Chapter 124: Eye

Question 1

What is the primary function of the eyelids?

Answer 1

Protect the ocular surface.

Question 2

What (4) functions do the eyelids perform to protect the ocular surface?

Answer 2

Provide mechanical barrier
Secrete lipid portion of tear film
Sweep away foreign bodies
Spread tear film and direct it to puncta

Question 3

Which eyelid (superior or inferior) is more mobile in dogs and cats?

Answer 3

Superior

Question 4

What muscle lowers the inferior eyelid?

Answer 4

Malaris mm.

Question 5

What (4) muscles raise the superior eyelid?

Answer 5

Levator anguli oculi
Levator palpebrae superioris
Müller’s
Frontalis

Question 6

What sphincter-like muscle brings the eyelids together?

Answer 6

Orbicularis oculi

Question 7

Levator palpebrae superioris and Müller’s are the only muscles of the eyelid not controlled by the facial nerve, what is their innervation?

Answer 7

Oculomotor (3)

Sensory to lids and cornea is all Trigeminal

Question 8

What ligaments stabilize the eyelid commisures?

Answer 8

Medial and lateral canthal ligaments (also prevent fissure from being circular).

Question 9

Why do ophthalmic surgeons like the conjunctiva?

Answer 9

It is redundant/abundant and rather loosely adhered - easy to biopsy and graft with.

Question 10

What are the four parts of the conjunctiva?

Answer 10

Palpebral
Bulbar/palperbral sides of the nictitans
Conjunctival fornix
Bulbar conjunctiva

Question 11

Lymphoid follicles in the conjunctiva are found where?

Answer 11

Tenon’s capsule / the substantia propria subadjacent to the epithelium.

Question 12

From a surgical standpoint, the most important property of the conjunctiva is its’ what?

Answer 12

Sectility - consistency that allows it to be cut smoothly with a knife.

Question 13

What are the two planes of the conjunctiva?

Answer 13

Between epithelium and Tenon’s capsule (grafts from here)
Deeper between Tenon’s capsule and the sclera (tumor resection and transconjunctival enucleation).

Question 14

Care must be taken to be gentle with the conjunctiva. What are some (6) ways to do so?

Answer 14

Use fine forceps: Castroviejo, Bishop-Harmon, Colibri
Fine suture (5-0 to 7-0)
Continuous pattern to minimize knots
Short tags/buried knots
Avoid sutures
Pocket technique - sutures on palpebral side of nictitans

Question 15

Many corneal diseases appear surgical, but may be better treated medically or with neglect, why?

Answer 15

Scarring is actually less and cornea transparency is important for vision.

Question 16

What is normal corneal thickness in dogs and cats?

Answer 16

0.5mm

Question 17

How thick is the nonkeratinized stratified squamous epithelium of the cornea?

Answer 17

6 cells

Question 18

What are the four layers of the cornea?

Answer 18

Epithelium
Stroma (thickest)
Descemet’s membrane
Endothelium

Question 19

Why is cornea transparent (6 reasons)?

Answer 19

Nonkeratinized
lack of vessels
lack of pigment
perfect alignment of stromal lamellae
smooth surface from tear film
relative dehydration

Question 20

Corneal innervation is supplied by what nerves?

Answer 20

Long ciliary nerves, from trigeminal

*Most branches are in anterior stroma/epithelium - maybe why superficial ulcers hurt more

Question 21

True or false? Dolichocephalic dogs and cats have higher corneal sensitivity/nerve fiber density compared to brachycephalics.

Answer 21

True.

Question 22

Dogs and cats have what type of orbit?

Answer 22

Open - the bony rim is incomplete.

Question 23

What (2) tissues are part of the orbit?

Answer 23

Muscles of mastication and soft palate

Question 24

What is the periorbita?

Answer 24

Fibrous connective tissue that surrounds the orbit and forms a cone that surrounds the extraocular muscles.

It is continuous with the dura of the optic nerve caudally and Tenon’s capsule rostrally.

Question 25

Lesions inside and outside the periorbita are called what?

Answer 25

Intraconal
and
Extraconal

Question 26

Where is the zygomatic salivary gland located?

Answer 26

The rostral, ventrolateral quadrant of the orbit