The Lens and Cataracts

Question 1

describe lens anatomy

Answer 1

1. anterior lens capsule: barrier
2. anterior epithelium: multiplies at equator, cells become lens fibers
3. lens fibers/cortex: protein/antigenic
4. nucleus

like a peanut M&M shaped like a regular M&M

Question 2

describe lens functional anatomy

Answer 2

1. transparent:
   -avascular, nonpigmented
   -due to protein composition of lens fibers; PERFECTLY arranged like clusters of bananas
   –junction at suture lines (where tips of bananas/lens fibers meet)
2. suspended in place by zonular fibers
   -extend from ciliary body
   -insert on capsule at equator
3. nutrition: aqueous humor (vitreous humor)

Question 3

describe lens function

Answer 3

fine tuning refractive structure that focuses image on retina

via accommodation; shifts or smushes to change shape to refract light differently

Question 4

describe cataracts

Answer 4

1. any opacity of lens
2. due to distribution of normal lens fiber protein or arrangement
   -affects ability of lens to focus image on retina and thus vision
3. should NOT alter PLRs
   -impacts image but does not block light passage
4. may cause LIU (lens induced uveitis)
   -disrupted protein leakage, antigenic

Question 5

describe cataract evaluation (6)

Answer 5

1. neuro-ophthalmic exam: blink and light reflexes, menace responses
2. ancillary tests (STT (KCS), fluorescein stain (ulcer), IOP (uveitis/glaucoma))
3. patient at eye level in a dim/dark environment; consider pharmacologic mydriasis (tropicamide)
4. RETROILLUMINATION:
   -collect tapetal/red reflex
   -cataracts will interrupt/alter the reflex
5. direct and slit beam/optic cross evaluation
   -use purkinje images and object overlay to localize lesion!
6. fundic exam (try; give you an idea of how significant the cataract is; our view in equates to their view out; if can’t look at retina bc cataract so big, cataract probably pretty big)

Question 6

how to differentiate cataracts from nuclear sclerosis?

Answer 6

1. nuclear sclerosis: age related (6-7+ years), opacification of lens nucleus
   -compression/increased density of lens nucleus with age from lifelong lens fiber addition
   -center of M&M gets denser!
   -does not significantly affect vision in animals or block tapetal/red reflex
   -easier to detect with pupil dilation bc can see is defined to center nucleus
2. cataracts mean surgery, nuclear sclerosis does not

Question 7

describe congenital cataracts

Answer 7

1. congenital (includes vascular): present at birth
2. may be inherited, secondary to in utero hiccup in development, or associated with other ocular abnormalities
3. examples are:
   -persistent pupillary membranes
   -persistent hyperplastic primary vitreous/tunica vasculosa lensitis

Question 8

describe inherited/genetic cataracts

Answer 8

1. most common etiology in dogs: presume cataracts are inherited until proven otherwise (trauma, etc.)
2. occur in many breeds:
   -usually bilateral but not always symmetrical
   -some with classic appearance/presentation: incipient posterior polar cataract; usually non-progressive in goldens and labs
3. affected animals should NOT be bred

Question 9

describe diabetic cataracts (3)

Answer 9

1. will basically always happen in dogs with diabetes due to too much glucose in the lens
2. usually bilateral, complete, develop rapidly, and cause blindness
   -separation/clefting of Y-sutures also common
3. hyperglycemia leads to overload of hexokinase, glucose metabolism shifted to sorbitol pathway, sorbitol is huge and pulls water in from aqueous and vitreous, causing water-logged cataract

-aldose reductase starts pathway, if can inhibit can prevent diabetic dogs getting cataracts

Question 10

describe post-inflammatory (toxic) cataracts (3)

Answer 10

1. uveitis: most common cataract etiology in cats and horses
2. evaluate for hallmarks of prior inflammation
   -uveitis: red eye, flare, miosis, low IOP
   -posterior synechiation: visible adhesion, pigment on ALC, pupillary irregularities/dyscoria, impaired pupil movement
   -iris hyperpigmentation
3. generally poor candidates for cataract surgery

Question 11

describe traumatic cataracts

Answer 11

1. blunt or penetrating trauma
2. beware lens capsular tears:
   >1.5mm in length less likely to self heal
   -may cause severe lens-induced uveitis refractory to treatment/phacoclastic uveitis
   -treatment is to control uveitis (topical and oral anti-inflam), prevent infections with oral Abx, and cataract surgery
3. lens capsule rupture in cats is associated with risk of post-traumatic sarcoma development; consider enucleation

Question 12

describe nutritional cataracts

Answer 12

1. may occur in puppies/kittens fed milk replacer
   -most likely due to arginine (+/- other AA) deficiency but not very common anymore
2. may help to add beef or liver baby food to milk replacer
3. associated with cataract formation at nuclear/cortical junction
   -often become smaller with age as nucleus compresses

Question 13

describe senila cataracts

Answer 13

-very common in dogs
-rarely affect vision
-may be due to photo oxidative mechanisms and/or UV damage (also have nuclear sclerosis)

Question 14

describe radiation-induced cataracts

Answer 14

1. in 10-28% of dogs with exposure to ionizing radiation where the eye is in the field
2. usually occur 6-12 months post RT; start equatorially, as well as anterior and posterior subcapsularly

Question 15

describe toxic cataracts

Answer 15

1. ketoconazole (and other drug) induced
2. secondary to progressive retinal atrophy/retinal degeneration
   -usually history of dim light visual deficits prior to ocular cloudiness

Question 16

describe infectious cataracts

Answer 16

1. septic implantation syndrome
   -penetrating trauma, infection seeded, cataract with progression and uveitis much later
2. encephalitozoon cuniculi or pasteurella spp. in rabbits and cats: cause iris or lens granuloma, uveitis

Question 17

describe cataract extent/size (FINISH)

Answer 17

1. incipient:
   -involve <10% of lens volume, should not significantly affect vision bc small
2. incomplete (immature): <10 but less than 99%
   -can be further subdivided into early and late incomplete
   -variably affect vision, depending on size and location within lens
3. complete (mature)
   -involve entire lens
   -associated with visual impairment
4. resorbing (hypermature): incinerate/melting
   -liquefying: with chronicity or rapid progression
   -hallmarks: sparkly, anterior lens capsule wrinkling, lens induced (phagolytic) uveitis)
   –iris hyperpigmentation and velveting, posterior synechiae

4a. moragnian: all cortex resorbed; nucleus sinks to bottom of lens capsule

5. intumescent: water-logged = physically swollen
   -may result in lens capsule rupture and phacoclastic uveitis
   -most commonly with diabetic cataracts

also referred to as stages but not all will progress through all of these extents!!

Question 18

describe cataract location (barely worry about)

Answer 18

1. capsular/subcapsular
2. cortical
3. equatorial
4. nuclear

can use axis of rotation and slit beam purkinje images to localize

Question 19

describe cataract age of onset (FINISH

Answer 19

1. congenital:
   -present since birth
   -may or may not be inherited
2. juvenile:
   -commonly inherited
   -from birth to abound 6 years
3. senile:
   -develop after 6-10 years of age
   -some degree of cataract formation in all dogs >13.5 years of age
   -usually do not significantly affect vision in animals

Question 20

describe cataract medical therapy

Answer 20

NONE!!!! cannot uncook an egg, cannot realign lens fibers at molecular level

1. N-acetyl carnosine (controversial):
   -antioxidant
   -ONE study demonstrated improved lens opacification in eyes with nuclear sclerosis or incomplete cataract
2. lanosterol
3. ocu-Glo: oral nutraceutical: may delay progression of degenerative retinal disease; theoretically ocular health and function boosting plus free-radical scavenging so won’t hurt just is expensive
4. kinostat only good possible preventative for diabetics
   -aldose reductase inhibitor to delay onset and reduce severity of cataracts in diabetics
5. can try to address/control/prevent lens induced uveitis

Question 21

describe phacolytic versys phacoclastic lens induced uveitis

Answer 21

phacoclytic: lens proteins slowly leak through capsule, typically mild

phacoclastic: sudden and more extensive release of lens proteins via capsular defect
-severe, medically refractory, common need emergency surgery

Question 22

describe treatment of cataracts; describe ideal candidates for surgery (5)

Answer 22

surgery!! don’t worry about too much

ideal candidates are:
1. healthy dog
2. otherwise healthy eye:
-no/controlled KCS, keratitis, LIU, NO glaucoma
-cataract not resorbing, vitreous not overly degenerated
3. manageable patient and client commiment
4. vision and QOL affected by cataract
5. normal ERG and ocular ultrasound

Question 23

describe post-op care of cataracts surgery (5)

Answer 23

essential for success!

1. aggressive topical and systemic anti-inflam therapy
2. topical lubricant +/- mydriatic, oral antibiotics
3. e collar
4. frequent rechecks to control inflammation and IOP
5. long term tapered meds and monitoring

Question 24

describe potential complications of cataracts surgery

Answer 24

1. inability to place IOL; IOL shift or luxation
2. corneal ulceration
3. uveitis (with synechiae)
4. infection
5. retinal detachment
6. glaucoma
7. failure to restore vision/vision loss/blindness
8. capsular opacity: fibrosis or lens fiber regrowth
9. corneal edema, pigmentation, or other opacity
10. KCS
11. need to remove eye

Question 25

how do you treat cataracts if surgery is not an option?

Answer 25

1. prevent/control/manage LIU 2. monitor for potential secondary glaucoma 3. lens resorption may result in improved (far sighted) vision 4. most visually impaired animals adjust well 5. salvage therapy for painful irreversibly blind eyes: enucleation

Question 26

describe lens luxation

Answer 26

due to zonular failure!! 1. primary: -inherited zonular ligament dysplasia -TERRIERS, spaniels, others -eventually bilateral 2. secondary to: -uveitis, cataract, glaucoma, NOT trauma unless severe or predisposed eye

Question 27

what are the 4 types of lens luxation?

Answer 27

1. lens instability: irido and/or phaco-donesis 2. subluxation 3. anterior luxation: -lens in anterior chamber -occurs mainly in PUPIL -can cause acute, severe, secondary glaucoma and warrant urgent lens removal surgery 4. posterior luxation

Question 28

describe treatment of lens luxation

Answer 28

1. address underlying cause if secondary, lower IOP (NO MITOTICS if lens anterior) 2. lensectomy (removal) 3. trans-corneal reduction of anterior lens luxation (TRALL) 4. medical management: -especially if lens posterior -caution with drugs that alter pupil size 5. enucleation