Early Results of Nidek Customized Aspheric Transition Zones (CATz) in Laser in situ Keratomileusis

Wavefront-guided versus wavefront-optimized laser in situ keratomileusis: contralateral comparative study

PURPOSE

To compare the outcomes of wavefront-guided and wavefront-optimized treatment in fellow eyes of patients having laser in situ keratomileusis (LASIK) for myopia.

SETTING

Medical and Vision Research Foundation, Tamil Nadu, India.

METHODS

This prospective comparative study comprised 27 patients who had wavefront-guided LASIK in 1 eye and wavefront-optimized LASIK in the fellow eye. The Hansatome (Bausch & Lomb) was used to create a superior-hinged flap and the Allegretto laser (WaveLight Laser Technologie AG), for photoablation. The Allegretto wave analyzer was used to measure ocular wavefront aberrations and the Functional Acuity Contrast Test chart, to measure contrast sensitivity before and 1 month after LASIK. The refractive and visual outcomes and the changes in aberrations and contrast sensitivity were compared between the 2 treatment modalities.

RESULTS

One month postoperatively, 92% of eyes in the wavefront-guided group and 85% in the wavefront-optimized group had uncorrected visual acuity of 20/20 or better; 93% and 89%, respectively, had a postoperative spherical equivalent refraction of +/-0.50 diopter. The differences between groups were not statistically significant. Wavefront-guided LASIK induced less change in 18 of 22 higher-order Zernike terms than wavefront-optimized LASIK, with the change in positive spherical aberration the only statistically significant one (P= .01). Contrast sensitivity improved at the low and middle spatial frequencies (not statistically significant) and worsened significantly at high spatial frequencies after wavefront-guided LASIK; there was a statistically significant worsening at all spatial frequencies after wavefront-optimized LASIK.

CONCLUSION

Although both wavefront-guided and wavefront-optimized LASIK gave excellent refractive correction results, the former induced less higher-order aberrations and was associated with better contrast sensitivity.

Corneal wavefront-guided retreatments for significant night vision symptoms after myopic laser refractive surgery

PURPOSE

To evaluate the results of corneal wavefront (WF)-guided enhancements in patients with night vision symptoms and significantly high positive spherical aberration (SA) after myopic laser refractive surgery.

DESIGN

Noncomparative, interventional case series.

METHODS

Twenty-eight eyes of 20 patients with significant night vision symptoms and positive corneal SA (Z(4)(0)) higher than 0.5 microm after myopic laser refractive surgery were included in the study at Vissum-Instituto Oftalmologico de Alicante, Spain. Enhancement surgery was planned to remove residual refractive error and corneal SA (Z(4)(0)) in all cases. All patients underwent corneal WF-guided excimer laser retreatments using the ESIRIS/SCHWIND excimer laser system (Schwind Eye Tech Solutions, Kleinostham, Germany). The main outcome measures were visual symptoms, change in corneal SA (Z(4)(0)), and corneal asphericity (Q-value).

RESULTS

Subjective reports of night vision symptoms were improved in all patients. Mean corneal SA (Z(4)(0)) decreased from 0.75 +/- 0.19 microm before surgery to 0.43 +/- 0.42 microm after surgery (P < .001). Mean asphericity in the 4.5-mm zone significantly decreased from 1.02 +/- 1.07 before surgery to 0.52 +/- 0.88 after surgery (P = .008), and the mean asphericity in 8 mm did not change significantly (P = .362). The mean spherical equivalent significantly shifted to hyperopia from -0.22 +/- 1.14 diopters (D) before surgery to 0.33 +/- 0.54 D after surgery (P = .025).

CONCLUSIONS

Cornea wavefront-guided retreatment was effective in improving subjective night vision symptoms, reducing corneal SA, and decreasing asphericity in eyes that underwent myopic laser refractive surgery.

Topography-guided Ablation for Treatment of Patients With Irregular Astigmatism

PURPOSE

To evaluate the customized aspheric treatment zone (CATz) topography-guided ablation for the correction of irregular astigmatism induced by initial corneal refractive surgery or corneal injury.

METHODS

CATz ablation was performed on 32 eyes of 28 patients. Each procedure was performed by photorefractive keratectomy (PRK) or LASIK using a NIDEK EC-5000 excimer laser. The eyes had decentered ablations, small optical zones, decreased best spectacle-corrected visual acuity (BSCVA), and asymmetrical astigmatism. Subjective symptoms, uncorrected visual acuity (UCVA), BSCVA, refraction, corneal topography, and higher order aberrations were measured. Mean follow-up was 161.9 +/- 129.9 days (range: 90 to 492 days).

RESULTS

Data obtained at final postoperative follow-up show that UCVA and BSCVA increased by > or = 2 lines after CATz ablation in 17 and 11 eyes and decreased in 4 and 2 eyes, respectively. Higher order aberrations were decreased in 16 eyes and increased in 1 eye. Topographical maps were improved with decreased surface regularity index (20 eyes) and surface asymmetry index (22 eyes). Seven eyes required further enhancement for residual refractive errors. Thirteen patients (15 eyes) claimed they were satisfied with the outcome, 6 patients (7 eyes) stated that the outcome was lower than expected, and 4 patients (4 eyes) stated they were dissatisfied.

CONCLUSIONS

CATz topographic ablation effectively improves the quality of vision and symptoms in the majority of patients with irregular corneal astigmatism from previous excimer laser refractive surgery. However, residual or induced refractive errors may need to be corrected with a second operation after CATz.

In-vitro- und In-vivo-Untersuchungen zur Presbyopiebehandlung mit Femtosekundenlasern

BACKGROUND

Ultrashort (femtosecond) laser pulses can generate precise cuts in biological tissue without damaging the surface. The application of femtosecond laser technology at the lens was evaluated with respect to a possible treatment of presbyopia.

MATERIALS AND METHODS

Femtosecond laser lentotomy was performed on 150 pig lenses in vitro. Cutting geometry and laser settings were optimized to generate smooth cuts with a minimum of produced gas bubbles. Four rabbit lenses were treated afterwards in vivo and were controlled for 3 months post-treatment. The lenses were then extracted and evaluated.

RESULTS

With suitable laser settings, light scattering due to residual gas bubbles could be almost completely avoided in pig lenses. A pulse energy of less than 1.2 microJ and a cutting geometry with spot separations of more than 5 microm are important. The rabbit lenses stayed macroscopically clear for 3 months in vivo. Only the cell structures directly adjacent to the laser focus were cut; structures 5-10 microm away appeared to be intact. No cataract formation occurred during this time.

CONCLUSION

Femtosecond laser application allows precise and smooth cuts inside pig and rabbit lenses without damage to adjacent tissue.

Zyoptix wavefront-guided versus standard photorefractive keratectomy (PRK) in low and moderate myopia: randomized controlled 6-month study

PURPOSE

To evaluate the refractive and aberrometric outcome of wavefront-guided photorefractive keratectomy (PRK) compared to standard PRK in myopic patients.

METHODS

Fifty-six eyes of 56 patients were included in the study and were randomly divided into two groups. The study group consisted of 28 eyes with a mean spherical equivalent (SE) of -2.25+/-0.76 diopters (D) (range: -1.5 to -3.5 D) treated with wavefront-guided PRK using the Zywave ablation profile and the Bausch & Lomb Technolas 217z excimer laser (Zyoptix system) and the control group included 28 eyes with a SE of -2.35+/-1.01 D (range: -1.5 to -3.5 D) treated with standard PRK (PlanoScan ablation) using the same laser. A Zywave aberrometer was used to analyze and calculate the root-mean-square (RMS) of total high order aberrations (HOA) and Zernike coefficients of third and fourth order before and after (over a 6-month follow-up period) surgery in both groups. Preoperative and postoperative SE, un-corrected visual acuity (UCVA), and best-corrected visual acuity (BCVA) were evaluated in all cases.

RESULTS

There was a high correlation between achieved and intended correction. The differences between the two treatment groups were not statistically significant for UCVA, BCVA, or SE cycloplegic refraction . Postoperatively the RMS value of high order aberrations was raised in both groups. At 6-month control, on average it increased by a factor of 1.17 in the Zyoptix PRK group and 1.54 in the PlanoScan PRK group (p=0.22). In the Zyoptix group there was a decrease of coma aberration, while in the PlanoScan group this third order aberration increased. The difference between postoperative and preoperative values between the two groups was statistically significant for coma aberration (p=0.013). No statistically significant difference was observed for spherical-like aberration between the two groups. In the study group eyes with a low amount of preoperative aberrations (HOA RMS lower than the median value; <0.28 microm) showed an increase of HOA RMS while eyes with RMS higher than 0.28 microm showed a decrease (p<0.05).

CONCLUSIONS

Zyoptix wavefront-guided PRK is as safe and efficacious for the correction of myopia and myopic astigmatism as PlanoScan PRK. Moreover this technique induces a smaller increase of third order coma aberration compared to standard PRK. The use of Zyoptix wavefront-guided PRK is particularly indicated in eyes with higher preoperative RMS values.

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.

Clinical Outcomes of CATz Versus OPDCAT

PURPOSE

To compare refractive outcomes, wavefront outcomes, and corneal asphericity indices (Q values) for patients treated with wavefront-guided or topography-guided custom ablations using the NIDEK Advanced Vision Excimer Laser System (NAVEX).

METHODS

A total of 196 eyes of 98 patients underwent wavefront-guided or topography-guided LASIK. A contralateral study of 28 eyes of 14 patients who underwent customized aspheric treatment zone (CATz) ablation in one eye and optical path difference customized aspheric treatment (OPDCAT) in the fellow eye comprised one part of the study. The second part of the study was a retrospective review of myopic LASIK using CATz in 84 eyes and LASIK using OPDCAT in 84 eyes. In the CATz-treated eyes, the preoperative mean spherical equivalent refraction was -4.06+/-1.69 diopters (D). In OPDCAT-treated eyes, the preoperative mean spherical equivalent refraction was -3.67+/-2.17 D.

RESULTS

In the CATz-treated eyes, 95% of eyes achieved > or = 20/20 best spectacle-corrected visual acuity (BSCVA) with 15% gaining lines of BSCVA. In the OPDCAT-treated eyes, 94.5% of eyes achieved > or = 20/20 vision with 4.5% gaining lines of BSCVA. The difference in lines gained between CATz and OPDCAT in the retrospective component was statistically significant (P<.005). OPDCAT-treated eyes showed a statistically significant worsening in OPD root-mean-square (OPD-RMS), higher order wavefront error, and corneal asphericity (P<.005) compared to preoperative in the retrospective portion of the study. In the contralateral arm of the study, OPD-RMS value was significantly higher (P<.005) in the OPDCAT eyes than the fellow CATz-treated eyes. OPDCAT-treated eyes show a larger change in the Strehl ratio compared to the CATz-treated eyes (P<.005).

CONCLUSIONS

The refractive outcomes were excellent and showed no clinically significant difference between CATz and OPDCAT treatments. The higher induction of aberrations with the OPDCAT ablations may be due to the fact that these treatments are based on Zernike polynomials to drive the ablation.

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.

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.

Alignment in Customized Laser in situ Keratomileusis

PURPOSE

To identify fundamentals of beam alignment in customized laser in situ keratomileusis (LASIK) with a special focus on the Nidek NAVEX system.

METHODS

Analysis of Nidek specifications and recommendations for beam alignment with regard to a critical case example are presented. The potential impact of misalignment (tilt and defocus) is calculated. Cyclotorsional error evaluation in a normal LASIK population was performed by video image comparison. Potential problems of infrared-based eyetracking systems are discussed.

RESULTS

The laser beam should be aligned with reference to the line of sight (LOS) when customized segmental laser ablation is applied. Only in cases with significant offset between the LOS and the visual axis it is recommended not to use segmental ablation and to manually align the beam toward the visual axis. Eye drift (tilt) as well as defocus should be avoided since undercorrection and irregular astigmatism can result. Almost 30% of eyes in a normal LASIK population showed a torsional error of 5 degrees to 10 degrees (9% more than 10 degrees) on video-based image comparison. Eye-trackers not only are defined by take-up speed and latency, but also by their sensibility (picking the real center of the pupil) and robustness (keeping it tracked during surgery). Errors due to parallax and reflex effects can systematically influence the performance of an eyetracker.

CONCLUSION

Correct alignment is difficult to achieve but is of fundamental importance in customized LASIK. Strict standardization and further improvement in the alignment strategy is necessary to achieve more consistent results in customized LASIK.

Comparison of Cross Cylinder Ablation Using the Optimized Ablation Transition Zone and the Torsion Error Detector for Correction of Astigmatism

PURPOSE

To compare the safety and efficacy of laser in situ keratomileusis (LASIK) in correcting high myopic astigmatism using two different ablation profiles using the Nidek EC-5000 CX II laser).

METHODS

Fifteen patients (25 eyes) had LASIK for compound myopic astigmatism, using the Optimized Ablation Transition Zone (OATz) ablation profile and activated torsion error detection (TED). Results were compared with those obtained with a cross cylinder ablation profile for myopic astigmatism.

RESULTS

For eyes treated with TED, on postoperative day 7, 76% had visual acuity equal to or better than baseline best spectacle-corrected visual acuity (BSCVA) and 56% of eyes had overcorrected astigmatism. On postoperative day 20, none of the eyes had residual astigmatism more than 1.00 D and 72% eyes were within +/-0.50 D cylinder; 92% of eyes had residual astigmatism within 30 degrees of the preoperative axis and 12% remained astigmatically overcorrected at 20 days. Eighty-eight percent of eyes were either fully corrected or had mild myopic astigmatism. Comparison of results with cross cylinder ablation showed that 24% had overcorrection and 60% of patients with high astigmatism were overcorrected up to 1.75 D and developed hyperopic astigmatism in the opposite axis. Results with the cross cylinder ablation profile were good up to 2.00 D of myopic astigmatism.

CONCLUSIONS

Correction of astigmatism using the OATz profile and TED with the Nidek EC-5000 CX II laser produced good results in high as well as pure astigmatism treatments, compared to the cross cylinder ablation profile. Ablation depth was greater in OATz with TED-based corrections. Overcorrections were less with OATz with TED, and residual astigmatism was at the same baseline axis, thereby increasing patient satisfaction.

Correlation of Wavefront Data and Corneal Asphericity With Contrast Sensitivity After Laser in situ Keratomileusis for Myopia

PURPOSE

To investigate the relationship between contrast sensitivity (CS), Zernike wavefront aberrations (WFA), and asphericity after laser in situ keratomileusis (LASIK) for myopia.

METHODS

LASIK was performed using the Nidek EC-5000 excimer laser with custom aspheric transition zone (CATz) ablations. Total and high order (HO) WFA of 71 eyes (37 patients) undergoing LASIK in March 2003 were measured before and at 1 month postoperatively with the Nidek OPD-Scan aberrometer at a 4-mm pupil entrance; asphericity was measured at 6 mm (Q index). Preoperative and 1 to 3-month postoperative contrast sensitivity were evaluated with the Vector Vision CSV-1000 at 3, 6, 12, and 18 CPD; the Area Under the Log Contrast Sensitivity Function (AULCSF) was calculated. Uncorrected-visual acuity (UCVA) was evaluated.

RESULTS

One month after LASIK, CS decreased significantly at 6 CPD and above (P<.05), then returned to normal at 3 months (P=.33). Postoperative AULCSF correlated with patient age (P=.04) but not with total WFA (P=.13), HO WFA (P=.50), or asphericity (P=.22). Postoperative Logmar UCVA correlated with postoperative total and HO WFA (P<.05). Postoperative total WFA correlated with spherical equivalent refraction (P<.0001); HO WFA correlated with Strehl ratio (P=.004) and asphericity (P=.03). The HO WFA increase was 0.065 microm (P<.05) and did not correlate with preoperative refraction (P=.40). Increase in asphericity correlated with corneal refractive change and was predicted by the parabolic Munnerlyn equation (P<.0001).

CONCLUSIONS

After LASIK, AULCSF was not dependent on WFA, but mainly on patient age. WFA results correlated well with postoperative spherical equivalent refraction, asphericity, and Strehl ratio. These conclusions support a published hypothesis that postoperative low amount of WFA does not completely fit contrast sensitivity measurements.