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.

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.

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 4 system. I provide theoretical and experimental evidence. The experimental setup consisted of two 4 systems of magnifications 1 and 1/3 with their corresponding wavefront sensors at their ends.

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.

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.

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.

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).

Radiation characterisation and dosimetric measurements of a femtosecond pulsed laser ablation system.

This work describes the radiation characterisation and dosimetric measurements performed on the low-energy micromachining station of the femtosecond STELA (Santiago TErawatt LAser) at the University of Santiago de Compostela (Spain). For this aim, ionisation chambers, solid state detectors, and radiochromic films were used. The results show the emission of pulsed x-ray produced by laser-accelerated electrons from the ablated material exhibiting both bremsstrahlung and characteristic radiation.

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.

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.

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.

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.

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.

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.

Lens aberrations and their relationship with lens sutures for species with Y-suture branches.

Work remains to be done to understand the origins of ocular aberrations. We analyze lens aberrations of several species with Y-suture branches (bovine, ovine, and porcine) and their relationship with suture distribution. Aberrations are measured in vitro with a point diffraction interferometer in 10 different eyes of each species.

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.

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.

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.

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.

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 View Article and Find Full Text PDF

Pupil tracking with a Hartmann-Shack wavefront sensor.

We present the theoretical background and experimental validation of a pupil tracking method based on measurement of the irradiance centroid of Hartmann-Shack aberrometric images. The experimental setup consists of a Hartmann-Shack (HS) sensor forming over the same camera the images of the eye's pupil and the aberrometric image. The calibration is made by comparing the controlled displacements induced to an artificial eye with the displacements estimated from the centroid of the pupil and of the HS focal plane.

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 contribution of the fixational eye movements to the variability of the measured ocular aberration.

The purpose of this work is to analyze the contribution of eye movements to the variability of the Zernike coefficients as determined with a Hartmann-Shack aberrometer. In order to isolate this effect we considered static aberrations tied to the eye pupil. We used several eye movements of different magnitude, both synthetic and corresponding to actual series recorded in our laboratory with different subjects.

Changes of ocular aberrations with gaze.

The dependence of the ocular aberrations on gaze has been studied in three eyes using a fast-acquisition, Hartmann-Shack wavefront sensor. Although there were some trends in the change of some aberration terms with gaze, the changes of most Zernike coefficients were smaller than their variability at each individual gaze position, due to the combined effects of microfluctuations of accommodation, eye movements, tear film dynamics, and measurement noise. For our particular experimental dataset, the confidence level at which the null hypothesis (i.