lens

Question 1

lens anatomy

Answer 1

derived from surface ectoderm

clear, colorless biconvex structure

refraction and accomodation

lens capsule, anterior epithelium, lens fiers, zonules

Question 2

components of lens

Answer 2

lens capsule-selective permeability, barrier function

anterior epithelium-mitotically active throughout life, source of lens fibers

cortex-outermost, younger portion of lens

nucleus-innermost, oldest portionof lens

equator-periphery of lens, zonular insertion

Question 3

Lens fibers

Answer 3

dervied from anterior epithelium

elongate and lose organelles-U shape

make up the cortex and nucleus

orderly arrangement

continuous growth

Question 4

Y suture

Answer 4

not actual structures but where the lens ribers meet

upright Y anteriorly, inverted Y posteriorly

Question 5

how does a lens age

Answer 5

lens increasingly compacted over time

newest fibers form in outer portion of lens

older fibers compact into nuclear–>nuclear sclerosis

Question 6

zonules

Answer 6

originate from ciliary body and insert onto lens capsule at equator

Question 7

factors contributing to lens transparency

Answer 7

barrier function of lens capsule

relative dehydration

lack of blood vessels

lack of pigment

loss of organelles from lens fibers

orderly arrangement of lens fibers

Question 8

lens nutrition

Answer 8

aqueous humor-glucose

anaerobic glycolysis-hexokinase converts ot lactic acid

small amount of aerobic glycolysis

Question 9

examination of lens

Answer 9

must dilate

retroillumination

slit beam

Question 10

lens opacification

Answer 10

heterogenous bright white appearance of purkinje 2

purkinje 3 not visible due to density of lens opacity

Question 11

slit beam

Answer 11

disruptionof homogenous beam anywhere between images 2 and 3 indicates lenticular lesion

absence of images indicates absence of structure

Question 12

Nuclear sclerosis

Answer 12

density of nucleas increases with age due to continuous growth of lens fibers

newest fibers formed in outer cortex older fibers compacted into nucleus

circular central lentcular clouding

does not block light-can see tapetal reflection clearly

used transillumination after pupillary dilation

Question 13

Cataracts

Answer 13

opacity within the lens

interferes with light transmission

opacity may be extremely small and cause no visual disturbance or may occupy the entire lens and cause blindness

Question 14

causes of cataract

Answer 14

anything that alters lens nutrition, energy metabolism, protein metabolism, osmotic balance, physical structure

inherited-#1 in dogs, Uveitis #1 cats, horses

degenerative

Metabolic disease

nutritional

trauma

toxins

glaucoma

radiation

Question 15

classification of cataract

Answer 15

based on size/stage of development-incipient, incomplete/immature, complete/mature, resorbing/hypermature

positions within lens-capsular, subcapsular, cortical, nuclear, equatorial

age of onset-congenital, juvenile, senile

etiology

Question 16

incipient cataract

Answer 16

occupies <10-15% of the lens

usually no detectable visual compromise

common in olders dogs

Question 17

incomplete/immature cataract

Answer 17

larger than incipient

tapetal reflection still visible

may or may not be associated with visual compromise

Question 18

complete/mature cataract

Answer 18

occupies all of the lens

tapetal reflection not visible

results in blindness

Question 19

resorbing/hypermature cataract

Answer 19

leakage of lens material through capsule into anterior chamber

loss of lens contents causes capsule to wrinkle

also see mineralization

occurs with chronicity

Question 20

morgagnian cataract

Answer 20

extensive resoprtion of lens cortex

cortex liquefies, allowing harder nucleus to sink

Question 21

degenerative/senile cataracts

Answer 21

degeneration of lens associated with aging

by 9.4 yeras, 50% of dogs have some degree of cataract

progression is very slow

Question 22

Diabetes mellitus cataracts

Answer 22

always bilateral

occurs in most diabetic dogs, rarely in cats

increased aqueous glucose saturates hexokinase in anaerobic glycolysis

excess glucose metabolized by aldose reductase in sorbitol pathway

build up of sortibol in lens creates osmotic gradient

associated with more dramatic uveitis

Question 23

nutritional cataracts

Answer 23

milk replacer-arginine deficiency, bilateral nuclear cataracts, usually triangular in shape, may become less visible over time as nucleas compacts

hypocalcemia-multiple incipient cataracts

Question 24

inherited cataracts cataracts

Answer 24

purebred dogs predisposed

usually recssive inheritance

other causes of cataracts excluded

most common etiology in dogs

Question 25

uveitis cataracts

Answer 25

disrupts nutrition to lens

inflammatory material and synechiae can also decrease lens transparency

most common cause of cataracts in cats and horses

Question 26

glaucoma cataracts

Answer 26

impaired lens nutrition

Question 27

trauma cataracts

Answer 27

blunt trauma via uveitis

penetrating trauma causes disruption of fiber arrangement, fluid influx, inflammation

Question 28

sequelae to cataract

Answer 28

vision impairment/blindness

lens-induced uveitis and complications of uveitis

glaucoma, lens luxation, retinal detachment

Question 29

phacolytic uveitis

Answer 29

slow leakage of lens protein

most obvious with hypermature/resorbing cataract

chronic, low-grade inflammation

Question 30

phacoclastic uveitis

Answer 30

sudden release of lens protein

secondary to penetrating ocular trauma, lens rupture

rapid progression, severe inflammation

requires rapid, aggressive intervention

Question 31

tx of cataracts

Answer 31

referral to ophthalmologist

monitoring

anti-inflammatory medications

phacoemulsification and intraocular lens implanation

Question 32

to maximize surigcal success for cataracts

Answer 32

perform surgery early in disease process

preop control of uveitis

intensive postop anti-inflammatory meds

diligent post op reevaluation

Question 33

lens subluxaiton

Answer 33

partial dislocation of lens s a result of degeneration of some but not all zonules

slight shifting of lens position

Question 34

luxation

Answer 34

degeneration of all zonules resulting in complete dislocation of lens

lens freely moves around within eye

Question 35

lens subluxation and luxation clinical signs

Answer 35

anterior lens luxation results in acute evidence of ocular pain

subluxation and posterior luxation may be asymptomatic

blepharospasm

epiphora

episcleral congestion

cloudy apperance to eye-corneal edema

cataract

Question 36

lens subluxation and luxation examination findings

Answer 36

aqueous flare

IOP may be elevated

vitreous in anterior chamber

tilted purkinje image 2

less distance between purkinje 1 & 2

more distance between purkinje 1 & 2

absence of purkinje 2

buphthalmos

visualization of equator

iridonesis

phacondonesis

Question 37

Answer 37

aphakic crescent

Question 38

causes of lens (sub)luxation

Answer 38

primary lens subluxation and luxation

secondary lens-uveitis, glaucoma, age-related degeneration, severe ocular trauma

Question 39

consequences of (sub)luxation

Answer 39

may occur acutely or in long term

glaucoma

uveitis

retinal detachment

refferal

Question 40

management of lens subluxation if shifting is small

Answer 40

micromotions of loose lens can induce uveitis

topical anti-inflammatory medications

continued monitoring for progression

miotic therapy

Question 41

management of lens subluxation-larger aphakic crescent or visible iridodonesis or phacodonesis

Answer 41

phacoemulsification and intraocular lens implanation

Question 42

intracapsular lens extraction

Answer 42

urgent referral

50% dogs visual and glaucoma free 1 year post op

enucleation

170-180 degrees corneal incision made along dorsal limbus

cornea is elevated and lens extracted

Question 43

latanoprost

Answer 43

encourage trapping of lens in vitreous cavity

concurrent anti-inflammatory therapy