Wavefront Aberrations Of Human Eyes Research Articles

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.

人眼入射波前像差和出射波前像差的差异

人眼入射波前像差和出射波前像差的差异

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.

Association analysis of accommodative microfluctuations and wavefront aberration in emmetropia and myopia in teenagers

Background When focusing on a target, the accommodative system exhibits small variations in power within a range, termed microfluctuations. Exploring the correlation between the characters of microfluctuations and the aberrations of the eyes through a critical period-teenager can deepen the understanding of the onset and development of myopia. Objective This study was to investigate the correlation between accommodative microfluctuations and wavefront aberrations of human eyes, and to explore the role of accommodative microfluctuations in the development of myopia. Methods A cross-sectional study was designed and performed. Fifty-four teenagers aged from 12 to 15 years were enrolled in this study in Eye Hospital, Wenzhou Medical University from 2010 to 2011, including 19 emmetropic subjects, 18 incipient myopic subjects and 17 progressive myopic subjects, who were chosen based on the refractive changes for the last two years. The accommodative response and microfluctuations were measured by WAM-5500 infrared autorefractor with RSVP at 25, 33 and 50 cm respectively, each RSVP distance was tested for 5 minutes. The accommodative values were divided into low frequency component (LFC) (0-0. 6 Hz), middle frequency component(MFC) (0. 6-0. 9 Hz) and high frequency component(HFC) (1. 0-1. 4 Hz) after Fourier spectrum analysis. The wavefront aberrations of the whole eye and corneal were recorded by i-Trace aberrometer and Humphrey corneal topography. The differences of accommodative response, microfluctuations and aberrations were evaluated and compared among the emmetropic group, incipient myopic group and progressive myopic group. The correlations of accommodation and aberrations were analyzed. This study followed Declaration of Helsinki, and informed consent was obtained from each subject. Results Under the 25 cm and 33 cm reading distance, the accommodative response values were (2. 78±0. 35)D and (2. 19±0. 27)D in the emmetropic group, which were significantly higher than (2. 44±0. 33)D and (1. 89±0. 35)D in the progressive myopic group (P=0. 002, 0. 003). LFC, MFC and HFC were remarkably increased as the reading distance decreased (Fdistance=8. 480, 14. 270, 21. 400; all at P 0. 05). Under the 25 cm and 33 cm reading distances, significant positive correlations were found between LFC and corneal coma, intraocular coma, whole ocular aberrations or intraocular higher order aberrations (all at P 0. 05). Conclusions In teenagers, the accommodative response of emmetropia is much stronger than that of progressive myopia, and the accommodative microfluctuation in emmetropia and incipient myopia is much less than that in progressive myopia. These shifts are possibly associated with the variability, and microfluctuations of accommodation is greater in progressive myopes than emmetropes. There are certain correlations between wavefront aberrations and accommodative microfluctuations. The refractive group differences in the accommodative microfluctuations may be related to differences in the wavefront between myopes and emmetropes. Under near reading distance, LFC is correlated with higher order aberrations. Key words: Accommodation, ocular/physiology; Myopia/physiopathology; Emmetropia; Refractive errors; Teenagers

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).

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.

Design and validation of a scanning Shack Hartmann aberrometer for measurements of the eye over a wide field of view

Peripheral vision and off-axis aberrations not only play an important role in daily visual tasks but may also influence eye growth and refractive development. Thus it is important to measure off-axis wavefront aberrations of human eyes objectively. To achieve efficient measurement, we incorporated a double-pass scanning system with a Shack Hartmann wavefront sensor (SHWS) to develop a scanning Shack Hartmann aberrometer (SSHA). The prototype SSHA successfully measured the off-axis wavefront aberrations over +/− 15 degree visual field within 7 seconds. In two validation experiments with a wide angle model eye, it measured change in defocus aberration accurately (<0.02μm, 4mm pupil) and precisely (<0.03μm, 4mm pupil). A preliminary experiment with a human subject suggests its feasibility in clinical applications.

Measurements of retinal aerial image modulation (AIM) for white light based on wave-front aberration of human eye

The aerial image modulation (AIM) curve of retina under the condition of white light is obtained based on the wave-front aberration of human eye. According to the relationship between the wavelength and defocus, we modify the monochromatic wave-front aberration data to calculate the modulation transfer function (MTF) of human eye in the white-light illumination. Combined with the measurement of contrast sensitivity function (CSF) for complete eye and visual acuity (VA) under the same luminance condition, we deduce the AIM curve in natural light. We find that AIM varies slightly at lower and intermediate spatial frequencies among different eyes; at higher frequencies AIM is the predominant factor for VA when the wave-front aberration is not significant. In addition, retinal AIM is expressed in terms of neural contrast sensitivity function (NCSF) which is the clinical valuable for ophthalmologists. Considering the real illumination circumstance, it is of practical significance to obtain the AIM curve and NCSF curve under white-light condition.

Optical study on the vision correction and supernormal vision based on the wave-front aberrations of human eye

In this paper we present the recent research results in the field of vision correction and supernormal vision according to the actual measurements of the wave-front aberrations and the corneal surface topography, the clinical detection of the visual function and the laser corneal refractive surgery, and the optimization of the optical system. These include the features of the aberrations of human eye with different pupil sizes, different fields of view and temporal accommodation, the influence of the polychromatic illumination of the visible wavelength on the supernormal vision, and the effect of the existing laser corneal refractive surgery on the wave-front aberrations of the eye. It is shown that the wave-front aberration of human eye is of temporal variation and of synthesis with multi impact factors. To achieve supernormal vision, an optimum engineering data for the customized laser corneal surgery should be firstly acquired, which may involve the dynamic free-form optical surface. Although the myopia can be corrected by the laser in situ keratomileusis (LASIK) in a certain degree, it brings about negative effects under scotopic conditions.

Evaluating Optical Quality of a Bifocal Soft Contact Lens in Near Vision Using a Shack–Hartmann Wavefront Aberrometer

To assess optical characteristics of bifocal soft contact lenses (BCLs) in use, we measured wavefront aberrations of human eyes, of eyes with a monofocal soft contact lens (MCL), and of eyes with a BCL. Modulation transfer functions (MTFs), Strehl ratios, and simulated images for far and near vision were produced with the measured aberrations. High order aberrations of subject 1 were significantly smaller than those of subject 2 (t-test, P = 0.001). We found that wearing the BCL improved the optical quality of an eye in subject 1, expressed as the horizontal MTF from 2 to 48 cycles per degree (cpd) for near vision and the Strehl ratio (t-test, P = 0.009 for Strehl ratio). But we did not find the same effect in subject 2. This difference may be due to the difference in the aberrations of the eyes of the two subjects.

Measurement of Wavefront Aberration of Human Eye Using Talbot Image of Two-Dimensional Grating

The measurement of human ocular aberration is now frequently performed because of the increase in refractive surgery on the human cornea. The Hartmann-Shack (H-S) wavefront sensor is considered to be the most useful wavefront sensor, and a calculation method for wavefront aberration has been established. New methods of measuring wavefront aberrations of human eyes, using the Talbot image of a two-dimensional grating as a wavefront sensor and local shift of the Talbot image to calculate tilt of the wavefront are shown. The shift of the Talbot image was determined by comparing the phases of fundamental spatial frequency between the grating and the local patch of the Talbot image by Fourier transformation. The actual experiment was performed using a modified commercially available wavefront analyzer. Using these methods, Talbot images were obtained from model eyes and a human eye, and wavefront shapes were successfully reconstructed. Wavefront aberrations can be measured even when the obtained image is degraded by defocusing or scattering.