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Medical and Mathematical Background
Published in Arwa Ahmed Gasm Elseid, Alnazier Osman Mohammed Hamza, Computer-Aided Glaucoma Diagnosis System, 2020
Arwa Ahmed Gasm Elseid, Alnazier Osman Mohammed Hamza
The retina is a multi-layered sensory tissue that lies at the back of the eye, and contains millions of photoreceptors that capture light rays and convert them into electrical impulses that will in turn convert them into images in the brain. The main photoreceptors in the retina are rods and cones. Rod cells are very sensitive to changes in contrast, even at low light levels, hence they are able to detect movement, but they are imprecise and insensitive to color located in the periphery of the retina and are used for scotopic vision (night vision). Cones are high precision cells capable of detecting the colors that are concentrated in the macula, the area responsible for photopic vision (day vision). The very central portion of the macula is called the fovea, which is where the human eye is able to best distinguish visual details. The loss of peripheral vision may cause damage to the macula and can result in the loss of central vision.
Endocrine Functions of Brain Dopamine
Published in Nira Ben-Jonathan, Dopamine, 2020
The retina contains three types of photoreceptors: rods, cones and intrinsically photosensitive retinal ganglion cells (ipRGCs). Rods are responsible for vision at low light levels (scotopic vision). Cones are active at higher light levels (photopic vision), are capable of color vision, and are responsible for high spatial acuity. Ganglion cells collect electrical messages of the visual signals from the two layers of neurons and serve as the final neuronal output of the retina [5]. The mammalian retina is not only a light-sensing tissue that conveys photic information to the brain, but it also has an intrinsic circadian system.
ENTRIES A–Z
Published in Philip Winn, Dictionary of Biological Psychology, 2003
Scotopic and photopic are functional states of the RETINA. A scotopic retina is dark adapted and responsive to lower light levels. A photopic retina is light adapted and responsive to higher light levels. Exposure of a scotopic retina to a bright light results in poor vision while light adaptation occurs, while exposure of a photopic retina to dim light results in poor vision (NIGHT BLINDNESS) while dark adaptation occurs. Scotopic vision is mediated by RODS while photopic vision is mediated by CONES. Photopic vision appears as COLOUR VISION while scotopic vision appears as shades of grey.
Increase in cortisol concentration due to standardized bright and blue light exposure on saliva cortisol in the morning following sleep laboratory
Published in Stress, 2021
Katja Petrowski, Stefan Bührer, Christian Albus, Bjarne Schmalbach
One fundamental influence of light on cortisol appears to be light exposure during the post-awakening period (Clow et al., 2010; Leproult et al., 2001; Scheer et al., 1999). Light-induced effects on the cortisol secretion are assumed to be mediated by retinal projections to the body’s central circadian pacemaker, the hypothalamic suprachiasmatic nucleus (SCN) which, in turn, affects the cortisol secretion from the adrenal cortex via different routes (Dickmeis, 2009; Ishida et al., 2005; Ulrich-Lai et al., 2006). It should be noted that scotopic vision (rods) is monochromatic and represents a single spectral sensitivity toward bright light and dim light, which is important at night time for lower light intensities, whereas photopic vision (cones) refers to a sensitivity to light colors. The light-detecting system that conveys time information to the SCN encompasses a subset of melanopsin-expressing retinal ganglion cells (mRGCs; Berson et al., 2002; Brainard et al., 2001; Hattar et al., 2002; Hattar et al., 2003). In the retina, rods and cones but, in particular, the photosensitive melanopsin-expressing retina ganglion cells are important for the circadian rhythm (Al Enezi et al., 2011). These photoreceptors are directly linked to the SCN via the retina-hypothalamic tract. Hereby, hormones are important drivers of the sleep-wake-up rhythm. In particular, melatonin is released in the evening (due to tiredness) while cortisol decreases, whereas cortisol is released more strongly in the morning to prepare the organism for the day.
Modelling the effect of commercially available blue‐blocking lenses on visual and non‐visual functions
Published in Clinical and Experimental Optometry, 2020
Hind S Alzahrani, Sieu K Khuu, Maitreyee Roy
The wavelength of light plays an important role in scotopic vision,2008 colour perception,2007 and regulation of non‐visual responses.2008 For example, previous studies have demonstrated that vision is more dependent on blue light under scotopic conditions than photopic vision.2003 The wavelength of approximately 507-nm in the blue‐green range is sufficient to activate the photopigment rhodopsin in human rod‐photoreceptors, which is the basis for scotopic vision.2008 Additionally, the absorption of blue light by S‐cones enhances visual acuity, and the S‐cone function is maximally activated at a wavelength of approximately 430-nm.2007 Intrinsically photosensitive retinal ganglion cells (ipRGCs) contain the photopigment melanopsin, which is most sensitive to blue light at a wavelength of approximately 480-nm2008 and is vital in controlling non‐visual physiologic responses in the human body including circadian entrainment, melatonin secretion, cognitive performance, mood, and mental activity.2011
Advances in understanding the mechanisms of retinal degenerations
Published in Clinical and Experimental Optometry, 2020
By using high‐resolution confocal microscopy and also specialised electron microscopy techniques, we have been able to dissect the circuits that are likely modulated by ATP. Our work shows that distinct P2X receptors are important for regulating cone (photopic) mediated circuits, while other P2X receptors mediate information processing in rod mediated (scotopic) pathways. The main circuit that subserves photopic vision involves cones synapsing with cone bipolar cells, which in turn communicate with ganglion cells. Labelling studies have revealed that P2X2 receptors are localised to ganglion cell terminals that are post‐synaptic to cone bipolar cells, suggesting a role in shaping ganglion cell function.16