Corneal Optical Aberrations Induced by Photorefractive Keratectomy

Assessment of Pupil Size and Angle Kappa in Refractive Surgery: A Population-Based Epidemiological Study in Predominantly American Caucasians

Purpose This retrospective study aims to establish normative values for pupil size, angle kappa, higher-order aberration, and astigmatism type in a largely Caucasian population in Utah, United States, utilizing the NIDEK OPD-Scan III system (Gamagori, Japan). Methods This study included 716 patients (1432 eyes) grouped based on spherical equivalence and age. Measurements were conducted under mesopic and photopic conditions. Statistical analysis involved Pearson's correlation and linear regression using the generalized estimating equation. NIDEK OPD-Scan III measured mesopic and photopic pupil size and angle kappa. The subjects were then grouped based on their spherical equivalence in diopters (D) and age in decades. The spherical equivalence groups were defined: >-6 D, -5.99 to -3 D, -2.99 to -0.25 D, -0.24 to 0.24 D, and >0.25 D (range 0.25-5.75 D). The higher-order aberration groups were based on the reason for the visit: laser-assisted in situ keratomileusis, photorefractive keratectomy, and small incision lenticule extraction as one group; cataract evaluation; and keratoconus. Astigmatism measurements were grouped into with-the-rule (WRT), against-the-rule (ATR), and oblique astigmatism, with further subgrouping into a young cohort (20-40 years) and an old cohort (>65 years).  Results Among 716 participants, 49.2% were men; the mean age was 42.1±15.5 (range 7-88 years). The average spherical equivalence for myopia eyes was -3.28±2.34 D, and 1.51±1.46 D for hyperopia eyes. The mean mesopic pupil size was 5.68 ± 1.09 mm; the photopic pupil size was 4.65±1.09 mm. Pearson's correlation coefficient for mesopic pupil size versus age was -0.551, and -0.42 for photopic pupil (p < 0.001); sphere vs mesopic pupil size was -0.200, and -0.173 for photopic pupil (p < 0.001). The regression analysis for mesopic pupil size versus age revealed a 0.39 mm decrease in average pupil size per decade increase in age, and 0.25 mm decrease per decade for photopic pupil. The regression analysis for mesopic pupil size versus sphere revealed a 0.22 mm decrease in average pupil size per 3D increase in sphere, and a 0.16 mm decrease 3 D increase in sphere for the photopic pupil. The mean mesopic angle kappa was 0.33 ± 0.15 mm; photopic angle kappa was 0.31±0.15 mm. Pearson's correlation coefficient for mesopic angle kappa vs spherical equivalence was 0.32, and 0.296 for photopic angle kappa (p <0.001 for both). Regression analysis for mesopic angle kappa vs spherical equivalence demonstrated a 0.051 mm increase in angle kappa per 3 D increase in spherical equivalence, and a 0.048 mm increase for photopic angle kappa (p < 0.001 for both). Among the higher-order aberration groups, the keratoconus group exhibited the highest levels. In terms of astigmatism type, WRT astigmatism was the most common in the young cohort, while ATR astigmatism was most prevalent in the older cohort. Conclusions The results of this study reveal significant associations between pupil size and increasing age, as well as between pupil size and increasingly positive refractive errors. These findings hold particular clinical relevance to older patients and individuals with hyperopia, as they undergo photoablative corneal refractive surgery or multifocal intraocular lens implantation. Understanding the established normative values for pupil size, angle kappa, higher-order aberration, and astigmatism type can aid clinicians in making more informed decisions and improving patient outcomes.

Comparison of Corneal Wavefront-optimized and Wavefront-guided Alcohol-assisted Photorefractive Keratectomy Using Schwind Amaris 750S Laser for Myopia

Purpose

To compare the visual outcomes and corneal aberrations between wavefront-optimized (WFO) and corneal wavefront-guided (WFG) photorefractive keratectomy (PRK) in low to moderate myopia.

Methods

Twenty-seven eyes treated with WFO and 29 eyes treated with WFG PRK using a Schwind Amaris 750S Excimer laser were included after 6 months of postoperative follow-up. Uncorrected distance visual acuity, corrected distance visual acuity, refractive errors, corneal higher-order aberrations (HOA) and corneal thickness obtained using a Scheimpflug system, and central ablation depth and volume were evaluated during the preoperative period and again at the postoperative 6-month visits.

Results

Postoperatively, uncorrected distance visual acuity, corrected distance visual acuity, manifest spherical equivalent, and refractive astigmatism were improved in both groups, and there was no statistically significant difference between the two groups. There was no significant difference in safety, efficacy, or predictability of the refractive outcome. Postoperative total corneal HOA root mean square (RMS), coma RMS, and spherical aberration were significantly increased in both groups. Among these, only spherical aberration showed a significant difference between the two groups, with greater increase in the WFO group at 6 months postoperatively. The changes in corneal HOA RMS and spherical aberration were smaller in the WFG group, and this benefit was marked in eyes with high HOA RMS (≥0.4 µm) and spherical aberration (≥0.2 µm). Even though ablation volume in the WFG group was much larger than that of the WFO group, there was no significant difference in postoperative central and peripheral corneal thickness between the two groups.

Conclusions

Both WFO and WFG PRK using a Schwind Amaris 750S laser for low to moderate myopia were safe and effective at improving visual and refractive outcomes. However, WFG PRK induced fewer spherical aberrations than WFO PRK and may be more advantageous for eyes with high HOA root mean square or spherical aberration.

A Prospective Study to Compare Visual Outcomes Between Wavefront-optimized and Topography-guided Ablation Profiles in Contralateral Eyes With Myopia

PURPOSE

To analyze refractive outcomes of wavefront-optimized (WFO) ablation and topography-guided custom ablation (TCAT) profiles using the Allegretto Wave excimer laser platform (Alcon Laboratories, Inc., Fort Worth, TX) in the treatment of myopia.

METHODS

Sixty eyes of 30 patients who underwent LASIK were included in this prospective interventional study. WFO ablation was performed in one eye (WFO group) and TCAT in the fellow eye (TCAT group). The WaveLight FS200 femtosecond laser (Alcon Laboratories, Inc.) was used to create the flap and Allegretto Wave excimer laser (Alcon Laboratories, Inc.) was used for photoablation. The Pentacam HR (Oculus Optikgeräte GmbH, Wetzlar, Germany) and Allegretto Topolyzer (Alcon Laboratories, Inc.) were used to measure the corneal aberrations. Refractive visual outcomes were also compared.

RESULTS

Accuracy, safety, and efficacy were similar in the two groups. The total root mean square (RMS) and RMS of lower order aberrations were significantly better in eyes that underwent TCAT (P < .05). There was a decrease in individual higher order aberrations in the TCAT group, with a statistically significant difference in the spherical aberrations (P = .02). The corneal asphericity (Q value) was not significantly different between the WFO (0.6 ± 0.1) and TCAT (0.51 ± 0.09) groups. The postoperative total RMS of higher order aberrations was lower in the TCAT group, but this was not statistically significant (P > .05). There was a more positive change in Q value and spherical aberrations in the WFO group, but this was not statistically significant.

CONCLUSIONS

TCAT and WFO ablation provided essentially equivalent outcomes after myopic LASIK, with induction of fewer lower order aberrations and higher order aberrations following TCAT ablation. [J Refract Surg. 2017;33(1):6-10.].

Postoperative Efficacy, Predictability, Safety, and Visual Quality of Laser Corneal Refractive Surgery: A Network Meta-analysis

PURPOSE

To compare the postoperative efficacy, predictability, safety, and visual quality of all major forms of laser corneal refractive surgeries for correcting myopia.

DESIGN

Systematic review and network meta-analysis.

METHODS

Search of MEDLINE, EMBASE, Cochrane Library, and the US trial registry was conducted up to November 2015. Randomized controlled trials (RCT) reporting in accordance with the eligibility criteria were included in this review. We performed a Bayesian random-effects network meta-analysis.

RESULTS

Forty-eight RCTs were identified. For efficacy (uncorrected visual acuity [UCVA]), there were no statistically significant differences between any pair of treatments analyzed. The SUCRA (surface under the cumulative ranking curve) ranking (from best to worst) was femtosecond-based laser in situ keratomileusis (FS-LASIK), LASIK, small-incision lenticule extraction, femtosecond lenticule extraction (FLEx), photorefractive keratectomy (PRK), laser epithelial keratomileusis (LASEK), epipolis (Epi)-LASIK, transepithelial PRK (T-PRK). For predictability (refractive spherical equivalent [SE]), a statistically significant difference was found when FS-LASIK was compared with LASIK (odds ratio [OR] 2.29, 95% credible interval [CrI] 1.20-4.14), PRK (OR 2.16, 95% CrI 1.15-4.03), LASEK (OR 2.09, 95% CrI 1.08-4.55), and Epi-LASIK (OR 2.74, 95% CrI 1.11-6.20). The SUCRA ranking (from best to worst) was FS-LASIK, T-PRK, LASEK, PRK, LASIK, Epi-LASIK. There were no statistically significant differences in the safety (best spectacle-corrected visual acuity) comparisons. For both postoperative higher-order aberrations (HOAs) and contrast sensitivity (CS), there were no statistically significant differences between any pair of treatments analyzed. The SUCRA ranking results show that some corneal surface ablation techniques (PRK and LASEK) rank highest.

CONCLUSIONS

This network meta-analysis shows that there were no statistically significant differences in either visual outcomes (efficacy and safety) or visual quality (HOAs and CS). FS-LASIK behaved better in predictability than any other type of surgeries.

Theoretical analysis for spherical aberration induction with low-order correction in refractive surgery

A theoretical foundation for the analysis of ocular aberration correction is developed. It enables a comparative study for two different refractive surgical approaches, namely, the conventional and the Q-preserved treatment modalities. A refractive surgical factor is identified that leads to a simple cubic function for the postoperative asphericity factor for the conventional treatment. A formulation is developed that paves the way for the calculation of the induction of spherical aberration for low-order aberration correction in refractive surgery. Opposite to the general belief, the Munnerlyn shape makes myopic LASIK more prolate, not oblate. A Monte Carlo simulation was conducted for 1000 eyes for these two refractive surgical modalities. It was found that, although the postoperative spherical aberration is similar for these surgical modalities, for the induction of spherical aberration from the ablation target shape, the conventional modality appears to be slightly more predictable.

Anterior corneal optical irregularity measured by higher-order aberrations induced by a broad beam excimer laser

BACKGROUND

The aim was to analyse anterior corneal optical irregularity in patients receiving photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) with a conventional broad beam laser.

METHODS

Pre- and post-operative anterior corneal aberrations including Zernike coefficients and root mean squares of higher-order aberrations were measured and derived with a Placido-ring-based corneal topographer and wavefront software, respectively, from 768 right eyes of patients receiving either PRK or LASIK for myopia with a conventional broad beam excimer laser in National Taiwan University Hospital, Taipei, Taiwan. Multiple linear regression models selected by Mallows' Cp criteria were used to evaluate predictability of surgically induced aberrations and relevant factors.

RESULTS

Mean attempted spherical equivalent correction was -7.37 ± 2.33 D (range: -16.5 to -1.95). Root mean squares of higher-order aberrations and variances of Zernike coefficients all increased significantly after surgery (p < 0.01). All post-operative higher-order aberrations increased with the amount of attempted myopic correction and secondary astigmatism increased with attempted cylindrical correction. LASIK surgery induced less coma and third-order aberrations but more fifth- and sixth-order aberrations than PRK, although squared partial correlation coefficients were low. Larger optic and transitional zones meant fewer higher-order aberrations after surgery. Younger patients tended to have more surgically induced aberrations in the 3.0 mm pupil zone.

CONCLUSIONS

Anterior corneal optical irregularity increased tremendously after refractive surgery by conventional broad beam lasers and correlated with greater attempted myopic correction, younger age and a smaller treatment zone. The effect of corneal flaps on post-operative corneal irregularity differed trivially.

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.

Validity of scaling zernike coefficients to a larger diameter for refractive surgery

PURPOSE

To investigate the validity of a Zernike rescaling algorithm to a larger wavefront diameter.

METHODS

Using 4256 preoperative wavefront examinations, the variability of inter-examination wavefront root-mean-square (RMS) was compared to the error induced due to scaling Zernike coefficients to a larger diameter. The validity of scaling Zernike coefficients was set when the error due to the scaling was the same as the variability of the inter-examination wavefronts. The inter-examination variability was calculated from eyes having at least 3 same-day, preoperative examinations over the same diameters. Error from scaling Zernike coefficients to a larger diameter was calculated by comparing the wavefront for a (scaled-up) set of Zernike coefficients to the wavefront of the average of Zernike coefficient sets at a larger diameter for the same eye. Wavefront diameters of 5, 5.5, 6, 6.5, and 7 mm were considered.

RESULTS

No significant difference was found for the variability for different pupil sizes. The error due to scaling Zernike coefficients to a larger pupil size was generally smaller than the inter-examination variability when the new diameter was 0.25 mm larger than the original diameter. The error was comparable to the inter-examination variability when the new diameter was 0.5 mm larger. The error became larger when the new diameter was >0.75 mm larger than the original diameter.

CONCLUSIONS

Rescaling Zernike coefficients from a smaller diameter to a larger one has practical applications in optical zone extension for wavefront-guided refractive surgery.

Advanced corneal surface ablation efficacy in myopia: changes in higher order aberrations

OBJECTIVE

To evaluate the change of ocular and corneal higher order aberrations (HOAs) after wavefront-guided advanced surface ablation (WF-ASA) for myopia using 4 different epithelial management techniques (AA-PRK, LASEK, Epi-PRK, and Epi-LASIK).

DESIGN

Retrospective single centre excimer database analysis.

PARTICIPANTS

Two hundred and forty eyes equally divided between the 4 WF-ASA techniques, matched for mean and range of required spherical correction.

METHODS

Ocular wavefront aberrations were measured using the wavescan aberrometer and corneal aberrations were obtained from corneal topography elevation maps and calculated by ray-tracing. All data were collected preoperatively and 3 months following treatment. The aberrations were described as Zernike polynomials, and analysis focused on total HOAs and spherical aberration (SA).

RESULTS

Three months postoperatively, there was a statistically significant surgically induced increase in total HOAs and SA both for ocular and corneal analysis (p < 0.001). There was no statistically significant difference in the induced ocular SA and HOAs between the groups, but the differences in induced corneal SA and HOAs were significant (p < 0.010). Ocular changes in SA were weakly correlated to preoperative SA (20.30, p < 0.001) but strongly correlated to applied spherical correction (20.68, p < 0.001). Surgically induced corneal SA was weakly correlated to preoperative corneal SA (20.34, p < 0.001) and applied spherical correction (20.46, p < 0.001).

CONCLUSIONS

Three months postoperatively, all procedures resulted in an increase in ocular and cornealHOAs and SA. Induced aberrations were most strongly correlated to the applied spherical power correction. Modifying the existing ablation pattern to compensate for induced HOAs might improve the outcome.

Long-term corneal wavefront aberration variations after photorefractive keratectomy for myopia and myopic astigmatism

PURPOSE

To analyze the higher-order corneal wavefront aberration during an 8-year follow-up after photorefractive keratectomy (PRK).

SETTING

IRCCS Fondazione G.B. Bietti, Rome, Italy.

DESIGN

Case series.

METHODS

Patients having PRK using the Technolas 217C excimer laser platform were divided into 3 groups according to the preoperative refraction as follows: low myopia, high myopia, and astigmatism. The preoperative and 1-, 4-, 6-, and 8-year postoperative root mean square (RMS) values of coma, spherical aberration, and total higher-order aberrations (HOAs) were calculated with 3.5 mm and 6.0 mm simulated pupils. The mean preoperative and postoperative higher-order corneal wavefront aberration maps, point-spread functions, and radial modulation transfer functions (MTFs) were represented to describe the impact of PRK on the optical quality of the anterior cornea.

RESULTS

The study enrolled 33 patients (66 eyes). Corneal spherical aberration was statistically significantly higher after PRK for simple myopia with 3.5 mm and 6.0 mm pupils (P<.05). The postoperative increase in coma was statistically significant in the high-myopia group with both pupil sizes (P<.05). Total RMS HOAs increased postoperatively with a 6.0 mm pupil in all groups (P<.05). The mean radial MTF was almost stable in all groups between preoperatively and postoperatively.

CONCLUSIONS

Higher-order corneal wavefront aberrations stabilized 1 year after PRK to treat myopia or myopic astigmatism. The effect of induced corneal HOAs tended to increase after correction of high myopia with large pupils, although without degrading the image optical quality of the cornea over the long term.

Higher-order aberration changes after Implantable Collamer Lens implantation for myopia

PURPOSE

To investigate the changes in higher-order aberrations (HOAs) induced by implantation of Implantable Collamer Lenses (STAAR Surgical) and to explain them in relation to the surgical incision and optical properties.

DESIGN

Prospective, observational case study.

METHODS

This study included 56 eyes undergoing Implantable Collamer Lens insertion for myopic correction. The corneal incision size was determined according to the amount of astigmatism. HOAs were measured before surgery and 3 months after surgery in 25 eyes having small superior incision (<3.2 mm) surgery and in 31 eyes with large superior incision (3.2 to 4.5 mm) surgery. Changes in spherical aberration, coma, trefoil, and total HOAs (third to sixth order) were analyzed. Laboratory measurements of aberration profiles of Implantable Collamer Lenses with different optical powers were performed to validate clinical measurements.

RESULTS

In the small-incision group, trefoil (Z(3)(-3)) and spherical aberration changed significantly (P=.004). In the large-incision group, in addition to trefoil and spherical aberration, total HOA changed significantly (mean change, 0.13 ± 0.17; P=.001). Significant correlations were observed among the incision size, the astigmatism induced, and the trefoil induced. Induced trefoil showed a predominant pattern at the orientation of the incision meridian. Optical measurement of aberrations of the Implantable Collamer Lenses confirmed the postoperative negative spherical aberration.

CONCLUSIONS

HOA changes after Implantable Collamer Lens insertion were increased trefoil and induced negative spherical aberration. These changes may be explained by the effect of the corneal incision and the negative spherical aberration in the Implantable Collamer Lens, respectively.

Effect of preoperative pupil size on quality of vision after wavefront-guided LASIK

PURPOSE

To evaluate the effect of preoperative pupil size on quality of vision after wavefront-guided LASIK.

DESIGN

Prospective study.

PARTICIPANTS

One hundred two eyes.

INTERVENTION

LASIK for mild to moderate myopia or astigmatism (preoperative manifest spherical equivalent, -3.99±1.42 diopters).

MAIN OUTCOME MEASURES

Questionnaires evaluating specific visual symptoms before and after surgery. Each eye was evaluated before surgery, and 1 week and 1, 3, 6, and 12 months postoperatively. Pupils were stratified according to size: small (≤5.5 mm), medium (5.6-6.4 mm), or large (≥6.5 mm). Mesopic pupil size and preoperative and postoperative variables were evaluated using an analysis of variance. A regression model was also performed to determine the correlation between mean spherical equivalent and cylinder and visual symptoms.

RESULTS

In the early postoperative period, there was no difference between the 3 groups with regard to any of the symptoms. At the final 12-month postoperative visit, patients with medium pupils experienced less glare at night than small pupils (P = 0.02), medium pupils had less halos than small or large pupils (P = 0.001 and P = 0.02, respectively), and medium pupils experienced greater satisfaction in visual improvement than small pupils (P = 0.014).

CONCLUSIONS

Twelve months after wavefront-guided LASIK surgery, large pupil size does not positively correlate with any postoperative visual symptoms.

Characterizing corneal shape after LASIK using a reference system intrinsic to the cornea

The reliability of using a reference system intrinsic to the cornea has been evaluated in order to characterize corneas of subjects after refractive surgery. Data on 90 eyes operated on by LASIK to correct myopia and astigmatism were considered. The corneal parameters (curvature radii and corneal asphericity) found with respect to this reference system are compared with the parameters provided directly by the corneal topographer. The corneal parameters referenced to the intrinsic main axes of the cornea allow a better characterization of the corneal geometry, showing lower variability and diminishing the dissimilarities between the different eyes. The use of these parameters reduces the discrepancies between the real experimental and the theoretically predicted values (21% mean relative error using intrinsic data versus 81% using the topographer data). To understand and reduce these differences is essential in refractive surgery.

Decision Assistant Wizard to standardize optimal outcomes in excimer laser refractive corneal surgery

PURPOSE

To assess a decision tree analysis system to further optimize refractive surgery outcomes.

METHODS

A 5-step decision tree, the Decision Assistant Wizard, based on previous experience with the SCHWIND AMARIS laser, was applied for selecting a customized refractive surgery treatment mode (aspheric aberration neutral, corneal wavefront-guided, or ocular wavefront-guided) to eliminate or reduce total aberration.

RESULTS

Using the Decision Assistant Wizard, 6467 LASIK treatments were performed over a 30-month period; 5262 and 112 for myopic and hyperopic astigmatism, respectively, using aspheric aberration neutral (AF) profiles, 560 using corneal wavefront-guided profiles, and 533 using ocular wavefront-guided profiles. Twenty-two (0.3%) retreatments were performed overall; 18 (0.3%) and 0 (0%) after myopic and hyperopic astigmatism, respectively, using AF, 3 (0.5%) after corneal wavefront-guided profiles, and 1 (0.2%) after ocular wavefront-guided profiles.

CONCLUSIONS

Decision Assistant Wizards may further optimize refractive surgical outcomes by providing the most appropriate ablation pattern based on an eye's anamnesis, diagnosis, and visual demands. The general principles may be applied to other laser systems; however, specifics will depend on manufacturers' specifications.

Effects of decentration of photorefractive keratectomy on the induction of higher order wavefront aberrations

PURPOSE

To evaluate the effects of ablation decentration on the induction of higher order wavefront aberrations (HOAs) in active eye-tracker-assisted myopic photorefractive keratectomy (PRK) using the VISX STAR S4 laser with ActiveTrak (Abbott Medical Optics [AMO]).

METHODS

Ninety-four myopic eyes (53 patients) were divided into three groups according to ablation decentration (group 1, ≤0.15 mm, 20 eyes; group 2, >0.15 to ≤0.30 mm, 54 eyes; and group 3, >0.30 mm, 20 eyes). The distances of ablation centers from the centers of the entrance pupils were analyzed using corneal topography. Wavefront errors were measured preoperatively and at 6 months after PRK using a VISX WaveScan aberrometer (AMO). Statistical analysis was performed to assess the influence of ablation decentration on PRK-induced HOAs.

RESULTS

The mean decentration was 0.23±0.10 mm (range: 0.04 to 0.52 7 mm). The magnitude of all HOAs was significantly increased at 6 months postoperatively (P<.05). Increases in PRK-induced HOAs including total HOA, coma, and spherical aberration were significantly different among the three groups (P<.05). Statistically significant differences were noted between pairs of data in group 1 versus group 3 for total HOA (P=.015), coma (P=.038), and spherical aberration (P=.038), and group 2 versus group 3 for coma (P=.049).

CONCLUSIONS

Ablation decentration >0.30 mm from the center of the entrance pupil was associated with greater induction of total HOA, coma, and spherical aberration after PRK, as compared with ablation decentration <0.15 mm. In addition, ablation decentration has a more significant influence on coma-inducing effects.

Wavefront-guided laser in situ keratomileusis in the treatment of high myopia by using the CustomVue wavefront platform

PURPOSE

To assess the efficacy, predictability, and safety of wavefront-guided laser in situ keratomileusis (LASIK) in the treatment of high myopia by using the Visx S4 CustomVue wavefront platform.

METHODS

A retrospective analysis of consecutive cases of eyes with high myopia (manifest refraction spherical equivalent >or= -6.00 D) that underwent non-physician-adjusted wavefront-guided LASIK by using the Visx S4 CustomVue wavefront platform. Forty-three eyes of 29 patients were included. Preoperative best spectacle-corrected visual acuity (BSCVA), manifest refraction, WaveScan refraction, postoperative uncorrected visual acuity (UCVA) and BSCVA, and manifest refraction were determined. The clinical outcomes were evaluated on the basis of standard formats and criteria. Data at 3 months postoperatively are presented.

RESULTS

Preoperatively, we found mean sphere was -6.89 +/- 1.08 D, mean cylinder was -0.97 +/- 0.75 D, and mean spherical equivalent (SE) was -7.38 +/- 1.20 D. Postoperatively, mean sphere was 0.02 +/- 0.40 D, mean cylinder was -0.40 +/- 0.40 D, and mean SE was -0.18 +/- 0.43 D. UCVA was 20/15 or better in 27.9% and cumulatively 20/20 or better in 58% of eyes. All eyes treated had at least 20/50 UCVA. Efficacy index was 0.94. Eighty-two percent of eyes were within 0.50 D and 97.6% were within 1.00 D of emmetropia at the 3-month follow-up visit. Ninety-one percent of eyes either maintained or gained 1 line of BSCVA. No eye lost >1 line of BSCVA. The safety index was 1.1.

CONCLUSIONS

The 3-month follow-up results of our study indicate that wavefront-guided LASIK by using the Visx S4 CustomVue wavefront platform is an effective, predictable, and safe treatment of high myopia.

Mesopic contrast sensitivity and ocular higher-order aberrations after overnight orthokeratology

PURPOSE

To investigate mesopic contrast sensitivity and night driving ability in eyes undergoing overnight orthokeratology, and to analyze the relationship among mesopic contrast sensitivity, ocular higher-order aberrations, and myopic correction.

DESIGN

Prospective, noncomparative, consecutive case series.

METHODS

In 44 eyes of 22 subjects (mean age +/- standard deviation [SD], 24.0 +/- 3.2 years) with orthokeratology, ocular aberrations and mesopic contrast sensitivity were determined before and three months after commencement of the procedure. Mean spherical equivalent refraction +/- SD was -2.34 +/- 0.99 diopters at baseline. Mesopic contrast sensitivity with and without glare was assessed using the Mesotest II (Oculus, Wetzlar, Germany).

RESULTS

Orthokeratology significantly reduced the log mesopic contrast sensitivity from 0.25 +/- 0.08 to 0.08 +/- 0.10 without glare (P < .0001, Wilcoxon) and from 0.21 +/- 0.11 to 0.07 +/- 0.10 with glare (P < .0001). The proportion of eyes that fulfilled the German standard recommendation level for night driving was 36%. The induced changes in log mesopic contrast sensitivity showed significant negative correlation with the changes in third-order (r = -0.490, P = .0013 without glare; r = -0.362, P = .0177 with glare; Spearman rank correlation coefficient) and fourth-order root mean square (r = -0.586, P = .0001 and r = -0.306, P = .0450, respectively). Furthermore, significant correlation was found between the amount of myopic correction and the induced changes in log mesopic contrast sensitivity (r = -0.442, P = .0038 without glare; r = -0.464, P = .0024 with glare). The induced changes in higher-order aberrations significantly correlated with the amount of myopic correction (P < .0001, Pearson correlation coefficient).

CONCLUSIONS

Mesopic contrast sensitivity after overnight orthokeratology is deteriorated significantly as ocular higher-order aberrations increase, and these changes depend on the amount of myopic correction.

[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.

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.

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.

Corneal changes and wavefront analysis after orthokeratology fitting test

PURPOSE

To evaluate corneal changes and ocular aberrations during an orthokeratology test.

DESIGN

A prospective, nonrandomized cohort study.

METHODS

Fourteen myopic patients (26 eyes) underwent an orthokeratology fitting test with the BE contact lens (Ultravision Pty, Ltd, Brisbane, Australia). Best spectacle-corrected visual acuity (BSCVA), uncorrected (Ultravision Pty, Ltd, Brisbane, Australia) visual acuity (UCVA), subjective cycloplegic refraction, biomicroscopy, corneal topography, optical pachymetry, and aberrometry were performed at baseline and one and eight nights orthokeratology. The short-term effect of orthokeratology using corneal topography, tomography, and ocular aberrations was evaluated.

RESULTS

The mean spherical equivalent changed from -2.24 +/- 0.98 diopters (D) at baseline to 0.15 +/- 0.76 D after the eight nights of lens wear (P = .001). All patients had an UCVA of 20/30, 69.2% with 20/20. Changes in central corneal pachymetry were not observed. There was a statistically significant increase in the temporal corneal thickness from night one, without any difference between nights one and eight (P > .001). A significant increase of higher-order root mean square values was observed from baseline (0.42 +/- 0.16 mum), night one (0.81 +/- 0.24 mum), and night eight (1.04 +/- 0.24 mum). Increases in coma (Z7+Z8) and spherical aberration (Z12) were observed. Positive horizontal (Z8) coma increased in right eyes, and negative horizontal (Z8) coma increased in left eyes (P < .001).

CONCLUSIONS

Myopia reduction resulting from rapid central corneal flattening and improvement of UCVA occurred after orthokeratology. Higher-order aberrations (HOAs), particularly spherical aberration and coma, increased significantly during the orthokeratology test. An increase of temporal pachymetry and differences in coma direction induced between the eyes may be related to the subclinical lens decentration temporally.

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.

Optical Quality of the Cornea After Overnight Orthokeratology

PURPOSE

To review changes in the optical quality of the cornea induced by overnight orthokeratology for myopia.

METHODS

Sixty-four eyes of 39 patients who underwent overnight orthokeratology for myopia were prospectively examined. Inclusion criteria were uncorrected visual acuity of 20/20 or better after treatment and a minimum follow-up of 3 months. To quantitatively assess changes in corneal regular and irregular astigmatism, videokeratography data were decomposed into spherical component, regular astigmatism, asymmetry, and higher-order irregularity using Fourier analysis. In addition, corneal wavefront aberrations were calculated by expanding anterior corneal height data from videokeratography into a set of orthogonal Zernike polynomials.

RESULTS

Although orthokeratology significantly reduced manifest refraction and improved uncorrected visual acuity, the asymmetry component, which is one of the features of irregular astigmatism, increased significantly from 0.35 +/- 0.22 to 0.64 +/- 0.40 D after treatment (P < 0.0001, paired t test). The increases in the asymmetry component significantly correlated with the amount of myopic correction (Pearson correlation coefficient, R = 0.40, P = 0.0009). Furthermore, the root-mean-square of third-order (coma-like) and fourth-order (spherical-like) aberrations significantly increased after orthokeratology (P < 0.0001, paired t test), and these increases showed significant positive correlations with the amount of myopic correction (Pearson correlation coefficient, R = 0.452, P = 0.0001 and R = 0.381, P = 0.0017, respectively).

CONCLUSION

Corneal irregular astigmatism and higher-order aberrations significantly increased even in clinically successful orthokeratology, and the increases correlated with the magnitude of myopic correction. A large myopic correction by orthokeratology should be avoided to not decrease corneal optical quality.

Relative Contribution of Central and Peripheral Aberrations to Overall High Order Corneal Wavefront Aberration

PURPOSE

To analyze the influence of specific combinations of corneal high order aberrations on the optical image quality of the cornea before and after photorefractive keratectomy (PRK) for low to high myopia and myopic astigmatism.

METHODS

Corneal topography was obtained for 80 eyes that underwent PRK using a scanning-spot excimer laser. The eyes were subdivided into three groups according to the preoperative refraction. The topographical data were imported into a custom software program that combined the Zernike high order terms having the same sign and angular frequency up to seventh order for 4-mm and 6-mm pupils, ie, coma and spherical aberrations, and midperipheral and peripheral high order aberrations.

RESULTS

Photorefractive keratectomy induced a significant amount of the root-mean-square (RMS) values of the combinations of midperipheral and peripheral high order aberrations over the smaller pupil size for deeper myopic ablations (P<.05). Over the larger pupil, spherical myopic ablations showed a significant increase (P<.05) of the RMS values of coma and spherical aberrations. In the astigmatism group, the combination of terms having higher angular frequency increased significantly (P<.05) after surgery both over 4-mm and 6-mm pupils.

CONCLUSIONS

After surface ablation, ablation depth and profile significantly influence the distribution and contribution of determined combinations of high order aberrations to the overall high order corneal wavefront aberration. Terms having high angular frequency were increased following large myopic correction and wide treatment zone. Quality of the whole corneal optics will be enhanced by designing future ablation profiles to compensate for peripheral high order optical aberrations.

Correlations Between Central and Peripheral Changes in Anterior Corneal Topography After Myopic LASIK and Their Implications in Postsurgical Contact Lens Fitting

PURPOSE

To investigate the changes in central and peripheral anterior corneal curvatures after myopic laser in situ keratomileusis (LASIK) and to correlate them with the manifest refractive change to discuss how such results could affect post-LASIK corneal topography profiles and midterm stability and their implications in postsurgical contact lens fitting.

METHODS

Topographic and refractive data from 18 eyes of 11 patients that had undergone myopic LASIK were collected for 6 months after surgery. Short-term and midterm topographic responses were investigated and correlated with spherical equivalent manifest refractive changes.

RESULTS

There was a strong correlation between eccentricity changes and manifest refractive change 15 days after surgery (r = 0.753, P < 0.001), with no significant changes thereafter for the following 6 months (r = 0.148, P = 0.114). A strong linear relationship was found between baseline manifest refraction and changes in corneal curvature at the center (r = 0.810, P < 0.001), 4-mm chord (r = 0.895, P < 0.001), and 6-mm chord (r = 0.696, P < 0.001). Statistically significant changes were also found after the first 15 days (P < 0.005) and showed a regression effect that affects the three zones. In this case, a weaker relationship was found between curvature regression and the final refractive change for the central location (r = 0.412, P = 0.004), 4-mm chord area (r = 0.430, P = 0.003), and 6-mm chord area (r = 0.283, P = 0.023). CONCLUSIONS.: After myopic LASIK, the anterior corneal dioptric power is expected to change, on average, approximately 77% of the attempted spherical equivalent correction at the center; 60% at the 4-mm chord region, where the stronger correlation between topographic and refractive change is found; and 30% at the 6-mm chord area. The paracentral area 4 mm from the center seems to be more likely to predict baseline corneal curvature from manifest refractive change. Some degree of regression in the midterm period is expected to occur after myopic LASIK, which shows a significant correlation with the manifest refractive change. Again, this effect is more evident and more accurately predicted at the 4-mm chord area. The results of the current study are of interest for those fitting contact lenses after myopic LASIK.

Comparison of higher-order aberrations after wavefront-guided laser in situ keratomileusis and laser-assisted subepithelial keratectomy

PURPOSE

To compare the higher-order aberrations (HOAs) in 70 eyes (38 patients) that had wavefront-guided laser in situ keratomileusis (LASIK) with those in 70 eyes (40 patients) that had wavefront-guided laser-assisted subepithelial keratectomy (LASEK) for the treatment of myopia.

SETTING

Department of Ophthalmology, Yonsei University College of Medicine, Myongdong Bal-geun sesang Eye Clinic, and Seran Eye Center, Seoul, Korea.

METHODS

In a prospective study, 140 consecutive eyes of 78 patients were treated with wavefront-guided LASIK or LASEK according to the patient's choice after each procedure had been thoroughly explained. The patients were followed for 6 months. Best corrected visual acuity (BCVA), uncorrected visual acuity (UCVA), manifest refraction, and wavefront aberrations were measured at baseline and 1, 3, and 6 months after surgery.

RESULTS

There were no significant differences in postoperative BCVA, UCVA, and manifest refraction between groups. The mean root-mean-square wavefront error of HOAs for a scotopic pupil in the wavefront-guided LASIK group was significantly smaller than that in the wavefront-guided LASEK group at 1 month. Analyzing individual Zernike coefficients, the spherical aberration and second coma were significantly smaller in the wavefront-guided LASIK group than in the wavefront-guided LASEK group at 1 month. This difference in HOAs between groups disappeared at 3 and 6 months.

CONCLUSIONS

The HOAs in the scotopic condition were not different between the wavefront-guided LASIK and LASEK groups beginning 3 months after surgery. However, the HOAs in the LASIK and LASEK groups had a different time course, especially in the case of spherical aberration. This finding suggests that postoperative changes in aberration contribute to the final outcome of wavefront-guided ablation.

CustomVue laser in situ keratomileusis treatment after previous keratorefractive surgery

PURPOSE

To evaluate the efficacy, predictability, and safety of Visx CustomVue wavefront-guided enhancement after previous keratorefractive surgery.

SETTING

Stanford University Eye Laser Center, Stanford, California, USA.

METHODS

A retrospective analysis was used to evaluate wavefront-guided enhancement in a preliminary set of 120 eyes of 102 patients. All eyes had previous keratorefractive surgery (photorefractive keratoplasty [PRK] in 1 eye, laser in situ keratomileusis [LASIK] in 119 eyes); the prekeratorefractive surgery spherical equivalent (SE) refraction ranged from -1.25 diopters (D) to -7.00 D. Primary outcome variables including uncorrected visual acuity (UCVA), manifest refraction, and complications were evaluated at 1 and 3 months.

RESULTS

At 1 month, the mean pre-enhancement SE was reduced from -0.91 D +/- 0.40 (SD) (range -2.375 to -0.125 D) to -0.13 +/- 0.33 D (range -1.25 to 0.75 D) with 91% of eyes within +/-0.5 D of emmetropia and 100% within +/-1.0 D. All eyes showed equal or improved UCVA (range 20/15 to 20/30) with 20/20 or better in 84 of 91 eyes. At 3 months, the mean was -0.20 +/- 0.32 D (range -0.75 to 0.75 D) with 100% of eyes within +/-0.75 D of emmetropia. All eyes showed equal or improved UCVA (range 20/15 to 20/30) with 20/20 or better in 74 of 84 eyes. Higher-order wavefront aberration analysis showed that the mean root-mean-square error was reduced from 0.39 +/- 0.14 microm (range 0.16 to 0.86 microm) to 0.34 +/- 0.12 microm (range 0.12 to 0.78 microm). Coma was reduced from 0.22 +/- 0.13 microm (range 0.02 to 0.71 microm) to 0.16 +/- 0.11 microm (range 0.01 to 0.62 microm), and trefoil was reduced from 0.16 +/- 0.09 microm (range 0.01 to 0.62 microm) to 0.11 +/- 0.07 microm (range 0.01 to 0.27 microm). Spherical aberration was unchanged from 0.14 +/- 0.14 microm (range -0.18 to 0.59 microm) to 0.14 +/- 0.14 microm (range -0.16 to 0.5 microm).

CONCLUSION

Preliminary data show that Visx CustomVue wavefront-guided enhancement after keratorefractive surgery is an effective, predictable, and safe procedure.

Interocular high-order corneal wavefront aberration symmetry

The interocular symmetry of the high-order corneal wavefront aberration (WA) in a population of myopic eyes was analyzed before and after photorefractive keratectomy (PRK). The preoperative and one-year postoperative corneal aberration data (from third to seventh Zernike orders) for 4- and 7-mm pupils from right and left eyes were averaged after correcting for the effects of enantiomorphism to test for mirror symmetry. Also, the mean corneal point-spread function (PSF) for right and left eyes was calculated. Preoperatively, a moderate and high degree of correlation in the high-order corneal WA between eyes was found for 4- and 7-mm pupils, respectively. Myopic PRK did not significantly change the interocular symmetry of corneal high-order aberrations. No discernible differences in the orientation PSF between eyes were observed one year after surgery in comparison with the preoperative state over the two analyzed pupils.

Ablationsprofile in der kornealen refraktiven Laserchirurgie

The predictability and quality of results in corneal refractive laser surgery are determined by a number of factors. Here, the calculation and choice of the ablation profile represent central elements. Our growing knowledge about the physical and optical properties of the eye in recent years has led to the development of different strategies in the generation of ablation profiles. This review describes the currently used ablation profiles with their advantages and disadvantages and provides an outlook on future methods for the calculation of ablation profiles.

Alcon LADARWave CustomCornea Retreatments

PURPOSE

To present our experience performing wavefront-guided ablations for the treatment of residual refractive error following previous refractive surgery.

METHODS

Four different cases are presented-1) primary wavefront-guided LASIK; 2) wavefront-guided lift-flap LASIK retreatment; 3) wavefront-guided photorefractive keratectomy (PRK) retreatment; and 4) wavefront-guided PRK over radial keratotomy retreatment. All procedures were performed with the Alcon CustomCornea laser platform. Uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), manifest refraction, and wavefront analysis (6.5-mm pupil) were performed preoperatively and 3 months after CustomCornea retreatment. The Alcon LADARWave device was used for wavefront measurements.

RESULTS

Total lower order and higher order aberrations were decreased following wavefront-guided retreatment, resulting in improved quality of vision. The maximum target offset (+ 0.75 diopters) can be used to prevent an overcorrection of defocus (myopia) when treating a significant amount of spherical aberration.

CONCLUSIONS

Wavefront-guided ablation was an effective treatment for residual lower and higher order aberrations following previous refractive surgery. Custom ablation treatment algorithms need to be developed specifically for retreatment procedures.

Higher-Order Aberrations in Eyes with Irregular Corneas after Laser Refractive Surgery

PURPOSE

To investigate the distribution of the eye's higher-order aberrations in postoperative laser refractive surgery patients with visual complaints and highly irregular corneal shapes.

DESIGN

Retrospective case-control study.

PARTICIPANTS

Thirty-three symptomatic postoperative LASIK and/or photorefractive keratectomy eyes with subjective visual complaints not corrected by spectacles more than 6 months after surgery are compared with 46 normal preoperative and 46 asymptomatic successful postoperative conventional LASIK eyes.

METHODS

Postoperative wave aberrations were measured for each patient using a Shack-Hartmann wavefront sensor (Zywave, Bausch & Lomb, Rochester, NY) over a 6-mm pupil. These measurements were averaged across patients with similar corneal topographic diagnoses (central islands, decentered ablations, a new group termed baby bowties, and irregularly irregular corneas).

MAIN OUTCOME MEASURES

Higher-order aberrations and corneal topography.

RESULTS

The average (+/-1 standard deviation) higher-order root-mean-square (rms) wavefront error values (third, fourth, and fifth orders) for the symptomatic patients was 1.31+/-0.58 microm. This was an average of 3.46 times greater than the average magnitude of normal preoperative eyes (mean rms, 0.38+/-0.14 microm), and an average of 2.3 times greater than the average magnitude of asymptomatic successful postoperative conventional LASIK eyes (mean rms, 0.58+/-0.21 microm) over a 6-mm pupil. Higher-order rms wavefront error increased with pupil size, roughly doubling for every millimeter of increasing pupil diameter. On average, eyes with central islands (n = 6) had the most vertical coma (Z3(-1); mean, -1.35+/-0.43 microm). Eyes with central islands and decentered ablations (n = 2) also had elevated amounts of spherical aberration (Z4(0); means of 0.83+/-0.11 microm and 0.69+/-0.29 microm, respectively) compared with successful postoperative LASIK eyes (mean of 0.42+/-0.20 microm). Eyes with a topographic central baby bowtie demonstrated the most secondary astigmatism (Z4(2) and Z4(-2); mean rms, 0.56+/-0.17 microm; n = 3), despite the lowest average higher-order rms (mean, 0.84+/-0.05 microm) among symptomatic topographic subgroups. Eyes with irregularly irregular corneas had a mean higher-order rms of 1.10+/-0.39 mum.

CONCLUSIONS

Symptomatic postoperative laser refractive surgery patients with irregular corneas have higher-order aberrations that are 2.3 to 3.5 times greater than asymptomatic postoperative LASIK and normal preoperative eyes, respectively. The higher-order aberrations seem to correlate with corneal topography.

Comparison of Corneal Higher-Order Aberrations Induced by Myopic and Hyperopic LASIK

OBJECTIVE

To compare the change in anterior corneal higher-order (third- to fifth-order) aberrations (HOAs) induced by myopic and hyperopic LASIK.

DESIGN

Retrospective comparative case series.

PARTICIPANTS

One hundred eyes (50 myopes and 50 hyperopes) of 59 patients were included. The mean preoperative spherical equivalent (SE) was -4.22+/-1.78 diopters (D; range, -1.25 to -8.00 D) in the myopic group (group A) and +2.72+/-1.25 D (range, +0.25 to +5.00 D) in the hyperopic group (group B).

INTERVENTION

LASIK was performed using a conventional spherocylindrical laser algorithm (Planoscan V2.9992, Bausch & Lomb/Technolas, Munich, Germany). Optical zone diameter was 6.70+/-0.32 mm (range, 6-7 mm) in group A and 6.59+/-0.19 mm (range, 6.5 to 7 mm) in group B. Third to fifth corneal HOA were computed for a pupil diameter of 6 mm from corneal topographic examinations before and 1 month after surgery.

MAIN OUTCOME MEASURES

Change in corneal HOAs, derived from corneal topography.

RESULTS

Total HOA root mean square (RMS) changed in group A by 0.167+/-0.180 microm (factor 1.53) and in group B by 0.341+/-0.341 microm (factor 1.89). The mean induction of coma RMS was significantly different in both groups (myopes, 0.092+/-0.195 microm; hyperopes, 0.252+/-0.305 microm; P<0.05). For spherical aberration (Z 4,0), the myopic group showed a significant increase (0.130+/-0.120 microm; factor 1.6; P<0.001), whereas the hyperopic group showed a significant decrease (-0.317+/-0.158 microm; factor 0.76; P<0.001). Fifth-order aberrations showed an increase in both groups, which was higher in group B (0.069+/-0.120 microm; factor 2.46) than in group A (0.005+/-0.065 microm; factor 1.49).

CONCLUSIONS

Myopic and hyperopic LASIK had different patterns of HOA induction. Myopic LASIK induced positive spherical aberrations and positive secondary astigmatism, whereas hyperopic LASIK induced negative spherical aberrations and negative secondary astigmatism. Hyperopic LASIK induced more third- and fifth-order comalike aberrations than myopic LASIK.

New intraocular lens technology

PURPOSE

To review the current status of phakic intraocular lenses (IOLs), intraocular treatment of presbyopia, and IOLs that filter some blue light.

DESIGN

Review of current information on the subject from numerous sources.

METHODS

Medline search and Internet search engines on the topics of phakic IOLs, presbyopia or multifocal IOLs, and blue light and macular degeneration.

RESULTS

An iris fixated phakic IOLs is now approved in the United States (US). There are concerns for corneal endothelial stability and late dislocation. Other approaches include anterior chamber fixation with concerns of corneal endothelial stability and pupil elongation, and posterior chamber fixation with concerns of cataract formation, IOL dislocation, and pigment dispersion. Intraocular treatment of presbyopia includes monovision, multifocal, and accommodative IOLs. Which approach is superior today is still not clear. There are IOLs designed to block some blue light to potentially lessen the risk of age-related macular degeneration (ARMD). While there is presumptive evidence of this, no definitive study shows such a correlation. Color perception issues are unlikely to be a problem. While decreased scotopic vision has been proposed, there is no study that proves this is an issue of clinical significance.

CONCLUSIONS

The IOL field is dynamic with many new choices. Phakic IOLs and treatment of presbyopia will be an increasingly important part of ophthalmology; however, there are important unresolved issues. With better evidence that blue light is an important variable in ARMD, such an approach could rapidly become the standard.

Pharmacological management of night vision disturbances after refractive surgery

PURPOSE

To evaluate the efficacy and safety of diluted aceclidine eyedrops in reducing night vision disturbances after refractive surgery.

SETTING

Department of Ophthalmology, Istituto Clinico Humanitas, Rozzano-Milano, Italy.

METHODS

This double-masked randomized clinical trial included 30 patients (60 eyes) with chronic night vision disturbance after refractive surgery. Patients were randomly allocated to receive (1) placebo, (2) aceclidine 0.016%, or (3) aceclidine 0.032%. Drugs were administered once or twice daily. Anterior segment, haze, uncorrected visual acuity, best corrected visual acuity, intraocular pressure, corneal maps, and scotopic pupil size were determined at baseline and at follow-up examinations (15 and 30 days after inclusion). Halos and double vision 4-step scales were built to determine subjective grading of night vision disturbance, and the root mean square (RMS) was calculated to determine objective changes in night vision disturbance.

RESULTS

The effect of diluted aceclidine started about 15 minutes after instillation and lasted for about 5 hours. No difference between the 2 dilutions could be found. Thirty-nine of 40 treated eyes showed a reduction in night vision disturbance. The mean reduction in halos and double vision grading was 1.42 +/- 0.5 (SD) and 1.14 +/- 0.4, respectively. A mean decrease in pupil size of 2.5 mm was measured. Thirty minutes after the instillation of diluted aceclidine, the topography-derived wavefront error showed a statistically significant reduction in RMS values (total, spherical, astigmatic, coma, and higher order), which was maintained for 5 hours. A transitory conjunctival hyperemia was the only side effect reported.

CONCLUSION

Diluted aceclidine seemed to be an effective and safe treatment for night vision disturbance following refractive surgery.

Wavefront technology: Past, present and future

After outlining what is meant by wavefront aberration, the history of the field of wavefront technology is sketched and methods for measuring ocular wavefront aberration are briefly described. The variations in aberration of the normal eye with the individual and their pupil size, accommodation and age are summarised. Potential contact lens applications are outlined, including the design and on-eye performance of single-vision lenses, lenses for presbyopes and keratoconics, orthokeratology, tear film studies, and the design and performance of customised contact lenses intended to minimise residual lens-eye wavefront error.

The Effect of Overnight Contact Lens Corneal Reshaping on Higher-Order Aberrations and Best-Corrected Visual Acuity

PURPOSE

The purpose of this study is to determine the effect of higher-order aberrations after Corneal Refractive Therapy (CRT) on best-corrected visual acuity (BCVA) and the impact of pupil size on BCVA.

METHODS

High-contrast (HC) and low-contrast (LC) Bailey-Lovie BCVA was measured in the morning before and after pupil dilation on 20 myopes (mean spherical equivalent -3.11 D +/- 0.96 D) under age 40. BCVA was measured again in the afternoon after dilation. Dilated am and pm aberrations were measured using the Complete Ophthalmic Analysis System (WaveFront Sciences). Patients were fit with CRT lenses in each eye. One month after finalizing the lens fit, BCVA and aberration testing were repeated. Average higher-order RMS error (third to sixth order), spherical aberration, third-, fourth-, fifth-, and sixth-order RMS error were calculated at each visit for a 3-mm and 5-mm pupil. BCVA and aberration data were analyzed using a repeated measures analysis of variance. Linear regression was used to describe the relationship between aberrations and BCVA reductions after CRT.

RESULTS

Mean refractive error changed by +3.33 D +/- 0.96 D. No clinically significant changes were found in HC BCVA post-CRT, whereas LC BCVA reductions of 0.07 logarithm of the minimum angle of resolution (logMAR) (nondilated, p = 0.002) and 0.12 logMAR (dilated, p < 0.001) were found. No additional decrease in HC BCVA was found after pupil dilation, whereas a mean additional decrease of 0.08 logMAR in LC BCVA was found with dilation post-CRT (p = 0.013). Higher-order RMS error increased for both 3-mm and 5-mm pupils (p < 0.0001) and remained stable between measurements. Spherical aberration increased for 5-mm pupils after CRT (p < 0.0001). For a 5-mm pupil, a 0.1-mum increase in spherical aberration was associated with an additional decrease in LC BCVA after pupil dilation post-CRT of 0.056 logMAR (R = 0.382, p = 0.004).

CONCLUSIONS

CRT results in reduced low-contrast BCVA as a result of increased higher-order aberrations. Higher-order aberrations appear to be relatively stable after CRT. Spherical aberration appears to drive additional low-contrast BCVA losses as pupil size increases.

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.

Functional optical zone after myopic LASIK as a function of ablation diameter

PURPOSE

To analyze spherical aberrations in patients who had myopic laser in situ keratomileusis (LASIK) with different optical zones and varying degrees of attempted corrections.

SETTING

Laser Refractive Center, University of California, Los Angeles, USA.

METHODS

This retrospective analysis comprised 78 eyes of 56 consecutive patients who had LASIK for myopia with the Alcon LADARVision excimer laser. The preoperative and 3-month postoperative functional optical zones (FOZs), a measure of spherical aberrations, were assessed in each eye. The change in FOZs was analyzed by size of the primary optical zone and degree of attempted correction.

RESULTS

The mean preoperative FOZ was 6.1 mm +/- 0.6 (SD) and the mean 3-month FOZ, 5.2 +/- 1.0 mm. The mean decrease was 0.9 +/- 1.0 mm (P < .0001). The mean decreases were 0.005 +/- 0.7 mm, 0.7 +/- 0.9 mm, and 1.6 +/- 0.9 mm in the low, moderate, and high attempted correction groups, respectively (P < .05), and 1.3 +/- 0.9 mm, 1.2 +/- 1.0 mm, 0.5 +/- 1.3 mm, and 0.3 +/- 0.7 mm in optical zone groups of 6.0 to 6.5 mm, 6.6 to 7.0 mm, 7.1 to 7.5 mm, and 7.6 to 8.0 mm, respectively (P < .05).

CONCLUSIONS

Larger optical zones had fewer postoperative spherical aberrations. Higher attempted corrections had larger increases in spherical aberrations. Larger treatment diameters minimized postoperative spherical aberrations.

Causes of spherical aberration induced by laser refractive surgery

PURPOSE

To develop a corneal model to better explain how refractive surgery procedures induce spherical aberration.

SETTING

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

METHODS

The preoperative cornea was modeled as a rotationally symmetric surface with various radii of curvature and asphericities. The postoperative cornea was defined as the difference between the preoperative cornea and an ablation thickness profile computed based on the Munnerlyn equation. A ray-tracing program and Zernike polynomial fitting were used to calculate the induced amount of spherical aberration assuming a fixed ablation depth per pulse or a variable ablation depth depending on the incidence angle of each pulse on the cornea. A biological eye model of the corneal surface change after laser refractive surgery was also developed to explain the induced spherical aberrations after myopic and hyperopic treatments.

RESULTS

The clinical data showed that positive spherical aberration was induced after myopic correction and negative spherical aberration increased after hyperopic correction. In contrast, assuming a fixed ablation depth per pulse, the theoretical prediction was that negative spherical aberration with myopic treatment and positive spherical aberration with hyperopic treatment would increase. However, when assuming a variable ablation depth per pulse caused by non-normal incidence of laser spot on the cornea, the theoretically predicted induction of spherical aberration tends to fit better with the myopic and hyperopic clinical data. The effect of a variable ablation depth accounted for approximately half the clinically observed amount of spherical aberration. The biological model of the corneal surface change used to explain this remaining discrepancy showed the magnitude of the biological response in myopic correction is 3 times smaller than in hyperopic correction and that the direction of the biological response in hyperopic treatment is opposite that in myopic treatment.

CONCLUSIONS

This nontoric eye model, which separates the effects of differences in ablation efficiency and biological corneal surface change quantitatively, explains how spherical aberration is induced after myopic and hyperopic laser refractive surgery. With the corneal topographic data, this model can be incorporated into the ablation algorithm to decrease induced spherical aberrations, improving the outcomes of conventional and customized treatments.

Corneal higher-order aberrations induced by overnight orthokeratology

PURPOSE

To evaluate corneal higher-order aberrations induced by overnight orthokeratology for myopia.

DESIGN

Prospective, noncomparative, consecutive, interventional case series.

METHODS

A prospective study was conducted in 64 eyes of 39 patients with overnight orthokeratology for myopia, who were followed up for at least 3 months and attained uncorrected visual acuity of 20/20 or better. Corneal height data were obtained with computerized videokeratography (TMS-2N, Tomey), and wavefront aberration was derived using Zernike polynomials. Higher-order aberrations of the cornea were calculated for 3- and 6-mm pupils.

RESULTS

Orthokeratology significantly reduced manifest refraction from -2.60 +/- 1.13 (mean +/- SD) diopters to -0.17 +/- 0.31 diopters (P < .0001, paired t test). Root-mean-square (RMS) of third-order (coma-like) aberrations significantly increased by orthokeratology for both 3-mm (P < .0001, paired t test) and 6-mm (P < .0001) pupils. Fourth-order RMS (spherical-like) aberrations increased significantly by the treatment for both 3-mm (P < .0001) and 6-mm (P < .0001) pupils. Vertical coma significantly changed from positive to negative for both 3-mm (P = .0323) and 6-mm (P < .0001) pupils. Horizontal coma significantly increased to the positive direction for both 3-mm (P < .0001) and 6-mm (P < .0001) pupils. Increases in the third- and fourth-order RMS showed significant positive correlations with the amount of myopic correction for 3-mm (Pearson correlation coefficient, r = .452, P = .0001 for third-order RMS, r = .381, P = .0017 for fourth-order RMS) and 6-mm (r = .499, P < .0001, r = .455, P = .0001) pupils.

CONCLUSIONS

Corneal higher-order aberrations significantly increased, even in clinically successful orthokeratology cases. The increases in the higher-order aberrations correlated with the magnitude of myopic correction.