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Ophthalmology > Lens > Flashcards

Lens Flashcards

1
Q

Where is the lens located?

A
  • Behind the iris
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2
Q

What holds the lens in place?

A
  • Zonules from the ciliary processes
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3
Q

Role of the lens

A
  • Accommodation or changes in shape
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4
Q

Characteristics of the lens

A
  • Transparent, avascular, non-innervated

- Biconvex and refractile

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5
Q

What is the lens composed of?

A
  • Protein and water (50-66%) in a relative state of dehydration
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6
Q

Can you see the fundus if the lens isn’t transparent?

A
  • No you cannot
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7
Q

What are the two parts of the lens?

A
  • Nucleus (center) and cortex
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8
Q

Which part of the lens contains the lens fibers?

A
  • The cortex
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9
Q

WHat are the three main pathologies of the lens?

A
  1. Loss of lens transparency
  2. Lens instability
  3. Lens perforation
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10
Q

Possible causes of loss of lens transparency

A
  • Nuclear sclerosis or cataract
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11
Q

Possible causes of lens isntability

A
  • Luxation or subluxation
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12
Q

What causes nuclear sclerosis?

A
  • Age related change
  • Lens fibers grow throughout life, leading the cortex to become expanded and nucleus to become more compressed and dehydrated
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13
Q

Why does the nucleus of the lens change appearance as it ages and becomes dehdyrated?

A
  • Scatters light differently than the cortex

- THis gives it a hazy appearance

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14
Q

What happens if the nucleus of the lens becomes opaque?

A
  • Nuclear cataract

- Can no longer see the fundus

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15
Q

How can you differentiate nuclear sclerosis from a cataract?

A
  • With nuclear sclerosis you can still see the fundus, which you cannot see with cataracts
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16
Q

At what age do dogs, cats, and horses get nuclear sclerosis?

A
  • Dogs over 6 years
  • Cats over 9 years
  • Horses over 15 years
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17
Q

Time course of nuclear sclerosis

A
  • Progresses with age
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18
Q

Diagnosing nuclear sclerosis

A
  • Fundus is visible, but must dilate to diagnose

- Cortex of lens will be transparent, and nucleus more dense

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19
Q

Visual impairment associated with nuclear sclerosis

A
  • Animal should still be visual, but may be impaired in dim light
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20
Q

What is a cataract?

A
  • Any OPACITY in the lens
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21
Q

Is a cataract ever normal?

A
  • NO NO
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22
Q

What are the four ways to describe cataracts?

A
  1. Age of onset
  2. Location in lens
  3. Stage of maturity
  4. Cause
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23
Q

Age of onset for cataracts

A
  • Congenital
  • Juvenile (<6 years)
  • Senile (>6 years)
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24
Q

What are the stages of maturity for cataracts?

A
  • Incipient
  • IMmature
  • Mature
  • Hypermature
  • Morgagnian
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25
Q

Cause of cataracts**

A
  • Primary (hereditary, no other ocular disease) vs secondary (other ocular disorder exists)
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26
Q

Incipient cataract appearance

A
  • <20% of lens involved

- Scattered opacities

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27
Q

Clinical relevance of incipient cataracts

A
  • Not usually a clinical problem
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28
Q

Immature cataract appearance

A
  • > 20% of lens but tapetal reflex is seen
29
Q

Clinical relevance of immature cataract

A
  • Clinically significant!
    This impairs vision
  • May cause lens induced uveitis
30
Q

Mature or hypermature cataract appearance

A
  • Lens opactiy that obstructs visualizing the fundus

- No tapetal reflex seen

31
Q

Is a patient with a hypermature cataract visual?

A
  • No

- Functionally blind

32
Q

Clinical relevance of mature and hypermature cataracts

A
  • patient is functionally blind

- These may cause lens induced uveitis

33
Q

What is the fundamental cause of lens induced uveitis

A
  • Lens proteins outside of the lens capsule are “tolerated” by the ocular immune system in small amounts
  • Exposure to increased protein levels from cataracts or lens perforations causes an immune reaction (Lens induced uveitis)
34
Q

Clinical significance of lens induced uveitis

A
  • Must be medically and/or surgically treated to avoid catastrophic damage to the eye
35
Q

Signs of LIU

A
  • Cataract or instability
  • Pain
  • Episcleral injection
  • Flare
  • KPs
  • Miosis
  • Pigment on lens capsule
  • Secondary glaucoma
36
Q

What are the four things that we must know about cataracts?

A
  1. Is it nuclear sclerosis or cataracts?
  2. What is causing it?
  3. Is it causing inflammation?
  4. It needs to be evaluated by an ophthalmologist
37
Q

Primary causes of cataracts

A
  • Inherited
  • Any age onset
  • Any location
  • Any degree of maturity
  • Most cataracts in dogs are inherited
  • Uncommon in cats and horses unless senile
38
Q

What is the cause of most cataracts in normal dogs?

A
  • Often inherited
39
Q

SEcondary causes of cataracts (three biggies and some other ones)

A
  • Diabetes mellitus***
  • Retinal degeneration (PRA in dogs)**
  • Uveitis***
  • Also: glaucoma, trauma, toxins, nutritional, electrical shock, hypocalcemia, radiation
40
Q

Pathophysiology of diabetic cataracts**** KNOW THIS *****

A

Hyperglycemia –> glucose in aqueous increases –> glucose imbibed into the lens –> overwhelms normal glycolysis pathway –> shunted to sorbital pathway –> aldose reductase –> sorbitols –> osmotic gradient –> water enters the lens and swells fibers

41
Q

Do cats get diabetic cataracts?

A
  • Most adult cats don’t have aldose reductase and do not develop diabetic cataracts
42
Q

How quickly does diabetic cataracts occur?

A
  • VERY QUICKLY
43
Q

WHat % of dogs with DM get cataracts within 6 months and 1 year?

A
  • 50% within 6 months

- 75% within 1 year

44
Q

What is the most common presenting sign for diabetic dogs?

A
  • Sudden blindness due to cataracts
45
Q

Treatment of dogs with diabetic cataracts

A
  • ALL DOGS should be treated to prevent lens induced uveitis (LIU)
  • REFER EARLY for cataract surgery
46
Q

Intumescent cataract

A
  • Rapid swelling of lens fibers due to water imbibition
  • Y-sutures separate and may cause lens capsule rupture leading to severe LIU
  • This is an emergency
  • Iris will be pushed forward
47
Q

Treatment of cataracts

A
  • No effective medical treatment
  • May give pred acetate but may not be significant enough
  • Treatment is determined by cause and condition of eye
48
Q

When should cataracts be removed, and how should they be removed?

A
  • Removed if causing LIU or affecting vision

- Remove by phacoemulsification

49
Q

What do you need to make sure is functional before doing phacoemulsification?

A
  • Must know if the retina is functional
  • Dazzle and pupil response will tell you good signs
  • Want to make sure the posterior segment is healthy
  • To do this, you run an electroretinogram
50
Q

What do an ERG?

A
  • See if the retina is functioning before surgery
51
Q

Process of ERG

A
  • Sedate and put electrodes near the eye
  • Shine a light at the eye
  • If they’re functioning, it will send a response
52
Q

E. cuniculi cataracts - when are rabbits infected?

A
  • In utero
53
Q

Appearance of E. cuniculi

A
  • White spot on the pupil

- Can have lens capsule rupture

54
Q

What causes cataracts with E. cuniculi?

A
  • E. cuniculi within the lens
55
Q

Sequelae of E. cuniculi cataracts

A
  • Lens capsule ruptures
  • Phacoclastic lens induced uveitis
  • Sx removal of lens is only treatment at this time
56
Q

Anterior lens luxation - how quickly should you treat?

A
  • THIS IS AN EMERGENCY

- REFER IT RIGHT AWAY

57
Q

Primary causes of anterior lens luxation, and who gets it?

A
  • Breed predisposition
  • Lens zonule defect
  • Jack Russell Terriers get it, Border Collies, Heelers, Siamese cats
58
Q

Secondary causes of anterior lens luxation

A
  • Chronic uveitis
  • Trauma
  • Glaucoma
  • Senility
59
Q

Age of patients who get anterior lens luxation?

A
  • young to middle aged
60
Q

Signs of anterior lens luxation

A
  • Pain

- Lens touching the endothelium damages the cells and leads to corneal edema

61
Q

Sequelae of anterior lens luxation

A
  • Secondary glaucoma likely
  • Emergency referral surgery
  • MAYBE can save the eye if it just happened
62
Q

Posterior lens luxation relative to anterior lens luxation

A
  • Less harmful initially and less painful
63
Q

Sequelae of posterior lens luxation

A
  • Unstable lens can cause uveitis and glaucoma, as well as retinal detachment
64
Q

Plan for posterior lens luxation

A
  • Keep pupil miotic with drugs to prevent anterior luxation
  • Is this a good idea?
  • Anti-inflammatory may be enough
65
Q

Lens subluxation appearance

A
  • Zonules and lens shifting
66
Q

Cause of lens subluxation

A
  • Can be caused by glaucoma
67
Q

Sequela of lens subluxation

A
  • Glaucoma
  • Pain
  • Uveitis
68
Q

Treatment for lens subluxation

A

-REFERRAL

Ophthalmology (8 decks)

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