7: the lens - pearce Flashcards
what are the components of the lens?
where are they located relative to each other?
capsule, anterior epithelium, cortex, nucleus, equator
nucleus is the center, cortex is around the nucleus and capsule is thin outer coating
where is the lens located?
in the patellar fossa
what structure suspends the lens in its location?
zonular fibers - run from ciliary body to lens
what occurs to the lens when zonular fibers break down?
lens luxation
what are “Y-sutures”?
under what circumstances are they more visible?
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
where are “Y-sutures” located?
and upside down “Y-sutures” ?
Y sutures are anterior and upside down Y sutures are peace signs
why do many other species have larger lenses than humans?
humans have high corneal refraction - vs other spp which depend on lens for refraction more than we do
what shape lens do water animals have?
and land animals?
water -> spherical
land -> ellipsoid
t/f
the lens is very vascular
false
the lens is AVASCULAR after birth
where does the lens derive its nutrition from?
the aqueous humor
[NOTE: this is why things wrong with the aqueous humor can be reflected in the lens]
what is the 1* metabolic pathway utilized by the lens?
hexokinase pathway
what molecule does the lens utilize for energy?
glucose -> metabolized into lactic acid [I think]
how does glucose enter the lens?
active transport and diffusion
when aerobic glycolysis is utilized in the lens, what pathway?
citric acid cycle
how does lens physiology change in diabetic patients?
inc blood glucose -> hexokinase pathway saturated -> shunt glucose towards alternative pathway -> aldose reductase enzyme -> sorbotol is produced
what alternative pathway is glucose shunted to in diabetic patients who have a saturated hexokinase pathway?
what is produced as a result?
aldose reductase enzyme
sorbotol is produced
how does sorbotol in the lens lead to cataracts?
sorbotol diffuses poorly across the lens
it has higher osmotic pressure so leads to intense lens swelling
aqueous humor is imbibed
t/f
the occurrence of cataracts is approximately equal in dogs and cats
why or why not
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
t/f
nuclear sclerosis is a form of cataracts
false
nuc sclerosis is an aging change, NOT a true lens opacity but a translucency
a cataract is a true lens opacity
how does nuclear sclerosis develop?
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
what is the presentation and appearance of nuclear sclerosis?
bilateral pearl like nuclear density spherical translucent fundus detail visible NOT a cataract
what is microphakia?
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
what is lenticonus?
etiology?
anterior or posterior protrusion of the lens
will see pointed profile / angle to the lens when it should be smooth
congenital
what is PHPV?
PHTVL?
persistend hyperplastic primary vitreous?
persistent hyperplastic tunica vasculosa lentis
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
what does a cataract look like?
focal or diffuse lens opacity
what is the prevalence of cataracts in dogs?
2.42%
t/f
dilation is important in order to dx cataract?
true - dilation allows more complete exam and should be done
t/f
cataracts can be diagnosed with either retro illumination or direct illumination?
true
under direct illumination, what is the appearance of nuclear sclerosis vs cataract?
nuc sclerosis appears hazy or translucent
cataracts appear white
under retro illumination, what do cataracts look like compared to nuclear sclerosis?
cataracts appear black
nuclear sclerosis appears clear
during a fundus exam, if cataracts are present, what will you see?
you will see a shadow on the retina/fundus
in what ways are cataracts classified?
stage of development position age of development etiology consistency
what are 4 classifications of cataracts based on stage of development?
incipient
immature
mature
hypermature
which stages of cataracts have a smokey appearance?
incipient, immature, mature
what stage of cataracts has a sparkly appearance?
hypermature
what stages of cataracts have a smooth capsule?
incipient, immature, mature
what is the texture of the capsule if a hypermature cataract?
wrinkled
what % of the lens is affected by incipient cataracts?
0-15%
what % of the lens is affected by immature cataracts?
15-98%
what % of the lens is affected by mature cataracts?
90-100%
what % of the lens is affected by hypermature cataracts?
OVER 100
what does intumescent mean?
swollen
what category of cataract typically has an intumescent appearance?
mature
what stage of cataracts has areas of re-absorption?
hypermature
what does a lens with a Morgagnian appearance have?
slightly suspended and dropped down - hyper mature - nuc becomes more liquid and NOT held up in the middle as well
how can cataracts be classified according to position?
capsular sub capsular cortical equatorial nuclear perinuclear anterior posterior
how can cataracts be classified based on age of development?
congenital developmenta juvenile senile acquired
what are 2 main classifications of etiology / pathogenesis for cataracts?
1*
2*
what is the nature of 1* cataracts?
inherited
what are some things that lead to 2* cataracts?
traumatic uveitis nutritional radiation diabetic toxic congenital senile
what is MC cause of cataracts in dogs?
1* - inherited
what is 2nd MC cause of cataracts in dogs?
2* to diabetes
what is MC cause of cataracts in cats and horses?
2* to uveitis
what dz does cataracts predispose patients to?
lens-induced uveitis
what are the 2 types of lens induced uveitis?
phacoCLASTIC
phacoLYTIC
what is the progression of lens induced uveitis?
leakage occurs and mounts an Aby response => proteins deposit in eye d/t the reaction
what is phacoclastic vs phacolytic lens induced uveitis?
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
what is the likely result if cataracts are neglected to be treated?
100% failure => enucleation
what are medical options to treat cataracts?
anti cataract drugs
anti inflammatory drugs
how effective are anti cataract drugs?
ineffective => typically delay professional care
what type of treatment is the only cure for cataracts?
surgery
what are 3 types of surgery of the lens?
- extra capsular extraction
- intra capsular extraction
- phacoemulsification
which 2 types of surgery of the lens are a large incision?
extra capsular extraction
intra capsular extraction
how is an extra capsular extraction performed?
what is incised and what stays?
- capsule is incised, lens extracted via manual extraction; large incision
- capsule stays
how is intra capsular extraction performed?
- the lens is removed with the entire lens capsule via manual extraction; large incision
how is phaco emulsification performed?
capsule is incised, automated extraction via irrigation / aspiration
small incision
capsule stays behind
at what point should a cataract be referred to specialist?
at initial diagnosis
what does the ophthalmologist evaluation consist of?
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
what is a major key to post operative success for cataract surgery?
eyedrops
what are common complications of cataract surgery?
uveitis
glaucoma
retinal detachment
less common: persistent corneal edema synechiae intraocular hemorrhage corneal ulceration suture failure
what meds are used before cataract surgery?
anti inflammatory
dilation
abx
what meds are used after cataract surgery?
anti inflammatory abx dilation maybe anti glaucoma maybe e collar (4-6 weeks)
what is pseudophakia?
a prosthetic lens
what is aphakia?
absence of lens
what is the appearance of an anterior lens luxation?
- ID lens in anterior chamber
- pupil margin obscured
- shallow / absent anterior chamber
- aphakic crescent
what breeds are prone to anterior lens luxation?
- jack russell
- other terrier breeds
- chinese crested
- shar-pei
what is etiology of primary etiology?
hereditary
common in terrier breeds
what are some common causes of 2* lens luxation?
- glaucoma [buphthalmos]
- uveitis [cats] - break down of lens fibers (zonular degeneartion)
- intraocular tumors
- cataracts
- blunt trauma
t/f
chronic or 2* luxation is a surgical emergency
false
NOT a surgical emergency
acute and 1* lens luxation leads to what condition?
2* glaucoma
t/f
acute primary luxation is a surgical emergency
true
t/f
acute 1* lens luxation is painful
false
what is vitreous presentation of an eye?
common in lens luxations
gel comes forward if the lens is not holding it in place - viterous sneaks around lens and into the pupil
what are 3 surgical options for anterior lens luxation?
- intracapsular lens extraction
- enucleation
- evisceration w prosthesis
what is the goal / prognosis associated w enucleation procedure?
comfort preservation only
when is intracapsular lens extraction performed to repair anterior lens luxation?
prognosis?
- visual animal with acute vision loss
- referral Sx: remove capsule and entire lens
- 50% chance for long-term vision and comfort
what is the prognosis of evisceration with prosthesis to repair anterior lens luxation?
comfort preservation only
what is the only anterior lens luxation surgery that has a chance for long term vision and comfort?
intra capsular lens extraction
what are 2 goals of medical management of anterior lens luxation?
*NOTE: these are done prior to referral
- lower IOP
- dec inflammation
what drugs are used to dec IOP to Tx anterior lens luxation?
- Mannitol [2mg/kg IV]
- carbonic anhydrase inhibitors
what are 2 carbonic anhydrase inhibitors used to Tx anterior lens luxation?
- topical dorzolamide
- oral methazolamide
what drugs are used to dec inflammation to Tx anterior lens luxation?
also what method of administration?
- prednisone acetate - topically
- other anti inflammatories - orally
when is lens trapping done to Tx anterior lens luxation?
what drugs do this?
ONLY if posterior lens luxation
synthetic PGs
