The Lens Flashcards
where is the lens located in the eye
posterior to iris
within a depression of the anterior vitrous (patellar fossa)
components of the lens
lens capsule
lens fibers (nucleus and cortex)
what are the lens zonules
suspensory ligaments of the ciliary body
attach the lens to the equator
what is the basic function of the lens
focus light onto the retina to produce a sharp image
what is the difference between nuclear sclerosis and a cataract
nuclear sclerosis does not cause clinically apparent visual loss
fundus visible through sclerotic lens
what is a cataract
any opacity of the lens or its capsule
how are cataracts classified
age of onset
location within the lens
state of maturation
etiology
is the opacity is moving in the opposite direction as the eye where is it located?
posterior part of the lens
what is an intumescent cataract
subtype of incomplete or complete cataract where the lens increase in size by imbibing fluid (becomes swollen)
increased lens size, shallow anterior chamber, separation clefts at y suture
intumescent cataracts is common with
diabetes
lens-induced uveitis is often induced by which type of cataract
intumescent
what are some causes of cataracts
inherited (most common in dogs)
chronic uveitis (most common in cats and horses)
metabolic
trauma
nutritional
toxic
senile degeneration
what is your top differential with inflammatory cataracts due to chronic uveitis
lens- induced uveitis
can be difficult to differentiate
what determines how significant the shunting of glucose is in diabetic cataracts
aldose reductase (AR)
dogs have high levels of AR, cats and humans have much lower levels
what is the earliest visable change seen with diabetic cataracts
equatorial lens vacuoles
cataracts often progress rapidly to mature, intumescent cataracts
what is a common cause of traumatic cataracts
penetrating injury to the lens (cat scratch-becuase cats are dicks)
progressive retinal atrophy (PRA) is a type of ______cataract
toxic (endogenous)
why is a targeted history important with progressive retinal atrophy (PRA)
dogs with PRA will lose rod photoreceptor function and display night blindness (often before devloping cataracts)
what are the 2 types of lens induced uveitis
phacoclastic - truamatic tears (cat scratch)
phacolytic - leakage of lens proteins (diabetes)
medical treatment of cataracts
dissolution - no proven medical benefit
anti-inflammatories - help prevent/control lens induced uveitis
what is the only proven and effective treatment of cataracts
phacoemulsification
lens luxation
complete displacement of lens from the lens zonules
anterior or posterior
when does lens luxation/subluxation occur
as a result of loss of zonular ligament support
primary lens luxation is an inherited disorder most commonly seen in what breed(s)
canine terrier breeds
what is the most common cause of secondary lens luxation in cats
chronic uveitis
how does chronic glaucoma cause lens luxation
enlargement of the globe can stretch/break zonular ligaments
clinical signs related to lens instability
aphakic crescent (crescent shaped area in which the lens in visibly displaced)
iridodonesis (Movement of the iris that occurs secondary to lens instability)
phacodonesis (Movement of the lens that occurs secondary to lens instability)
focal corneal edema (anterior lens luxation)
cataract
common finding with anertior lens luxation
lens equator is visable
details of pupil lost behind the lens
cataract will develope within days
treatment of anterior lens luxation in visual or potentially visual eye
medically stabilize - decrease IOP prior to referral (mannitol, carbonic anhydrase inhibitors, NO MIOTICS)
surgical emergency - referral for intracapsular lens extraction
subluxation treatment - prevent anterior lens luxation
medical therapy with miotic to trap lens - latanoprost
anti-inflammatories
