Clinical Anatomy of the Eye

Question 1

What is the orbit

Answer 1

surrounds and protects the eye, and its position affects the field and depth of vision

Question 2

How does the orbit differ between species?

Answer 2

The position in the skull - carnivores greater depth /field of vision
Humans most binocular vision

The construction - herbivores obit is enclosed (fully surrounded by bone), carnivores adn pigs open = wider opening of jaw

Question 3

What determines the orbit positioning of a species

Answer 3

Determined by the feeding behaviour.
Carnivores require greater depth of vision to enable accurate targeting of prey- positioned more rostrally)
Herbivores require greater field of vision to scan for predators while grazing. Positioned more laterally
Humans have the most binocular vision

Question 4

In carnivores what is the orbit made up of?

Answer 4

the frontal, lacrimal, zygomatic, sphenoid and palatine bones and completed by the orbital ligament which extends from the frontal process of the zygomatic bone to the zygomatic process of the frontal bone

Question 5

Horses additional part to orbital

And recap what made up of

Answer 5

additional bit of temporal bone that completes the bony part of orbit

the frontal, lacrimal, zygomatic, sphenoid and palatine bones

Question 6

What is the orbital fascia?

Answer 6

3 layered structure which lines the orbit:
Each layer is separated and encircled by adipose tissue
1. periorbita (outer) (lining bone)
2. fascia bulbi
3. fascial sheaths

Question 7

periorbita

Answer 7

The outer layer of the orbital fascia, the bit of fascia lining the bone

Question 8

Fascia Bulbi

Answer 8

part of orbital fascia
fascia surrounding the globe itself.
is separated from the sclera by loose connective tissue and attaches at the corneoscleral junction.
Lines eye caudally

Question 9

Fascial Sheaths

Answer 9

Part of orbital fascia - Fascia bulbi is continuous with fascial sheaths of the extraocular muscles

Question 10

Extraocular Muscles (name from diagram in clinical anatomy of the eye)

Answer 10

1. Flap up - Dorsal Rectus
2. Flap down - Ventral Rectus
3. Flap on side with nothing above or below - lateral rectus
4. Flap on side with Trochlear and dorsal oblique above and ventral oblique below - Medial rectus
5. circumference in eye - retractor bulbi
6. Optic nerve in centre

Question 11

What are the extraocular muscles innervated by?

Answer 11

1. Dorsal rectus - CN 3 (occular motor)
Ventral rectus -  CN 3
Lateral rectus CN 6 (abducens)
Medial rectus - CN 3
Dorsal oblique - CN 4 (trochlear)
Ventral oblique - CN 3
Retractor bulbi - CN 6

Question 12

What are the action of the extraocular muscles?

Answer 12

Dorsal rectus - Rotate eye upwards CN3 (oculomotor)
Ventral rectus - Rotate eye downwards CN3
Lateral rectus - Rotate globe laterally CN6 (abducens)
Medial rectus - Rotate globe medially CN3
Dorsal oblique - Rotate dorsal globe medially and ventrally CN4 (trochlear)
Ventral oblique - Rotate Ventral globe medially and dorsally CN3
Retractor bulbi - Retract globe into orbit, allows 3rd eyelid to move out CN 6

Question 13

Role of eyelid

Answer 13

1. The eyelids protect the eyeball
2. spread the tear film across the eye and into the lacrimal punctae
3. help to remove foreign material from the eye and can close to exclude light.

Question 14

Dogs and cats born with lids fused shut. At 10-14 days open, what is the eyelid opening called?

Answer 14

palpebral fissure.

Question 15

Talk about lid margins

Answer 15

1. Transition between skin adn conjunctiva
2. Intact margin is imperative for eyeball health
3. Lid margins are hairless, uppen may possess cilia though (eyelashes)
4. These cilia are associated with sebaceous (glands of Zeis) and modified sweat glands (glands of Moll which can become infected and cause a stye to form
5. Lids are supported by a tarsal plate, containing lipid - secreting meibomian (tarsal) glands that open the lid margin

Question 16

What are distichiae

Answer 16

abnormal hairs growing from the meibomian gland openings. They may cause corneal damage

Question 17

How does the tarsal plate compare in dog to cat

Role of tarsal plate
What gland?

Answer 17

Remember (cartilage) tarsal plate supports the lids and contain meibomian glands.
Dogs relatively poorly developed vs cat

Question 18

Talk anout canthus

Answer 18

1. upper and L lids meet medially and laterally at the medial and L canthus
2. Secured to bone by canthal/ palpebral ligaments. ** expect dog where lateral palpebral ligament poorly developed, function largely replaced by retractor anguli oculi muscle, innervated CN 7, running from lateral canthus

Question 19

What do the medial and lateral ligaments prevent

Answer 19

Palpebral fissure assuming a circular shape

Question 20

How do lids close

Answer 20

contraction of the circular orbicularis oculi muscle, which is innervated by the facial nerve (CN VII) This muscle also surrounds the lacrimal canaliculi and helps squeeze tears through drainage system

Question 21

What muscle lifts the medial upper eyelid?
What muscle is the main elevator of the upper lid?
Innervations

Answer 21

1. medial levator anguli oculi muscle ( inn by facial nerve 7 CN VII)
2. Main elevator of UL - levator palpebrae superioris CN 3 (oculomotor)

Question 22

Where does sensory innervation to the lids come from

Answer 22

1. via CN V (trigeminal)
2. nerve branches – the ophthalmic branch innervates most of the upper lid and the medial part of the lower lid
3. maxillary branch innervates the lower lid and joins with the ophthalmic branch to supply the lateral portion of the upper lid.

Question 23

How does sclera vary between species

Answer 23

The white of your eye

varying amounts of scleral exposure depending on species. Dogs expose a little sclera laterally, cats show very little sclera

Question 24

What is a lacrimal caruncle

Answer 24

Pink think medially in eye. Horses have

Question 25

What is inwards rolling of the lid?

Answer 25

PALPEBRAL ABNORMALITIES

1. caused by overlong lids and palpebral fissures
2. Entropion is inwards rolling of the eyelid, bringing haired skin into contact with the globe.
3. This traumatises the globe, leading often to corneal ulceration
4. think lambs!
5. problem exaggerated by loose medial/lateral canthal ligament

Question 26

Opposite of entropion

Answer 26

PALPEBRAL ABNORMALITIES
Ectropion
1. lid margin is loose and not in contact with the globe, so spreading of tears and removal of debris is ineffective
2. problem exaggerated by loose medial/lateral canthal ligament

Question 27

meibomian glands

Answer 27

Located under holes in U and L margin

produce lipid component of tear film - stops tears evaporating too quickly

Question 28

Dog prevents with ulcer on cornea. no trauma

Answer 28

Check if cilia growing from meibomian gland openings/ any other abnormal spots

Question 29

Facial nerve paralysis how does this present

Answer 29

droopy eyelid
unable to blink in response to facial stimuli
can still open eye

Question 30

Occulomotor deficit

What CN is this?

Answer 30

droopy eye

CN3

Question 31

How to test if nerves for blinking are working or not

Answer 31

tap medial and laterally

Question 32

Tear film portions come from…

Answer 32

1. Lipid portion part – meibomium gland- reduces evaportation and creates barrier at lid margin
2. Mucous/ Mucin layer – from conjunctival goblet cells, mixed with and stabilises aqueous layer
3. Aqueous layer portion (not humour) from lacrimal gland and 3rd eyelid – lubrication, protection and nutrition of corneal, limbal and conjunctival epithelium

Question 33

Where are meibomium glands found?

Answer 33

Tarsal plate

Question 34

Location of lacrimal caruncle in horse

Answer 34

medial canthus, like humans

Question 35

Why do rabbits have a vulnerable lacrimal drainage system?

Answer 35

Only one lacrimal punctum instead of 2 ALSO nasolacrimal duct druns over cheek teeth. Problems with CT impacts NLduct. Rabbit with sticky eyes, check mouth
Also NLduct has 2 sharp bends