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Describe fluid dynamics of the eye
- Aqueous humor flow:
- from ciliary body through pupil >
- into anterior chamber >
- through trabecular meshwork >
- into Schlemm's canal >
- into episcleral venous system
What is the uvea?
- Nourishing vascular tunic of the eye.
- Comprised of anterior uvea (iris, ciliary body) and posterior uvea (choroid)
- Failure of the globe to develop
- Technically often microphthalmia (vestigal remnant)
- very rare and usually bilateral
- Failure of division of optic stalk
- Example: toxic plant ingestion in pregnant ewes
- Defect in closure of optic fissure
- Retina can grow outward through defect > retrobulbar cyst
- This is the hallmark of Collie eye anomoly but is seen in other breeds and species
Persistent pupillary membranes
- Young dogs
- Persistent tunica vasculosa lentis adheres to anterior surface of lens > anterior polar lens opacity
- Breed predispositions: Basenjis, mastiffs, chows, Yorkshire terriers
- "Hairy eyeball"
- Plaque of haired skin in place of normal peripheral cornea
- Etiology unknown
- Clinical significance dependent on amount of irritation hair causes
- Bulbar conjuctiva>cornea
What is Glaucoma?
- Group of diseases
- Sustained IOP - compression of optic nerve & retina leads to blindness
- Dogs>>Cats, Horses
Pathophysiology of glaucoma
- Results from impaired aqueous outflow
- Primary: congenital, abnormal filtration angle - goniodysgenesis
- Secondary: Lens luxation, intraocular neoplasia, pre-iridal fibrovascular membrane (fibrosis between lens and Descemet's membrane)
Glaucoma: morphological changes
- Buphthalmos (megaglobus)
- Histologically: thin sclera, corneal ulcers, corneal oedema when IOP exceeds capacity of corneal endothelium Na+ pump
- Corneal striae: Breaks in Descemet's membrane secondary to corneal stretching - stain with fluoresceine, serpentine
- Corneal striae
- breaks in Descemet's membrane due to stretching of cornea
- Seen on clinical exam as serpentine tracts of deep corneal stromal opacity
- Morphologic change due to glaucoma
Sequelae of glaucoma
- Fixed dilated pupil - atrophy of iris & ciliary body
- Cataracts - stagnant aqueous flow, inadequate nutrients & waste buildup
- Retinal atrophy & degeneration
- Optic disc cupping
- Secondary glaucoma
- Metastatic lymphoma within anterior uvea and anterior chamber occluding trabecular network
List the disorders of extraocular structures
- Eyelids: entropion, ectropion
- Eyelashes: ectopic cilia, distichiasis
- Glands: cherry eye
Disorders affecting the cornea?
- Keratoconjunctivitis sicca
- Corneal ulcers
Disorders affecting the iris?
Disorders affecting the lens?
Disorders affecting the fundus?
- Retinal dysplasia
- Optic neuritis
- Retinal detachment
- Squamous cell carcinoma
- Hereford cow, medial limbus is most common location
- Corneal oedema adjacent to margin of carcinoma
Non-malignant melanoma: cutaneous melanocytoma
- Malignant melanoma
- Location matters!
- Ocular sarcoma
- Stromal sarcoma surrounding remnant of ruptured lens
What are the most common causes of damage to cornea?
3 main responses to corneal disease
- Adaptive cutaneous metaplasia: KCS, pigmentary keratitis, chronic eyelash irritation, chronic glaucoma
- Epithelial/stromal necrosis: feline herpesvirus, Moraxella bovis, Pseudomonas, mycotic keratosis in horses
Characterised by neovascularisation and cell infiltrates
- Corneal sequestrum
- Brown pigment probably porphyrins in tear film
- Corneal oedema, vascular ingrowth
- Infectious keratoconjunctivitis
- Moraxella bovis, common in summer
- Photophobia, blepharospasm, lacrimation
- Gross lesions: corneal oedema, vascularisation, ulceration, blindness
- Infectious bovine rhinotracheitis virus (BHV)
- shallow corneal ulcers
- foci of suppurative stromal keratitis
- conjunctival hyperaemia
- circumferential superficial vascular ingrowth towards central ulcers
- Anterior: Adhesion of iris to cornea
- Posterior: Adhesion of iris to lens
scarring or residual granulation tissue
What is hypopyon?
- Pus in the eye
- Accumulation of neutrophils and fibrin that settles ventrally in anterior chamber
What is aqueous flare?
Increased protein content within aqueous chamber, causing opacity
What is hyphema?
Haemorrhage in anterior chamber
What is anterior uveitis/iridocyclitis
Inflammation of iris and ciliary body
Equine recurrent uveitis: "Moon blindness"
- Frequent cause of blindness in horses
- Delayed type hypersensitivity reaction to Leptospira infection - thought to cause autoimmune response due to similarity in epitopes on bacteria and corneal/lens proteins
Cause of cataracts
- Opacity of lens
- retinal detachment
Pathogenesis of cataract formation in diabetics
Hyperglycaemia (>90mg/dl) saturates hexokinase in glycolysis pathway in lens, glucose shunted to sorbitol pathway, accumulation of sorbitol which osmotically attracts water, causes hydropic degeneration & rupture of lens fibres
What are the ocular manifestations of systemic hypertension?
- Recurrent intraocular haemorrhage
- Retinal detachment
What are the ocular manifestations of mycotic infections?
- Chorioretinitis +/- retinal detachment
- Granulomatous uveitis
What are the ocular manifestations of diabetes mellitus?
- Cataracts (especially in dogs)
- Diabetic retinopathy (microaneurisms)
What are the ocular manifestations of viral infections?
CDV - conjunctivitis, KCS, optic neuritis & retinitis
What are the ocular manifestations of septicaemias?
Fibrinous, suppurative, haemorrhagic
What are the ocular manifestations of DIC
What are the ocular manifestations of neoplasias
- Retinal detachment