7: the lens - pearce

Question 1

what are the components of the lens?

where are they located relative to each other?

Answer 1

capsule, anterior epithelium, cortex, nucleus, equator

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

Question 2

where is the lens located?

Answer 2

in the patellar fossa

Question 3

what structure suspends the lens in its location?

Answer 3

zonular fibers - run from ciliary body to lens

Question 4

what occurs to the lens when zonular fibers break down?

Answer 4

lens luxation

Question 5

what are “Y-sutures”?

under what circumstances are they more visible?

Answer 5

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

Question 6

where are “Y-sutures” located?

and upside down “Y-sutures” ?

Answer 6

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

Question 7

why do many other species have larger lenses than humans?

Answer 7

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

Question 8

what shape lens do water animals have?

and land animals?

Answer 8

water -> spherical

land -> ellipsoid

Question 9

t/f

the lens is very vascular

Answer 9

false

the lens is AVASCULAR after birth

Question 10

where does the lens derive its nutrition from?

Answer 10

the aqueous humor

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

Question 11

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

Answer 11

hexokinase pathway

Question 12

what molecule does the lens utilize for energy?

Answer 12

glucose -> metabolized into lactic acid [I think]

Question 13

how does glucose enter the lens?

Answer 13

active transport and diffusion

Question 14

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

Answer 14

citric acid cycle

Question 15

how does lens physiology change in diabetic patients?

Answer 15

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

Question 16

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

what is produced as a result?

Answer 16

aldose reductase enzyme

sorbotol is produced

Question 17

how does sorbotol in the lens lead to cataracts?

Answer 17

sorbotol diffuses poorly across the lens

it has higher osmotic pressure so leads to intense lens swelling

aqueous humor is imbibed

Question 18

t/f

the occurrence of cataracts is approximately equal in dogs and cats

why or why not

Answer 18

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

Question 19

t/f

nuclear sclerosis is a form of cataracts

Answer 19

false

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

a cataract is a true lens opacity

Question 20

how does nuclear sclerosis develop?

Answer 20

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

Question 21

what is the presentation and appearance of nuclear sclerosis?

Answer 21

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

Question 22

what is microphakia?

Answer 22

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

Question 23

what is lenticonus?

etiology?

Answer 23

anterior or posterior protrusion of the lens

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

congenital

Question 24

what is PHPV?
PHTVL?

persistend hyperplastic primary vitreous?

persistent hyperplastic tunica vasculosa lentis

Answer 24

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

Question 25

what does a cataract look like?

Answer 25

focal or diffuse lens opacity

Question 26

what is the prevalence of cataracts in dogs?

Answer 26

2.42%

Question 27

t/f dilation is important in order to dx cataract?

Answer 27

true - dilation allows more complete exam and should be done

Question 28

t/f cataracts can be diagnosed with either retro illumination or direct illumination?

Answer 28

true

Question 29

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

Answer 29

nuc sclerosis appears hazy or translucent cataracts appear white

Question 30

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

Answer 30

cataracts appear black | nuclear sclerosis appears clear

Question 31

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

Answer 31

you will see a shadow on the retina/fundus

Question 32

in what ways are cataracts classified?

Answer 32

``` stage of development position age of development etiology consistency ```

Question 33

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

Answer 33

incipient immature mature hypermature

Question 34

which stages of cataracts have a smokey appearance?

Answer 34

incipient, immature, mature

Question 35

what stage of cataracts has a sparkly appearance?

Answer 35

hypermature

Question 36

what stages of cataracts have a smooth capsule?

Answer 36

incipient, immature, mature

Question 37

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

Answer 37

wrinkled

Question 38

what % of the lens is affected by incipient cataracts?

Answer 38

0-15%

Question 39

what % of the lens is affected by immature cataracts?

Answer 39

15-98%

Question 40

what % of the lens is affected by mature cataracts?

Answer 40

90-100%

Question 41

what % of the lens is affected by hypermature cataracts?

Answer 41

OVER 100

Question 42

what does intumescent mean?

Answer 42

swollen

Question 43

what category of cataract typically has an intumescent appearance?

Answer 43

mature

Question 44

what stage of cataracts has areas of re-absorption?

Answer 44

hypermature

Question 45

what does a lens with a Morgagnian appearance have?

Answer 45

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

Question 46

how can cataracts be classified according to position?

Answer 46

``` capsular sub capsular cortical equatorial nuclear perinuclear anterior posterior ```

Question 47

how can cataracts be classified based on age of development?

Answer 47

``` congenital developmenta juvenile senile acquired ```

Question 48

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

Answer 48

1* | 2*

Question 49

what is the nature of 1* cataracts?

Answer 49

inherited

Question 50

what are some things that lead to 2* cataracts?

Answer 50

``` traumatic uveitis nutritional radiation diabetic toxic congenital senile ```

Question 51

what is MC cause of cataracts in dogs?

Answer 51

1* - inherited

Question 52

what is 2nd MC cause of cataracts in dogs?

Answer 52

2* to diabetes

Question 53

what is MC cause of cataracts in cats and horses?

Answer 53

2* to uveitis

Question 54

what dz does cataracts predispose patients to?

Answer 54

lens-induced uveitis

Question 55

what are the 2 types of lens induced uveitis?

Answer 55

phacoCLASTIC phacoLYTIC

Question 56

what is the progression of lens induced uveitis?

Answer 56

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

Question 57

what is phacoclastic vs phacolytic lens induced uveitis?

Answer 57

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

Question 58

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

Answer 58

100% failure => enucleation

Question 59

what are medical options to treat cataracts?

Answer 59

anti cataract drugs | anti inflammatory drugs

Question 60

how effective are anti cataract drugs?

Answer 60

ineffective => typically delay professional care

Question 61

what type of treatment is the only cure for cataracts?

Answer 61

surgery

Question 62

what are 3 types of surgery of the lens?

Answer 62

- extra capsular extraction - intra capsular extraction - phacoemulsification

Question 63

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

Answer 63

extra capsular extraction | intra capsular extraction

Question 64

how is an extra capsular extraction performed? what is incised and what stays?

Answer 64

- capsule is incised, lens extracted via manual extraction; large incision - capsule stays

Question 65

how is intra capsular extraction performed?

Answer 65

- the lens is removed with the entire lens capsule via manual extraction; large incision

Question 66

how is phaco emulsification performed?

Answer 66

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

Question 67

at what point should a cataract be referred to specialist?

Answer 67

at initial diagnosis

Question 68

what does the ophthalmologist evaluation consist of?

Answer 68

``` 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

Question 69

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

Answer 69

eyedrops

Question 70

what are common complications of cataract surgery?

Answer 70

uveitis glaucoma retinal detachment ``` less common: persistent corneal edema synechiae intraocular hemorrhage corneal ulceration suture failure ```

Question 71

what meds are used before cataract surgery?

Answer 71

anti inflammatory dilation abx

Question 72

what meds are used after cataract surgery?

Answer 72

``` anti inflammatory abx dilation maybe anti glaucoma maybe e collar (4-6 weeks) ```

Question 73

what is pseudophakia?

Answer 73

a prosthetic lens

Question 74

what is aphakia?

Answer 74

absence of lens

Question 75

what is the appearance of an anterior lens luxation?

Answer 75

- ID lens in anterior chamber - pupil margin obscured - shallow / absent anterior chamber - aphakic crescent

Question 76

what breeds are prone to anterior lens luxation?

Answer 76

- jack russell - other terrier breeds - chinese crested - shar-pei

Question 77

what is etiology of primary etiology?

Answer 77

hereditary common in terrier breeds

Question 78

what are some common causes of 2* lens luxation?

Answer 78

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

Question 79

t/f chronic or 2* luxation is a surgical emergency

Answer 79

false NOT a surgical emergency

Question 80

acute and 1* lens luxation leads to what condition?

Answer 80

2* glaucoma

Question 81

t/f acute primary luxation is a surgical emergency

Answer 81

true

Question 82

t/f acute 1* lens luxation is painful

Answer 82

false

Question 83

what is vitreous presentation of an eye?

Answer 83

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

Question 84

what are 3 surgical options for anterior lens luxation?

Answer 84

- intracapsular lens extraction - enucleation - evisceration w prosthesis

Question 85

what is the goal / prognosis associated w enucleation procedure?

Answer 85

comfort preservation only

Question 86

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

Answer 86

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

Question 87

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

Answer 87

comfort preservation only

Question 88

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

Answer 88

intra capsular lens extraction

Question 89

what are 2 goals of medical management of anterior lens luxation? *NOTE: these are done prior to referral

Answer 89

- lower IOP | - dec inflammation

Question 90

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

Answer 90

- Mannitol [2mg/kg IV] | - carbonic anhydrase inhibitors

Question 91

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

Answer 91

- topical dorzolamide | - oral methazolamide

Question 92

what drugs are used to dec inflammation to Tx anterior lens luxation? also what method of administration?

Answer 92

- prednisone acetate - topically | - other anti inflammatories - orally

Question 93

when is lens trapping done to Tx anterior lens luxation? what drugs do this?

Answer 93

ONLY if posterior lens luxation synthetic PGs