Lens and Vitreous Flashcards
1
Q
What is the anatomy of the lens?
A
- Parts:
- Lens capsule
- anterior
- posterior
- anterior lens epithelium
- lens fibers
- equator
- nucleus
- cortex
- Lens capsule
- Suspended between ciliary body processes and lens equator by zonules
- Y sutures = ‘lens seams’
- most mammals
- anterior upright ‘Y’
- Posterior upside down ‘Y’
2
Q
What is the physiology of the lens
A
- Continuous growth throughout life
- Epithelial cells from the lens fibers
- New fibers compress older fibers in the center
- Hardening of the nucleus with age = nuclear sclerosis
- Lens is transparent and avascular
- Nutrition from aqueous humor
- Main role is refraction - bending of light to focus on retina
3
Q
What congenital defects affect the lens?
A
- Persistent fetal vasculature
- Persistent hyaloid artery (or remnant)
- Pupillary membrane
- Iris-to-lens PPM (focal cataract)
- Axial anterior lens capsule pigment spots
4
Q
What is Nuclear Sclerosis?
A
- Normal aging process
- Visible as a grayish-blue haze
- Minimal Effect on vision
- Important to differentiate from Cataractss
- can retroilluminate and see through to perform fundic exam
- Decrease in accommodation
5
Q
What is a cataract?
A
- Opacity in the lens or capsule
- Should have a normal PLR and dazzle reflex
- Classification on:
- Etiology
- Age of onset
- Location in lens
- Stage of development
6
Q
What are the possible etiologies of cataracts?
A
- Hereditary (most common in dogs)
-
Metabolic
- Diabeties mellitus (#2 in dogs)
- Galactosemia
- experimental
- Milk replacer
- Hypocalcemia (hypoparathyroidism)
-
Secondary to Uveitis
- most common cause in cats and horses
-
Traumatic
- blunt or penetrating trauma
- electric cord shock or lightening strike
- Radiation
-
Toxic
- Ketoconazole
- Retinal degeneration (PRA)
7
Q
How are cataracts classified by age of onset?
A
- Congenital - present at birth
- Juvenile - young animals (1-5 years)
- Adult
- Senile - older animals
8
Q
Where can cataracts be located?
A
- Location:
- Capsular
- Subcapsular
- Nuclear
- Cortical
- Equatorial (peripheral)
- anterior/posterior
- Differentiate by direct exam
- must have pupil dilated
9
Q
What are the stages of cataracts?
A
-
Incipient
- punctate opacity
- <15% of lens
-
Immature
- between 15 - 99%
- some tapetal reflection remains
-
Mature
- complete opacification
- no tapetal reflection visible
- intumnescent - swollen lens fibers in diabetic dogs
- Absent menace response
-
Hypermature
- resorption of cataractous lens fibers
- Highly variable appearance: sparkling, wrinkled capsule
- Morgagnian cataract - complete resorption of cortex and the nucleus “sinks” to the bottom of the lens capsule
- May see tapetal reflection and patient may regain some vision
10
Q
What is the metabolism of the lens
A
- Glucose normally metabolized by anaerobic glycolysis
- High blood glucose results in elevated aqueous humor glucose, increasing lens glucose and overwhelming the hexokinase (HK) enzyme
- Excess glucose is metabolized by aldose reductase (AR) enzyme (polyol pathway) and converted to sorbital
- Sorbitol accumulates within lens (too large to diffuse in-and-out) and cause osmotic effect
- Fluid drawn into lens, causing cataract
11
Q
What are the possible sequela of cataracts?
A
- Phacolytic uveitis
- leakage of lens proteins through intact lens capsule
- Phacoclastic uveitis
- Rupture of lens capsule exposing lens proteins acutely
12
Q
How are cataract treated medically
A
- Prevent lens-induced uveitis
- Topical NSAIDs
- Flurbiprofen 0.03%
- Diclofenac 0.1%
- Ketorolac 0.5%
- Topical NSAIDs
- Monitor eye status and IOP
- For active LIU:
- topical steroid
- Oral NSAID
13
Q
What is Cataract Surgery? How is eligibility determined
A
- Ideally when mid-immature with no LIU
- Only true “cure”
- elective and $$$
- Considerations:
- Uveitis must be controlled
- General physical health of animal
- Temperament of animal
- Client commitment
- Surgical work-up
- Complete ophthalmic exam
- Physical exam
- special considerations for diabetics
- Gonioscopy
- Electroretinogram
- Ocular ultrasound
14
Q
What are the possible complications of Cataract Surgery?
A
- Most cases (85-90%) are successful
- The 10-15% that are unsuccessful are bad
- Post-op complications:
- Uveitis
- Glaucoma
- Retinal Detachment
- Endophthalmitis
- Complications occur more frequently in certain breeds, in younger dogs, and with hypermature cataracts
15
Q
What are the types of lens luxation?
A
- Subluxation - partial detachment of lens zonules
- may see “aphakic crescent” with retroillumination
- Luxation - complete detachment of lens zonules
- anterior - lens is anterior to iris (in anterior chamber)
- Posterior - lens is posterior to iris, often shifted into vitreous chamber
17
Q
What is the treatment for anterior lens luxation?
A
-
Emergency if recent and dog is visual (or was recently)
- Trans-corneal reduction if very acute
- Surgery: intracapsular lens extraction
- Treat secondary glaucoma
- Mannitol IV or glycerin PO
- Topical/oral carbonic anhydrase inhibitors
- Do Not give miotics (pilocarpine, latanoprost
- Trap lens in anterior chamber
- Secondary Lens luxation is not an emergency
