ocular pathology Flashcards
How to send eyeball to histopathology for best result?
Inject small amount of formalin (0.5 mL) into the vitreous of the eye (preserve retina):
- use 25g or smaller needle for injection
- inject close to the optic nerve
- leave the optic nerve (for orientation)
Location of conjunctiva
inside eyelid covering the sclera to the limbus
What are the potential infectious causes for conjunctivitis in cats?
- Chlamydophila felis
- herpesvirus
Infectious cause of conjunctivitis in bovine
Moraxiella bovis
Non-infectious causes of conjuctivitis
- allergy
- desiccation
What are conjunctivitis often associated with?
corneal disease
How does conjunctivitis react to chronic injury?
become more like skin (keratinization, pigmented)
What is this?
Dermoid
What is dermoid?
- a form of choristoma: normal tissue in abnormal place
- congenital
Why can dermoid be problematic?
can cause secondary corneal injury
What is the most common eyelid tumor of dogs?
Meibomian gland adenoma
What is this?
Meibomian gland adenoma
Where are meibomian gland adenoma commonly found?
eyelid margin
Characteristics of meibomian gland adenoma
- benign
- non- invasive
- cured with excision
What are meibomian adenoma commonly accompanied by?
chalazion: local granulomatous reaction due to leakage og gland contents
Treatment for dermoid
keratectomy
What are the species that are predisposed to conjunctival squamous cell carcinoma?
- poor pigmented breed cattle / horses
Characteristics of eyelid squamous cell carcinoma
- infiltrative
- have metastatic potential
- commonly ulcerative & hemorrhagic
Common location of conjunctival squamous cell carcinoma in cattle
on bulbar conjunctiva at the limbus
What is the common location to find conjunctival squamous cell carcinoma in horses?
third eyelid
What is the most common location to find conjunctival squamous cell carcinoma in cats?
skin of the eyelid
Characteristic of melanocytic tumor on dogs
prognosis depend on location:
- eyelid margin: benign
- conjunctiva: invasive & prone to reoccurrence
- limbus: benign
What are some non-specific responses of the cornea to injury in the corneal stroma?
- neovascularization
- edema
What are some non-specific responses of the cornea to injury in the corneal epithelium?
pigmentation (dogs common)
How are corneal stroma kept in dehydrated state?
Energy-dependent sodium pump:
- in endothelium
- removing solute from the corneal stroma (osmotic gradient)
Tight intra-cellular junction:
- epi- & endothelium
How does cornea get its nutrients if it is avascular?
- rely on passive diffusion of nutrients & oxygen from conjunctival & scleral blood vessel, tear film & aqueous humor
What are the factors that favors healing of the corneal injury?
- one time injury
- shallow defect
- healthy stroma
- no sepsis
- normal tear film
- epithelial promoting growth factors
What are the factors promoting corneal scarring formation
- ongoing injury
- deep defect
- damaged stroma
- sepsis
- numerous neutrophils
- deficient/altered tear film
fibroblast growth factor predominates
Corneal ulcer definition
loss of corneal epithelium +/- some of the stroma
The 4 layers of the cornea
- corneal epithelium
- basement membrane
- Descemet’s membrane
- corneal endothelium
Characteristics of superficial ulcer
minimal corneal stroma affected
Quality of corneal epithelium
hydrophobic
Quality of Decemet’s membrane
hydrophobic
Quality of corneal stroma
hydrophilic
How does fluorescent stain diagnose corneal ulcer?
corneal epithelium is hydrophobic while corneal stroma is hydrophilic
- hence stain sticks to corneal stroma
What do breaks in the corneal epithelium lead to?
stromal edema through absorption of tear film (tear & neutrophil)
What happens if the corneal ulceration is minor?
- corneal epithelium slides over the defect, providing a barrier
- mitosis in 24 h
What is necessary for the healing of cornea to be successful?
corneal epiuthelium must be able to adhere to underlying stroma
What can be the result of deep corneal ulcer?
exposition of the Decemet’s membrane resulting in decemetocele
Why is decemetocele an emergency?
thin cornea prone to rupture
What is keratoconjunctivitis sicca?
dry eye; decrease quantity of tears
What causes keratoconjunctivitis sicca?
auto-immune disease targeting the lacrimal gland
Characteristics of keratoconjunctiva sicca
- potentially progressive
- chronic trauma due to desiccation (epidermalization of the cornea)
- minimal corneal edema of the ulceration
What species are commonly affected by fungal keratitis?
horses
What causes fungal keratitis in horses?
iatrogenic following treatment of a corneal ulcer
What is often the pathogenic agent fro equine fungal keratitis?
Aspergillus spp
What does fungal keratitis often lead to?
keratomalacia
Why are superficial scraping/biopsies usually non-diagnostic of fungal keratitis in horses?
fungus usually found in deep cornea
What does herpesvirus often cause in kittens?
conjunctivitis
What does herpesvirus often cause in adult cats?
keratitis
Common presentation of herpesvirus in cats
- keratoconjunctivitis with purulent discharge
- accompanied by rhinotracheitis
What type of ulceration does herpesvirus cause on the cornea?
multifocal to coalescing punctate ulcer (dendritic ulcer
What causes infectious bovine keratoconjunctivitis
Moraxella bovis transmitted by fly vector & fomite
What can increase the severity of infectious bovine keratoconjunctivitis?
co-infection with IBR
How does bovine infectious keratoconjunctivitis cause corneal ulcer?
- bacteria invade epithelium causing small ulcer
- stromal exposure causes increase in neutrophil at the site
- keratomalacia
- healing via scarring
