Understanding the Human Eye

Visibility of Objects

• Objects are visible due to light reflecting off their surfaces
• Reflected light enters the eyes, allowing us to see

Structure of the Human Eye

• The human eye is roughly spherical

Outer Layer of the Eye: Cornea

• Cornea: Outer layer, white and transparent
  • Allows light to pass through
  • Refracts (bends) light entering the eye
  • Protects inner parts of the eye
  • Prevents foreign particles from entering

Inside the Eye

• Iris: Dark muscular structure behind the cornea
  • Determines eye color (e.g., blue eyes = blue iris)
  • Central opening called the Pupil
  • Functions like a camera shutter
    • Controls light entering the eye by adjusting pupil size
    • Shrinks in bright light, expands in dim light

Behind the Pupil: Lens

• Lens: Biconvex, thicker in the center than edges
  • A converging lens focusing light at one point
  • In a normal eye, this focus point is on the Retina
  • Defects can cause focus to be in front of or behind the retina

Inner Layer: Retina

• Retina: Inner layer at the back of the eye
  • Contains nerve cells that sense light
  • Two types of nerve cells:
    • Cones: Sensitive to bright light
    • Rods: Sensitive to dim light
  • Transmits messages to the brain via the Optic Nerve

Recap

• Outer part: Cornea (transparent, protective)
• Inside: Iris (colorful, adjusts pupil size)
• Behind pupil: Lens (converging, focuses light on retina)
• Retina: Nerve cells (cones and rods), message relay to brain via optic nerve

Next Steps

• Future videos will cover more about the lens and its functions