External Ocular Pathology Flashcards
Developmental anomalies of the globe
Anophthalmia
Microphthalmia
Cyclopia
Developmental anomalies of globe
Dermoid
Coloboma
Collie eye anomaly
Merle ocular dysgenesis
Anophthalmia
No development of optic vesicle
Usually bilateral
Uncommon - often misdiagnosed as severe microphthalmia
Microphthalmia
Miniature globe in normal sized orbit/socket
Involution following injury to globe
-in utero trauma
-ischemic injury
- infection
Cyclopia*
Single midline globe
If diplication of Intra ocular structures = Synophthalmia - often misdiagnosed
cause of cyclopia
Spontaneous - RARE
Ewe ingests Veratrum califonicum on day 14 of ingestion
Usually other developmental anomalies in other organs
Dermoid
Presence of haired skin in the corneal or conjunctival epithelium
CLIN SIG: depends on degree of corneal irritation caused by hair
Coloboma
Defect resulting from incomplete closure of optic fissure
Can result in outpouching of retina
One in the lesions of collie eye anomaly
Collie eye anomaly
Heritable disease of rough and smooth collies
Multiple concurrent anomalies
- choroid hypoplasia & hyperpigmentation
- posterior Coloboma
- retinal detachment
- microphthalmia
Merle ocular dysgenesis
Merle gene = color dilute
Homozygous dogs have light coat and can have multiple congenital ocular lesions
Merle gene congenital ocular lesions
Microphthalmos
Iris abnormalities: Coloboma, hypoplasia, persistent pupillary membranes
Lens abnormalities: microphakia (small lens), cataract, lens luxation
Sclera Coloboma
Retinal dysplasia or detachment
Extra ocular neoplasia
Squamous cell carcinoma
Meibomian Adenoma
Melanocytic neoplasms
Squamous cell carcinoma
Common in cattle & horses w non pigmented eyelids /conjunctiva exposed to sunlight
Cats: affects eyelids of white faced cats
Dogs = uncommon
Meibomian adenoma
Most common tumor of eyelid in dogs
Meibomia- modified sebaceous gland in eye
Similar to sebaceous adenoma = benign
Melanocytic neoplasms
Eyelid = benign —> melanocytoma
Limbus = benign
Conjunctiva = malignant melanoma
Corneal epithelium
Keeps tear film out of cornea
Corneal endothelium*
Not endothelium, specialized epitheliu, cells
Main job to actively pump out fluid /aqueous humor from the anterior chamber to keep cornea dehydrated
Corneal edema
Fluid in the interstitial space = blindness
Corneal responses to injury
Adaptive cutaneous metaplasia
Epithelial stromal necrosis
Wound healing/repair
Adaptive cutaneous metaplasia
Reponse to persistent mild irritation
Keratinization, epithelial hyperplasia, neovascularization - sprouting of new blood vessels from limbus
Epithelial/stromal necrosis
Response to more severe external injury
Corneal ulceration - secondary edema
Causes of epithelial/stroma necrosis
Dessication (KCS) - keratoconjunctivitis sicca, when eyelids don’t fully cover eye or inadequate production of eye fluid /tears
Mechanical injury
Chemicals
Infection
Keratomalacia
Secondary softening of the cornea, a result of infected corneal ulcer
desemetocele
Deep central corneal ulcer
High risk of rupturing leading to perforating ulcer
Wound healing/repair
Epithelium - sliding of cells followed by mitosis
Stroma - repaired stroma/collagen, not transparent with chronic/larger damage
Feline corneal sequestrum
Increased superficial stromal necrosis compared to normal corneal epithelial injury
Accumulation of brown pigment from tear film into corneal stoma
Central dark brown corneal pigment from iron(porphyria’s)
Persians and Himalayan’s= predisposed
Canine ulcerative keratitis
Endogenous trauma
-eye lash disorders, e troponin, KCS
Can result in secondary bacterial infection
Canine persistent ulcer syndrome
Boxer ulcer
Infectious bovine keratoconjunctivitis
“Pink eye”
Caused by moraxella bovis
Specific virulent strains are able to colonize in cornea
Transmitted by flies, direct contact or fomites
Differentiate from IBR
lesion for pink eye
Corneal ulcer that progresses to suppurative keratomalacia
Similar lesions in sheep/goats - chlamydia, mycoplasma
Feline herpes virus I
Causes keratitis and corneal ulceration
VERY COMMON
Corneal edema is secondary to ulceration
Canine pannus keratitis
German shepherd pannus
Chronic superficial keratitis
Lesions begin at lateral limbus and spreads toward central cornea = bilateral
Response to immunosuppressive therapy
Equine mycotic keratitis
Due to secondary fungal infection of corneal wound (exogenous trauma)
Aspergillus most common (like descemets membrane)
Can progress to suppurative keratomalacia and corneal perforation
Bovine conjunctivitis
Infectious bovine rhinotracheitis
Parasitic conjunctivitis
Infectious bovine rhinotracheitis
Caused by bovine herpes virus I
Does not produce corneal ulceration
Primary differential DX
- infectious bovine keratoconjunctivitis = corneal involvement, pink eye starts in cornea
Parasitic conjunctivitis
Thelazia
Inhabit conjunctival sac and lacrimal duct
Larvae transmitted by flies
Canine conjunctivitis common causes
Allergic disease
Mechanical irritation
Dessication
Nodular granulomatous episcleritis
NGE - canine conjunctivitis
Nodular lesion of episclera or conjunctiva
Proliforation of
- histiocytes
- fibroblasts
- lymphocytes
- Plasma cells
Feline conjunctivitis
Feline herpes virus I
Initial infection in young cats = keratitis (cornea)+ conjunctivitis
Recurring infection in older cats may cause conjunctivitis alone
Chlamydiophila felis
equine conjunctivitis
Habronemiasis
Nematode larvae of habronema deposited in conjunctiva
Lesion = eosinophilic granulomas
