For example, Müller used it to deduce the location of the photoreceptive layer in the retina and more recently it has found a variety of clinical applications. Visualization of the vasculature using kinetic techniques to move the shadow of the blood vessels has a rich history in vision science. This method displaces the shadow of the blood vessels on the retina, breaking stabilization and producing the entopic percept that we now refer to as the Purkinje tree ( see Fig 2A). In 1819, the Bohemian physiologist Johann Evangelist Purkinje (Czech spelling Jan Evangelista Purkyně) found that moving a candle across the visual field allows an observer to view their own retinal blood vessels. The amplitudes of these modulations are varied sinusoidally in time between the plotted positive (red) and negative (black) modulations and are then added to the background spectrum to produce the stimuli seen by the observer. On the right are plotted the spectral modulations that target each of the indicated cone class(es), with the targeted class(es) indicated at the upper right of each individual plot. C: All modulations are carried out around a rod-saturating background whose spectrum is shown at the left. B: The spectral sensitivities of the open-field cones ( upper panel) are filtered by the hemoglobin transmittance spectrum ( middle panel), resulting in wavelength-specific changes of the cone spectral sensitivities ( lower panel). 10.1371/001 Fig 1 Spectral sensitivities and apparatus.Ī: Schematic diagram of the retina showing the shadows cast by the retinal blood vessels lying in front of the photoreceptive layer of the retina. As the shadow of the vasculature is stabilized on the retina it is not perceived under normal viewing conditions. Between these two regions lies the penumbra, in which cones experience partial shadow. Cones positioned directly under the larger blood vessels lie in deep shadow and are termed umbral cones. As the blood vessels are thin, most of the retinal cone mosaic is in the open light field, receiving unobstructed, incident light ( Fig 1A). This network lies in front of the photoreceptive layer of the retina, thus casting shadows onto a set of cone photoreceptors. A fine network of retinal vessels supplies the inner retina with blood, with decreasing vessel diameter towards the fovea.
0 Comments
Leave a Reply. |
Details
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |