsecutive, observational study of the anterior corneal surface aberration profile of four hyperopic eyes previously implanted with an intracorneal hydrogel lens were studied by videokeratographic elevation maps before and 6 months after surgery.

RESULTS

Intracorneal hydrogel lenses reduced the optical performance in all four eyes by increasing the spherical aberrations by a mean factor of 1.87 and 1.95, coma aberrations by a mean factor of 2.98 and 3.01, and total higher order aberrations by a mean factor of 2.6 and 2.17 at 3.0-mm and 6.5-mm pupils, respectively (P<.005).

CONCLUSIONS

Intracorneal hydrogel lenses decreased the optical performance of the cornea by significantly increasing spherical, coma, and total higher order aberrations.

Wavefront's role in corneal refractive surgery

In the 5 years since the first wavefront-based LASIK treatment on normal eyes, the ophthalmology profession has had to confront a new language based on astronomy, optics and mathematics. Over this time wavefront technology has been used for diagnosis and treatment, and its application has made the profession define what is meant by good vision, and determine whether, with psychophysical and psychometric tests, it is possible understand how an individual perceives the world. The clinical application of wavefront technology has forced ophthalmologists and vision scientists with an engineering bias to talk to those with a biological bias, and to appreciate that if you try and change the corneal shape, its biological, anatomical and optical properties exist within a complex external eye environment. This perspective article demonstrates that wave-front analysis is a useful diagnostic tool, and that wavefront-based corneal refractive surgery is an improvement over conventional techniques. Its use by an ophthalmologist is a clinical decision specific to an individual patient.

Corneal first-surface aberration analysis of the biomechanical effects of astigmatic keratotomy and a microkeratome cut after penetrating keratoplasty

Astigmatic keratotomy (AK) was performed in a patient after penetrating keratoplasty (PKP) for keratoconus to reduce high post-PKP astigmatism. The procedure led to a significant decrease in astigmatism, but corneal higher-order aberrations (HOAs) increased. After PKP, the patient was scheduled for 2-step laser in situ keratomileusis (LASIK) to correct myopia and astigmatism. One day after the microkeratome cut, a decrease of -2.75 diopters in the spherical equivalent (SE) was noted. Although subjective manifest cylinder and corneal spherical aberrations were marginally affected, a marked decrease in coma and other HOAs could be observed. One month after the cut, the SE was unchanged. Excimer laser ablation was not performed as the patient was satisfied with the result and refused further treatment. This case shows that AK cuts can induce HOAs and a single microkeratome cut performed in corneal grafts can have strong biomechanical effects on lower-order aberrations and HOAs. If LASIK is planned after PKP, a 2-step approach is recommended to anticipate biomechanical effects and avoid overcorrection or undercorrection.

Topographic and biomechanical differences between hyperopic and myopic laser in situ keratomileusis

PURPOSE

To evaluate the size, shape, and uniformity of the videokeratographic functional optical zone (FOZ) after laser in situ keratomileusis (LASIK) in 2 cohorts of patients with equivalent amounts of preoperative myopic or hyperopic astigmatism.

SETTING

Pepose Vision Institute, St. Louis, Missouri, USA.

METHODS

Eyes with myopic or hyperopic astigmatism (n=27 in each group) that had LASIK with the Visx Star S3 laser were retrospectively selected to match for level of preoperative refractive error. Slit-scanning videokeratography was performed preoperatively and 6 months postoperatively and analyzed using custom software. The FOZ was calculated by analyzing refractive power maps using a region-growing algorithm. Difference maps were generated from slit images and compared for interval change in corneal elevation, tangential curvature, and refractive power. The difference maps were also averaged (mean difference maps) for each target population. A Zernike decomposition of corneal first-surface elevation was performed to compare postoperative values with baseline parameters.

RESULTS

The mean postoperative refractive sphere at 6 months was -0.17 diopter (D) +/- 0.66 (SD) and +0.25 +/- 0.85 D in the myopia group and hyperopia group, respectively, and the mean postoperative astigmatism, -0.49 +/- 0.32 D and -0.65 +/- 0.52 D, respectively (P=.11). Based on the refractive power maps, the mean preoperative and postoperative myopic FOZ was 33.09 +/- 7.30 mm(2) and 30.94 +/- 5.43 mm(2), respectively, and the mean hyperopic FOZ, 33.19 +/- 7.96 mm(2) and 37.99 +/- 6.88 mm(2), respectively. After LASIK, there was an increase in magnitude of negative anterior corneal surface spherical-like Zernike values in the myopia group (P<.0001) and an increase in magnitude of positive spherical-like Zernike values in the hyperopia group. Postoperatively, significant induction of corneal surface horizontal coma was noted in hyperopic eyes (P<.0001). Hyperopic eyes, on average, had larger topographic FOZs after LASIK, but with less uniformity of curvature and power change than myopic eyes.

CONCLUSIONS

Hyperopic LASIK, which involves more transition points along the ablation diameter, produced a less uniform topographic FOZ than typical myopic treatments. Less predictable biomechanical changes from the circumferential release of tension on collagen bundles after midperipheral hyperopic ablation and greater variation in beam centration and the angle of incidence may contribute to the greater variability in corneal curvature and power in hyperopic LASIK than in myopic LASIK.

Randomized prospective clinical study comparing induced aberrations with IntraLase and Hansatome flap creation in fellow eyes

PURPOSE

To measure and compare the changes in objective wavefront aberration and subjective manifest refraction after laser in situ keratomileusis (LASIK) flap creation with a mechanical microkeratome and a femtosecond laser.

SETTING

Private practice refractive surgery center, Irvine, California, USA.

METHODS

This randomized prospective study comprised 9 patients (18 eyes) treated with a 2-step LASIK procedure: lamellar keratectomy with a Hansatome microkeratome (Bausch & Lomb) or the IntraLase femtosecond laser in fellow eyes followed by non-wavefront-guided (standard) excimer laser treatment with the Technolas 217A (Bausch & Lomb) excimer laser 10 weeks later. Fellow eyes were matched to within 0.75 diopter (D) sphere and 0.50 D cylinder. Patients were followed for 3 months after excimer laser treatment. Preoperative and post-flap creation wavefront aberrometry using a Hartmann-Shack aberrometer and manifest refraction were compared between the 2 groups. The same tests were performed 3 months after excimer laser ablation.

RESULTS

Statistically significant changes were seen in defocus wavefront aberrations after Hansatome (P=.004) and IntraLase (P=.008) flap creation. A hyperopic shift in manifest refraction was noted in the Hansatome group after the creation of the corneal flap (P=.04); no statistically significant changes in manifest refraction were seen in the IntraLase group. Statistically significant changes in total higher-order aberrations (HOAs) (trefoil and quadrafoil Zernike terms) were seen after flap creation in the Hansatome group (P=.02). No significant changes in HOAs were noted after flap creation in the IntraLase group. After the flap was relifted and standard excimer laser ablation was performed, a statistically significant increase in coma occurred in the Hansatome group (P=.008). Standard refractive outcomes in the 2 groups were similar.

CONCLUSIONS

The creation of the LASIK flap alone can modify the eye's optical characteristics in low-order aberrations and HOAs. A significant increase in HOAs was seen in the Hansatome group but not in the IntraLase group. This may have significant clinical implications in wavefront-guided LASIK treatments, which are based on measurements made before flap creation.

Femtosecond laser versus mechanical keratome flaps in wavefront-guided laser in situ keratomileusis

PURPOSE

To compare the outcomes of wavefront-guided laser in situ keratomileusis (LASIK) performed using the IntraLase femtosecond laser with the outcomes using the Hansatome mechanical microkeratome.

SETTING

Private clinic, Overland Park, Kansas, USA.

METHODS

In a prospective contralateral-eye study performed under institutional review board supervision, 51 consecutive patients (102 eyes) had bilateral wavefront-guided LASIK for myopia using the Alcon LADARVision laser. One eye of each patient was randomized to have the flap created with the IntraLase femtosecond laser and the other flap using a standard compression head Hansatome microkeratome. All other treatment parameters were the same.

RESULTS

The IntraLase group had significantly better mean uncorrected visual acuity (UCVA) at all intervals from 1 day to 3 months postoperatively. The mean spheroequivalent at 3 months was more myopic with the Hansatome (-0.34 diopter [D] +/- 0.28 [SD]) than with the IntraLase (-0.19 +/- 0.24 D) (P<.01). The mean residual astigmatism at 3 months was also significantly higher in the Hansatome group than in the IntraLase group (0.32 +/- 0.25 D and 0.17 +/- 0.20 D, respectively) (P<.01). The differences in UCVA persisted after spheroequivalent outcomes were controlled for but equilibrated when the analysis was modified to control for manifest postoperative astigmatism. Aberrometry showed significantly higher astigmatism and trefoil in the Hansatome group. Recovery of corneal sensation and epithelial integrity was similar between groups.

CONCLUSIONS

The statistically better UCVA and manifest refractive outcomes after LASIK with the IntraLase femtosecond laser may be the result of differences in postoperative astigmatism and trefoil. These findings are consistent with previous findings of better astigmatic outcomes with the IntraLase laser and may have clinical significance for wavefront-guided treatments.

Wavefront-guided LASIK with the Zyoptix 3.1 system for the correction of myopia and compound myopic astigmatism with 1-year follow-up

OBJECTIVE

To assess safety, efficacy, predictability, stability, and change in aberrations after wavefront-guided LASIK for myopia and myopic astigmatism.

DESIGN

Prospective, nonrandomized, self-controlled trial.

PARTICIPANTS

Wavefront-guided LASIK was performed in 97 eyes in a 1-year trial. Treated eyes had a mean subjective manifest spherical equivalent (SE) of -5.22+/-2.07 diopters (D), with a range of -0.25 to -9.00 D of myopia and 0 to -3.25 D of astigmatism.

INTERVENTION

After a microkeratome cut, a wavefront-based excimer ablation (Zyoptix 3.1) was performed. The full treatment to achieve emmetropia of an early nomogram provided by the system manufacturer was used in all procedures.

MAIN OUTCOME MEASURES

Safety, efficacy, predictability, and stability were evaluated at 1, 3, and 12 months postoperatively. Wavefront changes of higher order aberrations (HOAs) at 1 year were determined for pupil sizes of 3.5 and 6 mm.

RESULTS

At 1 year postoperatively, uncorrected visual acuity (VA) was 20/20 or better in 83% of the eyes, and 20/40 or better in 98%. The mean subjective manifest SE at 1 year was -0.25+/-0.43 D; it was within 0.50 D in 77% and within 1.0 D in 95%. No eye lost > or =2 lines of best spectacle-corrected VA (BSCVA) at 1 year postoperatively; 40 eyes gained 1 line of BSCVA, and 5 eyes gained 2 lines. The total HOA root mean square (RMS) increased on average by a factor of 1.23+/-0.57 with a 3.5-mm pupil; for the 6 mm pupil, the increase factor was 1.52+/-0.36. No change or reduction in the total HOA RMS was observed in 45.5% of the eyes for a 3.5-mm pupil and in 20.6% for a 6-mm pupil. There was a significant increase of primary spherical aberration (Z 4,0) by a factor of 4.11+/-10.17 for 3.5-mm pupils and 4.31+/-6.76 for 6-mm pupils.

CONCLUSIONS

Wavefront-guided LASIK using Zyoptix 3.1 is an effective and safe procedure for the treatment of myopia and myopic astigmatism. Although in close to half of the eyes HOAs could be reduced, there was still undercorrection and induction of HOAs with the algorithm employed.

Aberrationen h�herer Ordnung nach Implantation einer irisgest�tzten Vorderkammerlinse (Ophtec Artisan�) in das phake Auge

BACKGROUND

The purpose of the present study is to demonstrate the change of higher order wavefront aberrations (HOA) after implantation of an iris claw pIOL.

METHODS

Thirteen eyes of seven patients were examined preoperatively and 1 month after implantation of an Artisan lens. The mean preoperative spherical equivalent was -10.69+/-1.92 D (-7.63 to -14.88 D). The diameter of the IOL optic was 6 mm and the lens was inserted though a tunnel incision at 12 o'clock. The root mean square (RMS) wavefront error was computed for all aberrations of the third to fifth order for pupil diameters of 3.5 and 6 mm.

RESULTS

On average, HOA RMS changed for a 3.5 mm pupil by 0.037+/-0.089 microm (6 mm pupil: 0.405+/-0.245 microm). Third-order aberrations changed by 0.031+/-0.098 microm (0.320+/-0.269 microm). For both pupil diameters, a notable increase of Z 3,-3 of 0.117+/-0.085 microm (0.596+/-0.350 microm) could be observed depending on the distance between the limbus and incision. Fourth-order aberrations changed on average by 0.018+/-0.037 microm (0.280+/-0.143 microm), namely Z 4,0 increased by 0.025+/-0.034 microm (0.296+/-0.164 microm).

CONCLUSION

After implantation of the Artisan lens HOA increased slightly. Particularly induction of Z 3,-3 and Z 4,0 contribute to the increase of HOA. The induction of trefoil ( Z 3,-3) is a result of the incision, whereas the increase of spherical aberration is due to the implant.

[Current state of wavefront guided corneal surgery to correct refraction disorders]

The present review describes the current status of wavefront-guided corneal surgery and up-to-date results. Wavefront-guided LASIK procedures performed to date achieved uncorrected vision of i.o or better in a larger number of patients than with conventional LASIK surgery, but the "eagle eye" has remained the exception. In part of the patients reductions of higher order aberrations could be obtained, but in the majority of ca-ses an increase was observed. This increase was however less than with conventional LASIK surgery. Correction of higher order aberrations has not yet been perfected since the predictability of corrections appears to be deserving of improvement on the one hand and aberrations are still induced by the technique on the other hand.

Laser in situ Keratomileusis for High Myopia Using a Small Ablation Zone and Large Aspheric Transition Zone

PURPOSE

To evaluate the efficacy and predictability of laser in situ keratomileusis (LASIK) using the Nidek NAVEX system with a small ablation (optical, OZ) zone and a large aspheric transition zone (OATz).

METHODS

We report a prospective nonrandomized study of LASIK for high myopia using a small ablation in 23 eyes of 18 patients. The optical zone was between 3 and 3.8 mm and transition zone (TZ) was between 7 and 7.8 mm. Preoperative examination included best-spectacle corrected visual acuity (BSCVA), refraction, and corneal topography. All eyes were measured by the Nidek OPD-Scan and data were imported to FinalFit software. Aspheric profile (OATz) numbers 5 to 7 were used. BSCVA, uncorrected spectacle visual acuity (UCVA), refraction, and subjective evaluation of glare and night vision by questionnaire were recorded after surgery.

RESULTS

At baseline, mean spherical equivalent refraction was -7.03 +/- 2.39 D (range -5.50 to -15.50 D). Postoperative UCVA was better than 20/25 in 95.65% of eyes 3 months after LASIK. Postoperative refraction was within +/- 0.50 D of emmetropia in 91.3% of eyes and within +/- 1.00 D in all eyes. No eye lost lines of BSCVA; 52.17% of eyes gained 1 line and 13.04% of eyes gained 2 lines. No patient reported significant glare or night vision problems on subjective questionnaire.

CONCLUSION

LASIK with a small ablation (optical) zone and high aspheric transition zone using the Nidek NAVEX system was effective, predictable, and relatively safe for correction of high myopia.

The effect of corneal flap on optical aberrations

PURPOSE

To evaluate the changes in ocular aberrations induced by corneal flap creation.

DESIGN

Prospective interventional nonrandomized clinical trial.

METHODS

This study included 15 patients who were scheduled for laser in situ keratomileusis. A nasal hinge flap was created, using the Nidek MK-2000 microkeratome and then replaced without performing laser ablation. The ocular aberrations were measured before and after flap creation using the Nidek Optical Path Difference Scanning System ARK-10000.

RESULTS

The root mean square wavefront errors of the higher-order optical aberrations (third-, fourth-, fifth-, and sixth-order aberrations) were not significantly altered at 1 week postsurgery compared with the preoperative values (P >.35).

CONCLUSIONS

Creating a corneal flap with the Nidek MK-2000 microkeratome did not induce changes in higher-order optical aberrations as measured with the Nidek Optical Path Difference Scanning System ARK-10000 during the early postoperative period.

Update on laser subepithelial keratectomy (LASEK)

PURPOSE OF REVIEW

This study reviews current concepts in laser subepithelial keratectomy (LASEK), variations in LASEK techniques, the role of pharmacology in LASEK, and optimizing outcomes in LASEK.

RECENT FINDINGS

Recent studies continue to support the use of LASEK over that of LASIK in the correction of refractive error. In addition, the advent of pharmacological/biologic intervention, improved algorithms, and wavefront technology have expanded the armamentarium available to ophthalmologists in the maximization of LASEK outcomes.

SUMMARY

LASEK offers an excellent profile in terms of both final outcome (uncorrected visual acuity) and safety (best corrected visual acuity). Untoward effects of LASEK are readily prevented/treated with a variety of agents. Postoperative pain can be ameliorated using topical and oral analgesia. Infection can be most effectively addressed with the fourth generation of fluoroquinolones. Haze may be treated or prevented using numerous remedies namely autologous serum, steroids, ascorbic acid, mitomycin-c, and NSAIDS. Wavefront combined with LASEK rather than with LASIK may offer the best refractive outcome.

Wavefront-optimized ablation profiles

PURPOSE

To describe a method for calculating wavefront-optimized ablation profiles to precompensate for the spherical aberration and higher-order astigmatism induced by myopic, hyperopic, and astigmatic corneal laser corrections.

SETTING

IROC-Institut für Refraktive und Ophthalmo-Chirurgie, and Institute for Biomedical Engineering, Swiss Federal Institute of Technology, Zürich, Switzerland.

METHODS

The basic ablation profile for myopic, hyperopic, and astigmatic correction is derived from the 2nd-order Zernike representation of wavefront aberrations. Including 4th-order spherical aberration and higher-order astigmatism in the theoretical calculation of the ablation profile allows precompensation for the expected amount of higher-order aberrations (HOAs). The shapes of wavefront-optimized ablation profiles are compared with the shapes of "classic" ablation profiles for myopic and astigmatic corrections.

RESULTS

The introduction of precompensating spherical aberration and higher-order astigmatism leads to a more aspheric ablation profile with a significant increase in ablation depth (up to 35%) in the midperiphery of the optical zone. The central ablation depth remains unchanged in the myopic correction but increases by 3% in cylinder correction.

CONCLUSIONS

Wavefront-optimized ablation profiles provide a simple method to precompensate for the expected 4th-order spherical aberration and higher-order astigmatism in the average eye. Further clinical studies must be performed to prove the theoretical results; demonstrate the reduction in HOAs; and predict safety, predictability, and stability of wavefront-optimized ablation profiles.

Variability of wavefront aberration measurements in small pupil sizes using a clinical Shack-Hartmann aberrometer

BACKGROUND

Recently, instruments for the measurement of wavefront aberration in the living human eye have been widely available for clinical applications. Despite the extensive background experience on wavefront sensing for research purposes, the information derived from such instrumentation in a clinical setting should not be considered a priori precise. We report on the variability of such an instrument at two different pupil sizes.

METHODS

A clinical aberrometer (COAS Wavefront Scienses, Ltd) based on the Shack-Hartmann principle was employed in this study. Fifty consecutive measurements were performed on each right eye of four subjects. We compared the variance of individual Zernike expansion coefficients as determined by the aberrometer with the variance of coefficients calculated using a mathematical method for scaling the expansion coefficients to reconstruct wavefront aberration for a reduced-size pupil.

RESULTS

Wavefront aberration exhibits a marked variance of the order of 0.45 microns near the edge of the pupil whereas the central part appears to be measured more consistently. Dispersion of Zernike expansion coefficients was lower when calculated by the scaling method for a pupil diameter of 3 mm as compared to the one introduced when only the central 3 mm of the Shack - Hartmann image was evaluated. Signal-to-noise ratio was lower for higher order aberrations than for low order coefficients corresponding to the sphero-cylindrical error. For each subject a number of Zernike expansion coefficients was below noise level and should not be considered trustworthy.

CONCLUSION

Wavefront aberration data used in clinical care should not be extracted from a single measurement, which represents only a static snapshot of a dynamically changing aberration pattern. This observation must be taken into account in order to prevent ambiguous conclusions in clinical practice and especially in refractive surgery.

Update on customized excimer ablations: recent developments reported in 2002

Customized corneal ablation is an exciting frontier in refractive surgery that incorporates wavefront technology to detect and correct higher order aberrations in addition to spherocylindrical refractive errors. The goal is to achieve super normal vision in terms of acuity and contrast. As the concept of wavefront customized ablations is still new, there are a number of aspects of its clinical application that need analysis and understanding. Numerous reports have appeared in the literature during the past year that address the developments, concerns, and limitations of wavefront technology and custom ablation. We have attempted to summarize and discuss the significant reports in this current review. Our focus is on the optical and physiologic limits of wavefront customized correction, including the effect of accommodation, aging, and flap creation on the aberration profile. In addition, we also present the laser technology requirements, and clinical outcomes of customized excimer ablations that are reported to date.

Separate effects of the microkeratome incision and laser ablation on the eye's wave aberration

PURPOSE

To study the optical changes induced by the microkeratome cut, the subsequent laser ablation, and the biomechanical healing response of the cornea in normal laser in situ keratomileusis (LASIK) eyes.

DESIGN

Prospective randomized clinical trial.

METHODS

A Hansatome microkeratome was used to cut a corneal flap in one eye (study eye) of 17 normal myopic patients and a subsequent laser ablation was performed 2 months after this initial microkeratome incision. Control eyes received conventional LASIK treatments at the latter time point. The wave aberration of both the study and contralateral control eyes were measured over a 6-mm pupil with a Shack-Hartmann wavefront sensor for all preoperative, postflap cut, and postablation visits.

RESULTS

The eye's higher order aberrations had a small, but significant increase (P =.03) of approximately 30% 2 months after cutting a flap. No systematic changes were observed in nearly all Zernike coefficients from their preoperative levels at 2 months postflap cut. A significant difference between the study and control eyes was observed for one trefoil mode, Z(3)(3) (P =.04).

CONCLUSIONS

There was a wide variation in the response of individual Zernike modes across patients after cutting a flap. The majority of spherical aberration induced by the LASIK procedure seems to be due to the laser ablation and not the microkeratome cut. In addition, the total and higher order root mean square of wavefront errors were nearly identical for both the study and control eyes 3-months after the laser ablation, indicating that a procedure in which the incision and the ablation are separated in time to better control aberrations does not compromise the outcome of a conventional LASIK treatment.

Comparison of Conventional Versus Wavefront-guided Laser in situ Keratomileusis in the Same Patient

PURPOSE

To verify whether there is any difference in visual outcome, including higher order aberrations, after performing laser in situ keratomileusis (LASIK) with conventional ablation and wavefront-guided ablation in myopic eyes of the same patient.

METHODS

This was a prospective randomized study of 20 myopic eyes (10 patients) who had LASIK using the Nidek NAVEX excimer laser system. Wavefront-guided customized ablation was used in the first eye of the patient (study group) and the other eye of the same patient was operated with conventional ablation (control group). Mean refractive error was similar between left and right eyes of the same patient. Preoperative examination included higher order aberration by Nidek OPD-Scan. Uncorrected and best spectacle-corrected visual acuity and higher order aberrations were recorded postoperatively.

RESULTS

Preoperative and postoperative best spectacle-corrected visual acuity was better than 20/40 (100%) after LASIK in both the conventional ablation and wavefront-guided customized ablation groups. Postoperative refraction was within +/- 0.50 D of emmetropia: 90% in the conventional group and 100% in the wavefront-guided group. No statistically significant difference in postoperative higher order aberrations was found between groups.

CONCLUSION

Postoperative visual outcome with both conventional LASIK and wavefront-guided customized ablation was not significantly different. Higher order aberrations did not significantly increase postoperatively in either group.