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Ophthalmology > Lens > Flashcards

Lens Flashcards

1
Q

What makes up the lens anatomy?

A 
Capsule (anterior and posterior)
Equator
Nucleus
Cortex
Zonules
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2
Q

Where does the lens get its nourishment?

A

glucose in the aqueous humor

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3
Q

What is a normal aging change of the lens?

A

Nuclear sclerosis

  • normal hardening of lens nucleus with age (~7 years in dogs)
  • altered light refraction
  • no vision loss
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4
Q

What is the pathogenesis of nuclear sclerosis?

A

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

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5
Q

What are the different stages of a cataract?

A

Incipient
Immature
Mature
Hypermature

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6
Q

Describe an incipient cataract

A

< 15% of the lens, good vision

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7
Q

Describe an immature cataract

A

15-90% opacity
Tapetal reflex present
Some vision

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8
Q

Describe a mature cataract

A

100% opacity
No tapetal reflex
Blind

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9
Q

Describe a hypermature cataract

A 
Lens fibers resorbing
"Sparkly" appearance
Wrinkling of the lens capsule
Blind
Lens induced uveitis may be present
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10
Q

Is there a PLR with cataracts?

A

Yes - regardless of stage or vision

If there is no PLR something else is going on

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11
Q

List some causes of cataracts

A 
Genetic (#1 in dog)
Diabetes Mellitus (dogs only)
Retinal degeneration/ Progressive Retinal Atrophy (PRA)
Uveitis
L
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12
Q

What is a cataract?

A

Opacity of the lens or its capsule

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13
Q

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

A

Cats have low aldose reductase (converts glucose to sorbitol)

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14
Q

How many dogs with DM will get cataracts?

A

100%

we can’t control DM well enough

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15
Q

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

A

Labradors

Poodles

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16
Q

How does retinal degeneration / Progressive retinal atrophy cause cataracts?

A

Diffusion of toxic metabolic products through vitreous from retina

17
Q

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

A

Cats and Horses = Chronic uveitis

Dogs = Genetics

18
Q

What is the pathogenesis of chronic uveitis causing cataracts?

A

Inflammatory mediators and by products affect lens nutrition

19
Q

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

A

Glaucoma

Retinal detachment

20
Q

What are the three types of lens instability?

A
  1. subluxation
  2. anterior luxation
  3. posterior luxation
21
Q

Causes of lens instability

A
  • Primary - genetic weakness of zonules
  • Sequelae of hypermature cataracts
  • Buphthalmic globe (chronic glaucoma)
22
Q

Breeds predisposed to primary lens instability

A

Terriers (especially jack russell)

23
Q

How do hypermature cataracts cause lens instability?

A

Lens resorption
Capsule shrinks
Zonules tear

24
Q

How does buphthalmic globe cause lens instability?

A

zonules break on one side

Subluxation

25
Q

When would you treat a lens luxation with enucleation?

A

Blind or painful eye

26
Q

What does pseudophakia mean?

A

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

27
Q

Aphakia

A

no lens

28
Q

When are dogs presented with genetic cataracts?

A

Juvenile < 1 year
Senile > 6 years

younger the dog – faster cataract develops – higher incidence of complication

29
Q

What is the pathogenesis of DM causing cataract?

A

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

30
Q

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

A

Hypermature or rapidly forming (DM or juvenile)

31
Q

What is the best stage to treat cataracts with surgery?

A

Immature cataract

Uveitis controlled

32
Q

What are characteristics of a patient for cataract surgery?

A

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

33
Q

What is the success rate for vision after cataract surgery?

A

80-90% for first year

Ophthalmology (5 decks)

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