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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.
41

The Mechanobiology of the Crystalline Lens

Kumar, Bharat January 2020 (has links)
No description available.
42

Shroom3 Localization and Apical Constriction during the Development of the Crystalline Lens in Mouse Embryos

Eckes, Melissa 25 August 2017 (has links)
No description available.
43

Accommodative microfluctuations, crystalline lens tension, ciliary body thickness, and refractive error in children

Schultz, Kristin E. 26 June 2009 (has links)
No description available.
44

A critical appraisal of the etiology of adult human lenticular opacification and an investigation into the role of metabolic factors in its pathogenesis

Meyer, David 12 1900 (has links)
Thesis (PhD)--Stellenbosch University, 2001 / ENGLISH ABSTRACT: The eye is that biological instrument which conveys the light of the external world into the inner world of the mind, wherein we receive the miraculous gift of vision. So precious is this gift, that Science must search for ways to keep this portal clear for the flow of light. Indeed, Science is called upon to “make war upon the bloody tyrant, Time.” (Shakespeare W. Sonnet No. 16). For, in the course of ageing, the lens grows cloudy and cataractous. In this battle between Science and Time, we are fortunate to live in an era in which Science is uncovering the molecular basis for the various obstacles to vision. The question arises, whether or not, the ruinous hand of time can be stayed. Due to unrelenting, progressive lens opacification, most of the elderly are destined to be subjected to loss of vision and with passage of time, even blindness. Globally the cataract surgery rate is inadequate to keep pace with the ever growing demand on financial and human resources created by the cataract problem. An immense challenge therefore is directed to primary eye care: “Can cataract be prevented or can its onset at least be postponed?” This laudable ultimate aim can only be achieved once the etiology of cataractogenesis is well understood. This dissertation seeks to examine two previously unrecognized etiological aspects that, if correctly understood and managed, have the potential to achieve preventive ophthalmological goals that may indeed help to stay the ‘ruinous hand of time’. The first aspect deals with the role of lipids and was examined using a study group of dyslipidemic subjects. The first part of the study concluded that dyslipidemic patients develop cortical lens opacities more frequently and at an earlier age than the normal population, and that cortical lens opacities should be regarded as one of the most reliable clinical signs of dyslipidemia. Furthermore, an extremely strong correlation was found to exist between low HDL Cholesterol levels and the development of opacities. Below a HDL-Cholesterol level of 1,5mmol/l, subjects had more than seven-fold higher risk of falling in the lens opacity subgroup than those with HDLCholesterol levels above 1,5mmol/l. An equally strong correlation was demonstrated between high (>5) LDLHDL ratios and the development of lens opacities. Subjects with a LDL:HDL-C ratio below 5 possessed a 2.35 times greater risk of having lenticular opacities than the group with a LDL:HDL-C ratio greater than 5. The prevention or retardation of dyslipidemia associated lens opacities is therefore possible, provided patients with a genetic predisposition are detected early and their blood lipids managed adequately. The second aspect deals with the relationship between age related cataracts and the acetylation status of the individual. This study compellingly submits that the slow acetylator pheno- and genotype may be regarded as a genetic indicator of risk for age related cataract. The ability accurately to classify a patient genotypically and phenotypically, may henceforth be useful in health counseling since, if an individual is identified as being a slow acetylator, additional preventative and precautionary measures may be taken, i.e. the prevention of UVexposure to the eye and caution with the ingestion of xenobiotics like caffeine, commercial dyes, food preservatives, and drugs. Furthermore, such a finding should be taken into account in the long term therapeutic management of glaucoma, with special regard to carbonic anhydrase inhibitors which are sulphonamide-related drugs and totally dependent on the N-acetyltransferase pathway for metabolism. These drugs may accumulate in the slow acetylator over time and exert toxic effects intra-ocularly, conceivably including cataractogenesis. The search for genetic and metabolic mechanisms that may contribute to human cataractogenesis should be pursued with great enthusiasm. This endeavour may help Science to achieve its primary objective, ablate the effects of Time and really aid in preventing cataracts in man. / AFRIKAANSE OPSOMMING: Die wondergawe van visie word vir ons moontlik gemaak deur die oog wat as biologiese instrument die lig van die buitewereld inlaat na die binnewereld van die brein. So kosbaar is hierdie gawe dat die Wetenskap deurgaans moet poog om die poort oop te hou. Inteendeel, die Wetenskap word gemaan deur Shakespeare in sy Sonnet nommer 16 om “oorlog te maak teen die bloeddorstige tiran, Tyd”. Soos ‘n mens ouer word, word die lens dof en ‘n katarak mag vorm. Ten spyte van hierdie stryd tussen ‘Wetenskap’ en ‘Tyd’ leef ons in die gelukkige era waarin die Wetenskap meer en meer leer van die verskeie obstruksies tot visie. Die vraag ontstaan of die rinnewerende hand van ‘Tyd’ gestuit sal kan word. Vanwee ongenaakbare, progressiewe lensvertroebeling is die meeste bejaardes bestem om aan visie verlies, en met verloop van tyd selfs blindheid, te ly. Die wereldwye katarakchirurgie tempo is nie voldoende om by te hou by die immergroeiende finansiele en mannekrag eise wat deur die katarak probleem gestel word nie. Daar word dus ‘n reuse uitdaging aan primere oogsorg gestel naamlik: “Kan katarakte nie eerder voorkom of die aanvang daarvan ten minste uitgestel word nie?” Hierdie prysenswaardige doelwit kan nie bereik word alvorens die etiologie van kataraktogenese goed verstaan word nie. Hierdie tesis ondersoek twee voorheen onerkende etiologiese aspekte wat, indien hulle korrek verstaan en hanteer word, beslis die potensiaal het om die gemelde voorkomende doelwitte te bereik en sekerlik te kan bydrae om die rinnewerende hand van Tyd te stuit. Die eerste aspek spreek die rol van lipiede aan deur te kyk na 'n studiegroep van dislipidemiese persone. Die eerste deel van die studie kom tot die gevolgtrekking dat dislipidemiese pasiente kortikale lens opasiteite meer dikwels en op ‘n vroeer ouderdom ontwikkel as die normale populasie en dat sulke opasiteite beskou moet word as een van die mees betroubare kliniese tekens van dislipidemie. Daar is ook ‘n baie sterk korrelasie gevind tussen lae HDL cholesterol vlakke en die voorkoms van opasiteite. Persone in die studie met ‘n HDL cholesterol vlak laer as 1,5mmol/l het ‘n sewe keer hoer kans gehad om in die lensopasiteit subgroep te val as die met ‘n HDL cholesterol vlak laer as 1,5mmol/l. ‘n Sterk korrelasie tussen ‘n hoe (>5) LDLHDL verhouding en die voorkoms van lens opasiteite is ook gevind. Persone met ‘n LDLHDL verhouding >5 het ‘n 2.35 maal groter risiko gehad om lensopasiteite te he as die met ‘n LDL:HDL verhouding van <5. Die voorkoming of vertraging van dislipiedemie geassosieerde lens opasiteite is dus moontlik, solank persone met ‘n genetiese geneigdheid daartoe vroeg ontdek en hulle bloedlipiede voldoende beheer word. Die tweede deel van die tesis handel oor die verhouding tussen ouderdoms verwante katarakte en die asetilasie status van die individu. Met oortuiging kom hierdie studie tot die gevolgtrekking dat die stadige asetilator fenoen genotipe as 'n genetiese merker vir ouderdoms verwante katarakte beskou moet word. Die vermoe om ‘n individu beide genotipies en fenotipies akkuraat te klassifiseer mag voorts bruikbaar wees in gesondheidsraadgewing. Indien ‘n individu geTdentifiseer is as ‘n stadige asetileerder, kan addisionele voorsorg maatreels getref word soos bv. die voorkoming van blootstelling van die oog aan UV lig sowel as omsigtigheid met die inname van xenobiotika soos kaffei'ene, kleurstowwe, voedsel preserveermiddels en geneesmiddels. Hierdie bevinding moet ook in berekening gebring word in die langtermyn terapeutiese hantering van gloukoom. Die koolsuuranhidrase inhibitore, dikwels gebruik in die behandeling van gloukoom, is sulfonamied-agtige middels en dus totaal afhanklik van die N-asetieltransferase pad vir hulle metabolisme. Hierdie middels kan ophoop in die stadige asetileerder en gegewe genoeg tyd, bes moontlik toksiese intra-okulere effekte tot gevolg he. Die soeke na genetiese en metaboliese meganismes wat mag bydra tot menslike kataraktogenese behoort nagestreef te word met groot entoesiasme. Hierdie strewe mag dalk net vir die 'Wetenskap' bystaan om sy primere mikpunt te bereik, die effek van ‘Tyd’ te neutraliseer en te help om katarakte werklik te voorkom.
45

Immune modulation on retinal ganglion cell survival in experimental glaucoma

Chiu, Kin, 趙健 January 2008 (has links)
published_or_final_version / Anatomy / Doctoral / Doctor of Philosophy
46

The novel mouse [gamma]A-crystallin mutation leads to misfolded protein aggregate and cataract

Cheng, Man-hei., 鄭文熙. January 2009 (has links)
published_or_final_version / Biochemistry / Master / Master of Philosophy
47

A Second Generation Ex-Vivo Accommodation Simulator: Design and Calibration

Nankivil, Derek 01 January 2008 (has links)
Presbyopia is the progressive decrease in accommodative ability with age, and it implies a major loss of visual function. Presbyopia is the only condition of the eye which affects everyone who lives beyond 50 years of age. As part of a joint effort, the Ophthalmic Biophysics Center at the Bascom Palmer Eye Institute and the Vision Cooperative Research Centre at the University of New South Wales, developed two different ex-vivo accommodation simulators (EVAS) to examine the mechanisms of accommodation and presbyopia, and to test and validate new ophthalmic surgical procedures such as lens refilling. The purpose of this thesis is to mechanically and optically calibrate the second generation instrument (EVASII), and to compare it to the first generation design (EVASI). To validate the optical measurements of EVASII, an optical calibration has been performed, yielding a lens power measurement system with a mean accuracy of ±0.56D. To enhance the optical capabilities and tissue dissection options, the mechanics of mounting the tissue has been improved by using magnetic mounts, and the mechanical calibration of EVASII, yielded a force measurement system with a mean uncertainty of ±0.81g Also, a comparison of EVASII and EVASI has been performed, showing that the results of the two systems are significantly different; however, both systems successfully simulate accommodation. Thus, general trends concerning efficacy and optimization of surgical procedures as well as age related accommodative changes can be compared for each individual system.
48

Dynamic Optical Model of the Primate Crystalline Lens and Implications for the Restoration of Accommodation

Borja, David 23 December 2008 (has links)
The human crystalline lens is a complex, inhomogeneous and dynamic optical element which enables the eye to adjust focus in a process known as accommodation. Age related changes in the optical and mechanical properties of the lens cause a loss in accommodative ability leading to a condition known as presbyopia. Several experimental surgical techniques are under development for the correction of presbyopia. The goal of this dissertation is to better understand the relationship between the crystalline lens shape, its non-uniform refractive index gradient and its optical power and their changes with age and accommodation. In this study direct lens power and shape measurements were acquired on isolated lenses, and on lenses mounted in a lens stretching system designed to simulate accommodation. Several lens shape and power measurement techniques were developed for this study including a Scheimpflug camera system optimized for imaging the crystalline lens. Direct measurements of lens shape and power were used to develop an age-dependent optical-mechanical model of the lens during accommodation. The study shows that the normal growth of the lens is a major contributor to the progressive loss of accommodation amplitude, independent of changes in the elastic properties of the lens. These findings suggest that accommodation can be restored by refilling the lens with a material having a uniform refractive index.
49

Epithelial-mesenchymal transition in the anterior segment of the eye

Chandler, Heather Lynn, January 2006 (has links)
Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 138-153).
50

The Effects of 1-(5-Iodonaphthalene-1-sulfonyl)-1H-hexahydro-1,4-diazepine hydrochloride (ML-7) on the Lens During Avian Accommodation In Situ

Luck, Sara 02 December 2009 (has links)
A previous study in chickens revealed that myosin light chain kinase (MLCK), f actin, and myosin are found on the crystalline lens. Their polygonal arrangement at the posterior surface resembles a muscle tissue, which suggests that these proteins may have a contractile role in accommodation. The ciliary muscle in chickens is skeletal in nature and, therefore, chickens were used to test the hypothesis that contractile microfilaments play a role in accommodation. Ciliary nerve-induced accommodation was measured in the presence of an MLCK inhibitor 1-(5-Iodonaphthalene-1-sulfonyl)-1H-hexahydro-1,4-diazepine hydrochloride (ML-7). Eyes of 6-day old white Leghorn chickens (gallus gallus domesticus) were enucleated in Tyrode’s saline solution while keeping the ciliary nerve intact. One eye was treated with ML-7 and the other eye was treated with vehicle only. Three concentrations of ML-7 were used: 1 µM, 10 µM, and 100 µM. Two experiments were carried out, one including a (3×10 min) wash and one without. Focal lengths of the vehicle- and ML-7-treated eyes were measured before, during and after accommodation. Immunoblots were used to detect the amount of phosphorylated myosin with and without the inhibitor. Focal lengths for accommodation were shorter than those at rest (p<0.001). In the wash experiment, vehicle-treated eyes had higher accommodative amplitudes compared to ML-7-treated eyes for all three dosage groups. In the no-wash experiment, only the 1 µM group demonstrated the same trend as the wash experiment. For the 10 µM and 100 µM groups, ML-7-treated eyes had higher accommodative amplitudes compared to vehicle-treated eyes. Immunoblots revealed varying amounts of inhibition within pairs of eyes as well as between birds for both experiments. Results from this experiment indicate that ML-7 was not effective at determining whether contractile microfilaments found on the lens contribute to accommodation.

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