bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantum Control of NaI Photodissociation Reaction Product States via Ultrafast Chirped Light Pulses
Authors: Bardeen C. J. , Cong P. , Kohler B. , Krause Jeffrey L. , Messina M. , Wilson K. R. , Yakovlev V. V.
Published: February 2023

Previous work by Herek, Materny, and Zewail has demonstrated that the timing between two ultrafast laser pulses can be used to control the branching ratio of Na* to Na production in the photodissociation of NaI [1]. In their approach, a transform limited pump pulse excites the ground ionic electronic state of NaI to the electronically excited covalent state and then a second transform limited pulse intercepts the evolving covalent wave packet and further excites to a higher lying state on which it dissociates into Na*+I. They showed that the branching ratio of Na to Na* production can be controlled by changing the timing between the two pulses. In this work we show that the Na to Na* production ratio can also be controlled at fixed pump-probe delay by varying the linear chirp of the pump laser pulse while keeping its spectrum and intensity versus time fixed. What is being controlled is the degree of localization or focusing of the wave packet at the time of its interception by the pump pulse, which carries a localized wave packet with greater probability away from the state decaying to Na up to the state decaying to Na*. It has been demonstrated both theoretically and experimentally that chirped ultrashort laser pulses can be used to focus nuclear wave packets of evolving quantum systems [2]. In our control scheme, the first control laser pulse ωc is tailored to focus the vibrational wave packet at a particular time and internuclear distance such that a second ultrafast light pulse ωp will intercept the wave packet and further excite it to the higher lying Na*+I state. We demonstrate both theoretically and experimentally that the degree of wave packet focusing caused by the control pulse can affect the Na* to Na branching ratio, and that this focusing and subsequent increase in the Na* to Na branching ratio is due to the linear chirp of the control pulse ωc.
Electron-Lattice Heating From Avalanche Ionization in Silicon with Near Infra-Red Ultrafast Laser Pulses
Authors: Pronko P.P. , Mourou G. , VanRompay P.A. , Liu X. , Du D. , Singh R. K. , Qian F.
Published: February 2023

Absorption and redistribution of ultrafast pulsed laser energy in silicon is examined with 800 nm radiation for pulse durations ranging from 80 fs to 7 ns. The results are successfully interpreted in terms of an avalanche ionization process. Thresholds for vaporization are measured and compared to a theoretical model that incorporates a two temperature electron-lattice heating process. Ionization layer thickness and time resolved melting and vaporization events are described in terms of a thermodynamic process involving the absorption of ionization energy by the lattice and its subsequent phase transformation to the liquid and vapor state. Nominal solid density ionization heating layers of 75 nm are extracted from the model and compared to results obtained from DC high field avalanche formulations. Our experimental results are found to provide a fit with, and continuation of, the avalanche ionization rate curve for silicon ID for electric field strengths extending to 4e7 volts/cm.
Ultrafast Equal Pulse Correlation Measurements in GaAs Structures with a Near-Field Microscope
Authors: Smith S. , Holme N.C.R , Kwok M. , Orr B.G. , Kopelman R. , Norris T.B.
Published: February 2023

Our work focuses on combining ultrafast time resolved spectroscopy with the subwavelength spatial resolution of Near-field Scanning Optical Microscopy (NSOM). We use a variant of the equal pulse correlation (EPC) [1] in combination with NSOM by sending both pump and probe pulses through a sub-200-nm NSOM tip [2]. While other workers in the field have sent one or both pulses to the sample via conventional far-field optics, our technique has two unique features which may be advantageous, and which form the subject of this paper. The first is an apparent decrease in the depth of field, and the second is the possibility to measure carrier transport with submicron spatial resolution. An arrangement sending both "pump" and "probe" pulses through the NSOM tip [3] may be advantageous when applying NSOM to "thick" samples, such as semiconductor materials and devices, because it appears to have a shallow depth of field built-in to it. We present measurements which put an upper bound on the depth of field in this type of experiment and show the main features of the data can be qualitatively reproduced by a simple dipole model.
Ultrafast Hole-Phonon Interactions in GaAs
Authors: Langot P. , Del Fatti N. , Tommasi R. , Vallée F.
Published: February 2023

Relaxation of photoexcited nonequilibrium carriers in semiconductors has been extensively investigated using time-resolved femtosecond techniques. These investigations have however focused on hot-electron relaxation dynamics and little is known on hole scattering processes. The different approach of cold-carrier investigation has been recently applied to this problem and it has been shown that hole thermalization can thus be selectively studied in direct gap intrinsic semiconductors using a femtosecond high-sensitivity two-color absorption saturation technique [1]. This is based on the fact that because of the larger k-space spreading of the heavy-hole distribution as compared to the electron one, the transient transmission change (ΔT/T) due to filling of large momentum states (i.e., for large probe photon excess energy) predominantly contains information on heavy-hole thermalization making possible investigation of cold-hole heating dynamics [1]. In contrast to carrier cooling, heating of cold-carriers by phonons is strongly dependent on the lattice temperature (the efficiency of phonon absorption is proportional to their occupation number) which permits separation of carrier-phonon interaction from other scattering processes. We have exploited this temperature dependence to perform the first direct investigation of hole-optical phonon interactions in bulk GaAs.
Energy Penetration of Ultrahigh Intensity Short Laser Pulses Into Overdense Plasmas Through Solitons
Authors: Kim A.V. , Abramyan L.A. , Mironov V.A.
Published: February 2023

Now light intensities above 1018W/cm2 have been routinely achieved by focusing the ultrashort pulses delivered by compact multiterawatt laser systems. At these intensities, the quiver velocity of the electrons is relativistic, so that both the single- particle and collective response become nonlinear functions of the incident field. Recently, particle-in cell simulation method was employed for the study of ultrahigh intensity laser-matter interaction [1, 2] which has demonstrated complex unsteady dynamics of the interaction. Nevertheless, basic physical processes responsible for capability of the laser pulse to directly penetrate an overdense plasma were not identified. In this report, we describe and analyze certain basic process relevant to the ultrahigh intensity interaction of relativistic laser pulses with the sharply edged overdense plasma. Our analysis based on the hydrodynamics description of a plasma will consist of two parts. First, we consider a stationary model of reflection of circularly polarized laser wave normally incident upon a collisionless, overdense plasma.
Tunable 50 fs pulses in the visible by up-conversion of parametrically generated pulses in the near infrared
Authors: Sueptitz M. , Kaindl R. , Lutgen S. , Woemer M. , Riedle E.
Published: February 2023

For the study of the ultrafast dynamics of elementary processes in physics, chemistry and biology femtosecond pulses in the visible and the UV are needed at spectral positions determined by the optical properties of the investigated system. Such pulses are not yet readily available at pulse lengths below 100 fs, despite the tunability of Ti: sapphire based systems in the near infrared. This is due to the fact that the group velocity mismatch (GVM) in nonlinear optical materials causes severe pulse lengthening in the nonlinear frequency conversion used for the generation of these pulses. We have used a multi-stage conversion scheme that by-passes these problems and is able to produce pulses of 50 fs length throughout the visible.
Sub-20-fs Multiterawatt Lasers
Authors: Barty C. P. J. , Guo T. , LeBlanc C. , Raksi F. , Rose-Petruck C. , Squier J. A. , Walker B. , Wilson K. R. , Yakovlev V. V. , Yamakawa K.
Published: February 2023

Recent advances in short pulse oscillator technology have led to the reliable generation of pulses as short as 7-fs in duration[1]. Amplification of such pulses to only modest energies (~1 J), would produce peak powers (100 TW) and peak intensities (>1021 W/cm2) which are equivalent to or greater than those currently produced by the largest Nd:Glass based laser facilities. Futhermore low-energy, ultrashort-duration, high-peak-power systems could operate at repetition rates that are > 4 orders of magnitude higher, thus opening wide areas of high field, ultrafast phenomena to rapid investigation. Amplification of pulses on the order of 10 fs, however, is severely limited by two concerns: 1) control of higher order phase distortion and 2) gain narrowing during amplification.. In this paper, we present results of a three stage amplification system developed at the University of California, San Diego in which we address these problems with an optimized, quintic-phase-limited expander and compressor design and with regenerative pulse shaping. This system is designed to produce nearly-diffraction-limited, > 1-J pulses of ~15-fs in duration. To date the first two stages of amplification have produced, 18-fs, 4.4-TW pulses at a repetition rate of 50 Hz and an average power > 10 W before compression. To our knowledge, these intermediate results represent the shortest terawatt pulses, the highest expansion ratio (>100,000 times) and the highest average power yet produced by a chirped pulse amplification system.
Two-photon excitation scanning microscopy with a compact, mode locked, diode- pumped Cr:LiSAF Laser
Authors: Svoboda K. , Denk W. , Knox W.H. , Tsuda S.
Published: February 2023

Laser scanning microscopy combined with two-photon excitation of fluorescence holds great promise in imaging biological systems. This two-photon excitation laser scanning microscopy (TPLSM) [1] yields intrinsic submicron three-dimensional resolution with much reduced background fluorescence and thus reduced photodamage. Although the advantages of TPLSM as compared to wide field fluorescence microscopy and confocal microscopy have been demonstrated in a number of applications [2], the large cost and utility requirements of mode locked Ti:sapphire laser systems and other femtosecond light sources have kept TPLSM out of reach for most biology labs. We demonstrate here that a recently developed compact solid state laser that is mode locked with a Saturable Bragg Reflector (SBR) [3] is well-suited for TPLSM. A SBR-modelocked Cr:LiSAF laser was pumped with a 0.5 W, 670 nm diffraction-limited MOPA (SDL), providing 90 fs pulses at 860 nm with CW power of 25-44 mW per beam (Fig. la). A single beam was directed into a laser scanning microscope consisting of a pair of galvomirrors, a relay lens, a dichroic mirror, a Zeiss water-immersion objective (63 x 0.9 NA), and a photomultiplier tube for the detection of fluorescence photons [2]. Rat cortical brain slices (300 μm thick) were prepared using standard techniques. For anatomical imaging, neocortical pyramidal cells that were deeply embedded in the tissue were dialyzed and voltage clamped using whole-cell electrodes containing 500 μM fluorescein dextran (MW = 3 kD). TPLSM imaging at low magnification (Fig. 1B) revealed primary and secondary dendrites and the initial segment of the axon. At high magnification single dendritic spines, the smallest neuronal compartments, became apparent (Fig. 1C, arrow). A series of images acquired at different focal planes (Δz = 1.6 μm) demonstrates the sectioning capabilities of the microscope (Fig. 1D-F). For functional imaging of physiological calcium responses, neurons were dialyzed with electrodes containing the calcium indicator Ca-green-1 (300 μM, Molecular Probes). Ca-green is a fluorophore that undergoes a large fluorescence intensity change in response to Ca2+ binding. Intracellular free calcium concentration changes evoked by single action potentials could easily be detected (Fig. 1G).
Coupled Bloch-Phonon Oscillations in Superlattices
Authors: Dekorsy T. , Kim A.M.T. , Kurz H. , Köhler K.
Published: February 2023

One of the most relevant phenomena determining the electronic and optoelectronic properties of semiconductors and semiconductor heterostructures is the interaction between charged carriers and lattice vibrations. Especially electron-LO-phonon interaction provides the dominant relaxation and scattering mechanism in polar compound semiconductors. A special class of material, the semiconductor superlattices, recently gained great attention due to the verification of the early prediction of Esaki and Tsu [1] to generate continuously tunable THz radiation from Bloch oscillation [2], where the Bloch oscillation frequency is solely determined by eFd/h (F is an applied electric field and d the superlattice period). Here we report on the first observation of Bloch oscillations in GaAs/Al0.3Ga0.7As superlattices with frequencies tuned in resonance with the LO phonon resonance of GaAs at 8.8 THz. These experiments give direct insight into the nature of electron-phonon interaction in semiconductors. In contrast to the assumption that electronic coherence is rapidly destroyed by electron-phonon interaction, we show that the electronic coherence retains and can be transferred to the lattice vibration due to the formation of coupled Bloch-phonon modes.
Phase-locked femtosecond photon echo: A new dimension in ultrafast spectroscopy
Authors: Wiersma Douwe A. , De Boeij Wim P. , Pshenichnikov Maxim S.
Published: February 2023

We report on phase-locked optical coherence experiments on the 10 fs timescale. While optical-phase sensitive experiments have been contemplated [1] and performed in the past on a 100 fs timescale [2], exploration of their true potential had to wait for the right fs laser to appear on the scene. It turns out that the almost ideal laser to perform these very subtle phase-locked experiments is the (cavity-dumped) mode-locked Ti:sapphire laser. This laser is capable not only of generating pulses of 10 fs or less [3], but exhibits also little amplitude noise, which is an important characteristics for stabilisation schemes based on an feedback loop. In our group we have gone one step further: our 13-fs cavity-dumped laser [4] and experimental set-up now functions under complete control of a PC computer such that fs photon echo experiments can be done uninterrupted for days if not weeks.
Coherent and incoherent dynamics of large molecules in solution studied on a 20 femtosecond time scale
Authors: Riedle E. , Hasche T. , Ashworth S. H. , Woerner M. , Elsaesser T.
Published: February 2023

The ultrafast dynamics of dye molecules in solution was studied in temporally and spectrally resolved experiments on a 20 fs time scale. To separate the contributions form the ground and the excited states, a two-color scheme was employed. Blue pulses were used to excite a small fraction of the molecules to higher excited electronic states Sn (n>1) and the evolving dynamics was probed with red pulses tuned to the S0-S1 transition [1]. Around delay zero, a pronounced coherent signal occurs. The coherent coupling of the two electronic transitions is due to coherent vibrational motion in the S0 state induced by an impulsive Raman process. The molecules promoted to Sn states give rise to a fast ground state bleaching on a 50 fs time scale that is followed by the picosecond onset of stimulated emission from the S1 state.
Jitter of 3-cycle laser pulses from a gas-filled capillary — Single-shot SPIDER pulse characterization at 1 kHz
Authors: Biegert J. , Kornelis W. , Steinmeyer G. , Tisch J. W. G. , Keller U. , Nisoli M. , Sansone G. , Stagira S. , Vozzi C. , De Silvestri S.
Published: February 2023

Up to now, the only technique capable of generating millijoule-level sub-10-fs pulses is based on spectral broadening in a gas-filled capillary with subsequent compression. Even though this technique is routinely being used, the exact nature of the processes involved in white-light generation processes is not fully understood. We present a measurement approach that opens up a new window to understanding femtosecond continuum generation processes. Aside from yielding a better understanding of the underlying physical principles, this has direct implications in how the pulses are subsequently compressed. More importantly, it might provide the answer to the question of whether a phase-locked pulse keeps its lock during this process.
Coherent spin-lattice interaction in a ferromagnetic metallic film
Authors: Bigot Jean-Yves , Guedoni Luca , Halte Valérie
Published: February 2023

A few years ago, it has been demonstrated that it is possible to demagnetize ferromagnetic metallic thin films using femtosecond optical pulses [1]. The magnetization dynamics of Ni and CoPt metallic films was then investigated with time resolved Kenmeasurements as a function of applied magnetic field and laser intensity when the materials undergoes its feno-paramagnetic phase transition. These observations have been confirmed with a variety of femtosecond techniques like for example the second order nonlinear Ken effect [2] or spin resolved two photon photoemission [3]. More recently, we have shown that, under a weak perturbation of the magnetization with pulses of 20 fs duration, the initial ultrafast spin dynamics follows the thermalization of the electronic populations to a Fermi-Dirac distribution [4], In this paper, we report the first observation of a coherent exchange of energy between the spins and the lattice while both populations are cooling down.
Time-domain interferometry for direct electric-field reconstruction by use of an acousto-optic programmable dispersive filter
Authors: Oksenhendler T. , Herzog R. , Kaplan D. , Tournois P. , Monmayrant A. , Joffre M.
Published: February 2023

We demonstrate a new version of spectral phase interferometry for direct electric-field reconstruction (SPIDER) [1]. This new phase-measurement method, hereafter referred to as time-domain SPIDER, is in fact a variant of HOT SPIDER [2] where frequency-domain interferometry is replaced here with time-domain interferometry.
Interferometric Assessment of the Surface Profile of Diffractive Bifocal Contact Lenses
Authors: Woods Russell L
Published: February 2023

Current diffractive bifocal contact lenses use surface relief variations over the diffractive zone to create relative phase delays giving a focusing effect.1, 2 To achieve the required phase delay the junctions in the diffractive zone must be about 1 to 4 µ m in height depending on the lens material.3, 4 Surface relief shape will influence the amount of light in the different diffractive foci.5, 6 For example, as the diffractive zone height increases more light will be found in the first order (near) focus.
Simplified Strategies for the Simulation of Progressive Addition Lenses
Authors: Fowler Colin W
Published: February 2023

Progressive addition lens surfaces are complex aspheric in form. Being non-rotationally symmetrical can make their analysis difficult. Much of the literature on their design is found in patents, which vary considerably in their information content. The starting point for this discussion arose out of a requirement to be able to demonstrate the design of PALs to optometry students, many of whom have limited mathematical background. The idea was to produce a computer program that would rapidly produce mean sphere and cylindrical error plots with the minimum of input parameters, so that different lens design concepts could be demonstrated very quickly. To this aim, three strategies have been used, with varying degrees of success.
Central and Lateral Static Distortion In Ophthalmic Lenses
Authors: Simonet Pierre , Bourdoncle Bernard , Miege Christian
Published: February 2023

Distortion is an aberration which is not related to the resolution of images formed by the periphery of an ophthalmic lens but merely to their shape. As noted by Bennett and Edgar (1979), relevant factors associated with distortion lie within the domain of visual perception, this could explain why, in the ophthalmic community, there was no uniform approach in the conceptualization and in the quantification of this aberration.
Zernike Polynomial Representations of Videokeratoscope Height Data
Authors: Schwiegerling Jim , Greivenkamp John E. , Miller Joseph M.
Published: February 2023

Placido-disk based videokeratoscopes measure the slope of the corneal surface in the meridional direction. The derivative of this slope data is related to the optical power distribution of the cornea. While the power map is widely used for clinical evaluation, information about the sag or height of the cornea is useful for determining the optical effects of the cornea. This sag data is calculated by integrating the slope data obtained by the videokeratoscope. A significant drawback to viewing the surface sag data is proper display of the pertinent height information. Small height variations on the surface are obscured by the axial symmetric aspheric sag corresponding to the base power of the cornea and a possible cylindrical sag corresponding to corneal astigmatism. In this paper, we will examine a method for decomposing corneal height data into Zernike polynomials, and show how to obtain base and astigmatic curvatures and powers from the expansion coefficients. These coefficients are used to calculate the parabolic and cylindrical components of the topography data. By removing these terms from the original height data, the residual higher-order height variations of the cornea are shown more clearly. Topographies of an eye with corneal astigmatism and an eye that underwent radial keratotomy are displayed using this technique.
Vision Science in the Developing World: Challenges, Opportunities, Problems, and Example
Authors: Enoch Jay M.
Published: February 2023

General problem: For some considerable period of time, world-wide human population has been growing exponentially. During the past several decades, infant and maternal mortality has been reduced, and world population has been aging rapidly. In the "under-developed world", population control is at best rudimentary. Fortunately, recent reports suggest that progress is being made in at least some venues. In parallel, there are limited resources for increasing food production (resulting from inefficient use of available farm lands, exhaustion and erosion of soils, and destruction of forests); inadequate provisions are made for health care and training of health care providers; restricted funds and personnel are available for provision of infrastructure; educational opportunities are limited; and social and health care "nets" are lacking for most individuals living in such settings. The entire situation is becoming ever less tenable.
Foveal Adaptation Abnormalities In Early Normal-Tension Glaucoma
Authors: Eisner Alvin , Samples John R. , Campbell Heidi M. K. , Cioffi George A.
Published: February 2023

The purpose of this study is to test the hypothesis that visual adaptation can be affected in glaucoma, particularly in normal (or "low") tension glaucoma. More specifically, this study aims to test the hypothesis that by taxing the adaptation capabilities of eyes with normal-tension glaucoma but only minimal field loss, time-dependent abnormalities can be elicited at the fovea.
Magnetic Resonance Images of the Ciliary Muscle and Lens in Presbyopes and Non-Presbyopes
Authors: Strenk Susan , Semmlow John L.
Published: February 2023

High resolution magnetic images of the eye have been achieved using a specially designed radio frequency receiver coil in conjunction with software modifications. These images provide direct evidence of changes in the ciliary body and lens during accommodation. Results indicate that in presbyopes the ciliary muscle continues to contract even though the lens is no longer capable of shape changes.
Disability Glare with Retinal Position of the Detection Stimulus and the Temporal Relations Between the Glare Source and Detection Stimulus as Variables
Authors: Meng Jeanette , Bichao Isabel Cristina , Yager Dean , Zhan Hong , Cheung Janice
Published: February 2023

One of the reasons that tests of disability glare have been developed is to attempt to provide a quick and reliable clinical estimate of how much a patient might suffer in visual impairment, in everyday life when confronted with a bright source of light in his or her visual environment. The main early complaint of many of these patients is that glare impairs their night driving.
Individual Differences in Dynamic Visual Acuity at low Luminance: Velocity and Contrast as Parameters
Authors: Zhan Hong , Yager Dean , Meng Jeanette
Published: February 2023

Traditional static visual acuity (SVA) tests are used to assess one's visual function when both observer and object are stationary, and usually with high luminance and high contrast. Another acuity measurement developed in laboratories, with relative motion between the observer and the object, is called dynamic visual acuity (DVA).
Neurophysiological evidence for long range facilitation in normal, but not amblyopic, human visual cortex
Authors: Polat Uri , Norcia Anthony M.
Published: February 2023

Lateral interactions play a prominent role in the spatial vision of both normal and amblyopic observers. These interactions have generally been reported to be inhibitory in both psychophysical (Cannon and Fullenkamp, 1991; Chubb, Sperling and Solomon, 1989) and physiological ((Kitano et al, 1994; Grinvald et ah, 1994) studies. More recently long range excitatory interactions have been found psychophysically (Polat and Sagi, 1993b, 1994a). The visibility of a small foveally viewed Gabor patch can enhanced by laterally placed Gabor patches of similar orientation. The sign of the effect, enhancement or suppression depends on target and flank separation and on the relative orientation of the target and its flanks. Maximal facilitation of threshold occurs for co-oriented, collinear targets that are separated by several wavelengths of the spatial frequency of the Gabor patches. Interactions occur over distances as large as several degrees.
The Topography of Visual Focal Attention
Authors: Mackeben Manfred
Published: February 2023

Visual attention can be seen as a computational resource that aids perception in any part of the visual field to which it is applied. This resource is limited, however, as it cannot be applied everywhere at the same time, but constitutes an attentional "focus". It has been known since the groundbreaking work of Helmholtz (1896) that attention has mobility and can be willfully deployed in the periphery of the visual field. In the absence of such "effort of will" it tends to return to the region in or near the center of the visual field.
Double-Pass Measurements of Retinal Image Quality in Green and Near Infrared Light
Authors: López-Gil Norberto , Artal Pablo
Published: February 2023

Recent double pass measurements of the ocular monochromatic modulation transfer function (MTF) have been obtained in visible light (1). Near infrared light has not been used before in the double pass technique despite that the retinal reflection factor is higher for larger wavelengths and that near infrared measurements would not affect the viewing conditions. One of the potential problems of using near infrared in the double pass is the larger retinal scattering. This should produce double pass retinal images with larger scattering halos, affecting in principle the estimates of the MTF. In this work, we evaluate the possibilities of using near infrared illumination in the double pass technique. We record double pass images of green (543 nm) and near infrared (780 nm) point sources and show that infrared and green estimates of the ocular MTF are similar.
A Hand-held Video Keratoscope for the Measurement of Corneal Astigmatism in Infants and Young Children
Authors: Miller Joseph M. , Mellinger Mark D. , Greivenkamp John E.
Published: February 2023

We have developed a hand-held video keratoscope (HVK) that is appropriate for use with infants and young children. We report the design features and performance characteristics of this instrument. It is difficult to measure corneal astigmatism in very young children using conventional equipment. Mandel (1) and Howland (2) developed still-photographic methods to image the corneal light reflections of either a ring keratoscope (1) or discrete set of point sources (2). We have previously described a remote keratometer (3) that permits simultaneous, binocular measurement of the corneal curvature, but it is too bulky to use in the field. Subsequently, a hand-held keratoscope has become available. The Alcon Portable Auto-keratometer (PAK) is convenient to use and accurate, and works well with three to five year old children, but does not work well with infants (4). We were encouraged by Wood et al (5) reporting their success in measuring infants with a hand-held video keratoscope. Our experience with infants led us to believe that frame-by-frame inspection would permit measurement of infants.
Astigmatism, Amblyopia, and Visual Disability Among a Native American Population
Authors: Dobson Velma , Tyszko Robert M. , Miller Joseph M. , Harvey Erin M.
Published: February 2023

It is well documented that there is a high prevalence of both astigmatism and visual disability among some Native American peoples. As shown in Table 1, the prevalence of astigmatism ≥1 diopter (D) among Native American school-age children ranges from 30% to 87%, whereas the prevalence of astigmatism ≥1 D among urban school-age children ranges from 2% to 7%.
The Effects of Cross-Spatial-Frequency Adaptation on Speed Discrimination
Authors: Chen Yue , Bedell Harold E. , Frishman Laura J.
Published: February 2023

The coding of stimulus speed has been accepted to be an important component of motion processing in the visual system. How this coding is implemented, however, is still not entirely clear. In terms of its relationship with spatial and temporal contents of moving targets, speed processing is often modeled as a two-stage process (e.g. Heeger, 1990; Smith & Edgar, 1994). In the first stage, initial speed estimates are generated within individual spatial- and temporal-frequency-tuned mechanism. In the second stage, the outputs of multiple spatio-temporal frequency mechanisms from the first stage are combined to produce the speed codes that are then invariant with respect to spatial frequency. This descriptive model for speed coding makes sense from both functional and experimental perspectives. Functionally, speed coding in the visual system should not vary with respect to spatial frequency; otherwise, non-identical speed coding among spatial frequency mechanisms would perceptually make the different spatial frequency components of a single target appear to move incoherently. Experimentally, it has been demonstrated that whereas the responses of neurons at early stages, such as in VI, are spatial-frequency-tuned, the responses of some neurons at later stages, such as in MT, have broader spatial frequency bandwidths (Newsome, Gizzi & Movshon, 1983), which presumably represent the combination of inputs from several lower-level spatial frequency mechanisms.
A Transcultural Adaptation of the Index of Visual Functioning: The French Version of the VF-14
Authors: Jacques Gresset OD , Boisjoly Hélène , Nguyen Quynh , Boutin Jean
Published: February 2023

In recent years, the development of disease or specific measures of functional status has provided additional insights to the functional status of patients following surgical procedures compared to the measures obtained from more traditional clinical outcome measures or from generic health status questionnaires (Patrick & Deyo, 1989). Several instruments related to functional impairment due to cataracts have been recently proposed (Mangione & al, 1992; Sloane & al, 1992; Brenner & al, 1993; Steinberg & al, 1994a). The index of visual functioning (VF-14 ®), and the Cataract Symptom Score ® (CSS) developed by Steinberg & al. (1994a) seem to be the more widely used (Steinberg & al. 1994b, Schein & al. 1994).
Clincal Version of the Vascular Entoptoscope
Authors: Nuñez Raul , Applegate Raymond A. , Bradley Arthur , Hendricks Janet J.
Published: February 2023

The posterior pole of the eye contains the anatomic fovea and foveola. These structures are highly specialized to maximize visual acuity. In foveola, the inner retinal layers down to the outer nuclear layer are displaced forming a pit, which contains the highest density of cones in the retina (147,000 cones per mm2). The retinal capillaries in the area of the fovea typically form concentrically arranged channels ending in a capillary loop approximately 0.5 mm across which outline a capillary-free zone known as the "foveal avascular zone" FAZ(1). The lateral displacement of inner retinal structures, including the retinal vasculature, presumably exists to leave an unobstructed light path to the site of phototransduction, thereby enhancing image quality. Because of the inverted nature of the retina (blood vessels lie between incoming light and the photoreceptors), it is possible for humans to view shadows of their own retinal vessels and their contents. Entoptic methods for their visualization of retinal blood vessels and blood flow were described in the nineteenth century(2), and recently entoptic visualization methods have been use to study the foveal capillary details and the foveal avascular zone (FAZ) size and shape (3-5), foveola vessels (4,6,7), macular blood flow (8,9) and capillary density around the FAZ (10).
Optical Quality of Progressive Addition Lenses
Authors: Pierre Simonet OD , Jocelyne Gagné
Published: February 2023

The optical characteristics of progressive addition lenses can be assessed by several techniques1-3. The most common is the measurement of peripheral powers using a scanning focimeter or an equivalent device4-8. However, when considering the optical performance of such lenses, these techniques do not take into account the limitations brought upon by the eye itself.
Reading With A Stand Magnifier Effect of Number of Letters on Reading Rate
Authors: Peli Eli , Fine Elisabeth M. , Kirschen Matthew P.
Published: February 2023

Increasing letter magnification leads to increased reading rates for most visually impaired observers (Legge et al., 1985a). However in most cases, increasing magnification reduces the number of letters simultaneously visible (often called the field of view or window size). When reading horizontally scrolled magnified text, four to five letters were needed to attain maximal reading rates (Legge et al., 1985b). We have recently replicated this finding for this passive reading condition. Whittaker and Lovie-Kitchen (1993) have reported that the number of letters needed for self-navigated reading is substantially larger. However, Beckmann and Legge (1991; Beckmann et al., 1993) reported that for self-navigated reading with a CCTV, only 5 letters were needed to achieve maximal reading rates.
Off-Axis Ocular Monochromatic Aberrations Estimated From Double Pass Measurements
Authors: Guirao Antonio , Artal Pablo
Published: February 2023

Although ocular aberrations increase largely for objects located off-axis, the peripheral image quality has been relatively ignored in comparison with the widely studied foveal optical performance. Previous work has been concentrated in the off-axis refraction and oblique astigmatism (1-3), and the overall image quality expressed through the modulation transfer function (MTF) obtained with the double pass method as a function of the retinal eccentricity (4-6). In this study, we perform an analysis of the monochromatic aberrations that affects the retinal images in the periphery. This extends previous works, where the use of conventional versions of the double pass apparatus failed to obtain information on the off-axis asymmetric aberrations, mainly coma. The results show the relative contribution of the main aberrations we found off-axis: defocus, astigmatism and coma.
Estimation of induced error due to decentration in photorefractive surgery
Authors: Sherr Evan A. , Webb Robert H.
Published: February 2023

Photorefractive keratectomy (PRK) consists of ablating the cornea with a laser beam. The intention is that the cornea be reshaped to a better optical figure. We have modeled the consequences of such a procedure that ablates away the right amount of material in the wrong place. Such an error turns out to be less disastrous than we had expected from anecdotal reports in the literature1.
Rod Ergs in Mice and Humans with Putative Null Mutations in the RDS Gene
Authors: Birch David G. , Travis Gabriel H. , Locke Kirsten G. , Hood Donald C.
Published: February 2023

Mutations causing autosomal dominant retinitis pigmentosa (RP) have been identified in RDS, the human homologue of the gene that was first identified and isolated as the cause of mouse "retinal degeneration slow" or rds (1, 2). The rds gene encodes rds/peripherin, an integral membrane glycoprotein located in outer segment disks (1, 3, 4). More than 15 distinct disease-causing mutations in the RDS gene have been reported (5). The clinical phenotypes include adRP, dominant retinitis punctata albescens, dominant butterfly shaped pigment dystrophy of the fovea and autosomal dominant macular degeneration (6). That RDS mutation can cause either RP and/or macular degeneration is consistent with the observation that the protein is expressed in both rods and cones, though its exact functional role in each photoreceptor must be different. Finally, there is an additional form of retinitis pigmentosa, digenic RP (7) that results from a combination of one mutation in RDS and one in R0M1. Neither mutation alone in a heterozygote causes degeneration.
Photopic temporal processing in patients with retinitis pigmentosa studied with the multi-focal ERG and psychophysical techniques
Authors: Felius Joost , Hood Donald C. , Swanson William H.
Published: February 2023

Deficits in cone temporal processing in eyes with retinitis pigmentosa (RP) have been reported for several decades. Specifically, an increased implicit time of the full-field 30-Hz flicker ERG response is considered typical in RP, as reviewed in (1). However, the relationship between this finding and visual function defects in psychophysical testing is not completely understood. Temporal abnormalities have also (but not always (2,3)) been found in psychophysical experiments (4-6), but it remains unclear if these changes reflect temporal slowing of the retina, a reduction in sensitivity, or a reduction in cone quantal catch. Also, variations in local retinal timing may introduce an uncertainty in the ERG, since primarily full-field stimuli are used. Normal focal ERGs have been reported in eyes with RP that had severely affected full-field ERGs (7,8). It is therefore difficult to know how the local retinal area tested psychophysically is affected.
Area Under Log Contrast Sensitivity Function: A Concise Method Of Following Changes in Visual Performance
Authors: Applegate Raymond A. , Hilmantel Gene , Howland Howard C.
Published: February 2023

The contrast sensitivity function (CSF) is defined by measuring contrast sensitivities at several spatial frequencies. Consequently, the analysis of change in the CSF (e.g., over time, as a result of intervention such as surgery, etc.) is not as straightforward as that of other single number outcomes such as acuity. The analysis of change in the CSF has been handled in a variety of ways including: 1) multivariate ANOVA analysis comparing CS data from all spatial frequencies measured simultaneously (Tomlinson & Caroline, 1988); 2) separate t-test on CS data at each spatial frequency measured (Krasnov, Avetisov, Makashova, & Mamikonian, 1988); and 3) reducing the function to single number such as using estimates of the peak of the CSF as given by the Pelli-Robson chart (Pelli, Robson, & Wilkins, 1988).
Fusion-Vergences: Some Facts and Some Fictions
Authors: Jampolsky Arthur
Published: February 2023

Fusion-vergence mechanisms in normal patients have been adequately described in the literature, but are inadequately described relative to the unique and remarkable sensory-motor adaptations in some frequently seen clinical oculomotor deviations. This presentation will focus on the differences from traditional physiologic notions of the spectrum of normal subjects, and those with heterophoria and intermittent exotropia. Gordon Walls' theory of ocular dominance, and especially exaggerated dominances, will be emphasized.1
Object based stimulus specification within a psychophysical testing platform
Authors: Carney Thom
Published: February 2023

Considerable time and effort is often required of the vision scientist to go from an idea about visual function to actually collecting data that answers the question. The process can include acquiring expensive hardware and writing software to generate the desired stimuli. In many cases the hardware is to expensive or existing tools lack the flexibility to adequately address the question. We have been designing a flexible tool/platform that simplifies the process of software design and functions on inexpensive video hardware. The platform includes an object oriented visual programming language with many built-in features to simplify the coding tasks common to most vision experiments. The system has multiple levels of user interaction, higher levels providing an abstract visual language for rapid development and lower levels that ensure complete flexibility in the design of experiments. This structure maximizes ease of use yet retains flexibility. To keep the system within the budget of the majority of vision researchers we have elected to develop a generic system which uses off-the-shelf graphics components.
Extent of single vision areas and determination of iso-perceived depth lines for symmetric fixation
Authors: Drobe Björn , Miège Christian , Pédrono Claude , Monot Annie
Published: February 2023

By mean of a dichoptic setup using only disparity and form cues, single vision areas of two observers were first determined at 40 cm fixation distance for eccentricities between -12° and +12°. In a second part, the observers had to adjust, vertical lines in order to set fronto-parallel planes in front and behind the fixation point, within the range of single vision. Both observers made systematic depth evaluation errors, setting a family of curves of increasing curvature instead of a succession of planes. Our results discredit a general rigid rule for the establishment of a relationship between perceived and physical space.
Temporal Tuning of Flicker-Sensitive Channels Derived from Individual Differences in De Lange Functions
Authors: Peterzell David H. , Dougherty Robert F. , Mayer Melanie J.
Published: February 2023

The human visual system's sensitivity to flicker, and the processes underlying this sensitivity, are generally understood. The system's sensitivity to flicker is described by a bandbass function that varies with flicker rate (de Lange, 1958a, b). The processes underlying the de Lange function include narrowly tuned bandpass channels that combine to determine sensitivity.
no b-wave: A potential mouse model of CSNB
Authors: Pardue Machelle T. , LaVail Matthew M. , Peachey Neal S.
Published: February 2023

The discovery of naturally-occurring gene defects in rodent strains has been pivotal in understanding human hereditary retinal diseases.
Effects of Degraded Vision on Task Performance and Subjective Confidence
Authors: Gibbs G.H. , Casson E.J.
Published: February 2023

Current vision standards for the Canadian Forces (CF), like preceding standards, are based on historical precedent and expert opinion.
Coma and Design Characteristics of Progressive Addition Lenses
Authors: Dorsch Rainer G. , Baumbach Peter
Published: February 2023

The visual performance of progressive addition lenses (PAL’s) is commonly described by calculation tools which do not include the pupil size as a parameter. In order to overcome this, the relative optical performance (ROP) was introduced [1, 2]. The ROP can be used for a qualitative and quantitative analysis as well as for a general characterization of different PAL designs.
Temporal Aspects of Letter Identification in the Peripheral Visual Field
Authors: Seiple William , Shnayder Yelizaveta , Kizhnerman Alexander , Holopigian Karen , Szlyk Janet
Published: February 2023

Many aspects of visual function have been shown to decrease in the peripheral retina. Letter acuity, grating acuity and contrast sensitivity all decrease as a function of retinal eccentricity (Westheimer, 1982). However, increased temporal sensitivity of the peripheral retina has been reported. For example, critical flicker frequency (CFF) and the peak of the modulation transfer functions increase with eccentricity (Hartman, Lachenmayer and Brettel, 1979; Virsu and Rovamo, 1979; Rovamo and Raninen, 1984; Tyler, 1985). We have previously documented, using electrophysiological and psychophysical techniques, that the locus of the increased temporal sensitivity of the peripheral retina begins at the level of the outer retina in humans (Seiple and Holopigian, 1996). In the current study, we examined whether the increased temporal detection sensitivity of the peripheral retina to uniformly illuminated targets was correlated with temporal aspects of letter identification. We also included a task which ensured central fixation in these experiments.
Dynamics of Refractive Changes and Lens and Ciliary Body Movements in Rhesus Monkey Eyes During Edinger-Westphal Nucleus Stimulated Accommodation
Authors: Glasser Adrian , Kaufman Paul L.
Published: February 2023

Few studies have explored dynamic changes in the accommodative elements of the eye in relation to presbyopia (Schaeffel, et al., 1993; Beers & Van Der Heijde, 1994, 1996; Kaufman, et al., 1997). In the normal human eye the only aspect of the accommodative apparatus readily accessible for dynamic studies is the lens. Although measurements of dynamic changes in lens thickness have been made (Beers & Van Der Heijde, 1994, 1996), they provide no information on the relationship between movements of the extralenticular accommodative apparatus and the refractive changes in the eye or how these relationships changes with age and presbyopia. Recent work has shown age changes in movements of the accommodative elements of the iridectomized rhesus monkey eye (Kaufman, et al, 1997). Further studies of age changes in the extralenticular accommodative apparatus are underway and we present for the first time, results from this work relating mechanical movements of the extralenticular accommodative apparatus to refractive and lenticular changes in the eyes of young accommodating rhesus monkeys. This work aims to characterize and describe normal dynamic relationships between the extralenticular accommodative apparatus and the lens. Rhesus monkeys are ideal subjects for these studies since young animals have high accommodative amplitudes, they develop presbyopia with the same relative age course as humans, and surgical removal of the iris and implantation of stimulating electrodes in the midbrain facilitates imaging of the ciliary body and lens equator during electrically stimulated accommodation (Crawford, et al., 1989; Neider, et al., 1990).