|Tipo di tesi||Tesi di dottorato di ricerca|
|Titolo||Metodi di stima dell’emodinamica oculare mediante flussimetra laser Doppler e riflettometria|
|Titolo in inglese||Methods of estimation of ocular hemodynamics in human fundus using laser Doppler flowmetry and ocular fundus reflectometry|
|Settore scientifico disciplinare||ING-INF/07 - MISURE ELETTRICHE E ELETTRONICHE|
|Corso di studi||Scuola di D.R. in INFORMATION AND COMMUNICATION TECHNOLOGIES (ICT)|
|Data inizio appello||2012-02-27|
|Disponibilità||Accessibile via web (tutti i file della tesi sono accessibili)|
La misurazione della perfusione sanguigna del fondo oculare è di interesse sia scientifico che clinico. Il suo valore scientifico risiede nella possibilità di comprendere la fisiologia dell’accoppiamento neurovascolore mentre le potenzialità cliniche riguardano la diagnosi precoce di alterazioni del flusso sanguigno associate a malattie oculari specifiche. La flussimetria Doppler e la riflettometria del fondo sono tecniche moderne per la misurazione non invasiva della perfusione oculare.
The measurement of blood perfusion in the ocular fundus is of scientific as well as clinical interest. Its scientific value lies in the possibility of gaining insight into physiology of deep vascular beds and clinical potential lies in the early assessment of alterations of blood flow associated with specific ocular diseases. Ocular fundus reflectometry and laser Doppler flowmetry are modern methods for non-invasive and continuous measurement of ocular perfusion and based on the scattering phenomenon of the reflected light. Ocular fundus reflectometry is a technique to measure the reflectance of a region of the ocular fundus. We developed an instrument for functional imaging of the neural tissues of the ocular fundus based on reflectance measurements to study the neuro-vascular coupling. We have developed a fully automatic registration algorithm based on differential multiscale framework for the processing of ocular fundus images with reduced computational time. This algorithm is reasonably efficient to determine relative translational displacement between the images and also to remove the geometric distortion. Simulation results performed on the fundus images show that differential multiscale framework based image registration algorithm provides an alignment precision about 90% and reduce the computational times up-to 30% of the time required by the general purpose algorithm. We had modified the fundus camera with an additional CCD video camera and synchronized with software to capture anterior segment of eyeball and ocular fundus. We developed software to align the fundus images by estimating the translation shifts in posterior eye through a calibration curve. We modified the illumination and image acquition systems and built an instrument applicable for clinical use to study the dynamics of visual pigments. Laser Doppler Flowmetry (LDF) determines noninvasively the relative flux of red blood cells (RBCs) of the fundus vessels. The technique is based on the values of the Doppler effect of low-power laser light scattered randomly by static structures and moving tissues. LDF output has been shown to be reproducible and able to measure flow in arbitary units. The effect of topical timolol maleate 0.5% on the choroidal circulation was investigated in 12 normal subjects. In a double masked, randomized design one eye received one drop of timolol and the fellow eye received one drop of placebo. Maximum velocity of red blood cells and volumetric blood flow rate was determined in each eye just before instillation of drops and then every 30 min upto 2 hours. Intraocular pressure was decreased by 8.3% in placebo-treated eyes (P <=0.001) and 16.1% in timolol-treated eyes (P <=0.0001). The mean heart rate was decreased significantly by 11.2% (P<=0.0001). No significant changes in artery blood pressure and perfusion pressure was detected. No significant differences in volumetric blood flow were observed in placebo-treated eyes or in timolol-treated eyes. The effect of pupil dilatation on choroidal blood flow was investigated in 24 young normal subjects. In all subjects, one eye was selected in random and received a drop of tropicamide 1%. Relative LDF parameters are measured in 12 eyes with 4mm artificial pupil placed directly in front of the eye. All the LDF parameters were recorded in every 3 min upto 30 min after application of the drop. Video recording of pupil size was obtained using a digital video camera. Following the administration of the drop, the pupil size was increased by 152% (P<=0.0001). No significant increases were observed in velocity, volume, and flow with 4 mm artificial pupil and a statistically significant increase were observed in LDF parameters without artificial pupil. The results indicate that the increase in LDF parameters without pupil is only due to the change in scattering geometry of the tissue and the penetration pattern of the laser light.