Évaluation de la photosensibilité rétinienne dans le but d'élucider le dérèglement neurochimique à l'origine du trouble affectif saisonnier et les mécanismes biologiques de la luminothérapie

Authors: Lavoie, Marie-Pier
Advisor: Hébert, Marc
Abstract: About 2.6% of Canadians suffer from Seasonal Affective Disorder (SAD), a syndrome characterized by cyclic depressive episodes occurring during fall and winter with remission in spring and summer. Although the etiology of SAD is unknown, the general consensus is that SAD patients could be more vulnerable to the decrease in light exposure in the fall/winter which could trigger some neurotransmitter dysregulation (possibly serotonin and/or dopamine). In the retina, these neurotransmitters are implicated in the modulation of photoreceptor sensibility. The electroretinogram (ERG) allows a direct and objective measure of these retinal dysregulations. Since light therapy (LT) is the treatment of choice for SAD and the therapeutic effect of LT appears to be mediated through the eyes and not the skin, it is possible to investigate the biological mechanism of LT using the ERG. The aim of this thesis is to better understand the circadian and methodology of electroretinogram (ERG) and evaluate the existence of a seasonal pattern in retinal sensitivity in SAD patients as well as the impact of LT. The first paper assesses the impact of photopic and scotopic ERG recording in a non pharmacologically dilated eyes. We report that it may be possible in research practice to perform ERG without dilating the eyes if the intensity of the flash is increased along with the adapting background. We also concluded that in clinical practice, the current standard flash is not adequate to yield to an optimal retinal stimulation. The second paper shows a correlation between diurnal variations (morning Vs evening) in retinal function and the presence of melatonin secretion in the saliva. These results bring precision of the impact of day versus night vision on the ERG response which could have some impact in research practice. Finally, the third paper demonstrates a seasonal pattern in retinal sensitivity in SAD patients and ERG changes associated with the therapeutic effect of LT. This study is the first to investigate cone and rod functions in SAD patients with the ERG as well as to report a biological effect of LT on retinal function in SAD patients. A the end, a new neurochemical model is proposed.
Document Type: Thèse de doctorat
Issue Date: 2007
Open Access Date: 12 April 2018
Permalink: http://hdl.handle.net/20.500.11794/19060
Grantor: Université Laval
Collection:Thèses et mémoires

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