The effects of random element loss on letter identification: Implications for visual acuity loss in patients with retinitis pigmentosa

AbstractThe hypothesis that reductions in Snellen acuities in patients with retinitis pigmentosa are due solely to losses of photoreceptors was tested by measuring the effects of random losses of sampling elements on letter identification. Sampling element losses were mimicked by setting the luminance of randomly selected pixels equal to the luminance of the surround. The amount of pixel blanking ranged from 0 to 90%. Letters varying in retinal subtense from 5 to 17 min arc were presented for 500 msec. Although letter identification accuracy decreased with increasing pixel blanking for all letter sizes, performance remained relatively high even when a majority of the pixels was blanked. The data suggest that unless the loss of cone photoreceptors in greater than 80%, loss of sampling elements alone can not account for letter acuities poorer than20/40. In addition to loss of cone photoreceptors in patients with RP, there are histological reports of photoreceptor abnormalities and psychophysical studies of visual sensory deficits. It is conceivable that these alone, or in combination with losses of photoreceptors, could account for decreased visual acuity. In a series of experiments, stimulus parameters were manipulated in order to mimic the effects of some of these abnormalities and deficits and the effects on letter identification were examined. The results of these experiments demonstrated that sampling element loss interacts with sensory factors (e.g. luminance and contrast sensitivity) and perceptual factors (e.g. set size and letter orientation) to reduce letter identification accuracy. The implication of these results is that decreases in letter acuity observed in patients with retinitis pigmentosa cannot be attributedsolely to a random loss of sampling elements in the underlying retina, but may be due to the combination of photoreceptor degeneration and other sensory and perceptual factors

Recording the Pattern Electroretinogrom: A Cautionary Note

It is possible to record a pattern electroretinogram (PERG) of near normal amplitude in a situation when the eye containing the active electrode is occluded. Because PERG recording requires high amplification and sensitive signal retrieval techniques, the electrode in the occluded eye records a distant potential from the unoccluded eye. Referencing the active electrode to an ipsilateral ear diminishes, but does not eliminate the referred PERG potential. Such unlooked for interaction may provide misleading data in situations where binocular viewing is used because of poor vision in one eye; therefore, occlusion of the eye not being tested should be undertaken whenever possible. Invest Ophthalmol Vis Sci 24: [796][797][798] 1983 While exploring the parameters for optimally recording the pattern electroretinogram (PERG), we discovered that a large response could be obtained from the eye that did not contain the active recording electrode. It is the purpose of this report to set forth the circumstances that give rise to the appearance of this unexpected response and also, because it is unwanted, the precautions that may be taken to minimize its occurrence. Materials and Methods. Three young adults with normal vision were used as subjects. All had 20/20 vision in each eye. An electronically generated, counterphase reversal checkerboard (11 pattern alternations/sec) was displayed on a Conrac Video monitor (mean luminance 50 cd/m 2 ). We have described our stimulus in terms of alternations/sec in order to avoid confusion that may be caused by the term "Hz." Our stimulus undergoes uniform global reversals of a repeating pattern. Here, reversals and rereversals are indistinguishable. The PERG and VER, being mass nonspike responses, are identical to each alternation. The fundamental period of both the stimulation and response, then, is the time between alternations and this period has been used for all phase calculations. At a distance of 71 cm the screen subtended 16 X 22°o f visual arc and the checks were 1 °/side. The check contrast was always maintained at 50%. A gold foil electrode was hooked over the lower lid of the left eye.' A pair of gold-plated earclip electrodes served as the reference and ground leads. Initial stage of amplification was provided by a Grass P9A; gain setting = 5K, band pass (6 db attenuation) set at 3 and 30 Hz. A trial consisted of 128 sweeps of 300 msec each summed on a Nicolet 1120/334B signal averager. One patient who for a period of 2 yrs had a unilateral meningioma impinging upon the left optic nerve was also tested. This 33-year-old woman was examined after surgery at a time when vision in her left eye consisted of only "light perception" in the superior quadrant. Ophthalmoscopically, the left eye showed a pale yellow disc and almost no sign of the nerve fiber layer reflex visible on red free light examination. Her right eye had normal (20/20) acuity, full visual field, and a normal appearing fundus. Results. The basic findings on normal subjects are shown in In the binocular viewing conditions we found that placing the reference electrode on the left (ipsilateral) ear instead of the right resulted in a 55% reduction, but not a complete elimination, of the amplitude of the referred PERG. We wondered whether recordings obtained when the left eye was occluded might simply be a visually evoked cortical response (VER) conducted to the eyeear electrode configuration. Accordingly, we repeated the condition shown i

Multifocal ERG findings in carriers of X-linked retinoschisis

Purpose To determine whether retinal dysfunction in obligate carriers of X-linked retinoschisis (XLRS) could be observed in local electroretinographic responses obtained with the multifocal electroretinogram (mfERG). Methods Nine obligate carriers of XLRS (mean age, 46.2 years) were examined for the study. Examination of each carrier included an ocular examination and mfERG testing. For the mfERG, we used a 103-scaled hexagonal stimulus array that subtended a retinal area of approximately 40° in diameter. The amplitudes and implicit times in each location for the mfERG were compared with the corresponding values determined for a group of 34 normally-sighted, age-similar control subjects. Results Mapping of 103 local electroretinographic response amplitudes and implicit times within a central 40° area with the mfERG showed regions of reduced mfERG amplitudes and delayed implicit times in two of nine carriers. Conclusions The mfERG demonstrated areas of retinal dysfunction in two carriers of XLRS. When present, retinal dysfunction was evident in the presence of a normal-appearing fundus. Multifocal ERG testing can be useful for identifying some carriers of XLRS

Binocular interaction : fusion or suppression of the visually evoked potential to dichoptic stimulation

In this study averaged visually evoked potentials were used to examine the nature of binocular processing of the visual system. Two different hypotheses have been proposed by earlier writers. The first assumed that the information from any one is suppressed at a given time, while the information from the other eye dominates in perception. An alternative hypothesis proposes that all information is processed and fused into a single percept. These two hypotheses were studied by manipulating the between line distances of grid patterns presented to the two eyes. Previously, characteristic responses have been found for the various pattern sizes. Again these differences were substantiated and were used to determine the contribution of each eye's input to the binocular responses. Pattern sizes presented to one eye were varied while holding constant the size of the pattern presented to the other. Three scalp recording sites were used: a midline occipital and two lateral occipital locations. Only the midline data was presented here. Averaged Visually Evoked Responses were obtained to each condition in a Binocular, Right, Binocular, Left flash order

A Comparison of Phoropic and Scotopic Electroretinogrophic Changes in Early Diabetic Refinoparhy

Previous studies of early diabetic retinopathy have shown that oscillatory potential (OP) amplitudes are reduced in many diabetic patients. OP amplitude is believed to be a more sensitive indicator of the development of future retinopathy than b-vvave amplitude of the scotopic electroretinogram (ERG). Because OPs measured to a bright white flash reflect both rod and cone system activity, it is important to compare OP amplitudes to photopic ERG measures as well as scotopic measures in early diabetic retinopathy. In this study, OPs and ERG responses were measured under photopic and scotopic conditions in a group of diabetic patients. Although OPs were reduced in amplitude in the diabetic group, several other parameters of the scotopic and photopic b-waves were impaired. The results indicate that b-wave activity may indicate retinal changes in early diabetic retinopathy in the same manner as the OPs. Invest Ophthalmol Vi

A platform for the discovery of new macrolide antibiotics.

The chemical modification of structurally complex fermentation products, a process known as semisynthesis, has been an important tool in the discovery and manufacture of antibiotics for the treatment of various infectious diseases. However, many of the therapeutics obtained in this way are no longer effective, because bacterial resistance to these compounds has developed. Here we present a practical, fully synthetic route to macrolide antibiotics by the convergent assembly of simple chemical building blocks, enabling the synthesis of diverse structures not accessible by traditional semisynthetic approaches. More than 300 new macrolide antibiotic candidates, as well as the clinical candidate solithromycin, have been synthesized using our convergent approach. Evaluation of these compounds against a panel of pathogenic bacteria revealed that the majority of these structures had antibiotic activity, some efficacious against strains resistant to macrolides in current use. The chemistry we describe here provides a platform for the discovery of new macrolide antibiotics and may also serve as the basis for their manufacture

Meteorological Integration for the Biological Warning and Incident Characterization (BWIC) System: General Guidance for BWIC Cities

The U.S. Department of Homeland Security (DHS) is responsible for developing systems to detect the release of aerosolized bioagents in urban environments. The system that accomplishes this, known as BioWatch, is a robust first-generation monitoring system. In conjunction with the BioWatch detection network, DHS has also developed a software tool for cities to use to assist in their response when a bioagent is detected. This tool, the Biological Warning and Incident Characterization (BWIC) System, will eventually be deployed to all BioWatch cities to aid in the interpretation of the public health significance of indicators from the BioWatch networks. BWIC consists of a set of integrated modules, including meteorological models, that estimate the effect of a biological agent on a city’s population once it has been detected. For the meteorological models in BWIC to successfully calculate the distribution of biological material, they must have as input accurate meteorological data, and wind fields in particular. The purpose of this document is to provide guidance for cities to use in identifying sources of good-quality local meteorological data that BWIC needs to function properly. This process of finding sources of local meteorological data, evaluating the data quality and gaps in coverage, and getting the data into BWIC, referred to as meteorological integration, is described. The good news for many cities is that meteorological measurement networks are becoming increasingly common. Most of these networks allow their data to be distributed in real time via the internet. Thus, cities will often only need to evaluate the quality of available measurements and perhaps add a modest number of stations where coverage is poor

Final Technical Report: Development of the DUSTRAN GIS-Based Complex Terrain Model for Atmospheric Dust Dispersion

Activities at U.S. Department of Defense (DoD) training and testing ranges can be sources of dust in local and regional airsheds governed by air-quality regulations. The U.S. Department of Energy’s Pacific Northwest National Laboratory just completed a multi-year project to develop a fully tested and documented atmospheric dispersion modeling system (DUST TRANsport or DUSTRAN) to assist the DoD in addressing particulate air-quality issues at military training and testing ranges

DUSTRAN 1.0 User’s Guide: A GIS-Based Atmospheric Dust Dispersion Modeling System

The U.S. Department of Energy’s Pacific Northwest National Laboratory just completed a multi-year project to develop a fully tested and documented atmospheric dispersion modeling system (DUST TRANsport or DUSTRAN) to assist the U.S. Department of Defense in addressing particulate air quality issues at military training and testing ranges. This manual documents the DUSTRAN modeling system and includes installation instructions, a user’s guide, and detailed example tutorials

The Ecology and Evolution of Social Behavior in The Crabs Sesarma Reticulatum and S. Cinereum

174 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1979.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD