the ocular surface Flashcards
what makes up the ocular surface
- conjunctiva
- corna
conjunctiva
- most exposed of all the mucous membranes
- relatively transparent
- blood vessels, globlet cells, lymphoid tissue, collagen and elastin
- variable amount of melanosis normal in dog
conjunctiva innervation
ciliary nerves
what does the conjunctiva line
eyelids, third eyelid, and reflects onto the globe
different parts/areas of conjunctiva
- palpebral conjunctiva
- nicitating membrane
- bulbar conjunctiva
- conjunctival fornix
layers of conjunctiva from superficial to deep
- bulbar conjunctiva
- episclera (loose fibrous elastic tissue)
- tenon’s capsule (thin fascial sheath)
- sclera
function of conjunctiva
increases mobility of eyelids and globe
- freely moveable except at limbus
- redundancy at fornix
barrier against microorganisms and prevent desiccation of cornea
- muscin produced by globlet cells
- traps debris
what is the cornea
- transparent front of outer fibrous tunic
- avascular - pre-corneal tear films
what is the limbus
- cornea meets the sclera
- transition zone between cornea and conjunctival epithelium
cornea innervation
ciliary nerves
histology
epithelium
- firmly adhered to underlying stroma
- 6-15 layers
stroma
- regularly arranged collagen
- avascular
single endothelial cell layer
- descemet’s membrane
transparency
cornea
- essential for vision
- results from (avascular, regularly arranged collagen, relatively dehydrated - endothelial Na, K-ATPase pump, epithelial barrier)
function of cornea
refraction of light
- smooth outer surface
- continuously replaces epithelium
- pre-corneal tear film
main barrier to penetration by micro-organisms
slit lamp biomicroscope
use to look at changes in corneal transperancy and integrity
SD-OCT (spectral domain optical coherence tomography)
- accurate evaluation of each component of cornea
- real-time evaluation with absence of corneal contact
conjunctival disease
- very common
- conjunctival vessels sensitive to irritation, easily congested
- conjunctivitis (most common)
corneal disease
- trauma - corneal ulcer
- tear film abnormalities - dry eye (KCS)
- corneal edema
- keratitis
- results in loss of transperancy, integrity, distrubed vision
loss of transparency
- corneal pathology results in loss of transparency
- disturbed vision
conjunctiva and cornea diagnostic tests
- schirmer tear test
- fluorescein dye
- rose bengal stain
- cytology, culture
- biopsy
- PCR
- corneal sensitivity and thickness
fluoresceine dye
- corneal integrity
- dye is hydrophilic (readily binds to exposed stroma, repelled by epithelium)
- corneal ulcer stains green
rose bengal stain
- devitalized epithelial cells (stain pink)
- FHV-1 dendritic ulcers
cytology
- frequently useful
normal
- sheets of epithelial cells
- large, round homogenous nuclei
- abundant cytoplasm
abnormal
- examine for cellular alterations, bacterial and inclusion bodies
0.5% proparacaine
- local anesthetic (dogs - 15-25 min, cats - 5 min)
- refrigerate
- epithelial toxic
culture
- bacteria cultured from conjunctival sac normal animals
- reserve for persistent, recurrent or non-responsive conjunctivitis
corneal sensitivity
- evaluates ophthalmic branch of CNV
- esthesiometer (semi-quantified device, sensitivity in different areas)
corneal thickness
- pachymetry
- simple, quick way to measure corneal thickness
pre-corneal tear film (PCTF)
- nourish, lubricate, cleanse ocular surface
- optical activity
- antibacterial
- alterations in tears dynamics (compromise function, inflammation, metaplasia, necrosis of ocular surface cells)
PCTF secretion
- tri-laminar fluid comprises (lipid, aqueous, mucin)
- complex interactions between layers
- transparent, tri-laminar tear film
function of aqueous layer
serves metabolic needs of avascular cornea (lubricates and cleanses
what is the aqueous layer produced by
- orbital lacrimal gland (majority)
- gland or third eyelid/accessory
aqueous layer innervation
by both sympathetic and parasympathetic
lipid layer
- meibomian glands (cholesterol waxy lipids
- retards evaporation
- contributes to tear film stability
mucin layer
- conjunctival globlet cells (mucin, conjunctival fornix)
- promotes smooth ocular surface
- traps bacteria, foreign material
- contributes to tear film stability
tear drainage
- lacimal puncta (tear ducts)
- slit-like openings at mucocutaneous junction upper and lower lids
- only inferior punctum rabbits
- enter puncrta by combination of gravity, capillary pull, and pump mechanism
nasolacrimal duct system
- tears flow through canalicular system, which coverges at lacrimal sac (lacrimal bone)
- continues as nasolacromal duct to nasal opening (puncta)
- nasal puncta (located in nasal vestibule at margin or alar fold)
PCTF disorders
- desiccation, inflammation of conjunctiva and cornea
- KCS (aqueous deficiency, dry-eye is most common ocular disease in dogs)
- melbomianitis/bleparitis (loss of tear film stability)
tear drainage abnormalities
- tear overflow (epiphoria)
- obstruction of nasolacrimal duct system (foreign body)
PCTF diagnostic tests
- schirmer tear test
- tear film breakup time
schirmer tear test
- measures volume of aqueous tears
- dog 15-20 mm/min
- values vary with age, breed
- cat - often lower than expected
- compare both eyes
- diagnostic test of choice for KCS
tear film break up (TBUT)
- lipid and mucin abnormalities - tear film stability
- time taken for first “dry spot” to appear on cornea after complete blink
- cats - 12-21 sec, dog - 20sec
abnormalities of drainage
- nasolacrimal patency (jones test, nasolacrimal duct flush)
- dacryocystohinography
jones test
- apply fluorescein and wait 4-10 min for it to appear in nares
- positive test = nasolacrimal duct system patent
- negative test = suspicious for obstruction
flush nasolacrimal duct
- syringe attached to lacrimal cannula or blunted needle
- cannulate superior punctum
- negative test confirms obstruction
