Eyelids
Function of the eyelid: Secrete __ portion of tear film
Lipid
True/False - conjunctival biopsy specimens are hard to obtain
False - they can be easily & quickly obtained
T-shaped
- Top of T parallels the free margin of nictating memb
- Shaft perpendicular to free edge
Normal corneal thickness
0.5mm
True/False - In dogs & cats, they have an open orbit
True - the orbital ligament completes the dorsolateral portion of the rim
__ = fibrous tissue thickening surrounding tarsal gland, poorly developed or absent
- Why eyelids are unstable & need to be in contact with ocular surface to maintain shape
Tarsus
2 surgical planes of conjunctiva
1) Plane between conjunctival epithelium and Tenon's capsule (used for harvesting conjunctival grafts)
2) Deeper plane - space between Tenon's capsule & sclera (used for tumor resection and transconjunctional enucleations)
Special feature of cats' nictating membranes vs dogs'
CATS - smooth m bands extending into nictating membrane -> allows it to retract & protrude nictating memb
DOGS - movement of nictating memb is passive when globe is retracted & orbital fat is displaced anteriorly, exposing nictating memb
How many cells thick is the outer layer of the cornea?
~6 cells (simple, nonkeratinized, stratified squamous epithelium)
___ = surrounds all the orbital structures & is a fibrous connective tissue by means of reflections & divisions forms the outer lining of the orbit & a cone that surrounds the extraocular muscles
Periorbita
Nerve that innervates the eyelid muscles
Facial nerve
Type and size of suture commonly used for suturing conjunctiva
5-0 to 7-0 polyglactin or polyglycolic acid on a taper or cutting needle
Posterior subconjunctiva
What is the thickest corneal layer?
Middle layer = stroma = aligned collagen, keratinocytes, fibrocytes, & ground substance
___ fills the interstices of the orbit & serves to cushion the eye and the orbital contents & maintain the eye within the plane of the orbital rim
Orbital fat body
Type of suture material that is best used for eyelid surgeries and why?
Polyglactin (Vicryl)
- Synthetic, absorbable, braided (multifilament)
- Soft when wet (good for apposition of eyelid margins)
Most important property of conjunctiva from a surgical standpoint & define it
Sectility = tissue consistency that allows it to be cut smoothly with a knife
- Ex) On the globe & fornix where conjunctiva is mobile, sectility is low --> hard to dissect this area with precision
Location of the seromucoid gland
Reasons why transparency is possible in the cornea
- Lack of vessels & pigment
- Perfect alignment of stromal lamella with few stromal cells
- Smooth optical surface produced by tear film
- Relative dehydration
Glands associated with orbit:
___ = located in rostral, ventrolateral quadrant of orbit
___ = just caudal to orbital rim in dorsolateral quadrant
Orbital lacrimal gland
1) Which nerve innervates the levator palpebrae superioris and Müller's mm respectively?
2) Which nerve brings sensation to the eyelids and corneal surface?
1) Oculomotor n & sympathetic n
2) Branches of trigeminal n
List the order of conjunctiva from outside (outer eyelids) to inside (globe)
1) Palpebral conjunctiva (most outer)
2) Conjunctival fornix
3) Palpebral side of nictating membrane
4) Bulbar side of nictating membrane
5) Conjunctival fornix
6) Bulbar conjunctiva
Seromucoid gland of the nictating membrane makes ~___% of tear films in dogs
35%
What nerve innervates the cornea?
- Majority of branches are in the anterior stroma & epithelium (why superficial ulcers are more painful than deeper ones)
List the boundaries of the orbit
1) Dorsolateral orbital boundary = muscles of mastication
2) Ventral orbital boundary = soft tissues of soft palate
3) Caudal aspect boundary = bone medially & muscle laterally
4) Caudomedial boundary = nn & aa that supply orbital structures - enter orbit through foramina or fissures through sphenoid bone