Ophth - posterior segment conditions Flashcards
What are some normal fundus variations?
Presence or absence of tapetum
Colour of tapetum
Amount of pigment of retinal pigment epithelium of non tapetal fundus
When does the tapetum tend to be blue?
When it is not fully developed - in puppies and kittens
Where is retinal pigmented epithelium found?
In the non tapetal fundus
Where is the optic disc found?
Can be in the tapetal or non tapetal fundus - varies between individuals
What is the difference between cats and dogs optic discs?
Cats - non myelinated, usually looks grey
Dogs - more white, can see blood vessels on it
What can cause blindness?
A lesion anywhere along the visual pathway can cause blindness
eg. Ocular media opacity - eye itself
Retinal dysfunction
Optic nerve dysfunction
Optic tract lesion
Chiasm lesion
Visual cortex lesion - in brain
Hoe can you test an animals retina?
Electroretinography
Pupillary light reflex
Dazzle reflex
Menace response
How does electroretinography work?
Electrode in gold contact lens is placed on eye, and needles are placed on head to ground and act as reference electrode
Shine measured intensity flash into eye
Electrode in contact lens collects retinal response
Measures electrical activity/action potential of stimulus
How does the pupillary light reflex work?
Light shone in one eye will cause both irises to constrict
Photoreceptors send impulse to chiasm - some run down other side down oculomotor nerve
What is the dazzle reflex?
Similar to pupillary light reflex but facial nerve causes eye to blink/squint
What is the menace response?
Advancing hand causes blink
When is the menace response developed in puppies and kittens?
Not until 8-14 weeks
What does cateracts look like on ocular ultrasound?
Opacity in the lens - hyperechoic (white) lens
What does detached retina look like on ocular ultrasound?
Like a seagull
What is a persistent hyaloid system?
Where the neonatal system hasnt regressed which can cause lens abnormalities, cateract or bleeding in the vitreous humour
What are two causes of vitreal opacity/haze?
Asteroid hyalosis
Synchisis scintillans
What is asteroid hyalosis? What does it look like?
When calcium phospholipids are suspended in the gel at back of the eye
Look like a starry sky - dont move
What is synchisis scintillans? What does it look like?
When mobile cholesterol particles in liquefied vitreous
Looks like a snow globe
What is vitreal syneresis? What can it lead to?
When the vitreous liquefies - can lead to retinal detachment
What is retinal dysplasia?
Abnormal retinal development during embryonic growth - dark lines/folds in the retinal sheet where layers have been incorrectly laid down
What are the two types of retinal dysplasia?
Multifocal
Total
What does retinal inflammation look like?
Hyporeflective tapetal lesions - dark patches
White/cream lesions in non-tapetum
What is active chorioretinitis?
Inflammation of the retina and choroid (closely associated structures)
What does active chorioretinitis look like?
Infiltrates of protein/cells across damaged blood retinal barrier
Multifocal bullous retinal detachments - look like blisters
What causes the bullous retinal detachments in active chorioretinitis?
Inflammatory fluid accumulating under the retina and pushing it off the choroid
What does inactive chorioretinitis look like?
Hyperreflective tapetal lesions
Pigmentation of the tapetum
Depigmentation in a non tapetal lesion
Why do you get hyperreflexctive tapetal lesions in inactive chorioretinitis?
The retina gets thinner
Can partially reattach - tapetum appears shinier in these areas as there is less tissue between you and the tapetum
What most commonly causes retinal haemorrhage?
Systemic hypertension - hypertensive retinopathy
What does hypertensive retinopathy cause?
Vascular tortuosity - wiggly
Vessel bleeding
Haemorrhages
Multifocal bullous detachments
What are the different types of retinal detachment?
Serous
Epulsive haemorrhage
Subretinal cellular infiltrate
Granuloma
Solid tissue/tumour
Tears/holes
What disease can cause retinal degeneration?
Inherited progressive retinal atrophy
What changes to the retina does inherited progressive retinal atrophy cause?
Hyperreflectivity - thin retina
Vascular attenuation - blood vessel atrophy as cells dying so dont need blood
Night blindness
What happens in inherited progressive retinal atrophy?
Rods and cones die - rods first
What is sudden acquired retinal degeneration (SARDs)?
Acute degeneration of the retina for unknown cause
There is no electrical activity in neurosensory retina
What does total retinal atrophy look like?
No blood vessels remaining
Very hyperreflective tapetum
What drug can cause total retinal atrophy?
Enrofloxacin
What is optic coloboma?
Missing tissue - the optic nerve did not develop
Blood vessels dont go all the way onto the optic nerve because its not there - disappear down it like a waterfall
What species are prone to optic nerve disease?
Collies - collie eye anomaly
What is collie eye anomaly?
Chorioretinal dysplasia
Bizarre branching vessels
Can cause haemorrhage and vision loss
What is optic neuritis? What does it look like?
Inflammation of the optic nerve head - looks fuzzy
What is papilloedema?
When the optic nerve head is pushed forward secondary to increased intracranial pressure
No exudate, cells, blood, blood vessels look straight as if they are climbing a hill
What is glaucoma?
Increase intraocular pressure - due to reduced draining of aqueous humour through the iridocorneal drainage angle
What is the normal intraocular pressure in the eye?
10-25mmHg
What intraocular pressure suggests glaucoma?
More than 30mmHg
What intraocular pressure suggests uveitis?
Less than 10mmHg
What are two inherited causes of primary canine glaucoma?
Goniodysgenesis - pectinate ligament dysplasia
Primary open angle glaucoma (POAG)
What are the clinical signs of glaucoma (non-chronic)?
Pain
Blindness
Conjunctival congestion
Episcleral hyperaemia - red eye
Corneal oedema - blue tint to eye
Mydriasis - dilated pupil
What are the clinical signs of chronic glaucoma?
Globe enlargement
Secondary lens luxation
Cataracts
Phthisis bulbi - shrunken globe due to degenerate ciliary body not producing aqueous
How do you diagnose glaucoma?
Tonometry - measure intraocular pressure
More than 30mmHg - suggests glaucoma
What are the different types of tonometers?
Indentation tonometry - cheap but tricky to use
Applanation tonometry - expensive, accurate but need local
Rebound tonometry - expensive, accurate, no local needed
What can you use to treat glaucoma medically?
Carbonic anhydrase inhibitors
Beta blockers
Prostaglandin analogues
How do carbonic anhydrase inhibitors treat glaucoma?
Inhibit the ciliary body from creating bicarbonate ions so cant draw water into aqueous
So reduce aqueous production
How do beta blockers treat glaucoma?
Reduce aqueous production
How do prostaglandin analogues treat glaucoma?
Increase aqueous outflow - open an outflow route for the aqueous through the uveoscleral outflow & out into more superficial blood vessels
When should you not use prostaglandin analogues to treat glaucoma?
In uveitis - pgs are pro-inflammatory
In cats - dont work
What surgical treatment is there for glaucoma patients that can still see?
Gonioimplant - increase outflow
Transcleral cyclophotocoagulation - decrease output of aqueous
What surgical treatment is there for glaucoma patients that are blind?
Enucleation
Evisceration and intrascleral prosthesis - prosthetic eye
