Lecture Notes: Vision and Accessory Structures of the Eye
Importance of Vision
- Vision is considered the most important special sense for humans.
- Humans rely heavily on vision compared to other senses.
Anatomy of the Eye
Eyeball
- Contains visual receptors that detect light and transmit information to the brain.
Accessory Structures
- Protect, lubricate, and support the eye.
- Include eyelids (palpebra), superficial epithelium, and lacrimal apparatus.
Eyelids (Palpebra)
- Upper and lower eyelids, a continuation of the skin.
- Functions:
- Protect the eye by covering it when closed.
- Distribute tears across the eye's surface to remove debris and keep it lubricated.
Important Features
- Eyelashes: Thick hairs that catch debris before they reach the eye.
- Palpebral Fissure: Gap between open eyelids.
- Medial Angle: Where eyelids meet near the nose.
- Lateral Angle: Where eyelids meet near the ear.
Glands in Eyelids
- Tarsal Glands: Sebaceous glands produce oily secretions to prevent eyelids from sticking.
- Help reduce tear evaporation.
- Insufficient tarsal gland activity can lead to dry eyes.
- Chalazion: Cyst formed from blocked tarsal glands.
- Stye: Infection of sebaceous gland linked to eyelash hair follicles.
Superficial Epithelium of the Eye
Components
- Lacrimal Caruncle: Glands producing thick secretions, known for "sleep" in the eyes.
- Conjunctiva:
- Palpebral Conjunctiva: Lines inner surface of eyelids.
- Bulbar Conjunctiva: Covers anterior part of the eye.
- Conjunctivitis (Pink Eye): Inflammation often caused by infection.
Lacrimal Apparatus
- Produces tears and facilitates their movement over the eye.
- Functions of tears:
- Lubricate the eye.
- Wash away debris and pathogens.
- Supply nutrients to the cornea and conjunctiva.
Tear Composition
- Tears contain water, salts, antibodies, and lysozyme (antibacterial enzyme).
Components of Lacrimal Apparatus
- Lacrimal Gland: Produces the majority of tear components.
- Lacrimal Ducts: Carry tears to the eye surface.
- Lacrimal Puncta: Openings that drain tears away from the eye.
- Lacrimal Canaliculi: Ducts connecting puncta to the lacrimal sac.
- Lacrimal Sac: Collects tears before draining into nasal cavity.
- Nasolacrimal Duct: Drains tears into the nasal cavity.
Tear Drainage Pathway
- Produced by Lacrimal Gland.
- Travel through Lacrimal Ducts to the eye surface.
- Drain through Lacrimal Puncta into Lacrimal Canaliculi.
- Collected in Lacrimal Sac.
- Drained via Nasolacrimal Duct into Nasal Cavity.
Crying
- Occurs when tear production exceeds drainage capacity, causing overflow and runny nose.
This lecture extensively covers the anatomy, function, and importance of the various structures involved in vision, emphasizing the accessory structures that support and maintain ocular health.