Pupil Expansion Research Articles

Polarization Volume Hologram for On‐Chip Wavefront Engineering

AbstractLiquid crystal (LC) planar optics have advanced wavefront engineering toward ultrathin designs, capturing widespread attention. However, most wavefront control in LC planar optics remains constrained to freespace due to limitations in the precision of freely controllable units. Here, LC on‐chip wavefront engineering is proposed and confirmed. By controlling the initial azimuth angle of the polarization grating, the initial phase can be engineered, as theoretically predicted by rigorous coupled‐wave analysis. Experimentally, the initial azimuth angle of a polarization volume hologram grating, used as a waveguide coupler, is ingeniously modulated using a holographic template. Consequently, several on‐chip optical elements, including lenses, vortex beam generators, and holograms, are demonstrated. Furthermore, exit pupil expansion and multiexposure technologies are adopted to enhance off‐chip functionality and enable multifunctional, highly integrated LC on‐chip photonic systems. The proposed LC on‐chip wavefront engineering may find applications in freeform optics, near‐eye displays, LIDAR, and integrated photonic systems.

Design of waveguide with double layer diffractive optical elements for augmented reality displays

We investigated a diffraction optical waveguide structure with a double layer coupling configuration. This double layer-coupled diffraction optical waveguide structure modulates light information through wavefront modulation for propagation within the optical waveguide and then reproduces the light information through further wavefront modulation, thus achieving optical information transmission. Analysis indicates that the theoretical maximum field of view can reach 90° × 90°. With an actual field of view set to 53° × 53°, an entrance pupil size of 3.2 × 3.2 mm², an eye relief of 10 mm, and 50 pupil expansion, the system’s total energy transmission efficiency is 37%, with field of view uniformity at 91% and uniformity within the eye movement range reaching 97%.

Pseudophakic cystoid macular oedema and posterior capsular opacification rates after combined phaco-trabeculectomy vs. phaco alone.

To assess the risk for pseudophakic cystoid macular oedema (PCME) and posterior capsular opacification (PCO) associated with combined cataract surgery and trabeculectomy compared to cataract surgery alone. Data analysis of subjects who underwent routine cataract surgery without and with concomitant trabeculectomy at the Department of Ophthalmology, Bristol Eye Hospital, the UK, between January 2008 and December 2017. Odds ratios (ORs) for PCME between the types of surgeries were calculated using univariate and multivariate regression analysis. Multivariate Cox regression controlling for age and gender was used to estimate the hazard ratio (HR) for neodymium-doped yttrium aluminium garnet (Nd:YAG) laser capsulotomies. This study included 56 973 cataract surgeries without and 288 with concomitant trabeculectomy (phaco-trab) with a mean follow-up time of 6.9 ± 4.2 years. Baseline variables (age and gender, diabetes, pseudoexfoliation, use of pupil expansion device and postoperative follow-up time) were comparable between the groups. Postoperative rates of PCME remained non-significant between the cataract surgery and phaco-trabe groups both in uni- and multi-variate analysis (OR 0.347, 95%CI 0.049-2.477, p = 0.291). Furthermore, in Cox regression analysis adjusted for the patients' age and gender, Nd:YAG laser capsulotomy rates remained non-significant between the cataract surgery and phaco-trabe groups (HR 1.250, 95%CI 0.883-1.769, p = 0.209). In our large cohort study, combining trabeculectomy with cataract surgery did not predispose to an increased PCME or Nd:YAG laser capsulotomy rates.

A Computational Framework for Intraoperative Pupil Analysis in Cataract Surgery

Pupillary instability is a known risk factor for complications in cataract surgery. This study aims to develop and validate an innovative and reliable computational framework for the automated assessment of pupil morphologic changes during the various phases of cataract surgery. Retrospective surgical video analysis. Two hundred forty complete surgical video recordings, among which 190 surgeries were conducted without the use of pupil expansion devices (PEDs) and 50 were performed with the use of a PED. The proposed framework consists of 3 stages: feature extraction, deep learning (DL)-based anatomy recognition, and obstruction (OB) detection/compensation. In the first stage, surgical video frames undergo noise reduction using a tensor-based wavelet feature extraction method. In the second stage, DL-based segmentation models are trained and employed to segment the pupil, limbus, and palpebral fissure. In the third stage, obstructed visualization of the pupil is detected and compensated for using a DL-based algorithm. A dataset of 5700 intraoperative video frames across 190 cataract surgeries in the BigCat database was collected for validating algorithm performance. The pupil analysis framework was assessed on the basis of segmentation performance for both obstructed and unobstructed pupils. Classification performance of models utilizing the segmented pupil time series to predict surgeon use of a PED was also assessed. An architecture based on the Feature Pyramid Network model with Visual Geometry Group 16 backbone integrated with the adaptive wavelet tensor feature extraction feature extraction method demonstrated the highest performance in anatomy segmentation, with Dice coefficient of 96.52%. Incorporation of an OB compensation algorithm improved performance further (Dice 96.82%). Downstream analysis of framework output enabled the development of a Support Vector Machine-based classifier that could predict surgeon usage of a PED prior to its placement with 96.67% accuracy and area under the curve of 99.44%. The experimental results demonstrate that the proposed framework (1) provides high accuracy in pupil analysis compared with human-annotated ground truth, (2) substantially outperforms isolated use of a DL segmentation model, and (3) can enable downstream analytics with clinically valuable predictive capacity. Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Real-world uptake of an innovative pupil expander device for cataract surgery: Implementation lessons learnt.

Cataract surgery in the eyes, where the pupil does not dilate despite using eye drops, is fraught with vision-threatening complications. About 11 per cent of eyes undergoing cataract surgery have non-dilating, small pupils. The increasing prevalence of benign prostatic hyperplasia (BPH), hypertension, diabetes and medications used for the same are the contributing factors. The recent Food and Drug Administration (FDA) approval for the use of miotic agents in the treatment of presbyopia will lead to a further rise in the number of non-dilating pupils. While pharmacological agents and other methods have been used, mechanical pupil expander devices are the only fail safe option. However, available devices had a steep learning curve and limitations which made them difficult to use, unpredictable and unsafe. With its patented single plane, hexagonal, notches and flanges design, the US FDA registered B-HEX Pupil Expander (Med Invent Devices Pvt. Ltd., India) overcame these limitations and fulfilled an unmet need. The B-HEX is machinable, rapidly produced, consistent, easy to use, safe, and affordable. Despite such advantages, implementation hurdles have restricted its availability to healthcare systems worldwide. Peer acceptance has been steadily growing, with the B-HEX becoming the market leader in India, as evidenced by numerous publications, videos and papers presented at international conferences and comments from opinion leaders endorsing its use. However, impractical regulatory requirements and resource constraints remain a great impediment to the global distribution of this novel invention. This has denied many patients the benefits of a superior and more affordable option. Though value continues to be added to the B-HEX by maintaining a strong intellectual property portfolio with internationally granted Patents and Trademark, increasing its user base, and garnering support from key opinion leaders, only a collaboration with the right partner will help scale up the global reach and make it a leader in the global market.

A randomized control study on post-operative iris distortion following small-pupil cataract surgery using B-HEX pupil expander versus Malyugin ring

BackgroundThe aim of the study was to evaluate postoperative pupil distortion following small pupil cataract surgeries performed using B-HEX and Malyugin rings (MR). MethodsA randomized control trial was conducted from June 2020 to June 2023 at a tertiary eye-care hospital. The study consisted of 64 participants for cataract surgery with small pupil. There were two groups, one undergoing surgery with the use of B-HEX pupil expander and other with MR intraoperatively and the rest of the surgery was proceeded as per the convention. Areas of preoperative and postoperative images was calculated, put into an online software and pupil distortion was calculated in percentage. Two-tailed t-test was used to see the difference between the two groups. ResultsMean age at presentation was 70.5 ± 10.12 years. Most common cause for small pupil was tamsulosin therapy. Mean size of small-pupil was 3.0 ± 1.1 mm. With the application of two rings, mean pupillary area preoperatively was 4178.23 ± 1589.46 and postoperatively was 6100.44 ± 2658.28 following the use of MR, respectively and 30,002.93 ± 13,193.40 preoperatively and 37,648.26 ± 15,207.01 postoperatively following the use of B-Hex ring respectively. Comparing baseline area from pupillary area at 1-month follow-up, a significant increase was noted for both the rings. Also, MR caused significantly more pupillary distortion compared to B-HEX ring (p < 0.05). ConclusionMR causes significantly more pupillary distortion in the postoperative period compared to B-HEX ring. Though, both the rings cause pupillary distortion, these devices expand the surgical area adequately, ease the procedure, decrease risk of complications achieving good functional visual outcomes.

3‐5: Distinguished Paper: Full‐color, Wide FoV Single‐layer Waveguide for AR Displays

We analyze the field‐of‐view (FoV) limitations in a single‐layer, full‐color waveguide‐based augmented reality display, revealing key influences from the waveguide's refractive index, exit pupil expansion (EPE) scheme, and combiner's angular response. Based on these analyses, we propose an optimized butterfly EPE scheme with gradient‐pitch polarization volume gratings (PVGs), achieving a theoretical diagonal FoV of 54.06° with a 16:10 aspect ratio.

P‐45: A simulation method for crossed‐type exit pupil based on polarization volume grating

We propose a simulation method for two‐dimensional (2D) crossed‐type exit pupil expansion based on polarization volume grating (PVG) applied in diffractive waveguide holographic display. The functions of turning and decoupling of the PVG are realized through two continuous Bragg regions, and the spatial director distribution of liquid crystal is combined with RCWA to model its diffractive characteristics and ray tracing simulation.

Corneal morphology following use of Malyugin versus B-hex pupil expansion rings in small pupil phacoemulsification

Aim: The aim of the study is to evaluate changes in corneal parameters following the use of the Malyugin ring (MR) and B-Hex ring (BhR) in small pupil phacoemulsification. Methods: A prospective cross-sectional study. 51 eyes with small pupil underwent phacoemulsification with the use of MR and BhR as pupil expansion techniques. Best-corrected visual acuity (BCVA), endothelial cell counts density (ECD), coefficient-of-variation (CV), hexagonality, central corneal thickness (CCT), and intraocular pressure (IOP) were recorded on preoperative day and postoperative day 1 and day 30. Results: Mean age at presentation was 70.9 ± 4.1 years. The most common cause for small pupils was alpha-blockers used in benign prostate hypertrophy, followed by diabetes mellitus and pseudo-exfoliation syndrome. Mean preoperative BCVA (3/60–6/12), IOP (17.12 ± 2.81 mmHg), CCT (530.96 ± 44.47 μ), ECD (2347.96 ± 298.09 cells/mm2), 6A (48.92% ± 6.34%) and CV (39.50 ± 3.49) changed to BCVA (6/9–6/6), IOP (18.69 ± 1.91 mm of Hg), CCT (536.04 ± 37.61 μ), endothelial cell count (2201.15 ± 276.75 cells/mm2), 6A (45.12% ±4.99%), and CV (37.57 ± 3.37) at day 30 postoperatively after use of MR. Similarly, mean preoperative BCVA (3/60–6/12), IOP (16.40 ± 2.42 mmHg), CCT (532.40 ± 36.14 μ), ECD (2433.68 ± 162.01 cells/mm2), 6A (48.84% ± 3.73%), and CV (39.36 ± 3.915) changed to BCVA (6/9–6/6), IOP (17.68 ± 2.75 mmHg), CCT (546.88 ± 31.25 μ), ECD (2322.08 ± 167.97 cells/mm2), 6A (46.36% ± 3.25%) and CV (38.96 ± 4.43) at day 30 post-operatively after use of BhR. The average change was clinically insignificant at day 30. Conclusion: MR and BhRs are safe pupil expansion devices and the corneal parameters are in the acceptable range of any routine phacoemulsification for senile cataracts. Nevertheless, B-hR shows relatively less alteration in corneal parameters, when compared to MR.

Full‐color, wide field‐of‐view single‐layer waveguide for augmented reality displays

AbstractIn the quest for more compact and efficient augmented reality (AR) displays, the standard approach often necessitates the use of multiple layers to facilitate a large full‐color field of view (FoV). Here, we delve into the constraints of FoV in single‐layer, full‐color waveguide‐based AR displays, uncovering the critical roles played by the waveguide's refractive index, the exit pupil expansion (EPE) scheme, and the combiner's angular response in dictating these limitations. Through detailed analysis, we introduce an innovative approach, featuring an optimized butterfly EPE scheme coupled with gradient‐pitch polarization volume gratings (PVGs). This novel configuration successfully achieves a theoretical diagonal FoV of 54.06° while maintaining a 16:10 aspect ratio.

Angular uniformity improvement of diffractive waveguide display based on region geometry optimization.

Augmented reality (AR) near-eye displays have significantly progressed due to advances in nanostructure fabrication. However, for diffractive waveguide AR displays requiring exit pupil expansion, the angular uniformity of each exit pupil position still needs to improve. In this paper, an angular uniformity improvement method based on region geometry optimization is proposed. This optimization method essentially introduces the interaction number of the light with the grating as one of the variables to manipulate the energy distribution. This distribution is obtained by the rigorous coupled wave analysis (RCWA) method and ray tracing process and is further optimized by a multi-objective genetic algorithm. A model is built, and the feasibility of the proposed method is verified. The diffractive waveguide system has a 10m m×10m m exit pupil size at the eye relief of 25mm and a field of view (FOV) of 21∘×12∘. After the optimization, the overall optical efficiency of the central field and the angular uniformity at the center exit pupil position increased from 0.9% and 66% to 3.1% and 80%, respectively.

Comparison of pupil expansion devices in small pupil phacoemulsification.

To study the outcomes of phacoemulsification in small pupils (≤4 mm) using pupil expansion devices at a tertiary eye care center in South India. The study design is prospective, randomized, comparative, and interventional. Mechanical pupil dilatation with iris retractors (group I), B-HEX ring (group II), and Gupta ring (group III) was compared with respect to pupil size achieved (intraoperative), total surgical time, device addition time, complications, endothelial cell loss, and postoperative best corrected visual acuity. Among 36 participants (12 in each group), the mean pupil size, total surgical time, and device addition time were maximum with iris retractors. Intraoperatively, sphincter tear was seen in two eyes in the iris retractors group and one eye in the Gupta ring group. In the B-HEX ring group, only two flanges of the ring could be engaged in two participants, one patient had iris bleeding (during stretching of the iris), and one patient had anterior lens capsular tear. Among all three groups, there was no statistically significant difference in best corrected visual acuity (BCVA), endothelial cell count, and coefficient of variation obtained in the preoperative period, postoperative Day 7 and Day 30, respectively. In our study, in more than 50% of cases, the cause of small pupil was idiopathic/senile. Among nonidiopathic causes, PXF was the most common association. Although iris retractors are cost-effective and give maximum intraoperative dilatation, there is a need of four additional side ports to be made, thus increasing the total surgical time and device addition time. On the other hand, B-HEX and Gupta ring provide comparable intraoperative dilation and device addition time and also have comparable postoperative outcomes in terms of postoperative pupil size and complications.

Compact pupil-expansion AR-HUD based on surface-relief grating.

Augmented reality head-up display (AR-HUD) using diffractive waveguide is a challenging research field. It can drastically reduce the system volume compared with AR-HUD based on freeform mirror. However, one of the remaining challenges that affects the performance of the diffractive waveguide is to expand the eye-box while maintaining the illuminance uniformity. In this paper, a one-dimensional pupil expansion diffractive optical waveguide system for AR-HUD is presented. The optimization of grating parameters is based on scalar diffraction theory and rigorous coupled wave analysis (RCWA). Then, the illuminance uniformity is optimized through non-sequential ray tracing. We simulate and construct a waveguide-based AR-HUD. The presented AR-HUD realized an exit pupil size of 80 mm × 15 mm and a field of view of 10° × 5° at the wavelength of 532 nm.

Design and Fabrication of 2D Exit Pupil Expansion Holographic Grating Waveguide with Large Field of View

Design and Fabrication of 2D Exit Pupil Expansion Holographic Grating Waveguide with Large Field of View

Accommodation-capable holographic waveguide head-up display with extended field of view

Augmented reality (AR) displays are enhancing user experiences by offering immersive three- dimensional (3D) content, with head-up display (HUD) being a prime application for driving safety. To enable AR-HUDs to provide sufficient information to driver, it is essential to ensure a wide field of view (FOV). Traditional methods like the magnifier principle have limitations stemming from optical aberrations and bulky form factor. Recently, optical waveguide has been used as pupil expander, which has attracted increasing attention as an optical element for compact form factor and exit-pupil expansion. However, waveguide display as exit-pupil expander only offer 2D images with infinite depth, causing mismatch issue between virtual content and real scenes. In this paper, we propose a lensless holographic waveguide display consisting of a laser light source, a spatial light modulator (SLM), a waveguide to generate accommodation-capable images, effectively extending FOV. The key distinction of this research lies in the optical design of the waveguide, which defines multiple shifted copies of the modulated wavefield as replicated virtual SLMs. A formalized algorithm is devised based on a bold assumption that numerous virtual SLMs replicated by a waveguide are considered as a single ultra-high resolution SLM. The effectiveness of the algorithm has been demonstrated through extensive validation through numerical observation simulations and optical experiments. Notably, optical experiments convincingly demonstrate the system’s ability to produce accommodation-capable true 3D content, with a four-fold extension of FOV compared to a single SLM at an observation distance of 150 mm. Additional optical experiments highlight the successful integration of AR technology, an important component for automotive HUD.

Study on Two-Dimensional Exit Pupil Expansion for Diffractive Waveguide Based on Holographic Volume Grating

Diffraction gratings are becoming a preferred option for waveguide head-mounted in–out coupling devices due to their flexible optical properties and small size and light weight. At present, diffraction waveguide coupling devices for AR head-mounted displays (HMD) have difficulties such as a long development cycle and complicated processing. In this paper, we first establish a set of two-dimensional (2D) grating ray tracing models, based on which we determine the initial architecture of the dual-region two-dimensional exit pupil expansion (2D-EPE) AR-HMD holographic waveguide diffraction system. Second, we propose a honeycomb coupled grating array and optimize the optical energy utilization and brightness uniformity of the holographic waveguide and use a custom dynamic linked library (DLL) function to implement the ray tracing of the 2D grating and add a probabilistic splitting function to the DLL, which reduces the single simulation time from 11.853 min to 1.77 min. We also propose a holographic lithography device composed of holographic optical elements (HOEs) and a method for preparing HOEs. Finally, in order to obtain the diffraction efficiency preoptimized by the above DLL for the uniformity of the exit pupil brightness and light energy utilization, we inverse design with the preparation process parameters as the optimization variables and develop the adaptable electromagnetic calculation program Holo-RCWA. Using Holo-RCWA with nondominated sorting genetic algorithm II (NSGA-II), we inverse design to obtain the process parameters satisfying the diffraction efficiency distribution, and the optimization time of the whole system is reduced from 2–3 days to 10 h. This work is of great significance for AR/VR applications.

Hybrid waveguide based augmented reality display system with extra large field of view and 2D exit pupil expansion.

For a waveguide display device, the field of view (FOV) is a key parameter for evaluating its optical performance. To address this issue, we propose a hybrid waveguide system, which is composed of two projectors, two in-couplers, two half-mirror arrays and an out-coupler. We use two projectors to generate the left and right parts of the output image separately, which can increase the upper limit of the FOV significantly. Unlike conventional waveguide-based system, we use half-mirror arrays instead of folding gratings to realize 2D exit pupil expansion. By doing so, the total internal reflection condition can always be met during the pupil expansion process. To solve the difficulty in designing collimating optical system with large FOV, we propose a method of tilting the projection system. The hybrid waveguide system can realize a FOV of 88°(H) × 53°(V).

Design optimization of polarization volume gratings for full‐color waveguide‐based augmented reality displays

AbstractReflective polarization volume gratings (PVGs) can be used as input and output couplers in a diffractive waveguide‐based augmented reality (AR). To improve the stability and wearing comfort, a thin and lightweight full‐color waveguide display is needed. In this paper, we propose a single full‐color waveguide AR display based on PVGs. By analyzing the optical system, we derived the field of view limit by optimizing a three‐layer PVG as an in‐coupler. Pairing with a single‐layer, thin PVG as an out‐coupler, we can achieve a relatively uniform exit pupil of 8 mm at horizontal pupil expansion direction.

The impact of case complexity in resident-performed cataract surgery.

To evaluate the association of capsular dye and/or a pupil expansion device (PED) usage on the rate of major complication in resident-performed cataract extraction. Resident cataract surgeries between 2016 and 2019 were included. The primary outcomes were anterior or posterior vitrectomy (AVx and PPVx). Cases were grouped by the use of a PED and/or capsular staining along with additional preoperative risk factors. Of the 1,348 cases, 371 (27.5%) documented capsular staining ("Dye-only"), 91 (6.8%) required pupil expansion ("PED-only"), and 100 (7.4%) used both capsular stain and a PED ("Both"). The remainder of cases (n=786, 58.3%) were classified as "Routine." Compared to the "Routine" group, "PED-only" and "Both" had significantly higher odds of an AVx (OR=2.90, 95% CI 1.27-6.19, P=0.01) and/or a PPVx (OR=2.33, 95% CI 1.07-5.12, P=0.04). Among the PPVx cases, the "PED-only" group has significantly higher odds than "Routine" and "Dye-only" (OR=4.64, 95% CI 1.68-12.79, P=0.01; and OR=6.48, 95% CI 1.7-25.0, P=0.005, respectively). In case-control analysis, vision, intraocular pressure, anterior chamber depth, axial length, cataract type, or severity had no significant overall association with complication. When compared to nuclear sclerotic cataract, posterior subcapsular (OR=7.86, 95% CI 1.46-42.47, P=0.017) and white/mature cataracts (OR=3.05, 95% CI 1.1-8.43, P=0.032) had increased odds of complication. Resident-performed cataract surgery frequently required capsular staining and/or a PED, and intuitively, these cases had a higher overall complication rate compared to routine cases. However, the use of a PED independently was associated with significantly higher odds of a major complication requiring an unplanned vitrectomy independent of predisposing factors.

Resident involvement in cataract surgery at the Veterans Health Administration: complications, case complexity, and the role of experience.

To characterize intraoperative complications, case complexity, and changes in complication rates with surgical experience for cataract surgeries involving residents at the Veterans Health Administration (VHA). All VHA facilities where cataract surgery was performed. Multicenter, retrospective cohort study. A retrospective review of all cataract surgeries within the VHA between July 2010 and June 2021 was conducted. Several parameters, including resident involvement, intraoperative complications, and case complexity as determined by Current Procedural Terminology codes, and use of pupil expansion or capsular support devices, were collected. Complication rates were compared between residents and attendings. Of 392 428 cataract surgeries completed across 108 VHA facilities, 90 504 were performed by attendings alone, while 301 924 involved a resident. Of these, 10 244 (11.3%) of attending cases were complex compared with 32 446 (10.7%) of resident cases. Pupil expansion devices were required in 8191 of attending cases (9.05%) and 31 659 (10.5%) of cases involving residents ( P < .001). Similarly, cases involving residents were more likely than attending-only cases to require a capsular support device (0.835% vs 0.586%, P < .001). Cases involving residents were more likely to have posterior capsular rupture (4.75% vs 2.58%, P < .001) and dropped nucleus (0.338% vs 0.198%, P < .001). Higher resident case volumes were associated with significantly lower complication rates for posterior capsular rupture, dropped nucleus, zonular loss, and suprachoroidal hemorrhage. Although residents had higher intraoperative complication rates than attendings, these rates were reduced with surgical experience. Residents were involved in a similar number of complex surgical cases as attendings.