Analysis of Intrasession Repeatability of Ocular Aberrometric Measurements and Validation of Keratometry Provided by a New Integrated System in Mild to Moderate Keratoconus.

PURPOSE: To evaluate the intrasession repeatability and validity of corneal curvature measurements provided by a new multifunctional device and to assess the intrasession repeatability of its ocular aberrometric measures. METHODS: This prospective study comprises 37 mild to moderate keratoconus eyes of 37 patients. In all cases, 3 repeated measures of corneal topography and ocular aberrometry were performed with the iDesign 2 system (iD2; Johnson & Johnson Vision Care Inc, Jacksonville, FL) and one keratometric measurement was performed with the intraocular lens-(IOL) Master 500 (Carl Zeiss Meditec Inc, Dublin, CA) and Sirius (CSO) (SIR) systems. RESULTS: The within-subject SD (Sw) was <0.50 D for all iD2 keratometric measurements, with intraclass correlation coefficient (ICC) >0.980. Sw and ICC for the keratometric axis were 2.60 degrees and 0.992, respectively. Concerning aberrations, all Sw values for high-order Zernike terms were ≤0.11 µm (ICC > 0.900), and all Sw values for refraction data were <0.75 D (ICC > 0.95), except for J45. No statistically significant differences were found between the devices in any keratometric parameter evaluated (P ≥ 0.222), but the limits of agreement between the devices were clinically relevant. The magnitude of K readings and astigmatism correlated significantly with the difference in these parameters between iD2 and SIR (0.432 ≤ r ≤ 0.489, P ≤ 0.041). CONCLUSIONS: The iD2 system provides consistent measures of keratometry and ocular aberrometry in eyes with mild to moderate keratoconus. Keratometric data obtained with this system in these eyes cannot be considered as interchangeable with data provided by intraocular lens-Master 500 and SIR.

Accuracy of wavefront aberrometer refraction vs manifest refraction in cataract patients: impact of age, ametropia and visual function.

BACKGROUND: To evaluate accuracy of WASCA wavefront aberrometry (WA) refraction in comparison to manifest refraction (MR) in an older population awaiting cataract surgery. METHODS: Prospectively, refractive errors of 130 eyes were determined by WA and MR. Mean age was 65.9 (SD 11.81), corrected distance visual acuity (CDVA) averaged 0.20 logMar (SD 0.57), mean manifest sphere was 0.23 dioptres (D, SD 3.39) and manifest astigmatism amounted to -1.25 D (SD 1.21). For further analysis, refractive values were transformed into power vector components: spherical equivalent (SE), Jackson cross cylinder at 0° and 45° (J0 and J45). The 'limits of agreement' approach, regression analysis, correlation analysis, and ANOVA were applied and additionally compared to 28 healthy eyes (mean VA -0.1 logMAR) of a group of young subjects (mean age 33.9). RESULTS: SE measures in myopia correlated highly between WA and MR (r = 0.917, p < .001). In hyperopia this correlation was moderately high (r = 0.800, p < .001). For all subjects, correlations between WA and MR for J0 and J45 were r = 0.742 (p < .001) and r = 0.760 (p < .001) respectively. WA measurements revealed larger agreement ranges with increasing myopia and astigmatism. Controlled for possible confounding variables of age, VA, and refractive state, no statistically significant effects were found. Across nearly all conditions, WA measured significantly higher myopic and astigmatic values than MR. Most effects were replicated in the reference group. CONCLUSIONS: WA refraction can provide valuable information in previously under-researched conditions such as reduced VA (cataract-related), advanced age, and hyperopia. However, loss of optical media transparency will inherently reduce accuracy of WA. Further studies are needed to define cut-off values for automated wavefront quality grading and intra-operative application of WA in refractive surgery.

Precision of a commercial hartmann-shack aberrometer: limits of total wavefront laser vision correction.

PURPOSE: To assess the intrasession and intersession precision of higher-order aberrations (HOAs) measured using a commercial Hartmann-Shack wavefront sensor (Zywave; Bausch & Lomb) in refractive surgery candidates. DESIGN: Prospective, experimental study of a device. METHODS: To analyze intrasession repeatability, 1 experienced examiner measured 30 healthy eyes 5 times successively. To study intersession reproducibility, the same clinician obtained measurements from another 30 eyes in 2 consecutive sessions at the same time of day 1 week apart. RESULTS: For intrasession repeatability, excellent intraclass correlation coefficients (ICCs) were obtained for total ocular aberrations, total HOAs, and second-order terms (ICC, > 0.94). The ICCs for third-order terms also were high (ICCs, > 0.87); however, fourth-order ICCs varied from 0.71 to 0.90 (Z(4)(0) = 0.90); and fifth-order ICCs were less than 0.85. For intersession reproducibility, only total ocular aberrations, total ocular HOAs, second-order terms, Z(4)(0), Z(3)(1), and Z(3-)(3) had ICCs of 0.90 or more. Bland-Altman analysis showed that the limits of agreement (were clinically too wide for most higher-order Zernike terms, especially for the third-order terms (> 0.21 µm). CONCLUSIONS: Total ocular aberrations, total HOAs, and second-order terms can be measured reliably by Zywave aberrometry without anatomic recognition. Third-order terms and Z(4)(0) are repeatable, but not as reproducible between visits. Fourth-order terms, except for Z(4)(0), and fifth-order terms are not sufficiently reliable for clinical decision making or treatment. Because the variability of Zywave can be a major limitation of a truly successful wavefront-guided excimer laser procedure, surgeons should consider treating HOA magnitudes that are more than the intrasession repeatability values (2.77 × S(w)) as those presented in this study.

[Contemporary applications of wavefront aberrometry in ophthalmology practice]. / Wspólczesne zastosowania aberrometrii w praktyce okulistycznej.

The aim of the article is to present and summarize the current knowledge of wavefront aberrations, methods and applications of aberrations measurement. Ideal optical system is stygmatic, which means that object point is imaged by optical system into the image point without deformation. Optical system of the eye is not ideal, it has aberrations. Aberrations limitate and determine visual quality. Wavefront aberrometers measure manochromatic low and high order aberrations. Wavefront aberrations are described by Zernike polinomials. More important wavefront sensor types are described in the article. In their practice authors use KR1W Topcon aberrometer. Authors also present difficulties in taking aberrometric measurements. In recent years quality of vision becomes the point of interest for vision scientists. Correction of high order aberrations is the future of optics.

Wide two-dimensional field laser ray-tracing aberrometer.

There is an increasing interest in measuring the peripheral optical quality of the eye. Optical aberrations have been studied extensively in the center of the visual field due to the development of Hartmann-Shack wavefront sensor. However, experimental data of the peripheral field of view are still scarce, partly due to the fact that this evaluation presents various challenges. Here, we propose a novel device based on the laser ray-tracing (LRT) aberrometer, which is well suited for measuring the off-axis aberrations. The proposed instrument is able to measure a wide (±40°) 2D visual field and is based on three main design principles: spiral-shaped sampling of the visual field, real-time detection of the eye's entrance pupil, and automatic shaping and delivering of the ray bundle that optimally samples the eye pupil. We present experimental data obtained on 11 healthy subjects and a novel analysis based on a 2D quadratic model of the aberrations as a function of visual field and azimuth. The obtained results are consistent with previous findings.

Intra- and intersession repeatability of a double-pass instrument.

PURPOSE: To evaluate the intra- and intersession repeatability of the optical quality parameters provided by the Optical Quality Analysis System (OQAS), which is based on the double-pass technique. METHODS: We performed optical quality measurements using the OQAS on 20 eyes of 10 healthy subjects who had best spectacle-corrected visual acuity of 20/20 or better. Measurements were performed by the same examiner in three different sessions that were separated by 10-min intervals. The subject's eye was realigned at the beginning of each session. During each session, three consecutive measurements were taken without realignment. The following optical quality parameters were analyzed: the modulation transfer function cutoff frequency (MTFcutoff), the Strehl ratio, the OQAS values (OV) at contrasts of 100%, 20%, and 9%, and the objective scatter index (OSI). RESULTS: The mean coefficients of repeatability obtained for the first session were 4.51 (MTFcutoff), 0.049 (Strehl ratio), 0.15 (OV 100%), 0.21 (OV 20%), 0.28 (OV 9%), and 0.11 (OSI), which were similar to those found in the second and third sessions. The confidence limits in the Bland and Altman charts when the intrasession repeatability was assessed (in a comparison of the first and second measurements of the first session) ranged from -3.16 to 3.94 (MTFcutoff), -0.060 to 0.069 (Strehl ratio), -0.12 to 0.18 (OV 100%), -0.20 to 0.23 (OV 20%), -0.29 to 0.27 (OV 9%), and -0.12 to 0.13 (OSI). The same limits when the intersession repeatability was assessed (in a comparison of the first and second sessions) ranged from -5.30 to 5.49 (MTFcutoff), -0.054 to 0.050 (Strehl ratio), -0.17 to 0.17 (OV 100%), -0.22 to 0.19 (OV 20%), -0.26 to 0.29 (OV 9%), and -0.12 to 0.13 (OSI). CONCLUSIONS: Our findings showed that OQAS is a clinical instrument with a good intra- and intersession repeatability and that the realignment of the eye does not introduce any additional variability in the measurements.

Clinical comparison of 6 aberrometers. Part 1: Technical specifications.

PURPOSE: To provide a detailed assessment of the techniques, technical features, and practical use of 6 aberrometers made available to our institution from September 2002 to January 2004. SETTING: Department of Ophthalmology, University Hospital Antwerp, Antwerp, Belgium. METHODS: A number of technical and practical parameters are listed for 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 including working principles, data acquisition, aberrometer alignment, wavefront calculation, and data analysis. Operator and patient comfort as well as practical advantages and disadvantages are discussed. CONCLUSION: All devices met at least half the following parameters: alignment, correction for source wavelength, data averaging, measurement quality check, and inhibition of accommodation.