Notes on Vision and Color Blindness

Refractive Errors

Myopia

  • Also known as nearsightedness.

Hyperopia

  • Also known as farsightedness.

Astigmatism

  • The inability to simultaneously focus light rays that enter the eye on different planes.
  • Corrected by a cylindrical lens.

Light Absorption and Color Detection

Cone and Rod Absorption

  • The X-axis of the graph represents the wavelength of light, which corresponds to color.
  • The Y-axis represents absorption, indicating how easily cones detect a particular color based on its absorption rate at a specific wavelength.
  • There are three types of cones: short, medium, and long, each corresponding to different wavelengths.
  • Short cones: 420nm
  • Medium cones: 534nm
  • Long cones: 564nm
  • Rods: 498nm
  • Cones have high absorption at a wavelength, meaning that they easily detect this color.

Color Blindness

Types of Cones

  • There are three major types of cones in the eye, each most stimulated by one of the primary colors of light: red, green, and blue.
  • In the absence of working cones, other cones can be stimulated inappropriately.

Hereditary Lack of Pigment

  • Color blindness is often due to a hereditary lack of a specific pigment in the eye (photopsin).
  • This prevents a person from being aware of certain differences among colors.
  • Mild cases may go unnoticed until tested.

Red-Green Color Blindness

  • Most common type of color blindness.
  • Occurs when red cones respond to green light or vice versa.
  • The patient has missing or damaged red or green cones that cannot appropriately respond to colored light.
  • Individuals are typically incapable of distinguishing red from green.
  • It is a sex-linked recessive trait, affecting approximately 8% of males and 0.5% of females.