bluuebunny/crossref_metadata_2025 huggingface dataset:
Metal-Semiconductor Contacts: Surface Morphology and BEEM
Authors: Ludeke R. , Prietsch M. , Samsavar A.
Published: February 2023

Ballistic Electron Emission Spectroscopy (BEEM) is a promising new variant of STM spectroscopy that allows the determination of Schottky barrier heights with high lateral resolution for relatively thick (≃100 Å) metal overlayers.1,2 The technique encompasses the injection of electrons or holes with an STM, which then reach the interface without scattering (ballistically). At the interface they will be reflected unless sufficient bias is applied between the tunneling tip and the metal overlayer to overcome the Schottky barrier height (see Fig. 1). Once the electrons reach the conduction band of the semiconductor they will be detected as a collector current Ic. Representative Ic vs VT, where VT, is the tip-to-metal bias, are shown in Fig. 2 for Ag and Au films on GaP(110). The Schottky barrier height is associated with the voltage threshold Vo beyond which a current can be detected. Because of the "soft" turn on of Ic, Vo is poorly defined unless the appropriate shape of the I-V curve is known from theoretical considerations. The imaging of the variations in Ic as a function of latcral position is referred to as a BEEM image, and has been associated with variations in Schottky barrier heights across the interface.1’3 We will show here that another and perhaps more dominant source of contrast in BEEM images is the surface topography, as surface gradients may result in current injections that reach the interface at angles substantially off-normal, a condition which drastically reduces the collector current intensities. The current variations in Fig. 2 are attributed to such variations in the injection angles. In order to quantify this notion we have also developed a model for the interface transport that includes non-classical transmission across the metal-semiconductor interface, as well as off-normal angles of incidence. An outline of these concepts will be presented here, as well as a quantitative comparison of the the model with topographic and BEEM data for several metals on GaP(110).
Scanning Tunneling Microscopy Studies Of Silicon Molecular Beam Epitaxy
Authors: Lagally M. G. , Mo Y.-W.
Published: February 2023

It has been recognized since the beginning of serious studies in surface science that kinetic processes underpin a whole range of surface phenomena, including, for example, phase transformations and ordering, epitaxial growth, and surface chemical behavior. However, with few exceptions, available techniques have not lent themselves well to obtaining a truly microscopic view of such kinetic processes. Because of its atomic resolution on the one hand, and the achievable wide field of view on the other (i.e., large dynamic range in resolution) scanning tunneling microcopy (STM) does afford this opportunity. In this talk, we briefly review the types of surface kinetics measurements that can be made using STM. It should be pointed out that the use of STM for studies of kinetics is one of the more recent applications of what is itself still a very young field; hence much remains to be accomplished. We have concentrated our investigations on the initial stages of molecular beam epitaxy of Si and Ge on Si(001) and will use this surface in our examples.
Sub-Monolayer Ablation of II-VI Semiconductor Surfaces
Authors: Brewer Peter , Zinck J.J. , Olson G.L. , Stuke M.
Published: February 2023

The pulsed laser ablation of compound semiconductors using above-bandgap radiation has been the subject of numerous experimental [1-4] and theoretical investigations [5]. Significant progress has been made in understanding the phenomenology of the ablation process, but many questions remain about the nature of the elementary ablation mechanism. It has recently been shown [5,6] that measurements of the velocity and angular distributions of particles ejected from the surface of a compound semiconductor during laser irradiation can be used to infer the energetics and dynamics of particle desorption, and thus provide useful information about the ablation mechanism. However, the interpretation of those experiments can be seriously complicated by the influence of near-surface collisions and changes in the surface structure and composition on the characteristics of the ejected particles. For example, multiple gas phase collisions have lead to inconsistencies between theoretical predictions [5] and experimental results [2] which show that the ejected products are characterized by translational temperatures that depend strongly on the angle and mass of the desorbed species. Likewise, the effect of surface damage on the behavior of the ejected particles may be manifested by non-stoichiometric and unstable yields, complex angular distributions, and flux characteristics arising from bulk diffusion processes.
Real Time Monitoring of Surface Reactions During Plasma Processing
Authors: Hirose Masataka , Miyoshi Yasutoshi , Miyazaki Seiichi
Published: February 2023

Reacting silicon surfaces in contact with the glow discharge of SiH4 or SiH4+CH4 have been studied by an FT-IR-ATR (Attenuated Total Reflection) technique. In the early stages of silicon film growth from a SiH4 plasma at a substrate temperature of 200°C, SiH2 is the major species on the surface, while at room temperature SiH3 and (SiH2)n chains are the dominant surface products. At a temperature of -95 °C, polymerization reactions among adsorbates proceeds on the surface to form polysilane. At the beginning of silicon carbide deposition on a silicon film from a SiH4+CH4 plasma, the surface hydrogen bonds are scavenged by CH3 radicals at room temperature, while they are stable at temperatures below -50°C.
Obtaining Bulk Electronic Structure with Atomic Resolution Using Spatially Resolved Electron Energy Loss Spectroscopy
Authors: Batson Philip E.
Published: February 2023

Recently, it has been shown that higher performance within the silicon-based technology can be obtained by using Si-Ge alloys in both strained and unstrained configurations. For instance, very high electron mobilities can be obtained in a strained Si quantum well structure formed by CVD deposition of Si on a relaxed Ge30Si70 substrate. [1] In addition, there remains the more difficult goal of obtaining optically active device structures within the Si-based technology. [2] In each of these cases, the relevant electronic structure of the device is completely dependent on the local structure, composition, and strain within a few Angstrom units of an internal interface. In the past, electron microscopy has been very successful at determining the local structure of buried interfaces and defects, but has not provided a good tool for measurement of either the bonding or the electronic structure in the same areas. Spatially Resolved EELS has therefore been devised as a technique to obtain the bulk electronic structure in a way that is compatible with electron microscopy so that direct comparisons can be made between electronic and atomic structure.
STM Measurements of the Interaction of Vacancies with Steps During Low-Energy Sputtering of Si(001)*
Authors: Swartzentruber B. S. , Matzke C. M. , Kendall D. L. , Houston J. E.
Published: February 2023

Spurred by the desire to control the pre-growth substrate morphology as well as the quality of epitaxial thin films several groups have investigated the effects of low-energy ion beam sputtering on the Si(001) surface morphology and growth kinetics. [1] To first order, low-energy sputtering can be understood as introducing surface vacancies which diffuse across terraces and annihilate at step edges and with adatoms. [2] The introduction of vacancy formation and diffusion as additional kinetic processes controlling surface morphology has led to interesting phenomenology, and the metaphor of vacancies as "anti-atoms" on the silicon surface is rather striking. For example, just as Si can be grown epitaxially on the Si(001) surface in a layer-by-layer growth mode, low-energy ion bombardment can result in the layer-by-layer removal of the surface atoms. [2]
Nanostructure fabrication via atom optics
Authors: Gupta R. , McClelland J. J. , Celotta R. J.
Published: February 2023

As electronic and magnetic devices continue to become smaller, the need for fabricating structures on the nanometer scale grows larger. In lithographic techniques, the fundamental limitation in making nano­scale structures is imposed by diffraction effects which limit the size of the structures to the order of the wavelength of light used. Consequently, technologies are being driven towards using photons of shorter wavelength and/or high energy electrons or ions to produce structures with the highest resolution.
Nanomachining of Silicon by Direct Laser Processing
Authors: Müllenborn M. , Dirac H. , Petersen J. W.
Published: February 2023

A laser direct write system consisting of a cw Ar ion laser with UV option, an acousto-optic modulator, high-quality optics for beam expansion and steering, and a reflective objective for focusing, has been designed to etch trenches into Si with nanometer resolution. The Si substrate, mounted in a process chamber, is exposed to Cl2 gas and heated above its melting point by the laser light. Upon melting, a fast etch reaction is initiated,1 resulting in an etched profile that corresponds directly to the induced melt. Translating the sample by high-resolution DC motor stages with a bidirectional repeatability of 25 nm, continuous, well-defined trenches are etched into the substrate with an extremely high writing speed of up to 100 mm/s. The trench width is completely determined by the melt size. By decreasing the laser power to the minimum required for melting, we have reached trench widths of less than 150 nm.
Zeke Photoelectron Spectroscopy as a Probe of Dissociative States
Authors: Strobel Andreas , Fischer Ingo , Müller-Dethlefs Klaus , Bondybey Vladimir E.
Published: February 2023

During the past decade zero kinetic energy photoelectron spectroscopy (ZEKE-PES)1 has become one of the most important techniques for gas-phase studies of molecular ions and ionic complexes. Compared to conventional photoelectron techniques a resolution enhancement by 2 to 3 orders has been achieved and even the rotational structure of larger polyatomic ions can be resolved.2
Vibronically-resolved measurement of correlated product-state distributions of ketene photolysis at 308 nm
Authors: Drabbels Marcel , Morgan Christopher G. , McGuire David S. , Wodtke Alec M.
Published: February 2023

One of the most fundamental observables of the prototypical photodissociation reaction, AB + ħω →A + B, is the correlated-product-state distribution,

P

n
¯

A

,

n
¯

B

, which gives the probability that fragment A is produced in quantum state

n
_

A

when fragment B is simultaneously produced in quantum state

n
_

B

. Determination of

P

n
¯

A

,

n
¯

B

is possible through quantum-state-specific translational energy measurements.
Two-Photon Time-of-flight Spectra of Rare Gas Excimers.
Authors: Lipson R.H. , Dimov S.S.
Published: February 2023

The spectroscopy of the rare gas excimers has been a subject of interest for many years, primarily because the dimers are recognized media for vacuum ultraviolet lasers. Lasing originates from electronically excited ungerade states and terminates on the repulsive wall of the gerade ground state potential energy curve. Excited gerade levels act as storage reservoirs from which ionization can occur, thereby reducing the gain of the laser1. There has also been effort in rationalizing the collisional and radiative relaxation pathways among gerade dimer excited states by considering the shapes of the molecular potential energy curves, and the numerous crossings between them. However, in many instances the potentials used have been model potentials, and not those derived from detailed spectroscopic analyses2.
Femtosecond probes of molecular and structural dynamics in liquid water: dependence on temperature and ionic solutes
Authors: Lotshaw William T. , Staver P. Randall , Palese Steven , Schilling Lynn , Miller R.J. Dwayne
Published: February 2023

The transient waveforms measured in the femtosecond time-resolved, optical heterodyne detected Raman-induced Kerr effect in liquid water (fs OHD-RIKE) are interpreted by the combination of a forced oscillator kinetic analysis and modal decomposition of the depolarized Raman spectrum deduced from a fast Fourier transform analysis of the discreetly sampled experimental observable. We recently presented an analysis of the fs OHD-RIKE dynamics observed in room temperature/atmospheric pressure liquid water accounting for the structural/vibrational dynamics over the inverse frequency range 0-600 cm-1[1].
Resonance Raman studies of I 3 – photodissociation in solution
Authors: Johnson Alan E. , Myers Anne B. , Ruhman Sanford , Banin Uri
Published: February 2023

The triiodide ion in solution has two strong, featureless electronic transitions spanning the blue to mid-uv spectral region which dissociate to

I

2
–

- and atomic iodine. Recent femtosecond pump-probe experiments have shown that the diiodide ion product is formed vibrating coherently. [1] Numerical simulations of the photodissociation event, both in the isolated molecule[2] and with solvent explicitly present, [3] are in qualitative agreement with the data, but rely on an empirical LEPS potential surface parameterized to reproduce the structureless absorption bands only. In order to explore the photodissociative potential surface more precisely, we have measured resonance Raman spectra, including absolute scattering cross sections, for

I

3
–

in ethanol, ethyl acetate, and acetonitrile at excitation wavelengths from 266 to 416 nm, as well as in the preresonant region at 488 nm.
New near infrared spectra of the CH2 radical
Authors: Chang Bor-Chen , Wu Ming , Hall Gregory E. , Sears Trevor J.
Published: February 2023

An analysis of the

b
˜

1

 

B
1

−

a
˜

1

 

A
1

electronic spectrum of methylene was first reported in 1966 by Herzberg and Johns.1 Since that time, numerous experimental and theoretical investigations have been carried out on this chemically important species. The two lowest singlet states in CH2 lie approximately 3000 and 12000 cm-1 above the ground

X
˜

3

 

B
1

state and correlate with a degenerate

1

Δ
g

state at the linear configuration of the molecule. This degeneracy leads to extreme complexity in the spectrum. The

a
˜

and

b
˜

states may be regarded as derived from a severe Renner-Teller effect in a linear singlet CH2 molecule and the resulting vibronic structure leads to a highly irregular band system, especially at energies near to that of the degenerate linear configuration, recently2 calculated to lie some 8800 cm-1 above the zero point level of the

a
˜

state. Although the visible region of the

b
˜

−

a
˜

spectrum has been extensively studied3,4 since the original work of Herzberg and Johns, there have been no experiments reported in the near infrared region due to less efficient dye laser operation at these wavelengths.
Fast sub-ppb Trace Gas Detection by Infrared Diode-Laser FM-Spectroscopy
Authors: Werle Peter
Published: February 2023

Sensitivity, specifity, high time resolution and cost effective simultaneous measurements of several components using operational systems are the main requirements for atmospheric research and air pollution monitoring1 Tunable diode lasers absorption spectroscopy (TDLAS) is increasingly being used to measure atmospheric trace gas concentrations down to low ppb-levels (10-9 volume mixing ratio). Semiconductor lead salt diode lasers give access to the mid infrared spectral region, where the most important atmospheric constituents have strong rotational vibrational absorption bands. The application of high frequency modulation (FM) schemes can further improve sensitivity and detection speed of modern instrumentation. Operational instruments are needed for fast airborne measurements and sensitive and reliable field measurements. The great number of gaseous pollutants and their generally low variable concentrations with large local differences pose challenging requirements to analytical techniques. Research in atmospheric chemistry requires highly sensitive techniques for measurement of concentrations of free radicals which determine the rate of photochemical destruction of most atmospheric pollutants.
Collisional Relaxation in Low-Pressure Photolytic Iodine Lasers
Authors: Nicholson J. , Rudolph W. , McIver J. , Hager G. , Tate R.
Published: February 2023

When the molecules in a gas are photolyzed by a short exitation pulse, the resulting initial velocity distribution can be broader and have a different mean velocity than the velocity distribution the gas has in thermal equilibrium. The velocity distribution then relaxes into thermal equilibrium, the mechanism for this relaxation being collisional. Using time-resolved Doppler spectroscopy, the corresponding relaxation time for C3F7I at 0.1 Torr has been measured to be approximately 5 μs [1], for example.
Picosecond-LIF-Spectroscopy with NO in a High Pressure Cell
Authors: Knaack A. , Offt A. , Mill T. , Walewski J. , Schade W.
Published: February 2023

Flame radicals are fragments of molecules with high reactivity and control the process of combustion to a high degree. Therefore, the knowledge of accurate number densities of these species is very important, e.g. when modelling flames. Because of the relative large cross sections compared to other optical methods, laser-induced fluorescence (LIF) spectroscopy is one of the most sensitive techniques for accurate determination of concentrations and temperatures [1]. However, when LIF is applied for quantitative diagnostics at high pressures (10 bar >p> 1 bar) and high temperatures, which is typical for industrial combustions, several problems associated with the LIF-method itself appear, and limit the accuracy of the method. The laser excites an upper level population of the molecule or atom under investigation, which decays by spontaneous emission and radiationless by collisional induced processes (quenching). The latter one reduces the fluorescence yield considerably, two or three orders of magnitude are typical for atmospheric pressure. If the measurements are performed with a time resolution better than the quenching rates, the LIF-intensities can be used to extract absolute number densities. However, this requires a laser and a detection system with picosecond time resolution. Since important atomic radicals like O, C, N, H or diatomic molecules like NO, CO and OH can only be excited from the ground state via two- or one photon absorption in the spectral range between 200 and 300 nm [2] a powerful ultraviolet laser system is required in these experiments. However, the quantitative interpretation of the picosecond LIF-intensity measurements still needs accurate quenching rate data for the relevant pressures and temperatures and the species that are present in the combustion process. In the data analysis also systematic influences like photodissociation effects by the strong uv-laser pulses have to be considered. Therefore, in this paper improved quenching rate measurements of NO with NO, N2 and O2 for pressures up to p=10 bar, and photodissociation effects of NO are reported.
Using Hextrees to Model 4 Space
Authors: Potter J. L.
Published: February 2023

Over the past several years, techniques have been developed for generating, manipulating and characterizing objects in quadtree and octree data organizations [Jackins and Tanimoto 1980, Samet 1981, Schneir 1981, Udupa 1982 and Yau 1983]. An important but less studied application of the octree and related data structures is to model 3d space not 3d objects. That is, the working environment of a robot can be modeled by placing objects in the various cells of an octree data structure which models the encompassing 3d space. This slight but important variation on object modeling is crucial in robotic applications where it is necessary not only to model object size and shape but object position and the voids between objects so that movements can be planned. A modified octree approach has been described which increases storage efficiency and allows planning of robotic arm movement [Lozano-Perez 1981]. The hextree model generalizes the octree concept to 4 dimensions so that objects moving in the environment can be modeled. This enables a robot system to predict (and thus avoid) collisions of objects in the environment including arms and manipulators under its control and external moving objects over which it has no direct control. Since the entire environment in space and time is modeled, paths for manipulator movement can be planned which avoid both stationary and moving objects.
A Distributed Problem-Solving Approach to Point Pattern Matching
Authors: Dodhiawala Rajendra T. , Cross George R.
Published: February 2023

We are developing a system to track the linear movement of cosmic ray particles in three dimensional space. This knowledge-based system applies techniques of distributed problem solving to image processing. Distributed problem solving is the cooperative solution of a single problem by a group of decentralized and loosely coupled knowledge sources. Mutual sharing of information is necessary because none of the knowledge sources is independently capable of arriving at the solution from the incomplete, and possibly inconsistent, information that is locally available to it.
Image Sensing and Transfer Using Quartz Fiber Scope in Hazardous Environment
Authors: Shimizu Takeo
Published: February 2023

Quartz optical fibers, having remarkably low transmission loss, have been developed rapidly for optical communication lines. On the other hand, making use of the merits of quartz optical fibers, their applications in the field of instrumentation have also been developed actively, one of which is the quartz image fiber. It is the image guide of so-called multicore optical fiber type having more than ten thousands independent cores in a single fiber of large diameter and compared with the conventional image guide mainly for medical use which has the bundled structure of a large number of glass fibers, it has the following features.
A Vehicle Identification System For Surveillance Applications
Authors: Bukaty Michael E.
Published: February 2023

Many surveillance applications require electronic imagers to provide real time or near real time pictures. An example might involve the security system of a sensitive facility where the monitoring of entering and exiting traffic is important. Since the objects of interest in this scenario are vehicles, it is possible to use a one-dimensional line scanner and let the vehicle self scan via its motion. The resulting image is two-dimensional with the vertical representing a spatial displacement and the horizontal time. The system consists of a Reticon 1 × 128 array, 8-bit Flash A/D, and TMS320 digital signal processor. The amount of light incident on a photodiode and integrated over time determines the value read by the A/D for that pixel. To achieve optimal operating range, the average value of all the pixels in the scan should be at the midpoint of the intensity range. This is accomplished by adjusting the integration time or the amount of time light is allowed to strike the element before it is interrogated. The adjustment procedure involves having two valid reads that occur at a fixed time interval. Between these two valid scans is a “dummy” read which has an adjustable time preceeding the next valid read.
Improvement of axial response in three-dimensional light focusing by use of dynamic phase compensation
Authors: Glückstad Jesper , Kawata Yoshimasa , Nakamura Osamu , Kawata Satoshi
Published: February 2023

The axial response of a high numerical aperture (NA) optical system is known to be very sensitive to any mismatch in refractive index between that of a specimen and that of an immersion medium. Light focused deeply into the specimen is usually strongly degraded by spherical aberration resulting from the refractive index mismatch. Even an extremely small amount of spherical aberration has been shown to be enough to produce a substantial degradation of the point spread function (PSF) far more in the depth than in the lateral direction. Various approaches to correcting these aberrations have been proposed in the literature. However, most approaches only consider first-order aberration correction and/or the proposed methods only work for a given and fixed focusing depth[1-3]. Here we will consider the possibility for dynamically compensating for all orders of spherical aberration resulting from refractive index mismatch by use of a phase-only spatial light modulator (SLM).
Shaping a focused laser beam by continuous wavefront control using a deformable mirror
Authors: Yoon Geun-Young , Jitsuno Takahisa , Nakatsuka Masahiro , Kato Yoshiaki
Published: February 2023

Uniform irradiation of laser beam is needed for the directly driven inertial confinement fusion, laser-chemistry and industrial applications such as laser welding, semiconductor processing and laser microfabrication. For improving the irradiation uniformity on a fusion target, several beam smoothing techniques such as a random phase plate (RPP)1, induced spatial incoherence (ISI)2, smoothing by spectral dispersion (SSD)3 and kinoform phase plate (KPP)4 have been proposed. The RPP has energy loss of ~ 15 % by a large diffraction angle, and the ISI and the SSD have imprint problems by instantaneous speckle pattern. The precise KPP with a continuous phase distribution is difficult to fabricate, even if the energy loss can be reduced to 5%. We are developing an active optical system to compensate (or control) a wavefront aberration included in a large-scale laser system for fusion. Shack-Hartmann wavefront sensor using a large F-number plastic micro-lens array5 and continuous faceplate type deformable mirror6 have been developed and their good performance has been demonstrated.
The electrical and optical properties of liquid devices for adaptive optics
Authors: Love Gordon D. , Buscher David F. , Purvis Alan , Robertson David J. , Sharpies Ray M.
Published: February 2023

The use of adaptive optics (AO) for wavefront compensation other than for atmospheric turbulence is an emerging, exciting field. The required system specifications will obviously be dependent on the particular application, and indeed may not be well-characterized for many of the potential uses. Liquid crystal spatial light modulators (LC-SLMs) are also an emerging technology within the field of AO. With this in mind we present here a summary of the specifications of both currently available and predicted LC-SLMs which may be used as wavefront correctors, and discuss how they may be particularly suited for use in non-astronomical AO systems.
Assessment of Foveal Function in Retinitis Pigmentosa
Authors: Alexander Kenneth R. , Hutman Lucinda P. , Fishman Gerald A.
Published: February 2023

Retinitis pigmentosa (RP) is a group of genetic retinal dystrophies characterized by nightblindness, visual field depression, intraretinal bone-spicule-like pigmentation, narrowing of the retinal vessels, and a reduction in the amplitude of the electroretinogram. Usher's syndrome is a variant of RP in which there is also a congenital neurosensory hearing defect. Although the loss of visual function in RP typically is more severe in the retinal periphery, there is ultimately a reduction in foveal function in a substantial number of RP patients.
The Focal EOG in Age-Related Macular Degeneration
Authors: Sunness Janet S. , Massof Robert W.
Published: February 2023

Studies of electrooculogram testing of patients with age-related drusen and macular degeneration (aka senile macular degeneration, or SMD) have shown differing results. Of the two largest studies, one1 showed most patients with severe SMD to have low Arden ratios and most patients with drusen to have normal Arden ratios, and the other2 showed one-third of patients with drusen and SMD to have abnormal EOGs, with no correlation to severity of the clinical picture. These studies were performed using a non-ganzfeld type of stimulation. A recent study by us3 of twenty-one patients with drusen and SMD, using ganzfeld EOG testing, found that all patients had normal Arden ratios.
Spatial Contrast Threshold Perimetry in Macular Degeneration*
Authors: Mitra Sunanda
Published: February 2023

Visual field defects are often not effectively detected by conventional clinical perimetry despite the presence of extensive pathophysiology in the neuronal pathways.1-2 In the case of localized retinal lesions resulting from macular degeneration, an accurate assessment of visual dysfunction across the central visual field is even a more formidable task. These uncertainties in the evaluation of visual function stem from our lack of understanding of the basic mechanisms underlying not only the disease processes3, but also the neural signal transmission processes.4 Regardless of the exactness of the existing models of neural filtering4, the use of grating patches as test-stimuli reveals differential sampling ability of the neuronal units in the presence of a pathology that is undetected by clinical perimetry.5,6 However, the structural inhomogeneity of the retina imposes further constraints on specific spatio-temporal domain, and the size of the grating patch to be used in detecting visual dysfunction in the local regions of the visual field.
Improved Imaging with the Scanning Laser Ophthalmoscope
Authors: Webb Robert H. , Hughes George W. , Wornson Douglas P.
Published: February 2023

A Scanning Laser Ophthalmoscope (SLO) allows observation of the ocular fundus with very little light<1,2>. The actual retinal location of a stimulus may be observed during testing<3-5>. Like all ophthalmoscopy, visualization with an SLO is degraded by ocular opacities and motion of the subject’s eye. The work we show here addresses these problems.
Ray-Tracing Analysis of the Optics of Paraxial Photorefraction
Authors: Tyler Christopher W. , Norcia Anthony M.
Published: February 2023

The concept of photographic refraction of the eye based on an in-focus photograph of the pupil image of a flash source slightly away from the optical axis was developed by Kaakinen (1979). For a flash source positioned below the optic axis running through the camera lens and the pupil, myopia with respect to the camera distance is revealed by a bright crescent appearing at the lower edge of the subject’s pupil, while hyperopia is shown by a crescent at the upper edge. We will call this method "paraxial photorefraction" to distinguish it from the coaxial method of photorefraction of Howland and Howland (1974), since in our optimized version the off-axis flash is within 1° from the optic axis.
Visual Evoked Potential Tuning Functions in Optic Neuritis and Optic Neuropathy
Authors: Johnson Mary A. , Miller Neil R.
Published: February 2023

The pattern-reversal visual evoked potential (VEP) is a sensitive measure of lesions of the anterior visual pathway; the VEP exhibits characteristic changes in idiopathic optic neuritis, optic neuritis associated with multiple sclerosis, ischemic optic neuropathy, compressive neuropathy, amblyopia and other disorders. It has been suggested that one can differentiate among optic neuritis, ischemic optic neuropathy and compressive optic neuropathy on the basis of latency and amplitude changes.1,2 Sometimes these differences are compelling. P1 latency delays in optic neuritis have been reported to be as long as 100 msec.3 In contrast, the VEP in compressive lesions may be extinguished, or severely reduced with only minimal delays in timing2. However, the distribution of amplitude reductions and timing delays for these 2 groups of patients overlap to the extent that VEPs recorded for a single check size will not always distinguish one group from the other.
A Criterion-Free and Parameter-Free Index of Diagnostic Test Performance
Authors: Massof Robert W.
Published: February 2023

Frequently claims are made in the clinical literature that a particular test or data reduction procedure provides diagnostic information that is superior in quality to that provided by alternative tests or procedures. Often these claims are based solely on an evaluation of the tests’ ’’sensitivity”, that is, an estimate of the percentage of diseased patients diagnosed correctly by the test. Relatively few such studies have also evaluated a test’s ’’specificity” an estimate of the percentage of patients not at risk, or normals who are diagnosed correctly by the test.
Peripheral Vision of Young Children with Normal and Abnormal Visual Development
Authors: Mayer D.L. , Cummings M.C. , Hansen R.M. , van Hof-van Duin J. , Fulton A.B.
Published: February 2023

The quantitative assessment of visual fields provides critical data for managing patients with neurological and ophthalmological disorders. However, the behavioral repertoire of infants and young children has precluded refined measurements of visual fields, and in clinical practice, visual field assessment is limited to "confrontation" methods. Previously described perimeter and procedures1 have been modified for quantitative evaluation of visual fields of young pediatric patients.
Development of Monocular VEP Acuities During The First Year of Life: Interocular Comparisons and Measurement Error
Authors: Hamer R.D. , A.M  , Norcia  , Tyler C.W. , Smith-Kettlewell
Published: February 2023

Recently, this laboratory has measured the development of binocular visual acuity in human infants from birth to one year of age using a new and efficient electrophysiological technique (Norcia and Tyler, 1985a). From a large sample of infants (N = 197) it was found that the logarithm of acuity increased linearly with age at about 0.25 octaves per month from 4.5 c/deg just after birth to 20 c/deg at 8 months postnatal age. In a separate analysis, Norcia and Tyler (1985b) established that the technique has an intra-session reliability of +0.2 octaves in the 17 to 25 week age range. While these data establish age norms and an estimate of reliability for binocular acuity, it is of importance for clinical studies to obtain similar data for monocular acuities and norms for interocular acuity differences.
Assessment of Macular Pigment in Retinitis Pigmentosa Using Digitized Television Fundus Reflectometry
Authors: Alexander Kenneth R. , Kilbride Paul E. , Fishman Marlene , Fishman Gerald A.
Published: February 2023

Recent measurements of the dark-adapted foveal spectral sensitivity of retinitis pigmentosa (RP) patients have shown that some patients have a considerably reduced sensitivity at short wavelengths (Alexander, Hutman and Fishman, 1985). Moreover, there is an inverse correlation between the relative sensitivity at short wavelengths and the absolute sensitivity at longer wavelengths, such that patients with the best overall sensitivity show the greatest reduction in short-wavelength sensitivity.
Studies of the residual rod signals in congenital stationary night blind patients?
Authors: Young Rockefeller S.L.
Published: February 2023

Our studies concern a recessively inherited form of congenital stationary night blindness that is associated with myopia (CSNB for short). Our results show that (i) rod responses measured by the ERG a-wave in the CSNB patients cannot explain the loss of night vision, (ii) Under certain conditions, the patients' psychophysical thresholds are rod-mediated, (iii) The rod-mediated thresholds adapt very poorly to steady background illumination.
Aging of the Human Lens
Authors: Pokorny Joel , Smith Vivianne C. , Lutze Margaret
Published: February 2023

The spectral transmission of the human lens is not uniform in the visible spectrum. The lens absorbs strongly in the ultra-violet and short wavelength region and is nearly transparent in the long wavelength region. The absorption of the lens increases during life, with the lens appearing obviously "yellower" in advanced years. Although these facts are well-accepted, there are two controversies concerning the age-related changes in the human lens: (a) are age-related increases in density a linear or an accelerated function of the age in years and (b) is the spectral density function of an "old" eye a scalar multiple of its spectral density function at an earlier period?
Interaction of age and illuminance in the Farnsworth-Munsell ioo-Hue test: Normative data and method of analysis
Authors: Knoblauch Kenneth , Saunders Felicia , Hynes Roger , Higgins Kent E. , de Monasterio Francisco
Published: February 2023

We have investigated the interaction of age, sex, and illumination level for the Farnsworth-Munsell 100 hue test, as a part of the development of a normal control group for another study. Seventy normal observers, 20 to 79 years of age, male and female, were tested monocularly at each of five illuminance levels (5.7, 18, 57, 180, and 1800 lux).
D-15 Test Results in People Aged Sixty and Older
Authors: Eisner Alvin
Published: February 2023

The Farnsworth Dichotomous Test for Color Blindness (Panel D-15), often called simply the D-15 test, is an easy to administer arrangement test which is designed to fail those individuals having severe color discrimination loss. The test is very successful at detecting and classifying congenital dichromacy or anomalous trichromacy in which color discrimination is very poor. Because the test is readily obtainable and is easy to administer and score, it often is used to ascertain visual loss due to acquired defects or changes. When used in this manner, either tritan errors (those errors associated with a decrease of blue cone mediated discrimination) or errors associated with a diffuse loss of chromatic discriminative ability are of interest. This paper discusses briefly the relationship between these types of errors and blue cone sensitivity as measured with a threshold task in a population of normal individuals aged sixty and older.
Image Enhancement of Nerve Fiber Layers in Glaucoma
Authors: Whiteside Steven , Ling Alice , Mitra Sunanda , Krile Thomas F. , Shihab Zuhair
Published: February 2023

Digital image enhancement and restoration techniques have been used in noninvasive diagnostic radiographic imaging for quite some time.1 Application of digital image processing to enhance fundus photographs is relatively recent. Basic problems in standardization, restoration of fundus images and development of an optimal image enhancement procedure for specific applications are being presently investigated by researchers.2,3,6 Enhancement of fundus photographs is of particular significance in diseases such as glaucoma where structural changes in the optic nerve head and retinal nerve fiber layers are indicative of the progression of the disease.4,5 We have examined the fundus photographs of a group of normal and glaucoma patients where structural changes in nerve fiber layers in specific zones of the fundus were highlighted when a combination of restoration and enhancement procedures were employed.6
Electrophysiological Assessment of Visual Deficit in Glaucoma
Authors: Sutija V.G. , Eiden S.B. , Horn D. , Cooper J. , Appleman W. , Wicker D.
Published: February 2023

Glaucoma is a progressive and irreversible damage to the optic nerve with a typical optic disc appearance (pallor, enlargement and cupping) and a specific pattern of sensitivity loss apparent on visual field testing. It develops in eyes with abnormal intraocular pressure dynamics. Although glaucoma is not curable, drug or surgical treatment can relieve the elevated intraocular pressure and slow down the progress of the optic nerve damage; the existing damage, however, cannot be reversed nor vision restored.
A functional investigation of the visual system using contrast modulated steady state VEPs
Authors: Orban G.A. , Spileers W. , Van Hulle M. , Maes H. , Oosterlinck A. , Missotten L.
Published: February 2023

Contrast Modulated Steady State VEPs (CMSS-VEP) were introduced by Orban and Orban in 1984. Computer-aided on-line sampling and off-line analysis has been developed. The actual sampling time is reduced to 22 minutes and the total time required for the complete test is about 45 minutes. This technique is presently applied to several patient groups in the Department of Ophthalmology, K.U.Leuven (Belgium).
Abnormal Pattern-Reversal Electroretinograms (PERGS) Associated with Ocular Hypertension (OHT): Relationship to Known Risk Factors for Primary Open-Angle Glaucoma
Authors: Trick Gary L. , Cooper Dorothy G. , Gordon Mae O. , Kolker Allan E. , Kass Michael A.
Published: February 2023

The pattern-reversal electroretinogram (PERG) is a bio­electrical signal which can be recorded from the cornea of the human eye when a contrast-reversing (i.e. phase-alternating) pattern is viewed. Although the retinal generators of this biopotential have not been precisely localized (1,2) considerable evidence suggests that the PERG is correlated with neural activity occurring in the proximal retina (3-5). PERG abnormalities often are associated with visual disorders that affect the proximal retina and optic nerve (6,7).
Absolute Ocular Fundus Dimensions measured by Multiple-Beam Interference Fringes
Authors: Wesemann W. , Baumbach P. , Rassow B.
Published: February 2023

The knowledge of the three spatial dimensions on the human fundus, in particular, the size and depth of optic disc and cup is highly desirable for ophthalmological diagnosis.
Fast Registration of Digital Retinal Images
Authors: Peli Eli , Augliere Reed , Timberlake George
Published: February 2023

Registration, or alignment, of retinal images taken at different times is frequently required in image-processing applications. Images that need to be registered may be separated by a few years and may show slow changes in the retina. Such changes include drusen, nerve fiber layer damage, and changes in optic disc cupping and pallor. Registration may also be required for pictures taken only a fraction of a second apart, as in measurement of dilution curves in fluorescein angiography or at video rates required in fundus perimetry using the scanning laser ophthalmoscope (SLO).
Fluorescein Angiography Using Computer Image Processing Technology
Authors: Rehkopf Paul G. , Warnicki Joseph W. , Friberg Thomas R. , Eller Andrew W.
Published: February 2023

Historically, acquisition and documentation of ocular fundus disease has been accomplished using fundus photography, as introduced by Nordenson and Zeiss,1,2. Fluorescein angiography has become a routine method for diagnosis of disorders which affect the retinal vasculature. Advances in microcomputer technology have now made it practical to acquire color and fluorescein images of the ocular fundus without the use of film. These images are readily accessible to the clinician for diagnostic and treatment purposes. This paper describes an ocular fundus imaging system used for real time acquisition, cataloging, retrieval, and analysis of color and fluorescein images of the ocular fundus.
Differential Spectrofluorophotometry in the Human Vitreous Body
Authors: Larsen Michael , Dalgaard Peter , Henrik-Lund-Andersen
Published: February 2023

Two quantitative aspects of of vitreous fluorophotometry methodology remain to be elucidated: The penetration of fluorescein monoglucuronide into the vitreous and the light transmission of the lens and its wavelength dependence.
Visual Function Over Drusen in Age-Related Macular Degeneration: Direct Measurements Using the Fundus Camera Stimulator
Authors: Sunness Janet S. , Johnson Mary A. , Massof Robert W.
Published: February 2023

Age-related macular degeneration (AMD) is a spectrum of conditions affecting the eyes of the elderly, and is the leading cause of severe visual loss in people over 60 years of age.(1) Drusen, white-yellow excrescences below the retinal pigment epithelium, are associated with the development of the vision-threatening complications of age-related macular degeneration. However, drusen are seen ophthalmoscopically in over 30% of the elderly population. The vision-threatening aspects of AMD (which occur in approximately 1-3% of patients with drusen per year) include the development of a subretinal neovascular membrane and disciform scarring, retinal pigment epithelial detachment, and retinal pigment epithelial atrophy. At present, it is not possible to predict which people with drusen will go on to lose vision. Since prompt treatment of a subretinal neovascular membrane with laser photocoagulation can significantly reduce the frequency of severe visual loss,(2) there has been increased attention focused on finding ophthalmologic or visual function changes in drusen patients which may segregate a high-risk group.
Can The Pupillary Responses in Man Provide an Estimate of the Absolute Sensitivity of the Visual Pathway?
Authors: Stewart Barbara E. , Young Rockefeller S.L.
Published: February 2023

Previous studies (Birch and Birch, 1987; Trejo and Cicerone, 1982; Schweizer, 1955) have used the pupillary light response to derive relative sensitivity estimates of the afferent visual pathway. The present study examines whether the pupillary response can provide an absolute sensitivity estimate. More specifically, this study addresses two questions: (i) Is a pupillary response elicited by flashes that are detected by the subject only 50% of the time? (ii) Does the pupil response occur on trials that the subject detects the flash, on trials that the subject does not detect the flash, or on both trials that are detected and not detected?
Vernier Acuity Measured Using the Sweep VEP
Authors: Norcia Anthony M. , Manny Ruth E. , Wesemann Wolfgang
Published: February 2023

There has been renewed interest in the family of visual hyperacuities (Westheimer, 1979). As a class the hyperacuities share the property of having resolution limits which are smaller than the scale of the cone spacing -- the limiting factor for two point and grating resolution. Of particular interest, both to theoreticians (Geisler, 1984; Watt, 1984; Klein and Levi, 1985; Wilson, 1986) and clinicians (Levi and Klein, 1982; Williams et al., 1984), has been the ability of observers to discriminate small vernier misalignments.
Externally Controlled Delivery of Dyes in the Eye: A Potential New Method to Assess Retinal Blood Circulation
Authors: Zeimer Ran C. , Khoobehi Bahram , Peyman Gholam A. , Magin Richard L. , Niesman Michael R.
Published: February 2023

A new drug and dye delivery system is proposed to allow repeated release of substances in the ocular vasculature under external control. The substances are encapsulated in heat-sensitive liposomes1 which are lysed by locally applying a heat pulse produced by an argon laser. The feasibility of lysing heat-sensitive liposomes by laser irradiation was first tested in vitro by encapsulating carboxyfluorescein and monitoring its release. The liposomes’ suspension was dialyzed, to remove the dye that was not encapsulated, and diluted 400 times in calf serum to mimic the dilution factor expected in humans following a slow intravenous injection of about 12cc of liposomes. The preparation was placed in a cuvette and incubated in a bath at 37°C or 38.5°C. A commercial ophthalmic argon laser was used to deliver pulses of blue light at 488nm. The cuvette was placed away from the focal plane to obtain a beam spot 2 mm in diameter which covered the whole sample. The amount of carboxyfluorescein released was assessed by measuring its fluorescence with a commercial fluorophotometer. The release yield was calculated as the ratio between the fluorescence of the irradiated sample and that of a controlled sample heated at he liposome transition temperature of 41°C. The results indicated that up to 85% of the original liposome content could be released by the exposure to the laser. We verified that the system behaved as anticipated by varying the incubating temperature. As the incubation temperature approached the transition temperature of 41°C, less energy was required to lyse the liposomes. Moreover, the release yield changed with energy in a manner similar to that of liposomes lysed by slowly heating the medium,1 indicating that the mechanism of release was not influenced by the fact that short pulses are used (50 to 500 msec). Of special importance was the observation that the non-irradiated liposomes exhibited minimal fluorescence due to concentration quenching while an intense fluorescence was present where carboxyfluorescein was released and diluted in the plasma following the lysis of the liposomes.