Lens

Question 1

What makes up the lens anatomy?

Answer 1

Capsule (anterior and posterior)
Equator
Nucleus
Cortex
Zonules

Question 2

Where does the lens get its nourishment?

Answer 2

glucose in the aqueous humor

Question 3

What is a normal aging change of the lens?

Answer 3

Nuclear sclerosis

• normal hardening of lens nucleus with age (~7 years in dogs)
• altered light refraction
• no vision loss

Question 4

What is the pathogenesis of nuclear sclerosis?

Answer 4

Continuous replication of epithelial cells moving to the equator –> lose nucleus –> elongate –> lens fibers

Question 5

What are the different stages of a cataract?

Answer 5

Incipient
Immature
Mature
Hypermature

Question 6

Describe an incipient cataract

Answer 6

< 15% of the lens, good vision

Question 7

Describe an immature cataract

Answer 7

15-90% opacity
Tapetal reflex present
Some vision

Question 8

Describe a mature cataract

Answer 8

100% opacity
No tapetal reflex
Blind

Question 9

Describe a hypermature cataract

Answer 9

Lens fibers resorbing
"Sparkly" appearance
Wrinkling of the lens capsule
Blind
Lens induced uveitis may be present

Question 10

Is there a PLR with cataracts?

Answer 10

Yes - regardless of stage or vision

If there is no PLR something else is going on

Question 11

List some causes of cataracts

Answer 11

Genetic (#1 in dog)
Diabetes Mellitus (dogs only)
Retinal degeneration/ Progressive Retinal Atrophy (PRA)
Uveitis
L

Question 12

What is a cataract?

Answer 12

Opacity of the lens or its capsule

Question 13

Why don’t cats get cataracts from DM but dogs do?

Answer 13

Cats have low aldose reductase (converts glucose to sorbitol)

Question 14

How many dogs with DM will get cataracts?

Answer 14

100%

we can’t control DM well enough

Question 15

What breeds commonly get cataracts from retinal degeneration/progressive retinal atrophy (PRA)?

Answer 15

Labradors

Poodles

Question 16

How does retinal degeneration / Progressive retinal atrophy cause cataracts?

Answer 16

Diffusion of toxic metabolic products through vitreous from retina

Question 17

What is the #1 cause of cataracts in cats and horses? Dogs?

Answer 17

Cats and Horses = Chronic uveitis

Dogs = Genetics

Question 18

What is the pathogenesis of chronic uveitis causing cataracts?

Answer 18

Inflammatory mediators and by products affect lens nutrition

Question 19

What are the two most common sequelae of lens induced uveitis?

Answer 19

Glaucoma

Retinal detachment

Question 20

What are the three types of lens instability?

Answer 20

1. subluxation
2. anterior luxation
3. posterior luxation

Question 21

Causes of lens instability

Answer 21

• Primary - genetic weakness of zonules
• Sequelae of hypermature cataracts
• Buphthalmic globe (chronic glaucoma)

Question 22

Breeds predisposed to primary lens instability

Answer 22

Terriers (especially jack russell)

Question 23

How do hypermature cataracts cause lens instability?

Answer 23

Lens resorption
Capsule shrinks
Zonules tear

Question 24

How does buphthalmic globe cause lens instability?

Answer 24

zonules break on one side

Subluxation

Question 25

When would you treat a lens luxation with enucleation?

Answer 25

Blind or painful eye

Question 26

What does pseudophakia mean?

Answer 26

placement of artificial intra-ocular lens into capsule = fake lens

Question 27

Aphakia

Answer 27

no lens

Question 28

When are dogs presented with genetic cataracts?

Answer 28

Juvenile < 1 year Senile > 6 years younger the dog -- faster cataract develops -- higher incidence of complication

Question 29

What is the pathogenesis of DM causing cataract?

Answer 29

increase plasma glucose --> hexokinase pathway in lens is overwhelmed --> shunts to aldose reductase pathway --> excess sorbitol production (sugar-alcohol) --> osmotic gradient --> pulls aqueous humor in --> fibers swell --> cataract

Question 30

Lens induced uveitis is most common with what type of cataracts?

Answer 30

Hypermature or rapidly forming (DM or juvenile)

Question 31

What is the best stage to treat cataracts with surgery?

Answer 31

Immature cataract | Uveitis controlled

Question 32

What are characteristics of a patient for cataract surgery?

Answer 32

Health well behaved functional retina (ERG + U/S)

Question 33

What is the success rate for vision after cataract surgery?

Answer 33

80-90% for first year