The Lens Flashcards
what are lens sutures?
where mature lens fibers attach end-to-end
what does the lens separate?
anterior from posterior segment
what is aphakic crescent?
space between pupil and lens equator
what are contraindications for pupil dilation?
glaucoma
lens instability
how can you assess for lens clarity?
direct illumination
retroillumination
what does parallax help with?
determining anterior vs posterior lesions
what is nuclear sclerosis?
aging change
increased lens fiber density scatters light
lens fibers are normal but there are more of them
what can cataracts be due to?
increases in water content
changes in protein content
altered nutrition
altered metabolism
oxidative stress
do cats develop diabetes mellitus cataracts?
no
what is a morgagian cataract like?
cortex liquefies faster than nucleus
regains tapetal reflection
has any medication or supplement been shown to reverse cataracts?
no
what are treatments for anterior lens luxation?
lens removal
trans-corneal lens repositioning
enucleation
what are potential consequences of posterior luxation/subluxation in a dog?
glaucoma
retinal detachment
how can you treat Encephalitozoon cuniculi?
fenbendazole
anti-inflammatories
cataract surgery
enucleation
how much of the focusing power does the lens provide?
25%
where are newer cells of the lens as it grows throughout life?
newer on outside
older on inside
how does glucose get to cells in the lens?
diffuses in from aqueous humor
what extends 360 degrees from ciliary body to lens capsule?
lens zonules
what is normal when using a slit beam to evaluate anterior chamber depth?
parallel lines with some space between
what is direct illumination?
uses light to illuminate lesion of interest
what is indirect illumination?
uses tapetal reflection to illuminate lesion of interest
what is parallax?
axis of rotation: anterior vs posterior lesions
how can you identify nuclear sclerosis?
pearly/hazy nucleus but clear cortex of lens
retroillumination to differentiate from cataract
what is a cataract?
any opacity that blocks light passage in the lens
what commonly causes cataracts in dogs?
diabetes
juvenile/inherited
retinal degeneration
uveitis
what normally metabolizes glucose in the lens?
hexokinase enzyme
what does increased glucose in the aqueous humor cause?
aldose reductase enzyme shunts towards sorbitol pathway
sorbitol accumulates and increases osmotic pressure
what happens in intumescent cataract?
diabetes or rapidly progressive juvenile cataract
lens swelling, shallow anterior chamber
lens sutures pull apart
what are equatorial vacuoles indicative of?
impending cataract formation
how is lens induced uveitis managed?
topical NSAIDs, steroids
atropine
oral NSAIDs, steroids (no oral steroids if diabetes mellitus)
what screening should you do prior to cataract surgery?
schirmer tear test
intraocular pressure
electroretinogram
ocular ultrasound
which breeds are predisposed to primary lens luxation?
terriers
australian cattle dog
chinese crested
shar pei
what drug should you avoid with anterior lens luxation in a dog?
latanoprost
what is posterior luxation like in a dog?
often asymptomatic
medical management with miotics to prevent anterior movement
why do cats tolerate anterior luxation better than dogs?
bigger anterior chamber
what is Encephalitozoon cuniculi?
protozoan parasite found inside lens capsule
what is feline ocular post-traumatic sarcoma like?
multiple histologic variants
very aggressive locally
