Aberrations Of Human Eye Research Articles

Corneal higher order aberrations by Sirius topography and their relation to different refractive errors

PurposeTo compare the root mean square (RMS) of anterior corneal higher-order aberrations (HOAs) in ametropic and emmetropic eyes.MethodsThis retrospective observational study was conducted at the Department of Ophthalmology, Tishreen University Hospital, Latakia, Syria. Study eyes were divided into four groups based on refractive error: mild-to-moderate myopia, hypermetropia, myopic astigmatism, and emmetropic eyes as controls. The following anterior corneal HOAs were evaluated using the Scheimpflug-Placido Sirius (CSO, Italy) tomographer over 6 mm pupil: Root mean square (RMS) total corneal HOAs, RMS trefoil, RMS coma and RMS spherical aberrations.ResultsRMS values of total HOAs, trefoil and coma showed statistically significant differences in all four groups (P < 0.05, all). HOAs were noted to be lowest in the control group (0.18 ± 0.09, 011 ± 0.08 and 0.09 ± 0.08 μm, respectively) and highest in the myopic astigmatism group (0.31 ± 0.16, 0.15 ± 0.12, 0.17 ± 0.14 μm, respectively). RMS spherical aberration was lowest in the astigmatism group (0.00 ± 0.16 μm) with a statistically significant difference from that in the control group (0.05 ± 0.07 μm, P = 0.049).ConclusionThe mean RMS values of total HOAs, trefoil and coma were highest in the astigmatism group and lowest in the control group. However, spherical aberration was minimal in the astigmatism group. A better understanding and targeted treatment of higher-order aberrations in ametropic human eyes, and in particular eyes with astigmatism, may enhance visual quality and performance in the treatment of refractive errors. Recognising atypical HOAs may also assist in the early detection of pathological conditions such as keratoconus.

Application of Adaptive Optics in Ophthalmology

The eye, the photoreceptive organ used to perceive the external environment, is of great importance to humans. It has been proven that some diseases in humans are accompanied by fundus changes; therefore, the health status of people may be interpreted from retinal images. However, the human eye is not a perfect refractive system for the existence of ocular aberrations. These aberrations not only affect the ability of human visual discrimination and recognition, but restrict the observation of the fine structures of human eye and reduce the possibility of exploring the mechanisms of eye disease. Adaptive optics (AO) is a technique that corrects optical wavefront aberrations. Once integrated into ophthalmoscopes, AO enables retinal imaging at the cellular level. This paper illustrates the principle of AO in correcting wavefront aberrations in human eyes, and then reviews the applications and advances of AO in ophthalmology, including the adaptive optics fundus camera (AO-FC), the adaptive optics scanning laser ophthalmoscope (AO-SLO), the adaptive optics optical coherence tomography (AO-OCT), and their combined multimodal imaging technologies. The future development trend of AO in ophthalmology is also prospected.

Measurement of the peripheral aberrations of human eyes: A comprehensive review

It has been nearly 50 years since the first glimpse of the relationship between myopia and peripheral refractive errors. According to experiments on both animals and humans, the eyes with hyperopic peripheral vision appear to be at higher risk of developing myopia than those with myopic peripheral refractive errors. Despite the first measurement of peripheral refraction being achieved by a modified manual optometer, the concept of emmetropization triggered a rapidly increasing number of studies on peripheral aberrations. Not only the horizontal off-axis aberrations but also the meridional aberrations at different angles are measured by researchers during the development of peripheral aberrations measuring techniques. According to the differences among the working principles, a variety of techniques have been adopted for performing such measurements. The methods developed to realize the high-performance measurement involve the subject cooperating actively by rotating the head or eyes, the rotation of the whole optical path, and the combination of measurements of many light paths. This paper provides a review of the peripheral aberrations measuring techniques and their current status. This article also highlights the development trend of the measuring techniques of peripheral aberrations and practical applications of peripheral aberration measurements, such as the control of the accommodation, the measuring time, and the dynamic range problem of the wavefront sensor. Although wavefront sensing peripheral measurement is widely recognized for its capability to reveal both lower-order aberrations and higher-order aberrations, the efficiency of an autorefractometer is incomparable. The current study reveals that the most widely used peripheral aberration measurement methods are the use of an open field autorefractometer and Hartman-shack wavefront sensor-based techniques.

Design and characterization of a safe Shack–Hartmann type aberrometer for making in-vivo measurements: Heuristic approximation

The Shack–Hartmann technique is one of the most commonly used methods for measuring the optical aberrations of human eyes in−vivo. However, hazardous exposure could occur when the incident beam is focused on the retina if the illuminating system is not calibrated properly. This work describes in detail the steps taken to develop an experimental Shack–Hartmann type aberrometer with safe incident radiation for use on human eyes in−vivo. Preliminary results using a model eye indicate that the system is reliable. To ensure that no damage was done to the volunteer’s eyes, we decided in a heuristic approximation, to use only 2% of the maximum permissible radiation power suggested by the ANSI standard for the safe use of lasers. The ocular aberrations of a group of volunteers were measured with our system and the results were compared with those obtained with a commercial aberrometer. Despite the lower energy applied to the volunteer’s eyes, the experimental system showed to be efficient and accurate. The repeatability of the results was confirmed by comparing successive measurements of the aberrations of the experimental system, with smaller variations than those obtained with the Shack–Hartmann wavefront sensor.

Analytical method for the transformation of Zernike polynomial coefficients for scaled, rotated, and translated pupils.

Zernike polynomials provide an excellent metric basis for characterizing the wavefront aberrations of human eyes and optical systems. Since the Zernike expansion is dependent on the size, position, and orientation of the pupil in which the function is defined, it is often necessary to transform the Zernike coefficients between different pupils. An analytic method of transforming the Zernike coefficients for scaled, rotated, and translated pupils is proposed in this paper. The normalized coordinate transformation functions between the polar coordinates of the transformed pupil and the Cartesian coordinates of the original pupil are given. Based on the Cartesian and polar representations of Zernike polynomials, the coefficients' transformation matrix can be derived directly and conveniently. The first 36 terms of standard Zernike polynomials are used to validate the proposed method. For different types of transformation, transformation rules of individual Zernike terms are systematically analyzed, revealing how individual terms of the original pupil transform into terms of the transformed pupil. Numerical examples are presented to demonstrate the validity of the proposed method. Further application of the proposed method to the alignment of pupil-decentered off-axis optical systems is discussed.

Application and Development of Wavefront Sensor Technology

Wavefront sensing technology can directly test the phase distribution of wavefront distortion and has the advantages of simple operation, real-time and large dynamic range. It is widely used in adaptive optics, laser beam quality diagnosis, laser atmospheric communication, optical element and optics system detection, quantitative phase microscope, human eye aberration measurement and other fields. This paper mainly elaborates application and development of wavefront sensing technology in different fields. Combining with the research, wavefront sensing technology is utilized in the high-volume detection of aspherical mobile phone injection and the application advantages in aspheric injection molding lenses error, test efficiency and the number of quality evaluation parameters are illustrated.

Shack-Hartmann wavefront sensor with large dynamic range by adaptive spot search method.

A Shack-Hartmann wavefront sensor (SHWFS) that consists of a microlens array and an image sensor has been used to measure the wavefront aberrations of human eyes. However, a conventional SHWFS has finite dynamic range depending on the diameter of the each microlens. The dynamic range cannot be easily expanded without a decrease of the spatial resolution. In this study, an adaptive spot search method to expand the dynamic range of an SHWFS is proposed. In the proposed method, spots are searched with the help of their approximate displacements measured with low spatial resolution and large dynamic range. By the proposed method, a wavefront can be correctly measured even if the spot is beyond the detection area. The adaptive spot search method is realized by using the special microlens array that generates both spots and discriminable patterns. The proposed method enables expanding the dynamic range of an SHWFS with a single shot and short processing time. The performance of the proposed method is compared with that of a conventional SHWFS by optical experiments. Furthermore, the dynamic range of the proposed method is quantitatively evaluated by numerical simulations.

SU‐G‐IeP4‐09: Method of Human Eye Aberration Measurement Using Plenoptic Camera Over Large Field of View

Purpose:The measurement based on Shack‐Hartmann wave‐front sensor(WFS), obtaining both the high and low order wave‐front aberrations simultaneously and accurately, has been applied in the detection of human eyes aberration in recent years. However, Its application is limited by the small field of view (FOV), slight eye movement leads the optical bacon image exceeds the lenslet array which result in uncertain detection error. To overcome difficulties of precise eye location, the capacity of detecting eye wave‐front aberration over FOV much larger than simply a single conjugate Hartmann WFS accurately and simultaneously is demanded.Methods:Plenoptic camera's lenslet array subdivides the aperture light‐field in spatial frequency domain, capture the 4‐D light‐field information. Data recorded by plenoptic cameras can be used to extract the wave‐front phases associated to the eyes aberration. The corresponding theoretical model and simulation system is built up in this article to discuss wave‐front measurement performance when utilizing plenoptic camera as wave‐front sensor.Results:The simulation results indicate that the plenoptic wave‐front method can obtain both the high and low order eyes wave‐front aberration with the same accuracy as conventional system in single visual angle detectionand over FOV much larger than simply a single conjugate Hartmann systems. Meanwhile, simulation results show that detection of eye aberrations wave‐front in different visual angle can be achieved effectively and simultaneously by plenoptic method, by both point and extended optical beacon from the eye.Conclusion:Plenoptic wave‐front method possesses the feasibility in eye aberrations wave‐front detection. With larger FOV, the method can effectively reduce the detection error brought by imprecise eye location and simplify the eye aberrations wave‐front detection system comparing with which based on Shack‐Hartmann WFS. Unique advantage of the plenoptic method lies in obtaining wave‐front in different visual angle simultaneously, which provides an approach in building up 3‐D model of eye refractor tomographically.Funded by the key Laboratory of High Power Laser and Physics, CAS Research Project of National University of Defense Technology No. JC13‐07‐01; National Natural Science Foundation of China No. 61205144

Español

The usual configuration for a system that measures ocular aberrations uses an infrared beam, which is focused on the retina, in order to act as a secondary source of radiation. The back reflected light from the retina emerges through the eye's optical system modulated with the total aberrations. This aberrated wavefront is measured with a Shack-Hartmann type sensor. An ocular aberrometer, could be connected, in a closed loop, with a deformable mirror in order to assemble an experimental setup of adaptive optics (AO). It is useful in ophthalmic instruments because improves the lateral resolution. In this work, the analysis of repeatability of the measurements for an experimental setup that allows measuring the aberrations of an in-vivo human eye is shown. This system will be used as part of an adaptive optics system for a fundus camera.

Statistical characteristics of aberrations of human eyes after small incision lenticule extraction surgery and analysis of visual performance with individual eye model.

Preoperative and postoperative wavefront aberrations of 73 myopic eyes with small incision lenticule extraction surgery are analyzed in this paper. Twenty-eight postoperative individual eye models are constructed to investigate the visual acuity (VA) of human eyes. Results show that in photopic condition, residual defocus, residual astigmatism, and higher-order aberrations are relatively small. 100% of eyes reach a VA of 0.8 or better, and 89.3% of eyes reach a VA of 1.0 or better. In scotopic condition, the residual defocus and the higher-order aberrations are, respectively, 1.9 and 8.5 times the amount of that in photopic condition, and the defocus becomes the main factor attenuating visual performance.

Measurements of contrast sensitivity by an adaptive optics visual simulator

We developed an adaptive optics visual simulator (AOVS) to study the relationship between the contrast sensitivity and higher-order wavefront aberrations of human eyes. A desired synthetic aberration was virtually generated on a subject eye by the AOVS, and red laser light was used to measure the aberrations. The contrast sensitivity was measured in a psychophysical experiment using visual stimulus patterns provided by a large-contrast-range imaging system, which included two liquid crystal displays illuminated by red light emitting diodes from the backside. The diameter of the pupil was set to 4 mm by an artificial aperture, and the retinal illuminance of the stimulus image was controlled to 10 Td. Experiments conducted with four normal subjects revealed that their contrast sensitivity to a high-spatial-frequency vertical sinusoidal grating pattern was lower in the presence of a horizontal coma aberration than in the presence of a vertical coma or no aberrations (p < 0.02, Nagai method).

Comparison of wavefront aberrations in rabbit and human eyes

BackgroundThe rabbit is one of the most common animal models used for preclinical safety evaluation of new cataract surgery and laser vision‐correction technologies in ophthalmic research; however, the distributions of wavefront aberrations in rabbit eyes are unknown. The purpose of this study was to investigate the similarities and differences of wavefront aberrations between rabbit and human eyes.MethodsMonochromatic wavefront aberrations of left and right eyes of 12 rabbits and 12 human subjects with normal vision were measured by a commercial aberrometer (WaveScan Wavefront System, Abbott Medical Optics Inc, California, USA). Comparison of wavefront aberrations in rabbit and human eyes is based on a 6.0-mm pupil.ResultsThe rabbit eyes have an average spherical refraction of 1.51 ± 0.83-D and a cylindrical refraction of ‐1.03 ± 0.63-D. The average spherical refractive error of the human eyes used in this study was ‐2.03 ± 2.59-D with a cylindrical refraction of ‐1.27 ± 1.01-D. The average wavefront error root‐mean‐square (RMS) from higher‐order aberrations is 0.34 μm in rabbits (6.0-mm pupil), which is higher compared to the wavefront error RMS value of human eyes (0.26 μm). The largest higher‐order aberration in rabbit eyes is vertical coma (Z7, 0.19 ± 0.16 μm), whereas the largest higher‐order aberration in human eyes is spherical aberration (Z12, 0.07 ± 0.13 μm). Wavefront error RMS, vertical coma and some higher‐order aberrations are significantly correlated between the right and left rabbit eye.ConclusionCompared to wavefront aberrations in the human eye measured in this study, the rabbit eye has less refractive error but larger higher‐order aberrations both in wavefront error RMS and some higher‐order aberration terms. Similar to human eyes, wavefront error and some higher‐order aberrations are significantly correlated between the right and left rabbit eye.

Wavefront aberration changes caused by a gradient of increasing accommodation stimuli.

The aim of this study was to investigate the wavefront aberration changes in human eyes caused by a gradient of increasing accommodation stimuli. This is a prospective, single-site study. Healthy volunteers (n=22) aged 18-28 years whose refraction states were emmetropia or mild myopia, with astigmatism <1 diopter (D), were included in this study. After dilating the right pupil with 0.5% phenylephrine drops, the wavefront aberration of the right eye was measured continuously either without or with 1, 2, 3, 4, 5, or 6D accommodation stimuli (WFA1000B psychophysical aberrometer). The root mean square (RMS) values of the total wavefront aberrations, higher-order aberrations, and 35 individual Zernike aberrations under different accommodation stimuli were calculated and compared. The average induced accommodations using 1, 2, 3, 4, 5, or 6D accommodation stimuli were 0.848, 1.626, 2.375, 3.249, 4.181, or 5.085 D, respectively. The RMS of total wavefront aberrations, as well as higher-order aberrations, showed no significant effects with 1-3 D accommodation stimuli, but increased significantly under 4, 5, and 6 D accommodation stimuli compared with relaxed accommodation. Zernike coefficients of significantly decreased with increasing levels of accommodation. Higher-order wavefront aberrations in human eyes changed with increased accommodation. These results are consistent with Schachar's accommodation theory.

用特殊眼模型研究人眼像差与色差对视觉的影响

用特殊眼模型研究人眼像差与色差对视觉的影响

Construction of special eye models for investigation of chromatic and higher-order aberrations of eyes

An achromatic element eliminating only longitudinal chromatic aberration (LCA) while maintaining transverse chromatic aberration (TCA) is established for the eye model, which involves the angle formed by the visual and optical axis. To investigate the impacts of higher-order aberrations on vision, the actual data of higher-order aberrations of human eyes with three typical levels are introduced into the eye model along visual axis. Moreover, three kinds of individual eye models are established to investigate the impacts of higher-order aberrations, chromatic aberration (LCA+TCA), LCA and TCA on vision under the photopic condition, respectively. Results show that for most human eyes, the impact of chromatic aberration on vision is much stronger than that of higher-order aberrations, and the impact of LCA in chromatic aberration dominates. The impact of TCA is approximately equal to that of normal level higher-order aberrations and it can be ignored when LCA exists.

人眼像差校正仪视网膜动态稳像研究

The unconsciousshake of human eye leads to the random variations of image position,and makes it impossible to observe a specific area.To solve the problem,during the object imaging,a real time"calculation-movement"stabilizing image algorithm was presented based on image matching theory.It uses a series of continuously grabbed images that focus on nearly the same area of retina.Therefore,it is possible to find the center area of the image through"sampling-calculaiton",and do the correlation between the center area and that of the first image so as to get the direction and amplitude of movement,finally move the picture according the results.Repeat this process to stabilize the series of images and remove those unmatched images,which make the object image nearly on the same position.The results indicates that the algorithm can overcome the random variation problem of object image position and stabilize the retinal image in real time for the adaptive optics imaging setup;overcome the problem that one cannot focus on the same area for a long time because of laser′s strongly irritation,and realize the retina and blood capillary observation with the same setup and same algorithm;make it possible to get anpatched image with large field of view.

Diurnal Variations in Ocular Aberrations of Human Eyes

Purpose: To investigate the diurnal variations in ocular wavefront aberrations over two consecutive days in young adult subjects.Materials and methods: Measurements of both lower-order (sphero-cylindrical refractive powers) and higher-order (third and fourth-order aberration terms) ocular aberrations were collected for 30 young adult subjects at 10 different times over two consecutive days using a Hartmann–Shack aberrometer. Seventeen subjects were myopic and 13 were emmetropic. Five sets of measurements were collected each day at approximately 3 hourly intervals, with the first measurement taken at ∼9 am and the final measurement at ∼9 pm.Results: Spherical equivalent refraction (p = 0.029) and spherical aberration (p = 0.043) were both found to undergo significant diurnal variation over the two measurement days. The spherical equivalent was typically found to be at a maximum (i.e. most hyperopic) at the morning measurement, with a small myopic shift of 0.37 ± 0.15 D observed over the course of the day. The mean spherical aberration of all subjects (0.038 ± 0.048 μm) was found to be positive during the day and gradually became more negative into the evening, with a mean amplitude of change of 0.036 ± 0.02 μm. None of the other considered sphero-cylindrical refractive power components or higher-order aberrations exhibited significant diurnal variation over the two days of the experiment (p > 0.05). Except for the lower-order astigmatism at 90/180 degree (p = 0.040), there were no significant differences between myopes and emmetropes in the magnitude and timing of the observed diurnal variations (p > 0.05).Conclusions: Significant diurnal variations in spherical equivalent and spherical aberration were consistently observed over two consecutive days of measurement. Research and clinical applications requiring precise refractive error and wavefront measurements should take these diurnal changes into account when interpreting wavefront data.

An objective inspection method of visual acuity based on wave front aberrations of human eye

Visual acuity is an important vision evaluation index. Visual acuity examination has great practical and clinical significance. Objective visual acuity detection method based on the wave front aberrations of human eyes is explored in this paper. The wavefront aberrations of human eyes were measured with the Hartmann–Shack wavefront sensor and modulation transfer function was computed from the wave front aberrations. The maximum spatial resolution of human eye was obtained from modulation transfer function and the retinal aerial image modulation. Visual acuity can be derived from the maximum spatial resolution of human eye. Visual acuity of randomly selected 15 eyes was examined with the objective method based on wavefront aberrations of human eyes and with the subjective visual chart method as well. The test results show that the visual acuity values are basically the same when visual acuity is tested with the two methods. The inspection method of visual acuity based on wavefront aberrations of human eyes possesses advantages of objectivity, rapidity and accuracy, without the shortcomings of the visual chart method of slowness and subjectivity relying much on subject cognition and statement.

A method to design aspheric spectacles for correction of high-order aberrations of human eye

Aiming at the correction of high-order aberrations of human eye with spectacles, a design method of aspheric spectacles is proposed based on the eye’s wavefront aberrations data. Regarding the eyeball and the spectacles as a whole system-the lens-eye system-the surface profiles of the spectacles are achieved by optimization procedure of lens design. Different from the conventional optometry, in which the refraction prescription is acquired with a visual chart, the design takes into account the two aspects of actual human viewing, eyeball rolling and certain distinct viewing field. The rotation angle of eyeball is set to be ±20° as wearing spectacles, and the field of view is set to be ±7° which is especially important as watching screen display. The individual eye model is constructed as the main part of the lens-eye system. The Liou eye model is modified by sticking a thin meniscus lens to the crystalline lens. Then the defocus of the individual eye is transferred to the front surface of the meniscus lens, and the astigmatism and high-order aberrations are transferred to the front surface of the cornea. 50 eyes are involved in this research, among which 36 eyes have good enough visual performance already after sphero-cylindrical correction. 10 eyes have distinct improvement in vision and 4 eyes have no visual improvement by further aspheric correction. 6 typical subject eyes are selected for the aberrations analysis and the spectacles design in this paper. It is shown that the validity of visual correction of aspheric lens depends on the characteristics of the eye’s wavefront aberrations, and it is effective for the eye with larger astigmatism or spherical aberration. Compared with sphero-cylindrical correction only, the superiority taken by the aspheric correction is mainly on the improvement of MTF at a larger field of view. For the best aspheric correction, the MTF values increase by 18.87%, 38.34%, 44.36%, 51.29% and 57.32% at the spatial frequencies of 40, 80, 100, 125 and 150 cycles/mm, respectively.

Effects of single mode's high-order aberrations on visual acuity corrected using adaptive optics technique

To analyze the effects of single mode's high-order aberration on visual acuity in real time dynamically corrected using adaptive optics technique. Control study. In a dark room, twelve young healthy volunteers were administrated with 5 g/L phenylephrine to fully dilate the right eye's pupil to a diameter over 6 mm. The subjects' myopia and astigmatism were fully corrected using optical lenses. Coma, trefoil, spherical aberration and other forth-order aberrations except for spherical aberration were corrected using adaptive optics, and 100% contrast visual acuity was simultaneously measured. All single mode's high-order aberrations were fully corrected, whereas other aberrations remained unchanged. Mean visual acuity of subjects was improved by 0.021 LogMAR, 0.017 LogMAR, 0.022 LogMAR and 0.025 LogMAR after correction of coma, trefoil, spherical aberration and other forth-order aberrations except for spherical aberration, respectively. Ratio of change in visual acuity was (-0.40 ± 1.22) LogMAR/µm, (-0.20 ± 0.61) LogMAR/µm, (-0.80 ± 1.44) LogMAR/µm and (-0.30 ± 0.57) LogMAR/µm, respectively. There was a linear correlation between visual acuity after correction of single mode's different high-order aberrations and RMS of residual aberrations (R(2) = 0.13, P < 0.01). Among high-order aberrations in normal human eye, spherical aberration generates a most impact on visual acuity, followed by coma, other forth-order aberrations except for spherical aberration and trefoil. A linear correlation was found between change in visual acuity and RMS of residual aberrations.