A novel accelerometer based on light modulation has been designed and a prototype device manufactured. The device utilises the change in refractive index brought about by stress induced by the applied vibration. A detailed mathematical analysis of several feasible sensing designs has been performed to aid the design process. A mathematical model has been developed to assess the performance characteristics of the light modulated accelerometer the results of which were also used as a design tool. The prototype accelerometer was tested, from 1 g to 50 g between frequencies of 25 Hz to 2000 Hz, on a vibration system under three modulation schemes. The acceleration response of the device was seen to be linear over the testing range whilst the frequency response dropped off initially and levelled off at approximately 1 kHz. An experimental accelerometer was also assembled on the vibration table so that various materials could easily be tested without having to undergo precise machining. The acceleration and frequency responses showed similar behaviour to those obtained with the prototype accelerometer. However, the actual response levels varied with each material. To aid in the development of the accelerometer the stress-optic and thermo-optic coefficients have been determined for a range of polymeric materials. The stress optic coefficient was determined for polycarbonate, polymethyl methacrylate, polvinyl chloride and araldite epoxy resin using a circular polariscope and two interferometer configurations up to the yield stress of the materials tested. Each material showed a constant coefficient over the testing range. The results obtained using each technique were in good agreement with each other and the limited literature data available. The thermal variation of refractive index was also determined for the same materials. The Abbe refractometer was used for the determination between 5 and 140°C using five wavelength sources and two interferometer configurations using a HeNe laser from -50°C to approximately 30° above the glass transition temperatures. The change in index was found to be linear over the temperature range tested. However, at the glass transition temperature a change in gradient was observed with each material. Two simple mathematical relationships were used to predict the thermo-optic coefficient. These gave values reasonably close to those obtained in experiment.

This thesis analyzes the problem of design analog fiber optic link for transmission high frequency signals. Analog fiber optic link will be used in system for detection and localization a partial discharge activity MOSAD-PD-UHF, where will replace existing solution with coaxial cables, which is not appropriate for highly noise environment. MOSAD-PD-UHF system is developed in department of theoretical and experimental electrical engineering. At the first, MOSAD-PD-UHF system and individual parts of optical chain are theoretical described. In following part are compared a few commercially available analog fiber optic link and design of chosen transmit and receive module are described. . The thesis final part deals with construction of optical link and measured parameters are discussed.

Despite the fact that frequency modulation (FM) was firstly applied to radio signaling 80 years ago (1936, by Edwin Howard Armstrong), it has never been deployed in fiber-optic communication systems. In this thesis, a novel frequency modulated fiber-optic communication system with optical discriminator is proposed. The noise configuration and anti-dispersion property of the FM system are investigated through an analytical model that has been derived and validated with numerical simulations. The performance of the proposed FM system is compared with an amplitude modulated (AM) fiber-optic communication system, owing to the fact that the widely used modulation formats, intensity modulation and quadrature amplitude modulation (QAM), can be extracted as a model of the basic AM format. Depending on the property of the filter, two types of frequency discriminators are discussed: the leading edge filter (LEF) and the tail edge filter (TEF). Since the amplified spontaneous emission (ASE) noise is averagely distributed without any frequency dependence, the noise characteristics are not affected by the choice of the frequency discriminator. However, when it comes to the dispersion impairment, the difference between two frequency discriminators is dramatic because the distortion induced by dispersion strongly hinges on the operated frequency. The results show that, with the presence of noise, the proposed FM scheme can lead to one or two orders of magnitude enhancement in the system’s output signal-to-noise ratio (SNR) as compared to that of the conventional AM scheme. Also, with the presence of dispersion, it is proved that the span of the FM system can reliably reach 110km with bit rate up to 10Gbit/s, surpassing the AM system with a maximum signal reach of 70km. A real application, with the presence of both noise and dispersion, demonstrates the overall superiority of the FM system’s performance over that of the AM system. The obtained results suggest a promising future for the FM technique in fiber-optic communication. / Thesis / Master of Applied Science (MASc)

No description available.

Optic Nerve Hypoplasia (ONH) is the leading cause of childhood blindness in developed nations and its prevalence has been rising. Yet, we know little about the genetic, molecular, or cellular mechanisms underlying ONH. A previous study described ONH in a cohort of patients with mutations in CASK, an X-linked gene with established roles in neural development and synaptic function. I have demonstrated that heterozygous deletion of CASK in mice (Cask+/-) recapitulates many of the phenotypes observed in patients with CASK mutations, including ONH. This includes reduced optic nerve size, reduced numbers of retinal ganglion cells (RGCs), reduced RGC axonal diameter, and deficits in vision-related tasks. Further analysis on a homozygous partial loss of function variant (Caskfl/fl) also displayed ONH with reduced numbers of RGCs. In order to understand the mechanisms underlying CASK-associated ONH, I explored whether RGCs, the projection neurons of the retina and the cells whose axons comprise the optic nerve, generate CASK. Indeed, mRNA analysis revealed expression of CASK by a large cohort of RGCs. In order to assess whether loss of CASK from a majority of RGCs leads to ONH, I crossed a conditional allele of CASK (CASKfl/fl) with transgenic mice that express Cre Recombinase (Cre) in RGCs. Deletion of CASK from RGCs did not further alter ONH size nor RGC survival. These results demonstrate that loss of CASK signaling in this discrete neuronal populations is not sufficient to lead to further disruption in the assembly of the subcortical visual circuit, suggesting a non-cell autonomous mechanism for loss of CASK in ONH. / Doctor of Philosophy / The connection between the eye and the brain is crucial for successful vision. Impairment of this connection by either loss of the retinal neurons that project axons to the brain or damage to the nerve (optic nerve) lead to blindness. This occurs in a disease called Optic Nerve Hypoplasia (ONH), which is the leading cause of childhood blindness in developed countries. Discovering the risk factors associated with this disease and mechanisms underlying the disease can help us build tools to treat and repair the optic nerve. Previously, mutations in the CASK gene were found in patients with ONH. Here, I developed a mouse model of CASK mutations to phenocopy the human patients, and used this model to explore the development of ONH. For example, with this mouse model I described for the first time, the timeline of disease progression. Surprisingly, I also showed that loss of CASK specifically from the neurons whose axons generate the optic nerve did not lead to ONH, suggesting that ONH may develop from a failure of a network of cells, rather than just one population of cells.

No / The purpose of the research was to describe a software package (Discus) for investigating clinicians' subjective assessment of optic disc damage [diagnostic accuracy in detecting visual field (VF) damage, decision criteria, and agreement with a panel of experts] and to provide reference data from a group of expert observers. Optic disc images were selected from patients with manifest or suspected glaucoma or ocular hypertension who attended the Manchester Royal Eye Hospital. Eighty images came from eyes without evidence of VF loss in at least four consecutive tests (VF negatives), and 20 images from eyes with repeatable VF loss (VF positives). Software was written to display these images in randomized order, for up to 60 s. Expert observers (n = 12) rated optic disc damage on a 5-point scale (definitely healthy, probably healthy, not sure, probably damaged, and definitely damaged). Optic disc damage as determined by the expert observers predicted VF loss with less than perfect accuracy (mean area under receiver-operating characteristic curve, 0.78; range, 0.72 to 0.85). When the responses were combined across the panel of experts, the area under receiver-operating characteristic curve reached 0.87, corresponding to a sensitivity of ∼60% at 90% specificity. Although the observers' performances were similar, there were large differences between the criteria they adopted (p < 0.001), even though all observers had been given identical instructions. Discus provides a simple and rapid means for assessing important aspects of optic disc interpretation. The data from the panel of expert observers provide a reference against which students, trainees, and clinicians may compare themselves. The program and the analyses described in this article are freely accessible from http://www.discusproject.blogspot.com/.

Background: Cryptococcal induced visual loss is common and increasingly becoming a debilitating consequence in survivors of cryptococcal meningitis (CM). Conflicting reports of the optic neuritis and papilloedema models of visual loss have delayed the introduction of effective interventional strategies for prevention and treatment of visual loss in CM. Qualitative and quantitative diffusion-weighted imaging (DWI) and diffusion tensor imaging (DTI) of the optic nerves have proven useful in the examination of the microstructure of the optic nerve especially in optic neuritis. Its application has been extrapolated to other optic nerve disorders such as ischaemic optic neuropathy and glaucoma. The aim of this study is to elucidate the pathogenesis of cryptococcal-induced visual loss using diffusion imaging of the optic nerve as an investigational tool. Method: Full ethical approval was obtained from the Greys Hospital, Department of Health and University of KwaZulu Natal Ethics Committees. Reliable and reproducible optic nerve diffusion techniques were first developed and optimized on 29 healthy volunteers at Greys Hospital, Neurology and Radiology departments using a Philips 1.5 Tesla Gyroscan. Informed consent was also obtained from 95 patients suffering from CM (≥18 yrs. of age), 14 patients with papilloedema and 14 patients with optic neuritis from other causes, recruited from Greys and Edendale Hospitals. Patients underwent full neuro-ophthalmological assessments, CSF examination, haematological workup, CD4 count, (viral load for some), electrophysiological assessment of vision [Visual evoked potential (VEP) and Humphreys visual fields (HVF)], Magnetic Resonance Imaging (MRI) scan of the brain and orbits and DWI and DTI of the optic nerves. Results and Discussion: Visual loss is common in CM, occurring in 34.6-48%. Optic neuritis was uncommon as evidenced by a lack of signal change and lack of enhancement within the optic nerve in all patients scanned. The peri-optic CSF space was not dilated and the optic nerve diameter was not increased regardless of CSF pressure and visual status. Swollen optic discs occurred in only 25% of patients whereas raised intracranial pressure (> 20cmCSF) was demonstrated in 69-71% of patients. Therefore visual loss could not be explained by papilloedema alone. The VEP P100 latency was shown to be a useful screening test for subclinical optic nerve disease in CM, but HVF was not. The optic nerve diffusion imaging used was reliable and reproducible and produced diffusion parameters equivalent to other investigators in the field. Neither optic nerve movement nor the CSF signal was demonstrated to impact significantly on optic nerve diffusion parameters. Optic nerve diffusion imaging did not demonstrate similarities between CM and papilloedema or optic neuritis regardless of CSF pressure or vision. Conclusion: The rarity of optic neuritis in CM and the disparity between papilloedema and visual loss together with the lack of support from diffusion studies suggest a 3rd mechanism of visual loss viz. the optic nerve compartment syndrome. Good clinical support is provided by a case report for this hypothesis that shows re-opening of the peri-optic CSF space and return of the peri-optic CSF signal on MRI with lowering of intracranial pressure and antifungal treatment. / Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2013.

Diss. (sammanfattning) Stockholm : Karol. inst., 2003. / Härtill 5 uppsatser.

Indiana University-Purdue University Indianapolis (IUPUI) / Hydrocephalus affects 1 in 1,000 newborns and nearly 1,000,000 Americans, leading to an increase in intercranial pressure due to the build-up of cerebrospinal fluid. There are numerous complications that arise as a result of hydrocephalus, but this study focuses on optic disc edema. The subarachnoid space surrounding the optic nerve contains cerebrospinal fluid. The cerebrospinal fluid increases in hydrocephalus, putting pressure on the optic nerve. The additional intracranial pressure has been proposed to cause axoplasmic stasis within the retinal ganglion cell axons, leading to axonal damage and retinal ischemia. The purpose of this study was to determine the effects of hydrocephalus on the optic disc and retina in several animal models of hydrocephalus. This study uses two genetic and two injury-induced models of hydrocephalus in addition to immunohistochemistry and histological stains to examine the optic disc, thickness of retinal layers, and numbers of retinal cells. This study serves as preliminary work to help build the case that hydrocephalus causes cell loss in the retina, as well as swelling of the retinal ganglion cell axons, leading to axoplasmic stasis and cell death. / Indefinitely

Ophthalmic diseases such as glaucoma are associated with progressive changes in the structure of the optic disc (OD) and parapapillary atrophy (PPA). These structural changes may therefore have relevance to other systemic diseases. The size and location of OD and PPA can be used as registration landmarks for monitoring changes in features of the fundus of the eye. Retinal vessel evaluation, for example, can be used as a biomarker for the effects of multiple systemic diseases, or co-morbidities. This thesis presents the first computer-aided measuring tool that detects and quantifies the progression of PPA automatically on a 2D retinal fundus image in the presence of image noise. An automated segmentation system is described that can detect features of the optic nerve. Three novel approaches are explored that extract the PPA and OD region approximately from a 2D fundus image. The OD region is segmented using (i) a combination of active contour and morphological operations, (ii) a modified Chan-Vese algorithm and (iii) a combination of edge detection and ellipse fitting methods. The PPA region is identified from the presence of bright pixels in the temporal zone of the OD, and segmented using a sequence of techniques, including a modified Chan-Vese approach, thresholding, scanning filter and multi-seed region growing methods. The work demonstrates for the first time how the OD and PPA regions can be identified and quantified from 2D fundus images using a standard fundus camera.