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Color Vision Factoids

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Color Vision Factoids 4/9/2019 Color Vision Factoids Color Vision • Color is a sensory perception • Human awareness of color arises out of subjective visual experiences in which given sensations are ascribed names. • Color names have remarkable consistency throughout diverse cultures. • There are approx. 7 million colors that the normal individual can theoretically see ! Normal Color Vision • Normal individuals can discriminate • The electromagnetic spectrum approximately 150 different colors in encompasses the full range of photon the energy spectrum. • Rods and cones absorb photons • There are over between 400 – 700 nm 7500 color names in the English language. Physiology of Color Vision • Three different types of cones: b. green cones (medium wavelength) a. red cones (long wavelength) - contain erythrolabe - contain chlorolabe - preferentially absorbs 570 -590 nm light - preferentially absorbs 535-550 nm of light 1 4/9/2019 Cones c. blue cones (short wavelength): Cones have - contains cyanolabe overlapping - preferentially absorbs 440-450 nm spectral light sensitivities. Rods cannot distinguish one color from another. Rods Cones Rods are long and Cones are short and narrow in shape. plump. They are They have no color responsible for ability. They have a color vision, fine chemical called vision and photopic rhodopsin. vision (day vision). Their primary They have (3) action is involved chemicals: in scotopic vision cyanolabe, erythrolabe (night vision) and chlorolabe. The retina converts light energy into Vitamin-A is obtained electric energy by photochemistry. from food and stored in the liver. Vitamin-A is converted to retinol (a light absorbing chemical). This is released into the blood stream and is eventually captured by the retinal pigment epithelium. 2 4/9/2019 Color Physics . * Lights can be characterized by the sensation perceived when they hit the retina...for example… short wavelength = blue long wavelength = red When light strikes another medium, the Most objects absorb light at specific speed and the wavelength decrease. wavelengths of light. Black objects Shorter wavelengths are slowed (bent) absorb most light rays. White objects more than the longer ones. This reflect most light rays and transmit (or phenomenon explains why a prism reflect) not just one wavelength, but an breaks up white light assortment of them. into the colors of the White light is a combination of ALL spectrum. visible wave lengths. Normal Color Vision Any color is described by three major An object will have hue because it traits . reflects and transmits light of a given * Hue: attribute denoted by red, green yellow, etc. wavelength.The addition of black to a * Brightness (luminance): quantity of hue produces various shades. light coming from the color * Saturation (chroma): index of the purity (richness) of a hue. 3 4/9/2019 Color Vision Primary Colors: red, green and blue Trichromats: normal color vision have all (3) cone pigments Dichromats: have (2) cone pigments Monochromats: have (1) cone pigment Color Vision Defects: Tips Congenital Defects • 7-8% males affected • Congenital deutans are most common • 0.4% females affected • Tritans are most likely acquired Defect is transmitted through female (X • If someone has very poor vision – think chromosome) and is male predominant. Males have re-green defects if they inherit a of a monochromat defective gene from their mother. Affected • Retina disease usually causes blue- males can pass the gene to all their daughters yellow but none of their sons. Females who inherit only one defective gene • Optic nerve disease usually causes red- are carriers. Females who inherit the gene green from both parents are affected . There are three types of inherited color vision defects: a. monochromats: true “color blind” as they cannot see any colors (hues). They only see degrees of grays, black and white. Also have poor vision, nystagmus and photophobia. Gene inherited from both parents. One cone pigment. 4 4/9/2019 Red – Green Defect b. dichromats: can tell some hues People with red-green defects have apart. (2) cone pigments. Divided difficulty distinguishing between reds, into: greens and yellows but can discriminate a. protanopia: red-green defect between blue and yellow. Protanopes often b. deuteranopia: red-green defect can name red and green correctly because c. tritanopia: blue-yellow defect green looks lighter than red. “ope” think NOPE ! deuteranope: no green If someone has an “opia” – they are deficient red-green confusion in a color identification. protanopia: no red tritanopia: no blue blue-yellow confusion red-blind at cannot see the difference between blue-yellows but wavelengths > 650 can see red-green. Rare, nm occurs equally in males vs. females. red-green confusion “anomaly” is a decrease in Color “Blind” sensitivity In “anopia”, the ability to detect color is absent, an “anomaly” means that they have decrease in sensitivity to determining that particular color. * Protanomaly: red cone deficiency with poor red-green discrimination Youtube.com 5 4/9/2019 Color Vision Testing: Ishihara Plates * Deuteranomaly: green color deficiency with poor red-green discrimination although red appears brighter * Tritanomaly: blue cone deficiency with poor blue-yellow discrimination Ishihara Plates (pseudoisochromatic plates): Advantages: * colored dots of gray and complementary * Easy to perform colors arranged in various patterns * Good screening for congenital * easily seen by trichromats but not by deficiencies as well as Type I & II acquired dichromats. Disadvantages: * designed to find red-green deficiencies * Cannot distinguish tritans * Does not allow for protan-deutan ONE EYE AT A TIME WITH CORRECTION!!! proficiencies All pts. see Red-green Red-green Red-green Red-green Color vision defect: cannot see all of the following: As 12 see as “3” see as “5” see as “70” See as “21” Red-green Red-green Red-green Red-green See as “35” see as “2” see as “5” see as “17” Cannot see (all of the following) 6 4/9/2019 Color Vision Testing: Farnsworth D-15 Panel Test • Subset of the 100 hue test • Caps have same saturation and • (15) caps with a reference number brightness but different hues. • Patient arranges the caps according to color of preceding cap • Red-green test * test records • Good for acquired color defects from confusion of isochromatic hues retinal disease (ex: deutans confuse • 25 foot candles of light need (MacBeth green and red-purples whereas protans confuse lamp) blue greens and reds) Advantages: * Fast * Easy to perform Disadvantages: * Does not discriminate between trichromats and dichromats * INSTRUCTIONS ! Color Vision Testing: Farnsworth-Munsell 100 Hue Test • (85) colored caps arranged in (4) groups • Incorrect placement causes points to be plotted further from the center in an axis • correct ordering produces a circle in like distribution the center of the diagram Advantages: can measure full nature of character and extent Both Farnsworth are more accurate than Ishihara Disadvantages: time consuming inconvenient patient must be able to understand directions 7 4/9/2019 Color Vision Testing: Color Vision Testing: Hardy-Rand-Rittler Anomaloscope • Yellow-blue test or red-green test Patient sees a split image in the viewer. • Background is neutral gray on which a They tries to match yellow on the bottom half with red-green mixture series of colored circles, crosses and in the upper half. You control triangles are imposed. the luminance of yellow and * Can determine mild, medium or severe mixture of the red-green. Protanomalous uses too red. Deuteranomalous uses too much green. 8 .
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