Lecture 15 4/7/25 Flashcards
(31 cards)
What is a cataract?
opacity of the lens of the eye that does not allow light through
How do cataracts differ from nuclear sclerosis?
in sclerosis the lens appears hazy but light can still get through and vision is not affected
How are cataracts classified?
based on how much of the lens is opaque
What are the characteristics of incipient cataracts?
-very little cataract; less than 15% of lens
-often focal
-fundic reflex is still strong
-functional vision is normal
-can usually see some of the fundus on exam
-too early for surgical intervention
What are the characteristics of immature cataracts?
-easier to see the cataract
-some fundic reflection remaining
-functional vision still OK when early immature
-functional vision progressively worsens as cataracts become later immature
-retina difficult or impossible to see
-optimal stage for surgery
What are the characteristics of mature cataracts?
-entire lens is opaque
-no fundic reflex is visible
-not a bad stage for surgical intervention
What are the characteristics of hypermature cataracts?
-lens material can begin to liquify and become more soluble
-proteins that leak out of lens capsule incite inflammation due to being immunogenic
-wrinkling of anterior lens capsule
-glittery appearance to liquified lens material
-fundic reflex and ability to see retina are variable and based on amount on lens material resorption
-lower surgical success; more inflammation and higher secondary glaucoma rates
What are the characteristics of diabetic cataracts?
-diabetes is one of the most common causes of cataracts in dogs
-85% of diabetic dogs develop them within a year of diagnosis
-diabetic cataracts progress very quickly
How does diabetes cause cataracts?
-glucose enters the lens and is metabolized by anaerobic glycolysis
-intralenticular glucose levels exceed the saturation point of hexokinase
-glucose molecules are “left over” and can enter other metabolic pathways like the sorbitol pathway
-end products of sorbitol pathway are sorbitol and fructose, which cannot exit the lens like glucose
-retained sorbitol and fructose create a hyperosmotic environment in the lens
-lens swells, lens fibers break down, and cataract formation begins
What is important about the permanence of diabetic cataracts?
lens opacity cannot be reversed even if a normal blood glucose is reached
Why is an aldose reductase inhibitor used to prevent cataract formation in diabetic dogs?
aldose reductase is the first enzyme in the sorbitol pathway; inhibiting it prevents the formation of sorbitol and fructose in the lens
What are the two most common causes of cataracts?
-hereditary
-diabetes
Why do dogs with cataracts still have positive PLRs?
even with mature cataracts, enough photons get through to incite PLRs
Why do dogs with cataracts typically still have a menace response?
the menace response is very crude and only requires a small amount of remaining vision to be positive
What are the characteristics of an electroretinogram?
-test done in anticipation of cataract surgery
-electrodes are placed around eye and a light is flashed into eye
-electrodes feed into a voltage meter to determine amount of electricity produced in response to the flash
-normal ERG indicates retinas are functioning and animal can regain vision with cataract surgery
What is the most common cause of a bad ERG in dogs with cataracts?
progressive retinal atrophy
What is the purpose of ocular ultrasound?
done in anticipation of cataract surgery to detect or rule out retinal detachment
What is phacoemulsification?
method of choice for cataract surgery in which liquefaction of the lens is done in order to allow for lens removal through a smaller incision
What is intracapsular lens removal?
-lens and enveloping lens capsule are removed together
-no cuts are made into the capsule
-ciliary zonules must be disrupted
-reserved for removing luxated lenses
What is extracapsular lens removal?
-hole is created in anterior lens capsule
-lens is removed from remaining “capsular bag”
-equatorial capsule and posterior capsule are left in place
-can be accomplished manually or with phacoemulsification
What is an intraocular lens?
a prosthetic intraocular lens that is placed within the capsular bag
What does phakic mean?
an eye with a normal biological lens
What does aphakic mean?
an eye without a lens
What does pseudophakic mean?
an eye with a prosthetic intraocular lens
