The Lens and Cataracts Flashcards
describe lens anatomy
- anterior lens capsule: barrier
- anterior epithelium: multiplies at equator, cells become lens fibers
- lens fibers/cortex: protein/antigenic
- nucleus
like a peanut M&M shaped like a regular M&M
describe lens functional anatomy
- 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) - suspended in place by zonular fibers
-extend from ciliary body
-insert on capsule at equator - nutrition: aqueous humor (vitreous humor)
describe lens function
fine tuning refractive structure that focuses image on retina
via accommodation; shifts or smushes to change shape to refract light differently
describe cataracts
- any opacity of lens
- due to distribution of normal lens fiber protein or arrangement
-affects ability of lens to focus image on retina and thus vision - should NOT alter PLRs
-impacts image but does not block light passage - may cause LIU (lens induced uveitis)
-disrupted protein leakage, antigenic
describe cataract evaluation (6)
- neuro-ophthalmic exam: blink and light reflexes, menace responses
- ancillary tests (STT (KCS), fluorescein stain (ulcer), IOP (uveitis/glaucoma))
- patient at eye level in a dim/dark environment; consider pharmacologic mydriasis (tropicamide)
- RETROILLUMINATION:
-collect tapetal/red reflex
-cataracts will interrupt/alter the reflex - direct and slit beam/optic cross evaluation
-use purkinje images and object overlay to localize lesion! - 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)
how to differentiate cataracts from nuclear sclerosis?
- 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 - cataracts mean surgery, nuclear sclerosis does not
describe congenital cataracts
- congenital (includes vascular): present at birth
- may be inherited, secondary to in utero hiccup in development, or associated with other ocular abnormalities
- examples are:
-persistent pupillary membranes
-persistent hyperplastic primary vitreous/tunica vasculosa lensitis
describe inherited/genetic cataracts
- most common etiology in dogs: presume cataracts are inherited until proven otherwise (trauma, etc.)
- 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 - affected animals should NOT be bred
describe diabetic cataracts (3)
- will basically always happen in dogs with diabetes due to too much glucose in the lens
- usually bilateral, complete, develop rapidly, and cause blindness
-separation/clefting of Y-sutures also common - 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
describe post-inflammatory (toxic) cataracts (3)
- uveitis: most common cataract etiology in cats and horses
- 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 - generally poor candidates for cataract surgery
describe traumatic cataracts
- blunt or penetrating trauma
- 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 - lens capsule rupture in cats is associated with risk of post-traumatic sarcoma development; consider enucleation
describe nutritional cataracts
- may occur in puppies/kittens fed milk replacer
-most likely due to arginine (+/- other AA) deficiency but not very common anymore - may help to add beef or liver baby food to milk replacer
- associated with cataract formation at nuclear/cortical junction
-often become smaller with age as nucleus compresses
describe senila cataracts
-very common in dogs
-rarely affect vision
-may be due to photo oxidative mechanisms and/or UV damage (also have nuclear sclerosis)
describe radiation-induced cataracts
- in 10-28% of dogs with exposure to ionizing radiation where the eye is in the field
- usually occur 6-12 months post RT; start equatorially, as well as anterior and posterior subcapsularly
describe toxic cataracts
- ketoconazole (and other drug) induced
- secondary to progressive retinal atrophy/retinal degeneration
-usually history of dim light visual deficits prior to ocular cloudiness
describe infectious cataracts
- septic implantation syndrome
-penetrating trauma, infection seeded, cataract with progression and uveitis much later - encephalitozoon cuniculi or pasteurella spp. in rabbits and cats: cause iris or lens granuloma, uveitis
describe cataract extent/size (FINISH)
- incipient:
-involve <10% of lens volume, should not significantly affect vision bc small - 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 - complete (mature)
-involve entire lens
-associated with visual impairment - 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
- 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!!
describe cataract location (barely worry about)
- capsular/subcapsular
- cortical
- equatorial
- nuclear
can use axis of rotation and slit beam purkinje images to localize
describe cataract age of onset (FINISH
- congenital:
-present since birth
-may or may not be inherited - juvenile:
-commonly inherited
-from birth to abound 6 years - 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
describe cataract medical therapy
NONE!!!! cannot uncook an egg, cannot realign lens fibers at molecular level
- N-acetyl carnosine (controversial):
-antioxidant
-ONE study demonstrated improved lens opacification in eyes with nuclear sclerosis or incomplete cataract - lanosterol
- 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
- kinostat only good possible preventative for diabetics
-aldose reductase inhibitor to delay onset and reduce severity of cataracts in diabetics - can try to address/control/prevent lens induced uveitis
describe phacolytic versys phacoclastic lens induced uveitis
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
describe treatment of cataracts; describe ideal candidates for surgery (5)
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
describe post-op care of cataracts surgery (5)
essential for success!
- aggressive topical and systemic anti-inflam therapy
- topical lubricant +/- mydriatic, oral antibiotics
- e collar
- frequent rechecks to control inflammation and IOP
- long term tapered meds and monitoring
describe potential complications of cataracts surgery
- inability to place IOL; IOL shift or luxation
- corneal ulceration
- uveitis (with synechiae)
- infection
- retinal detachment
- glaucoma
- failure to restore vision/vision loss/blindness
- capsular opacity: fibrosis or lens fiber regrowth
- corneal edema, pigmentation, or other opacity
- KCS
- need to remove eye
how do you treat cataracts if surgery is not an option?
- prevent/control/manage LIU
- monitor for potential secondary glaucoma
- lens resorption may result in improved (far sighted) vision
- most visually impaired animals adjust well
- salvage therapy for painful irreversibly blind eyes: enucleation
describe lens luxation
due to zonular failure!!
- primary:
-inherited zonular ligament dysplasia
-TERRIERS, spaniels, others
-eventually bilateral - secondary to:
-uveitis, cataract, glaucoma, NOT trauma unless severe or predisposed eye
what are the 4 types of lens luxation?
- lens instability: irido and/or phaco-donesis
- subluxation
- anterior luxation:
-lens in anterior chamber
-occurs mainly in PUPIL
-can cause acute, severe, secondary glaucoma and warrant urgent lens removal surgery - posterior luxation
describe treatment of lens luxation
- address underlying cause if secondary, lower IOP (NO MITOTICS if lens anterior)
- lensectomy (removal)
- trans-corneal reduction of anterior lens luxation (TRALL)
- medical management:
-especially if lens posterior
-caution with drugs that alter pupil size - enucleation
