Shack-Hartmann Wave Research Articles

Interaction of Monochromatic and Chromatic Aberrations in Pseudophakic Patients.

To measure monochromatic aberrations at various wavelengths in eyes implanted with the Clareon monofocal aspheric intraocular lens (IOL) (Alcon Laboratories, Inc., Fort Worth, TX). The authors estimated longitudinal chromatic aberration (LCA), modulation transfer functions (MTFs), and the impact of interactions between chromatic and monochromatic aberrations on retinal image quality. Ten patients (age: 68.4 ± 3.21 years) were measured in two experiments: (1) Hartmann-Shack wave aberrations at five visible wavelengths (480 to 700 nm) and (2) best subjective focus at each wavelength. Objective and psychophysical LCAs were obtained from the Zernike defocus and psychophysical best focus, respectively. MTFs were calculated for the closest wavelengths to the peak sensitivity of the three cone classes (S [480 nm], M [555 nm], and L [564 nm]) using the measured aberrations and chromatic difference of focus. The degradation produced by LCA was estimated as the visual Strehl ratio for green divided by the visual Strehl ratio for blue and red. The root mean square for higher order aberrations (HOAs) ranged from 0.0622 to 0.2084 µm (700 nm, 4.3-mm pupil). Monochromatic visual Strehl ratio was above 0.35 in all patients. LCA was 1.23 ± 0.05 diopters (D) (psychophysical) and 0.90 ± 0.11 D (objective). Visual Strehl ratio decreased by a factor ranging from 1.38 to 3.82 on chromatic defocus from green to blue. There was a significant correlation between native visual Strehl ratio and the degradation produced by LCA (ie, visual Strehl555/visual Strehl480). The Clareon IOL compensates for spherical aberration, with postoperative wave aberrations dominated by astigmatism and other HOAs, being highly subject-dependent. The impact of LCA in blue is largely dependent on the magnitude of monochromatic aberrations. [J Refract Surg. 2020;36(4):230-238.].

Influence of across-pupil sutures on the optical quality of intraocular lenses.

In cases of pupillary capture after previous transscleral fixation of an intraocular lens (IOL), an across-pupil suture technique is sometimes used to stabilize the IOL. We investigated the optical effects of 10-0 polypropylene sutures placed across the pupil. Optical performance was evaluated using the optical bench metrology system, and a single-piece IOL was used in an optical bench system consisting of a model eye, a high-resolution Hartmann-Shack wave front sensor, and an image capturing device with 2.0, 3.0, 4.0, and 4.5mm apertures with distance focus. To simulate across-pupil sutures, two 10-0 polypropylene sutures were placed 2mm apart across the pupil. The focus image, spherical aberration, and image quality were measured and compared with and without sutures. When pupil size increased, spherical aberration increased, irrespective of sutures. No difference was found in spherical aberration with and without sutures, and image qualities at 17.6 and 35.2 cycles per degree were not affected by the across-pupil sutures. The differences in optical quality using across-pupil 10-0 polypropylene sutures were clinically negligible.

Night myopia is reduced in binocular vision.

Night myopia, which is a shift in refraction with light level, has been widely studied but still lacks a complete understanding. We used a new infrared open-view binocular Hartmann-Shack wave front sensor to quantify night myopia under monocular and natural binocular viewing conditions. Both eyes' accommodative response, aberrations, pupil diameter, and convergence were simultaneously measured at light levels ranging from photopic to scotopic conditions to total darkness. For monocular vision, reducing the stimulus luminance resulted in a progression of the accommodative state that tends toward the subject's dark focus or tonic accommodation and a change in convergence following the induced accommodative error. Most subjects presented a myopic shift of accommodation that was mitigated in binocular vision. The impact of spherical aberration on the focus shift was relatively small. Our results in monocular conditions support the hypothesis that night myopia has an accommodative origin as the eye progressively changes its accommodation state with decreasing luminance toward its resting state in total darkness. On the other hand, binocularity restrains night myopia, possibly by using fusional convergence as an additional accommodative cue, thus reducing the potential impact of night myopia on vision at low light levels.

A modified Hartmann–Shack aberrometer for measuring stray light in the anterior segment of the human eye

To examine the use of a modified Hartmann-Shack wave front aberrometer (WASCA; Carl Zeiss Meditec AG, Germany) to measure objective stray light caused by forward light scatter from the anterior segment of the human eye. HELIOS Klinikum Erfurt/Institute of Biomedical Engineering and Informatics, Ilmenau University of Technology, Germany. Scatter parameters, including the Michelson contrast and cross-sectional area at half height (CAHM) were examined in Hartmann-Shack images from ten subjects with a cataract in one eye and an intraocular lens (IOL) in the other. The parameters were compared between each eye. Light scatter was then measured in 40 healthy subjects (age range, 23-75 years) with spherical ametropia ranging from -0.25 to 0.25 diopters. The subjects were divided into three age groups; 23-35, 36-50, and 51-75 years. Light scatter was also measured using four alternative methods. CAHM and contrast were significantly different between the eyes with the cataract and the IOL (P = 0.007 and P = 0.004, respectively). CAHM (r = 0.557, P < 0.001) and contrast (r = -0.467, P < 0.001) were both significantly correlated with age. There were significant differences in CAHM and contrast between the age groups. The modified wave front aberrometer can be used to measure stray light, although its diagnostic sensitivity in individual patients must be improved.

基于4F系统的哈特曼-夏克传感器测量透镜焦距

基于4F系统的哈特曼-夏克传感器测量透镜焦距

基于4F系统的哈特曼-夏克传感器测量透镜焦距

基于4F系统的哈特曼-夏克传感器测量透镜焦距

哈特曼夏克波前探测器对传导冷却端面抽运板条激光放大器的波前畸变测试

哈特曼夏克波前探测器对传导冷却端面抽运板条激光放大器的波前畸变测试

Peripheral optical errors and their change with accommodation differ between emmetropic and myopic eyes

The progression of myopia is thought to be controlled by the retinal image quality, but its triggering factors are not yet well known. The differences between the peripheral optics in emmetropic and myopic eyes might explain why some eyes become myopic. The present study further investigates peripheral optical quality and how it is affected by accommodation. The refraction and aberrations of the right eyes of five emmetropes and five myopes were measured using a laboratory Hartmann-Shack wave front sensor, specially designed for peripheral measurements with an open field of view. The off-axis optical quality was assessed in steps of 10 degrees out to +/-40 degrees horizontally and +/-20 degrees vertically for two different states of accommodation (targets at 0.5 D and 4.0 D). As expected, the emmetropes had a higher relative peripheral myopia, that is, more positive c(2)(0) coefficient, than the myopes. The new results of this study are that this well-known difference was found to be asymmetric over the visual field and that it increased with accommodation. This increase was because the relative peripheral defocus profile of the myopes did not show a consistent change between far and near vision, whereas the emmetropes became relatively more myopic in the periphery with accommodation. These findings may indicate a difference between emmetropic and myopic eyes that could be an important clue to understand myopia progression.

Aberrations of the Human Eye across the Horizontal Visual Field

Aberrations of the human eyes in the horizontal visual field were measured with modified Hartmann-Shack wave front sensor. The characteristic of third to tenth order Zernike aberration rms both temporally and nasally out to 50° is as follows: considerable differences occur among subjects in the pattern of aberrations, particularly for the dominating second-order aberrations; the third to tenth order Zernike aberrations increase with the visual angle, but the increscent magnitude decreases as the Zernike order increases; in despite of imperfect symmetry, the increscent magnitude is the same on the whole; the third-order Zernike aberrations increases up to 2 times from 0° to ±50° visual angle, the forth-order up to 1.8 times, and the fifth to tenth order up to 1.7~1.3 times.

Characterization of gas targets for laser produced extreme ultraviolet plasmas with a Hartmann-Shack sensor

A table top extreme ultraviolet (EUV)-source was developed at Laser-Laboratorium Göttingen for the characterization of optical components and sensoric devices in the wavelength region from 11 to 13 nm. EUV radiation is generated by focusing the beam of a Q-switched Nd:YAG laser into a pulsed xenon gas jet. Since a directed gas jet with a high number density is needed for an optimal performance of the source, conical nozzles with different cone angles were drilled with an excimer laser to produce a supersonic gas jet. The influence of the nozzle geometry on the gas jet was characterized with a Hartmann-Shack wave front sensor. The deformation of a planar wave front after passing the gas jet was analyzed with this sensor, allowing a reconstruction of the gas density distribution. Thus, the gas jet was optimized resulting in an increase of EUV emission by a factor of two and a decrease of the plasma size at the same time.

Investigation of the propagation characteristics of excimer lasers using a Hartmann–Shack sensor

For wave front distribution measurements of excimer laser radiation, a Hartmann–Shack wave front sensor with 40×30 subapertures and a field of view adapted to the lateral laser beam profile was utilized. The peak-to-valley wave front resolution is λ/12 and the dynamic range 100λ per subaperture at 248 nm. Time-averaged propagation characteristics were determined for several combinations of resonator configuration and laser medium from the ns down to the fs pulse length regime. Above that, time-resolved measurements were carried out on a KrF excimer laser, showing a reduction of the beam divergence during the laser pulse by a factor of 1.6. This transient behavior is discussed on the basis of a simple geometrical model. The theoretical results are in qualitative agreement with the experiment.

How good can vision be?

Is 20/15 or 20/10 the best vision we can expect? We know that some patients have better corrected visual acuity than others, even with the best refractive correction in each case. Why is this the case? It may be that there is a difference in retinal receptor spacing, neurologic connections, scatter in the ocular media, some irregularity of the interfaces and/or optical aberrations. In recent years, there have been great strides made in the measurement of the optics of the eye. Instrumentation, such as the Hartmann-Shack Wave Front Analyzer, which essentially traces many rays through the pupil of the in vivo human eye, has been developed. This procedure presents a collimated beam of laser light through the pupil and then analyzes the pattern of the wave front reflected back from the retina. From the pattern of the reflected rays, the quality of the optical system is determined and the aberrations quantified. Such instrumentation allows one to analyze the optics of an individual patient’s eye. This opens the possibility to devise techniques to correct higher-order aberrations such as spherical aberration and coma. To experimentally correct the aberrations of the eye, adaptive optics has been used. Adaptive optics is used in sophisticated astronomical telescopes to correct for aberrations induced by turbulence in the atmosphere. The aberrations are corrected with either a deformable mirror (the shape of the mirror is changed in local regions to correct the aberrations) or an array of lenslets (very small lens units) where the power of each small lens unit can be changed. With such systems, higher-resolution photographs of the fundus have been obtained, including photos of individual rods.1 As this technology is advanced to the point where routine clinical measurements of ocular aberrations are possible, combined with the micronlevel lathing that now is available, it may become feasible to correct many aberrations. This could mean that 20/5 to 20/10 acuity may become common. Contact lenses are the best candidate for such corrections, as they can be maintained over the pupil. With spectacles, once you look away from the optical center of the lens the aberrations will change and one will lose the positive effect. There are a number of obstacles to be overcome. One being developing easily used clinical measuring instrumentation. Another is individual lens production to the accuracy required, although this is now possible. However, lathe-cut lenses are rotationally symmetrical which may correct some of the aberrations of the eye but many are not symmetric around the central axis. Lens movement also may be a problem. It does appear that better vision is possible. The question will be if the improvement will enhance vision enough that patients will appreciate the difference. Will the cost of the instrumentation and manufacturing make it practical? Only time and experimentation will tell. In the mean time, we need to just do a better job correcting residual astigmatism, and preventing surface drying and surface deposits.