Topic 12 Ocular Appendages Flashcards
what is the conjunctiva?
thin and almost transparent mucous membrane that lines the inside of the eyelids and on the anterior surface of the eyeball.
what are the 3 regions of the conjunctiva?
- Palpebral/Tarsal conjunctiva (lining the lids-upper palpebral & lower palpebral)
- Bulbar conjunctiva (lining the exposed part of the globe/sclera)
- Forniceal conjunctiva (junction of the palpebral & bulbar conjunctiva- upper & lower fornix)
what are the 2 layers of the conjuctiva?
Epithelium
•Consists of non-keratinised epithelium & goblet cells.
•Goblet cells provide mucin (inner layer of the tear film which lines the corneal epithelium).
Stroma
•Contains the accessory glands of Krause and Wolfring. (contribute the middle layer of the tear film-the aqueous layer)
what is the 2 blood supply of the conjunctiva?
Anterior ciliary arteries and lacrimal artery
what is the nerve supply of the conjunctiva?
Trigeminal nerve (CN5)
what are eyelashes/cilia and what is their function
- located in both eyelids, usually grow outward
- part of the defence mechanism of the eye, initiate reflex blink on the slightest contact with foreign particles
what are the 5 layers of the eyelid?
- skin
- sub-cutaneous tissue
- muscles
- sub-muscular areilar tissue
- tarsal plate
what does the skin of the eyelid contain? (Glands included)
-outermost layer of the eyelids
contains the
- cilia (eyelashes), defence mechanism-reflex blink
- sweat glands, Glands of Moll
- sebaceous glands (Glands of Zeis) contributes to the lipid layer of the tear film
what does the sub-cutaneous tissue of the eyelid contain?
Connective tissue below the skin
what does the muscle layer of the eyelid contain? (4 muscles) what are their functions?
- Levator Palpebrae Superioris (LPS) muscle aids in elevation of the upper eyelid (lid opening)
- Tarsal/Muller’s muscle keeps the upper eyelid open (sustains eyelid opening)
- Orbicularis Oculi muscle helps with eyelid closure
- Riolan’s muscle insures good closure of the lid
what does the sub-muscular areolar tissue layer of the eyelid contain?
connective tissue below the muscle layer
what does the tarsal plate layer of the eyelid contain?
- posterior most layer of the eyelids
- fibrous tissue plate that gives shape & firmness to the lids
- contains the meibomian/tarsal glands which contribute to the lipid layer of the tear film
what are the 3 main functions of the eyelid?
- reflex blink initiated by the eyelashes
- lid movements (opening & closure)
- blinking aids in spreading of tears and keeps the ocular surface moist. Also removes dust
what is the 2 blood supply and 4 nerve supply to the eyelid?
Facial artery
Lacrimal artery
Trigeminal nerve (CN5) upper eyelid, lower eyelid
Facial nerve (CN7) Orbicularis oculi muscle, Riolan muscle, lower eyelid
Oculomotor nerve (CN3) LPS muscle
Sympathetic branch Muller’s muscle
what is the function of the eyebrows? What are the muscles associated with eyebrow movement?
Functions: prevents sweat from dripping into the eyelids
plays a role in facial expression
Orbicularis oculi (depression) occipito frontalis (elevation)
what is the blood supply and nerve supply of the eyebrows?
Blood supply: Supraorbital artery, Supratrochlear artery
Nerve supply: Facial nerve (CN7)
what is Bell’s phenomenon?
-eyes rotate upwards under closed lid
defense mechanism so that cornea will not be damaged even when eyes are closed
what is Bell’s palsy/Facial nerve palsy/CN7 palsy? list 5 main characteristics and the affected structures
- loss of forehead & brow movements (due to Frontalis muscle weakness)
- inability to close the eyes (lagophthalmos) (due to Orbicularis oculi and riolan muscle weakness)
- drooping of the lower eyelid
- excessive tearing on the affected side (due to droopy lower lid and defective tear drainage)
- droopy appearance of the affected side of the face, drooping of the lower lip (due to facial muscles weakness)
what are the secretion and drainage structures of the lacrimal apparatus?
Secretion: Lacrimal gland, accessory glands of Krause & Wolfring
Drainage: Puncta, Canaliculi, Lacrimal sac, Naso-lacrimal duct
what are the 3 layers of the tear film inner to outer?
- mucin layer
- aqueous layer
- lipid layer
what are the 4 functions of the mucin layer?
- decrease surface tension of the tear film by forming a hydrophilic coating over the hydrophobic corneal epithelium, so enhances the spread & stability of the tear film
- lubricate the ocular surface and reduces lid-globe friction during blinking
- hydrates the underlying corneal epithelium
- provide the foundations for a smooth optical surface by covering the irregular corneal surface
what are the 6 functions of the aqueous layer? (Nutrition, immunity and lubrication)
- enables gaseous exchange
- hydrating medium for epithelial cells (keeps the cornea moist) and carries metabolites to them
- flush away noxious substances
- provide a delivery route for white blood cells and immunoglobulins to epithelium (immune response)
- antibacterial activity: contains lysozyme
- lubricate the lid-globe interface to reduce friction when blinking
what are the 4 functions of the lipid layer?
- forms a hydrophobic layer
- reduce evaporation of aqueous layer of the tear film
- forms a tears meniscus along the lid margins to prevent overflow of tears at the lid margins
- prevent lid margins from sticking together
what are the 5 steps of tear movement?
- lacrimal fluid passes from lacrimal gland into conjunctival fornix
- tears are swept across cornea by lid closure
- movements of tears in lacrimal rover
- contraction of orbicularis oculi shortens the canaliculi and expands the lacrimal sac
- tears pass into lacrimal sac and nasaolacrimal duct
what is the role of blinking in tear drainage?
During pre-blink, tears enters the puncta by capillary action
During blinking, orbicularis oculi contracts and pulls on the lateral wall of the lacrimal sac aspiring the tears into the sac
After blink, orbicularis oculi relaxes, sac collapses and tears are drained into the nasolacrimal duct
what is the 2 blood supply and 2 nerve supply of the lacrimal apparatus?
lacrimal artery
medial palpebral artery
Trigeminal nerve (CN5) Tear secretion Facial nerve (CN7) Tear drainage
What is the diff between spontaneous blink and reflex blink?
Spontaneous: natural, normal body function
Reflex: external stimuli cause eye to blink as a defence mechanism
What are the glands/ cells that produce the 3 layers of tear film?
Lipid layer meibomian gland (in tarsal plate of eyelid) & glands of Zeis ( in skin of eyelid)
aqueous layer accessory glands of Krause & wolfring (basal secretion) lacrimal gland (reflex secretion)
These glands are found in lacrimal system
mucin layer conjunctival goblet cells
*basal secretion is basic secretion and occurs for all 3 layers
Reflex secretion is associated with yawning, crying etc and only occurs of aq layer
