Clinical anatomy of the eye

Question 1

How is the visual field and eye location different in predator and prey species?

Answer 1

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

Question 2

Which bones make up the orbit?

Answer 2

Frontal, lacrimal, palatine, zygomatic and sphenoid

Question 3

Which species have an incomplete bony orbit?

Why is this?

Answer 3

Dog and cat

Needed for the mandible to be able to open up widely

Question 4

What completes the orbit in dog and cats?

Answer 4

Lacrimal orbital ligament

Question 5

What completes the bony orbit in an ox?

Answer 5

The zygomatic process of the frontal bone and the frontal process of the zygomatic bone meeting

Question 6

Which 3 components make up the orbital fascia?

Answer 6

Periorbita
Fascia bulbi
Orbital muscles

Question 7

Which 3 nerves innervate the extraoccular muscles?

Answer 7

Trochlear
Occulomotor
Abducens

Question 8

Which ocular muscles are innervated by the trochlear nerve?

Answer 8

Only the dorsal oblique

Question 9

Which ocular muscles are innervated by the abducens nerve?

Answer 9

Lateral rectus

Retractor bulbi

Question 10

Birds and snakes do not possess which extraocular muscle?

Answer 10

Retractor bulbi

Question 11

What are the functions of the eyelids?

Answer 11

• 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

Question 12

What is the palpebral fissure?

Answer 12

Eyelid opening

Question 13

Which muscles closes the eye?

Answer 13

Orbicularis oculi

Question 14

Which glands produce the lipid component of the tear film?

Answer 14

Tarsal/Meibomian glands

Question 15

Which nerves supply motor supply to the eyelids?

Answer 15

Facial and occulomotor

Question 16

Sensory supply to the eyelid is by which nerve?

Answer 16

Trigeminal

Question 17

Which muscle is the main elevator of the upper eyelid?

Answer 17

Levator palpebrae superioris

Question 18

What is the conjunctiva?

Answer 18

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

Question 19

What is the fornix?

Answer 19

Where the conjunctiva folds back on itself

Question 20

What is the nictitating membrane?

Answer 20

A reflection of conjunctiva containing a T-shaped cartilage support, it sits ventromedially in the conjunctival sac

Question 21

Where is the aqueous part of the tear film produced?

Answer 21

The gland of the 3rd eyelid

Question 22

What is the function of each part of the tear film?

Answer 22

Lipid - reduces evaporation and creates a barrier at the lid margin
Mucin - mixed with and stabilised aqueous layer
Aqueous - lubrication, protection

Question 23

Where is the mucin layer of the tear film produced?

Answer 23

Conjunctival goblet cells

Question 24

How is the lacrimal drainage system in the rabbit vulnerable?

Answer 24

• 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

Question 25

What are the 3 layers that make up the globe, what is the name of each ?

Answer 25

- outer fibrous layer: sclera and cornea - middle vascular layer: uvea - inner neural layer: retina

Question 26

Which layer of the globe is present at the front of the eye, what is the function of this layer?

Answer 26

Sclera and cornea = fibrous layer | Allows light into the eye

Question 27

How is the eye divided?

Answer 27

``` Posteriorly = everything behind the lens Anteriorly = Between the iris and cornea - in front of the lens ```

Question 28

What is the cornea?

Answer 28

The front, fibrous layer of the eye - rostral surface

Question 29

What is the function of the cornea?

Answer 29

To transmit and refract light

Question 30

What is the limbus?

Answer 30

The junction between the cornea and the sclera

Question 31

What is the scelera?

Answer 31

The white of the eye

Question 32

Which 5 layers make up the cornea, from outer to inner

Answer 32

- Anterior Epithelium - Bowman's layer - Stroma - Descemet's membrane - Endothelium

Question 33

What makes up the stroma of the cornea?

Answer 33

Lamellae of collagen fibrils Keratocytes Proteoglycans

Question 34

Which layer of the cornea gets thicker with age?

Answer 34

Descemet's membrane

Question 35

What is the function of the endothelium layer?

Answer 35

Produce the Descemet's membrane

Question 36

What is the only species able to regenerate their corneal endothelium layer?

Answer 36

Rabbits

Question 37

Where are most pain fibres of the cornea found?

Answer 37

Anterior epithelium

Question 38

What is the lamina cribrosa?

Answer 38

Perforated zone of the sclera where the optic nerve exits the back of the eye

Question 39

What makes up the uvea?

Answer 39

Anterior uvea = iris and ciliary body | Posterior uvea = choroid

Question 40

Name the parts of the eye that is pigmented and highly vascularised

Answer 40

Uvea | Choroid

Question 41

What is the function of the iris?

Answer 41

It is a sphincter that varies the amount of light entering the posterior segment of the eye It also alters depth of focus

Question 42

What is produced by the ciliary body?

Answer 42

Aqueous humour

Question 43

Which part of the eye is suspended by the ciliary body?

Answer 43

The lens

Question 44

Where is the choroid found in the eye?

Answer 44

The uveal layer between the sclera and retina

Question 45

Which layers form the choroid?

Answer 45

- Suprachoroidea: heavily pigmented and elastic - Large vessel layer - Medium vessel layer - Choriocapillaris: fenestrated capillaries

Question 46

Which part of the eye maintains intraocular pressure?

Answer 46

Aqueous humour

Question 47

Which processes produce the aqueous humour?

Answer 47

- Diffusion of solutes - Ultrafiltration - Active secretion

Question 48

Where does the aqueous humour drain?

Answer 48

At the iridocorneal angle to the sclera venous plexus

Question 49

How does the production of the aqueous humour lead to glaucoma?

Answer 49

If production is more than drainage

Question 50

What fills the posterior segment of the globe?

Answer 50

Vitreous humour

Question 51

What is the vitreous humour made up of?

Answer 51

It is a hydrogel - 99% water and hyaluronic acid

Question 52

What is the function of the lens?

Answer 52

Focuses light onto the retina

Question 53

What is the function of the lens reliant on?

Answer 53

- Transparency - Stable position - Ability to change shape

Question 54

Which structures are visible in the fundus?

Answer 54

- optic disc - retina - retinal pigment epithelium - choroid

Question 55

How does the appearance of the optic disc differ in cats and dogs?

Answer 55

Cat - round and dark | Dog - light and triangular