Tear film, the globe and cornea Flashcards
What are the 3 components to tear film?
Aqueous layer
Mucin layer
Lipid layer
What produces the lipid layer of tear film? Where are these located?
Meibomian/tarsal glands
Tarsal plate in eyelids
What is the function of the lipid layer of tear film?
Reduces evaporation
Hold tears within palpebral fissure
The mucin layer is mixed into which other layer? What does it do?
Mixed into aqueous layer
Helps stabilise it
What produces the mucin layer of tear film?
Goblet cells in conjunctiva
What produces the aqueous layer of tear film?
Lacrimal and nicititans gland
What is the function of the aqueous layer?
Lubricate, protect and provide nutrition
For corneal, limbal and conjunctival epithelium
What control is tear film under? (Nervous system)
Autonomic
What nerve mainly supplies tear film production?
Lacrimal nerve of ophthalmic branch of trigeminal
Where is the main lacrimal gland located?
Dorsolateral orbit
What do the lacrimal puncture open into?
Lacrimal canaliculi
What encircles the lacrimal canaliculi and why?
Obicularis oculi
Pumps tears along tear duct system
Where do the lacrimal canaliculi meet? Where is this located? Which species is this poorly developed?
Lacrimal sac
Located in lacrimal fossa of lacrimal bone
Poorly developed lacrimal bone in cat and dog
Where does the lacrimal sac empty into? Where does this empty into?
Nasolacrmal duct
Nasal cavity
The obicularis oculi muscle controls blinking. What is the function of blinking?
Spread tear film
Help drain nasolacrimal gland (pumps tears along duct system)
Give 3 reasons why rabbits have a vulnerable lacrimal drainage system
Runs over cheek teeth (dental disease damages nasolacrimal duct)
Only one lacrimal punctual
2 sharp bends in the duct = block easily
The globe/eyeball shape varies between species. What shape globe do cattle and horses have?
Slightly flattened
What are the 3 layers to the globe/eyeball?
Fibrous layer
Uvea
Neural layer
What is the function of the fibrous layer of the globe?
Supports shape of eyeball
What is the function of the uvea?
Provides nutrition
Alters light transmission
What is within the neural layer of the globe?
Retina = light detection
What divides the eye into anterior and posteior segments?
Lens
The anterior segment of the globe is further divided into anterior and posterior chambers. What divides these?
Iris
What is the outermost layer of the front of the eye? What does it do? Does it have conjunctiva?
Cornea
Dome shape focuses vision No
What are the 4 layers of the cornea?
Anterior epithelium
Stroma
Descemet’s membrane
Endothelium
What does the anterior epithelium of the cornea contain?
Squamous cells at surface
Columnar cell at base
Lots of pain receptors
What does the stroma of the cornea contain?
Collagen fibrils - form lamellae
Keratocytes
Proteoglycans
Pressure receptors
What gives the cornea its clarity?
Collagen fibrils that form lamellae in the stroma
What produces Descemet’s membrane?
Endothelium
What dess the endothelium of the cornea do?
Produces Descemets membrane
Maintains stromal hydration
Is the endothelium of the cornea able to regenerate?
No
Except in rabbit
Damage to the cornea is painful as it is highly innervated. What nerve innervates it?
CN V (trigeminal)
Where are pain receptors and pressure receptors in the cornea?
Pain receptors in anterior epithelium
Pressure receptors in stroma
How does damage to the epithelium or endothelium cause prevention of light transmission and cause ulcers?
Allows fluid to enter the stroma
Corneal oedema disrupts lamellae
Does the epithelium of the cornea heal well after damage? How?
Yes
By neighbouring cells, stem cells at limbus and mitosis
What happens when the cornea is damaged?
Neovascularisation = blood vessels grow from limbus to aid healing
When the cornea is damaged, neovascularisation occurs. It can be superficial or deep. Where do these new vessels come from?
Superficial = from conjunctiva blood vessels Deep = ciliary plexus
What happens to blood vessels from neovascularisation after corneal damage has healed?
Vessels narrow
Leave ghost vessels
May cause pigmentation
