Chapter 124: Eye Flashcards
What is the primary function of the eyelids?
Protect the ocular surface.
What (4) functions do the eyelids perform to protect the ocular surface?
Provide mechanical barrier
Secrete lipid portion of tear film
Sweep away foreign bodies
Spread tear film and direct it to puncta
Which eyelid (superior or inferior) is more mobile in dogs and cats?
Superior
What muscle lowers the inferior eyelid?
Malaris mm.
What (4) muscles raise the superior eyelid?
Levator anguli oculi
Levator palpebrae superioris
Müller’s
Frontalis
What sphincter-like muscle brings the eyelids together?
Orbicularis oculi
Levator palpebrae superioris and Müller’s are the only muscles of the eyelid not controlled by the facial nerve, what is their innervation?
Oculomotor (3)
Sensory to lids and cornea is all Trigeminal
What ligaments stabilize the eyelid commisures?
Medial and lateral canthal ligaments (also prevent fissure from being circular).
Why do ophthalmic surgeons like the conjunctiva?
It is redundant/abundant and rather loosely adhered - easy to biopsy and graft with.
What are the four parts of the conjunctiva?
Palpebral
Bulbar/palperbral sides of the nictitans
Conjunctival fornix
Bulbar conjunctiva
Lymphoid follicles in the conjunctiva are found where?
Tenon’s capsule / the substantia propria subadjacent to the epithelium.
From a surgical standpoint, the most important property of the conjunctiva is its’ what?
Sectility - consistency that allows it to be cut smoothly with a knife.
What are the two planes of the conjunctiva?
Between epithelium and Tenon’s capsule (grafts from here)
Deeper between Tenon’s capsule and the sclera (tumor resection and transconjunctival enucleation).
Care must be taken to be gentle with the conjunctiva. What are some (6) ways to do so?
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
Many corneal diseases appear surgical, but may be better treated medically or with neglect, why?
Scarring is actually less and cornea transparency is important for vision.
What is normal corneal thickness in dogs and cats?
0.5mm
How thick is the nonkeratinized stratified squamous epithelium of the cornea?
6 cells
What are the four layers of the cornea?
Epithelium
Stroma (thickest)
Descemet’s membrane
Endothelium
Why is cornea transparent (6 reasons)?
Nonkeratinized
lack of vessels
lack of pigment
perfect alignment of stromal lamellae
smooth surface from tear film
relative dehydration
Corneal innervation is supplied by what nerves?
Long ciliary nerves, from trigeminal
*Most branches are in anterior stroma/epithelium - maybe why superficial ulcers hurt more
True or false? Dolichocephalic dogs and cats have higher corneal sensitivity/nerve fiber density compared to brachycephalics.
True.
Dogs and cats have what type of orbit?
Open - the bony rim is incomplete.
What (2) tissues are part of the orbit?
Muscles of mastication and soft palate
What is the periorbita?
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.
