The Lens

Question 1

where is the lens located in the eye

Answer 1

posterior to iris

within a depression of the anterior vitrous (patellar fossa)

Question 2

components of the lens

Answer 2

lens capsule

lens fibers (nucleus and cortex)

Question 3

what are the lens zonules

Answer 3

suspensory ligaments of the ciliary body

attach the lens to the equator

Question 4

what is the basic function of the lens

Answer 4

focus light onto the retina to produce a sharp image

Question 5

what is the difference between nuclear sclerosis and a cataract

Answer 5

nuclear sclerosis does not cause clinically apparent visual loss

fundus visible through sclerotic lens

Question 6

what is a cataract

Answer 6

any opacity of the lens or its capsule

Question 7

how are cataracts classified

Answer 7

age of onset

location within the lens

state of maturation

etiology

Question 8

is the opacity is moving in the opposite direction as the eye where is it located?

Answer 8

posterior part of the lens

Question 9

what is an intumescent cataract

Answer 9

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

Question 10

intumescent cataracts is common with

Answer 10

diabetes

Question 11

lens-induced uveitis is often induced by which type of cataract

Answer 11

intumescent

Question 12

what are some causes of cataracts

Answer 12

inherited (most common in dogs)

chronic uveitis (most common in cats and horses)

metabolic

trauma

nutritional

toxic

senile degeneration

Question 13

what is your top differential with inflammatory cataracts due to chronic uveitis

Answer 13

lens- induced uveitis

can be difficult to differentiate

Question 14

what determines how significant the shunting of glucose is in diabetic cataracts

Answer 14

aldose reductase (AR)

dogs have high levels of AR, cats and humans have much lower levels

Question 15

what is the earliest visable change seen with diabetic cataracts

Answer 15

equatorial lens vacuoles

cataracts often progress rapidly to mature, intumescent cataracts

Question 16

what is a common cause of traumatic cataracts

Answer 16

penetrating injury to the lens (cat scratch-becuase cats are dicks)

Question 17

progressive retinal atrophy (PRA) is a type of ______cataract

Answer 17

toxic (endogenous)

Question 18

why is a targeted history important with progressive retinal atrophy (PRA)

Answer 18

dogs with PRA will lose rod photoreceptor function and display night blindness (often before devloping cataracts)

Question 19

what are the 2 types of lens induced uveitis

Answer 19

phacoclastic - truamatic tears (cat scratch)

phacolytic - leakage of lens proteins (diabetes)

Question 20

medical treatment of cataracts

Answer 20

dissolution - no proven medical benefit

anti-inflammatories - help prevent/control lens induced uveitis

Question 21

what is the only proven and effective treatment of cataracts

Answer 21

phacoemulsification

Question 22

lens luxation

Answer 22

complete displacement of lens from the lens zonules

anterior or posterior

Question 23

when does lens luxation/subluxation occur

Answer 23

as a result of loss of zonular ligament support

Question 24

primary lens luxation is an inherited disorder most commonly seen in what breed(s)

Answer 24

canine terrier breeds

Question 25

what is the most common cause of secondary lens luxation in cats

Answer 25

chronic uveitis

Question 26

how does chronic glaucoma cause lens luxation

Answer 26

enlargement of the globe can stretch/break zonular ligaments

Question 27

clinical signs related to lens instability

Answer 27

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

Question 28

common finding with anertior lens luxation

Answer 28

lens equator is visable

details of pupil lost behind the lens

cataract will develope within days

Question 29

treatment of anterior lens luxation in visual or potentially visual eye

Answer 29

medically stabilize - decrease IOP prior to referral (mannitol, carbonic anhydrase inhibitors, NO MIOTICS)

surgical emergency - referral for intracapsular lens extraction

Question 30

subluxation treatment - prevent anterior lens luxation

Answer 30

medical therapy with miotic to trap lens - latanoprost

anti-inflammatories