The Lens Flashcards
What type of cataract typically occurs in diabetic patients?
Intumescent cataract
(intumescent means swollen… due to sorbitol causing osmotic shifts)
What is the most common pathology to occur to the lens?
- Cataracts
- Lens luxation
What is the purpose of lens zonules?
suspensory ligaments connect the ciliary body to the lens
What characteristics of the lens is responsible for its clear structure?
- No blood vessels
- No pigment
- Ordered cell arrangement
- Soluble crystalline proteins
(some similar characteristics as the cornea)
What is the basic function of the lens?
Focus light onto the retina to produce a sharp image (accommodation)
What is a normal aging change of the lens that can be seen in older pets?
Nuclear sclerosis (hazy cloudy eye - NOT a cataract)
How can you differentiate nuclear sclerosis of the lens vs a cataract?
- No apparent vision loss with nuclear sclerosis
- Tapetum reflection and fundus still visible with nuclear sclerosis
(not able to see the back of the eye with cataracts unlike NS)
You are trying to determine the location of a cataract within the lens. When the patient moves their right eye to the left, the opacity moves in the opposite direction (to the left). What can you determine?
Posterior lens cataract - opacity moves in the opposite direction as the eye
You are trying to determine the location of a cataract within the lens. When the patient looks down, the opacity moves down too. What can you determine?
Anterior cataract - moves with the eye
You are trying to determine the location of a cataract within the lens. When the patient looks down, the opacity moves up within the lens. What can you determine?
Posterior cataract - moves in the opposite direction as the eye
What is parallax, and why is it useful when trying to diagnose a cataract?
- Helps determine the depth and location of cataracts
- Move the eye and see how the opacity moves in relation to the lens
What are the 4 stages of cataract maturation?
- Incipient
- Incomplete/Immature
- Complete/Mature
- Resorbing/ Hypermature
What is an incipient cataract?
- Small opacity < 20% of the lens affected (focal)
- Tapetal reflection still visible
- No significant vision loss
What is a incomplete cataract and how does it appear?
- Any cataract between incipient and complete
- Tapetal reflection still visible
- Like looking at cracked glass (streaky opacity)
What is a complete cataract?
- When 100% of the lens is affected (entire lens opacity)
- Can’t see tapetum reflection
- Eye is blind
What is a resorbing cataract and how does it appear?
- When the lens cortex liquefies
- Capsule wrinking
- Deep anterior chamber
- Tapetum reflection may return
- Sparkly lens with wrinkled capsule
(associated with lens induced uveitis… proteins leaking out of lens causing secondary uveitis)
What is an intumescent cataract and how does it appear?
- Lens becomes swollen and increases in size
- Anterior chamber becomes shallow
- Seen in diabetic patients
- Can be a complete or incomplete cataract
- Y cleft of the lens can be seen
What is the most common cause of cataracts in dogs vs cats and horses?
Dogs - inherited
Cats and horses - inflammatory (Chronic uveitis causing secondary cataracts)
Knowing the most common cause of cataracts in horses and cats, how can the eye appear other than opacity of the lens?
- Look for signs of concurrent uveitis (keratic precipitates, hypopyon, color changes to the iris, episcleral injection)
(most common cause of cataracts in horses and cats)
What is the pathophysiology behind diabetes mellitus resulting in secondary cataract formation?
- Glucose converted to sorbitol by aldose reductase
- Pulls water into the lens causing swelling, denatures lens proteins
What is the most common cause of metabolic cataracts?
Diabetes mellitus
Why is metabolic cataracts less common in cats than dogs?
Dogs have high levels of aldose reductase which converts glucose to sorbitol in the eye
(cats have less aldose reductase, less likely for diabetes mellitus to cause cataracts)
What is the earliest visible changes that can be seen in patients with diabetic cataracts?
- Equatorial lens vacuoles within the periphery of the lens
(progressives rapidly to mature, intumescent cataract)
What is the most common cause of nutritional cataracts?
Puppies and kittens fed milk replacement instead of moms milk
What causes endogenous toxic cataracts?
- Associated with retinal disease / progressive retinal atrophy
- Degenerating photoreceptors releasing toxic substances into vitreous
- IMPT to exclude prior to pursuing cataract surgery
What causes senile cataracts?
Photooxidative injury (UV light)
(usually small and doesn’t impair vision, but can range from incomplete to complete)
What are common sequelaes to cataracts?
- Visual impairment
- Lens induced uveitis
- Glaucoma
- Retinal detachment
(If advanced - can lead to permanent blindness, cataract surgery not an option of choice at this point)
What is the phacoclastic form of lens induced uvietis?
- BAD
- Severe form associated with traumatic tear of the lens capsule
What is the phacolytic form of lens induced uvietis?
- Milder than the phacoclastic form
- Slow leakage of lens proteins from a cataract
- Suspect in any red eye with a cataract!!
- Tx with topical steroid or NSAID
What is the medical treatment protocol for patients with cataracts?
- Anti-inflammatories (Topical NSAID - Diclofenac) usually life long
(helps control lens-induced uveitis/ secondary uveitis, reduces incidence of secondary glaucoma)
What is the surgical treatment option for patients with cataracts?
- Phacoemulsion (make a corneal incision and suck out the cataract using a vibrating probe)
- Place an artificial lens (pseudophakia)
When should animals be referred for cataract surgery?
At the time the cataract is first detected
(early referral has highest chance of success)
List the primary causes of lens luxation
- Inherited disorder in terrier breeds
- Abnormal degeneration of zonular ligaments
List the secondary causes of lens luxation
- Chronic uveitis (most common in cats)
- Glaucoma (enlargement of globe can stretch and break zonular fibers)
- Trauma (uncommon)
What should you suspect in any terrier with a painful eye?
Anterior lens luxation
