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PURPOSE: To evaluate peripheral refraction and contrast detection sensitivity in pseudophakic patients implanted with a new type of inverted meniscus intraocular lens (IOL) (Art25; Voptica SL) that was designed to provide better peripheral optics. METHODS: One month after cataract surgery, in 87 eyes implanted with the Art25 IOL, peripheral contrast detection sensitivity was measured psychophysically at 40° visual angle, both horizontally and vertically, and compared with a control group of 51 eyes implanted with standard biconvex IOLs. Thirty-one eyes with the Art25 IOL and 28 eyes from the control group were randomly selected to also measure peripheral refraction using a scanning Hartmann-Shack wavefront sensor along 80° in the horizontal meridian. RESULTS: Most patients achieved emmetropia and good visual acuity, and no significant adverse events were observed after cataract surgery with Art25 IOLs. Peripheral contrast detection sensitivity was significantly better ( P < .01) in the group with the Art25 IOL in both directions (7.78 ± 3.24 vs 5.74 ± 2.60 vertical, 10.98 ± 5.09 vs 7.47 ± 3.96 horizontal), which was in agreement with the optical quality improvement in the periphery due to a reduction of defocus (1.97 and 1.21 diopters [D] at 40° temporal and nasal sides) and astigmatism (1.17 and 0.37 D at 40° temporal and nasal sides) that was statistically significant ( P < .01) from 20° of eccentricity. CONCLUSIONS: Patients implanted with a new inverted meniscus IOL present a reduced amount of peripheral defocus and astigmatism compared to patients implanted with standard biconvex IOLs. This improvement in optical quality leads to better contrast detection sensitivity measured at 40° of eccentricity. [ J Refract Surg . 2022;38(4):229–234.]

Current intraocular lenses (IOLs) are designed to substitute the cataractous crystalline lens, optimizing focus at the fovea. However, the common biconvex design overlooks off-axis performance, leading to a reduced optical quality in the periphery of the retina in pseudophakic patients compared to the normal phakic eye. In this work, we designed an IOL to provide better peripheral optical quality, closer in that respect to the natural lens, using ray-tracing simulations in eye models. The resulting design was a concave-convex inverted meniscus IOL with aspheric surfaces. The curvature radius of the posterior surface was smaller than that of the anterior surface by a factor that depended on the IOL power. The lenses were manufactured and evaluated in a custom-built artificial eye. Images of a point source and of extended targets were directly recorded at various field angles with both standard and the new IOLs. This type of IOL produces superior image quality in the whole visual field, being a better surrogate for the crystalline lens than the commonly used thin biconvex intraocular lenses.

An instrument for fast and objective measurement of the peripheral refraction in the human eye is presented. The apparatus permits the automatic estimation of both defocus and astigmatism at any retinal eccentricity by scanning a near infrared beam. The design includes a Hartmann-Shack wavefront sensor and a steering mirror, which operate in combination with a compounded eyepiece for wide field operation. The basic scanning protocol allows the estimation of refraction in a circular retinal patch of 50 deg diameter (±25 from central fixation) in 3 sec. Combined with additional fixation points, wider retinal fields can be sampled to achieve a whole field. The instrument underwent calibration and testing, and its performance for real eyes was assessed in 11 subjects of varying age and refraction. The results show high repeatability and precision. The instrument provides a new tool for the investigation of peripheral optics in the human eye.

Hartmann–Shack aberrometry is a widely used technique in the field of visual optics but, high-speed and accurate processing of Hartmann–Shack images can be a computationally expensive/resource intensive task. While some advancements have been made in achieving high-performance processing units, they have not been specifically designed for processing Hartmann–Shack images of the human eye with Graphics Processing Units. In this work, we present the first full-Graphics Processing Unit implementation of a Hartmann–Shacksensor algorithm aimed at accurately measuring ocular aberrations at a high speed from high-resolution spot pattern images. The proposed algorithm, called PaPyCS (Parallel Pyramidal Centroid Search), is inherently parallel and performs a very robust centroid search to avoid image noise and other artifacts. This is a field where the use of Graphics Processing Units have not been exploited despite the fact that they can boost Adaptive Optics systems and related closed-loop approaches. Our proposed implementation achieves processing speeds of 380 frames per second for high resolution (1280x1280 pixels) images, in addition to showing a high resilience to system and image artifacts that appear in Hartmann–Shack images from human eyes: more than 98% of the Hartmann–Shack images, with aberrations of up to 4 μ m Root Mean Square for a 5.12mm pupil diameter, were measured with less than 0.05 μ m Root Mean Square Error, which is basically negligible for ocular aberrations.

Purpose To clinically validate an adaptive optics visual simulator (VAO) that measures subjective refraction and visual acuity. Setting Optics Laboratory, University of Murcia, Murcia, Spain. Design Prospective case series. Methods Using the adaptive optics visual simulator, 2 examiners measured the subjective refraction and visual acuity in healthy eyes of volunteers; 1 examiner also used a trial frame as a gold standard. The interexaminer reproducibility and agreement with the gold standard were estimated using the following statistical parameters: limits of agreement from Bland-Altman analysis, significance between differences (P value), and intraclass correlation coefficient (ICC). Results Seventy-six eyes of 38 volunteers were measured. Interexaminer reproducibility for subjective refraction was excellent (ICC ≥0.96; P > .05), with low 95% confidence interval (CI) values for the power vectors M (spherical equivalent of the given refractive error), J0 (Jackson cross-cylinder, axes at 180 degrees and 90 degrees), and J45 (Jackson cross-cylinder, axes at 45 degrees and 135 degrees) (±0.51 diopter [D], ±0.14 D, and ±0.14 D, respectively). No significant differences in subjective refraction and visual acuity were found between the visual simulator and gold standard (P > .05), with 95% CIs for M, J0, and J45 (subjective refraction) of ±0.67 D, ±0.14 D, and ±0.16 D, respectively, and a ±0.10 logarithm of the minimum angle of resolution (visual acuity). Conclusion Subjective refraction results using the adaptive optics visual simulator agreed with those of the gold standard and can be used as the baseline for visual simulation of any optical corneal profile or intraocular lens design for refractive surgery patients.

The purpose of this work is to study the dynamics of the accommodative response as a function of the subject's refractive error, as a first step in determining whether an anomalous accommodative function could affect emmetropization or trigger myopia progression. A secondary goal was to establish potential relationships between the speed of accommodation and other parameters in the accommodation process. Parameters related to the speed and amplitude of accommodation, convergence, miosis, and change in high-order aberrations were measured during the accommodative process for 2.8 D demand in 18 young healthy subjects (mean age 25.0 ± 4.7 years) with a range of refractive errors between 0 and -7.5 D (spherical equivalent). Measurements were performed in real time (25 Hz) with an open-view binocular Hartmann-Shack (HS) sensor using a GPU-based processing unit. Correlation coefficients were calculated between refractive error and each computed variable. Additionally, the speed of accommodation was correlated with all the other parameters in the study. Correlation coefficients with refractive error had non-zero values for several parameters of the accommodative response but p-values were higher than 0.05 except in two cases: with pupil miosis speed (R = –0.49, p = 0.041) and with lag of accommodation (R = –0.57, p = 0.014). Additionally, correlation values with p-value < 0.05 were found between accommodation speed and convergence duration (R = 0.57, p = 0.014), convergence speed (R = 0.48, p = 0.044), and pupil miosis amplitude (R = 0.47, p = 0.049). We did not find strong evidence of a link between myopia and altered dynamics of the accommodation process. Only miosis speed was found to be correlated to refractive error with p

An efficient and robust pupil tracking system is an important tool in visual optics and ophthalmology. It is also central to techniques for gaze tracking, of use in psychological and medical research, marketing, human–computer interaction, virtual reality and other areas. A typical setup for pupil tracking includes a camera linked to infrared LED illumination. In this work, we evaluate and parallelize several pupil tracking algorithms with the aim of accurately estimating the pupil position and size in both eyes simultaneously, to be applied in a high-speed binocular pupil tracking system. To achieve high processing speed, the original non-parallel algorithms have been parallelized by using CUDA and OpenMP. Modern graphics processors are designed to process images at high temporal frequencies and spatial resolution, and CUDA enables them to be used for general-purpose computing. Our implementation allows for efficient binocular pupil tracking at high speeds for high-resolution images (up to 988 fps with images of $$1280\times 1024$$ pixels) using a state-of-the-art GPU.

Spatial Light Modulators (SLMs) are widely used in several fields of optics such as adaptive optics. SLMs based on Liquid Crystal (LC) devices allow a dynamic and easy representation of two-dimensional phase maps. A drawback of these devices is their elevated cost, preventing a massive use of the technology. We present a more affordable approach based on the serial arrangement of vertical aligned LC devices, with characteristics of phase modulation similar to a widely used parallel aligned LC device. We discuss the peculiarities of the approach, the performance and some potential areas of applications.

PURPOSE Quality of vision in patients who have undergone corneal refractive surgery depends upon the optimal centration of the procedures used. The center of the pupil is used as a reference point in some corneal ablation procedures. The achromatic axis would be a more sensible option from an optical point of view, but it is not as readily detectable. As an alternative, other refractive techniques, like the small aperture corneal inlay for presbyopia correction, use the corneal reflex (first Purkinje image). To assess the relative position of these two marks, we developed a new instrument to simultaneously measure both the first Purkinje image (PI) and the intersection of the achromatic axis with the pupil plane. METHODS The apparatus records images of the pupil and the PI when illuminated with a circle of infrared light-emitting diodes. A second optical path allows determination of the achromatic axis by using a subjective method. Both the positions of the PI and the achromatic axis intersection are determined simultaneously. RESULTS A series of data were obtained in 48 eyes. The mean location of the achromatic point relative to the PI was [x = -0.05 ± 0.15 mm; y = 0.09 ± 0.18 mm]. Considered individually, in 55% of eyes, the distance between locations is less than 0.2 mm, and in 95% of eyes, distances are less than 0.4 mm. CONCLUSIONS On average, achromatic axis crossing of the pupil and PI locations coincides within measurement errors. Although there was some intersubject variability, differences in location were less than 0.6 mm in all measured eyes.

Presbyopia, the loss of the eye’s accommodation capability, affects all humans aged above 45–50 years old. The two main reasons for this to happen are a hardening of the crystalline lens and a reduction of the ciliary muscle functionality with age. While there seems to be at least some partial accommodating functionality of the ciliary muscle at early presbyopic ages, it is not yet clear whether the muscle is still active at more advanced ages. Previous techniques used to visualize the accommodation mechanism of the ciliary muscle are complicated to apply in the older subjects, as they typically require fixation stability during long measurement times and/or to have an ultrasound probe directly in contact with the eye. Instead, we used our own developed method based on high-speed recording of lens wobbling to study the ciliary muscle activity in a small group of pseudophakic subjects (around 80 years old). There was a significant activity of the muscle, clearly able to contract under binocular stimulation of accommodation. This supports a purely lenticular-based theory of presbyopia and it might stimulate the search for new solutions to presbyopia by making use of the remaining contraction force still presented in the aging eye.

Pupil tracking under infrared illumination is an important tool for many researchers in physiological visual optics and ophthalmology. It is also a relevant topic for gaze tracking which is used in psychological and medical research, marketing, human-computer interaction, virtual reality and other areas. A typical setup can be either a low-cost webcam with some infrared LEDs or glasses with mounted cameras and infrared illumination. In this work, we evaluate and parallelize several pupil tracking algorithms with the aim of estimating the pupil's position and size with high accuracy in order to develop a high-speed pupil tracking system. To achieve high processing speed the original non-parallel algorithms have been parallelized by using CUDA and OpenMP. Graphics cards are designed to process images at very high frequencies and resolutions, and CUDA enables them to be used for general purpose computing. Our experimental results show that pupil tracking can be efficiently performed at high speeds with high-resolution images (up to 530 Hz with images of 1280x1024 pixels) using a state-of-the-art GP-GPU.

The chromatic behavior of diffractive optical elements, exhibiting 2π-wrapped phase profiles, implemented into liquid crystal spatial light modulators (LC-SLM) is described. A wrapped phase map is only equivalent to the original continuous profile for the design wavelength while at other wavelengths there are unwanted phase jumps and the profile does not correspond to a pure defocus. For those conditions the wrapped profile behaves as a multiple order lens (multi-focal lens). The optical power dispersion for each order is linearly proportional to the wavelength, while the energy of each order depends on the design wavelength and the material dispersion. For practical purposes, for most of the visible range only first order (main defocus) is relevant but two other orders may also be considered depending on the actual PSF of the system. As an application, we demonstrate that the longitudinal chromatic aberration of the eye can be compensated by the diffractive lens dispersion when the appropriate defocus is programmed into the SLM.

Corneal small aperture inlays provide extended depth of focus as a solution to presbyopia. As this procedure is becoming more popular, it is interesting to compare its performance with traditional approaches, such as monovision. Here, binocular visual acuity was measured as a function of object vergence in three subjects by using a binocular adaptive optics vision analyzer. Visual acuity was measured at two luminance levels (photopic and mesopic) under several optical conditions: 1) natural vision (4 mm pupils, best corrected distance vision), 2) pure-defocus monovision ( + 1.25 D add in the nondominant eye), 3) small aperture monovision (1.6 mm pupil in the nondominant eye), and 4) combined small aperture and defocus monovision (1.6 mm pupil and a + 0.75 D add in the nondominant eye). Visual simulations of a small aperture corneal inlay suggest that the device extends DOF as effectively as traditional monovision in photopic light, in both cases at the cost of binocular summation. However, individual factors, such as aperture centration or sensitivity to mesopic conditions should be considered to assure adequate visual outcomes.

A novel LCoS device capable for 6-Pi phase modulation was confronted to a 2-Pi LCoS system. Chromatic aberration was significantly smaller than in the eye. The 6-Pi LCoS device presents advantages for being incorporated in AO for visual applications.

The spatio-temporal Fourier transform is usually applied to determine the velocity of an object from a series of standard light intensity frames. In this paper the technique has been extended to determine the object acceleration. The techniques for velocity and acceleration determination based on the spatio-temporal Fourier transform have been applied to experimental low light level images. Under these conditions, the processing time is reduced so that, in those cases in which it is necessary to quickly obtain the object velocity or acceleration, low light level conditions would be advantageous, using intensity filters if necessary.

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.

We have developed a hybrid adaptive optics visual simulator, combining two different phase manipulation technologies: an optically-addressed liquid crystal phase modulator, with a relatively slow temporal response but capable of producing abrupt or discontinuous phase profiles with high fidelity; and a membrane deformable mirror, restricted to smooth profiles but with a temporal response allowing close-loop compensation of the eye's aberration fluctuations. As proof of concept, objective results as a function of defocus are presented for a phase element structured as discontinuous radial sectors, generated with the liquid crystal modulator while the deformable mirror was used to correct the system aberrations and, further, to introduce the aberrations of two real subjects. The hybrid adaptive optics visual simulator is specially intended as a tool for developing new ophthalmic optics elements, where it opens the possibility to explore designs with irregularities and/or discontinuities.

A novel adaptive optics system is presented for the study of vision. The apparatus is capable for binocular operation. The binocular adaptive optics visual simulator permits measuring and manipulating ocular aberrations of the two eyes simultaneously. Aberrations can be corrected, or modified, while the subject performs visual testing under binocular vision. One of the most remarkable features of the apparatus consists on the use of a single correcting device, and a single wavefront sensor (Hartmann-Shack). Both the operation and the total cost of the instrument largely benefit from this attribute. The correcting device is a liquid-crystal-on-silicon (LCOS) spatial light modulator. The basic performance of the visual simulator consists in the simultaneous projection of the two eyes' pupils onto both the corrector and sensor. Examples of the potential of the apparatus for the study of the impact of the aberrations under binocular vision are presented. Measurements of contrast sensitivity with modified combinations of spherical aberration through focus are shown. Special attention was paid on the simulation of monovision, where one eye is corrected for far vision while the other is focused at near distance. The results suggest complex binocular interactions. The apparatus can be dedicated to the better understanding of the vision mechanism, which might have an important impact in developing new protocols and treatments for presbyopia. The technique and the instrument might contribute to search optimized ophthalmic corrections.

Liquid crystal on Silicon (LCOS) spatial phase modulators offer enhanced possibilities for adaptive optics applications in terms of response velocity and fidelity. Unlike deformable mirrors, they present a capability for reproducing discontinuous phase profiles. This ability also allows an increase in the effective stroke of the device by means of phase wrapping. The latter is only limited by the diffraction related effects that become noticeable as the number of phase cycles increase. In this work we estimated the ranges of generation of the Zernike polynomials as a means for characterizing the performance of the device. Sets of images systematically degraded with the different Zernike polynomials generated using a LCOS phase modulator have been recorded and compared with their theoretical digital counterparts. For each Zernike mode, we have found that image degradation reaches a limit for a certain coefficient value; further increase in the aberration amount has no additional effect in image quality. This behavior is attributed to the intensification of the 0-order diffraction. These results have allowed determining the usable limits of the phase modulator virtually free from diffraction artifacts. The results are particularly important for visual simulation and ophthalmic testing applications, although they are equally interesting for any adaptive optics application with liquid crystal based devices.

Retinal sampling poses a fundamental limit to resolution acuity in the periphery. However, reduced image quality from optical aberrations may also influence peripheral resolution. In this study, we investigate the impact of different degrees of optical correction on acuity in the periphery. We used an adaptive optics system to measure and modify the off-axis aberrations of the right eye of six normal subjects at 20 degrees eccentricity. The system consists of a Hartmann-Shack sensor, a deformable mirror, and a channel for visual testing. Four different optical corrections were tested, ranging from foveal sphero-cylindrical correction to full correction of eccentric low- and high-order monochromatic aberrations. High-contrast visual acuity was measured in green light using a forced choice procedure with Landolt C's, viewed via the deformable mirror through a 4.8-mm artificial pupil. The Zernike terms mainly induced by eccentricity were defocus and with- and against-the-rule astigmatism and each correction condition was successfully implemented. On average, resolution decimal visual acuity improved from 0.057 to 0.061 as the total root-mean-square wavefront error changed from 1.01 mum to 0.05 mum. However, this small tendency of improvement in visual acuity with correction was not significant. The results suggest that for our experimental conditions and subjects, the resolution acuity in the periphery cannot be improved with optical correction.

The concept of Adaptive Optics Visual Simulation applies to the use of an Adaptive Optics system to manipulate ocular aberrations in order to perform visual testing through a modified optics. It can be of interest both to study the visual system and to design new ophthalmic optical elements. In this work, we describe an apparatus based on a liquid crystal programmable phase modulator and explore its capabilities as a tool in the early stages of the design of ophthalmic optical elements with increased depth of field for presbyopic subjects. To illustrate the potential of the instrument, we analyze the performance of two phase profiles obtained by a hybrid optimization procedure. The liquid crystal Adaptive Optics Visual Simulator can be used to experimentally record the point spread function for different vergences in order to objectively measure depth of focus, to perform different psychophysical experiments through the phase profile in order to measure its impact on visual performance, and to study the interaction with the eye's particular aberrations. This approach could save several steps in current procedures of ophthalmic optical design and eventually lead to improved solutions.

We have designed and assembled an instrument for objective measurement of the eye’s wave aberrations for different wavelengths with no modifications in the measurement path. The system consists of a Hartmann-Shack wave-front sensor and a Xe-white-light lamp in combination with a set of interference filters used to sequentially select the measurement wavelength. To show the capabilities of the system and its reliability for measuring at different wavelengths, the ocular aberrations were measured in three subjects at 440, 488, 532, 633 and 694 nm, basically covering the whole visible spectrum. Even for the shortest wavelengths, the illumination level was always several orders of magnitude below the safety limits. The longitudinal chromatic aberration estimates and the wavelength dependence of coma and spherical aberration, as examples of higher-order aberration terms, were compared to the predictions of a chromatic eye model, with good agreement. To our knowledge, this is the first report of a device to objectively determine the spectral fluctuations in the ocular wavefront.

To explore the impact of spherical aberration (SA) on contrast sensitivity using an adaptive optics vision simulator to determine the optimal amount of SA to include in customized corrections of wavefront aberrations.Laboratorio de Optica, Universidad de Murcia, Murcia, Spain, and AMO Groningen BV, Groningen, The Netherlands.An adaptive optics vision simulator consisting of a wavefront sensor, a 97-segmented deformable mirror to induce and correct aberrations of the eye, and a visual testing path was constructed for this study. The deformable mirror allows the effective ocular wavefront aberration to be manipulated and the resulting visual performance to be measured simultaneously. Subjective measurements of contrast sensitivity at 15 cycles per degree were performed with a 4.8 mm pupil in 5 subjects with different levels of naturally occurring SA. Contrast sensitivity was measured when SA values of -0.09 microm, 0.0 microm, 0.09 microm, and 0.182 microm were induced when the other natural aberrations of the eye were present, when the aberrations were corrected, and at defocus values of +/-0.25 diopter (D) and +/-0.50 D.Subjects experienced peak contrast sensitivity performance with varying levels of SA when their natural aberrations were present; however, average contrast performance peaked at 0 mum of SA. When all higher-order aberrations were corrected, all 5 subjects' peak performance occurred at 0 microm of SA.The adaptive optics vision simulator reduced the root-mean-square wavefront aberration of the eye by up to a factor of 4 and allowed noninvasive testing of the visual performance resulting from any ocular wavefront aberration introduced by customized correction procedures. This study showed that, on average, contrast performance peaked when SA was completely corrected.

The human eye is affected by large chromatic aberration. This may limit vision and makes it difficult to see fine retinal details in ophthalmoscopy. We designed and built a two-triplet system for correcting the average longitudinal chromatic aberration of the eye while keeping a reasonably wide field of view. Measurements in real eyes were conducted to examine the level and optical quality of the correction. We also performed some tests to evaluate the effect of the corrector on visual performance.

We have studied the temporal dynamics of the near response (accommodation, convergence and pupil constriction) in healthy subjects when accommodation was performed under natural binocular and monocular viewing conditions. A binocular open-view multi-sensor based on an invisible infrared Hartmann-Shack sensor was used for non-invasive measurements of both eyes simultaneously in real time at 25Hz. Response times for each process under different conditions were measured. The accommodative responses for binocular vision were faster than for monocular conditions. When one eye was blocked, accommodation and convergence were triggered simultaneously and synchronized, despite the fact that no retinal disparity was available. We found that upon the onset of the near target, the unblocked eye rapidly changes its line of sight to fix it on the stimulus while the blocked eye moves in the same direction, producing the equivalent to a saccade, but then converges to the (blocked) target in synchrony with accommodation. This open-view instrument could be further used for additional experiments with other tasks and conditions.

Three-dimensional ultrahigh resolution optical coherence tomography (UHR OCT) and adaptive optics (AO) are combined using a liquid crystal programmable phase modulator (PPM) as a correcting device for the first time. AO is required for correcting ocular aberrations in moderate and large pupils in order to achieve high resolution retinal images. The capabilities of the PPM are studied using polychromatic light. Volumetric UHR OCT images of the living retina with AO, obtained with up 25000 A scans/s and high resolution (~5x5x3 µm; transverse (x) x transverse (y) x axial) are recorded, enabling visualization of interesting intraretinal morphological structures. Cellular retinal features, which might correspond to groups of terminal bars of photoreceptors at the level of the external limiting membrane, are resolved. Benefits and limitations of the presented technique are finally discussed.

The prospects to combine AO and OCT both theoretically and experimentally are presented. The possibility to significantly improve the performance of ophthalmic UHR OCT systems by means of AO is proved. Moreover, the expected transversal resolution when using larger pupil sizes in the eye in combination with AO should enable the study for the first time of many retinal structures never detected before in the living retina

Reflection densitometry has been widely used to measure the density difference of the bleachable cone photopigments in human eyes. Most such measurements make a series of assumptions concerning the amount of scattered light to derive an estimate of the true cone photopigment density from the density difference measurements. The current study made three types of measurements of the light returning from the eye before and after bleaching: the amount of light returning in the “directed” reflection, which is a double-pass estimate of the cone photopigment density; the amount of light in undirected or diffuse reflection; and the amount of fluorescence from lipofuscin in the RPE, which provides a single-pass measurement of optical density difference. For a 1 deg foveally fixated field, the density difference estimates for the three measurements were 0.68, 0.21, and 0.22 respectively. The lipofuscin fluorescence was found to be unguided. The background density difference was non-negligible and very close to the single pass estimate from fluorescence. These measurements each involve potentially different pathways of light through the retina, and therefore place different constraints on models of these pathways. A simple model comparing the directional and the fluorescence optical densities produced retinal coverage estimates around 70–75%. Estimates of the shape factor of the single pass optical Stiles–Crawford effect were evaluated from the dark-adapted and bleached fluorescence measurements. The values were closer to those obtained from psychophysical methods than to the double pass optical Stiles–Crawford shape factors obtained directly from retinal reflectometry.

A liquid crystal programmable phase modulator (PPM) is used as correcting device in an adaptive optics system for three-dimensional ultrahigh-resolution optical coherence tomography (UHR OCT). The feasibility of the PPM to correct high order aberrations even when using polychromatic light is studied, showing potential for future clinical use. Volumetric UHR OCT of the living retina, obtained with up 25,000A-scans/s and high resolution enables visualization of retinal features that might correspond to groups of terminal bars of photoreceptors at the external limiting membrane.

A liquid crystal programmable phase modulator (PPM) was evaluated acting as the active element on an adaptive optics system. This device (Hamamatsu X7550) consists of an optically-addressed liquid crystal spatial light modulator coupled to an intensity light modulator through an optical system that removes pixelation. Therefore, it is theoretically free from the diffraction patterns produced by the pixel structure in the electrically-addressed liquid crystal devices.

Measurement of the eye’s wave aberrations has become fairly standard in recent years. However, most studies have not taken into account the possible influence of the polarization state of light on the wave aberration measurements. The birefringence properties of the eye’s optical components, in particular corneal birefringence, can be expected to have an effect on the wave aberration estimates obtained under different states of polarization for the measurement light. In the work described, we used a psychophysical aberrometer (the spatially resolved refractometer) to measure the effect of changes in the polarization state of the illumination light on the eye’s wave aberration estimates obtained in a single pass. We find, contrary to our initial expectation, that the polarization state of the measurement light has little influence on the measured wave aberration. For each subject, the differences in wave aberrations across polarization states were of the same order as the variability in aberrations across consecutive estimates of the wave front for the same polarization conditions.

We have designed and built a binocular Hartmann-Shack wave-front sensor using a single microlens array and camera for real-time aberration measurement of both eyes in an open-view configuration. Furthermore, the use of a long wavelength (1050 nm) laser diode makes the illumination source completely invisible, so that measurements can be unobtrusively performed while the subject stares at the visual world under realistic conditions. The setup provides a large dynamic range and simultaneous measurements of convergence, pupil size, accommodation, and aberrations. The open-view design not only offers the possibility of measuring the subject's ocular optics under natural conditions but also allows coupling the device with other existing vision testing instruments and setups, which increases its potential to become a powerful tool for different visual optics studies.

Correction of spherical (SA) and longitudinal chromatic aberrations (LCA) significantly improves monocular visual acuity (VA). In this work, the visual effect of SA correction in polychromatic and monochromatic light on binocular visual performance is investigated. A liquid crystal based binocular adaptive optics visual analyzer capable of operating in polychromatic light is employed in this study. Binocular VA improves when SA is corrected and LCA effects are reduced separately and in combination, resulting in the highest value for SA correction in monochromatic light. However, the binocular summation ratio is highest for the baseline condition of uncorrected SA in polychromatic light. Although SA correction in monochromatic light has a greater impact monocularly than binocularly, bilateral correction of both SA and LCA may further improve binocular spatial visual acuity which may support the use of aspheric-achromatic ophthalmic devices, in particular, intraocular lenses (IOLs).

We evaluated the performance of a liquid-crystal spatial light modulator for static correction of the aberrations in the human eye. By applying phase-retrieval techniques to pairs of double-pass images we first estimated the wave aberration of the eye to be corrected. Then we introduced the opposite phase map in the modulator, which was placed in a plane conjugated with the eye’s pupil, and we recorded double-pass images of a point source before and after correction of the aberrations. In a slightly aberrated artificial eye a clear improvement was obtained after correction, and, although diffraction-limited performance was not achieved, the results were close to the theoretical predictions. In the two living eyes that we studied some benefit also appeared in the correction, but the performance was worse than that expected. We evaluated possible explanations for the relatively poor performance that was obtained in the human eye: an incorrect estimate of the ocular aberration, the limited spatial resolution of the modulator, and the dynamic changes in the ocular aberrations. Based on the results in the artificial eye, the first problem was not considered to be a major source of error. However, we showed that the spatial resolution of the liquid-crystal spatial light modulator limits the maximum correction to be attained. In addition, the changes in the ocular optics over time also impose a limit in the performance of static corrections.

The spatio-temporal Fourier transform is usually applied to determine the velocity of an object from a series of standardlight intensity frames. In this paper the technique is extended to also determine the object acceleration. Although thistechnique is useful in standard illumination conditions, we have applied it to experimental low-light-level images, whichrequire a shorter processing time.KEYWORDS: Acceleration measurement, Low-light-level images, Spatio-temporal Fourier transform.1. INTRODUCTIONThe tracking of a moving object from series of images is an interesting topic with applications in many different fieldsas, for example, free-space laser communications1 ,robotguidance2, etc. The simplest procedure to track an object is todetermine its centroid3. However, the spatio-temporal Fourier transform of a series of frames has been proved to be anattractive alternative technique for the object velocity determination4. This technique has already been analyzed fromdifferent points of view57 providing good results even under adverse conditions8.One of the difficulties that presents the spatlo-temporal Fourier transform is its sensitivity to the presence of anacceleration different from zero. In this case it is not possible to obtain good estimates of the velocity using this technique.For low acceleration values, this technique provides velocity estimates different from the exact value. If the acceleration ishigh, it is not possible to obtain any velocity estimate applying this technique.To solve this problem, a new technique based on the spatio-temporal Fourier transform has been developed to obtainnot only the velocity but also the acceleration. Once the acceleration has been estimated, the determination of the velocityis possible.The technique has been checked using series of experimental low-light-level frames. The use of this kind of imagesprovides a fairly good estimation accuracy, reducing the processing time required to characterize the object movement9'10.2. THE SPATIO-TEMPORAL FOURIER TRANSFORMTo develop the spatio-temporal Fourier transform technique we assume an object moving over a negligible background.We will consider two possible types of movements: constant velocity and constant acceleration.Let us consider a moving object. The image at time c1, described by i(x,t), is related to the image at time tjby

Two methods to obtain the autocorrelation central value from clipped photon-counting data are presented. They are based on the statistical analysis of the total number of counts in one frame. One of themethods requires a smaller number of frames to provide a good statistical accuracy while the other has a wider intensity range of applicability. These are the first techniques that overcome the problem of the autocorrelation central hole due to the clipping in photon-counting detection. I .- INTRODUCTION The autocorrelation (AC) and its Fourier transform, the power spectrum, are moving-invariantfunctions which are commonly used in image recovery from a series of photon-limited frames[i ,2]. For faint moving sources, the short exposure time necessary to freeze the image and the low photon-countingrate cause one frame to be composed of only a few photoevents.To obtain each frame, photon-counting detectors must be used and a gain of about 5x1 O allows singlephotoevent detection. Due to the image intensifier properties, the photoevents are extended spots. When aCOD or similar equipment is used to record the image, the spread of each photoevent makes it impossibleto distinguish between photons which are too close and therefore are considered as a single count. Thisproduces the photon counting hole in the AC function[3]. The clipping can be considered as a simplifiedmodel of this problem[4]. In clipped detection, two photons arriving to the same pixel are considered as asingle count. This makes the AC central value to be equal to zero, producing a one-pixel hole. This holemakes object recovery from the clipped AC function impossible.The influence of clipped detection on the AC function has been widely studied[5,6J. Several techniqueshave been developed to overcome the problem[4,7]. All of these techniques are based on the statisticalanalysis of the photon rate in each pixel of the frame. However, it can be demonstrated that this kind ofanalysis cannot give better results than the direct evaluation of the clipped AC. Moreover, none of theseprocedures are able to evaluate the central value of the AC.In this paper we propose two methods to obtain the AC central value from clipped data, based on the

We propose a technique to obtain directly from a series of photon-limited frames, the spectrum of an object moving with constant velocity. Instead os averaging statistical functions as the auto or triple correlations or their Fourier transforms, our method averages the series of frame spectra once the phase factor due to the movement has been removed. Two different procedures to obtain this phase factor are studied: the temporal derivative of the spectrum logarithm and the temporal Fourier transform of the series of spatial spectra. The latter method involves a larger number of calculations but it produces much better results, especially when only a small number of frames are available. Finally, the recovery technique is checked for a simulated experiment in which a one-dimensional object is reconstructed from a short series of photon-limited frames.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We have developed a hybrid adaptive-optics visual simulator (HAOVS), combining two different phase-manipulation technologies: an optically addressed liquid-crystal phase modulator, relatively slow but capable of producing abrupt or discontinuous phase profiles; and a membrane deformable mirror, restricted to smooth profiles but with a temporal response allowing compensation of the eye's aberration fluctuations. As proof of concept, a phase element structured as discontinuous radial sectors was objectively tested as a function of defocus, and a correction loop was closed in a real eye. To further illustrate the capabilities of the device for visual simulation, we recorded extended images of different stimuli through the system by means of an external camera replacing the subject's eye. The HAOVS is specially intended as a tool for developing new ophthalmic optics elements, where it opens the possibility to explore designs with irregularities and/or discontinuities.

We propose a series of procedures to construct an image as similar as possible to that detected in good illumination conditions (standard image), starting from a low light level (L3) image. In L3 conditions, only a small number of photopulses are detected in the whole image area. An image taken in these conditions appears like a few isolated light points over a dark background. This makes it nearly impossible to recognize an object represented on it. We have developed a method based on the L3 image statistics in order to estimate the intensity received by each pixel. This method consist of a spatial average performed by a photon counting mask and can be used to construct a standard image from only one L3 image. As a second step, we have studied some histogram operations to eliminate the heavy statistics dependence that remains in the post-mask image. The best results correspond to the histogram specification but, to perform it, it would be necessary to know the standard image histogram. The last step of our work is the development of a fitting method to obtain this standard image histogram. This fitting is based on the statistical behavior of the L3 image and can be done using only a post-mask histogram as data.

A compact mode-locked Ti:sapphire laser, emitting a broad spectrum of 277 nm bandwidth, centered at 790 nm, was used to measure the dependence of the aberrations of the human eye with wavelength in the near infrared region. The aberrations were systematically measured with a Hartmann-Shack wave-front sensor at the following wavelengths: 700, 730, 750, 780, 800, 850, 870 and 900 nm, in four normal subjects. During the measurements, the wavelengths were selected by using 10 nm band-pass filters. We found that monochromatic high order aberrations, beyond defocus, were nearly constant across 700 to 900 nm wavelength in the four subjects. The average chromatic difference in defocus was 0.4 diopters in the considered wavelength band. The predictions of a simple water-eye model were compared with the experimental results in the near infrared. These results have potential applications in those situations where defocus or higher order aberration correction in the near infrared is required. This is the case of many imaging techniques: scanning laser ophthalmoscope, flood illumination fundus camera, or optical coherence tomography.

Merging of ultrahigh-resolution optical coherence tomography (UHR OCT) and adaptive optics (AO), resulting in high axial (3 microm) and improved transverse resolution (5-10 microm) is demonstrated for the first time to our knowledge in in vivo retinal imaging. A compact (300 mm x 300 mm) closed-loop AO system, based on a real-time Hartmann-Shack wave-front sensor operating at 30 Hz and a 37-actuator membrane deformable mirror, is interfaced to an UHR OCT system, based on a commercial OCT instrument, employing a compact Ti:sapphire laser with 130-nm bandwidth. Closed-loop correction of both ocular and system aberrations results in a residual uncorrected wave-front rms of 0.1 microm for a 3.68-mm pupil diameter. When this level of correction is achieved, OCT images are obtained under a static mirror configuration. By use of AO, an improvement of the transverse resolution of two to three times, compared with UHR OCT systems used so far, is obtained. A significant signal-to-noise ratio improvement of up to 9 dB in corrected compared with uncorrected OCT tomograms is also achieved.

Adaptive optics for the human eye has two main applications: to obtain high-resolution images of the retina and to produce aberration-free retinal images to improve vision. Additionally, it can be used to modify the aberrations of the eye to perform experiments to study the visual function. We have developed an adaptive optics prototype by using a liquid crystal spatial light modulator (Hamamatsu Programmable Phase Modulator X8267). The performance of this device both as aberration generator and corrector has been evaluated. The system operated either with red (633nm) or infrared (780nm) illumination and used a real-time Hartmann-Shack wave-front sensor (25 Hz). The aberration generation capabilities of the modulator were checked by inducing different amounts of single Zernike terms. For a wide range of values, the aberration production process was found to be linear, with negligible cross-coupling between Zernike terms. Subsequently, the modulator was demonstrated to be able to correct the aberrations of an artificial eye in a single step. And finally, it was successfully operated in close-loop mode for aberration correction in living human eyes. Despite its slow temporal response, when compared to currently available deformable mirrors, this device presents advantages in terms of effective stroke and mode independence. Accordingly, the programmable phase modulator allows production and compensation of a wide range of aberrations, surpassing in this respect the performance of low-cost mirrors and standing comparison against more expensive devices.

The wave aberration of the human eye has been measured by means of a Hartmann-Shack wave-front sensor in a population of normal subjects. The set of data has been used to compute the phase distribution, the power spectrum, and the structure function for the average eye to analyze the statistics of the ocular aberration considered as a phase screen. The observed statistics fits the classical Kolmogorov model of a statistically homogeneous medium. These results can be of use in understanding the average effect of aberrations on the retinal image and can serve as a tool to analyze the consequences of ocular-aberration compensation by adaptive optics, customized ophtalmic elements, or refractive surgery.

A description of a Hartmann-Shack sensor to measure the aberrations of the human eye is presented. We performed an analysis of the accuracy and limitations of the sensor using experimental results and computer simulations. We compared the ocular modulation transfer function obtained from simultaneously recorded double-pass and Hartmann-Shack images. The following factors affecting the sensor performance were evaluated: the statistical accuracy, the number of modes used to reconstruct the wave front, the size of the microlenses, and the exposure time.

In a previous paper it was shown that when the Fourier transform technique is applied to binary images (low light level images where the photocurrent distribution is clipped to be binary or one-bit digital images), the processing time necessary for the spectrum estimate is considerably reduced.

When detecting in low-light-level conditions, the dead time that appears in actual intensified image detectors increases both the systematic and the statistical error in the centroid estimate. We develop a simple technique to reduce these errors. This technique enables extending, with a good level of accuracy, the applicability of experimental methods involving the centroid measurement to those fields dealing with faint light sources.

This PDF contains the communication on "Object movement characterization from low-light-level images."

8 pages, 7 figures.-- PMID: 16697435 [PubMed].-- Printed version published on Sep 2006., Wave aberrations degrade the optical quality of the eye relative to the diffraction limit, but there are situations in which having slightly aberrated optics can provide some relative visual benefits. This fact led us to consider whether interactions among aberrations in the eye’s wavefront produce an advantage for image quality relative to wavefronts with randomized combinations of aberrations with the same total RMS error. Total ocular wave aberrations from two experimental groups and corneal wave aberrations from one group were measured and expressed as Zernike polynomial expansions through the seventh-order. In a series of Monte Carlo simulations, modulation transfer functions (MTFs) for the measured wave aberrations were compared to distributions of artificial MTFs for wavefronts created by randomizing the sign or orientation of the aberrations, while maintaining the RMS error within each Zernike order. In a control condition, "synthetic" model eyes were produced by choosing each individual aberration term at random from individuals in the experimental group, and again MTFs were compared for original and randomized signs. Results were summarized by the MTF ratio: real MTF/mean simulated MTF, as a function of spatial frequency. For a 6 mm pupil, the mean MTF ratio for total ocular aberrations was greater than 1.0 up to 60 cycles per degree, suggesting that the eye’s aberrations are not independent and that there may be a positive functional consequences to their interrelations. This positive relation did not hold for corneal aberrations alone, or for the synthetic eyes., Financial support was provided by National Institute of Health Grant EYO4395 to S.A. Burns.