Jacobi-Fourier phase masks as ophthalmic elements to correct presbyopia.

PURPOSE: Investigations into the correction of presbyopia have considered lens design, clinical implications and the development of objective metrics such as the visual Strehl ratio. This study investigated the Jacobi-Fourier phase mask as an ophthalmic element in the correction of presbyopia. The goal was to develop a contact or intraocular lens whose performance was largely insensitive to changes in pupil diameter. METHODS: Numerical simulations based on Fourier optics were performed to evaluate three different Jacobi-Fourier polynomials, with the aim of providing a range of clear vision (1 Dioptre (D)). Performance was evaluated for three pupil sizes (6, 4 and 2 mm), while polychromatic images were simulated using three different wavelengths (656.3, 587.6 and 486.1 nm). The Neural Transfer function was included in the simulation. To validate the method and results, we used the Visual Strehl combined objective metric (VSCombined) currently used in visual optics. This metric gives more weight to the phase transfer function and is more suitable for non-symmetrical phase functions. RESULTS: Numerical validation showed the suitability of the Jacobi-Fourier phase masks for extending the range of clear vision of presbyopic eyes, providing a visual acuity of at least 0.10 logMAR (6/7.5 Snellen) at all distances between 1 and 6 m. The results show a range of clear vision of 1D was not affected by changes in pupil size, an increase in retinal image contrast accompanied by image artefact reduction by increasing the radial order of the Jacobi-Fourier phase mask and a reduction of wavelength dependence of the retinal images. These results are supported by simulated images and the objective criterion VSCombined. CONCLUSIONS: The use of Jacobi-Fourier phase masks as ophthalmic elements for presbyopic correction show promising results, with a good range of clear vision and reduced dependence on pupil size and chromatic aberration.

What should be done to the measured Zernike coefficients when conjugating the pupil and wavefront sensor planes with a 4f system: discussion.

The aim of this paper is to describe and demonstrate what should be done to the measured Zernike coefficients when conjugating the pupil and wavefront sensor planes with a 4f system. I provide theoretical and experimental evidence. The experimental setup consisted of two 4f systems of magnifications 1 and 1/3 with their corresponding wavefront sensors at their ends. Spherical and cylindrical trial lenses were measured. In addition, I measured a phase plate with high-order aberrations. I show that the Zernike coefficients of the wavefront expansion at two planes conjugated by a 4f system are related independently of the magnification of the 4f system by the following equation: bi=(-1)nai, with n being the order of the radial Zernike polynomial.

Suitability of DIALux for designing UVC disinfection cabins.

During the present Sars-CoV-2 pandemic, there has been an increase in the development of UVC disinfection systems. Researchers and members of the lighting community shifted their interests to this new field to help develop systems for disinfecting facemasks and other small equipment. In this paper we show that it is possible to use DIALux to simulate the irradiance distribution provided by a lamp emitting in the UVC range. We will compare the results provided by DIALux with those obtained from Zemax OpticStudio in three different scenarios. We compared the minimum, maximum, and mean irradiance at the detection plane. The differences between the two software were less than 12%, 2%, and 6%, respectively. We also compared the contour maps of isoirradiance lines. We conclude that DIALux is well suited for UVC lighting design in the UVC range. We think that this finding will contribute to increasing the design and manufacturing of new UVC disinfection systems needed to fight against the Sars-CoV-2 pandemic.

Wavefront coding with Jacobi-Fourier phase masks for retinal imaging.

Wavefront coding is a technique that combines optical phase elements and digital signal processing in order to increase the effective depth of focus of optical systems. The success of wavefront coding lies in the design of a suitable phase mask placed at the system's aperture. This element allows for image formation invariant under the effects of different second-order optical aberrations. In optical systems limited by temporally or spatially varying high-order aberrations, the use of wavefront coding has not been fully demonstrated. Here we propose the choice of Jacobi-Fourier shaped phase masks to produce sharp and clear retinal images of living eyes. To demonstrate the potential use of the technique, we analyze the performance of the Jacobi-Fourier phase masks through experimental simulations to alleviate aberrations for different eye aberrations. We will show that the best mask choice is robust to noise while keeping acceptable resolution and reducing image artefacts.

UV light dosage distribution over irregular respirator surfaces. Methods and implications for safety.

The SARS-CoV-2 pandemic has led to a global decrease in personal protective equipment (PPE), especially filtering facepiece respirators (FFRs). Ultraviolet-C wavelength is a promising way of decontamination, however adequate dosimetry is needed to ensure balance between over and underexposed areas and provide reliable results. Our study demonstrates that UVGI light irradiance varies significantly on different respirator angles and propose a method to decontaminate several masks at once ensuring appropriate dosage in shaded zones. An UVGI irradiator was built with internal dimensions of 69.5 × 55 × 33 cm with three 15 W UV lamps. Inside, a grating of 58 × 41 × 15 cm was placed to hold the masks. Two different flat fold respirator models were used to assess irradiance, four of model Aura 9322 3 M of dimensions 17 × 9 × 4 cm (tri-fold), and two of model SAFE 231FFP3NR (bi-fold) with dimensions 17 × 6 × 5 cm. An STN-SilverNova spectrometer was employed to verify wavelength spectrum and surface irradiance. A simulation was performed to find the irradiance pattern inside the box and the six masks placed inside. These simulations were carried out using the software DIALUX EVO 8.2. The data obtained reveal that the irradiance received inside the manufactured UVGI-irradiator depends not only on the distance between the lamps' plane and the base of the respirators but also on the orientation and shape of the masks. This point becomes relevant to assure that all the respirators inside the chamber receive the correct dosage. Irradiance over FFR surfaces depend on several factors such as distance and angle of incidence of the light source. Careful irradiance measurement and simulation can ensure reliable dosage in the whole mask surface, balancing overexposure. Closed box systems might provide a more reliable, reproducible UVGI dosage than open settings.

Potential use of cubic phase masks for extending the range of clear vision in presbyopes: initial calculation and simulation studies.

PURPOSE: In this paper we analyse the potential use of a non-symmetrical optical element, a cubic phase mask, for extending the range of clear vision of presbyopic eyes. Additionally, we will discuss the appropriateness of the visual Strehl ratio to analyse this sort of presbyopic solution based on non-symmetrical phase masks contrasted with through-focus retinal images. METHODS: In order to evaluate the performance of the cubic phase mask we employed computational Fourier Optics to compute the different visual Strehl criteria as well as simulate the retinal images. The through focus real part of the modulation transfer functions and retinal images were computed for four object distances 6.0, 1.0, 0.6 and 0.4 m which correspond to far, intermediate and near vision conditions for optotypes of visual acuity of 0.1 and 0.0 logMAR (Snellen 6/7.5 and 6/6; 0.8 and 1 in decimal Snellen). For the experimental validation we built an artificial eye consisting of a plano-convex lens with a focal length of 25.4 mm and 0.5 numerical aperture, a variable diaphragm, a 3× objective and an ORCA 285 Hamamatsu Photonics camera 8.1 µm pixel size (resulting in an effective pixel size of 2.7 µm). A set of four different VA charts adapted to monitor different visual acuities (ranging between 0.0 and 0.20 logMAR) were placed at different object distances 6, 1.0, 0.6 and 0.4 m from the artificial eye. RESULTS: Both numerical and experimental validation showed the suitability of the cubic phase mask for extending the range of clear vision of presbyopic eyes, providing at least a visual acuity of 0.1 logMAR (6/7.5 Snellen, 0.8 decimal Snellen) at all distances. The results show that it is possible to choose between promoting far or near vision by changing the magnitude of the defocus component. It is also possible to extend the range of clear vision, by increasing the magnitude of the cubic component. But this increment will cause a reduction in the contrast of the images as it can be observed from the Visual Strehl values and the retinal images generated numerically. CONCLUSIONS: A cubic phase mask in the shape 7.07 µm × (Z9 -Z6 )-0.9 µm × Z4 is a good solution for obtaining a range of clear vision with at least 0.1 logMAR visual acuity (and close to 0.0 logMAR, 6/6, 20/20 and decimal Snellen 1.0) between 6.0 and 0.4 m for a pupil diameter of 5.0 mm. Our results seem to be a good starting point for future studies of this type of cubic phase mask solutions for presbyopia.

Single-pulse laser ablation threshold of borosilicate, fused silica, sapphire, and soda-lime glass for pulse widths of 500 fs, 10 ps, 20 ns.

In this work, we report a comparative study of the laser ablation threshold of borosilicate, fused silica, sapphire, and soda-lime glass as a function of the pulse width and for IR laser wavelengths. We determine the ablation threshold for three different pulse durations: τ=500 fs, 10 ps, and 20 ns. Experiments have been performed using a single laser pulse per shot in an ambient (air) environment. The results show a significant difference, of two orders of magnitude, between the group of ablation thresholds obtained for femtosecond, picosecond, and nanosecond pulses. This difference is reduced to 1 order of magnitude in the soda-lime substrate with tin impurities, pointing out the importance of the incubation effect. The morphology of the marks generated over the different glass materials by one single pulse of different pulse durations has been analyzed using a scanning electron microscope (FESEM ULTRA Plus). Our results are important for practical purposes, providing the ablation threshold data of four commonly used substrates at three different pulse durations in the infrared regime (1030-1064 nm) and complete data for increasing the understanding of the differences in the mechanism's leading ablation in the nanosecond, picosecond, and femtosecond regimes.

Wavefront-coding technique for inexpensive and robust retinal imaging.

We propose a hybrid optical-digital imaging system that can provide high-resolution retinal images without wavefront sensing or correction of the spatial and dynamic variations of eye aberrations. A methodology based on wavefront coding is implemented in a fundus camera in order to obtain a high-quality image of retinal detail. Wavefront-coded systems rely simply on the use of a cubic-phase plate in the pupil of the optical system. The phase element is intended to blur images in such a way that invariance to optical aberrations is achieved. The blur is then removed by image postprocessing. Thus, the system can provide high-resolution retinal images, avoiding all the optics needed to sense and correct ocular aberration, i.e., wavefront sensors and deformable mirrors.

Estimating the eye aberration coefficients in resized pupils: is it better to refit or to rescale?

In order to work in a consistent way with Zernike aberration coefficients estimated in different pupils, it is necessary to refer them to a common pupil size. Two standard approaches can be used to that end: to rescale algebraically the coefficients estimated in the original pupil or to refit them anew using the wavefront slope measurements available within the new one. These procedures are not equivalent; they are affected by different estimation errors that we address in this work. Our results for normal eye populations show that in case of reducing the pupil size it is better to rescale the original coefficients than to refit them using the measurements contained within the smaller pupil. In case of enlarging the pupil size, as it can a priori be expected, the opposite holds true. We provide explicit expressions to quantify the errors arising in both cases, including the expected error incurred when extrapolating the Zernike estimation beyond the radius where the measurements were made.

Fluence ablation threshold dependence on tin impurities in commercial soda-lime glass.

In this paper, we study the reduction in the fluence ablation threshold induced by tin impurities incorporated in float soda-lime glass during the fabrication process. The laser system used in the experiments was a Nd:YVO4 laser operating at 1064 nm with a pulse duration of 20 ns. The fluence ablation thresholds found were 112 J/cm2 for the tin side and 920 J/cm2 for the tin-free side, which means a reduction of nearly 1 order of magnitude. The fluence ablation threshold reduction permits the manufacturing of narrower grooves with small level of roughness, obtaining quality elements in low-cost soda-lime substrates.

Signal-to-noise ratio and aberration statistics in ocular aberrometry.

We define a signal-to-noise ratio (SNR) for eye aberrometry in terms of the sensor geometry, measurement noise, and population statistics. The overall estimation error is composed of three main contributions: the bias in the estimated modes, the truncation error, and the error due to the noise propagation. This last term can be easily parametrized by the proposed SNR. We compute the overall error as well as the magnitude of its three components for a typical sensor configuration, population statistics, and different SNR. We show that there are an optimum number of Zernike aberration modes to be retrieved in each case.

Attraction of Insects to Ornamental Lighting Used on Cultural Heritage Buildings: A Case Study in an Urban Area.

Artificial light at night (ALAN) reduces insect populations by altering their movements, foraging, reproduction, and predation. Although ALAN is mainly associated with streetlights and road networks, the ornamental illumination of monuments is making an increasing (but not well-studied) contribution. We compared insect attraction to two different types of light sources: a metal halide lamp (a type currently used to illuminate monuments) and an environmentally sound prototype lamp (CromaLux) comprising a combination of green and amber LEDs. The experiment was performed within the pilot CromaLux project in Santiago de Compostela (NW Spain). The abundance and diversity of the insects captured between June and October 2021 in the areas surrounding both light sources and in an unlit area were compared. By limiting the light emitted to amber and green, the CromaLux lamps reduced the number and diversity of insects, morphospecies, and orders attracted to the light, with similar numbers captured as in the unilluminated area, while a greater diversity of insects was captured beside the metal halide lamp. This effect has been demonstrated for almost all insect orders trapped, especially in Diptera, Lepidoptera, Coleoptera, Hemiptera, and Hymenoptera. On the contrary, Psocoptera showed a similar attraction to the CromaLux and metal halide lamps, a phenomenon whose causes deserve further investigation. As expected, Diptera were the most diverse and abundant insects in all samples, but the abundance of Lepidoptera was unexpectedly low (4%), which is in line with the worldwide evidence of the progressive decline of populations of this group. The study findings provide evidence that selecting specific wavelengths for ornamental lighting reduces the attraction of insects while maintaining adequate illumination of monuments for aesthetic purposes, resulting in a lower environmental impact on nocturnal insects. This study provides reference data for developing principles of good practices leading to possible regulatory and legal solutions and the incorporation of specific measures for artificial lighting of monuments and urban structures.

Low-cost adaptive astigmatism compensator for improvement of eye fundus camera.

In this work we show a conceptually simple and cheap means by which to improve retinal image quality in fundus cameras. We will explain how to build a low-cost variable astigmatism-correcting device with a pair of identical commercial ophthalmic lenses. We have developed and tested a low order aberration compensation device capable of correcting astigmatism prescriptions up to -8.00 D with no significant addition of higher order aberrations. A theoretical description of the device, calibration, and improvement in retinal images without employing any image restoration technique will be shown.

Wavefront sensing with critical sampling.

Different types of nonredundant sampling patterns are shown to guarantee completeness of the basis formed by the sampled partial derivatives of Zernike polynomials, commonly used to reconstruct the wavefront from its slopes (wavefront sensing). In the ideal noise-free case, this enables one to recover double the number of modes J than sampling points I (critical sampling J=2I). With real data, noise amplification makes the optimal number of modes lower I

Closed-loop adaptive optics with a single element for wavefront sensing and correction.

We propose a closed-loop adaptive optical arrangement based on a single spatial light modulator that simultaneously works as a correction unit and as the key element of a wavefront sensor. This is possible by using a liquid crystal on silicon display whose active area is divided into two halves that are respectively programmed for sensing and correction. We analyze the performance of this architecture to implement an adaptive optical system. Results showing a closed-loop operation are reported, as well as a proof of concept for dealing with aberrations comparable to those typically found in human eyes.

Adaptive astigmatism-correcting device for eyepieces.

PURPOSE: We describe how to construct a low-cost and robust variable astigmatism-correcting device manufactured using a pair of identical commercial ophthalmic lenses. METHODS: Variable astigmatism power can be obtained by relative rotation of two cross cylinders with the same prescription (for this work: S = +2.00 D, C = -4.00 D was used). The rotation of the whole ensemble allows the user to choose the astigmatism axis. RESULTS: The lens system presented here is able to correct astigmatism for eyepieces, compensating eyeglasses prescriptions from -8.00 to 0.00 D without generation of higher order aberrations and always with mean sphere power close to 0. Theoretical description of the piece, calibration, measurement of aberrations, and examples of use within a microscope are included. CONCLUSIONS: An inexpensive and robust variable-astigmatism device for eyepieces can be manufactured using two equal ophthalmic lenses. The system is robust in the sense that small misalignments only minimally affect mean sphere power and do not affect higher order aberrations. This unique device can be adapted to many users.

Reconfigurable Shack-Hartmann sensor without moving elements.

We demonstrate wavefront sensing with variable measurement sensitivity and dynamic range by means of a programmable microlens array implemented onto an off-the-shelf twisted nematic liquid crystal display operating as a phase-only spatial light modulator. Electronic control of the optical power of a liquid lens inserted at the aperture stop of a telecentric relay system allows sensing reconfigurability without moving components. Results of laboratory experiments show the ability of the setup to detect both smooth and highly aberrated wavefronts with adequate sensitivity.

Direct and inverse discrete Zernike transform.

An invertible discrete Zernike transform, DZT is proposed and implemented. Three types of non-redundant samplings, random, hybrid (perturbed deterministic) and deterministic (spiral) are shown to provide completeness of the resulting sampled Zernike polynomial expansion. When completeness is guaranteed, then we can obtain an orthonormal basis, and hence the inversion only requires transposition of the matrix formed by the basis vectors (modes). The discrete Zernike modes are given for different sampling patterns and number of samples. The DZT has been implemented showing better performance, numerical stability and robustness than the standard Zernike expansion in numerical simulations. Non-redundant (critical) sampling along with an invertible transformation can be useful in a wide variety of applications.

Pupil size stability of the cubic phase mask solution for presbyopia.

Presbyopia correction involves different types of studies such as lens design, clinical study, and the development of objective metrics, such as the visual Strehl ratio. Different contact lens designs have been proposed for presbyopia correction, but performance depends on pupil diameter. We will analyze the potential use of a nonsymmetrical element, a cubic phase mask (CPM) solution, to develop a contact or intraocular lens whose performance is nearly insensitive to changes in pupil diameter. We will show the through focus optical transfer function of the proposed element for different pupil diameters ranging from 3 to 7 mm. Additionally, we will show the images obtained through computation and experiment for a group of eye charts with different visual acuities. Our results show that a CPM shaped as 7.07 µm*(Z33-Z3-3)-0.9 µmZ20 is a good solution for a range of clear vision with a visual acuity of at least 0.1 logMar from 0.4 to 6 m for pupil diameters in the 3- to 7-mm range. Our results appear to be a good starting point for further development and study of this kind of CPM solution for presbyopia.

Development of optokinetic tracking software for objective evaluation of visual function in rodents.

The aim of this study was to develop software that performs the optokinetic tracking assessment without the involvement of experimenters to increase the objectivity of the test. To check the effectiveness of the software, several videos were analyzed and the results were compared to those produced by two experimenters. Videos consisted of visual acuity and contrast sensitivity tests on normal animals and pigmented P23H rats (animal model of retinitis pigmentosa). Our software showed a reasonably high success rate: in approximately 78% of the cases, both the software program and the experimenters were in agreement, including the direction of rotation. The software detected 7% false positive cases, 10% false negative cases, and it was wrong in 5% of the cases. Decrease in visual function with age in pigmented P23H rats was observed from the first time interval, although minimum thresholds were found in visual parameters at advanced ages. We developed simple software based on current functions included in the Matlab image processing toolbox that was able to recognize, with a reasonably high percentage of success, the subtle head movements of the rodent produced when visual perception of the optokinetic optotype occurs.