Complete Ophthalmic Analysis System Research Articles

Fourier tools for the evaluation of refractive multifocal designs

This paper presents innovative tools and methodologies for the theoretical assessment of optical properties in refractive multifocal designs. Utilizing lens segmentation techniques and classical Fourier optics, these tools can be of help evaluating multifocal contact lenses, intraocular lenses, small aperture designs, and corneal inlays. As an example of their utility, this study presents the through-focus Visual Strehl ratios in the frequency domain of 12 multifocal contact lenses from four companies, derived from the sagittal power profiles obtained with a NIMO equipment (LAMBDA-X) for three base prescriptions (− 6.00 D, − 3.00 D, and + 1.00 D). The contact lenses are also assessed alongside higher-order aberrations obtained from 65 eyes, measured using a Wavefront Sciences Complete Ophthalmic Analysis System (AMO). Diameter variations, corresponding to individual pupil sizes (2.45–6.27 mm), were considered in the evaluation. These novel tools enable the theoretical evaluation of multifocal solutions without the need for prototypes. In the case examples presented, they differentiate between lenses tailored for different presbyopic age groups, offer guidance on optimizing hyperfocal distance in contact lens design, and underscore the relevance of the effective aperture effect. Notably, this paper introduces the pioneering conversion of sagittal powers of multifocal solutions into an equivalent wavefront and optical quality metric, with potential applications in myopia control assessments. The author hopes that readers recognize and utilize these tools to advance the field of refractive multifocality.

Accommodation lags are higher in myopia than in emmetropia: Measurement methods and metrics matter.

PurposeTo determine whether accommodative errors in emmetropes and myopes are systematically different, and the effect of using different instruments and metrics.MethodsSeventy‐six adults aged 18–27 years comprising 24 emmetropes (spherical equivalent refraction of the dominant eye +0.04 ± 0.03 D) and 52 myopes (−2.73 ± 0.22 D) were included. Accommodation responses were measured with a Grand Seiko WAM‐5500 and a Hartmann–Shack Complete Ophthalmic Analysis System aberrometer, using pupil plane (Zernike and Seidel refraction) and retinal image plane (neural sharpness—NS; and visual Strehl ratio for modulation transfer function—VSMTF) metrics at 40, 33 and 25 cm. Accommodation stimuli were presented to the corrected dominant eye, and responses, referenced to the corneal plane, were determined in the fellow eye. Linear mixed‐effects models were used to determine influence of the refractive group, the measurement method, accommodation stimulus, age, race, parental myopia, gender and binocular measures of heterophoria, accommodative convergence/accommodation and convergence accommodation/convergence ratios.ResultsLags of accommodation were affected significantly by the measurement method (p < 0.001), the refractive group (p = 0.003), near heterophoria (p = 0.002) and accommodative stimulus (p < 0.05), with significant interactions between some of these variables. Overall, emmetropes had smaller lags of accommodation than myopes with respective means ± standard errors of 0.31 ± 0.08 D and 0.61 ± 0.06 D (p = 0.003). Lags were largest for the Grand Seiko and Zernike defocus, intermediate for NS and VSMTF, and least for Seidel defocus.ConclusionsThe mean lag of accommodation in emmetropes is approximately equal to the previously reported depth of focus. Myopes had larger (double) lags than emmetropes. Differences between methods and instruments could be as great as 0.50 D, and this must be considered when comparing studies and outcomes. Accommodative lag increased with the accommodation stimulus, but only for methods using a fixed small pupil diameter.

Experimental investigation of accommodation in eyes fit with multifocal contact lenses using a clinical auto-refractor.

Multifocal or multi-zone contact lenses are increasingly being fit to young eyes in an attempt to control myopia progression. However, success in achieving this aim may depend on how much the eye accommodates. The purpose of the current work was to evaluate the ability of an open-field clinical autorefractor to measure on-axis refractive state and accommodation in eyes fit with multifocal contact lenses (CLs). Refractive state was measured with a Grand Seiko WAM-5500 autorefractor (www.grandseiko.com) and a clinical Shack-Hartmann Complete Ophthalmic Analysis System (COAS) aberrometer (www.wfsci.com) in subjects fit bilaterally with single vision aspheric contact lenses, centre distance, and centre near zonal multifocal CLs, and an experimental myopia control multi-zone bifocal CLs (MiSight). Autorefractor measurements were obtained when aligned with the pupil centre, pupil margin, and mid-periphery. Accuracy of refractive state measurements was evaluated using a fully presbyopic (62-year-old) dilated (pupil diameter = 7.1 mm) eye measured through known added spherical powers (trial lenses) of +1.00 D to +6.00 D. Refractive state and accommodation were measured for seven young myopic eyes (23.71 ± 2.87 years) with six target vergences ranging from -0.33 D to -5.00 D. Irrespective of the CL fitted, measured changes in refractive state of the calibration eye were within ≤0.25 D of the added sphere power and the slope (measured refractive state/trial lens power) was approximately -1.0 D/D for both Shack-Hartmann (COAS) aberrometer and Grand Seiko instruments. Also, the Grand Seiko data were highly repeatable (mean measurement standard deviation = 0.04 D) as long as measurements occurred at the same pupil location, but exhibited a hyperopic bias that increased to +1.00 D when eyes were fit with CLs containing significant negative spherical aberration. Centre and marginal refractive states could differ by >3.00 D due to the combined spherical aberration contained in the eye plus the different CL designs. Measured refractive states of young accommodating eyes also varied with measurement location in the pupil. The accommodation gains were similar at each pupil location, irrespective of contact lens design. With consistent sampling at the same pupil location, the open field Grand Seiko clinical autorefractor proved an effective tool for assessing the on-axis refractive state and accommodative responses of eyes fit with multi-zone bifocal and multifocal CLs.

Choroidal Thickness and Peripheral Myopic Defocus during Orthokeratology.

To investigate whether significant thickening occurs in the human choroid in response to chronic peripheral myopic defocus during overnight orthokeratology. Subjects were nine children 11 to 15 years old (mean [±SD] age, 13.61 [±1.25] years). Measurements were taken at baseline and after 1, 3, 6, and 9 months of successful orthokeratology. Choroidal thickness in central, superior, temporal, and nasal gazes were measured using the Zeiss Cirrus HD-OCT. The Lenstar LS 900 biometer provided a secondary measure of subfoveal choroidal thickness. Peripheral ocular length was measured in the same four fields of gaze with the Zeiss IOLMaster. Corneal and optical changes from orthokeratology were monitored throughout the study by corneal topography (Humphrey ATLAS), aberrometry (Complete Ophthalmic Analysis System), and central and peripheral autorefraction (Grand Seiko) after tropicamide 1% cycloplegia. All subjects had acceptable acuity and physiologic response to overnight wear. After 1 month, central refractive error (mean ± SD) became significantly less myopic (-2.25 ± 0.95 diopters [D] vs. -0.24 ± 1.03 D), keratometric values flattened by 1.6 D, the shape factor (Q) became more oblate (-0.28 ± 0.05 vs. +0.34 ± 0.41), and spherical aberration became more positive (+0.14 ± 0.08 μm vs. +0.46 ± 0.15 μm; all p = 0.008). Peripheral refractive error remained -1.0 to -3.5 D myopic in all fields of gaze throughout the study. There were no consistent, significant changes in choroidal thickness or ocular length at any retinal location during the study (all p > 0.051). Lenstar measurement of choroidal thickness was unsuccessful because of the absence of choroidal peaks associated with thicker choroids (rs = -0.66, p < 0.0001). The choroid did not show long-term thickening during orthokeratology despite the presence of substantial amounts of peripheral myopic defocus. Apparent inhibition of ocular growth was not attributed to an optical artifact of choroidal thickening, although smaller amounts of thickening or greater biological activity independent of thickening cannot be ruled out.

Predicting Through-Focus Visual Acuity with the Eye’s Natural Aberrations

To develop a predictive optical modeling process that utilizes individual computer eye models along with a novel through-focus image quality metric. Individual eye models were implemented in optical design software (Zemax, Bellevue, WA) based on evaluation of ocular aberrations, pupil diameter, visual acuity, and accommodative response of 90 subjects (180 eyes; 24-63 years of age). Monocular high-contrast minimum angle of resolution (logMAR) acuity was assessed at 6 m, 2 m, 1 m, 67 cm, 50 cm, 40 cm, 33 cm, 28 cm, and 25 cm. While the subject fixated on the lowest readable line of acuity, total ocular aberrations and pupil diameter were measured three times each using the Complete Ophthalmic Analysis System (COAS HD VR) at each distance. A subset of 64 mature presbyopic eyes was used to predict the clinical logMAR acuity performance of five novel multifocal contact lens designs. To validate predictability of the design process, designs were manufactured and tested clinically on a population of 24 mature presbyopes (having at least +1.50 D spectacle add at 40 cm). Seven object distances were used in the validation study (6 m, 2 m, 1 m, 67 cm, 50 cm, 40 cm, and 25 cm) to measure monocular high-contrast logMAR acuity. Baseline clinical through-focus logMAR was shown to correlate highly (R² = 0.85) with predicted logMAR from individual eye models. At all object distances, each of the five multifocal lenses showed less than one line difference, on average, between predicted and clinical normalized logMAR acuity. Correlation showed R² between 0.90 and 0.97 for all multifocal designs. Computer-based models that account for patient's aberrations, pupil diameter changes, and accommodative amplitude can be used to predict the performance of contact lens designs. With this high correlation (R² ≥ 0.90) and high level of predictability, more design options can be explored in the computer to optimize performance before a lens is manufactured and tested clinically.

Peripheral defocus and myopia progression in myopic children randomly assigned to wear single vision and progressive addition lenses.

To determine the effect of progressive addition lenses (PALs) and single vision lenses (SVLs) on peripheral defocus in myopic children, and to compare the effect of myopic versus hyperopic peripheral defocus on foveal myopia progression. Eighty-four myopic children aged 6 to 11 years with spherical equivalent (SE) cycloplegic autorefraction between -0.75 diopters (D) and -4.50 D were randomly assigned to wear SVLs or PALs. Aberrometry measurements of the eye and spectacles were made centrally, 30° nasally, temporally, and superiorly, and 20° inferiorly on the retina using a Complete Ophthalmic Analysis System for Vision Research (COAS-VR). The association between peripheral defocus and the 1-year change in central myopia was investigated. SVLs caused a hyperopic shift in peripheral defocus at all locations (all P ≤ 0.0003). PALs caused a myopic shift in peripheral defocus in three of four locations measured (all P ≤ 0.01) with the greatest shift superiorly due to the PAL addition (-1.04 ± 0.30 D). Superior retinal defocus when wearing either SVLs or PALs was associated with the 1-year change in central myopia. The adjusted 1-year change in central SE myopia was -0.38 D for children with absolute superior myopic defocus (n = 67) and -0.65 D for children with absolute superior hyperopic defocus (n = 17; difference = 0.27 D; P = 0.002). PALs caused a myopic shift in peripheral defocus. Superior myopic defocus was associated with less central myopia progression. These data support the continued investigation of optical designs that result in peripheral myopic defocus as a potential way to slow myopia progression. (ClinicalTrials.gov number, NCT00335049.).

The effects of spherical aberration on static accommodative responses in emmetropes and myopes

To compare the effects of spherical aberration (SA) on accommodative responses between emmetropes (EMs), stable myopes (SMs), and progressing myopes (PMs). The accommodative responses (AR) induced by negative lenses from 0 to -5 D in 1 D steps were measured with a Complete Ophthalmic Analysis System (COAS) for 10 emmetropes (EMs), 13 stable myopes (SMs), and 9 progressing myopes (PMs). Three types of AR were calculated from wavefront aberration data based on ocular foci within a paraxial area, natural pupil area, and a 3.5 mm-diameter annular pupil area. The accommodative stimulus response curves (ASRCs) were compared between the three groups and between the three AR conditions. The difference in the slope of ASRC was significant between the three AR conditions (p < 0.0001) but it was not significant between the three refractive groups. In each group, the slope of ASRC for the accommodative response measured within the paraxial area of the pupil (paraxial AR) was significantly steeper than that measured for the natural pupil (total AR) and also for that estimated for the 3.5 mm-diameter annular pupil (p < 0.01). The difference in the y-intercept of ASRC between the three AR conditions was also significant (p = 0.02) but not between the three refractive groups. The y-intercept of ASRC for paraxial AR was more positive than that for total AR in SMs (p < 0.01) and in PMs (p < 0.05); the y-intercept of ASRC for the 3.5 mm peripheral AR was more positive than that for total AR in SMs (p < 0.05). The spherical aberration of the eye has a significant effect on the slope of ASRC and is less in PMs than in EMs and SMs.

Evaluation of Image Quality Metrics for the Prediction of Subjective Best Focus

Seven existing and three new image quality metrics were evaluated in terms of their effectiveness in predicting subjective cycloplegic refraction. Monochromatic wavefront aberrations (WA) were measured in 70 eyes using a Shack-Hartmann based device (Complete Ophthalmic Analysis System; Wavefront Sciences). Subjective cycloplegic spherocylindrical correction was obtained using a standard manifest refraction procedure. The dioptric amount required to optimize each metric was calculated and compared with the subjective refraction result. Metrics included monochromatic and polychromatic variants, as well as variants taking into consideration the Stiles and Crawford effect (SCE). WA measurements were performed using infrared light and converted to visible before all calculations. The mean difference between subjective cycloplegic and WA-derived spherical refraction ranged from 0.17 to 0.36 diopters (D), while paraxial curvature resulted in a difference of 0.68 D. Monochromatic metrics exhibited smaller mean differences between subjective cycloplegic and objective refraction. Consideration of the SCE reduced the standard deviation (SD) of the difference between subjective and objective refraction. All metrics exhibited similar performance in terms of accuracy and precision. We hypothesize that errors pertaining to the conversion between infrared and visible wavelengths rather than calculation method may be the limiting factor in determining objective best focus from near infrared WA measurements.

Monochromatic aberrations of the human eye and myopia

Background: The relationship between monochromatic aberrations of the human eye and myopia has been investigated extensively over the past decade or so but the results are inconclusive. Wide age range, narrow refractive error range and large individual variations are common confounding factors in previous studies. To address these shortcomings, we conducted a two‐part study. The first part set out to determine whether the monochromatic aberrations in myopic eyes are different from those in the non‐myopic eyes in adults. Subjects were drawn from a narrow age band to minimise the confounding effect of age. The second part of this study compared the monochromatic aberrations of the more myopic and less myopic eyes of anisometropes.Methods: Monochromatic aberrations were measured for 5-mm pupils using the Complete Ophthalmic Analysis System (COAS) Wavefront Analyzer in 116 subjects with refractive spherical equivalent between ‐10.38-D and +1.38-D and in 26 anisometropes. Measurements were done in a dark room with natural pupils. The refractive errors, corneal curvatures and axial lengths of the eyes were measured under natural accommodation.Results: Highly myopic eyes had significantly smaller root mean square (RMS) values of fourth order (p = 0.015) and spherical aberrations (p = 0.009) than non‐myopic eyes. The correlation coefficient was 0.2354 (p = 0.011) between fourth‐order aberrations and refractive spherical equivalents and 0.2817 (p = 0.002) between spherical aberration and refractive spherical equivalents. Less myopic eyes of the anisometropes showed significantly larger total higher‐order, third‐order and spherical aberrations than the more myopic eyes (p < 0.05, p < 0.05 and p < 0.01, respectively).Conclusions: Our study shows that spherical aberration is associated with refractive error. More myopic eyes tended to have smaller amounts of spherical aberration, however, the ‘cause or effect’ question remains. Longitudinal studies are needed to further investigate the relationship between monochromatic aberrations and refractive development.

Comparison of two artificial tear formulations using aberrometry

Background: This study investigates the effect of artificial tears of different viscosities on aberrations of healthy eyes.Methods: We recruited subjects from the student population of the Northeastern State University Oklahoma College of Optometry. Using the Complete Ophthalmic Analysis System (COAS), aberrometry measurements were taken every second for 60-seconds with a blink every 10-seconds. We made measurements of the naked eye, then after instillation of TheraTears non‐preserved drops, and after instillation of SystanePF, a more viscous formulation. Zernike coefficients up to the sixth order were recorded and analysed. We evaluated changes in spherical and astigmatic dioptric powers and coma‐like, spherical aberration‐like and total higher‐order aberration (HOA) RMS values as a function of time.Results: Both drops yielded significantly higher values than the naked eye for HOA RMS and cylindrical power as well as a hyperopic shift in spherical equivalent (p < 0.001, paired t‐test). SystanePF, the more viscous tear, showed significantly higher values than TheraTears in HOA RMS and cylinder in all inter‐blink periods (p < 0.001, paired t‐test).Conclusions: This study shows artificial tears can have a measurable and significant impact on aberrations of healthy eyes. This effect is sustained for at least one minute and its magnitude appears to be related to the viscosity of the tear formulation.

Comparison of the ocular wavefront aberration between pharmacologically‐induced and stimulus‐driven accommodation

To compare the ocular wavefront aberration between pharmacologically- and stimulus-driven accommodation in phakic eyes of young subjects. The aberration structure of the tested eye when accommodating was measured using the Complete Ophthalmic Analysis System (COAS; AMO WaveFront Sciences, Albuquerque, NM, USA). It was used in conjunction with a purposely-modified Badal optometer to allow blur-driven accommodation to be stimulated by a high contrast letter E with a vergence range between +0.84 D and -8.00 D. Pharmacological accommodation was induced with one drop of pilocarpine 4%. Data from six subjects (age range: 23-36 years) with dark irides were collected. No correlation was found between the maximal levels of accommodative response achieved with an 8 D blur-driven stimulus and pharmacological stimulation. Pharmacological accommodation varied considerably among subjects: maximum accommodation, achieved within 38-85 min following application of pilocarpine, ranged from 2.7 D to 10.0 D. Furthermore, although the changes of spherical aberration and coma as a function of accommodation were indistinguishable between the two methods for low levels of response, a characteristic break in the pattern of aberration occurred at higher levels of pilocarpine-induced accommodation. This probably resulted from differences in the time course of biometric changes occurring with the two methods. Measuring the pilocarpine-induced accommodative response at only one time point after its application may lead to misleading results. The considerable inter-individual differences in the time course of drug-induced accommodative response and its magnitude may lead to overestimation or underestimation of the corresponding amplitude of normal, blur-driven accommodation. Stimulating accommodation by topical application of pilocarpine is inappropriate for evaluating the efficacy of 'accommodating' IOLs.

The effect of altering spherical aberration on the static accommodative response

To investigate the effect of altering the spherical aberration (SA) of the eye on the static accommodative response. Participants were fitted with nominally afocal contact lenses with controlled amounts of SA of either -0.2, -0.1, 0.0, +0.1 or +0.2 microm for a 5-mm pupil. Measurements of SA and root mean square (RMS) total aberration for the eye plus lens for each participant were determined with a Complete Ophthalmic Analysis System aberrometer. Accommodation was stimulated either by placing targets at different dioptric distances from the eye, or by using a fixed distance target and placing negative-powered lenses in front of the eye. Accommodation responses were determined with a Shin-Nippon autorefractor. For both stimuli situations, the slope of the accommodation stimulus-response function was lowest for the lenses with +0.2 microm SA, and increased as the amount of SA was reduced. There was a significant negative correlation between SA and slope. Lag of accommodation at 33 cm correlated well with added SA, but did not correlate with total RMS error. There was no significant difference between the responses at 30 min after lens wear started and the responses after 1 h. Adding negative SA to the eye generally improves the slope of the accommodation stimulus-response curve and decreases lag of accommodation, and positive added SA depresses the slope of the stimulus-response curve and increases lag. The effect seems to be specific to SA, as there was no relationship between lag and RMS error. Altering SA may be a viable way of changing accommodative functions in clinical situations.

Dynamic Simulation of the Effect of Soft Toric Contact Lenses Movement on Retinal Image Quality

To report the development of a tool designed to dynamically simulate the effect of soft toric contact lens movement on retinal image quality, initial findings on three eyes, and the next steps to be taken to improve the utility of the tool. Three eyes of two subjects wearing soft toric contact lenses were cyclopleged with 1% cyclopentolate and 2.5% phenylephrine. Four hundred wavefront aberration measurements over a 5-mm pupil were recorded during soft contact lens wear at 30 Hz using a complete ophthalmic analysis system aberrometer. Each wavefront error measurement was input into Visual Optics Laboratory (version 7.15, Sarver and Associates, Inc.) to generate a retinal simulation of a high contrast log MAR visual acuity chart. The individual simulations were combined into a single dynamic movie using a custom MatLab PsychToolbox program. Visual acuity was measured for each eye reading the movie with best cycloplegic spectacle correction through a 3-mm artificial pupil to minimize the influence of the eyes' uncorrected aberrations. Comparison of the simulated acuity was made to values recorded while the subject read unaberrated charts with contact lenses through a 5-mm artificial pupil. For one study eye, average acuity was the same as the natural contact lens viewing condition. For the other two study eyes visual acuity of the best simulation was more than one line worse than natural viewing conditions. Dynamic simulation of retinal image quality, although not yet perfect, is a promising technique for visually illustrating the optical effects on image quality because of the movements of alignment-sensitive corrections.

Validation of aberrometry‐based relative peripheral refraction measurements

To validate aberrometry-based relative peripheral refraction (RPR) measurements and to examine RPR differences in the nasal and temporal horizontal visual field. Thirty subjects underwent cycloplegia in the right eye. Ten measurements each were made centrally, 30 degrees nasally on the retina and 30 degrees temporally on the retina using the Complete Ophthalmic Analysis System (COAS) aberrometer and the Grand Seiko WR-5100K autorefractor in random order. A 2-mm COAS analysis diameter was used to approximate the Grand Seiko autorefractor measurement beam diameter. Nasal and temporal RPR were calculated as the difference between the average nasal or temporal spherical equivalent and the average central spherical equivalent. Repeated measures ANOVAs were used to test for significant differences between the RPR readings of each instrument in each retinal location (nasal or temporal) and to examine refractive error in each direction of gaze for both instruments. Central spherical equivalent refractive error as measured by the Grand Seiko autorefractor ranged from +0.63 D to -8.41 D (mean +/- S.D. = -2.63 D +/- 2.05 D). There were no significant differences between the instruments for RPR measurements (p = 0.34). The nasal RPR was significantly more hyperopic than the temporal RPR (mean +/- S.D. = +0.45 D +/- 1.04 D, p = 0.02). Spherical equivalent refractive error in all directions of gaze was more myopic with the COAS than with the Grand Seiko autorefractor (mean +/- S.D. = -0.41 D +/- 0.61 D, p < 0.0001). RPR measurements with the COAS are feasible and equivalent to those made with the Grand Seiko autorefractor. The COAS can be used to simultaneously collect RPR and peripheral aberration data. Nasal and temporal RPR measurements were significantly different in our sample.

Wavefront aberration and its association with intraocular pressure and central corneal thickness in myopic eyes

To investigate the association between intraocular pressure (IOP), central corneal thickness (CCT), or both and wavefront aberrations in the anterior cornea and the whole eye in myopia. Wenzhou Medical College, Wenzhou, Zhejiang, China. Seventy myopic subjects were tested with a Humphrey corneal topographer for wavefront aberrations in the anterior corneal surface and with a wavefront aberration-supported cornea ablation wavefront analyzer (Complete Ophthalmic Analysis System, Carl Zeiss Meditec) for wavefront aberrations in the whole eye. The IOP and CCT were measured with a noncontact Canon tonometer and a Tomey pachymeter, respectively. Relationships between the wavefront aberrations and the IOP and CCT were analyzed. Four corneal Zernike aberrations were significantly correlated with the IOP, including defocus (Z4) (r = 0.36, P<.01 for right eye; r = 0.31, P<.05 for left eye), y-axis coma (Z7) (r = 0.32, P<.05 for right eye), spherical aberration (Z12) (r = 0.34, P<.02 for both eyes), and secondary astigmatism (Z13) (r = -0.35, P<.01 for right eye; r = -0.37, P<.01 for left eye). In the whole eye, 3 Zernike aberrations were significantly correlated with IOP: trefoil (Z6) (r = 0.31, P<.05 for right eye), spherical aberration (Z12) (r = 0.34, P<.02 for right eye; r = 0.30, P<.05 for left eye), and secondary astigmatism (Z13) (r = -0.45, P<.01 for right eye; r = -0.30, P<.05 for left eye). However, only a single Zernike aberration (Z11) was significantly correlated with CCT (r = -0.29, P<.05 for right eye). Intraocular pressure was associated with wavefront aberrations in both the cornea and the whole eye, and its association was not limited to symmetrical aberrations but included asymmetric higher-order aberrations as well. In contrast, CCT was very weakly associated with wavefront aberrations.

The Precision of Wavefront Refraction Compared to Subjective Refraction and Autorefraction

To determine the precision (repeatability) of several methods of calculating refraction from higher-order wavefront aberration data and to compare these wavefront refractions with lower-order (LO) wavefront refraction, subjective refraction, and autorefraction. Four clinicians refracted 16 normal participants aged 23.6 +/- 1.2 years, 69% female with an average spherical equivalent refractive error of -3.03 +/- 2.55 D, median sphere -2.50 D (minimum -7.50, maximum +4.75), and median cylinder -0.50 D (minimum -3.00, maximum 0). Participants were cyclopleged and underwent subjective refraction, autorefraction on two machines (Nidek AR-800, Topcon KR-8000), and wavefront sensing using the Wavefront Sciences Complete Ophthalmic Analysis System. Wavefront error was used to calculate: LO refraction, refractions that incorporated higher-order spherical and astigmatism terms from up to the 4th, 6th, and 10th orders (PCM4, PCM6, and PCM10), and a method based on optimizing image quality metrics [wavefront analysis technology (WAT) refraction]. Within and between examiner agreements for total dioptric difference were determined using Bland-Altman limits of agreement (LOA). The interexaminer LOA for individual measurements for M, J0, J45 were: Topcon (+/-0.18, +/-0.10, +/-0.06), Nidek (+/-0.28, +/-0.16, +/-0.09), LO (+/-0.17, +/-0.10, +/-0.06), PCM4 (+/-0.26, +/-0.09, +/-0.06), PCM6 (+/-0.37, +/-0.17, +/-0.34), PCM10 (+/-0.54, +/-0.32, +/-0.40), WAT (+/-0.28, +/-0.20, +/-0.15), and subjective refraction (+/-0.48, +/-0.20, +/-0.13) and averaging across three measures LOA: Topcon (+/-0.15, +/-0.08, +/-0.05), Nidek (+/-0.21, +/-0.13, +/-0.07), LO (+/-0.12, +/-0.06, +/-0.04), PCM4 (+/-0.16, +/-0.05, +/-0.04), PCM6 (+/-0.23, +/-0.09, +/-0.19), PCM10 (+/-0.29, +/-0.19, +/-0.24), and WAT (+/-0.18, +/-0.12, +/-0.10). The within-examiner LOA for M, J0, J45 were: Topcon (+/-0.08, +/-0.04, +/-0.02), Nidek (+/-0.13, +/-0.07, +/-0.05 D), LO (+/-0.11, +/-0.07, +/-0.04), PCM4 (+/-0.17, +/-0.07, +/-0.04 D), PCM6 (+/-0.28, +/-0.12, +/-0.24 D), PCM10 (+/-0.42, +/-0.24, +/-0.32 D), and WAT (+/-0.19, +/-0.14, +/-0.09 D). All objective refractions except for PCM10 were more repeatable across clinicians than subjective refraction. The precision of all refractions were improved by an expected amount through averaging over multiple measurements. Wavefront refractions were not as precise as standard autorefractions, although not clinically significantly worse.

Influence of eyelid position on wavefront aberrations

To investigate the influence of eyelid position on wavefront aberrations. In study 1, the right eyes of 43 non-cyclopleged subjects were evaluated using the Complete Ophthalmic Analysis System (COAS) aberrometer. In study 2, the right eyes of the 23 cyclopleged subjects were evaluated using the Optical Pathway Difference Scan aberrometer. Measurements were made with wide-open and deliberately narrowed palpebral apertures in these subjects. In study 3, the influence of eyelashes on the COAS output was investigated in 20 subjects by placing artificial eyelashes in front of the eye, in close proximity to the natural eyelashes. For study 1, the total root mean square (RMS) of the third- and fourth-order aberrations with the wide-open lids was significantly different from the narrowed lid position after the correction for multiple comparisons. There was a difference in the Zernike coefficient of the defocus (C4), 90/180 astigmatism (C5), vertical coma (C7) and spherical aberration terms (C12) between the narrowed and wide-open positions. For study 2, changes were observed with the narrowed lid position in the overall RMS of the third and fourth orders, and total coma aberrations, as well as the specific Zernike coefficients of the C5 and C7 terms. However, none of these changes were significant after the multiple comparison correction. The corneal topography also showed remarkable changes in the superior corneal zone. Placing artificial eyelashes in front of the eye significantly affected some Zernike terms and the RMS of the second and fourth orders, and total coma aberrations, for particular pupil sizes. Deliberate narrowing of the palpebral aperture can influence the wavefront aberrations significantly. The corneal curvature distortion in response to eyelid pressure may account for some of the effect on aberration change. Eyelashes interfering with the light path within the pupil zone distort the output from the COAS, causing significant errors.

Comparison of Aberrometer and Autorefractor Measures of Refractive Error in Children

The purpose of this study was to evaluate and compare the Complete Ophthalmic Analysis System (COAS) G200 Aberrometer (Wavefront Sciences Inc., Albuquerque, NM) and Canon RK-F1 Autorefractor (Canon Inc., Tokyo, Japan) for measuring refractive errors in young children. The Sydney Myopia Study is a population-based study of refractive error and eye health in young Australian children. Cycloplegic refractions were performed on 1504 school year 1 students (mostly 6 years old) and 890 school year 7 (mostly 12 years old) students using both the COAS G200 Aberrometer and Canon RK-F1 autorefractor. Refractive data were analyzed using power vectors. Mean differences and 95% limits of agreement were determined for refractive components between the two instruments. The mean age +/- standard deviation was 6.7 +/- 0.4 years (range, 5.5-9.1 years) and 12.6 +/- 0.5 years (range, 11.1-14.4 years) for the year 1 and year 7 students, respectively. Mean paired differences for the M component (spherical equivalent) between the COAS G200 and Canon RK-F1 were <0.25 D in both age groups and were statistically significant in the year 1 group only (p < 0.001). Small significant differences were found in the astigmatic components (J0 and J45) in both groups. A smaller coefficient of agreement for the M component was found in the older group (0.54 D), whereas the coefficients of agreement of the astigmatic components (J0 and J45) were similar for both groups. The COAS G200 aberrometer was an easy-to-use instrument for the measurement of refractive error in children. In addition to being able to measure higher and lower order aberrations, the COAS G200 provides refractive error measurements comparable to those of an autorefractor.

Evaluation of a clinical aberrometer for lower-order accuracy and repeatability, higher-order repeatability, and instrument myopia

Refractive surgery has stimulated the development of aberrometers, which are instruments that measure higher-order aberrations. The purpose of this study was to test one clinical aberrometer, the Complete Ophthalmic Analysis System (COAS), for its accuracy, repeatability, and instrument myopia for measuring sphere and astigmatism and its repeatability for measuring higher-order aberrations. Aberrations of 56 normal eyes (28 subjects) were measured with and without cycloplegia using a COAS, a conventional autorefractor and by subjective refraction. We evaluated lower-order accuracy (sphere and astigmatism) of the COAS and autorefractor by comparing that data with that of subjective refraction. We also tested COAS lower- and higher-order repeatability for 5 measurements taken in less than 1 minute. We evaluated instrument myopia by comparing cycloplegic and noncycloplegic measurements of the same eye. Data were analyzed for a 5.0-mm-diameter pupil. Mean COAS spherical error was between -0.1 and +0.4 diopters (D), depending on cycloplegia and the kind of sphere power computation selected. Cylinder power errors were less than 0.1 D. COAS repeatability coefficients were better than 0.25 D, and instrument myopia was less than 0.4 D. These were comparable with those of autorefraction. Higher-order repeatability was sufficient to allow reliable measurement of normal third-order aberrations and spherical aberration. Accuracy, repeatability, and instrument myopia of the COAS are similar to those of a conventional autorefractor. Accuracy and repeatability are also similar to those of subjective refraction. Like an autorefractor, the COAS provides instantaneous, objective measurements of sphere and astigmatism, but it also measures higher-order aberrations. We found that it is capable of reliably measuring problematic higher-order aberrations and is therefore a valuable asset for modern clinical eye care.

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

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. 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. 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). 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.