Eye Anatomy and Physiology

Introduction

• The eye contains numerous sensory receptors, about 70% of them.
• Acts as a crucial window to the world with significant protection.
• Surrounded by fat, bony orbit for sturdy protection.

Accessory Structures

Lacrimal Apparatus

• Components: Lacrimal gland and ducts.
• Function: Produces lacrimal fluid (tears) containing mucus, antibodies, lysozymes for moisture and cleanliness.
• Process: Tears produced superior laterally; blink spreads fluid over the eye; excess drains into the nasolacrimal duct.
• Lacrimal Caruncle: Produces oil to keep the eye moist; excess can form "eye crust" or "eye coopers."

Conjunctiva

• Membrane covering the inner eyelid and anterior eye.
• Produces mucus for moisture; infection leads to conjunctivitis (pink eye).

Other Structures

• Eyebrows and Eyelashes: Divert sweat and keep particles out.
• Extrinsic Eye Muscles: Allow eye movement and help maintain shape.
  • Types: 2 oblique muscles, 4 rectus muscles.
  • Important muscles: Superior oblique, superior rectus, lateral rectus, medial rectus, inferior rectus, inferior oblique.

Eye Structure

Layers (Tunics)

• Fibrous Tunic: Outermost layer.
  • Sclera: White, opaque, protective, muscle attachment.
  • Cornea: Clear, avascular, allows light entry, nutrient delivery via aqueous humor.
• Vascular Tunic (Choroid)
  • Choroid: Vascular, pigmented, absorbs light.
  • Ciliary Body: Around lens with smooth muscle and suspensory ligaments to adjust lens shape.
  • Iris: Colored eye part, controls pupil size via smooth muscle; pupil allows light passage.
• Sensory Tunic (Retina)
  • Outer Pigmented Layer: Absorbs light.
  • Neural Layer: Contains photoreceptors, bipolar cells, ganglion cells; axons form optic nerve.

Internal Segments

• Anterior Segment: Contains aqueous humor, supports avascular structures like cornea.
• Posterior Segment: Contains vitreous humor, gel-like for maintaining shape and pressure.

Photoreceptors

• Rods: Dim light, peripheral vision; located peripherally in the retina.
• Cones: Bright light, color vision, high acuity; concentrated in macula lutea and fovea centralis.

Special Regions

• Macula Lutea: High concentration of cones, focused light target.
• Fovea Centralis: Highest concentration of cones.
• Optic Disc: Blind spot where optic nerve exits; no photoreceptors.

Conclusion

• Eye anatomy includes complex structures ensuring protection, moisture, movement, and vision.
• Understanding these components is vital for comprehending visual physiology.