physiological optics 2

• Color vision is important in daily life, from differentiating a sunrise to a sunset, identifying traffic lights, and in professions requiring good color vision
• Trichromacy, also known as Trichromatic or Normal Color Vision, requires primary colors to see different hues and saturation
• Characteristics of Trichromacy:

  • The spectrum of a glowing solid presents an uninterrupted series of hues from Red (above 760mu) to Violet (380mu)
  • No Black, Gray, or White areas or bands in this series
  • Individuals can recognize a large number of hues
• Dyschromatopia, or color blindness, is a defective color vision described by Dalton in 1774
• Classifications of Dichromacy:

  • Protanopia or Red-Blind (Daltonism)
  • Deuteranopia or Green-Blind
  • Tritanopia or Blue-blind
• Dichromacy involves individuals who use only two colors of the spectrum to elicit all color sensations
• Tritanopia is a rarer dichromatic condition, known as blue-blindness, and can also appear as yellow blindness (Tetartanopia)
• Achromatopia or Monochromatopia is the entire absence of color sensations, where the spectrum appears only as a series of grays of different intensities
• Anomalous Trichromasy involves individuals who recognize the three fundamental colors but with some differences from the normal
• Causes of Dyschromatopia:

  • Hereditary and incurable
  • Male-sex-linked characteristics carried by a gene in the X chromosomes
  • Can be acquired by disease of the eye or brain, like occipital lobe injury
  • Excessive alcohol or tobacco can also cause color blindness
• Spectrum Test for blindness involves matching colors of the spectrum with mixtures of the three fundamental colors
• Tests for color blindness include:

  • Farnsworth D-15 panel test
  • Jennings Self-recording
  • Edridge-Green beads
  • Holmgren Wool Test
• Pattern Test methods:

  • Ishihara Test Cards: numeral printed in dots of varying sizes, hues, and saturation, surrounded by dots of other colors
  • Pseudo-Isochromatic Plates (AOC)
• Theories of Color Vision:

  • Color sensation is a psychological phenomenon
  • Activity of cortical cells is specific
  • Seeing is a physio-chemical process
  • Nerve impulse is not specific (Mueller’s Law)
  • Sense organ is specific
• Law of Specific Energies (Mueller’s Law) states that all nerve impulses are fundamentally alike, and the result of a nerve impulse in the effector is not determined by the nature of the organ in which the impulse originated
• Helmholtz Theory (Physical Theory, Young-Helmholtz Theory) emphasizes the nature of stimulation, assuming the visual mechanism is stimulated in three ways by all wavelengths of light
• Hering’s Theory (Psychological Theory, Opponent Colors Theory) emphasizes the nature of sensations, resolving visual experiences into 6 elementary qualities: untoned (White, Black), toned (Red, Green, Yellow, Blue)
• Ladd-Franklin Theory (Chemical Theory, Evolution Color Theory, Genetic Theory) attempts to show how three primary retinal stimulations can cause four primary color sensations, stating that white is the mother of all colors