Ophthalmology conditions of the lens and retina Flashcards
Lens embryology and anatomy
Forms from ectoderm invagination
Anterior epithelium forms anterior lens capsule
Posterior epithelium forms the lens
SO the lens capsule at front is much thicker than at back
How is the lens kept transparent
Because the lens crystalline proteins have cysteine amino acids with SH groups that attract the right amount of water to keep the lens transparent
- If these aggregate get cataracts
Which part of the lens forms before birth and what grows through life
Lens nucleus forms before birth
Cortical fibres grow through life; lens ageing
How does nuclear sclerosis occur
Due to compaction of the lens nucleus with age causing an increased refractive indec and greying of the tissue
How to look at cataracts with direct distant ophthalmoscope
Use 10 dioptres (this is the anterior segment)
Difference between how a cataract and nuclear sclerosis look on ophthalmoscope
Cataract is solid white; can see spiders web of black across lens
Nuclear sclerosis is a haze; can still see the vessels at the back of the eye
What type of congenital cataracts do we see in cocker spaniels and west highland whites
Anterior capsule opacities because anterior epithelium is abnormally proliferating
What type of non-congential inherited cataract do we see in retrievers
posterior subcapsular cataract that is usually non progressive
How are diabetic cataracts formed
With high glucose in lens, get saturation of hexokinase
–> So gets acted upon by aldose reductase to form sorbitol
Sorbitol has much higher osmotic potential than glucose so sucks water into the lens which rutures the fibres and causes lens to expand
How does progressive post-PRA metabolic cataracts work
Esp in cockers and miniature poodles
Get cataract due to damage of lens by toxic metabolites of lipid peroxidation formed during retinal degeneration
How is sunlight involved in senile cataract formation
Causes photo-oxidation of cysteine AAs in lens proteins, causing disulphide bridgge formation and aggregation of crystallin proteins
= catacts
What is the gold standard cataract surgery
Phacoemulsification
- Make incision into lens, fire ultrasonic water in to break up the cataract
Success rate 80%; but expensive
Why are diabetic cataracts prone to causing lens-induced uveitis
Because excess water causing lens swelling creates micro-fractures in lens capsule (which can’t expand) and allows lens proteins out; causing inflammatory reaction
Criteria for successful cataract surgery
No other ocular disease
No other systemic disaese
What does it suggest if an animal stops wanting to go out at night
May have progressive retinal atrophy; rods are damaged first and these are responsible for night vision
Why do we avoid cataract surgery in cases with retinal detachment
Reomval of lens causes more damage and detachment and can make animal go blind
What are some signs of lens luxation
- Acute glaucoma due to blockage of aqueous drainage
- Aphakic crescent; if lens has gone anterior
- Corneal oedema where the lens has abbutted the cornea
- Iridodonesis (wobble of iris now lacking lens support)
What is primary lens luxation
Where lens luxates due to inherited weakness in the zonules
- Get total detachment of the lens
Terriers have congenital zonule weakness
What is secondary lens luxation
Where globe expands due to glaucoma and zonules are torn due to enlargement so lens comes out of place
–> The lens stays behind the iris so is subluxated
What is Haabs streir
White line in eye due to fracture of descemets membrane as eye has expanded due to glaucoma (can be seen therefore in secondary lens luxation cases)
How to tell the difference between corneal and lens opacity
If the detail of the iris is clear then probably a lens problem
If there is whiteness on front of eye and iris not clear; will be corneal
What does a too thick or too thin retinal vein suggest
Too thick; hypertension
Too thin; retinal degeneration, anaemia etc
Where does detachment in retinal detachment occur
In the virtual space between the photoreceptors and the retinal pigment epithelium
What is retinal dysplasia
An inherted abnormality in retinal development
Can range from streaks, spots to complete detachment
In labradors it is associated with skeletal dysplasia
What is involved in collie eye anomaly
Optic nerve head coloboma
Chorioretinal dysplasia; just see a huge vessel in choroid and white sclera instead of lots of small vessels
+ retinal issues; retinal detachment, haemorrhage
How does generalised progressive retinal atrophy work
= inherited degeneration
Rods have genetic defect so die; then cones die due to oxidative stress as rods not there to use up O2
Present with night blindness progressing to total blindness
Presentation of generalsied progressive retinal atrophy
Hyperreflective tapetum because rods not there to absorb light
Very white optic nerve
Thin retinal blood vessels; BECAUSE high O2 so don’t get stimulation of VEGF cytokines to keep them there normally
Which breed has generalised progressive retinal atrophy NOT been bred out of
PRogressive rod cone degeneration in poodles, labs, cocker spaniels
–> Because don’t present until 5-6 years old and have bred by this time
How can we test for PRA using electroretinography
Use high intensity blue light; rods see this less than a high intensity red light
What causes retinal pigment epithelial dystrophy
Disease of retinal pigment epithelium; causes it to stop phagocytosing and removing photoreceptor debris at end of day
–> Get blobs of photoreceptor debris on retina
+ linked with vitamin E deficiency
What infectious causes can lead to chorioretinal inflammation and localised degeneration
herpes virus
Distemper virus
Visceral larva migrans
Why do we still see a pupillary light reflex in sudden acquired retinal degeneration i.e rods and cones are dead
Because there are opsins in ganglion cells which can do the PLR
What is sudden acquired retinal degeneration
Where an antibody mediated response against a molecule in the phototransduction pathway (recovorin) causes photoreceptor to stay ‘on’ and undergo apoptosis
So see acute blindness
Retina LOOKS normal but there is a flat electroretinogram
What things are associated with sudden acquired retinal degeneration
Increased blood liver enzymes, cushings disease
Small breeds of middle age
What does box carring of retinal vessels suggest
Hypertension
Use amlodipine to reduce systemic blood pressure and prevent retinal detachment
How can anaemia lead to retinal haemorrhage
Vascular endothelium is ischaemic so dysfunctions and can cause haemorrhge
What do grey spots in the retina often with overlying retinal detachment suggest
Posterir uveitis
How does taurine deficiency retinopathy present
Central retinal degeneration and tapetal hyperreflectivity
0 Normalising siet will stop further progression
How can vitamin E deficiency lead to progressive blindness and ataxia
Get deposition of lipofuscin in brain and retina
–> Causes retinal pigment epithelial dystrophy signs
Where do inhertied non-congenital cataracts start from in boston terrior/staffie/mini schnauzer
Suture lines
= progressive
Where do inherited cataracts in retrivers start frmo
POsterior subcapsule
= non-progressive usually
Where do inherited non-congenital cataracts start in adghan, poodle, welshs pringer, GSD
Equator
Progresses to blindness except in GSD doesn’t
What what cause a hyperreflective retina with lear boundaries of the lesion
Infectious causes of chorioretinal inflammation
e.g distemper, herpes virus, visceral larval mirans
