Refractive Surgery, Optical Aberrations, and Visual Performance

Three-Month Clinical Outcomes to Correct Myopia or Myopic Astigmatism Using a Femtosecond Laser for Lenticule Creation With Automated Centration and Cyclotorsion Compensation

PURPOSE

To individually evaluate the clinical outcomes for right and left eyes in the first 3 months after laser-assisted lenticule extraction for myopia and myopic astigmatism with the use of the new ATOS femtosecond laser system (Smart-Sight; SCHWIND eye-tech-solutions).

METHODS

A total of 331 eyes from 168 patients (166 right eyes and 165 left eyes) consecutively treated with SmartSight lenticule extraction were retrospective analyzed after a 3-month follow-up period. Patients' mean age was 26 ± 6 years (range: 18 to 47 years) and mean preoperative spherical equivalent (SEQ) was -5.07 ± 1.92 diopters [D] (range: -1.50 to -11.25 D) with a mean astigmatism of -1.04 ± 0.85 D (range: 0.00 to -4.00 D). At 3 months of follow-up, visual acuity, SEQ and cylinder, safety index, efficacy index, corneal higher order aberrations, and intraocular pressure (IOP) were analyzed. Furthermore, refractive and visual outcomes were also analyzed for the right and left eyes individually. All lenticule extraction treatments were performed with the SmartSight treatment method of the SCHWIND ATOS femtosecond laser.

RESULTS

At 3 months after surgery, mean SEQ was -0.12 ± 0.19 D and 98% of eyes were within ±0.50 D of the SEQ. All eyes were within ±1.00 D of the SEQ. Astigmatism of 0.50 D or less was achieved in 99% of eyes. The change in Snellen lines (difference between preoperative corrected distance visual acuity and postoperative uncorrected distance visual acuity) showed a gain of one or more lines in 13% and in 85% of the eyes the same was achieved. There was a loss of one or more lines at 3 months of follow-up in 1.6%. The safety index was 1.03 and efficacy index was 1.02. No significant difference between the right and left eyes was found.

CONCLUSIONS

The 3-month follow-up data show that SmartSight treatment for correction of myopia and myopic astigmatism with the SCHWIND ATOS is a safe, efficient, and accurate procedure. It provided excellent results in terms of visual recovery, predictability, and higher order aberrations. [J Refract Surg. 2024;40(1):e30-e41.].

Patient-reported quality of vision in a prospective randomized contralateral-eye trial comparing LASIK and small-incision lenticule extraction

PURPOSE

To compare patient-reported quality of vision and visual symptoms in participants undergoing laser in situ keratomileusis (LASIK) and small-incision lenticule extraction (SMILE).

SETTING

Byers Eye Institute, Stanford University, Palo Alto, California.

DESIGN

Prospective randomized contralateral-eye clinical trial.

METHODS

Patients with myopia were randomized to receive wavefront-guided femtosecond LASIK in one eye and SMILE in the fellow eye. Participants reported the presence and severity of adverse visual symptoms through the Patient-Reported Outcomes With Laser In Situ Keratomileusis questionnaire and reported which eye had better vision at the preoperative and the postoperative 1-month, 3-month, 6-month, and 12-month visits.

RESULTS

80 eyes of 40 participants were treated. There was no difference in the presence or severity of double vision, glare, halos, or starbursts between eyes that underwent LASIK or SMILE at each visit ( P ≥ .85 for each comparison). Scaled scores for the presence of visual symptoms improved from the preoperative visit to the postoperative month 12 visit for double vision (88 vs 97, P = .03), glare (77 vs 92, P = .02), halos (68 vs 87, P < .01), and starbursts (60 vs 86, P < .01). At the postoperative month 12 visit, 17 (46%) of 37 participants preferred the vision from the eye that underwent LASIK compared with 7 (19%) of 37 who underwent SMILE. The preferred eye was correlated with uncorrected distance visual acuity ( r = 0.52, P < .01).

CONCLUSIONS

Rates of visual symptoms were similar for LASIK and SMILE, and visual symptoms improved with time. More patients preferred vision from the eye that underwent LASIK compared with SMILE.

Contralateral Eye Study of Topography Guided versus Q Value Adjusted Photorefractive Keratectomy in Myopia and Myopic Astigmatism

Purpose of the Study

To compare visual outcome, higher order aberrations (HOAs) of topography guided and Q value adjusted ablation in the fellow eye of patients undergoing photorefractive keratectomy (PRK) for the correction of myopia and myopic astigmatism.

Methods

Prospective randomized controlled interventional clinical study. The eyes of 52 patients undergoing PRK for myopia and astigmatism were included, that is, 104 eyes in total. In each patient, eyes were randomly allocated to group I: one eye received topography guided PRK using Contoura ablation software, or group II: the other eye received Q value adjusted PRK using Custom Q ablation software.

Follow-Up

Six months.

Results

At the end of 6 months, LogMAR UDVA was -0.04 ± 0.12 and -0.05 ± 0.11 (p = 0.688), while LogMAR CDVA was -0.06 ± 0.09 and -0.06 ± 0.1 in group I and group II, respectively (p = 0.972). Both groups showed a progressive oblate shift with time. This oblate shift was insignificantly less in group I by Topolyzer at 6mm, 15° and 30° at 6 months (p = 0.102, p = 0.138, p = 0.245, respectively). Topolyzer identified a significant difference between the change in coma and trefoil in both groups at 6 months (p<0.001 and p = 0.001, respectively). This was caused by the significant worsening of coma in group II (p<0.001) and the significant improvement of trefoil in group I (p = 0.007). No significant difference was found between groups in the change of ISV or ABR (p = 0.955 and 0.982, respectively). Ablation depth is a significant predictor of ΔQ at 6mm, 15° and 30° (p = 0.009, 0.039 and 0, respectively). No significant difference was found in the Strehl ratio or contrast sensitivity, although they were insignificantly better in group I (p = 0.785 and p = 0.745, respectively).

Conclusion

TG PRK and CQ PRK yielded similar results regarding UDVA, CDVA, MRSE, safety, predictability and contrast sensitivity. Both groups showed a progressive oblate shift, which was less in the TG group but the difference was statistically insignificant. TG PRK showed significantly improved trefoil HOA as compared to CQ PRK.

PRESBYOPIA MANAGEMENT WITH DIFFRACTIVE PHAKIC POSTERIOR CHAMBER IOL

OBJECTIVE

To evaluate safety and refractive efficiency after posterior chamber diffractive implantable phakic contact lens (IPCL) surgery.

MATERIAL AND METHODS

A prospective non-randomized case-series study was performed on 54 myopic eyes of 27 patients who had undergone diffractive IPCL surgery. Corneal endothelial cell density (ECD), central corneal thickness (CCT), intra-ocular pressure (IOP), vault, uncorrected distance (UDVA), spherical equivalent (SE) and defocus curve, were all evaluated twelve months after surgery. The presence of cataracts was evaluated by slit-lamp during a postoperative follow-up.

RESULTS

Mean age was 47 ± 2.62 years-old. Mean SE decreased, from -5.95 ± 2.56 D in a pre-operative stage, to -0.25 ± 0.25 D twelve months after surgery. Achieved UDVA was 20/20 in 24.1% of all cases, 20/25 in 74.1% of them, and 20/32 in all remaining cases. No eyes suffered lost lines of vision. The binocular defocus curve was 0.06 ± 0.05 logMAR for a -3.0 D of defocus; 0.11 ± 0.04 logMAR for a -1.5 D of defocus, and 0.08 ± 0.03 logMAR for a 0 D of defocus. Twelve months after surgery, mean ECD had decreased by 1.43 %, whereas mean CCT had increased by 0.06 %, without any significant statistical difference (p = 0.28 and p = 0.93 respectively). No difference (p: 0.86) in the vault was observed at 6 months vs.12 months, as well as between IOP measurements (p = 0.22). There were no non-intra or postoperative complications, and, specifically, no cataracts developed either.

CONCLUSIONS

Diffractive IPCL was implanted safely. Corneal endothelial CD, CCT, vault, and IOP remained stable twelve months after surgery. Visual acuity for distance, intermediate and near sight were achieved without spectacles.

Changes of corneal topographic measurements and higher-order aberrations after surgery for exotropia

Purpose

To analyze changes in corneal topographic measurements and higher-order aberrations (HOAs) after horizontal muscle surgery for exotropia.

Design

Retrospective, observational study.

Methods

A total of 131 eyes of 121 patients who had undergone surgery for exotropia were included. The eyes with unilateral lateral rectus (ULR) or bilateral lateral rectus (BLR) recession(s) were assigned to group A, and those with unilateral lateral rectus recession & medial rectus resection (R&R) to group B. Corneal topographic measurements and HOAs were compared between the preoperative and postoperative periods using a Placido-dual Scheimpflug analyzer (Galilei 2^TM, Ziemer, Port., Switzerland) for each group.

Results

In group A, simulated keratometery (sim K) was significantly changed until 3 months postoperatively relative to the preoperative value (postoperative 1 week, p = 0.017; 1 month, p = 0.037; and 3 months, p = 0.023, respectively). All steep K (steep sim K, steep-Kpost, and TCP-steep K) parameters also were significantly changed at postoperative 1 month (p<0.001, p = 0.015, p<0.001, respectively), but not at 3 months. Among the higher-order aberrations, spherical aberration (Z₄⁰) and secondary horizontal astigmatism (Z₄²) at postoperative 1 week had significantly changed from the preoperative values, as had horizontal quadrafoil (Z₄⁴) at 1 month. However, in group B, only vertical quadrafoil (Z₄^-4) showed statistically significant changes, at postoperative 1 and 3 months. None of the other postoperative parameters was significantly different from the corresponding preoperative value.

Conclusion

Lateral rectus recession induced changes in both corneal topographic measurements and HOAs, whereas R&R did so only in HOAs. These changes might explain some patients' complaints about poor quality of vision.

Effectiveness of Technolas torsional eye tracking system on visual outcomes after photorefractive keratectomy

Purpose

To investigate the efficacy of Technolas 217Z eye tracking system (torsional component) in corneal surface irregularity and high order aberrations (HOAs) after photorefractive keratectomy

Methods

Patients with compound myopic astigmatism among persons demanding refractive surgery in Khatam-al-Anbia Eye Hospital with the mean age of 29 years were enrolled in this double-blind randomized interventional study. The mean spherical equivalent (SE) of refractive error was −4.75 diopters(D) (range: −1.5 to −7.0), and the mean astigmatism was 3 D (range:1.0–4). Many studies were performed for each patient including: A complete eye examination, visual acuity and Monocular contrast sensitivity evaluation, and refraction. Corneal topography, Orbscan II, and wavefront aberrometry were conducted. One eye was randomly assigned for aspheric treatment and applying eye tracking system. The other eye was treated without torsional eye tracking system. The outcome measures were uncorrected visual acuity (UCVA), best corrected visual acuity (BCVA), contrast sensitivity, corneal irregularity index in 3 mm and 5 mm optical zones in Orbscan II, and mean total HOAs at the 6-monthvisit.

Results

Fifty eyes of 25 patients were enrolled. Mean UCVA was improved significantly in both the study and control groups in the 6-month post-operative follow-up. There was no significant difference between the 2 groups in UCVA and BCVA (P = 0.185 and P = 0.176, respectively). Total HOAs increased in both groups after PRK. However, they were lower in eyes treated with the eye tracking system (P < 0.001). Corneal irregularity index in 3 mm and 5 mm central zones in Orbscan II was significantly lower in the study group (P = 0.045 and P = 0.031 respectively). Contrast sensitivity function was not different in the 2 groups (P = 0.15).

Conclusion

Our study findings suggest that applying ‘Technolas 217z’ eye tracker system (Bausch and Lomb Advanced) results in a more regular anterior surface of cornea. Therefore, we recommend it for surface laser refractive surgery.

Clinical outcomes between optical path difference custom aspheric treatment and optimized prolate ablation photorefractive keratectomy in myopia exceeding 8 diopters

PURPOSE

Comparison of visual acuity, refractive, and wavefront outcomes associated with optimized prolate ablation (OPA) and optical path difference custom aspheric treatment (OPDCAT) algorithms for correction of myopia exceeding 8 diopters (D).

PATIENTS AND METHODS

Patients were randomly assigned to have photorefractive keratectomy (PRK) with OPA (n=32) or OPDCAT (n=21) algorithms. Visual acuity, manifest refraction, ocular and corneal higher-order aberrations, corneal asphericity, modulated-transfer function, and point-spread function were compared 1, 3, and 6 months postoperatively.

RESULTS

Mean manifest-refraction spherical equivalents at 6 months were -0.24 D in both groups. All patients in both groups had an uncorrected-distance visual acuity of 20/20 or better. Predictability (±1 D from intended refraction) at 6 months was 94% in the OPA group, and in the OPDCAT group it was 86%. The OPA group had less induced corneal and ocular spherical aberrations (SAs) than the OPDCAT group. Postoperative corneal asphericity change was lowest in the OPA group. Both the groups exhibited significantly-improved AreaRatio-Total value and insignificantly deteriorated AreaRatio-HO value throughout the postoperative period. The OPA group had significantly-higher AreaRatio-Total compared with OPDCAT group at both 1 and 6 months after the operation. Six months after surgery, the Strehl ratio had decreased in both groups, and there was no significant difference between the groups.

CONCLUSION

The OPA algorithms yielded higher-objective visual quality and predictability, induced less corneal and ocular SAs, and preserved more preoperative-corneal asphericity than the OPDCAT algorithms.

Accounting for the phase, spatial frequency and orientation demands of the task improves metrics based on the visual Strehl ratio

Advances in ophthalmic instrumentation have allowed high order aberrations to be measured in vivo. These measurements describe the distortions to a plane wavefront entering the eye, but not the effect they have on visual performance. One metric for predicting visual performance from a wavefront measurement uses the visual Strehl ratio, calculated in the optical transfer function (OTF) domain (VSOTF) (Thibos et al., 2004). We considered how well such a metric captures empirical measurements of the effects of defocus, coma and secondary astigmatism on letter identification and on reading. We show that predictions using the visual Strehl ratio can be significantly improved by weighting the OTF by the spatial frequency band that mediates letter identification and further improved by considering the orientation of phase and contrast changes imposed by the aberration. We additionally showed that these altered metrics compare well to a cross-correlation-based metric. We suggest a version of the visual Strehl ratio, VScombined, that incorporates primarily those phase disruptions and contrast changes that have been shown independently to affect object recognition processes. This metric compared well to VSOTF for letter identification and was the best predictor of reading performance, having a higher correlation with the data than either the VSOTF or cross-correlation-based metric.

Q-value customized ablation (custom-Q) versus wavefront optimized ablation for primary myopia and myopic astigmatism

Comparison between treatment with wavefront optimized and custom-Q laser-assisted in situ keratomileusis (LASIK) ablations. Our study included 400 eyes of 200 patients divided into two equal groups. All patients were treated for myopia and myopic astigmatism with LASIK. The first group was treated with wavefront optimized ablation and the second group with custom-Q ablation. They were examined preoperatively and postoperatively to assess asphericity, image quality, and other classical outcome parameters. The wavefront optimized ablation group comprised 200 eyes with a mean spherical equivalent refraction (SE) of -5.2188 diopters (D) (range: -1.15 to -10.50 D); the mean Q-value changed from 0.30 preoperatively to 0.06 postoperatively. The custom-Q ablation group also comprised 200 eyes with a mean SE of -5.1575 D (range: -1.35 to -9.00 D); the mean Q-value changed from 0.32 preoperatively to 0.03 postoperatively. A statistically significant difference in postoperative change in Q-values (P = 0.02) and in postoperative visual acuity (P = 0.42) between the two groups was noted. There was no difference between the two groups regarding refractive correction. There was a marginally significant change in BSCVA (best spectacle-corrected visual acuity) between the two groups, and less impairment in the corneal asphericity in the custom-Q group.

Visual and aberrometric outcomes in eyes with an angle-supported phakic intraocular lens

PURPOSE

To evaluate the postoperative changes in spherical aberration and the point-spread function (PSF) induced by the implantation of a new angle-supported phakic intraocular lens (pIOL).

SETTING

Department of Ophthalmology, St. Bassiano Hospital, Bassano del Grappa, Italy.

DESIGN

Prospective nonrandomized cohort study.

METHODS

Eyes with high myopia had implantation of an Acrysof Cachet angle-supported pIOL. Preoperative and postoperative total spherical aberration and PSF were measured using a Luneau 80 Wave+ wavefront aberrometer (high-resolution Hartmann-Shack technology) at a fixed entrance pupil scan size of 5.0 mm under pharmacologic mydriasis. Preoperative and postoperative data were analyzed and compared using the Student t test.

RESULTS

Thirty-five eyes of 18 patients were included in the statistical analysis. The Student t test for paired data (95% confidence interval) showed a statistically significant difference between preoperative data and postoperative data. The mean preoperative total spherical aberration Z(4,0) was -0.001 μm ± 0.076 (SD) preoperatively and -0.13 ± 0.11 μm postoperatively (P≤.05). The mean PSF was 0.28 ± 0.15 preoperatively and 0.34 ± 0.16 postoperatively (P<.05).

CONCLUSION

Implantation of the angle-supported pIOL in eyes with high myopia improved the quality of vision, inducing negative spherical aberration and increasing the PSF under mesopic conditions.

Optical quality after myopic photorefractive keratectomy and laser in situ keratomileusis: comparison using a double-pass system

PURPOSE

To use a double-pass system to compare the optical quality after photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) for mild to moderate myopia.

SETTING

Universitat Politècnica de Catalunya, Terrassa, Barcelona Institute of Ocular Microsurgery, Barcelona, Spain.

DESIGN

Comparative case series.

METHODS

Optical quality was assessed with a clinical double-pass system preoperatively and 3 months after PRK or LASIK. The modulation transfer function (MTF), retinal image quality parameters (MTF cutoff frequency, Strehl ratio), and intraocular scattering (objective scatter index [OSI]) were calculated.

RESULTS

This study evaluated 34 eyes that had PRK and 55 eyes that had LASIK. Both PRK and LASIK had a statistically significant impact on retinal image quality, although no significant differences between the techniques were observed. The MTF at 30 cycles per degree decreased by a factor of 1.50 in the PRK group and by a factor of 1.32 in the LASIK group. The MTF cutoff frequency decreased by a factor of 1.04 in the PRK group and by a factor of 1.06 in the LASIK group. The Strehl ratio decreased by a factor of 1.10 and 1.07, respectively. Photorefractive keratectomy and LASIK increased the objective scatter index by factors of 1.48 and 1.57, respectively. Significant correlations between the preoperative refraction and the OSI were found.

CONCLUSIONS

Retinal image quality was similarly reduced with PRK and LASIK, with no significant differences between the 2 methods. Some PRK patients had a residual refractive error that might have been related to corneal-wound healing still present 3 months postoperatively.

Wavefront analysis and Zernike polynomial decomposition for evaluation of corneal optical quality

Wavefront-guided excimer laser refractive surgery and new customized intraocular lens and contact lens designs are major clinical applications of corneal wavefront analysis. Other therapeutic applications include corneal disorders, conventional excimer laser refractive surgery, incisional techniques and cataract surgery, corneal transplantation, intrastromal corneal ring segment implantation, and crosslinking therapy. Basic data regarding corneal wavefront aberrations, such as distribution in the population and changes with aging, are essential for understanding the nature of each aberration and correcting it. Corneal aberrometry also improved our comprehension of the optical effects of the aforementioned topics while helping us assess the success of the procedures. Zernike polynomials are representations of the higher- and lower-order aberrations of the cornea, allowing a mathematical approach to their determination. Polynomials are used to model individual components of the wavefront in familiar terms. This article reviews the current knowledge of the wavefront aberrations of the human cornea and analyzes studies in the fields of anterior segment surgery and/or therapy, diseases, and optical quality in the context of this knowledge.

Three-month clinical outcomes with static and dynamic cyclotorsion correction using the SCHWIND AMARIS

PURPOSE

To evaluate intraoperative static and dynamic cyclotorsions and postoperative outcomes on astigmatism and high-order aberration in astigmatic or aberrated eyes that underwent laser in situ keratomileusis treatments with advanced cyclotorsion control using the SCHWIND AMARIS.

METHODS

Fifty eyes (30 for aberration neutral and 20 for corneal wavefront) were treated. Treatments were planned with Custom Ablation Manager and ablations were performed using the SCHWIND AMARIS. Laser in situ keratomileusis flaps were cut with an LDV femtosecond laser. Cyclotorsional movements were evaluated for static cyclotorsion component (SCC) for mean and repeatability, and for dynamic cyclotorsion component (DCC) for mean and amplitude. Clinical outcomes were evaluated for predictability, refractive outcome, safety, and wavefront aberration.

RESULTS

Registration rates were 90% for SCC and 98% for DCC. SCC was within ± 5 degrees in 64% of cases. Repeatability of SCC was ± 1 degree in 88% of cases. Mean DCC was within ± 1 degree in 98% of cases, partly compensating for SCC. DCC amplitude was within ± 2 degrees in 84% of cases. At 3-month follow-up, 88% of eyes were within ± 0.50 diopter (D) of astigmatism. Mean defocus was -0.06 ± 0.24 D and astigmatism was 0.27 ± 0.20 D. Best spectacle-corrected visual acuity improved in 42% of eyes versus 2% losing 1 line. In corneal wavefront-customized treatments, coma, trefoil, spherical aberration, and root mean square high-order magnitudes at 6-mm analysis diameter were reduced by -0.04, -0.13, -0.04, and -0.10 μm, respectively.

CONCLUSIONS

Laser in situ keratomileusis with advanced cyclotorsion compensation using the SCHWIND AMARIS is safe and predictable and yields superior visual outcomes. Refractions and high-order aberrations were reduced to subclinical values without applying additional nomograms, showing the excellent performance of the system.

Long-term results of phakic refractive lens implantation in eyes with high myopia

PURPOSE

To evaluate the long-term results of phakic refractive lens (PRL; Carl Zeiss Meditec) implantation in eyes with high myopia.

METHODS

In this retrospective, noncomparative, interventional case series, 143 myopic eyes of 82 patients were treated for high myopia with the implantation of the silicone PRL in the posterior chamber.

RESULTS

Mean follow-up was 3.8±1.7 years (range: 1 to 6 years). Six years postoperatively (n=34), a statistically significant reduction was noted in the cycloplegic spherical equivalent from -14.08±4.00 diopters (D) (range: -24.88 to -4.75 D) before PRL implantation to -0.45±0.62 D (range: -1.00 to 1.00 D) (P<.001). At 6 years, 67.6% (23 eyes) and 91.2% (31 eyes) were within ±0.50 and ±1.00 D of target refraction, respectively. Mean logMAR uncorrected and corrected distance visual acuity improved significantly (P<.001) (counting fingers preoperatively in all eyes to 0.17±0.15 [range: 0.54 to -0.06] and 0.19±0.19 [1.00 to -0.08] to 0.07±0.10 [range: 0.30 to -0.10], respectively). Complications included anterior capsule damage (3 eyes), temporary intraocular pressure increase (14 eyes), pigment dispersion (1 eye), and PRL decentration (1 eye). No eyes presented any signs of cataract up to 6 years postoperatively.

CONCLUSIONS

Long-term results show that PRL implantation is an effective and safe method for treating high myopia.

Transient increase of higher-order aberrations after lateral rectus recession in children

The changes of higher-order aberrations (HOAs) after bilateral lateral rectus muscle recession were evaluated. Forty eyes of 20 children were enrolled and their wavefront information was assessed until postoperative 3 months. Even though the root mean square (RMS) of total aberration was not changed, the RMS of HOA was transiently increased at postoperative 1 week and returned to baseline level after 1 month. Among individual Zernike coefficient, secondary astigmatism, quadrafoil, secondary coma, secondary trefoil, and pentafoil showed similar tendency with the RMS of HOA. However, coma, trefoil, and spherical aberration were not changed. Regarding recession amount, it did not correlate with any Zernike coefficient. In summary, our data imply that the HOAs are transiently increased after lateral rectus recession surgery. These results are in collusion with previous reports that strabismus surgery induced transient corneal astigmatism.

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.

Analysis of optimized profiles for 'aberration-free' refractive surgery

PURPOSE

To provide a model of an aberration-free profile and to clinically evaluate the impact of treatments based upon these theoretical profiles in the post-operative cornea.

METHODS

Aberration-free profiles were deduced from the Zernike expansion of the difference between two corneal cartesian-ovals. Compensation for the focus-shift effects of removing corneal tissue were incorporated by preserving the location of the optical focus of the anterior corneal surface. Simulation of the surgical performance of the profile was performed by means of simulated ray-tracing through a cornea described by its anterior surface and pachymetry. Clinical evaluation was retrospectively analysed in terms of visual outcomes, corneal wavefront aberration and asphericity changes at 3-month follow-up compared to the baseline on 100 eyes treated for compound myopic astigmatism.

RESULTS

The proposed 'aberration-free' profiles theoretically preserve aberrations, becoming more oblate asphericity after myopic treatments, and more prolate after hyperopic ones. In the clinical evaluation, 94% of eyes were within +/-0.50 D of emmetropia. BSCVA improved significantly (p < 0.001). Induced corneal aberrations at 6-mm were below clinically relevant levels: 0.123 +/- 0.129 microm for HO-RMS (p < 0.001), 0.065 +/- 0.128 microm for spherical aberration (p < 0.001) and 0.058 +/- 0.128 microm for coma (p < 0.01), whereas the rate of induced aberrations per achieved D of correction were -0.042, -0.031, and -0.030 microm D(-1) for HO-RMS, SphAb, and coma (all p < 0.001). Induction of positive asphericity correlated to achieved correction (p < 0.001) at a rate 3x theoretical prediction.

CONCLUSIONS

'Aberration-free' patterns for refractive surgery as defined here together with consideration of other sources of aberrations such as blending zones, eye-tracking, and corneal biomechanics yielded results comparable to those of customisation approaches. Having close-to-ideal profiles should improve clinical outcomes decreasing the need for nomograms, and diminishing induced aberrations after surgery.

Corneal multifocality with excimer laser for presbyopia correction

PURPOSE OF REVIEW

To offer a comprehensive perspective on corneal multifocality created by excimer laser surgery, with the different approaches used for the purpose and its reported outcomes.

RECENT FINDINGS

Three different approaches have been used for corneal multifocality: transitional multifocality, central presbyLasik (center for near) and peripheral presbyLasik (peripheral cornea for near). Although central presbyLasik creates a bifocal cornea, the other techniques increase the depth of focus based on the ablation of the peripheral cornea. Transitional multifocality creates intentionally an increase in coma aberration. According to the reported results, both central and peripheral presbyLasik obtain adequate spectacle independence simultaneously for far and for near. A neuroadaptation process is necessary for peripheral presbyLasik. Transitional techniques have a very limited use and very few outcomes reported.

SUMMARY

The level of scientific evidence from the literature is enough to consider that presbyLasik is a useful tool in the correction of presbyopia. However, most of the techniques are still under development in clinical investigations and further clinical data will validate the outcomes reported for the different techniques.

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.

Suitability of Filofocon A and PMMA for experimental models in excimer laser ablation refractive surgery

Experimental corneal models in plastic (in PMMA, and more recently in Filofocon A, a contact lens material) have been proposed recently to overcome some of the limitations of the theoretical approaches aiming at improving the predictability of corneal reshaping by laser ablation. These models have also been proposed for accurate assessment of corneal laser ablation patterns. In this study Filofocon A and PMMA optical and ablation properties were studied using an experimental excimer laser set-up. The effective absorption coefficient and the ablation thresholds of these materials were obtained as a function of the number of pulses. Both materials follow a Beer-Lambert law in the range of fluences used in refractive surgery, and the number of incubation pulses is less than 4 (PMMA) and 2 (Filofocon A) above 140 mJ/cm2. We found that above 40 pulses for Filofocon A and 70 pulses for PMMA, ablation threshold and effective absorption coefficients can be considered constant (F th = 90 mJ/cm2 and alpha eff = 36000 cm(-1), for Filofocon A, and F th = 67 mJ/cm2 and alpha eff = 52000 cm(-1) for PMMA, respectively). The absence of ablation artifacts (central islands), a lower number of incubation pulses, a lower pulse-number dependence of the ablation threshold, and a good correspondence between alpha eff and the absorption coefficient alpha estimated from spectroscopic measurements make Filofocon A a more appropriate material than PMMA for experimental models in refractive surgery and for calibration of clinical lasers.

Advances in technologies for laser-assisted in situ keratomileusis (LASIK) surgery

Laser-assisted in situ keratomileusis (LASIK) has become the most widely used form of refractive surgery today. The objective of this surgical technique is to modify the anterior corneal shape by ablating tissue from the stroma by means of the excimer laser after creating a hinged corneal flap. This way, we are able to change the refractive status of the patient, providing better unaided vision. Continuous improvements in the original technique have made the surgical procedure safer, more accurate and repeatable. These progressions are due to the development of novel technologies that are the responsible for new surgical instrumentation, which makes the surgical procedure easier for the surgeon, and better excimer laser ablation algorithms, which increase the optical quality of the ablation and thus the safety of the vision correction procedure. This article aims to describe the more relevant advances in LASIK that have played an important role in the spread and popularity of this technique.

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.

[Aspheric profiles for refractive laser ablation of the cornea]

Conventional ablation profiles for excimer lasers for myopic refractive correction of the cornea are of spheric geometry. Therefore, they induce additional imaging aberrations into the optical system of the eye, most notably spherical aberration. This is a major cause of the observed deterioration of visual quality after such corrections, especially under low illumination and ensuing larger pupil diameter. Therefore, aspheric ablation profiles compromizing the preexisting imaging/visual quality of the eye as little as possible are currently being developed and optimized for all laser platforms. Employed methods include customized correction profiles on the basis of individual wavefront data of the anterior corneal topography on the one hand, and correction profiles that minimize the induced spherical aberration in a "standardized" way on the other hand. We demonstrate for a particular laser platform how such profiles must be developed and optimized. Mathematical theoretical calculations appear to be an indispensable but insufficient prerequisite. The biological reaction of the corneal stroma and epithelium ("biodynamic response") can only be determined experimentally and must lead to adjustment of the calculated ablation algorithm. The results show that aspheric profiles developed on this basis can lead to significant reduction of induced spherical aberration. The obtainable effect is, however, limited by the biological response and the ensuing peripheral ablation depth and volume.

[Application of wavefront analysis in clinical and scientific settings. From irregular astigmatism to aberrations of a higher order--Part II: examples]

In recent years, wavefront analysis has ceased to be purely a laboratory application and emerged as a method used in ophthalmological diagnosis. This development has been promoted mainly by the widespread use of wavefront-guided LASIK (laser in situ keratomileusis). However, aberrometry is still not a common diagnostic technique, and for many ophthalmologists interpretation of the results is difficult. The second part of this serial paper reviews findings that are relevant for the ophthalmological community and highlights current scientific applications in this area.

Changes in higher order aberrations after wavefront-guided PRK for correction of low to moderate myopia and myopic astigmatism: two-year follow-up

PURPOSE

To assess efficacy, safety, and changes in higher order aberrations after wavefront-guided photorefractive keratectomy (PRK) in comparison with conventional PRK for low to moderate myopia with myopic astigmatism using a WASCA Workstation with the MEL 70 G-Scan excimer laser.

METHODS

A total of 126 myopic or myopic-astigmatic eyes of 112 patients were included in this retrospective study. Patients were divided into two groups: Group 1, the study group; and Group 2, the control group. Group 1 consisted of 78 eyes treated with wavefront-guided PRK. Group 2 consisted of 48 eyes treated with spherocylindrical conventional PRK.

RESULTS

Two years postoperatively, in Group 1, 5% of eyes achieved an uncorrected visual acuity (UCVA) of 0.05; 69% achieved a UCVA of 0.00; 18% of eyes experienced enhanced visual acuity of -0.18 and 8% of -0.30. In Group 2, 8% of eyes achieved a UCVA of 0.1; 25% achieved a UCVA of 0.05; and 67% achieved a UCVA of 0.00 according to logMAR calculation method. Total higher-order root-mean square increased by a factor 1.18 for Group 1 and 1.6 for Group 2. There was a significant increase of coma by a factor 1.74 in Group 2 and spherical aberration by a factor 2.09 in Group 1 and 3.56 in Group 2.

CONCLUSIONS

The data support the safety and effectiveness of the wavefront-guided PRK using a WASCA Workstation for correction of low to moderate refractive errors. This method reduced the number of higher order aberrations induced by excimer laser surgery and improved uncorrected and spectacle-corrected visual acuity when compared to conventional PRK.

Clinical Ocular Wavefront Analyzers

PURPOSE

To provide a summary of the methods used by clinical wavefront analyzers and their historical, current, and future applications.

METHODS

Review of the literature and authors' experience with the various devices.

RESULTS

A wide range of clinical wavefront aberrometers, which use different principles, are available to clinicians and researchers.

CONCLUSIONS

Applications of wavefront analyzers in vision sciences range from assessment of refractive error, refractive surgery planning, evaluation of outcomes, optimization of contact lenses and IOL designs, evaluation of pathology relating to optical performance of the eye, and evaluation of accommodation alterations.

Corneal Asphericity and Spherical Aberration

PURPOSE

To summarize the various values of asphericity in different notations and present how corneal asphericity, corneal curvature, and entrance pupil diameter influence the longitudinal spherical aberration of the anterior corneal surface.

METHODS

After the conversion factors between the different asphericity notations were described, finite ray tracing through a conic section that models the anterior cornea profile was performed. The anterior cornea was given a range of curvatures and asphericities and a range of entrance pupil diameters.

RESULTS

If the value of asphericity remains constant, longitudinal spherical aberration increases with the square of the entrance pupil diameter. If the pupil diameter remains fixed, the spherical aberration becomes a function of the value of asphericity, the refractive index, and the radius of curvature. If the refractive index, pupil diameter and asphericity are considered constant, the spherical aberration will decrease if the corneal surface flattens and increase as the cornea becomes steeper. In this way, with the same shape factor and with the same starting apical radius, longitudinal spherical aberration became a function of the surgically induced refractive change. With equal curvature, the longitudinal spherical aberration becomes negative if the surface is more prolate than perfect Cartesian oval; it will become positive if it is less prolate, spherical, or oblate.

CONCLUSIONS

A conversion chart for corneal asphericity notations with the corresponding spherical aberration and a diagram reporting values of asphericity necessary to maintain the physiological value of the corneal spherical aberration after refractive procedures may be useful tools in corneal surgery.

Burst-shot infrared digital photography to determine scotopic pupil diameter

PURPOSE

To evaluate the usefulness of infrared digital photography for determining scotopic pupil size by comparing infrared digital photography with a Colvard pupillometer (Oasis Medical).

SETTING

Department of Ophthalmology, Ajou University School of Medicine, Suwon, Korea.

METHODS

Scotopic pupil size in 50 eyes of 25 healthy individuals was measured with a Colvard pupillometer and a digital camera (DSC-F828) using infrared burst shots after 5 minutes of dark adaptation. Measurements were performed by 2 independent examiners (E1 and E2). The digital photograph images were read using the ruler function of Adobe Photoshop 7.0 by 2 independent readers (R1 and R2). Agreement and repeatability were analyzed using the comparison method described by Bland and Altman.

RESULTS

The mean scotopic pupil diameter measured using the Colvard pupillometer was 6.69 mm +/- 0.78 (SD) (E1) and 6.70 +/- 0.71 mm (E2). The mean scotopic pupil diameter measured from the digital photograph images was 6.67 +/- 0.75 mm (E1) and 6.66 +/- 0.78 mm (E2). The mean difference between E1 and E2 with both devices was small; however, the result with the infrared digital camera was marginally smaller than with the Colvard pupillometer. The limits of agreement were -0.01 +/- 0.70 mm with the Colvard pupillometer and 0.01 +/- 0.20 mm with the digital photograph image. The digital photograph image showed better agreement. The coefficient of interrater repeatability was smaller for the digital photograph image (0.39) than for the Colvard pupillometer (0.70).

CONCLUSIONS

Scotopic pupil measurement using an infrared digital camera with a burst shot had good agreement with the Colvard pupillometer and better repeatability. The infrared digital camera is less expensive, and pupil unrest can be overcome by taking serial images.

The relationship between anterior corneal aberrations and contrast sensitivity in conventional LASIK

PURPOSE

To evaluate the changes of anterior corneal aberrations before and after laser in situ keratomileusis (LASIK) and to assess the correlation between contrast sensitivity and anterior corneal aberrations.

METHODS

Right eyes of 51 patients including 6 males and 45 females undergoing conventional LASIK from September 2000 to July 2003 were enrolled. The calculation of anterior corneal aberrations before and after LASIK was obtained by analyzing the corneal topography from TMS-1 by using VOL-CT Version 6.23 software. Contrast sensitivity was measured after LASIK with an MCT 8000 under daytime and nighttime settings and with glare conditions. The differences of the Zernike coefficients and root mean square (RMS) of anterior corneal aberrations before and after LASIK were analyzed. The changes of contrast sensitivity at 1.5, 3, 6, 12, and 18 cpd were added separately for daytime and nighttime contrast sensitivity with and without glare after LASIK and were correlated with the changes of anterior corneal aberrations.

RESULTS

Vertical coma, RMS of coma-like RMS of spherical-like, RMS of trefoil-like and RMS of higher-order anterior corneal aberrations increased significantly after LASIK surgery. There were no significant correlations between the changes of anterior corneal aberrations and the changes of contrast sensitivity at daytime and nighttime, with and without glare. Contrast sensitivity at daytime and nighttime decreased at each spatial frequency after LASIK.

CONCLUSIONS

LASIK surgery induces changes of the anterior corneal aberrations. However, changes in anterior corneal aberrations did not correlate with the changes of contrast sensitivity at daytime and nighttime, with and without glare.

Q-factor customized ablation profile for the correction of myopic astigmatism

PURPOSE

To compare the results of the Q-factor customized aspheric ablation profile with the wavefront-guided customized ablation pattern for the correction of myopic astigmatism.

SETTING

Institute for Refractive and Ophthalmic Surgery, Zurich, Switzerland.

METHODS

Thirty-five patients were enrolled in a controlled study in which the nondominant eye was treated with the Q-factor customized profile (custom-Q study group) and the dominant eye was treated with wavefront-guided customized ablation (control group). Preoperative and 1-month postoperative high-contrast visual acuity, low-contrast visual acuity, and glare visual acuity, as well as aberrometry and asphericity of the cornea, were compared between the 2 groups. All eyes received laser in situ keratomileusis surgery, and the laser treatment was accomplished with the Wavelight Eye-Q 400 Hz excimer laser.

RESULTS

For corrections up to -9 diopters (D) of myopia, there were no statistically significant differences between the 2 groups regarding any visual or optical parameter except coma-like aberrations (3rd Zernike order), where the wavefront-guided group was significantly better 1 month after surgery (P = .002). For corrections up to -5 D (spherical equivalent), the Q-factor optimized treated eyes had a significantly smaller shift toward oblate cornea: DeltaQ15 = 0.25 in Q-factor customized versus DeltaQ15 = 0.38 in wavefront-guided treatment (P = .04).

CONCLUSIONS

Regarding safety and refractive efficacy, custom-Q ablation profiles were clinically equivalent to wavefront-guided profiles in corrections of myopia up to -9 D and astigmatism up to 2.5 D. Corneal asphericity was less impaired by the custom-Q treatment up to -5 D of myopia.

Traumatic cataract and other adverse events with the implantable contact lens

PURPOSE

To evaluate the surgical outcome and adverse events associated with implantation of the implantable contact lens (ICL) for the correction of high myopia or high hyperopia.

SETTING

Helsinki University Eye Hospital, Helsinki, Finland.

METHODS

In this nonrandomized prospective clinical trial, the ICL V4 was implanted in 26 eyes of 13 patients with normal enrollment criteria (younger than 45 years, a clinically clear crystalline lens) (Group 1) and the V2, V3, or V4 were implanted in 38 eyes of 22 patients with heterogeneous criteria (older than 45 years or opacities in the crystalline lens) (Group 2). The main outcome measures were lens opacity classification system (LOCS II) assessment and transparency analysis of the lens.

RESULTS

In Group 1, microdensitometric assessment showed no decrease in crystalline lens transparency and no statistically significant increase in crystalline lens density at any follow-up examination (P>.05). The incidence of anterior subcapsular (AS) opacities was 7.7%, and no eye developed clinically significant cataract during the mean follow-up of 13.2 months +/- 12.3 (SD). No myopic eye lost a line of best corrected visual acuity (BCVA); 50.0% of hyperopic eyes lost 1 line of BCVA. Sixty-eight percent of myopic eyes and 75.0% of hyperopic eyes were within +/-1.0 diopter of the predicted refraction. In Group 2, the incidence of AS opacities was 47.4% and 10 eyes (26.3%) developed clinically significant cataract during the mean follow-up of 30.9 +/- 18.0 months. The visual and refractive results were similar to those in Group 1 at 1 month, but due to progressive AS opacities in the crystalline lens, 23.4% of eyes lost BCVA lines during the follow-up. Intraoperative complications were few and insignificant.

CONCLUSIONS

Implantation of the ICL for correction of high myopia or high hyperopia appears to be a safe procedure with good visual and refractive results immediately. There was no decrease in the transparency or increase in the density of the crystalline lens with the latest generation of the ICL device in the normal group, indicating enhanced safety. Progressive lens opacification in the heterogeneous group shows there are risk factors for cataract formation; ie, type V3 ICL, preexisting lens opacities, and older patient age. Anterior subcapsular opacities are most likely the result of trauma.

Phakic refractive lens implantation in high myopic patients: one-year results

PURPOSE

To evaluate the efficacy and safety of implantation of a new posterior chamber phakic refractive lens (PRL, Ciba Vision Surgical) in highly myopic eyes.

SETTING

Department of Ophthalmology, Medical School, University of Crete, Vardinoyannion Eye Institute of Crete, Crete, Greece.

METHODS

Thirty-four myopic eyes of 19 patients were treated for high myopia with implantation of a silicone PRL in the posterior chamber. Mean patient age was 29.0 years +/- 7.9 (SD) (range 18 to 44 years). Manifest refraction in spherical equivalent (MR), uncorrected (UCVA) and best corrected (BCVA) visual acuity (decimal scale), intraocular pressure, higher-order aberrations (root-mean-square [RMS] wavefront error measured with a Shack-Hartmann wavefront sensor WASCA analyzer [Carl Zeiss, Meditec]), possible complications, and subjective symptoms were evaluated.

RESULTS

Phakic refractive lenses were successfully implanted in all eyes. Mean follow-up was 17.17 +/- 3.76 months (range 12 to 24 months). There was a statistically significant reduction in the MR (from -14.70 D +/- 2.65 D [range -20.75 D to -10.50 D] to -0.61 D +/- 0.89 D [range -2.25 D to 1.00 D]) (P<.001). Twenty-seven (79%) and 15 eyes (44%) were within +/-1.00 D and +/-0.50 D of target refraction, respectively. Mean UCVA significantly improved (from counting fingers to 0.62 +/- 0.28 (range 0.08 to 1.20) (P<.001). Mean BCVA also improved from 0.70 +/- 0.24 (range 0.10 to 1.00) to 0.85 +/- 0.24 (range 0.10 to 1.20) (P<0.001). Overall, there was a mean increase in BCVA of 1.5 +/- 1.5 lines (range loss of 2 lines to gain of 5 lines). There was no statistically significant difference in higher-order aberrations after PRL implantation (pre-PRL RMS: 0.18 microm +/- 0.08 microm [range 0.09 microm to 0.38 microm]; post-PRL RMS: 0.21 microm +/- 0.08 microm; [range 0.05 microm to 0.38 microm]) (P =.12).

CONCLUSION

The PRL showed encouraging results in treating high myopia. Additional patients and longer follow-up period are needed to detect the long-term efficacy and safety of this refractive lens.

Quality of vision following clinically successful penetrating keratoplasty

PURPOSE

To evaluate visual function following clinically successful penetrating keratoplasty (PKP).

SETTING

Department of Ophthalmology, Ege University, School of Medicine, Izmir, Turkey.

METHODS

Patient group (PG) included 9 patients (12 eyes) who had clinically successful PKP in our department. The control group (CG) included 12 people (18 eyes) who had no ocular disease other than refractive errors. Those with a visual acuity level less than 20/25 were not included in the study. Contrast sensitivity levels and light threshold values of the central retina were measured; scanning-slit corneal topography-pachymetry and aberrometric analysis were performed.

RESULTS

There were no statistical difference in terms of age (32.55 years +/- 9.25 (SD) in PG, 36.75 +/- 5.85 years in CG; P =.53), cylinder power in plus form (2.60 +/- 1.25 diopter (D) in PG, 2.79 D +/- 2.51 D in CG; P =.88), and spherical equivalent of refractive errors (-3.66 +/- 3.57 D in PG, -5.52 +/- 3.37 D in CG; P =.29) between the PG and CG. Cambridge low-contrast grating scores were 96.5 +/- 41.1 in grafted eyes and 148 +/- 27.7 in CG (P =.004). Central retinal light sensitivity was measured as 29.91 +/- 2.39 db in PG and 33.08 +/- 1.56 db in CG (P =.001). In corneal topographic analysis, mean kappa intercept was 0.69 +/- 0.37 mm in PG and 0.55 +/- 0.24 mm in CG (P =.20). Lower-order Zernike root mean squares (RMS) were 7.30 +/- 3.89 microm for PG and 8.58 +/- 3.46 microm for CG (P =.37). However, higher-order Zernike RMS were 2.15 +/- 0.78 in PG and 0.38 +/- 0.10 in CG, which is a statistically significant difference (P<.001).

CONCLUSIONS

Even though the clinically successful PKP patients have correctable amount of spherocylindrical refractive errors with spectacle lenses, they still have reduced visual quality because of the significantly high amount of higher- order aberrations when compared with naturally occurring refractive errors.

Pupil Size in Refractive Surgery Candidates

PURPOSE

To assess pupil size measurements obtained under scotopic and mesopic conditions with the Procyon pupillometer and under photopic conditions with the Humphrey videokeratographer.

METHODS

The pupil sizes of 96 candidates for refractive surgery (192 eyes) were measured with the Procyon pupillometer PS2000 SA and the Humphrey Atlas 992 corneal topographer. Anisocoria and pupillary unrest were analyzed according to gender (two groups: 51 females and 45 males), age (five groups: 20 to 30 yr, 31 to 40 yr, 41 to 50 yr, 51 to 60 yr, older than 60 yr) and level of refraction (five groups: >-6.00 D SE, -6.00 to -3.00 D SE, -3.00 to 0 D SE, 0 to +2.50 D SE, +2.50 to +5.00 D SE).

RESULTS

The median value of pupil diameter measured with the Procyon pupillometer at the scotopic (0.04 lux), mesopic-low (0.4 lux), and mesopic-high (4 lux) levels of illumination were 6.54+/-0.88 mm; 5.62+/-0.95 mm, and 4.09+/-0.76 mm, respectively. The median pupil size with the Humphrey topographer was 3.65+/-0.62 mm. Pupillary unrest was highest at the mesopic-high level of illumination, with a median value of 0.31+/-0.34 mm. Median pupil size measured with both instruments at all light levels dropped significantly after the fifth decade of life (P<.05, ANOVA).

CONCLUSIONS

The Procyon pupillometer and Humphrey videokeratographer revealed an inverse correlation between the pupil size and the age, but no relationship with gender or level of refraction. The Procyon pupillometer provides an objective method for measuring pupil size at controlled light levels with a permanent printed record.

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.

The Duet-Kelman Lens: A New Exchangeable Angle-supported Phakic Intraocular Lens

PURPOSE

We describe a new model of angle-supported phakic intraocular lens, the Duet-Kelman lens, the design of which incorporates two separate supporting parts. The haptic and the optic are separately implanted and then fixed together inside the eye. The lens allows optic or haptic exchange depending on the anatomical, refractive, and visual outcome of the patient. Results of the initial pilot study are presented.

METHODS

Three patients (three eyes) were implanted with the Duet-Kelman lens and were followed for a minimum of 6 months. Surgery was performed under topical anesthesia.

RESULTS

Surgery was feasible through a 2.5-mm incision, without complications. Refractive and visual results were stable in all eyes. Haptic exchange was done in one eye that developed pupil ovalization.

CONCLUSION

In this pilot study of three eyes, the Duet-Kelman phakic intraocular lens offered small incision size and potential exchange of the haptic or the optic.

Increase in Corneal Asphericity After Standard Laser in situ Keratomileusis for Myopia is not Inherent to the Munnerlyn Algorithm

PURPOSE

Standard refractive surgery for myopia induces a shift in corneal asphericity toward positive values, resulting in an increase of spherical aberration. Analytical studies of changes in theoretical corneal shape after application of standard algorithms have yielded controversial conclusions. This study tries to resolve this controversy and discusses causes of optical degradation after refractive surgery.

METHODS

Computationally, we subtracted from real preoperative corneas the ablation depth given by the Munnerlyn equation and the parabolic approximation of the Munnerlyn equation. We compared the predicted postoperative corneal asphericity (and corneal spherical aberration) with real postoperative corneal asphericities of the same eyes, after laser in situ keratomileusis (LASIK).

RESULTS

Corneal asphericity increased after LASIK in real eyes, with an increase proportional to the amount of correction. This increase was not predicted by the computational application of the Munnerlyn algorithm, which predicted a slight decrease of corneal asphericity. The parabolic approximation of the Munnerlyn algorithm produced an increase in corneal asphericity that correlated with the amount of correction, but was less than the clinical findings.

CONCLUSION

Potential causes for increased asphericity (radial changes in laser efficiency, epithelial healing, and biomechanical response) are discussed. These conclusions are important for the design of optimized and customized ablation algorithms, since the theoretical performance of a given ablation algorithm (ie, Munnerlyn algorithm) can differ drastically from real outcomes.