Lecture 37: Special Senses (Eye) Flashcards
Describe the general embryologic origin of the eye? What is a developmental feature of carnivore eyes?
it is an outpouching of the brain
in carnivores it continues to develop 5-6 weeks after birth
List the 3 layers of the globe and their respective components
outer fibrous layer
- cornea
- sclera
middle vascular layer/uvea
- iris
- clilary body
- choroid
- +/- tapetum lucidum
inner nervous layer
- retina
What are the compartments of the eye and their contents
Aqueous humor in the anteroir and posterior chambers
Vitreous humor
What is the function of the eye
gathers light and transforms it to electrical signals
- it requires a clear cornea
What are the main adnexa structures of the eye
3rd eyelid/nictitating membrane
eyelid (distribute tears)
conjunctiva
- palpebral conjunctiva
- bulbar conjunctiva (covers the globe surface)
orbit (bone)
Describe the capacity for the eye to respond to injury
it has a limited number of responses
it has a limited capacity of healing and regeneration
- except the lens and cornea because when they regenerate their function will decrease
What are important considerations when submitting an eye for histo
use a 25G needle to inject formalin into vitreous humor
- inject next to the optic nerve
immerse the eye in formalin
need rapid fixation because it will autolyse quickly
Define uveitis
inflammation of the uvea
anterior uveitis = iris and ciliary body
panuveitis = all uvea is inflammed
Define the 2 types of opthalmitis
endopthalmitis = inflammation of uvea and all 3 chambers of the eye
panopthalmitis = inflammation of the uvea and all 3 chambers of the eye and sclera
Define hypopyon
neutrophil and fibrin accumulation ventrally in the anterior chamber
Define hyphema
blood in the anterior chamber of the eye
Define phthisis bulbi
end stage eye atrophy and collapse and fibrosis
What are the layers of the cornea
- tear film
- anterior epithelium (renewed weekly - no pigment or keratin)
- corneal stroma (dehydrated paralled collagen strands, low kieratin)
- descemets membrane
- endothelium (no regeneration)
no blood vessels or pigment
What are 3 types of damage that can affect the cornea
dessication
trauma
chemical injury
What are the defense mechanisms of the cornea
blinking and the tear film
- antimicrobial
- removes debris
- there are a few leukocytes
Define keratitis
inflammation of the cornea
Define neovascularization
development of blood vessels from the limbus
What are 2 responses to injury the cornea undergoes
erosion
ulceration (chronic irritation and trauma)
What type of disease can dessication of the cornea cause? What causes it?
dry eye
due to…
- breed related (when eyes don’t fully close)
- glaucoma
- defective eyelids
What is the pathogenesis of chronic keratitis
abnormal tear production or trauma
chronic corneal irritation
stimulates corneal epithelial metaplasia
- development of rete pegs/pigmentation/fibrosis/vascularization
What is the main consequence of superficial ulcers?
corneal edema
How are superficial ulcers repaired
epithelial regeneration
rapid process
What are indolent ulcers? What animals are they common in?
failure of normal ulcer healing
- the new epithelium doesn’t adhere to the stroma of the eye
dogs
What is another name for a melting ulcer? What is the pathogenesis?
keratomalacia
ulceration causes an increase in lytic enzymes resulting in stromal malacia/necrosis
What are the common causative agents of keratomalacia
gram - bacteria
fungi like aspergillus
Give 1 example of keratomalacia in horses
keratomycosis/fungal keratitis due to aspergillus
secondary to immunosuppression or antibiotic use
What is a descmetocele? What are the sequelae?
A deep ulcer that reaches the descemets membrane
causing
- edema
- neovascularization
- perforation
- iris prolapse
Can you use fluoroscein to detect a descmetocele?
No
What is a corneal sequestrum? What animals is it more common in?
A fragment of necrotic cornea
- forms secondary to chronic ulcers
more common in cats (himalayan and siamese prone)
- can also occur in horses and dogs
What is the gross appearance of a corneal sequestrum
brown pigment in the superficial stroma
List 7 possible outcomes/consequences of corneal ulcers
it resolves! (if superficial and the inciting cause is removed)
indolent ulcer
melting ulcer
descmetocele
corneal sequestrum
perforation/iris prolapse
phthisi bulbi
What is the pathogenesis of keratoconjunctivitis sicca?
immune mediated lacrimal adenitis
results in less of a tear film and dessication
What animals are primarily affected by keratoconjunctivitis sicca?
dogs
What are the common sequelae of keratoconjunctivitis sicca
ulcerative keratitis
cutaneous metaplasia of the cornea
What is a dermoid
ectopic hair growth on the cornea or bulbar conjunctiva
What is another name for infectious bovine keratoconjunctivitis? What are the common causative agents?
pink eye
morexella boxis mainly
- also (morexella bovoculi, mycoplasma, and infectious bovine rhinotracheitis)
What animals does bovine keratoconjuctivitis affect? What are 3 main risk factors
small ruminants
- calves > adults
summer
dusty
flies
What are the associated lesions for bovine keratoconjunctivitis
red conjunctiva
edema
central corneal ulceration
+/- corneal rupture, iris prolapse, phthisis bulbi
What animals are most affected by herpesvirus keratitis? What is the causative agent?
cats
- especially kittens in shelters
feline herpesvirus 1
What structures does herpesvirus keratits affect? What are the lesions
feline herpes virus 1
- upper resp
- cornea
- conjunctiva
increase risk of secondary bacterial infection
rhinotracheitis
conjunctivitis
serous/mucopurulent nasal discharge
keratitis only occurs in adults
- corneal ulceration (dendritic branching ulcer) is pathogneumonic
What is another name for chronic superficial keratitis? What animals are most affected?
pannus
dogs
- GSD
- sighthounds
What is the pathogenesis of chronic superficial keratitis? List 2 risk factors
immune mediated destruction due to altered antigens on the cornea
- bilateral
risk =
- high altitude
- solar radiation
What are the gross lesions of chronic superficial keratitis
thick lateral conjunctiva
pigmented corneal plaques
neovascularization
List 3 types of corneal neoplasias
limbal melanocyte neoplasia
squamous cell carcinoma
hemangiosarcoma
What animals are primarily affected by limbal melanocyte neoplasias? What is the cell of origin? What are the gross features?
dogs mainly (also cats)
melanocytes
dark pigment
What are persistent papillary membranes? Why do they occur? What is their significance?
They are congenital and incidental (unless they contact the cornea)
fibrovascular structures that persist in the lens
What animals are uveal cysts most common in? What are uveal cysts?
old dogs
- also cats (burmese)
cysts in the iris or free floating in the anterior chamber that can cause fluid accumulation in the anterior chamber
- benign
- a degenerative change
What is the significance of uveal cysts?
usually no significance
- degenerative change and benign
in golden retrievers and wolfhounds it can predispose to glaucoma and pigmentary uveitis
What is another name for phacoclastic uveitis? What causes it (2 examples)?
lens induced uveitis
ex.
rabbits with Encephalitozoon cunniculi
dogs with diabetes
What is the pathogenesis?
due to trauma and rupture of the lens capsule
- it will develop 2 weeks after trauma
lens protein is seen as foreign
- result in immune mediated inflammation and granulomatous endopthalmitis
What is another name for equine recurrant uveitis? What is it associated with?
moon blindness
it is the #1 cause of glaucoma, cataracts, and blindness in horses
What are the lesions associated with recurrent uveitis
lymphoplasmocytic uveitis
amyloid accumulation in the posterior surface of the ciliary body
What is the pathogenesis of recurrent uveitis
immune mediated
may be associated with leptospira infection
associated to spotted appoloosa breed
List 7 potential consequences of uveitis
synechiae (adhesion betweeen the iris and the lens/cornea)
retinal detachment
cataracts
corneal neovascularization
pre-iridial fibrovascular membrane (granulation tissue forming in front of the iris - it can cause synechiae)
glaucoma
phthisis bulbi
List an example of an infectious agent that can cause uveitis in cattle, cats, and rabbits respectively
cattle - malignant catarhhal fever
cats - FIP
rabbits - E cunniculi
systemic fungi
Compare the most common type of uveal neoplasia in cats and dogs
melanocyte tumors
dog = iris/ciliary body
- benign
cat = diffuse iris melanoma
- malignant
- multifocal hyperpigmentation of iris
- can cause glaucoma
- tx = enucleation
What is the lens’s primary response to injury?
cataract
- increased opacification
can be congenital or acquired
What is the pathogenesis of diabetic cataracts
hyperglycemia causes increased glucose in the aqueous humor
the lens absorbs glucose and converts it to sorbitol
there is a hyperosmotic effect in the lens causing osmotic stress and swelling
lens damage occurs resulting in fibrin and epithelium deposition
= cataracts (bilateral and progressive)
What is the primary sequelae of diabetic cataracts
can cause lens rupture
= phacoclastic uveitis
What is another name for nuclear sclerosis? What causes it?
lenticular sclerosis
due to old age and degeneration
What are the gross lesions of nuclear sclerosis?
cloudy blue discoloured lens
- not opaque
bilateral and symmetrical
Compare nuclear sclerosis with cataracts
nuclear sclerosis
low/no impact on vision
- can still see the tapetum lucidum reflection
cataracts
- vision impairment
- wont see the tapetum lucidum reflection
Compare the 2 types of lens luxation
anterior luxation is very painful and can increase the risk of glaucoma
posterior luxation has little consequence
they can cause the development of cataracts
What causes lens luxation
either congential or acquired (due to trauma or glaucoma)
What is the main type of lens neoplasia
feline post traumatic ocular syndrome
What causes feline post traumatic ocular syndrome? What is the cell of origin?
secondary to a primary eye trauma
from the lens epithelium
- infiltrative and recognized late in the disease process
How is a normal retina held in place? What layers are most likely to detach?
normally it is held on by the retinal pigmented epithelium by the pressure of the vitreous fluid
detachment usually occurs between the retinal pigmented epithelium and the outer nuclear membrane
What are 2 main causes of retinal detachment?
uveitis
endopthalmitis
What are 2 mechanisms of retinal detachment? What is the consequence?
exudative detachment
- increased vascular permeability resulting in edema pushing the retina off
traction detachment
- fibrin and exudate in the vitreous humor that pulls the retina off
= ischemic degeneration (no nutrients from the choroid
- can also be an artifact of being dead
