Anatomy of the Eye: Conjunctiva and Eyelids

Conjunctiva

• The conjunctiva is a clear protective layer of tissue sitting on top of the white part of the eye.
• The conjunctiva forms the back of the eyelids and helps keep contact lenses in place.
• Conjunctivitis is an infection of the conjunctiva and causes red, dilated blood vessels.

Eyelids

• Eyelids are made of two layers, the anterior lamella, which contains muscles, and the posterior lamella, which is formed by the tarsal plate.
• The tarsal plate is a tough layer giving the eyelids shape and structure.
• Meibomian glands, located within the tarsal plate, release oil into the tear film through pores at the eyelid base.
• This oil prevents rapid tear evaporation.
• Clogged Meibomian gland pores can cause a backflow of lipid and granulous reactions, characterized by a hard, non-tender lump on the eyelid.

Stye

• A stye is a small, localized infection on the eyelid that is self-limited, red, and very tender.

Eyelid Muscles

• Orbicularis oculi muscle:
  • Circular muscle surrounding the eyes that closes them.
  • Controlled by cranial nerve 7 (facial nerve).
  • Patients with Bell's palsy have difficulty closing their eyes.
• Levator palpebrae superioris muscle:
  • Ribbon-like muscle pulling the eyelid open.
  • Controlled by cranial nerve 3 (oculomotor nerve).
  • Damage to cranial nerve 3 causes a drooping eyelid (ptosis).
  • Mnemonic for remembering nerve function: "3 opens the eye" (like a pillar); "7 closes the eye" (like a fish hook).

Lacrimal System

• The lacrimal system produces and drains tears.
• Accessory glands in the conjunctiva produce most tears.
• The lacrimal gland, located in the corner of the eye, produces reflex tears.
• Tears drain through the:
  • Punctum: Small openings in the eyelids.
  • Canaliculi: Tiny tubes connecting the punctum to the lacrimal sac.
  • Lacrimal sac: Small pouch collecting tears.
  • Nasolacrimal duct: Duct draining collected tears into the inferior meatus of the nose.
• Plugging a punctum can help with dry eye by preventing the rapid draining of tears.
• An eyelash stuck in a punctum can cause excessive tearing.

Nasolacrimal Duct

• Drains tears from the eye into the nose.
• Visible as a small hole in axial CT scans.
• Damage to the nasolacrimal duct, from facial fractures, can lead to excessive tearing.

Upper Lid Lacerations

• Medial (inner) upper lid lacerations are the most worrisome because they can cut the canalicular structure.
• Surgical repair involves placing a tube through the canalicular system to maintain drainage during healing.

Globe

• The globe is the term for the eyeball.

This quiz explores the anatomy and functions of the conjunctiva and eyelids, detailing their roles in eye protection and health. It covers conditions like conjunctivitis and styes, along with the structure of eyelid muscles. Enhance your understanding of these essential eye components.