Visual-discrimination deficits after lesions of the centrifugal visual system in pigeons (Columba livia)

1992 ◽  
Vol 9 (3-4) ◽  
pp. 225-233 ◽  
Author(s):  
Uwe Hahmann ◽  
Onur Güntürkün
Keyword(s):  
Visual Acuity ◽  
Visual Field ◽  
Early Detection ◽  
Visual System ◽  
Visual Discrimination ◽  
Visual Analysis ◽  
Linear Regression Analysis ◽  
Columba Livia ◽  
Viewing Distance ◽  
Bilateral Lesions

AbstractThe effects of bilateral lesions of the centrifugal visual system (CVS) on the visual-discrimination capacity were studied in pigeons. Three different behavioral experiments, each testing different aspects of visual analysis, were performed. In the first two experiments, a grain-grit discrimination task and a visual-acuity determination, stimuli were presented in the frontal binocular visual field. A third experiment investigated the early detection of slow moving objects, introduced into the monocular lateral visual field. After bilateral lesions in the nucleus isthmo-opticus (ION) and in the ectopic nucleus isthmo-opticus (EION), a multiple linear regression analysis was employed to correlate the postoperative performance in all three tasks with the amount of structure loss within ION and EION. Deficits in the grain-grit discrimination procedure were a function of the ION lesion extent and did not depend on EION damage. Thus, these two structures could be functionally differentiated for the first time. Neither the ION nor the EION seems to be involved in visual- acuity performance or the early detection of large shadows moving forward through the visual field. Our data support the hypothesis that the CVS is involved in pecking and food selection among static stimuli at a short viewing distance in ground-feeding birds such as pigeons and chickens.

The visual acuity for the lateral visual field of the pigeon (Columba livia)

1993 ◽  
Vol 33 (12) ◽  
pp. 1659-1664 ◽  
Author(s):  
Uwe Hahmann ◽  
Onur Güntürkün
Keyword(s):  
Visual Acuity ◽  
Visual Field ◽  
Columba Livia

Rating Visual System Impairment using the Sixth Edition: Technical Aspects

2011 ◽  
Vol 16 (6) ◽  
pp. 7-11
Author(s):  
Bernard R. Blais
Keyword(s):  
Visual Acuity ◽  
Visual Field ◽  
Visual System ◽  
Visual Fields ◽  
Visual Field Loss ◽  
Test Procedures ◽  
Reasonable Estimate ◽  
Sixth Edition ◽  
Functional Vision ◽  
Vision Defects

Abstract Use of The Visual System section of the AMA Guides to the Evaluation of Permanent Impairment (AMA Guides), Sixth Edition, requires knowledge and skills in ophthalmology and assessing impairment. Visual acuity usually is measured using symbols (letters, numbers, pictures, or other symbols) presented in a letter chart format. The Visual Acuity Scale (VAS) is a linear scale with fixed increments and provides a reasonable estimate of acuity-related visual abilities; the associated impairment rating is a reasonable estimate of acuity-related performance loss. This article shows how to perform visual acuity calculations and how to assess impairment of visual fields, including visual field test procedures and calculations. Additional factors can lead to a loss of functional vision and can limit the individual's ability to perform activities of daily living and include contrast sensitivity, glare sensitivity, color vision defects, and binocularity, stereopsis, suppression, and diplopia. If functional vision is affected and is not accounted for by visual acuity or visual field loss, the impairment rating of the visual system can be adjusted but should be limited to an increase of the impairment rating of the visual system by, at most, 15 points (ie, less severe than the total loss of one eye). The ability to rate visual impairment requires significant knowledge and education, and therefore a physician trained in ophthalmology should perform the visual examination and visual system impairment rating.

Nonorganic Vision Loss

2019 ◽  
pp. 93-96
Author(s):  
Matthew J. Thurtell ◽  
Robert L. Tomsak
Keyword(s):  
Visual Acuity ◽  
Visual Field ◽  
Visual System ◽  
Clinical Features ◽  
Visual Function ◽  
Vision Loss ◽  
Good Prognosis ◽  
Management Approach ◽  
Permanent Damage ◽  
Visual Field Constriction

Nonorganic vision loss is common but can be challenging to diagnose and treat. In this chapter, we begin by reviewing the clinical features that suggest nonorganic vision loss. We next describe the maneuvers that can be used to demonstrate intact visual function in the patient who reports decreased visual acuity in one or both eyes. We then describe strategies to evaluate the patient who has visual field constriction. We describe the features that help to distinguish organic visual field constriction from nonorganic visual field constriction. Lastly, we discuss the management approach, which includes reassuring the patient that there is no evidence of permanent damage to the visual system and a good prognosis for spontaneous recovery.

scholarly journals Epidemiological Findings of Refractive Errors and Amblyopia among the Schoolchildren in Hatta Region of the United Arab Emirates

2021 ◽  
pp. 1-7
Author(s):  
Salam Chettian Kandi ◽  
Hayat Ahmad Khan
Keyword(s):  
Visual Acuity ◽  
Visual Field ◽  
United Arab Emirates ◽  
Refractive Error ◽  
Screening Program ◽  
Low Vision ◽  
Refractive Errors ◽  
Vision Screening ◽  
Screening Programs ◽  
School Based

<b><i>Introduction:</i></b> Uncorrected refractive errors and amblyopia pose a major problem affecting schoolchildren. We had previously observed that many schoolchildren in the Hatta region presented to the ophthalmology clinic with uncorrected refractive errors and amblyopia, which led us to undertake this research. As per the WHO, the term “visual impairment” can be “low vision” or “blindness.” Based on the presenting vision, “low vision” is defined for children who have vision of &#x3c;6/18 to 3/60 or having visual field loss to &#x3c;20° in the better-seeing eye. Children defined to have “blindness” have presenting vision of &#x3c;3/60 or corresponding visual field of &#x3c;10°. <b><i>Purpose:</i></b> To estimate the magnitude of uncorrected refractive errors and amblyopia among the schoolchildren aged 6–19 years and to assess the efficacy of school-based refractive error screening programs in the Hatta region of the United Arab Emirates. <b><i>Methods:</i></b> An epidemiological, cross-sectional, descriptive study was conducted on the entire student population studying in the government schools of the region. Those who failed the Snellen visual acuity chart test and those who were wearing spectacles were evaluated comprehensively by the researcher in the Department of Ophthalmology of the Hatta Hospital. Data were entered in the Refractive Error Study in School Children (RESC) eye examination form recommended by the WHO, and were later transferred to Excel sheets and analyzed by SPSS. <b><i>Results:</i></b> 1,591 students were screened and evaluated from the end of 2016 to mid-2017. About 21.37% (<i>n</i> = 340) had impaired vision with 20.9% (<i>n</i> = 333) refractive errors, of which 58% were uncorrected. Among the refractive error group, 19% (64 subjects) had amblyopia (4% of total students). The incidence of low vision was 9.5% and blindness was 0.38%. Low vision was found to be 9.5% and blindness 0.38%, taking in to account presenting visual acuity rather than best-corrected visual acuity for defining low vision and blindness. <b><i>Conclusion:</i></b> A significant number of students were detected to have uncorrected refractive errors among the vision impaired group (59%, <i>n</i> = 197) despite a school-based vision screening program in place. Seventy-eight percent of the amblyopia cases (<i>n</i> = 50) were found to be in the 11–19 years age group. Noncompliance with optical corrections was the reason for the high number of cases. A rigorous vision screening program and refractive services, complimented with awareness among parents and teachers, are recommended.

On Why Objects Appear Smaller in the Visual Periphery

2019 ◽  
Vol 31 (1) ◽  
pp. 88-96 ◽  
Author(s):  
Wladimir Kirsch ◽  
Roland Pfister ◽  
Wilfried Kunde
Keyword(s):  
Visual Field ◽  
Visual System ◽  
Structural Properties ◽  
Spatial Attention ◽  
Visuospatial Attention ◽  
Peripheral Target ◽  
Perceptual Distortion ◽  
Visual Periphery ◽  
Peripheral Location ◽  
Exogenous Cue

An object appears smaller in the periphery than in the center of the visual field. In two experiments ( N = 24), we demonstrated that visuospatial attention contributes substantially to this perceptual distortion. Participants judged the size of central and peripheral target objects after a transient, exogenous cue directed their attention to either the central or the peripheral location. Peripheral target objects were judged to be smaller following a central cue, whereas this effect disappeared completely when the peripheral target was cued. This outcome suggests that objects appear smaller in the visual periphery not only because of the structural properties of the visual system but also because of a lack of spatial attention.

scholarly journals Vision as oculomotor reward: cognitive contributions to the dynamic control of saccadic eye movements

2021 ◽  
Author(s):  
Christian Wolf ◽  
Markus Lappe
Keyword(s):  
Eye Movements ◽  
Visual Field ◽  
Visual System ◽  
Dynamic Control ◽  
Saccadic Eye Movements ◽  
Saccade Target ◽  
Cognitive Mechanisms ◽  
Foveal Vision ◽  
Subsequent Behavior ◽  
High Level

AbstractHumans and other primates are equipped with a foveated visual system. As a consequence, we reorient our fovea to objects and targets in the visual field that are conspicuous or that we consider relevant or worth looking at. These reorientations are achieved by means of saccadic eye movements. Where we saccade to depends on various low-level factors such as a targets’ luminance but also crucially on high-level factors like the expected reward or a targets’ relevance for perception and subsequent behavior. Here, we review recent findings how the control of saccadic eye movements is influenced by higher-level cognitive processes. We first describe the pathways by which cognitive contributions can influence the neural oculomotor circuit. Second, we summarize what saccade parameters reveal about cognitive mechanisms, particularly saccade latencies, saccade kinematics and changes in saccade gain. Finally, we review findings on what renders a saccade target valuable, as reflected in oculomotor behavior. We emphasize that foveal vision of the target after the saccade can constitute an internal reward for the visual system and that this is reflected in oculomotor dynamics that serve to quickly and accurately provide detailed foveal vision of relevant targets in the visual field.

scholarly journals Trends in the Retinal Nerve Fiber Layer Thickness Changes with Different Degrees of Visual Field Defects

2020 ◽  
Vol 2020 ◽  
pp. 1-6
Author(s):  
Wenhui Geng ◽  
Dabo Wang ◽  
Jing Han
Keyword(s):  
Regression Analysis ◽  
Visual Field ◽  
Linear Regression ◽  
Nerve Fiber ◽  
Retinal Nerve Fiber Layer ◽  
Linear Regression Analysis ◽  
Simple Linear Regression ◽  
Fiber Layer ◽  
Simple Linear Regression Analysis ◽  
Rnfl Thickness

Purpose. To explore the disease progression of primary open-angle glaucoma (POAG) in individuals with different degrees of VF defects by analyzing the trends in retinal nerve fiber layer (RNFL) changes at each stage. Methods. A total of 39 patients (77 eyes) were divided into three groups based on the severity of glaucomatous visual field (VF) loss: the first group included patients with mild baseline VF defects (mild group; n = 21 eyes). The second group included patients with moderate VF defects (moderate group; n = 18 eyes). The third group included patients with severe baseline VF defects (severe group; n = 38 eyes). For all patients, slit-lamp biomicroscopy of the anterior and posterior segments and detailed fundus and optic disc inspections were performed, the intraocular pressure (IOP) was measured by Goldman tonometry, best-corrected visual acuity (BCVA) was measured, the RNFL thickness was measured by OCT, and the VF was assessed by the Octopus perimeter. All the groups were followed up postoperatively for 18 months. Results. The mean RNFL thickness was recorded for all the visits. Using simple linear regression analysis, we found that the R2 values of the three groups were 0.988, 0.982, and 0.814, respectively, and the slopes of mean RNFL thickness changes for mild, moderate, and severe baseline VF defects were −0.088, −0.082, and −0.015, respectively. Moreover, we used simple linear regression analysis to explore whether and how the speed of RNFL thinning differs across groups. The R2 values of the three groups were 0.982, 0.978, and 0.805, respectively, and the slopes for mild, moderate, and severe baseline VF defects were 0.089, 0.085, and 0.017, respectively. Conclusion. The rate of RNFL thinning is linear; RNFL thinning is the fastest in individuals with mild baseline VF defects, followed by those with moderate baseline VF defects. In individuals with severe VF defects, changes in the RNFL thickness do not appropriately reflect the progression of the disease. The clinical trial is registered with ChiCTR2000028975.

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