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.