Colour Blindness Ishihara Charts


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Colour Blindness Ishihara Charts

  2. 2. What is it? <ul><li>Colour blindness is a color vision deficiency, it is the inability to perceive differences between some of the colors that others can distinguish. </li></ul><ul><li>It is most often of genetic nature, but may also occur because of eye, nerve, or brain damage, or exposure to certain chemicals. </li></ul><ul><li>The English chemist John Dalton published the first scientific paper on the subject in 1798, &quot;Extraordinary facts relating to the vision of colours&quot;, after the realization of his own color blindness. </li></ul>
  3. 3. Color blindness <ul><li>It is sometimes classed as a disability. </li></ul><ul><li>In certain situations color blind individuals have an advantage over those with normal color vision. </li></ul><ul><li>There are some studies which conclude that color blind individuals are better at penetrating certain color camouflages. </li></ul>
  4. 4. Background <ul><li>The normal human retina contains two kinds of light cells: </li></ul><ul><li>the rod cells (active in low light) </li></ul><ul><li>the cone cells (active in normal daylight) </li></ul><ul><li>Normally, there are three kinds of cones, each containing a different pigment, which are activated when the pigments absorb light. </li></ul><ul><li>The sensitivity of normal color vision actually depends on the overlap between the absorption spectra of the three systems: different colors are recognized when the different types of cone are stimulated to different extents. </li></ul><ul><li>Many of the genes involved in color vision are on the X chromosome, making color blindness more common in males than in females. </li></ul>
  5. 5. Genetic modes of inheritance <ul><li>Color blindness can be inherited genetically. </li></ul><ul><li>It is most commonly inherited from mutations on the X chromosome but the mapping of the human genome has shown there are many causative mutations – mutations capable of causing color blindness originate from at least 19 different chromosomes. </li></ul><ul><li>These are some of the inherited diseases known to cause color blindness: </li></ul><ul><li>Cone dystrophy, </li></ul><ul><li>Cone-rod dystrophy, </li></ul>
  6. 6. Genetic modes of inheritance (contd.) <ul><li>Achromatopsia (aka Rod Monochromatism, aka Stationery Cone Dystrophy, aka Cone Dysfunction Syndrome), </li></ul><ul><li>Blue cone monochromatism, Retinitis pigmentosa (initially affects rods but can later progress to cones and therefore color blindness), </li></ul><ul><li>Diabetes, </li></ul><ul><li>Age-Related Macular degeneration, </li></ul><ul><li>Retinoblastoma, </li></ul><ul><li>and Leber's congenital amaurosis. </li></ul>
  7. 7. Genetic modes of inheritance (contd.) <ul><li>Inherited color blindness can be congenital (from birth), or it can commence in childhood or adulthood. </li></ul><ul><li>It can be stationary, that is, remain the same throughout a person's lifetime, or progressive. Color blindness always pertains to the cone photoreceptors in retinas as the cones are capable of detecting the color frequencies of light . </li></ul>
  8. 8. Genetic modes of inheritance(contd.) <ul><li>The reason males are at a greater risk of inheriting an X linked mutation is because males only have one X chromosome and females have two (XX); if a woman inherits a normal X chromosome in addition to the one which carries the mutation, she will not display the mutation. Men do not have a second X chromosome to override the chromosome which carries the mutation. If 5% of variants of a given gene are defective, the probability of a single copy being defective is 5%. </li></ul>
  9. 9. Other causes <ul><li>Other causes of color blindness include brain or retinal damage caused by Shaken Baby Syndrome, accidents and other trauma which produce swelling of the brain in the occipital lobe, and damage to the retina caused by exposure to ultraviolet light. </li></ul><ul><li>Types </li></ul><ul><li>There are many types of color blindness. </li></ul><ul><li>The most common are red-green hereditary photoreceptor disorders, but it is also possible to acquire color blindness through damage to the retina, optic nerve, or higher brain areas </li></ul>
  10. 10. Classification of color deficiencies <ul><li>Color vision deficiencies can be classified as </li></ul><ul><li>Acquired </li></ul><ul><li>Inherited : There are three types of inherited or congenital color vision deficiencies: monochromacy, dichromacy, and anomalous trichromacy. </li></ul><ul><li>Monochromacy , also known as &quot;total color blindness&quot;, is the lack of ability to distinguish colors; caused by cone defect or absence. Rod monochromacy (achromatopsia) is a rare, nonprogressive inability to distinguish any colors as a result of absent or nonfunctioning retinal cones. </li></ul><ul><li>Cone monochromacy is a rare, total color blindness that is accompanied by relatively normal vision, electoretinogram, and electrooculogram. </li></ul>
  11. 11. <ul><li>Dichromacy is a moderately severe color vision defect in which one of the three basic color mechanisms is absent or not functioning. </li></ul><ul><li>Protanopia is a severe type of color vision deficiency caused by the complete absence of red retinal photoreceptors. </li></ul><ul><li>Deuteranopia is a color vision deficiency in which the green retinal photoreceptors are absent, moderately affecting red-green hue discrimination. It is a form of dichromatism. </li></ul>Classification of color deficiencies (contd.)
  12. 12. Classification of color deficiencies (contd.) <ul><li>Tritanopia is an exceedingly rare color vision disturbance in which there are only two cone pigments present and a total absence of blue retinal receptors. </li></ul><ul><li>Anomalous trichromacy is a common type of inherited color vision deficiency, occurring when one of the three cone pigments is altered in its spectral sensitivity </li></ul>
  13. 13. <ul><li>Treatment and management </li></ul><ul><li>There is generally no treatment to cure color deficiencies. </li></ul><ul><li>Certain types of tinted filters and contact lenses may help an individual to better distinguish different colors. </li></ul><ul><li>This may enable the wearer to pass some color blindness tests, but they have little practical use. </li></ul><ul><li>Driving motor vehicles </li></ul><ul><li>Some countries (e.g. Romania and Turkey) have refused to grant individuals with color blindness driving licenses. </li></ul>
  14. 14. <ul><li>Color blindness and occupations </li></ul><ul><li>Color blindness may make it difficult or impossible for a person to engage in certain occupations. </li></ul><ul><li>Persons with color blindness may be legally or practically barred from occupations in which color perception is an essential part of the job ( e.g., mixing paint colors), or in which color perception is important for safety ( e.g., operating vehicles in response to color-coded signals). </li></ul>
  15. 15. Diagnosis The Ishihara color test <ul><li>It consists of a series of pictures of colored spots, </li></ul><ul><li>It is the test most often used to diagnose red-green color deficiencies. </li></ul><ul><li>A figure (usually one or more Arabic digits) is embedded in the picture as a number of spots in a slightly different color, and can be seen with normal color vision, but not with a particular color defect. </li></ul><ul><li>The full set of tests has a variety of figure/background color combinations, and enable diagnosis of which particular visual defect is present. </li></ul><ul><li>Most clinical tests are designed to be fast, simple, and effective at identifying broad categories of color blindness. </li></ul><ul><li>I WOULD NOW LIKE YOU TO TAKE THE FOLLOWING COLOUR BLINDNESS TEST </li></ul>
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  25. 25. SCOREBOARD Your eyes are not sharp enough to spot colour differences and you must visit the eye doctor– POOR 0-3 CORRECT I advice you to visit the eye doctor - OK 4-6CORRECT You have no signs of colour blindness – EXCELLENT! 7-9 CORRECT YOUR SCORE AND ABILITY NO. OF CORRECT ANSWERS
  26. 26. LASTWORDS By now, my friends you must have understood that your eyes are very precious; so we must take a pledge that we will – “ HANDLE OUR EYES WITH CARE”