Nitric oxide-dependent changes in Schistosoma mansoni gene expression.
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Biomedical subjects
William Morgan
Publications and source records attributed to William Morgan.
Structure and function of myelinated nerve fibers in the rabbit eye following ischemia/reperfusion injury.
The rabbit eye presents a valuable model to study the effects of vascular occlusion on the function and structure of myelinated nerve fibers. The rabbit eye has a band of myelinated nerve fibers within the intraocular compartment that are supplied by a narrow band of retinal vasculature. These vessels were transiently occluded ( approximately 8 hours) using laser photocoagulation and the transmission of electrical signals along the nerve fibers was assessed by recording the visual evoked response (VER). Morphological damage was assessed by histological techniques. The ischemic insult produced no permanent change in retinal function as assessed by electroretinography, but the VER was suppressed, indicating failure of nerve fiber transmission. Histologically, the visible damage to the region supported by the retinal vasculature worsened following reperfusion, showing evidence of demyelination and necrosis followed by macrophage responses and gliosis. This rabbit model of ischemia/reperfusion of the retinal vasculature offers a rare opportunity to reliably study the response of myelinated nerve fibers to ischemia/reperfusion insults and has demonstrated the susceptibility of myelinated nerve fibers to such insults.
Animals↗
Active heading control in simulated flight based on vertically extended contours.
In two experiments, we manipulated the properties of 3-D objects and terrain texture in order to investigate their effects on active heading control during simulated flight. Simulated crosswinds were used to introduce a rotational component into the retinal flow field that presumably provided the visual cues used for heading control An active control task was used so that the results could be generalized to real-world applications such as flight simulation. In Experiment 1, we examined the effects of three types of terrain, each of which was presented with and without 3-D objects (trees), and found that the presence of 3-D objects was more important than terrain texture for precise heading control In Experiment 2, we investigated the effects of varying the height and density of 3-D objects and found that increasing 3-D object density improved heading control, but that 3-D object height had only a small effect. On the basis of these results, we conclude that the vertical contours improved active heading control by enhancing the motion parallax information contained in the retinal flow.
Adult↗
Optic disc hemorrhage in Asian glaucoma patients.
PURPOSE: To assess the prevalence of optic disc hemorrhage in Asian patients with established glaucoma using a recently described, highly sensitive detection method. MATERIALS AND METHODS: Patients entering a trial of glaucoma filtering surgery in Southeast Asia (The Singapore 5FU Study) were assessed for the presence or absence of optic disc hemorrhage using stereo flicker chronoscopy of stereophotograph pairs. RESULTS: A total of 167 patients (117 males and 50 females) were assessed, of whom 128 were Chinese. Primary open-angle glaucoma was diagnosed in 90 patients, primary angle-closure glaucoma in 69 patients, and pseudoexfoliative or pigment dispersion glaucoma in 7 patients. Five eyes of 5 patients had disc hemorrhage at enrollment (5/167), a rate of 2.99%. Four patients with disc hemorrhage had primary open-angle glaucoma and 1 had primary angle-closure glaucoma. There were no significant differences in global visual field indices, AGIS scores, or intraocular pressures between eyes with and without disc hemorrhage. All disc hemorrhages were seen in eyes prior to trabeculectomy. CONCLUSIONS: The prevalence of disc hemorrhage in the current study was comparable to that seen in primary open-angle glaucoma in clinic-based studies of white patients, but far less than that reported in normal-tension glaucoma studies. Hemorrhages were more common in primary open-angle glaucoma than primary angle-closure glaucoma.
Ethnicity↗
Telemedicine-friendly, portable tonometers: an evaluation for intraocular pressure screening.
PURPOSE: To evaluate the intraocular pressure (IOP) readings from two portable, telemedicine-friendly tonometers for suitability in glaucoma screening. METHODS: 213 eyes of 107 consenting patients attending an eye clinic were tested with an I-care tonometer and a Pulsair-Easy Eye puff-air tonometer. Gold standard IOP was measured with a Goldmann applanation tonometer (GAT). Effect of central corneal thickness, anterior chamber depth and refractive errors on IOP measurements were also analysed. RESULTS: The mean difference of IOP by GAT and both the portable tonometers was +/- 2.2 mmHg. The analysis indicates minimal difference between IOP readings of both the portable tonometers. The mean difference between two consecutive readings by I-care was 0.01 mmHg. Using 21 mmHg as a threshold for suspected glaucoma, both the portable digital tonometers reported a sensitivity of 38% and specificity of >95%. In the subjects studied, central corneal thickness had statistically significant influence on IOP measurements while refractive errors and anterior chamber depth had no significant influence on IOP measurements with any tonometry. CONCLUSION: The IOP readings by both portable tonometers are comparable and were within clinically acceptable range from GAT. These portable tonometers are useful tools for IOP screening.
Adult↗