LED stimulation setup for retinal recordings
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LED-pohjainen stimulussysteemi verkkokalvon sähköisiin mittauksiin
Retinal degenerative diseases such as glaucoma and age-related macular degeneration are one of the leading causes of blindness worldwide. Currently, there are a limited amount of treatment methods for these diseases. Therefore, many studies conducted in the field of vision research examine the functioning of the retina and try to find possible treatment methods for different retinal degenerative diseases. The most common way of studying the functioning of retinal cells is to record an electroretinogram (ERG). ERG is a light-evoked extracellular field potential that sums up the activity of retinal cells. Different wave components of ERG can be attributed to specific cell layers, thus enabling tracking of the origin of possible abnormalities in the ERG. ERG can be recorded both from humans and animals, and in vision research, mice and rats are popular animal models because of their genetic manipulations. Their retinas also correspond well with the human peripheral retina and their photoreceptors are quite similar to human photoreceptors. The retina is typically stimulated by light in vision research. The objective of this thesis is to construct a reliable light stimulation setup for retinal recordings of isolated mouse retinas. This thesis designs, constructs, and tests such stimulation setup. In the literature part of the thesis, the theory related to the functioning of the eye as well as the working principle of the ERG is discussed. In the research part, the stimulation setup is designed and constructed. As a result, the functioning of the setup is tested. The light source of the stimuli is a light-emitting diode (LED) that has a wavelength of 505 nm in order to cover the peak absorption wavelengths of the mouse retina. The LED has to be able to produce stimulus pulses with adjustable intensities, durations, forms, and frequencies. The LED is controlled via a stimulus generator and an LED controller. The light beam is guided from the LED to the retinal sample with a liquid light guide. Furthermore, the light beam is homogenized and gathered with diffuser and condenser lenses and its intensity is decreased with neutral density filters. The recording of the ERG is done with a microelectrode array (MEA) that is placed inside a Faraday cage. The retinal sample is placed on the MEA plate and kept alive with continuous perfusion. The setup was tested in order to evaluate its functionality. The testing was done by calibrating the light output and by recording ERGs from isolated mouse retina. The light calibration results showed linear intensity behaviour and an ability to produce different waveforms. The ERG recordings showed typical waveforms. The setup met the requirements and it can therefore be regarded as successful.