COLOR VISION - Physiology Lecture SlideshowCOLOR VISION - Physiology Lecture Slideshow

Physics of Light

 Light:
Electromagnetic energy whose wavelength is
between 400 nm and 700 nm


 Visual description of an observer by which he distinguishes two fields of same size,
shape and structure by difference in spectral activity.

  • Purely sensory phenomenon and not a physical attribute
  • Perception of colour depends upon spectral composition of light:
  • coming from an object &
  • emanating from surrounding
  • State of light adaptation of subject
     Primary Colors : Red, Green,Blue
     Secondary Colors : Cyan, Magenta,Yellow

Color sense

 Ability of the eye to discriminate between different colors excited by
light of different wavelengths
 Function of cones
 Better appreciated in photopic vision
 In scotopic vision all colors seen as gray-called Purkinje shift

Young Helmholtz Maxwell Theory

 Trichromatic theory
 Postulates three different receptors maximally sensitive to
wavelength in different regions of visual spectrum.
 Three peaks are
440 to 450 nm – blue spectrum
535 to 550 nm – green spectrum
570 to 590 nm – red spectrum

Color sensation

 Determined by relative frequency of impulses from each cone
 A given color consists of admixture of 3 primary colors in different
 Yellow color perception is due to simultaneous stimulation of red
and green

Color Interpretation

White Color

 Stimulation of all red, green & blue cones
gives white color
 No single wavelength of light matching to
white color
 For getting white color all the cones must
be stimulated at the same equally

Color Blindness

 Three types

  1. Trichromats
  2. Dichromats
  3. Monochromats

Color Blindness

 When a single group of color receptive cones is missing from the
eye, the person is unable to distinguish some colors from others
 Between 525 and 675nm wavelength green, yellow, orange, and
red colors are perceived
 Appreciated by the red and green cones
 Any of the two cones is missing, the person is unable to distinguish
these colors
 Known as red green color blindness

 Loss of red cones is called a protanope
 Visual spectrum is shortened at longer wavelength end due to
absence of red cones
 Color-blind person who lacks green cones is called a deuteranope
 Normal visual spectrum because red cones are able to detect the
long wavelength red color

Red-green Color Blindness

 Is a genetic disorder occurs exclusively in males
 Genes in female X chromosome code for the
respective cones
 Females are carrier for color blindness
 Color blindness almost never occurs in females
 Reason:
X chromosome carry the genes so one of the X
chromosome might have gene of color vision

Color Vision Charts

 Ishihara Chart
 Friends Chart
 Edridge-green lantern
 Holmgrens wool matching method

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