Topic 12: Ocular Appendages Flashcards
What are ocular appendages
Structres attached to the eyeball. Aka ocular adnexa
Describe conjunctiva and its location
A thin, almost transparent mucous membrane that lines the inside of the eyelids and anterior surface of the eyeball
Describe the regions of conjunctiva
(1) palpebral/tarsal conjunctiva: lines upper and lower lids
(2) forniceal/fornix: junction between (upper and lower) palpebral/tarsal and bulbar
(3) bulbar conjunctiva: lines the exposed part of the sclera
Explain layers of the conjunctiva
(1) epithelium: non-keratinised, made up of goblet cells (provide mucin that make up mucus layer of tear film)
(2) stroma: BVs and fibres, contains Accessory Glands Of Krause And Wolfring (lacrimal glands that produce aqueous layer of tear film)
State blood and nerve supply of conjunctiva
Anterior ciliary artery (limbal BVs) & Lacrimal artery
CN5 (trigeminal nerve - ophthalmic & maxillary division)
Describe eyelashes
- aka celia. Short and curved hairs located in both eyelid margins, grow upward & outward
- longer and more numerous on upper lid
- defense mechanism: initiate reflex blink on the slightest contact with foreign particles (each follicle surrounded by nerves with low threshold of excitation)
State the layers of the eyelid
(Anterior-most) skin, subcutaneous tissue, muscles, submascular areolar tissue, fibrous layer/tarsal plate (posterior-most)
Explain skin layer of eyelid
- outermost. Soft, elastic, fine
- contains cilia: reflex blink
- contains sweat glands (modified= glands of moll)
- contains gland of Zeis (sebaceous gland) that contributes to the lipid layer of TF
Explain subcutaneous & submuscular layer of eyelid
Connective tissue below skin. Has no fat so that skin can roll easily
Connective tissue below muscle
Explain muscle layer of eyelid
(1) LPS (levator palpebrae superioris) muscle aids in elevation of upper lid. Voluntary action
(2) muller/tarsal muscle sustains LPS action/keeps upper eyelid open. Involuntary action ie. keeping lids open when awake
(3) OO (Orbicularis oculi) muscle helps with eyelid closure
(4) Riolan’s muscle ensures good closure of lid (upper & lower lids in close contact)
Explain fibrous layer/tarsals plate of eyelid
- Innermost, in contact with palpebar conjunctiva
- made up of dense fibrous tissues: makes eyelid have shape and firmness
- contains meibomian/tarsal glands which contribute to the lipid layer of the tear film
Summarise functions of the eyelid
To protect the cornea
(1) defense mechanism: reflex blink by eyelashes
(2) lid movements
(3) blinking aids in spreading of tears and keeps ocular surface moist
State blood & nerve supply of eyelids
Facial artery & lacrimal artery
CN5 (trigeminal) - upper & lower lids
CN7 (facial nerve) - lower lids, OO, riolans muscle (lid closure)
CN3 (oculomotor) - LPS, tarsal muscle (lid open)
Explain function, nerve & blood supply of eyebrows
F: prevent sweat from dripping into eyelids, facial expression
NS: CN7 (facial) - orbicularis oculi (depresses eyebrow) & frontalis muscle (elevate eyebrow)
BS: supraorbital artery, supratrochlear artery
Explain bells phenomenon
Normal eye phenomenon. Eyes rotate upward under closed lid
Explain bells palsy
An ocular pathology
- weakness/paralysis of CN7/facial nerve
- loss of forehead & brow movements (due to frontalis muscle weakness)
- inability to fully close eye of affected side (due to orbicularis oculi muscle & riolans muscle weakness)
- drooping of lower eyelid, excessive tearing on affected side (droopy lower lid and defective tear drainage)
- droopy appearance of affected side, droopy lower lip (due to facial muscle weakness)
State lacrimal apparatus structures according to their function
Secretion: lacrimal gland, accesory gkands of krause and wolfring
Drainage: puncta, canaliculi, lacrimal sac, naso-lacrimal duct
Describe the layers of tear film
(1) mucus layer - in contact with corneal epithelium, hydrophillic, contributed by goblet cells
(2) aqueous layer - middle layer, hydrophillic, contributed by lacrimal gland & accessory lacrimal gland of krause & wolfrings
(3) lipid layer - in contact with atmosphere, hydrophobic, contributed by meibomian gland & gland of zeis
Explain function of mucin TF
(1) decrease surface tension of tear film (hydrophillic coating over the hydrophillic corneal epithelium) to enhance SPREAD & STABILITY of TF
(2) lubricate ocular surface & reduces lid-globe friction during blinking
(3) hydrates underlying corneal epithelium
(4) provides foundation for a smooth optical surface by covering irregular corneal spaces
Explain function of aqueous of TF
(1) enables gaseous exchange
(2) hydrating medium for epithelial cells & carries metabolites to them
(3) flush away noxious substances
(4) provide delivery route for WBC and immunoglobulins to epithelium for immune response
(5) lubricate lid-globe interface to reduce blink friction
(6) contains lysozyme for antibacterial activity
Explain function of lipid TF
(1) forms hydrophobic layer
(2) reduces evaporation of aqueous TF
(3) forms tears meniscus along lid margins to prevent outflow of tears there
(4) prevents lid margins from sticking tgt
Explain blinking for tear circulation & drainage
Pre-blink: tears enter puncta by capillary action
During blinking: OO contracts and pulls on the lateral wall of lacrimal sac, pushing the tears into sac
Post-blink: OO relaxes, sac collapses, and tears are drained into the nasolacrimal duct
State blood and nerve supply to lacrimal apparatus
Lacrimal artery & medial palpebral artery
CN5/trigeminal for tear secretion
CN7/facial for tear drainage
explain spontaneous blink and its functions
involuntary, occurs at periodic intervals when awake and NOT DEPENDENT ON RETINAL STIMULATION
(1) maintains moisture of the exposed globe surface by preventing evaporation of TF
(2) spreads & distributes a uniform layer of tears
(3) assists in drainage of tears
