DOCSLIB.ORG

Night Vision in the Elderly: Consequences for Seeing Through a ‘‘Blue Filtering’’ Intraocular Lens

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Night Vision in the Elderly: Consequences for Seeing Through a ‘‘Blue Filtering’’ Intraocular Lens 1518 PERSPECTIVE Br J Ophthalmol: first published as 10.1136/bjo.2005.073734 on 18 October 2005. Downloaded from Night vision in the elderly: consequences for seeing through a ‘‘blue filtering’’ intraocular lens J S Werner ............................................................................................................................... Br J Ophthalmol 2005;89:1518–1521. doi: 10.1136/bjo.2005.073734 Relative scotopic spectral sensitivity depends only on the spectral sensitivity maximum. Their analyses considered the percentage change in sensitivity. rhodopsin photopigment and ocular media absorption Here, we shall consider the same issue, but spectra. Rhodopsin is well characterised so the relative illustrated more traditionally in logarithmic units scotopic spectral sensitivity function can be calculated for so that the losses can be seen in the context of the full range of scotopic sensitivity. It will be intraocular lenses (IOLs) of known spectral density. In a shown why IOL absorption of light at wave- recent perspective, Mainster and Sparrow concluded that lengths near the sensitivity maximum is no more an IOL with short wave absorbing chromophores would important for scotopic vision than absorption at any other wavelengths. We shall also consider provide more retinal protection than conventional IOLs, but some aspects of scotopic vision not discussed by the practical consequences for scotopic vision are unclear. Mainster and Sparrow. In particular, the con- This paper uses published experiments to examine the sequences of IOL absorption spectra are evalu- ated in terms of scotopic spatial contrast implications for scotopic vision of the IOLs analysed by sensitivity as a quantitative index of pattern, or Mainster and Sparrow. A 14.6% reduction in scotopic form, vision. sensitivity is expected for a SN60AT (AcrySof Natural) compared to a SA60AT (Conventional AcrySof) IOL under SCOTOPIC SPECTRAL SENSITIVITY WITH AN IOL CONTAINING CHROMOPHORES broadband illumination (equal quantum spectrum). This ABSORBING SELECTIVELY AT SHORT effect (0.07 log unit) is visually insignificant in relation to WAVELENGTHS the ,4.0 log unit range of scotopic sensitivity. More The absorption spectrum of an IOL can be used to calculate the relative spectral sensitivity for importantly, it is expected that scotopic contrast sensitivity scotopic vision because the rods contain only one would be reduced by only ,0.01 log unit. It is thus type of photopigment, rhodopsin, and scotopic improbable that a difference in scotopic vision between sensitivity depends only on the number of quanta absorbed by the photopigment. While observers with the Natural and Conventional IOLs could be some wavelengths are more likely to be absorbed reliably detected using broadband stimuli. than others because of the chromophores in the http://bjo.bmj.com/ ........................................................................... photopigment and preretinal filtering (primarily by the lens), once absorbed, all wavelengths produce the same effects. Rushton3 calls this the cotopic vision refers to vision in darkness, principle of univariance. This principle has and its importance for human behaviour important implications for evaluating the effect Shas often been overlooked by practising of IOL absorption spectra. Both photochemical ophthalmologists. Expressed in terms of mea- hazards and scotopic sensitivity depend upon on October 3, 2021 by guest. Protected copyright. sured light levels, the scotopic range is below a absorbed photons and the probability of absorp- 22 luminance level of about 23.8 log cd m .It tion is wavelength dependent. Considered in encompasses the stimulus range from absolute terms of absorbed photons, photochemical threshold (fewer than 100 quanta delivered to hazards are wavelength dependent, but scotopic the cornea under ideal conditions) to a retinal vision is not. Put another way, IOL absorption at illuminance of ,0.3 photopic trolands, which is short wavelengths is no more consequential for about the maximum light level encountered at scotopic vision than absorption at middle or long 1 ....................... night under natural conditions. Thus, scotopic wavelengths. vision spans approximately 4 log units of ambi- The crystalline lens, or an IOL, will necessarily Correspondence to: ent illumination. Scotopic vision is mediated by a cause a decrease in sensitivity (increase thresh- J S Werner, Department of Ophthalmology & Vision single class of photoreceptors, the rods. Scotopic old) by an amount equivalent to its spectral Science, Section of vision is not, however, synonymous with rod absorption. Thus, when rhodopsin density (a Neurobiology, Physiology vision because rods and cones overlap in their logarithmic scale) is compared with log spectral & Behavior, University of range of sensitivity by about 3 log units, the sensitivity of an aphakic observer, the two curves California Davis, 4860 Y Street, Suite 2400, range known as mesopic vision. are essentially identical with a small correction 4 Sacramento, CA 95817, The importance of intraocular lens (IOL) for the spectral density of the cornea. This USA; jswerner@ucdavis. absorption spectra on scotopic vision was principle has been demonstrated for the scotopic edu recently discussed by Mainster and Sparrow.2 spectral sensitivity functions of phakic5 and Accepted for publication They noted that chromophores that may be 1 July 2005 useful in protecting the retina from the ‘‘blue Abbreviations: CSF, contrast sensitivity function; IOL, ....................... light’’ hazard also absorb near the scotopic intraocular lens www.bjophthalmol.com Night vision in the elderly 1519 Br J Ophthalmol: first published as 10.1136/bjo.2005.073734 on 18 October 2005. Downloaded from 0 ) 2 0.0 Retinal sensitivity –1 –0.5 –2 –1.0 –3 Blue filtering IOL Log sensitivity (quanta/s/deg –1.5 Log scotopic sensitivity (quanta) –4 350 400 500450 550 600 700650 302010 40 50 60 70 80 90 Wavelength (nm) Age (years) Figure 1 Calculated log scotopic sensitivity plotted in terms of quanta Figure 2 Scotopic sensitivity plotted as a function of age. Symbols delivered to the cornea as a function of wavelength. Calculations are represent thresholds for test lights of 0.04 degree diameter, 10 ms based on a rhodopsin nomogram and 20 D IOLs. Open symbols, flashes, 520 nm presented at 6 degrees nasal along the horizontal Conventional (Alcon SA60AT) and solid symbols, Natural (Alcon meridian. The solid line represents the linear regression fitted to these SN60AT). points. The broken line represents the linear regression obtained when the data are corrected for ocular media density and sensitivity is specified at the retina. The dotted line shows the loss in sensitivity pseudophakic6 observers. Figure 1 utilises this principle to expected from an equal quantum spectrum filtered by an AcrySof compare the expected scotopic spectral sensitivity function Natural IOL. for observers with the SN60AT (AcrySof Natural) and SA60AT (Conventional AcrySof) IOLs. The optical densities through a 1.5 mm exit pupil conjugate with the eye pupil. (2log transmission) of the IOLs were provided by the This effectively bypasses any age related variation as a result manufacturer based upon measurements in saline solution. of pupillary miosis. Following 30 minutes of dark adaptation, This results in somewhat different values from that in the sensitivity was measured for 10 ms, 520 nm circular test analysis by Mainster and Sparrow who used the data of Lin et lights of varying diameters that were superimposed and al7 for the conventional IOL (measured in saline) and concentric with a 10˚, 640 nm circular background. This transmission values from the manufacturer for the natural background was selected to suppress cone sensitivity with no IOL (measured in air). The two conditions of measurement influence on rod sensitivity. The test lights were imaged differ in Fresnel reflection losses, which result in different along the horizontal meridian, 6˚nasal from a foveal fixation transmission values. For this reason, our analyses are based point. Figure 2 shows results for one stimulus diameter; on measurements of both IOL types under identical condi- essentially the same results were obtained for other tions (immersed in balanced salt solution). diameters. The solid line is based on the linear regression The curves presented in figure 1 are consistent with equation fitted to the raw data representing stimuli delivered analyses by Mainster and Sparrow2; however, the figure uses to the cornea. The broken line is from the regression equation conventional logarithmic ordinates to place the effect on obtained after correcting the data to specify sensitivity at the http://bjo.bmj.com/ scotopic sensitivity in perspective. Relative to the range of retina—that is, corrected for age related changes in the ocular scotopic sensitivity, the greater density of the AcrySof Natural media.14 This is what would be expected in a population of IOL for wavelengths between 400 nm and 50 nm would seem aphakes or pseudophakes with a conventional IOL.46 to be trivial for natural (broadband) illuminants when Although much of the loss in scotopic sensitivity is the result integrated across the visible spectrum. Such an integration of the ocular media density, it is clear from these results that is appropriate because this is what the rods do—count age related losses in scotopic sensitivity cannot be explained absorbed photons independent of wavelength. Indeed, the solely by preretinal
Load more

Recommended publications
  • Visual Purple and the Photopic Luminosity Curve
    Br J Ophthalmol: first published as 10.1136/bjo.32.11.793 on 1 November 1948. Downloaded from THE BRITISH JOURNAL OF OPHTHALMOLOGY NOVEMBER, 1948 by copyright. COMMUNICATIONS VISUAL PURPLE AND THE PHOTOPIC LUMINOSITY- CURVE* BY H. J. A. DARTNALL http://bjo.bmj.com/ FROM THE VISION RESEARCH UNIT, 'MEDICAL RESEARCH COUNCIL, INSTITUTE OF OPHTHALMOLOGY, LONDON Introduction THE precise relationship which has been established between the scotopic luminosity curve a'nd visual purple (Dartnall & Goodeve, 1937; Wald, 19138) leads one to expect that the photopic luminositv on September 26, 2021 by guest. Protected curve is'similarly related to some " photopic " pigment or pig- ments. This latter hypothesis has given rise to considerable speculation, particularly since the evidence for the existence of retinal pigments, other than the various forms of visual purple, is not unequivocal. In any case there is no evidence for such additional pigments in the human retina. Visual purple mediates scotopic- vision by virtue of the photo- chemical changes it undergoes on exposure to light. The rate of * Received for Publication, July 12, 1948. Br J Ophthalmol: first published as 10.1136/bjo.32.11.793 on 1 November 1948. Downloaded from 794 H. J. A. DARTNALL any photochemical change is gQverned by the value of the product y Ia where y is the quantqm efficiency of the process and Ia the intensity of the absorbed light expressed in quanta per second. Since the eye in the photopic condition is much less sensitive than in the scotopic state it follows that the value of y la must be correspondingly smaller for the photopic process.
    [Show full text]
  • The Purkinje Rod-Cone Shift As a Function of Luminance and Retinal Eccentricity
    Vision Research 42 (2002) 2485–2491 www.elsevier.com/locate/visres Rapid communication The Purkinje rod-cone shift as a function of luminance and retinal eccentricity Stuart Anstis * Department of Psychology, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0109, USA Received 14 September 2000; received in revised form 25 June 2002 Abstract In the Purkinje shift, the dark adapted eye becomes more sensitive to blue than to red as the retinal rods take over from the cones. A striking demonstration of the Purkinje shift, suitable for classroom use, is described in which a small change in viewing distance can reverse the perceived direction of a rotating annulus. We measured this shift with a minimum-motion stimulus (Anstis & Cavanagh, Color Vision: Physiology & Psychophysics, Academic Press, London, 1983) that converts apparent lightness of blue versus red into apparent motion. We filled an iso-eccentric annulus with radial red/blue sectors, and arranged that if the blue sectors looked darker (lighter) than the red sectors, the annulus would appear to rotate to the left (right). At equiluminance the motion appeared to vanish. Our observers established these motion null points while viewing the pattern at various retinal eccentricities through various neutral density filters. Results: The luminous efficiency of blue (relative to red) increased linearly with eccentricity at all adaptation levels, and the more the dark-adaptation, the steeper the slope of the eccentricity function. Thus blue sensitivity was a linear function of eccentricity and an exponential function of filter factor. Blue sensitivity increased linearly with eccentricity, and each additional log10 unit of dark adaptation changed the slope threefold.
    [Show full text]
  • Adjustment of Lighting Parameters from Photopic to Mesopic Values in Outdoor Lighting Installations Strategy and Associated Evaluation of Variation in Energy Needs
    sustainability Article Adjustment of Lighting Parameters from Photopic to Mesopic Values in Outdoor Lighting Installations Strategy and Associated Evaluation of Variation in Energy Needs Enrique Navarrete-de Galvez 1 , Alfonso Gago-Calderon 1,* , Luz Garcia-Ceballos 2, Miguel Angel Contreras-Lopez 2 and Jose Ramon Andres-Diaz 1 1 Proyectos de Ingeniería, Departamento de Expresión Gráfica Diseño y Proyectos, Universidad de Málaga, 29071 Málaga, Spain; [email protected] (E.N.-d.G.); [email protected] (J.R.A.-D.) 2 Expresión Gráfica en la Ingeniería, Departamento de Expresión Gráfica Diseño y Proyectos, Universidad de Málaga, 29071 Málaga, Spain; [email protected] (L.G.-C.); [email protected] (M.A.C.-L.) * Correspondence: [email protected]; Tel.: +34-951-952-268 Abstract: The sensitivity of the human eye varies with the different lighting conditions to which it is exposed. The cone photoreceptors perceive the color and work for illuminance conditions greater than 3.00 cd/m2 (photopic vision). Below 0.01 cd/m2, the rods are the cells that assume this function (scotopic vision). Both types of photoreceptors work coordinately in the interval between these values (mesopic vision). Each mechanism generates a different spectral sensibility. In this work, Citation: Navarrete-de Galvez, E.; the emission spectra of common sources in present public lighting installations are analyzed and Gago-Calderon, A.; Garcia-Ceballos, their normative photopic values translated to the corresponding mesopic condition, which more L.; Contreras-Lopez, M.A.; faithfully represents the vision mechanism of our eyes in these conditions. Based on a common Andres-Diaz, J.R. Adjustment of street urban configuration (ME6), we generated a large set of simulations to determine the ideal light Lighting Parameters from Photopic to point setup configuration (luminance and light point height vs.
    [Show full text]
  • Photopic and Scotopic – the “Eyes” Have It
    Photopic and Scotopic – The “eyes” have it Dick Erdmann GE Specification Engineer In the human eye the perceived brightness of illumination depends of color. It takes more energy in the blue or red portion of the color spectrum to create the same sensation of brightness as in the yellow-green region. When it comes to sensing light in the human eye there are two main light-sensing cells called rods and cones. If one took a tube and looked straight ahead through it so that it allowed the field of view to be restricted 2 degrees, light photons would fall on the part of the eye called the fovea that consists mainly of cones. The peripheral area surrounding the fovea consists of both rods and cones with the rods outnumbering the cones about 10:1. Cones have a peak response in the yellow-green region of about 555 nano-meters and rods have a peak response in the bluish-green area of about 505 nano-meters. Because both the rods and cones have been shown to have different sensitivities to colors they can be represented by two different sensitivity curves called Photopic Curves (representing the cone) and Scotopic Curves (representing the rod). Years ago it was thought that the cones were responsible for daytime vision and rods for nighttime vision. Because of this, light meters that measure lighting levels such as footcandles, lumens, lux, etc. are weighted to the cone activated part of the eye ignoring the effect of rod-activated vision. But according to a study by Dr. Sam Berman and Dr.
    [Show full text]
  • Chromatic Function of the Cones D H Foster, University of Manchester, Manchester, UK
    Chromatic Function of the Cones D H Foster, University of Manchester, Manchester, UK ã 2010 Elsevier Ltd. All rights reserved. Glossary length. If l is the path length and a(l) is the spectral absorptivity, then, for a homogeneous isotropic CIE, Commission Internationale de l’Eclairage – absorbing medium, A(l)=la(l) (Lambert’s law). The CIE is an independent, nonprofit organization Spectral absorptance a(l) – Ratio of the spectral responsible for the international coordination of radiant flux absorbed by a layer to the spectral lighting-related technical standards, including radiant flux entering the layer. If t(l) is the spectral colorimetry standards. transmittance, then a(l)=1Àt(l). The value of a(l) Color-matching functions – Functions of depends on the length or thickness of the layer. For a wavelength l that describe the amounts of three homogeneous isotropic absorbing medium, fixed primary lights which, when mixed, match a a(l)=1Àt(l)=1À10Àla(l), where l is the path length monochromatic light of wavelength l of constant and a(l) is the spectral absorptivity. Changes in the radiant power. The amounts may be negative. The concentration of a photopigment have the same color-matching functions obtained with any two effect as changes in path length. different sets of primaries are related by a linear Spectral absorptivity a(l) – Spectral absorbance of transformation. Particular sets of color-matching a layer of unit thickness. Absorptivity is a functions have been standardized by the CIE. characteristic of the medium, that is, the Fundamental spectral sensitivities – The color- photopigment. Its numerical value depends on the matching functions corresponding to the spectral unit of length.
    [Show full text]
  • 17-2021 CAMI Pilot Vision Brochure
    Visual Scanning with regular eye examinations and post surgically with phoria results. A pilot who has such a condition could progress considered for medical certification through special issuance with Some images used from The Federal Aviation Administration. monofocal lenses when they meet vision standards without to seeing double (tropia) should they be exposed to hypoxia or a satisfactory adaption period, complete evaluation by an eye Helicopter Flying Handbook. Oklahoma City, Ok: US Department The probability of spotting a potential collision threat complications. Multifocal lenses require a brief waiting certain medications. specialist, satisfactory visual acuity corrected to 20/20 or better by of Transportation; 2012; 13-1. Publication FAA-H-8083. Available increases with the time spent looking outside, but certain period. The visual effects of cataracts can be successfully lenses of no greater power than ±3.5 diopters spherical equivalent, at: https://www.faa.gov/regulations_policies/handbooks_manuals/ techniques may be used to increase the effectiveness of treated with a 90% improvement in visual function for most One prism diopter of hyperphoria, six prism diopters of and by passing an FAA medical flight test (MFT). aviation/helicopter_flying_handbook/. Accessed September 28, 2017. the scan time. Effective scanning is accomplished with a patients. Regardless of vision correction to 20/20, cataracts esophoria, and six prism diopters of exophoria represent series of short, regularly-spaced eye movements that bring pose a significant risk to flight safety. FAA phoria (deviation of the eye) standards that may not be A Word about Contact Lenses successive areas of the sky into the central visual field. Each exceeded.
    [Show full text]
  • Color Vision Mechanisms
    11 COLOR VISION MECHANISMS Andrew Stockman Department of Visual Neuroscience UCL Institute of Opthalmology London, United KIngdom David H. Brainard Department of Psychology University of Pennsylvania Philadelphia, Pennsylvania 11.1 GLOSSARY Achromatic mechanism. Hypothetical psychophysical mechanisms, sometimes equated with the luminance mechanism, which respond primarily to changes in intensity. Note that achromatic mech- anisms may have spectrally opponent inputs, in addition to their primary nonopponent inputs. Bezold-Brücke hue shift. The shift in the hue of a stimulus toward either the yellow or blue invariant hues with increasing intensity. Bipolar mechanism. A mechanism, the response of which has two mutually exclusive types of out- put that depend on the balance between its two opposing inputs. Its response is nulled when its two inputs are balanced. Brightness. A perceptual measure of the apparent intensity of lights. Distinct from luminance in the sense that lights that appear equally bright are not necessarily of equal luminance. Cardinal directions. Stimulus directions in a three-dimensional color space that silence two of the three “cardinal mechanisms.” These are the isolating directions for the L+M, L–M, and S–(L+M) mech- anisms. Note that the isolating directions do not necessarily correspond to mechanism directions. Cardinal mechanisms. The second-site bipolar L–M and S–(L+M) chromatic mechanisms and the L+M luminance mechanism. Chromatic discrimination. Discrimination of a chromatic target from another target or back- ground, typically measured at equiluminance. Chromatic mechanism. Hypothetical psychophysical mechanisms that respond to chromatic stimuli, that is, to stimuli modulated at equiluminance. Color appearance. Subjective appearance of the hue, brightness, and saturation of objects or lights.
    [Show full text]
  • Transmission of Scotopic Signals from the Rod to Rod-Bipolar Cell in the Mammalian Retina
    Vision Research 44 (2004) 3269–3276 www.elsevier.com/locate/visres Transmission of scotopic signals from the rod to rod-bipolar cell in the mammalian retina W. Rowland Taylor a,*, Robert G. Smith b a Neurological Sciences Institute, Oregon Health and Sciences University––West Campus, 505 NW 185th Avenue, Beaverton, OR 97006, United States b Department of Neuroscience, University of Pennsylvania, Philadelphia, PA Received 15 June 2004; received in revised form 27 July 2004 Abstract Mammals can see at low scotopic light levels where only 1 rod in several thousand transduces a photon. The single photon signal is transmitted to the brain by the ganglion cell, which collects signals from more than 1000 rods to provide enough amplification. If the system were linear, such convergence would increase the neural noise enough to overwhelm the tiny rod signal. Recent studies provide evidence for a threshold nonlinearity in the rod to rod bipolar synapse, which removes much of the background neural noise. We argue that the height of the threshold should be 0.85 times the amplitude of the single photon signal, consistent with the saturation observed for the single photon signal. At this level, the rate of false positive events due to neural noise would be masked by the higher rate of dark thermal events. The evidence presented suggests that this synapse is optimized to transmit the single photon signal at low scotopic light levels. Ó 2004 Elsevier Ltd. All rights reserved. Keywords: Retina; Synaptic transmission; Single photon; Photoreceptor; Visual threshold; Scotopic vision 1. Introduction produced by single photons are carried by only a few neurons, whereas all the rods and postreceptoral Many mammals have evolved excellent night vision, neurons in the pool generate noise.
    [Show full text]
  • Cone Fundamentals and CIE Standards
    Cone fundamentals and CIE standards Andrew Stockman UCL Institute of Ophthalmology, London, UK Address UCL Institute of Ophthalmology, 11-43 Bath Street, London EC1V 9EL, UK Corresponding author: Stockman, Andrew ([email protected]) Abstract A knowledge of the spectral sensitivities of the long- (L-), middle- (M-) and short- (S-) wavelength-sensitive cone types is vital for modelling human color vision and for the practical applications of color matching and color specification. After being agnostic about defining standard cone spectral sensitivities, the Commission Internationale de l' Éclairage (CIE) has sanctioned the cone spectral sensitivity estimates of Stockman & Sharpe [1] and the associated measures of luminous efficiency [2,3] as “physiologically-relevant” standards for color vision [4,5]. These can be used to model mean normal color vision at the photoreceptor level and postreceptorally. Both LMS and XYZ versions have been defined for 2-deg and 10-deg vision. Built into the standards are corrections for individual differences in macular and lens pigment densities, but individual differences in photopigment optical density and the spectral position of the cone photopigments can also be accommodated [6,7]. Understanding the CIE standard and its advantages is of current interest and importance. 1 Color perception and photopic visual function are inextricably linked to and, indeed, limited by the properties of the three cone photoceptors: the long- (L-), middle- (M-) and short- (S-) wavelength-sensitive cones. This short review covers the derivation of the recent “physiologically- relevant” Commission Internationale de l' Éclairage (CIE) 2006; 2015 cone spectral sensitivities and luminous efficiency functions for 2-deg and 10-deg vision [4,5] and provides background details about cone spectral sensitivities and trichromatic color matching.
    [Show full text]
  • Comparative Visual Function in Predatory Fishes from the Indian River Lagoon Author(S): D
    Comparative Visual Function in Predatory Fishes from the Indian River Lagoon Author(s): D. Michelle McComb, Stephen M. Kajiura, Andrij Z. Horodysky, and Tamara M. Frank Source: Physiological and Biochemical Zoology, Vol. 86, No. 3 (May/June 2013), pp. 285-297 Published by: The University of Chicago Press Stable URL: http://www.jstor.org/stable/10.1086/670260 . Accessed: 16/07/2013 16:00 Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at . http://www.jstor.org/page/info/about/policies/terms.jsp . JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected]. The University of Chicago Press is collaborating with JSTOR to digitize, preserve and extend access to Physiological and Biochemical Zoology. http://www.jstor.org This content downloaded from 152.3.102.242 on Tue, 16 Jul 2013 16:00:41 PM All use subject to JSTOR Terms and Conditions 285 Comparative Visual Function in Predatory Fishes from the Indian River Lagoon D. Michelle McComb1,* Introduction Stephen M. Kajiura2 Teleost fishes represent a speciose vertebrate lineage that ra- Andrij Z. Horodysky3 diated into distinct aquatic habitats that present unique diver- Tamara M. Frank4 gent light qualities (Jerlov 1968). Selective pressure on the pi- 1Harbor Branch Oceanographic Institute at Florida Atlantic scine eye has resulted in an extensive array of both 2 University, Fort Pierce, Florida 34946; Biological Sciences, morphological and physiological adaptations to maximize vi- Florida Atlantic University, Boca Raton, Florida 33431; sual function under differing light conditions.
    [Show full text]
  • Radiometric and Photometric Measurements with TAOS Photosensors Contributed by Todd Bishop March 12, 2007 Valid
    TAOS Inc. is now ams AG The technical content of this TAOS application note is still valid. Contact information: Headquarters: ams AG Tobelbaderstrasse 30 8141 Unterpremstaetten, Austria Tel: +43 (0) 3136 500 0 e-Mail: [email protected] Please visit our website at www.ams.com NUMBER 21 INTELLIGENT OPTO SENSOR DESIGNER’S NOTEBOOK Radiometric and Photometric Measurements with TAOS PhotoSensors contributed by Todd Bishop March 12, 2007 valid ABSTRACT Light Sensing applications use two measurement systems; Radiometric and Photometric. Radiometric measurements deal with light as a power level, while Photometric measurements deal with light as it is interpreted by the human eye. Both systems of measurement have units that are parallel to each other, but are useful for different applications. This paper will discuss the differencesstill and how they can be measured. AG RADIOMETRIC QUANTITIES Radiometry is the measurement of electromagnetic energy in the range of wavelengths between ~10nm and ~1mm. These regions are commonly called the ultraviolet, the visible and the infrared. Radiometry deals with light (radiant energy) in terms of optical power. Key quantities from a light detection point of view are radiant energy, radiant flux and irradiance. SI Radiometryams Units Quantity Symbol SI unit Abbr. Notes Radiant energy Q joule contentJ energy radiant energy per Radiant flux Φ watt W unit time watt per power incident on a Irradiance E square meter W·m−2 surface Energy is an SI derived unit measured in joules (J). The recommended symbol for energy is Q. Power (radiant flux) is another SI derived unit. It is the derivative of energy with respect to time, dQ/dt, and the unit is the watt (W).
    [Show full text]
  • Color Vision and Night Vision Chapter Dingcai Cao 10
    Retinal Diagnostics Section 2 For additional online content visit http://www.expertconsult.com Color Vision and Night Vision Chapter Dingcai Cao 10 OVERVIEW ROD AND CONE FUNCTIONS Day vision and night vision are two separate modes of visual Differences in the anatomy and physiology (see Chapters 4, perception and the visual system shifts from one mode to the Autofluorescence imaging, and 9, Diagnostic ophthalmic ultra- other based on ambient light levels. Each mode is primarily sound) of the rod and cone systems underlie different visual mediated by one of two photoreceptor classes in the retina, i.e., functions and modes of visual perception. The rod photorecep- cones and rods. In day vision, visual perception is primarily tors are responsible for our exquisite sensitivity to light, operat- cone-mediated and perceptions are chromatic. In other words, ing over a 108 (100 millionfold) range of illumination from near color vision is present in the light levels of daytime. In night total darkness to daylight. Cones operate over a 1011 range of vision, visual perception is rod-mediated and perceptions are illumination, from moonlit night light levels to light levels that principally achromatic. Under dim illuminations, there is no are so high they bleach virtually all photopigments in the cones. obvious color vision and visual perceptions are graded varia- Together the rods and cones function over a 1014 range of illu- tions of light and dark. Historically, color vision has been studied mination. Depending on the relative activity of rods and cones, as the salient feature of day vision and there has been emphasis a light level can be characterized as photopic (cones alone on analysis of cone activities in color vision.
    [Show full text]