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Image Intensifier System
Published in Robert J. Parelli, Principles of Fluoroscopic Image Intensification and Television Systems, 2020
Conventional fluoroscopy, without image intensification, has two serious limitations: it produces a statistically inferior image and one too dim for photopic (daylight) vision. In the early 1950s, the x-ray image intensifier was developed, which has revolutionized fluoroscopy. Its image is bright enough for scotopic vision and small enough to be conveniently coupled to cine, television, or spot-film cameras.
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.
Draw a dark adaptation curve and identify the component parts and their significance
Published in Nathaniel Knox Cartwright, Petros Carvounis, Short Answer Questions for the MRCOphth Part 1, 2018
Nathaniel Knox Cartwright, Petros Carvounis
The significance of this is that in photopic conditions the high-energy light signal allows appreciation of colour, gives excellent central visual acuity and relies on spatial summation with the signal being transmitted via the cone pathway. In rod-mediated scotopic vision visual acuity is poorer, colour vision absent and temporal summation of the light signal crucial. Thus in bright light the cone pathway predominates and in dim conditions the increased sensitivity of rods to light and their ability to use temporal summation mean they are most important.
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
Non-surgical treatment options for presbyopia
Published in Expert Review of Ophthalmology, 2018
Nonoptical methods of treatment as yet remain controversial or unproven. Use of pharmaceutical agents to produce monocular or binocular pupillary miosis [33] and, through the resultant increased ocular depth-of-focus, improve near vision, is fundamentally unattractive as it reduces retinal illuminance in eyes, which already have lower transmittance than in the young. Hence, there are obvious adverse impacts on mesopic and scotopic vision. In the monocular case where the retinal illuminance in each eye differs, the Pulfrich effect may occur, leading to false judgments of the trajectory of moving objects and possible hazard [123]. The use of lipoic acid-based products to reduce the rigidity of the crystalline lens [40] is as yet unproven and may not be free of unwanted side effects.