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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

On the Campbell and Stiles-Crawford effects and their clinical importance

Dunnewold, Cornelis Johan Willem. January 1900 (has links)
Thesis (doctoral)--Rijksuniversiteit te Utrecht.

Interictal visual system function in migraine : a psychophysical approach

McColl, Shelley L. January 2002 (has links)
Visual manifestations of migraine are largely considered transient, without permanent sequelae. Recent findings raise the possibility of persistent ocular and neural manifestations. This thesis investigates visual function in migraine during the period between episodes by applying various psychophysical tests to two migraine groups (migraine with aura ( n = 20) and migraine without aura (n = 20)) and comparing the results to those of a nonheadache control group (n = 20). Tests were designed to address the level of visual system involvement, and to investigate the extent to which selective visual processes, specifically, motion and other forms of temporal modulation are adversely affected in migraine. / The first experiment assessed global processing of complex form and motion in Glass patterns. Compared to nonheadache participants, the migraine groups demonstrated significantly elevated motion detection than motion discrimination thresholds. In contrast, average form detection thresholds were almost identical between subject groups. The second experiment measured perimetrically, in each eye, global motion sensitivity in fifteen localized visual field regions and compared these results in the same subjects to those obtained from conventional luminance-based perimetry. Perimetry testing revealed that two-thirds of migraineurs had localized deficits in motion coherence. Almost all motion field defects occurred in regions of normal sensitivity to the luminance targets. Over 80% of migrainous visual field defects were nonhomonymous, indicating that dysfunction occurs largely prior to the optic chiasm. Homonymous defects were also detected, raising the possibility of postchiasmal dysfunction, although several of these defects may represent independent monocular losses. The stability of a sample of field defects was retested after a 4--6 week delay. Sixty-percent of the motion defects persisted. These regions could support normal resolution acuity, but in most cases, not the discrimination of small increments in speed in globally coherent motion. / Also included is a study of the spatial and temporal frequency characteristics of visual discomfort to grating patterns. Visual discomfort was experienced by a greater proportion of migraineurs than nonheadache controls, and at significantly lower levels of stimulus contrast in migraineurs than in controls. Gratings modulated at high temporal frequencies were particularly effective in eliciting discomfort in migraineurs. / Comparison of individual results across the various tests suggests that functional deficits in migraine (i) are demonstrated on tasks that involve global motion and other forms of temporal modulation, (ii) occur primarily prior to the optic chiasm, but may, in some cases, also involve higher-levels of the visual pathway. Theoretical and clinical implications on migraine pathology and the visual system are discussed.

Complex visual hallucinations associated with deficits in vision : the Charles Bonnet Syndrome

Schultz, Geoffrey Robert January 1995 (has links)
The Charles Bonnet syndrome is characterized by complex visual hallucinations in people without psychopathology or disturbance of normal consciousness. This thesis highlights the association of visual deficits with the syndrome, and proposes that it is analogous to the perception of phantom limbs; both conditions arise when normal sensory input to the brain is severely reduced. The five studies that comprise this thesis systematically gather information on the syndrome to answer three basic questions: how can the hallucinations be classified, what are the clinical implications for individuals who experience them, and what might cause the hallucinations. Study 1 examines 64 cases described in the literature. Demographic information on the hallucinators, properties of the hallucinations, initiating factors, as well as etiological mechanisms are reviewed. Study 2 examines the properties of the hallucinations in a sample of 60 subjects and reveals, by statistical analysis, a dimension of the hallucinatory experience that ranges from discrete, singular perceptual experiences to multiple changing experiences. Studies 3 and 4 examine the mental status of hallucinators score within the normal range on tests of anxiety, depression, and psychological symptomology and exhibit no evidence of gross cognitive impairment. A detailed analysis of results show that a small proportion of hallucinators score within the normal range on tests of anxiety, depression, and psychological symptomology and exhibit no evidence of gross cognitive impairment. A detailed analysis of results show that a small proportion of hallucinators endorse comparatively more symptom-oriented items than the remainder of hallucinators, as well as more items non-hallucinators (in Study 4). Finally, Study 5 examines the performance of two hallucinating groups as well as a group of visually impaired non-hallucinating on threshold estimation and signal detection tasks. The results of the combined studies indicate

Vision impairment in older adults : adaptation strategies and the Charles Bonnet syndrome

Knight, Lelia. January 2006 (has links)
Adaptation to vision impairment was studied by telephone interviews with 78 legally blind adults (mean age 79.5) who had received rehabilitation services from an agency in upstate New York. Data were collected on demographics, health, activity levels, social support, blindness data, adaptation to vision loss (AVL scale, Horwitz and Reinhardt, 2005), and symptoms of Charles Bonnet Syndrome (CBS). Using multiple regression and logistic regression, the most significant predictors of high AVL scores were found to be good interpersonal communication and a relative living close by, while predictors of CBS were self-reported health issues, especially diabetes, and fewer trips into the community. Very few respondents reported receiving any information on CBS from eye care providers. This suggests that doctors should consider discussing CBS with patients, and that both social workers and doctors need a better understanding of CBS, as symptoms could easily be mistaken for mental illness, causing inappropriate referrals.

Visual stress in migraine : subjective and psychophysiological responses to intense visual stimulation

Crotogino, Jennifer January 2002 (has links)
This dissertation assesses whether intense visual stimulation can act as a stressor to migraine sufferers between attacks, and whether subjective and psychophysiological reactions to these stimuli can clarify how migraine attacks may be triggered. / The first study assessed thresholds of light-induced discomfort and pain in migraine sufferers and non-migrainous controls during a non-headache period. Two instruction sets were compared to assess whether information presented to participants would affect thresholds. The results showed that migraineurs had significantly lower thresholds for light-induced pain. However, this effect was most apparent in those who had heard the negatively biased instructions reinforcing the need to control contextual factors when assessing subjective phenomena such as visual discomfort. / The second study assessed subjective and psychophysiological responses of female migraine sufferers and female controls during exposure to visual stimuli incorporating spatial and temporal characteristics that are most likely to be bothersome to migraineurs. Two control stimuli were included to assess responses during similar, but theoretically less aversive conditions. Migraine sufferers had higher heart rate and more frequent electrodermal responses than controls at all points of the study, including baseline and recovery. However, while migraineurs reported higher anxiety during the intense conditions, and reported more visual and somatic complaints than controls during various viewing conditions, they did not show heart rate, heart rate variability or electrodermal changes that would suggest clear changes in autonomic function in response to aversive visual stimulation. / The third study assessed ambulatory electrocardiograms to investigate whether autonomic changes would be evident in the period leading up to, during or following a migraine. Three individuals were assessed on a day when they experienced a naturally occurring headache, and on a day when they were not. No obvious pattern of autonomic change was detected before or after headache, although there was some evidence that a pattern of increased heart rate and decreased vagal tone may accompany headache. / In summary, the results confirm that migraine sufferers are more sensitive to intense visual stimulation than controls, but do not support the contention that exposure results in widespread autonomic changes. Since interictal visual discomfort is a common in migraine, further research is needed to clarify how it can be incorporated into models of migraine pathophysiology.

Literature review on children myopia

Li, Zeyu, 黎泽宇 January 2010 (has links)
published_or_final_version / Public Health / Master / Master of Public Health

When sight closes in : the effects of field of view on wayfinding and spatial representation /

Guterman, Pearl S. January 2009 (has links)
Thesis (M.A.)--York University, 2009. Graduate Programme in Psychology. / Typescript. Includes bibliographical references (leaves 97-104). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:MR51540

Field perceptions of the Vision Initiative for Children's preschool vision screening training model

Nottingham Chaplin, P. Kay. January 1900 (has links)
Thesis (Ed. D.)--West Virginia University, 2006. / Title from document title page. Document formatted into pages; contains vii, 211 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 151-178).

A submission for the Shorney prize, 1965 /

Lowe, Ronald F. January 1965 (has links) (PDF)
Thesis (Shorney Prize Entry)--University of Adelaide, 1965. / A submission for the Shorney Prize 1965. Typescript.

The problem of vision in its relationship to public health a thesis submitted in partial fulfillment ... Master of Science in Public Health ... /

Scholes, William A. January 1939 (has links)
Thesis (M.S.P.H)--University of Michigan, 1939.

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