Clinical anatomy of the eye Flashcards
How is the visual field and eye location different in predator and prey species?
Eyes are more towards the front in predators - binocular overlap
Prey species have a larger field of view but they don’t have binocular overlap
Which bones make up the orbit?
Frontal, lacrimal, palatine, zygomatic and sphenoid
Which species have an incomplete bony orbit?
Why is this?
Dog and cat
Needed for the mandible to be able to open up widely
What completes the orbit in dog and cats?
Lacrimal orbital ligament
What completes the bony orbit in an ox?
The zygomatic process of the frontal bone and the frontal process of the zygomatic bone meeting
Which 3 components make up the orbital fascia?
Periorbita
Fascia bulbi
Orbital muscles
Which 3 nerves innervate the extraoccular muscles?
Trochlear
Occulomotor
Abducens
Which ocular muscles are innervated by the trochlear nerve?
Only the dorsal oblique
Which ocular muscles are innervated by the abducens nerve?
Lateral rectus
Retractor bulbi
Birds and snakes do not possess which extraocular muscle?
Retractor bulbi
What are the functions of the eyelids?
- Spreads the tear film across the eye, towards the drainage system
- Protection of the eye
- Allows removal of foreign material
- Controls light into the eye
What is the palpebral fissure?
Eyelid opening
Which muscles closes the eye?
Orbicularis oculi
Which glands produce the lipid component of the tear film?
Tarsal/Meibomian glands
Which nerves supply motor supply to the eyelids?
Facial and occulomotor
Sensory supply to the eyelid is by which nerve?
Trigeminal
Which muscle is the main elevator of the upper eyelid?
Levator palpebrae superioris
What is the conjunctiva?
A thin, highly vascularised, translucent mucus membrane which lines the inside of the lids - it has goblet cells which produce the mucus part of the tear film
What is the fornix?
Where the conjunctiva folds back on itself
What is the nictitating membrane?
A reflection of conjunctiva containing a T-shaped cartilage support, it sits ventromedially in the conjunctival sac
Where is the aqueous part of the tear film produced?
The gland of the 3rd eyelid
What is the function of each part of the tear film?
Lipid - reduces evaporation and creates a barrier at the lid margin
Mucin - mixed with and stabilised aqueous layer
Aqueous - lubrication, protection
Where is the mucin layer of the tear film produced?
Conjunctival goblet cells
How is the lacrimal drainage system in the rabbit vulnerable?
- only one lacrimal puncta compared to the usual 2
- nasolacrimal duct runs over the cheek teeth so problems with these affects the duct
- It has 2 sharp bends which can cause blockage
What are the 3 layers that make up the globe, what is the name of each ?
- outer fibrous layer: sclera and cornea
- middle vascular layer: uvea
- inner neural layer: retina
Which layer of the globe is present at the front of the eye, what is the function of this layer?
Sclera and cornea = fibrous layer
Allows light into the eye
How is the eye divided?
Posteriorly = everything behind the lens Anteriorly = Between the iris and cornea - in front of the lens
What is the cornea?
The front, fibrous layer of the eye - rostral surface
What is the function of the cornea?
To transmit and refract light
What is the limbus?
The junction between the cornea and the sclera
What is the scelera?
The white of the eye
Which 5 layers make up the cornea, from outer to inner
- Anterior Epithelium
- Bowman’s layer
- Stroma
- Descemet’s membrane
- Endothelium
What makes up the stroma of the cornea?
Lamellae of collagen fibrils
Keratocytes
Proteoglycans
Which layer of the cornea gets thicker with age?
Descemet’s membrane
What is the function of the endothelium layer?
Produce the Descemet’s membrane
What is the only species able to regenerate their corneal endothelium layer?
Rabbits
Where are most pain fibres of the cornea found?
Anterior epithelium
What is the lamina cribrosa?
Perforated zone of the sclera where the optic nerve exits the back of the eye
What makes up the uvea?
Anterior uvea = iris and ciliary body
Posterior uvea = choroid
Name the parts of the eye that is pigmented and highly vascularised
Uvea
Choroid
What is the function of the iris?
It is a sphincter that varies the amount of light entering the posterior segment of the eye
It also alters depth of focus
What is produced by the ciliary body?
Aqueous humour
Which part of the eye is suspended by the ciliary body?
The lens
Where is the choroid found in the eye?
The uveal layer between the sclera and retina
Which layers form the choroid?
- Suprachoroidea: heavily pigmented and elastic
- Large vessel layer
- Medium vessel layer
- Choriocapillaris: fenestrated capillaries
Which part of the eye maintains intraocular pressure?
Aqueous humour
Which processes produce the aqueous humour?
- Diffusion of solutes
- Ultrafiltration
- Active secretion
Where does the aqueous humour drain?
At the iridocorneal angle to the sclera venous plexus
How does the production of the aqueous humour lead to glaucoma?
If production is more than drainage
What fills the posterior segment of the globe?
Vitreous humour
What is the vitreous humour made up of?
It is a hydrogel - 99% water and hyaluronic acid
What is the function of the lens?
Focuses light onto the retina
What is the function of the lens reliant on?
- Transparency
- Stable position
- Ability to change shape
Which structures are visible in the fundus?
- optic disc
- retina
- retinal pigment epithelium
- choroid
How does the appearance of the optic disc differ in cats and dogs?
Cat - round and dark
Dog - light and triangular
