Vision and Color Blindness Notes

Vision Defects

Myopia

  • Myopia, also known as nearsightedness, is a refractive error where distant objects appear blurry while close objects are seen clearly.

Hyperopia

  • Hyperopia, also known as farsightedness, is a refractive error where close objects appear blurry while distant objects are seen clearly.

Astigmatism

  • Astigmatism is a refractive error where the eye cannot focus light rays that enter on different planes simultaneously.
  • It is corrected with a cylindrical lens.

Color Blindness

  • Color blindness is typically a hereditary condition resulting from a lack of a specific pigment (photopsin) in the eye.
  • This pigment deficiency prevents a person from perceiving certain color differences.
  • Individuals with mild color blindness might not realize they have the condition until tested.
  • Red-green color blindness is the most prevalent type.
  • In red-green color blindness, the red cones may respond to green light, or vice versa.

Cone Types and Light Absorption

  • There are three major cone types in the eye, each sensitive to a primary color of light: red, green, and blue.
  • Each cone type is most effectively stimulated by its corresponding color.
  • In the absence of properly functioning cones, other cones may be inappropriately stimulated.

Red-Green Color Blindness Details

  • Red-green color blindness occurs when red cones respond to green light or vice versa.
  • Patients with this condition have missing or damaged red or green cones that cannot respond appropriately to colored light.
  • As a result, they are incapable of distinguishing red from green.
  • Red-green color blindness is a sex-linked recessive trait, affecting approximately 8% of males and 0.5% of females.

Wavelength and Absorption

  • The X-axis on the provided graph represents the wavelength of light corresponding to color, ranging from 400nm to 750nm.
  • The Y-axis represents absorption, indicating that cones with high absorption at a particular wavelength easily detect that color.
  • Different types of cones and rods have different absorption peaks:
    • Rods peak at approximately 498nm.
    • Short cones peak at approximately 420nm.
    • Medium cones peak at approximately 534nm.
    • Long cones peak at approximately 564nm.