Maxwellian View Research Articles

VAC-free near-eye display with thin form factor

Thin form factor and vergence-accommodation conflict-free (VAC-free) display are what the head-mounted near-eye display (NED) systems pursue all along. In this paper, we propose a NED system, with a waveguide providing parallel backlights to a display panel along different directions sequentially in each eye-piece. A converging lens is attached to a display panel, converging the directional backlights from corresponding waveguide to different viewpoints, respectively. The waveguide, display panel and converging lens of an eye-piece are closely stacked for a thin form factor, and the directional backlight guarantees a narrow beam from each pixel for VAC-free Super Multi-View (SMV) and/or Maxwellian view display. VAC-free effect is experimentally demonstrated in our proof-of-concept NED system of 11 mm in thickness.

Pattern electroretinogram, blue-yellow visual evoked potentials and the risk of developing visual field defects in glaucoma suspects: a longitudinal “survival” analysis with a very long follow-up

PurposeEstimating glaucoma suspects’ risk for visual field defects helps to avoid under- and over-treatment. In this retrospective, longitudinal cohort study with a very long follow-up, we studied whether pattern electroretinograms (PERG) amplitudes and blue-on-yellow visual evoked potential (BY-VEP) latencies can predict visual field defects.MethodsParticipants of the Erlangen Glaucoma Study were examined with PERG and BY-VEP between 9/1991 and 8/2001. Stimuli were created using an optical bench with Maxwellian view and consisted of vertical gratings (0,88 cpd) in a 32° field for both PERG and BY-VEP. Patients were treated according to clinical standards and performed standard automated perimetry (SAP) annually. Retrospectively, patients with normal SAP at baseline were selected. Primary endpoint was conversion to perimetric glaucoma. Predictive value was modeled using Kaplan–Meier analyses and a multivariate cox proportional hazards model with the continuous variables PERG amplitude, BY-VEP peak time and SAP square-root of loss variance (sLV) after stratification for Jonas classification of the optic discs.ResultsOf 412 patients (288: Jonas 0, 103: I, and 21: II; baseline age: 20–60 years), 65 converted to perimetric glaucoma during follow-up (0.5–23.3 years; median 5.5 years). Optic disc classification was a strong risk factor for conversion (log rank p < 0.0001), and patients with more advanced changes progressed earlier. In the multivariate analysis (log rank p = 0.005), only PERG amplitude remained an independent risk factor after stratification for optic disc morphology (p = 0.021), with a ~ 30% higher risk per μV amplitude decrease.ConclusionsPERG helps to estimate glaucoma suspects’ risk for visual field defects.

Potential vision tester using adaptive optics, Maxwellian view, and small pupil.

We demonstrate a free-space, trolley-mounted potential vision tester (PVT), designed to study and improve the accuracy of visual acuity (VA) measurements in the aging eye. Key features include a high-resolution visual display presented in Maxwellian view, a 3 mm pupil to limit wavefront (WF) aberrations, and a moderate cost deformable mirror to induce or correct higher order optical aberrations. The visual display supported accurate measurement of visual acuities down to 20/5. The moderate cost, piezo deformable mirror induced seven nominal aberrations, calibrated as 0, -0.32, -0.23, + 0.27, and +0.39 microns spherical aberration; + 0.49 microns Y coma; and -0.51 microns X coma. A custom Hartmann Shack (HS) calibration (HSc) system demonstrated that induced aberrations were repeatable and stable. A Badal optometer provided the coarse focus. WF aberrations were measured for five normal subjects with a commercially available HS device (HSP) (OCULUS Pentacam AXL Wave), providing estimates of WF errors for 3 mm and other pupil sizes. VA was measured using four alternative forced-choice for a single black on white E stimulus in each trial. Using the method of constant stimuli yielded robust standard deviation measurements. The 50% fit for VA plotted against induced aberration resulted in linear functions for each subject for the range of our positive and negative spherical aberration data. Subjects differed, but higher order terms were unnecessary to describe data across spherical aberrations.

Poster Session: Towards Understanding Retinal Processing of Single-Cone Scale Stimulation.

The magnocellular (M) visual pathway can be distinguished from its finer-grained parvocellular (P) counterpart by its stronger response gain to contrasts near human detection threshold. This distinction is found when stimulus size is matched to the relatively large receptive field size of M cells, but it is less clear if preserved at smaller spatial scales. We examined foveal detection thresholds in tandem with a masking paradigm known to desensitize the M pathway. We used a custom DLP display in Maxwellian view to present either 3 or 23 arcmin spots for 100 ms against a uniform gray disk (1° VA) surrounded by a 0.5 cpd, 100% contrast, square wave grating flickered at 7 frequencies ranging from 0 to 30 Hz. Detection data were fit with psychometric functions to estimate threshold and thresholds were normalized to the static (0 Hz) condition. Relative sensitivity was fit with a modified impulse response function and compared to a constant model with ANOVA. With masking we found a significant reduction in sensitivity for large (23arcmin) increments (mean=0.39 log units; n=4; p<0.01) and decrements (0.31 log units; n=4; p=0.02)at 8.3Hz. By contrast, no significant masking effect was observed for small spot increments or decrements (p>0.05). These data suggest that the M pathway is not the primary determinant of small spot thresholds under the conditions studied. Further investigation with adaptive optics may be necessary to fully elaborate single-cone processing in the fovea.

P‐90: Evaluating Maxwellian view design with a non‐equal weighting matrix

In this work, we proposed an algorithm to evaluate any reflective polarization volume hologram (R‐PVH) Maxwellian view design based on a non‐equal weighting matrix of the field of view and gaze angle. A continuous eye movement from 0 to 17 degrees towards the ear is considered. The comparison of the eyebox of the example designs is presented after using the weighting matrix of the field of view and gaze angle. This algorithm gives us a method to evaluate any design based on the weighted distance to the center of the pupil.

A five-primary Maxwellian-view display for independent control of melanopsin, rhodopsin, and three-cone opsins on a fine spatial scale.

Independent spatiotemporal control of the stimulation of the five photoreceptor classes requires a display with as many primary lights to probe their isolated spatial and temporal responses. No such system exists with suitable performance properties. We present a system to construct a five-primary display from commercially available three-primary digital light processing projectors. It optimizes the set of five primary lights required to maximize the achievable contrast of a single photoreceptor class in a silent substitution protocol, including where the background chromaticity is first specified. From these chosen five primaries, we describe a method to convert complex three-primary (RGB) images to five-primary representations with complete specification of the photoreceptor excitations at each pixel. Key to enabling this multiple display system with a single HDMI connection is a novel control protocol implemented in a deterministic field-programmable gate array controller that splits the data into five video streams to allow nearly synchronous presentation of primary image data through multiple displays. Each pixel is controlled over 9.5 bits for each primary over a single frame for measurement of threshold-level vision. In addition to a large contrast gamut, the Maxwellian view offers high retinal illumination to support the investigation of five opsin-based responses to complex spatiotemporal images with a truly silent substitution protocol, while avoiding the confounding effects of uncontrolled photoreceptor excitations as occurs in four-primary systems. The customizable primaries facilitate this display translation to species with different photoreceptor spectral responses, and the optics are designed for integration into microscopes for use as a stimulus generator in physiological experiments.

Effect of the spectral power distribution on visual performance of subjects implanted with intraocular lenses with or without a blue light-filter under night-driving conditions

In old subjects, the effect on visual performance of the interaction between the spectral power distribution of street lamps and the different types of intraocular lenses (IOLs) is unknown. Contrast threshold (CT) and reaction time (RT) were analysed in off-axis vision at mesopic illumination conditions provided by high-pressure sodium and metal-halide lamps, using a Maxwellian view optical system. Four groups of subjects participated: 10 young subjects, 20 elderly subjects with cataracts and the same subjects after cataract surgery were divided into two groups, 10 subjects implanted with a blue light-filtering and 10 subjects with a non-blue light-filtering IOL (NBIOL). Age-related cataract impairs detection and reaction capabilities; tasks that are nevertheless improved after surgery. The type of lamp does not affect both tasks in the case of the blue light-filtering IOL group, but it does in the NBIOL group. When comparing the two lenses, no detrimental effect of the blue light filter is observed in both tasks. In conclusion, at representative night-driving conditions, the spectral power distribution of the street lamp does not have a clinically relevant effect on visual tasks such as CT and visual RT in pseudophakic subjects, regardless of the type of IOL implanted.

A simple method for comparing peripheral and central color vision by means of two smartphones.

Information on peripheral color perception is far from sufficient, since it has predominantly been obtained using small stimuli, limited ranges of eccentricities, and sophisticated experimental conditions. Our goal was to consider the possibility of facilitating technical realization of the classical method of asymmetric color matching (ACM) developed by Moreland and Cruz (1959) for assessing appearance of color stimuli in the peripheral visual field (VF). We adopted the ACM method by employing two smartphones to implement matching procedure at various eccentricities. Although smartphones were successfully employed in vision studies, we are aware that some photometric parameters of smartphone displays are not sufficiently precise to ensure accurate color matching in foveal vision; moreover, certain technical characteristics of commercially available devices are variable. In the present study we provided evidence that, despite these shortages, smartphones can be applied for general and wide investigations of the peripheral vision. In our experiments, the smartphones were mounted on a mechanical perimeter to simultaneously present colored stimuli foveally and peripherally. Trying to reduce essential discomfort and fatigue experienced by most observers in peripheral vision studies, we did not apply bite bars, pupil dilatation, and Maxwellian view. The ACM measurements were performed without prior training of observers and in a wide range of eccentricities, varying between 0 and 95°. The results were presented in the HSV (hue, saturation, value) color space coordinates as a function of eccentricity and stimulus luminance. We demonstrated that our easy-to-conduct method provided a convenient means to investigate color appearance in the peripheral vision and to assess inter-individual differences.

Large Depth of Range Maxwellian-Viewing SMV Near-Eye Display Based on a Pancharatnam-Berry Optical Element

In order to overcome the accommodation and convergence (A-C) conflict that commonly causes visual fatigue in AR display, we propose a Maxwellian-viewing-super-multi-view (MV-SMV) near-eye display system based on a Pancharatnam-Berry optical element (PBOE). The PBOE, which is constituted with an array of high-efficiency polarization gratings, is implemented to direct different views to different directions simultaneously, constructing the 3D light field. Meanwhile, each view is like a Maxwellian view display that possesses a small viewpoint and a large depth of field (DOF). Hence, the MV-SMV display can display virtual images with correct accommodation depth cue within a large DOF. We implement a proof-of concept MV-SMV display prototype with 3 × 1 and 3 × 2 viewpoints using a 1D PBOE and a 2D PBOE, respectively, and achieve a DOF of 4.37 diopters experimentally.

Waveguide-type Maxwellian near-eye display using a pin-mirror holographic optical element array.

We propose a novel, to the best of our knowledge, waveguide-type optical see-through Maxwellian near-eye display for augmented reality. A pin-mirror holographic optical element (HOE) array enables the Maxwellian view and eye-box replication. Virtual images with deep depth of field are presented by each pin-mirror HOE, alleviating the discrepancy between vergence and accommodation distance. The compact form factor is achieved by the thin waveguide and HOE couplers.

Optical stimulation systems for studying human vision.

This chapter describes the most common setups that scientists use for generating light stimulation, from lab-made approaches to commercially available technologies. The studied optical stimulation systems are divided into nonimage-forming and image-forming arrangements. Two classical systems widely used are among the first: the Maxwellian view system and the Ganzfeld stimulator. Between the image-forming arrangements, the focus is on approaches that consider off-the-shelf devices and the recent appearance of multi-primary displays, which allow the inclusion of more primaries and the generation of stimulation for independent and combined photoreceptor and postreceptoral excitations. Some of the several limitations that can have important implications in research practice are also examined, such as those related to color gamut, sampling frequency, light range, and spatial resolution. Since experimentation on how optical radiation is processed by the human neural system requires the reliability of the parameters and variables under study to be assured, the characterization and consequent calibration of experimental devices are essential. Therefore the chapter discusses a set of characterization and calibration principles that researchers should consider when carrying out experiments with the described optical stimulators. Outstanding characteristics are stimulator response curve, primaries' spectral power distribution, additivity, modulation transfer function, and temporal stability. Finally, some possible sources of artifacts that researchers should consider when these stimulators are used are presented. Throughout this last section, data based on different optical stimulator measurements is provided.

PyPlr: A versatile, integrated system of hardware and software for researching the human pupillary light reflex

We introduce PyPlr—a versatile, integrated system of hardware and software to support a broad spectrum of research applications concerning the human pupillary light reflex (PLR). PyPlr is a custom Python library for integrating a research-grade video-based eye-tracker system with a light source and streamlining stimulus design, optimisation and delivery, device synchronisation, and extraction, cleaning, and analysis of pupil data. We additionally describe how full-field, homogenous stimulation of the retina can be realised with a low-cost integrating sphere that serves as an alternative to a more complex Maxwellian view setup. Users can integrate their own light source, but we provide full native software support for a high-end, commercial research-grade 10-primary light engine that offers advanced control over the temporal and spectral properties of light stimuli as well as spectral calibration utilities. Here, we describe the hardware and software in detail and demonstrate its capabilities with two example applications: (1) pupillometer-style measurement and parametrisation of the PLR to flashes of white light, and (2) comparing the post-illumination pupil response (PIPR) to flashes of long and short-wavelength light. The system holds promise for researchers who would favour a flexible approach to studying the PLR and the ability to employ a wide range of temporally and spectrally varying stimuli, including simple narrowband stimuli.

33‐2: Student Paper: Optimized Liquid‐Crystal Dammann Grating for Eyebox Expansion in Maxwellian‐View Displays

A liquid crystal Dammann grating film is designed and fabricated for eyebox expansion in Maxwellian view near‐eye displays. By inserting the Dammann grating into the Maxwellian view system, we show that full color operation and enlarged eyebox are achieved, while keeping the system compact and lightweight.

31‐3: Continuous High‐Efficiency Beam Deflector for AR/VR Devices

The use of Augmented/Virtual Reality (AR/VR) and near‐eye displays (NED) can cause eye fatigue due to the mismatch of the accommodation and convergence (AC) distances. Maxwellian view displays (retina‐projection display) have the potential to bypass AC mismatch by projecting the image directly onto the retina. In this approach, the final image always stays in focus at the retina by converging the rays at the eye pupil, therefore, making tthe focus depth independent. However, the narrow eyebox size can hinder the employment of this approach. Therefore, there is a need for a beam steering device with high‐efficiency, continuous steering capabilities that, in combination with an eye‐tracking system, could expand the application of AR/VR systems. In this paper, we represent a novel approach to a fully tunable beam steering device based on the Pancharatnam‐Berry phase in a liquid crystal. This device maintains a high efficiency that, along with an eye‐tracking system, can potentially address the limitations in Maxwellian view systems.

Full-color retinal-projection near-eye display using a multiplexing-encoding holographic method.

We propose a novel method to construct an optical see-through retinal-projection near-eye display using the Maxwellian view and a holographic method. To provide a dynamic full-color virtual image, a single phase-only spatial light modulator (SLM) was employed in conjunction with a multiplexing-encoding holographic method. Holographic virtual images can be directly projected onto the retina using an optical see-through eyepiece. The virtual image is sufficiently clear when the crystal lens can focus at different depths; the presented method can resolve convergence and accommodation conflict during the use of near-eye displays. To verify the proposed method, a proof-of-concept prototype was developed to provide vivid virtual images alongside real-world ones.

Enlarging the Eyebox of Maxwellian Displays with a Customized Liquid Crystal Dammann Grating

The Maxwellian view offers a promising approach to overcome the vergence-accommodation conflict in near-eye displays, however, its pinhole-like imaging naturally limits the eyebox size. Here, a liquid crystal polymer-based Dammann grating with evenly distributed energy among different diffraction orders is developed to enlarge the eyebox of Maxwellian view displays via pupil replication. In the experiment, a 3-by-3 Dammann grating is designed and fabricated, which exhibits good efficiency and high brightness uniformity. We further construct a proof-of-concept Maxwellian view display breadboard by inserting the Dammann grating into the optical system. The prototype successfully demonstrates the enlarged eyebox and full-color operation. Our work provides a promising route of eyebox expansion in Maxwellian view displays while maintaining full-color operation, simple system configuration, compactness, and lightweight.

Maxwellian near-eye display with an expanded eyebox.

Maxwellian view systems can be employed to circumvent the vergence-accommodation conflict in near-eye displays (NEDs), which directly project images onto the retina regardless of the human eye's depth of focus. However, Maxwellian view optics typically have a limited eyebox, which prevents broader applications of this architecture in NEDs. Here, we demonstrate a thin-film two-dimensional beam deflector composed of multi-twist broad-band Pancharatnam-Berry deflectors to mitigate this limitation via eyebox replication. Based on experimental validation, our proposed design can display always-focused full-color images within a 9 mm × 9 mm eyebox and thus mitigate the limitation of conventional Maxwellian displays while adding negligible weight and volume.

First Evaluation of a Retinal Imaging Laser Eyewear System Based Low Vision Aid.

PurposeWe conducted this trial to investigate a new wearable laser-eyewear (LEW). Images of an integrated camera are projected to the retina by a RGB-Laser (<1µW) and MEMS-mirror system. This enables a full-color live video as augmented reality embedded in the field of vision of the wearer. Thin parallel laser beams are projected following the principle of Maxwellian view through the center of the ocular lens to ensure independency of refractive errors. We performed a study with healthy subjects to test this independency.Materials and MethodsLEW was tested in 20 healthy subjects (aged between 21 and 60 years) with hyperopia, myopia, astigmatism and/or presbyopia. Subjects underwent standardized visual acuity (VA) measurements (ETDRS) without any correction, with LEW and with best correction.ResultsWe found no significant correlation between refraction and VA while using LEW in linear regression (r=0.17). Still, younger participants performed better in terms of VA with the device compared to older participants despite no differences in BCVA (p<0.01). The achievable VA with LEW was in general reduced compared to uncorrected VA (0.50 vs 0.40 logMAR). Only myopic subjects reached a significantly higher VA using LEW (p<0.001). Presbyopic subjects showed enhanced near VA (0.25 logMAR) by reading at 15cm with LEW without any further necessary refractive correction. Nearly all patients (80%) showed stereopsis without need for additional adjustments.ConclusionOur investigation could verify the independence of LEW of refractive errors. Therefore, the technology seems to be especially useful in patients with untreatable corneal conditions, e.g., after corneal burns, to achieve higher VA since the thin laser should penetrate even corneal opacities with less scattering.

The flicker Pupil Light Response (fPLR).

PurposeThe photoreceptor classes driving the flicker pupil light response (fPLR) to monochromatic sinusoidal temporal modulation are largely unknown. Here, we determine the photoreceptor inputs to the fPLR.MethodsThe 0.5-Hz fPLR was measured in healthy observers using a Maxwellian view (41° diameter) pupillometer at five narrowband wavelengths (short: 409 nm; intermediate: 462, 507, 530 nm; and long: 592 nm) over ∼10 log units of irradiance spanning scotopic to photopic levels (5.6 to 15.6 log quanta·cm−2·s−1; −6.9 to 3.6 log cd·m−2). The relative photoreceptor contributions to the fPLR were then derived from these amplitude-irradiance functions using a criterion fPLR.ResultsThe fPLR amplitude is small (≤ 3.9 ± 3.1%; mean ± SEM) below 8.0 log quanta·cm−2·s−1 then increases with retinal irradiance in accordance with a Hill function that asymptotes between 13.0 to 15.0 log quanta·cm−2·s−1 (wavelength dependent). The Hill slope is steepest for the intermediate wavelengths. Further increases in irradiance (>15.0 log quanta·cm−2·s−1) produce a distinct suppression of the fPLR for the intermediate wavelengths. The fPLR phase delay shows a linear decrease with increasing irradiance. The spectral sensitivity of the fPLR is dominated by inner retinal melanopsin ganglion cell and outer retinal rod photoreceptor inputs to the afferent pupil control pathway; the relative melanopsin : rhodopsin weighting decreases with the transition from photopic to scotopic lighting.ConclusionsThe fPLR can be used as a marker of melanopsin and rod interactions during the flicker stimulation and to quantify their contributions to the post-illumination pupil response (PIPR).Translational RelevanceThese irradiance and wavelength responses will be useful in standardizing the measurements of the fPLR using chromatic pupillometry.

Focus-free head-mounted display based on Maxwellian view using retroreflector film.

In this study, a focus-free retinal projection display based on a Maxwellian view was implemented. The display was constructed using simple and cost-effective passive components, such as a retroreflector film, beam splitter, and a pinhole. As a part of the system, the pinhole and display serve as a pinhole projector, which projects images through a small exit pupil. The retroreflector film and the beam splitter form the conjugate image of the pinhole near an observer. By locating the center of the crystalline lens of an eye at the conjugate pinhole, the projected images are focused on the retina and are seldomly changed by the accommodative response of the lens. For the practical implementation of the system, a collimating lens was used as an imaging lens combined with a pinhole. The point spread function of the system was derived to theoretically demonstrate that the system exhibits focus-free features at accommodation distances of 0.25, 0.5, and 1m. The experiments conducted to demonstrate the feasibility of the system are presented under the same accommodation condition as the analysis.