Legacy Theses and Dissertations (1940-2009)
Permanent URI for this collectionhttps://hdl.handle.net/10657/6771
This collection gathers digitized University of Houston theses and dissertations dating from 1940.
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Browsing Legacy Theses and Dissertations (1940-2009) by Author "Abplanalp, Paul"
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Item An investigation of the predictability of corneal swelling(1984) Johnson, Murray H.; Boltz, Roger L.; Abplanalp, Paul; Godio, Louis B.The corneal swelling response to hypoxia created by a contact lens varies considerably from patient to patient. This response is therefore an important consideration in the wearing of extended-wear contact lenses. It would be valuable to have a predictive test that could identify the edema-prone patient based on the physiological corneal response to a single lens. In order to establish whether such a test is feasible, it is first necessary to examine whether (a) the corneal swelling rate (as a function of oxygen level as controlled by lens thickness) is stable enough for individual subjects and across subjects to allow predictability, and (b) the amount of swelling with identical lenses is repeatable for individual subjects. The purpose of this study was to investigate these two aspects of corneal swelling by using 38% water content hydrogel lenses of different thicknesses in both open and closed eye conditions. [...]Item Differences in balance and visual characteristics in a group of brain injured patients(1982) Winkler, Patricia Ann; Rosner, Jerome; Bedell, Harold E.; Abplanalp, Paul; Littell, Elizabeth H.Postural stability was measured using a biostereometric sensor in 20 brain-injured subjects and 10 normals. Measurements of stability were recorded for two minutes with eyes open, eyes closed and one eye open in both sitting and standing positions. Based on results of postural measures with both eyes open or closed, brain-injured subjects could be divided into two groups; those whose balance is better with eyes open (E.O. group) and those whose balance is better with eyes closed (E.C. group). Thus, this study documents the clinical impression that some brain-injured subject's static balance is destabilized by vision. A battery of visual sensory, oculomotor and perceptual functions were then examined to identify the extent to which differences in balance in the E.O. and E.C. groups could be explained by differences in one or more of these functions. The E.C. group performed worse on all visual tests as a whole, having significantly worse scores on tests of binocular vision (fine gross) and eye alignment. Many brain-injured subjects may be more readily rehabilitated using monocular vision or without vision. Further investigation of the role of binocular vision in normal postural control may clarify how abnormal binocular vision in brain-injured subjects can result in poor balance.Item The oculomotor reference in humans with bilateral macular disease(1985) White, Janis M.; Bedell, Harold E.; Abplanalp, Paul; Flom, Merton; Randall, Jose T.; Zuber, B. L.In persons with normal vision, there is a very stable system in which the fovea serves as the oculomotor reference (the retinal locus about which eye movements are neurologically centered) and the direction reference (the retinal locus which, when stimulated, gives rise to the sensation of direct viewing). Although a shift in the oculomotor and direction references away from the fovea would presumably maximize redisual vision in persons who acquire bilateral macular disease, it is not known whether such shifts occur in these patients. The present study shows that the oculomotor reference, and perhaps the direction reference, is shifted to a nonfoveal locus in some patients with bilateral macular disease. Eye movements during attempted steady fixation and during saccadic tracking were analyzed for twenty-one patients with bilateral macular disease (Stargardt's disease or age-related maculopathy) using videorecordings showing the fixation target's image on each patient's fundus. Seven of the patients had eye movements which were clearly centered about a nonfoveal locus (located close to one of the major meridia). Specifically, during fixation, the target's image was maintained in a circumscribed area, the size of which was related to the eccentricity of the nonfoveal locus. The meridia of fixation saccades were complementary to those of the drifts, similar to normal foveal fixation. No fixation movement carried the target's image from the eccentric locus and toward the fovea. Refixational saccades of these seven patients caused the arget's image to be redirected to the nonfoveal locus used for fixation. Although the latencies of the initial saccades were abnormally long, the sequences of saccades were otherwise normal. The endpoints of initial saccades were clustered; the amount of clustering tended to be related to the eccentricity of the fixation locus. Second saccades had normal latencies and endpoints that tended to be more clustered than those of the first. No saccade imaged the target at the fovea. There was evidence to suggest that the direction reference as well was shifted to the nonfoveal fixation locus in these seven patients. In contrast, eye movements of the other fourteen patients ruled out a shift of the motor reference to a specific, nonfoveal locus. During fixation, such eye movements included the imaging of the target in a broad area around the edge of the macula and/or fixation movements which directed the target's image from the eccentric locus and toward the fovea. In response to displacements of the target, the failure to consistently make Tefixational saccades, saccades with scattered endpoints, and/or saccades which directed the target's image to the fovea ruled out a shift of the oculomotor reference. The motor-reference shift occurred in patients whose onset of bilateral macular disease was early or late in life. This shift apparently took years to occur. Based on a model of saccadic processing, two possible mechanisms that could underly the motor-reference shift are discussed. The point from which retinal error signals are computed could shift to the nonfoveal locus. Alternately, a constant could be added into the signal of spatial target position to which the signal of current eye position is compared.