Week 32 Lacrimal system and Eyelids

• What is the Tarsal Plate?

  The tarsal plate is a dense connective tissue structure within the eyelid that provides shape and firmness. It also houses the meibomian glands, which produce the oily layer of the tear film.
• What Does "Palpebral" Refer To?

  "Palpebral" refers to anything related to the eyelids. For example, the palpebral conjunctiva lines the inside of the eyelid, including both the tarsal and orbital parts.
• Functions of Eyelids

  • Protection: Blinking shields the eye from trauma and light.
  • Tear Management: Spreads and stabilizes the tear film.
  • Debris Removal: Clears particles from the ocular surface.
• Gross Anatomy of the Eyelids

  • Upper Eyelid: Covers ~1/6th of the cornea in primary gaze, larger and more mobile.
  • Lower Eyelid: Covers the inferior limbus and extends to the cheek.
  • Palpebral Sulci: Separate the tarsal and orbital sections, deepening with age.
  • Palpebral Fissure: Space between lids (~30mm wide, ~10mm high in adults).
• Canthi and Associated Structures

  • Medial Canthus: Separated from the eye by the tear lake.
  • Lateral Canthus: Contacts the eyeball.
  • Caruncle: A small pink area with sebaceous and sweat glands.
  • Plica Semilunaris: A crescent-shaped fold of conjunctiva, a vestigial remnant of the third eyelid.
• Eyelid Margins and Lashes

  • Margins: ~2mm wide, ~30mm long, split into anterior (with lashes) and posterior (with meibomian glands) sections.
  • Upper Lashes: ~100–150 lashes, curve upward.
  • Lower Lashes: ~50–75 lashes, curve downward.
  • Grey Line: A subtle landmark dividing the anterior and posterior margins, useful in surgery.
• Glands of the Eyelids

  • Meibomian Glands: Secrete meibum to prevent tear evaporation (~26–40 in the upper lid, ~21–30 in the lower lid).
  • Glands of Zeis: Sebaceous glands that lubricate lashes and the lid margin.
  • Glands of Moll: Modified sweat glands that can form cysts if blocked.
• Muscles of the Eyelid

  • Orbicularis Oculi: Closes the eyelid, aids tear drainage (CN VII).
  • Levator Palpebrae Superioris: Elevates the upper eyelid (CN III).
  • Müller’s Muscle: Provides additional eyelid elevation (~2mm) via sympathetic innervation.
• Eyelid Skin & Tissue Layers

  • Skin: Thinnest in the body, highly mobile.
  • Subcutaneous Tissue: Loose and stretchable, prone to swelling.
  • Fibrous Tissue:
  • Tarsal Plates: Provide structure, house meibomian glands.
  • Orbital Septum: Barrier against infection.
  • Palpebral Ligaments: Anchor the lids to the orbit.
• What is unique about the skin of the eyelids?

  The eyelid skin is the thinnest in the body (~0.5mm), highly mobile, and prone to age-related laxity (e.g., dermatochalasis).
• Why is swelling or bruising common around the eyelids?

  The subcutaneous tissue is loose, areolar connective tissue without fat, allowing for easy swelling or bruising (e.g., periorbital edema, "black eye").
• Which muscle is responsible for closing the eyelids?

  The orbicularis oculi (innervated by CN VII - Facial Nerve) closes the eyelids.
• What are the parts of the orbicularis oculi and their functions?

  • Palpebral Portion: Involuntary blinking.
  • Orbital Portion: Forceful eyelid closure.
  • Lacrimal Portion: Aids tear drainage by compressing the lacrimal sac.
• Which muscle raises the upper eyelid?

  Levator palpebrae superioris (innervated by CN III - Oculomotor Nerve) raises the upper eyelid.
• What is the role of Müller’s muscle?

  Müller’s muscle (smooth muscle with sympathetic innervation) assists the levator muscle, providing ~2mm of additional upper lid elevation.
• What structures provide structural support to the eyelids?

  • Tarsal Plate: Dense connective tissue.
  • Orbital Septum: Connective tissue barrier preventing infection spread.
  • Palpebral Ligaments: Anchor the tarsal plates to the orbital margins.
• What causes ptosis?

  Ptosis is the drooping of the upper eyelid, often due to dysfunction of the levator muscle or its CN III innervation.
• How do the eyelids receive arterial blood supply?

  • Ophthalmic artery (main source).
  • Lacrimal artery (lateral aspect).
  • Infra-orbital artery (lower eyelid).
• What is the venous drainage pathway of the eyelids?

  Veins drain into the forehead, temple veins, and the ophthalmic vein, which connects to the cavernous sinus (clinically relevant for orbital infections).
• How do the eyelids drain lymph?

  • Medial 1/3: Submandibular lymph nodes.
  • Lateral 2/3: Parotid lymph nodes.
• What are the components of the lacrimal gland, and how is it innervated?

  • Orbital (larger) and palpebral lobes.
  • Parasympathetic (CN VII): Main tear production.
  • Sympathetic: Modulates secretion.
  • Sensory (CN V₁ - lacrimal nerve).
• What are the three layers of the tear film?

  1. Mucous Layer (Goblet cells): Spreads tear film, stabilises, and provides antimicrobial protection.
  2. Aqueous Layer (Lacrimal gland): Delivers nutrients, lubricates, and contains immune defense proteins.
  3. Lipid Layer (Meibomian glands): Reduces evaporation, smooths the optical surface, and seals the lids during closure.
• How do tears drain from the eye?

  Puncta → Canaliculi → Lacrimal sac → Nasolacrimal duct → Inferior meatus of the nasal cavity.
• What clinical conditions affect the tear drainage system?

  • Epiphora: Excessive tearing due to obstruction (e.g., punctal stenosis, nasolacrimal duct obstruction).
  • Infections: Lacrimal drainage connects to venous sinuses, posing a risk for orbital or intracranial infections.
• How does blinking help with tear drainage?

   

  Blinking contracts the orbicularis oculi, closing the puncta and compressing the lacrimal sac to push fluid into the nasolacrimal duct. Sac expansion after blinking draws fluid from the puncta.