Evaluation of refractive error measurements of the Wavescan Wavefront system and the Tracey Wavefront aberrometer

Wavefront aberrometry repeatability and agreement—A comparison between Pentacam AXL Wave, iTrace and OPD‐Scan III

INTRODUCTION

To compare intrasession agreement and repeatability of wavefront aberration measurements from three different aberrometers obtained using Hartmann-Shack, ray tracing and automated retinoscopy methods, as well as their interdevice agreement.

METHODS

Three consecutive measurements were obtained using the Pentacam AXL Wave, the iTrace and the OPD-Scan III in 47 eyes of 47 patients. Wavefront refractions, root mean square of total aberrations (RMS total), RMS of higher-order aberrations (HOA) and second-, third- and fourth-order HOAs were exported for 4-mm pupils. Wavefront refractions were converted into vector components: M, J₀ and J₄₅ . Intrasession agreement and repeatability were evaluated using intraclass correlation coefficients (ICCs) and repeatability coefficients (RCs); interdevice agreement was assessed using the Bland-Altman method.

RESULTS

The intrasession agreement and repeatability of RMS HOA were comparable between the three devices; both the Pentacam AXL Wave and the OPD-Scan III had better intrasession agreement and repeatability for the RMS total than the iTrace (p ≤ 0.02). Intrasession repeatability for the majority of second- and third-order aberrations was better on the Pentacam AXL Wave than on the iTrace (p ≤ 0.01) and OPD-Scan III (p ≤ 0.04), although their agreement and repeatability in spherical aberration were comparable (p ≥ 0.24). Significant systematic differences and proportional bias were detected for almost all refraction power vectors and Zernike coefficients among the three devices.

CONCLUSIONS

In this study, all three devices provided good-to-excellent agreement for aberration measurements. Most of the individual Zernike's components were not exchangeable between different aberrometers. Their relative intrasession performance in agreement and repeatability varied significantly across different ocular aberration parameters.

Long-Term Evaluation of Visual Outcomes and Patient Satisfaction after Binocular Implantation of a Bioanalogic Lens

Purpose

Long-term evaluation of the visual refractive outcomes and the quality of life after implantation of the WIOL-CF (Medicem, Czech Republic) in both eyes.

Design

retrospective, nonrandomized noncomparative case series.

Methods

50 eyes of 25 patients, including 11 women (44%) and 14 men (56%). The age range of the patients was 38 to 77 years (mean age 55.48 ± 10.97 years). All patients underwent bilateral implantation of the WIOL-CF. Exclusion criteria were previous ocular surgeries except for cataract surgery and refractive lens exchange, irregular corneal astigmatism of >1.0 diopter, and ocular pathologies or corneal abnormalities. Postoperative examinations were performed at 14 days and 3, 6, 12 months of surgery; the last follow-up was between 24 and 36 months after the procedure. All exams included manifest refraction, monocular uncorrected visual acuity (UCVA) and distance-corrected visual acuity (DCVA) in 5 m (Snellen), monocular uncorrected visual acuity in 70 cm and 40 cm (Jeager) and binocular UCVA, DCVA in 5 m, 70 cm, and 40 cm, binocular contrast sensitivity (CS) under photopic conditions, binocular defocus curves, high-order aberrations, quality-of-vision VF-14 questionnaire, and spectacle independence.

Results

Significant improvement in monocular visual acuity at all distances was demonstrated; the mean postoperative spherical equivalent was 0.32 ± 0.45D. The postoperative means of binocular distance UCVA and BCVA were also improved (p < .001) and so were the mean uncorrected intermediate VA (2.053 ± 1.268) and near uncorrected VA (2.737 ± 1.447). There was a significant improvement in contrast sensitivity at all spatial frequencies and higher-order aberration, compared to preoperative results.

Conclusions

The evaluation of a WIOL-CF showed good distance, intermediate, and near visual acuity. Contrast sensitivity increased after surgery in all spatial frequencies. Patient satisfaction was high despite some optical phenomena. The rate of postoperative spectacle independence also turned out high. Financial Disclosure. No author has a financial or proprietary interest in any material or method mentioned.

Corneal Astigmatism Measurements Comparison among Ray-Tracing Aberrometry, Partial Coherence Interferometry, and Scheimpflug Imaging System

Purpose

To investigate interdevice agreement among corneal topography/ray-tracing aberrometry (iTrace), partial coherence interferometry (IOLMaster), and Scheimpflug imaging (Pentacam) for the measurement of corneal astigmatism.

Methods

The analysis included 90 eyes of 90 subjects without ocular disease. The main outcome measures were corneal cylinder power and axis of astigmatism. All corneal astigmatism measurements were converted to two perpendicular components by using vector analysis. Interdevice agreement was assessed using Bland–Altman analysis, paired sample t-test, and one-way analysis of variance.

Results

No significant interdevice difference existed in the astigmatism magnitude, cardinal component, and oblique component (all P > 0.05). On comparing iTrace wavefront and simulated keratometry (SimK) astigmatism, significant differences were observed in the astigmatism magnitude and oblique component (both P < 0.01), but not in the cardinal component (P=0.687). On comparing Pentacam pupil 3 mm and corneal vertex 3 mm axial astigmatism, significant difference was observed in the astigmatism magnitude (P < 0.001), but not in the cardinal and oblique components (both P > 0.05).

Conclusions

The iTrace, IOLMaster, and Pentacam devices could be used interchangeably for corneal astigmatism measurement. However, the measurement difference in iTrace wavefront and SimK astigmatism and Pentacam pupil 3 mm and vertex 3 mm axial astigmatism should be considered in clinic practice.

Dysfunctional Lens Index Serves as a Novel Surgery Decision-Maker for Age-Related Nuclear Cataracts

Purpose: To study the correlations between subjective and objective cataract metrics with dysfunctional lens index. To investigate the potential of the DLI as a novel surgery decision-maker. Methods: In this prospective, cross-sectional study, we measured the dysfunctional lens index (DLI), Lens Opacities Classification System III nuclear opalescence (LOCS III NO) grading, preoperative corrected distance visual acuity (CDVA), objective scatter index (OSI) and Scheimpflug-based average lens density (ALD) in eyes with nuclear cataract. Eyes were classified as Surgical and Non-Surgical groups. Correlations among the DLI, OSI, ALD, LOCS III NO grading, and preoperative CDVA were analyzed. The receiver operating characteristic (ROC) curve analysis was performed for DLI, OSI, and CDVA to determine optimal cut-off values to separate between surgical and non-surgical cataracts. Results: The DLI showed the strongest correlation with the OSI (r= -0.712, P< .001), followed by LOCS III NO score (r= -0.661, P< .001), ALD (r= -0.596, P< .001) and preoperative CDVA (r= 0.563, P< .001). The area under ROC curves (AUCs) of the DLI, OSI and preoperative CDVA curve were 0.972, 0.912 and 0.844 (All P< .001), respectively. The DLI cut-off value of 5.7 implied higher levels of sensitivity (91.67%) and specificity (91.84%) than the OSI cut-off value of 2.9 and the CDVA cut-off value of 0.55 (sensitivity of 89.58% and 71.92%; specificity of 81.63% and 85.71%, respectively). Conclusion: The surgery criterion of DLI ≤ 5.7 behaved better than the surgery criterions of OSI ≥ 2.9 and preoperative CDVA ≤ 0.55 in discrimination between surgical and non-surgical nuclear cataracts.

Wavefront aberrations and retinal image quality in different lenticular opacity types and densities

To investigate wavefront aberrations in the entire eye and in the internal optics (lens) and retinal image qualities according to different lenticular opacity types and densities. Forty-one eyes with nuclear cataract, 33 eyes with cortical cataract, and 29 eyes with posterior subcapsular cataract were examined. In each group, wavefront aberrations in the entire eye and in the internal optics and retinal image quality were measured using a raytracing aberrometer. Eyes with cortical cataracts showed significantly higher coma-like aberrations compared to the other two groups in both entire eye and internal optic aberrations (P = 0.012 and P = 0.007, respectively). Eyes with nuclear cataract had lower spherical-like aberrations than the other two groups in both entire eye and internal optics aberrations (P < 0.001 and P < 0.001, respectively). In the nuclear cataract group, nuclear lens density was negatively correlated with internal spherical aberrations (r = −0.527, P = 0.005). Wavefront technology is useful for objective and quantitative analysis of retinal image quality deterioration in eyes with different early lenticular opacity types and densities. Understanding the wavefront optical properties of different crystalline lens opacities may help ophthalmic surgeons determine the optimal time to perform cataract surgery.

The efficiency of aspheric intraocular lens according to biometric measurements

Purpose

To analyze internal spherical aberration in pseudophakic eyes that underwent aspheric intraocular lens (IOL) implantation, and to investigate the relationships between biometric data and the effectiveness of aspheric IOL implantation.

Methods

This retrospective study included 40 eyes of 40 patients who underwent implantation of an IOL having a negative spherical aberration of -0.20 μm (CT ASPHINA 509M; Carl Zeiss Meditec Inc., Germany). The IOLMaster (version 5.0; Carl Zeiss AG, Germany) was used for preoperative biometric measurements (axial length, anterior chamber depth, central corneal power) and the measurement of postoperative anterior chamber depth. The spherical aberrations were measured preoperatively and 3 months postoperatively using the iTrace (Tracey Technologies, Houston, TX, USA) at a pupil diameter of 5.0 mm. We investigated the relationships between preoperative biometric data and postoperative internal spherical aberration, and compared biometric measurements between 2 subgroups stratified according to internal spherical aberration (spherical aberration ≤ -0.06 μm vs. spherical aberration > -0.06 μm).

Results

The mean postoperative internal spherical aberration was -0.087 ± 0.063 μm. Preoperative axial length and residual total spherical aberration showed statistically significant correlations with internal spherical aberration (p = 0.041, 0.002). Preoperative axial length, postoperative anterior chamber depth, IOL power, and residual spherical aberration showed significant differences between the 2 subgroups stratified according to internal spherical aberration (p = 0.020, 0.029, 0.048, 0.041 respectively).

Conclusion

The corrective effect of an aspheric IOL is influenced by preoperative axial length and postoperative anterior chamber depth. Not only the amount of negative spherical aberration on the IOL surface but also the preoperative axial length should be considered to optimize spherical aberration after aspheric IOL implantation.

Comparison of short-term refractive surgery outcomes after wavefront-guided versus non-wavefront-guided LASIK

PURPOSE

To evaluate and compare visual and refractive outcomes after laser-assisted in situ keratomileusis (LASIK) surgery for the correction of myopia or myopic astigmatism using 3 different treatment protocols.

METHODS

We included 736 eyes of 369 patients (age 18-62 years) divided into 3 groups: 235 eyes of 118 patients (MEL80 group) undergoing LASIK using optimized aspheric ablation profiles (MEL80 excimer laser; Carl Zeiss Meditec), 248 eyes of 124 patients (Wavescan group) undergoing wavefront-guided (WFG) LASIK (STAR S4IR excimer laser + Wavescan aberrometer; Abbott Medical Optics), and 253 eyes of 127 patients (iDesign group) undergoing WFG LASIK (STAR S4IR excimer laser + iDesign system; Abbott Medical Optics). Visual and refractive outcomes were evaluated 2 months after surgery.

RESULTS

A total of 91% (215/235), 95% (237/248), and 99% (251/253) of eyes achieved a postoperative uncorrected distance visual acuity of 0.0 logMAR (≈20/20) in the MEL80, Wavescan, and iDesign groups, respectively. Postoperative spherical equivalent (SE) was within ±0.5 D in 95% (223/235), 98% (242/248), and 100% (253/253) of eyes in these same 3 groups, respectively. Likewise, manifest cylinder was below 0.50 D in 95% (223/235), 97% (241/248), and 100% (253/253) of eyes. Significant differences in postoperative SE and cylinder were found between the MEL80 and iDesign groups (p&lt;0.05).

CONCLUSIONS

All evaluated LASIK treatment protocols are predictable and effective for the correction of myopia. The treatment planned with a high resolution aberrometer obtained the best postoperative refractive outcomes.

Comparison of ocular aberrations measured by a Fourier-based Hartmann-Shack and Zernike-based Tscherning aberrometer before and after laser in situ keratomileusis

PURPOSE

To assess agreement between a Hartmann-Shack aberrometer (Wavescan) and a Tscherning aberrometer (Wavelight Allegro Analyzer) and their respective agreement with manifest refraction before and after laser in situ keratomileusis (LASIK).

SETTING

Stanford Eye Laser Center, California, USA.

DESIGN

Prospective comparative observational study.

METHODS

Multiple readings were obtained both aberrometers preoperatively and 12 months after wavefront-guided LASIK. Sphere, cylinder, spherical equivalent (SE), defocus Z(2,0), astigmatism Z(2,2), spherical aberration Z(4,0), coma Z(3,1), trefoil Z(3,3), and total higher-order aberrations (HOAs) were compared using intraclass correlation coefficients (ICCs) (perfect agreement = 1; disagreement = 0).

RESULTS

In the 100 study eyes, preoperative agreement was good to excellent between the aberrometers for the parameters of defocus, astigmatism, and spherical aberration (ICC: 0.8, 0.9, and 0.7, respectively) but was poor for coma, trefoil, and total HOAs (ICC: 0.6, -0.2, and 0.4, respectively). At 12 months, ICCs worsened for all parameters (ICC: defocus = 0.6; astigmatism = 0.2; spherical aberration = 0.6; coma = 0.4; trefoil = -0.3; total HOAs = 0.4). Preoperative agreement of sphere, cylinder, and SE was good to excellent between the manifest refraction and both aberrometers (ICC Hartmann-Shack: 0.98, 0.95, and 0.97, respectively; ICC Tscherning: 0.97, 0.92, and 0.98, respectively). However, agreement was poor to fair between the manifest refraction and both aberrometers at 12 months (ICC Hartmann-Shack: 0.4, 0.1, and 0.4, respectively; ICC Tscherning: 0.03, 0.02, and 0.2, respectively).

CONCLUSIONS

Although some HOAs measured with both aberrometers agreed preoperatively, such agreement might not persist after LASIK. Spherocylinder measurements with both aberrometers seemed to agree closely with the manifest refraction before LASIK, but not at 12 months.

FINANCIAL DISCLOSURE

Dr. Manche has equity in Calhoun Vision, Inc., Krypton Vision, Seros Medical, LLC, and Veralas and is a consultant to Best Doctors, Gerson Lehrman Group.

[Assessment of a 3D digital orthoptic test platform]

PURPOSE

To compare standard orthoptic tests with a novel digital 3D orthoptic platform, 3DeltaEasy(©) from Orthoptica(®).

MATERIALS AND METHODS

This study tests the 3D digital orthoptics platform, 3DeltaEasy(©) from Orthoptica(®) and compares it to the corresponding standard orthoptic tests. This platform consists of a computer equipped with dedicated software, a video projector and 3D liquid crystal glasses. Three tests were compared: Wirt test, measurement of horizontal and vertical phorias, and the horizontal fusional amplitude in convergence and divergence. A total of 102 subjects, 53 males (52 %) and 49 females (48 %), aged between 9 years and 72 years (mean age 33±16.4 years) were examined at the ophthalmologic department of the Brest Hospital (France) and included in this observational cross-sectional study. Subjects recruited in this study were patients requiring orthoptic screening or therapy. Patients without their optimal visual corrections were excluded. All patients underwent both ophthalmological and orthoptic examination including Wirt fly stereotest with polarizing spectacles, cover tests to evaluate and measure the horizontal and vertical deviation of the lines of sight, horizontal vergence ranges using prism bar and their equivalent tests implemented in the digital 3D orthoptic tests 3DeltaEasy(©) from Orthoptica(®).

RESULTS

All data were processed using MedCalc Statistical Software version 14.12.0 (MedCalc Software bvba, Ostend, Belgium). The main result of this study is that 3DeltaEasy(©) and the classical Wirt test are correlated (Spearman's coefficient of rank correlation: ρ=0.74; P<0.0001), cover tests are equivalent for intermediate and far vision (paired t-test; P=0.46 and P=0.51), and horizontal and vertical vergence range are comparable for distance vision (paired t-test; P=0.34 and P=0.94).

CONCLUSION

New digital 3D tools could easily substitute for some orthoptic tests with better ergonomics. Eventually, by increasing the number of tests performed, it could substitute for nearly all tests.

Comparison of two types of visual quality analyzer for the measurement of high order aberrations

AIM

To compare the difference and agreement of KR-1W and iTrace for measurement of high order aberrations.

METHODS

KR-1W and iTrace were respectively used in a group of healthy people (40 volunteers, 32 eyes) to measure the high order aberration (HOA) of corneal, internal and total ocular. The clinical difference and agreement of two instruments were respectively evaluated by paired-samples t-test and Bland-Altman analysis.

RESULTS

The paired-samples t-test showed that the corneal HOA measured by the two instruments had no statistical differences (P>0.05); but the internal and total ocular HOA had significant statistical differences (P<0.05), and the mean results measured by iTrace were higher than that of KR-1W. However, Bland-Altman analysis revealed that the HOA of corneal and internal were all in 95% limits of agreement; and just one point of total ocular HOA was beyond the 95% limits of agreement.

CONCLUSION

KR-1W and iTrace were consistent well in the measurement of corneal, internal and total ocular HOA, especially for the cornea.

Evaluation of patient visual comfort and repeatability of refractive values in non-presbyopic healthy eyes

AIM

To evaluate the intra-operator repeatability in healthy subjects using the WAM-5500 auto-kerato/refractometer and the iTrace aberrometer, to compare the refractive values and the subjective refraction obtained with both devices and to determine which of these three spherocylindrical corrections allows the subject to achieve the best visual comfort.

METHODS

Forty-two non-presbyopic healthy eyes of 42 subjects were enrolled in this prospective study. Refractive values were compared, evaluating the repeatability, the relationship between the methods and the best visual comfort obtained.

RESULTS

Sphere, cylinder and axis results showed good intraclass correlation coefficients (ICC); the highest ICC was obtained using the spherical refraction with the autorefractometer and the aberrometer, achieving levels of 0.999 and 0.998, respectively. The power vector (PV) was calculated for each refraction method, and the results indicated that there were no statistically significant differences between them (P>0.05). Direct comparison of PV measurements using the three methods showed that aberrometer refraction gave the highest values, followed by the subjective values; the autorefractometer gave the lowest values. The subjective method correction was most frequently chosen as the first selection. Equal values were found for the autorefractometer and the aberrometer as the second selection.

CONCLUSION

The iTrace aberrometer and the WAM-5500 auto-kerato/refractometer showed high levels of repeatability in healthy eyes. Refractive corrections with the aberrometer, the autorefractometer and subjective methods presented similar results, but spherocylindrical subjective correction was the most frequently selected option. These technologies can be used as complements in refractive evaluation, but they should not replace subjective refraction.

Repeatability of topographic and aberrometric measurements at different accommodative states using a combined topographer and open-view aberrometer

PURPOSE

To evaluate the repeatability of corneal first-surface aberrations and aberrometric measurements of a combined aberrometer-topographer (iTrace Visual Function Analyzer) for 5 accommodative stimuli.

SETTING

Department of Ophthalmology, Goethe-University, Frankfurt, Germany.

DESIGN

Prospective case series.

METHODS

Eyes of young adults with low to moderate myopia or hyperopia were examined in 2 measurement series comprising 3 corneal topography measurements and wavefront measurements focusing on targets at 5 distances (0.4, 0.5, 0.6, 1.0, and 4.0 m). Repeatability was analyzed using the standard deviation (SD) within 6 measurements and the coefficient of repeatability (CoR) by Bland-Altman analysis of the means of the 2 measurement series.

RESULTS

Fifty eyes (50 subjects) were evaluated. The lowest calculated mean SD/CoR measurements using the aberrometer function at 5 target distances were 0.07 μm/0.14 μm for total ocular aberrations root mean square (RMS), 0.07 μm/0.16 μm for lower-order aberrations (LOAs) RMS, 0.03 μm/0.66 μm for higher-order aberrations (HOAs) RMS, 0.10 diopter (D)/0.22 D for sphere, 0.08 D/0.13 D for cylinder, and 0.09 D/0.21 D for the spherical equivalent (SE). Repeatability of the total RMS, LOAs RMS, sphere, and SE measurements improved with increasing target distance (P < .01 for aberrometric values; P < .03 for refractive values). Measurement reproducibility using the corneal topographer showed mean SDs/CoRs of 0.19 μm/0.41 μm for total RMS, 0.19 μm/0.39 μm for LOAs RMS, and 0.08 μm/0.23 μm for HOAs RMS.

CONCLUSION

The aberrometer showed satisfactory results for measurement repeatability at all target distances and declining repeatability with increasing accommodation effort.

FINANCIAL DISCLOSURE

No author has a financial or proprietary interest in any material or method mentioned.

Univariate and bivariate polar value analysis of corneal astigmatism measurements obtained with 6 instruments

PURPOSE

To compare the corneal astigmatism measurements from 6 instruments in preoperative assessment for toric intraocular lens (IOL) implantation.

SETTING

Institute of Vision Research, Department of Ophthalmology, Yonsei University College of Medicine, Seoul, South Korea.

DESIGN

Prospective comparative observational study.

METHODS

This study included patients with cataract and more than 1.00 diopter (D) of corneal astigmatism. For preoperative evaluation of toric IOL implantation, the net astigmatism was evaluated using manual keratometry, autokeratometry, partial coherence interferometry (PCI) (IOLMaster), corneal topography/ray-tracing aberrometry (iTrace), scanning-slit topography (Orbscan), and Scheimpflug imaging (Pentacam). All net astigmatisms were converted to polar values. Using the astigmatism measurements from manual keratometry as a standard, Bland-Altman analysis, linear mixed-model, and bivariate graphic analysis were performed.

RESULTS

The study group comprised 257 eyes of 141 patients. Bland-Altman plots showed good agreement between manual keratometry and each instrument for polar values. There was no significant between-instrument difference in KP(90) and KP(135) in the linear mixed model analysis or in bivariate polar values in bivariate confidence ellipses.

CONCLUSION

The corneal astigmatism measurements from autokeratometry, PCI, corneal topography/ray-tracing aberrometry, scanning-slit topography, and Scheimpflug imaging were comparable to those from manual keratometry and can be used interchangeably with manual keratometry to measure corneal astigmatism.

Ocular wavefront aberrations in patients with macular diseases

BACKGROUND

There have been reports that by compensating for ocular aberrations using adaptive optical systems it may be possible to improve the resolution of clinical retinal imaging systems beyond what is now possible. To develop such a system to observe eyes with retinal disease, understanding of ocular wavefront aberrations in individuals with retinal disease is required.

METHODS

Eighty-two eyes of 66 patients with macular disease (epiretinal membrane, macular edema, macular hole, etc.) and 85 eyes of 51 patients without retinal disease were studied. Using a ray-tracing wavefront device, each eye was scanned at both small and large pupil apertures, and Zernike coefficients up to the sixth order were acquired.

RESULTS

In phakic eyes, third-order root mean square errors in the macular disease group were statistically greater than in the control group, an average of 12% for 5-mm and 31% for 3-mm scan diameters (P < 0.021). In pseudophakic eyes, there was also an elevation of third-order root mean square, on average 57% for 5-mm and 51% for 3-mm scan diameters (P < 0.031).

CONCLUSION

Higher-order wavefront aberrations in eyes with macular disease were greater than in control eyes without disease. This study suggests that such aberrations may result from irregular or multiple reflecting retinal surfaces. Modifications in wavefront sensor technology will be needed to accurately determine wavefront aberration and allow correction using adaptive optics in eyes with macular irregularities.

Back-calculation to model strategies for pretreatment adjustment of the ablation sphere in myopic wavefront laser in situ keratomileusis

PURPOSE

To examine strategies for adjusting the ablation sphere in myopic wavefront laser in situ keratomileusis (LASIK) with reference to preoperative manifest refraction.

SETTING

Refractive Surgery Service, Moorfields Eye Hospital, London, United Kingdom.

METHODS

The variance in the 3-month postoperative manifest refraction spherical equivalent (MRSE) results in 295 consecutive cases of myopic wavefront LASIK treated with a nonsystematic, intuitive approach to pretreatment adjustment of the ablation sphere was compared with the variance in modeled results obtained by back-calculation using 4 systematic strategies: (1) no adjustment (No Adj), (2) addition of the difference between the preoperative MRSE and the preoperative 4.0 mm pupil wavefront refraction spherical equivalent (WRSE) (4.0 mm), (3) addition of the difference between the preoperative MRSE and the preoperative maximum pupil WRSE (Max), and (4) addition of the difference between the preoperative MRSE and the preoperative effective blur (EB). The EB is a theoretical value for the dioptric SE of all aberrations at the pupil size calculated for the Hartmann-Shack images acquired (wavefront diameter). A stratified analysis of results for different wavefront diameters was also performed.

RESULTS

Variance in the postoperative MRSE was least (0.116) when nonsystematic, intuitive adjustments to the ablation sphere were used. In ascending order, the back-calculated variance was as follows: EB (0.142; P = .09, Bartlett test), 4.0 mm pupil (0.163; P = .004), No Adj (0.171; P = .001), and Max (0.225; P<.0001). There was a strong trend toward reduced variance in results in patients with a larger wavefront diameter.

CONCLUSION

Back-calculation to model results with different pretreatment ablation adjustment strategies may be useful to eliminate unpromising new approaches before clinical trials.

Corneal thickness association with ocular and corneal high-order aberrations

PURPOSE

To investigate the association among central corneal thickness, peripheral corneal thickness (PCT), and wavefront aberrations in the anterior cornea, posterior cornea and the whole eye in myopia.

METHODS

Sixty-four eyes of 64 myopic subjects were evaluated with a Pentacam rotating Scheimpflug camera (Oculus, Inc., WA) corneal topographer for: (1) wavefront aberrations from the anterior and posterior corneal surface, (2) corneal thickness (central and peripheral), and (3) with a wavefront aberration-supported cornea ablation wavefront analyzer (Wavescan, Visx, Inc., Santa Clara, CA) for wavefront aberrations generated in the whole eye. Relationships between the wavefront aberrations and corneal thickness were analyzed.

RESULTS

The mean age of subjects was 34.75 +/- 10.08 years. The central corneal thickness was 550.5 +/- 28.459 microm. The mean peripheral thickness was 629.9 +/- 32.1 microm. Central and PCTs were not significantly correlated with corneal or ocular high-order aberrations. Intraocular pressure was significantly correlated with ocular trefoil (r = -0.307, P=0.001).

CONCLUSIONS

Central and PCT were not significantly associated with either anterior or posterior corneal Zernike aberrations; in addition, no association with the whole ocular wavefront aberrations was found.

Objective and subjective preoperative refraction techniques for wavefront-optimized and wavefront-guided laser in situ keratomileusis

PURPOSE

To determine which of 3 methods for measuring preoperative refractive error yields the best refractive outcomes after wavefront-guided (Visx Star S4) or wavefront-optimized (WaveLight Allegretto Wave) excimer laser in situ keratomileusis (LASIK).

SETTING

Emory Eye Center and Emory Vision, Emory University, Atlanta, Georgia, USA.

METHODS

This retrospective analysis of LASIK, performed from June to December 2007, analyzed sphere, cylinder, and spherical equivalent (SE) refractions generated from 3 methods (manifest refraction, aberrometer autorefraction [CustomVue WaveScan], corneal analyzer autorefraction [Nidek ARK-10000 OPD]), actual programmed treatment, and absolute deviation from ideal treatment (deviation) for each technique.

RESULTS

In the wavefront-guided group (63 eyes, 33 patients), manifest refraction and aberrometer autorefraction generated similar deviation for sphere and SE; both were significantly better than corneal analyzer autorefraction (P= .02 and P= .03, respectively). Aberrometer autorefraction generated less cylinder deviation than the other methods (both P= .003). In the wavefront-optimized group (61 eyes, 36 patients), manifest refraction generated less deviation for sphere and SE than aberrometer autorefraction or corneal analyzer autorefraction (sphere: P= .005 and P= .009, respectively; SE: P= .005 and P= .002, respectively). Manifest refraction and aberrometer autorefraction cylinder generated similar deviation, while aberrometer autorefraction was less than corneal analyzer autorefraction (P= .041).

CONCLUSIONS

Overall, manifest refraction was most accurate in generating postoperative emmetropia with both laser treatments; however, aberrometer autorefraction produced the least cylinder deviation for wavefront-guided treatment. Corneal analyzer autorefraction produced the least accurate results with both lasers.

Objective accommodation measurements in pseudophakic subjects using an autorefractor and an aberrometer

PURPOSE

To compare objective measures of accommodation with the WR-5100K autorefractor and iTrace aberrometer to subjective push-down and defocus tests in normal phakic subjects and pseudophakic subjects with standard monofocal intraocular lenses (IOLs).

SETTING

University of Houston, College of Optometry, Houston, Texas, USA.

METHODS

The push-down test and defocus curves were used to stimulate and measure accommodation subjectively in pseudophakic subjects. For objective testing, a near target was pushed up and refraction measured objectively. For comparison, the same objective measurements were performed in phakic subjects. Calibration tests were performed with soft contact lenses in phakic subjects with varying refractive error and in pseudophakic subjects.

RESULTS

Fifteen phakic subjects (mean age 28.9 years+/-5.52 [SD]) and 10 pseudophakic subjects (mean age 66.2+/-11.23 years) participated. Subjectively measured accommodative amplitude in the pseudophakic group was 3.28+/-1.11 diopters (D) in the right eye and 3.64+/-1.38 D in the left eye. Defocus curves in the pseudophakic group had a range of 2.00 D for distance-corrected visual acuity of 20/40 or better. Objective measurements in the pseudophakic group were 0.11+/-0.50 D with the autorefractor and 0.10+/-0.47 D with the aberrometer. Contact lens calibrations showed good agreement with the 1:1 line.

CONCLUSIONS

The subjective tests overestimated accommodative amplitude relative to the objective measures. The autorefractor and aberrometer were accurate, reliable, and appropriate for objective accommodation measurements in pseudophakes. Objective accommodation measurements such as these can be used to evaluate the performance of accommodating IOLs.

Objective accommodation measurements in prepresbyopic eyes using an autorefractor and an aberrometer

PURPOSE

To test the repeatability of the iTrace wavefront aberrometer (Tracey Technologies, Inc.) and the WR-5100K autorefractor (Grand Seiko Co., Ltd.) and to measure accomodation in young and phakic prepresbyopic subjects.

SETTING

University of Houston, College of Optometry, Houston, Texas, USA.

METHODS

This study comprised 30 young adults and 15 prepresbyopic subjects. Accommodation was stimulated with near charts presented at various distances. Measurements were repeated 3 times for each target distance with both instruments. For test-retest reliability, the entire protocol was repeated on 3 additional days in 3 prepresbyopic subjects as well as twice on the same day in the young adults.

RESULTS

The mean age was 25.5 years +/- 3.25 (SD) (range 21 to 31 years old) in the young adult group and 41.2 +/- 2.98 years (range 38 to 49 years) in the prepresbyopic group. Bland-Altman analysis of repeated measures of the young subjects had limits of agreements (LoA) of 1.58 diopters (D) or less for each instrument and when compared between instruments. Normalized mean stimulus response functions in the prepresbyopic group were similar for the 2 instruments. Bland-Altman analysis of the accommodation measurements between the 2 instruments showed a mean difference of 0.07 D and an LoA of 0.70 D. Repeated measures of 3 prepresbyopic subjects had a range of standard deviations from 0.07 to 0.51 D.

CONCLUSION

The accommodative responses measured with the 2 instruments were not significantly different, and testing showed both instruments to be suitable for objective measurement of accommodation in a phakic prepresbyopic population with low accommodative amplitudes.

Performance of a new binocular wavefront aberrometer based on a self-imaging diffractive sensor

PURPOSE

To compare the performance of the Ophthonix Z-View diffractive aberrometer with two different Hartmann-Shack aberrometers.

METHODS

The Ophthonix Z-View was compared with the Alcon LADARWave and VISX WaveScan using 4 model eyes and 68 human eyes. Comparisons using three fixed, single-surface model eyes each with a different wavefront pattern were used to determine higher order accuracy. Lower order accuracy, linearity, and higher order repeatability were tested with a fourth model eye with a movable retinal surface. Manifest refraction spherical equivalent and the calculated spherical equivalent refraction of the aberrometers were compared in 68 human eyes.

RESULTS

The Z-View was more accurate with lower noise compared to the WaveScan and LADARWave systems for higher order measurements of the fixed model eyes. Total root-mean-square difference from surface topography derived average values for all model eye configurations were 0.48, 0.95, and 0.74 microm for the Z-View, WaveScan, and LADARWave aberrometers, respectively. Average inter-measurement standard deviations for the fixed model eyes were 0.024, 0.025, and 0.034 microm for the Z-View, WaveScan, and LADARWave aberrometers, respectively. Results were similar among the systems for measuring the movable retina surface model eye and comparing manifest refraction spherical equivalent of the patients.

CONCLUSIONS

Data gathered using one variable and several fixed-parameter model eyes showed good correlation to predicted values for all of the aberrrometers with one exception. A significant difference was found in the measurement of one individual fixed model eye with one of the three aberrometers. The wavefront refraction provided by the Z-View correlated well with the results of manifest refraction.

Comparison of laser ray-tracing and skiascopic ocular wavefront-sensing devices

PURPOSE

To compare two wavefront-sensing devices based on different principles.

METHODS

Thirty-eight healthy eyes of 19 patients were measured five times in the reproducibility study. Twenty eyes of 10 patients were measured in the comparison study. The Tracey Visual Function Analyzer (VFA), based on the ray-tracing principle and the Nidek optical pathway difference (OPD)-Scan, based on the dynamic skiascopy principle were compared. Standard deviation (SD) of root mean square (RMS) errors was compared to verify the reproducibility. We evaluated RMS errors, Zernike terms and conventional refractive indexes (Sph, Cyl, Ax, and spherical equivalent).

RESULTS

In RMS errors reading, both devices showed similar ratios of SD to the mean measurement value (VFA: 57.5+/-11.7%, OPD-Scan: 53.9+/-10.9%). Comparison on the same eye showed that almost all terms were significantly greater using the VFA than using the OPD-Scan. However, certain high spatial frequency aberrations (tetrafoil, pentafoil, and hexafoil) were consistently measured near zero with the OPD-Scan.

CONCLUSION

Both devices showed similar level of reproducibility; however, there was considerable difference in the wavefront reading between machines when measuring the same eye. Differences in the number of sample points, centration, and measurement algorithms between the two instruments may explain our results.

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.

Operator-induced errors in Hartmann-Shack wavefront sensing: Model eye study

PURPOSE

To evaluate the effects of instrument realignment and angular misalignment during the clinical determination of wavefront aberrations by simulation in model eyes.

SETTING

Aston Academy of Life Sciences, Aston University, Birmingham, United Kingdom.

METHODS

Six model eyes were examined with wavefront-aberration-supported cornea ablation (WASCA) (Carl Zeiss Meditec) in 4 sessions of 10 measurements each: sessions 1 and 2, consecutive repeated measures without realignment; session 3, realignment of the instrument between readings; session 4, measurements without realignment but with the model eye shifted 6 degrees angularly. Intersession repeatability and the effects of realignment and misalignment were obtained by comparing the measurements in the various sessions for coma, spherical aberration, and higher-order aberrations (HOAs).

RESULTS

The mean differences between the 2 sessions without realignment of the instrument were 0.020 microm +/- 0.076 (SD) for Z(3)(-1)(P = .551), 0.009 +/- 0.139 microm for Z(3)(1)(P = .877), 0.004 +/- 0.037 microm for Z(4)(0) (P = .820), and 0.005 +/- 0.01 microm for HO root mean square (RMS) (P = .301). Differences between the nonrealigned and realigned instruments were -0.017 +/- 0.026 microm for Z(3)(-1)(P = .159), 0.009 +/- 0.028 microm for Z(3)(1) (P = .475), 0.007 +/- 0.014 microm for Z(4)(0)(P = .296), and 0.002 +/- 0.007 microm for HO RMS (P = 0.529; differences between centered and misaligned instruments were -0.355 +/- 0.149 microm for Z(3)(-1) (P = .002), 0.007 +/- 0.034 microm for Z(3)(1)(P = .620), -0.005 +/- 0.081 microm for Z(4)(0)(P = .885), and 0.012 +/- 0.020 microm for HO RMS (P = .195). Realignment increased the standard deviation by a factor of 3 compared with the first session without realignment.

CONCLUSIONS

Repeatability of the WASCA was excellent in all situations tested. Realignment substantially increased the variance of the measurements. Angular misalignment can result in significant errors, particularly in the determination of coma. These findings are important when assessing highly aberrated eyes during follow-up or before surgery.

Accuracy, Repeatability, and Clinical Application of Spherocylindrical Automated Refraction Using Time-Based Wavefront Aberrometry Measurements

PURPOSE

To evaluate the clinical utility of spherocylindrical automated refraction (AR) based on time-based wavefront technology compared with subjective manifest refraction (MR) for the purpose of prescribing eyeglasses.

DESIGN

Prospective observational case series.

PARTICIPANTS

A convenience sample of 105 eyes of 53 patients (ages 19 to 87) with corrected acuity no worse than 20/40(-2).

METHODS

Manifest refraction was performed on all subjects followed by three consecutive wavefront measurements at both a 4-mm and 6-mm optical zone using the 3D Wave OPD Scan ARK 10,000 aberrometer.

MAIN OUTCOME MEASURES

Repeatability of multiple consecutive ARs; difference in the sphere, cylinder, and axis of AR compared with MR; difference between the corrected visual acuity based on AR- and MR-derived acuity.

RESULTS

Repeatability analysis showed that the initial wavefront refraction was not significantly different from the mean of the three refractions. At the 4-mm zone, the absolute value (+/- standard deviation) of the difference between the initial AR compared with the MR was 0.34+/-0.28 diopters (D) for sphere, 0.22+/-0.21 D for cylinder, and 12.5+/-15.8 degrees for axis. At the 6-mm zone, these values were 0.32+/-0.29 D for sphere, 0.25+/-0.24 D for cylinder, and 11.8+/-14.6 degrees for axis. When 4-mm AR visual acuity was superior to MR acuity (19.0% of eyes) it was 0.28+/-0.24 Snellen lines better, and when inferior (53.3% of eyes) it was 0.47+/-0.37 lines worse. When 6-mm AR acuity was superior to MR acuity (16.2% of eyes) it was 0.32+/-0.22 Snellen lines better, and when inferior (60.0% of eyes) it was 0.48+/-0.48 lines worse. The absolute value of the difference in spherical equivalent of the first AR measurement at the 4-mm zone compared with the MR value was 0.33+/-0.23 D, and at the 6-mm zone it was 0.30+/-0.27 D.

CONCLUSIONS

The wavefront-derived AR values reflect the physical optical system, but not necessarily subjectively derived values, and the impact of this disagreement on patient satisfaction is unknown. Future studies evaluating this technology and its role in clinical ophthalmology are warranted.

Accuracy of the WASCA Aberrometer Refraction Compared to Manifest Refraction in Myopia

PURPOSE

To evaluate the accuracy of myopic refraction by a single measurement using the Wavefront Supported Custom Ablation (WASCA) aberrometer (Carl Zeiss Meditec AG, Jena, Germany).

METHODS

We retrospectively compared the refractive errors obtained by manifest refraction and wavefront refraction (WASCA) in 50 eyes of 25 consecutive myopic patients undergoing laser refractive surgery. The sphere ranged from -1.00 to -8.25 diopters (D) and cylinder from 0 to -3.75 D. WASCA measurements under cycloplegia were made and WASCA refractions calculated for a 6-mm analysis zone using the Seidel method within the WASCA. We used the manifest refraction as our best estimate of the true refractive error, therefore accuracy was defined as the difference between manifest refraction and that of the WASCA. Correlation coefficients and mean vector errors between manifest and WASCA refraction were calculated.

RESULTS

High correlation was shown between manifest and WASCA refractions, with correlation coefficients (R2) of 0.97, 0.85, and 0.79 for M, J180, and J45, respectively. Mean power vector error (standard deviation) was 0.22 D (0.39), +0.03 D (0.21), and +0.03 D (0.13) for M, J180, and J45, respectively. Total dioptric power vector error was 0.43 D with 74% eyes within 0.50 D.

CONCLUSIONS

When measuring normal myopic eyes, the concordance between manifest and WASCA refractions was found on average to be high; however, outlier measurements occurred.

Clinical comparison of 6 aberrometers Part 2: Statistical comparison in a test group

PURPOSE

To compare and mutually validate the measurements of 6 aberrometers: the Visual Function Analyzer (Tracey), the OPD-Scan (ARK-10000, Nidek), the Zywave (Bausch & Lomb), the WASCA (Carl Zeiss Meditec), the MultiSpot Hartmann-Shack device, and the Allegretto Wave Analyzer.

SETTING

University Hospital Antwerp, Antwerp, Belgium.

METHODS

This prospective study was conducted on a group of 44 healthy eyes with refractions ranging from -5.25 diopters (D) to +5.25 D (cylinder 0 to -2 D). For each aberrometer and each eye, the averaged Zernike data were used to calculate various kinds of root-mean-square (RMS). These parameters, together with the refractive parameters, were then analyzed with a repeated-measures analysis of variance (ANOVA) test, complemented by paired t tests. A similar analysis was done for the comparison of the variances of these parameters.

RESULTS

The aberrometers gave comparable values for all studied parameters with the following exceptions: The OPD-Scan underestimated the polynomials describing 4- and 5-fold symmetries, and the Visual Function Analyzer slightly overestimated the astigmatism terms. The 3rd-order radial RMS value was different for each device, as well as the RMS in the central 2.0 mm zone. The WASCA presented the lowest variance.

CONCLUSION

These results suggest that in healthy eyes, all aberrometers produced globally similar results but they may vary in some details.

Comparison of higher-order wavefront aberrations with 3 aberrometers

PURPOSE

To evaluate the agreement of higher-order aberrations (HOAs) between aberrometers based on the Hartmann-Shack wavefront technology.

SETTING

Department of Ophthalmology, Tri-Service General Hospital, Taipei, Taiwan.

METHODS

Three clinical aberrometers WaveScan (Visx Inc.), LADARWave (Alcon Inc.), and Zywave (Bausch & Lomb Inc.) were used to measure HOAs in 34 cycloplegic eyes in 17 subjects. All the measurements in each subject were performed in 1 visit to reduce the impact of biologic fluctuation of HOAs. Each device was operated by an independent experienced operator, and the operators were blind to the data obtained from the other aberrometers. Root mean square (RMS) of coma, spherical aberration, and total 3rd- and 4th-order HOAs were compared between any 2 devices by a paired t test.

RESULTS

WaveScan had the lowest mean RMS, whereas Zywave reported the highest mean RMS for any HOAs. The coefficients of variation were similar between any 2 devices. Paired t tests of RMS yielded a P value <.01 in 9 of 12 comparisons. In general, the largest discrepancies of HOA measures were between WaveScan and Zywave, and similar data were found between LADARWave and WaveScan. More than 80% of the absolute difference of HOA RMS between LADARWave and WaveScan, 50% to 78% between LADARWave and Zywave, and 38% to 59% between WaveScan and Zywave were within +/-0.1 microm.

CONCLUSIONS

Significant discrepancies in HOA measurements were found among the 3 popular aberrometers. The HOA RMS data were closer between LADARWave and WaveScan, and HOA RMS by Zywave was generally higher than the other 2 devices. The 3 devices had comparable measurement variation.

Wavefront-guided laser in situ keratomileusis using the WaveScan system for correction of low to moderate myopia with astigmatism: 6-month results in 277 eyes

PURPOSE

To assess the safety and effectiveness of wavefront guided LASIK surgery using the Visx WaveScan system for correction of low to moderate myopia with astigmatism.

SETTING

Multicenter study at 6 sites in the United States.

METHODS

In this prospective nonrandomized clinical trial, treatments were performed at 6 sites in the United States using the WaveScan (CustomVue) guided excimer laser. A total of 351 eyes were enrolled, and 277 eyes were analyzed at 6 months.

RESULTS

At 6 months, 94% of eyes achieved an uncorrected visual acuity (UCVA) of 20/20 or better and 74% achieved a UCVA of 20/16 or better. Sixty-nine percent of eyes had the same or better postoperative UCVA than their preoperative best spectacle-corrected visual acuity (BSCVA). Ninety percent of eyes were within +/-0.5 diopter of intended correction. No eye lost more than 1 line of BSCVA. Total higher-order root-mean square (RMS), coma, and spherical aberration values were stable (P<.05).

CONCLUSION

The data support the safety and effectiveness of the WaveScan-guided customized laser ablation using the Visx Star S4 system for correction of low to moderate myopia with astigmatism.

Wavefront Analysis in Normal Refractive Surgery Candidates

PURPOSE

To quantify the higher order aberrations of refractive surgery candidates and compare the wavefront-determined refractions with manifest refractions refined with a +/- 0.25 Jackson cross cylinder.

METHODS

Results of 226 consecutive patients (418 eyes) were analyzed with the WaveScan WavePrint system (VISX, Santa Clara, Calif). Only patients with normal eyes without previous surgery were included.

RESULTS

The mean spherical equivalent refraction determined with wavefront analysis was -3.40 +/- 3.14 diopters (D) (range: -10.72 to +5.41 D). The largest amount of higher order aberrations was detected with : a 6-mm pupil diameter (coma 0.14 +/- 0.08 microm; trefoil 0.10 +/- 0.07 microm; spherical aberrations 0.09 +/- 0.07 microm). The mean root-mean-square of higher order aberrations and total aberrations were 0.23 +/- 0.11 microm and 4.00 +/- 2.45 microm, respectively. No statistically significant correlation was noted between higher order aberrations and gender (P = 0.7) or between higher order aberration and refractive level (P > .59). The mean differences in spherical equivalent refraction, sphere, and cylinder between WaveScan measurements and manifest refraction were 0.36 +/- 0.41 D, 0.40 +/- 0.44 D, and 0.28 +/- 0.32 D, respectively.

CONCLUSIONS

This study provides reference values for higher order aberrations in normal refractive surgery candidates. Wavefront analysis also proved to be a valuable tool for objectively measuring preoperative refractive error.

Wavefront's role in corneal refractive surgery

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

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

Relationship Between Cycloplegic and Wavefront-derived Refraction

PURPOSE

To compare cycloplegic refractions to preoperative wavefront-derived refractions from three Hartmann-Shack-based wavefront devices.

METHODS

Ninety-nine eyes of 55 subjects were evaluated preoperatively using the LADARWave, WaveScan, and Zywave aberrometers. With cycloplegic refraction as the standard, the spherical equivalent refraction, sphere, and cylinder were compared to the wavefront-derived refractions using the three wavefront devices.

RESULTS

The LADARWave unit showed the highest correlation between wavefront-derived sphere and mean spherical equivalent refraction values relative to cycloplegic refraction, followed by Zywave and WaveScan. The WaveScan unit exhibited higher variability than the LADARWave or Zywave. Although Alcon Laboratories (LADARWave) and Bausch & Lomb Surgical (Zywave) recommend dilation, VISX specifically recommends against dilation in their WaveScan unit. All devices showed high cylinder error vectors when the cycloplegic cylinder was greater than 1.00 D.

CONCLUSION

Although wavefront-derived refractions appeared to correlate well to cycloplegic refractions, further research is required to reduce variability and improve the calculation of cylinder terms.