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In the photoreceptors, exposure to light hyperpolarizes the membrane in a series of graded shifts. The outer cell segment contains a photopigment. Inside the cell the normal levels of cyclic guanosine monophosphate (cGMP) keep the Na+ channel open, and thus in the resting state the cell is depolarised. The photon causes the retinal bound to the receptor protein to isomerise to trans-retinal. This causes the receptor to activate multiple G-proteins. This in turn causes the Ga-subunit of the protein to activate a phosphodiesterase (PDE6), which degrades cGMP, resulting in the closing of Na+ cyclic nucleotide-gated ion channels (CNGs). Thus the cell is hyperpolarised. The amount of neurotransmitter released is reduced in bright light and increases as light levels fall. The actual photopigment is bleached away in bright light and only replaced as a chemical process, so in a transition from bright light to darkness the eye can take up to thirty minutes to reach full sensitivity. Chen, Janglin; Cranton, Wayne; Fihn, Mark (2016). Handbook of visual display technology (2nded.). Cham, Switzerland: Springer. ISBN 9783319143460. OCLC 962009228. Arshavsky VY, Burns ME (2012). "Photoreceptor signaling: supporting vision across a wide range of light intensities". J Biol Chem. 287 (3): 1620–1626. doi: 10.1074/jbc.R111.305243. PMC 3265842. PMID 22074925. Why Samsung makes Retina Displays– but not for its own tablets". Wired magazine. April 4, 2012 . Retrieved June 4, 2013. Wässle H, Boycott BB (1991). "Functional architecture of the mammalian retina". Physiol. Rev. 71 (2): 447–480. doi: 10.1152/physrev.1991.71.2.447. PMID 2006220.
Retina display? Everything you need to know | Macworld What is a Retina display? Everything you need to know | Macworld
A recent University of Pennsylvania study calculated that the approximate bandwidth of human retinas is 8.75 megabits per second, whereas a guinea pig's retinal transfer rate is 875 kilobits per second. [82] In simple terms, Apple ‘converts’ a device’s display to Retina by doubling the number of pixels vertically and horizontal, meaning it has four times as many pixels as its non-Retina counterpart. Inner segment / outer segment layer – inner segments and outer segments of rods and cones, the outer segments contain a highly specialized light-sensing apparatus. [16] [17] Retinal tears. American Society of Retina Specialists. https://www.asrs.org/patients/retinal-diseases/26/retinal-tears. Accessed Feb. 10, 2020. a b Kolb, Helga (1995). "Simple Anatomy of the Retina". Webvision. PMID 21413391 . Retrieved 1 January 2018.Curace Enrico M.; Auricchio Alberto (2008). "Versatility of AAV vectors for retinal gene transfer". Vision Research. 48 (3): 353–359. doi: 10.1016/j.visres.2007.07.027. PMID 17923143. S2CID 9926758.
Retinal problems: Types, symptoms, and treatments Retinal problems: Types, symptoms, and treatments
Shepherd, Gordon (2004). The Synaptic Organization of the Brain. New York: Oxford University Press. pp. 217–225. ISBN 978-0-19-515956-1. The white blood cells in the capillaries in front of the photoreceptors can be perceived as tiny bright moving dots when looking into blue light. This is known as the blue field entoptic phenomenon (or Scheerer's phenomenon). Examples include Sony’s Xperia Z5 Premium which has a resolution of 3,860 x 2,160 pixels – just shy of 4K – on a 5.5in screen, giving it a pixel density of a monstrous 806ppi. And Samsung’s Galaxy S6 has a resolution of 1440 x 2560 pixels – known as Quad HD or QHD – on a 5.1in screen, giving it a pixel density of 577ppi.
Apple says it’s the most colour-accurate LCD screen on any phone, and it has a high brightness and contrast ratio which allows it to display a wide colour gamut for HDR video and photos.
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