Structure of the Eye and Iris Reflex

Overview

• The lecture explores the structure of the eye and the iris reflex, focusing on how the eye responds to changes in light intensity.

Key Structures of the Eye

1. Cornea

   • Transparent to allow light passage.
   • No blood vessels; receives oxygen by diffusion from the air.
   • Refracts (bends) light as it enters the eye.

2. Iris

   • The colored part of the eye.
   • Controls the size of the pupil to regulate light entry.

3. Pupil

   • Not a physical structure but a gap in the iris.
   • Allows light to pass through to the lens.

4. Lens

   • Refracts light.
   • Can change shape to adjust refraction and focus light onto the retina.

5. Retina

   • Composed of cone cells and rod cells.
   • Cone Cells: Detect color; less effective in low light.
   • Rod Cells: More light-sensitive; enable black and white vision.

6. Fovea

   • A region on the retina rich in cone cells for clear vision.

7. Optic Nerve

   • Transmits impulses from receptor cells in the retina to the brain.

The Iris Reflex

• Protects the retina from damage by adjusting pupil size based on light intensity.
• Bright Light: Pupil constricts (gets smaller) to reduce light entry.
• Low Light: Pupil dilates (gets larger) to increase light entry.

Muscle Involvement

• Circular Muscles
  • Contract in bright light, making the pupil smaller.
• Radial Muscles
  • Contract in low light, making the pupil larger.
  • Named "radial" for their arrangement like the radius of a circle.

Conclusion

• Understanding the structure of the eye and the iris reflex is essential to comprehend how the eye adapts to different lighting conditions.