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IP 11 Ophthalmology > 7: the lens - pearce > Flashcards

7: the lens - pearce Flashcards

1
Q

what are the components of the lens?

where are they located relative to each other?

A

capsule, anterior epithelium, cortex, nucleus, equator

nucleus is the center, cortex is around the nucleus and capsule is thin outer coating

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2
Q

where is the lens located?

A

in the patellar fossa

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3
Q

what structure suspends the lens in its location?

A

zonular fibers - run from ciliary body to lens

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4
Q

what occurs to the lens when zonular fibers break down?

A

lens luxation

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5
Q

what are “Y-sutures”?

under what circumstances are they more visible?

A

fibers produced by epithelial cells located at the equator - elongate from the equator and go all the way around the lens and connect to each other on the suture lines

become more visible with cataracts

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6
Q

where are “Y-sutures” located?

and upside down “Y-sutures” ?

A

Y sutures are anterior and upside down Y sutures are peace signs

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7
Q

why do many other species have larger lenses than humans?

A

humans have high corneal refraction - vs other spp which depend on lens for refraction more than we do

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8
Q

what shape lens do water animals have?

and land animals?

A

water -> spherical

land -> ellipsoid

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9
Q

t/f

the lens is very vascular

A

false

the lens is AVASCULAR after birth

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10
Q

where does the lens derive its nutrition from?

A

the aqueous humor

[NOTE: this is why things wrong with the aqueous humor can be reflected in the lens]

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11
Q

what is the 1* metabolic pathway utilized by the lens?

A

hexokinase pathway

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12
Q

what molecule does the lens utilize for energy?

A

glucose -> metabolized into lactic acid [I think]

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13
Q

how does glucose enter the lens?

A

active transport and diffusion

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14
Q

when aerobic glycolysis is utilized in the lens, what pathway?

A

citric acid cycle

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15
Q

how does lens physiology change in diabetic patients?

A

inc blood glucose -> hexokinase pathway saturated -> shunt glucose towards alternative pathway -> aldose reductase enzyme -> sorbotol is produced

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16
Q

what alternative pathway is glucose shunted to in diabetic patients who have a saturated hexokinase pathway?

what is produced as a result?

A

aldose reductase enzyme

sorbotol is produced

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17
Q

how does sorbotol in the lens lead to cataracts?

A

sorbotol diffuses poorly across the lens

it has higher osmotic pressure so leads to intense lens swelling

aqueous humor is imbibed

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18
Q

t/f

the occurrence of cataracts is approximately equal in dogs and cats

why or why not

A

false

MC in dogs b/c they have the aldose enzyme reductase

cats do NOT have the enzyme so they do not really get cataracts

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19
Q

t/f

nuclear sclerosis is a form of cataracts

A

false

nuc sclerosis is an aging change, NOT a true lens opacity but a translucency

a cataract is a true lens opacity

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20
Q

how does nuclear sclerosis develop?

A

lens fibers continue to grow throughout life -> become more numerous and compress the nucleus of the lens -> nucleus becomes firm/hard b/c of compression from additional lens fibers forming -> dec in accommodation

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21
Q

what is the presentation and appearance of nuclear sclerosis?

A 
bilateral
pearl like nuclear density
spherical
translucent
fundus detail visible
NOT a cataract
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22
Q

what is microphakia?

A

a congenital abnormality

small lens
* if you can see the edges of the lens, it is too small or luxated

often seen with other ocular mal formations

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23
Q

what is lenticonus?

etiology?

A

anterior or posterior protrusion of the lens

will see pointed profile / angle to the lens when it should be smooth

congenital

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24
Q

what is PHPV?
PHTVL?

persistend hyperplastic primary vitreous?

persistent hyperplastic tunica vasculosa lentis

A

the persistence of the primary vitreous vessel after birth

normal: lens if vascularized in the embryo - the 1 vitreous is a large vessel that has a net of vessels, the tunica vasculosas - giving the lens a red color

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25
Q

what does a cataract look like?

A

focal or diffuse lens opacity

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26
Q

what is the prevalence of cataracts in dogs?

A

2.42%

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27
Q

t/f

dilation is important in order to dx cataract?

A

true - dilation allows more complete exam and should be done

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28
Q

t/f

cataracts can be diagnosed with either retro illumination or direct illumination?

A

true

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29
Q

under direct illumination, what is the appearance of nuclear sclerosis vs cataract?

A

nuc sclerosis appears hazy or translucent

cataracts appear white

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30
Q

under retro illumination, what do cataracts look like compared to nuclear sclerosis?

A

cataracts appear black

nuclear sclerosis appears clear

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31
Q

during a fundus exam, if cataracts are present, what will you see?

A

you will see a shadow on the retina/fundus

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32
Q

in what ways are cataracts classified?

A 
stage of development
position
age of development
etiology
consistency
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33
Q

what are 4 classifications of cataracts based on stage of development?

A

incipient
immature
mature
hypermature

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34
Q

which stages of cataracts have a smokey appearance?

A

incipient, immature, mature

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35
Q

what stage of cataracts has a sparkly appearance?

A

hypermature

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36
Q

what stages of cataracts have a smooth capsule?

A

incipient, immature, mature

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37
Q

what is the texture of the capsule if a hypermature cataract?

A

wrinkled

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38
Q

what % of the lens is affected by incipient cataracts?

A

0-15%

39
Q

what % of the lens is affected by immature cataracts?

A

15-98%

40
Q

what % of the lens is affected by mature cataracts?

A

90-100%

41
Q

what % of the lens is affected by hypermature cataracts?

A

OVER 100

42
Q

what does intumescent mean?

A

swollen

43
Q

what category of cataract typically has an intumescent appearance?

A

mature

44
Q

what stage of cataracts has areas of re-absorption?

A

hypermature

45
Q

what does a lens with a Morgagnian appearance have?

A

slightly suspended and dropped down - hyper mature - nuc becomes more liquid and NOT held up in the middle as well

46
Q

how can cataracts be classified according to position?

A 
capsular
sub capsular
cortical
equatorial
nuclear
perinuclear
anterior
posterior
47
Q

how can cataracts be classified based on age of development?

A 
congenital
developmenta
juvenile
senile 
acquired
48
Q

what are 2 main classifications of etiology / pathogenesis for cataracts?

A

1*

2*

49
Q

what is the nature of 1* cataracts?

A

inherited

50
Q

what are some things that lead to 2* cataracts?

A 
traumatic
uveitis
nutritional
radiation
diabetic
toxic
congenital
senile
51
Q

what is MC cause of cataracts in dogs?

A

1* - inherited

52
Q

what is 2nd MC cause of cataracts in dogs?

A

2* to diabetes

53
Q

what is MC cause of cataracts in cats and horses?

A

2* to uveitis

54
Q

what dz does cataracts predispose patients to?

A

lens-induced uveitis

55
Q

what are the 2 types of lens induced uveitis?

A

phacoCLASTIC

phacoLYTIC

56
Q

what is the progression of lens induced uveitis?

A

leakage occurs and mounts an Aby response => proteins deposit in eye d/t the reaction

57
Q

what is phacoclastic vs phacolytic lens induced uveitis?

A

phacoclastic is “catastrophic” - ruptured lens capsule and severe immune reaction as a result

phacolytic is a gradual leakage that occurs during the progression of cataracts => capsule remains intact and a mild to moderate immune reaction occurs

58
Q

what is the likely result if cataracts are neglected to be treated?

A

100% failure => enucleation

59
Q

what are medical options to treat cataracts?

A

anti cataract drugs

anti inflammatory drugs

60
Q

how effective are anti cataract drugs?

A

ineffective => typically delay professional care

61
Q

what type of treatment is the only cure for cataracts?

A

surgery

62
Q

what are 3 types of surgery of the lens?

A
  • extra capsular extraction
  • intra capsular extraction
  • phacoemulsification
63
Q

which 2 types of surgery of the lens are a large incision?

A

extra capsular extraction

intra capsular extraction

64
Q

how is an extra capsular extraction performed?

what is incised and what stays?

A
  • capsule is incised, lens extracted via manual extraction; large incision
  • capsule stays
65
Q

how is intra capsular extraction performed?

A
  • the lens is removed with the entire lens capsule via manual extraction; large incision
66
Q

how is phaco emulsification performed?

A

capsule is incised, automated extraction via irrigation / aspiration
small incision
capsule stays behind

67
Q

at what point should a cataract be referred to specialist?

A

at initial diagnosis

68
Q

what does the ophthalmologist evaluation consist of?

A 
vision deficit
progression of the cataract
amenable patient
patient health - general anesthesia
client commitment - financial and time

absence of pathologic processes - minimum ophthalmic database
glaucoma risk - gonioscopy
retinal function - ERG (electroretinogram)
retinal attachment - ocular u/s

69
Q

what is a major key to post operative success for cataract surgery?

A

eyedrops

70
Q

what are common complications of cataract surgery?

A

uveitis
glaucoma
retinal detachment

less common:
persistent corneal edema
synechiae
intraocular hemorrhage
corneal ulceration
suture failure
71
Q

what meds are used before cataract surgery?

A

anti inflammatory
dilation
abx

72
Q

what meds are used after cataract surgery?

A 
anti inflammatory
abx
dilation maybe
anti glaucoma maybe
e collar (4-6 weeks)
73
Q

what is pseudophakia?

A

a prosthetic lens

74
Q

what is aphakia?

A

absence of lens

75
Q

what is the appearance of an anterior lens luxation?

A
  • ID lens in anterior chamber
  • pupil margin obscured
  • shallow / absent anterior chamber
  • aphakic crescent
76
Q

what breeds are prone to anterior lens luxation?

A
  • jack russell
  • other terrier breeds
  • chinese crested
  • shar-pei
77
Q

what is etiology of primary etiology?

A

hereditary

common in terrier breeds

78
Q

what are some common causes of 2* lens luxation?

A
  • glaucoma [buphthalmos]
  • uveitis [cats] - break down of lens fibers (zonular degeneartion)
  • intraocular tumors
  • cataracts
  • blunt trauma
79
Q

t/f

chronic or 2* luxation is a surgical emergency

A

false

NOT a surgical emergency

80
Q

acute and 1* lens luxation leads to what condition?

A

2* glaucoma

81
Q

t/f

acute primary luxation is a surgical emergency

A

true

82
Q

t/f

acute 1* lens luxation is painful

A

false

83
Q

what is vitreous presentation of an eye?

A

common in lens luxations

gel comes forward if the lens is not holding it in place - viterous sneaks around lens and into the pupil

84
Q

what are 3 surgical options for anterior lens luxation?

A
  • intracapsular lens extraction
  • enucleation
  • evisceration w prosthesis
85
Q

what is the goal / prognosis associated w enucleation procedure?

A

comfort preservation only

86
Q

when is intracapsular lens extraction performed to repair anterior lens luxation?

prognosis?

A
  • visual animal with acute vision loss
  • referral Sx: remove capsule and entire lens
  • 50% chance for long-term vision and comfort
87
Q

what is the prognosis of evisceration with prosthesis to repair anterior lens luxation?

A

comfort preservation only

88
Q

what is the only anterior lens luxation surgery that has a chance for long term vision and comfort?

A

intra capsular lens extraction

89
Q

what are 2 goals of medical management of anterior lens luxation?

*NOTE: these are done prior to referral

A
  • lower IOP

- dec inflammation

90
Q

what drugs are used to dec IOP to Tx anterior lens luxation?

A
  • Mannitol [2mg/kg IV]

- carbonic anhydrase inhibitors

91
Q

what are 2 carbonic anhydrase inhibitors used to Tx anterior lens luxation?

A
  • topical dorzolamide

- oral methazolamide

92
Q

what drugs are used to dec inflammation to Tx anterior lens luxation?

also what method of administration?

A
  • prednisone acetate - topically

- other anti inflammatories - orally

93
Q

when is lens trapping done to Tx anterior lens luxation?

what drugs do this?

A

ONLY if posterior lens luxation

synthetic PGs

IP 11 Ophthalmology (13 decks)

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