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SEM 5: SAM 1 > The Lens > Flashcards

The Lens Flashcards

1
Q

What type of cataract typically occurs in diabetic patients?

A

Intumescent cataract

(intumescent means swollen… due to sorbitol causing osmotic shifts)

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2
Q

What is the most common pathology to occur to the lens?

A
  • Cataracts
  • Lens luxation
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3
Q

What is the purpose of lens zonules?

A

suspensory ligaments connect the ciliary body to the lens

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4
Q

What characteristics of the lens is responsible for its clear structure?

A
  • No blood vessels
  • No pigment
  • Ordered cell arrangement
  • Soluble crystalline proteins

(some similar characteristics as the cornea)

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5
Q

What is the basic function of the lens?

A

Focus light onto the retina to produce a sharp image (accommodation)

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6
Q

What is a normal aging change of the lens that can be seen in older pets?

A

Nuclear sclerosis (hazy cloudy eye - NOT a cataract)

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7
Q

How can you differentiate nuclear sclerosis of the lens vs a cataract?

A
  • No apparent vision loss with nuclear sclerosis
  • Tapetum reflection and fundus still visible with nuclear sclerosis

(not able to see the back of the eye with cataracts unlike NS)

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8
Q

You are trying to determine the location of a cataract within the lens. When the patient moves their right eye to the left, the opacity moves in the opposite direction (to the left). What can you determine?

A

Posterior lens cataract - opacity moves in the opposite direction as the eye

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9
Q

You are trying to determine the location of a cataract within the lens. When the patient looks down, the opacity moves down too. What can you determine?

A

Anterior cataract - moves with the eye

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10
Q

You are trying to determine the location of a cataract within the lens. When the patient looks down, the opacity moves up within the lens. What can you determine?

A

Posterior cataract - moves in the opposite direction as the eye

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11
Q

What is parallax, and why is it useful when trying to diagnose a cataract?

A
  • Helps determine the depth and location of cataracts
  • Move the eye and see how the opacity moves in relation to the lens
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12
Q

What are the 4 stages of cataract maturation?

A
  1. Incipient
  2. Incomplete/Immature
  3. Complete/Mature
  4. Resorbing/ Hypermature
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13
Q

What is an incipient cataract?

A
  • Small opacity < 20% of the lens affected (focal)
  • Tapetal reflection still visible
  • No significant vision loss
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14
Q

What is a incomplete cataract and how does it appear?

A
  • Any cataract between incipient and complete
  • Tapetal reflection still visible
  • Like looking at cracked glass (streaky opacity)
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15
Q

What is a complete cataract?

A
  • When 100% of the lens is affected (entire lens opacity)
  • Can’t see tapetum reflection
  • Eye is blind
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16
Q

What is a resorbing cataract and how does it appear?

A
  • When the lens cortex liquefies
  • Capsule wrinking
  • Deep anterior chamber
  • Tapetum reflection may return
  • Sparkly lens with wrinkled capsule

(associated with lens induced uveitis… proteins leaking out of lens causing secondary uveitis)

17
Q

What is an intumescent cataract and how does it appear?

A
  • Lens becomes swollen and increases in size
  • Anterior chamber becomes shallow
  • Seen in diabetic patients
  • Can be a complete or incomplete cataract
  • Y cleft of the lens can be seen
18
Q

What is the most common cause of cataracts in dogs vs cats and horses?

A

Dogs - inherited
Cats and horses - inflammatory (Chronic uveitis causing secondary cataracts)

19
Q

Knowing the most common cause of cataracts in horses and cats, how can the eye appear other than opacity of the lens?

A
  • Look for signs of concurrent uveitis (keratic precipitates, hypopyon, color changes to the iris, episcleral injection)

(most common cause of cataracts in horses and cats)

20
Q

What is the pathophysiology behind diabetes mellitus resulting in secondary cataract formation?

A
  • Glucose converted to sorbitol by aldose reductase
  • Pulls water into the lens causing swelling, denatures lens proteins
21
Q

What is the most common cause of metabolic cataracts?

A

Diabetes mellitus

22
Q

Why is metabolic cataracts less common in cats than dogs?

A

Dogs have high levels of aldose reductase which converts glucose to sorbitol in the eye

(cats have less aldose reductase, less likely for diabetes mellitus to cause cataracts)

23
Q

What is the earliest visible changes that can be seen in patients with diabetic cataracts?

A
  • Equatorial lens vacuoles within the periphery of the lens

(progressives rapidly to mature, intumescent cataract)

24
Q

What is the most common cause of nutritional cataracts?

A

Puppies and kittens fed milk replacement instead of moms milk

25
Q

What causes endogenous toxic cataracts?

A
  • Associated with retinal disease / progressive retinal atrophy
  • Degenerating photoreceptors releasing toxic substances into vitreous
  • IMPT to exclude prior to pursuing cataract surgery
26
Q

What causes senile cataracts?

A

Photooxidative injury (UV light)

(usually small and doesn’t impair vision, but can range from incomplete to complete)

27
Q

What are common sequelaes to cataracts?

A
  • Visual impairment
  • Lens induced uveitis
  • Glaucoma
  • Retinal detachment

(If advanced - can lead to permanent blindness, cataract surgery not an option of choice at this point)

28
Q

What is the phacoclastic form of lens induced uvietis?

A
  • BAD
  • Severe form associated with traumatic tear of the lens capsule
29
Q

What is the phacolytic form of lens induced uvietis?

A
  • Milder than the phacoclastic form
  • Slow leakage of lens proteins from a cataract
  • Suspect in any red eye with a cataract!!
  • Tx with topical steroid or NSAID
30
Q

What is the medical treatment protocol for patients with cataracts?

A
  • Anti-inflammatories (Topical NSAID - Diclofenac) usually life long

(helps control lens-induced uveitis/ secondary uveitis, reduces incidence of secondary glaucoma)

31
Q

What is the surgical treatment option for patients with cataracts?

A
  • Phacoemulsion (make a corneal incision and suck out the cataract using a vibrating probe)
  • Place an artificial lens (pseudophakia)
32
Q

When should animals be referred for cataract surgery?

A

At the time the cataract is first detected

(early referral has highest chance of success)

33
Q

List the primary causes of lens luxation

A
  • Inherited disorder in terrier breeds
  • Abnormal degeneration of zonular ligaments
34
Q

List the secondary causes of lens luxation

A
  • Chronic uveitis (most common in cats)
  • Glaucoma (enlargement of globe can stretch and break zonular fibers)
  • Trauma (uncommon)
35
Q

What should you suspect in any terrier with a painful eye?

A

Anterior lens luxation

SEM 5: SAM 1 (35 decks)

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