Lecture Eight: Lens and Cataracts

The lens is made of surface ectoderm, whereas most of the eye is made of neuroectoderm and mesoderm. So, it is seen as foreign antigen material, causing an inflammatory response.

Describe the embryology of the lens.

A = ciliary body

B = zonules

C = lens

Label this diagram.

Anterior capsule

Which side of the lens capsule is thicker and has epithelial cells?

Posterior capsule

Which side of the lens capsule is thinner and has no endothelial cells?

Accommodation (changes shape or position to focus light on the retina, allowing visualization of near or far objects)

What is the primary function of the lens?

- Non-pigmented

- Avascular

- Precise organization of fibers

- Few organelles

- Relatively dehydrated

- Precise crystalloid protein ratios

How does the lens maintain transparency? (6)

1/3 of the way around the lens (normal to see Y sutures in cats and dogs)

Each suture extends how far around the lens?

Nuclear sclerosis

What am I describing?

- Lens fibers increase in density and become clinically apparent in the center of the lens

- compacted inward (lens nucleus) but remain normal

- Normal aging change

- Bilateral and symmetric

- Doesn't interfere (much) with vision

- Can visualize the tapetal reflex through it

- You can look through nuclear sclerosis to the retina with an ophthalmoscope

- Nuclear sclerosis is bilaterally symmetrical

How can you differentiate nuclear sclerosis from a cataract?

Mydriasis (large pupil)

- Allows you to evaluate symmetry and location of the lens opacity

What is imperative to accurate lens diagnosis?

It doesn't (think of frosted glass — light still gets through)

How does cataract affect the PLR?

- Microphakia

- Spherophakia

- Colobomas

What are the diseases of shape of the lens? (3)

Cataract

What are the diseases of transparency of the lens? (1)

Subluxation and luxation

What are the diseases of position of the lens? (1)

False — it is NEVER normal.

T/F: it is normal to see the equator of the lens

Microphakia

What am I describing?

- Congenitally small lens

- Allows visualization of the lens equator and zonules

- Doesn't need treatment

- May be associated with cataract or other lens abnormalities

None

What is the treatment for microphakia?

Spherophakia

What am I describing?

- Congenitally round lens

- Frequently accompanies microphakia

- Need a slit lamp to diagnose

Coloboma

What am I describing?

- "Flattened" area of lens equator

- May be accompanied by dysplasia ciliary processes

- May be associated with progressive cataract

Cataract

Any opacity of the lens

- Anterior subcapsular

- Anterior cortical

- Equatorial

- Lamellar / perinuclear

- Nuclear

- Posterior cortical

- Posterior subcapsular

- Axial

What are the 8 location classifications of cataracts?

Incipient cataract

What am I describing?

- Cataract

- <10% of total lens volume

Immature cataract

What am I describing?

- Cataract

- 11-99% of total lens volume

- Further divided into early and late

Mature cataract

What am I describing?

- 100% of lens is cataractous

Immature cataract

What am I describing?

- Cataract

- 11-99% of total lens volume

- Further divided into early and late

Hypermature cataract

What am I describing?

- Cataract

- Resorbtion of lens material

- Starting to shrivel up!

Morgagnian cataract

What am I describing?

- Cataract

- All cortical material has been resorbed, leaving behind nucleus

- liquified!

dilate, distance exam, examine in dark

Overall, how is a cataract examined?

Hereditary

What is the most common overall cause of cataracts in dogs?

Diabetes mellitus (85% of diabetic dogs develop cataracts within 18 months of diagnosis)

What systemic disease commonly causes cataracts in dogs?

senile

? animals generally get cortical/complete cataracts

- The normal glycolysis pathway is overwhelmed because of elevated glucose

- So, it shifts to the sorbitol pathway where aldose reductase is the rate limiting enzyme

- Results in a swollen, cataractous lens

- sutures a good indicator

Describe the pathophysiology of diabetic cataracts.

Start topical anti-inflammatories (NSAID) early

What should you do when you start to see cataracts in diabetic dogs?

scattered dots

what do you see with nutritional cataract?

Penetrating trauma

(Blunt/penetrating) trauma is more often associated with cataractogenesis.

1. Chronic Uveitis - MOST COMMON CAUSE IN CATS

2. Retinal degeneration - posterior polar

3. Persistent hyaloid artery

4. Posterior synechia, PPM, etc.

Secondary cataracts can develop due to various ocular diseases that disrupt lens metabolism and transparency. These include ? (4)

Secondary to chronic uveitis*******!!!

What is the most common cause of cataracts in cats?

posterior polar

retinal degeneration =

1. Location within the lens

2. Extent of lens involved

3. Etiology

4. Age of onset - congenital, juvenile, adult, senile

5. Shape, appearance

Many ways to classify cataracts?

Active cataract formation/progression (often diabetic)

What does the presence of vacuoles indicate?

- rapid progression (often diabetic)

- Risk for rupture if severe - refer for surgery QUICKLY

Intumescent (swollen) cataract?

Phacoemulsification

- Make a 3 mm incision, use ultrasound energy to break up the cataractous lens, and aspirate it through the same handpiece

What is the surgical treatment of choice for cataracts?

1. visual impairment

2. Phacolytic uveitis (lens-induced uveitis)

3. Phacoclastic uveitis

sequelae of cataracts?

Lens induced uveitis seen with cataracts

(Lens capsule is intact, but lens proteins are leaking through)

What is phagolytic uveitis?

- All cataracts larger than incipient

- Topical anti-inflammatory for life

What size cataracts are associated with clinically significant lens-induced uveitis? What is the treatment?

- Glaucoma

- Retinal detachment

- Posterior synechiae

- Keratitis

What are 4 consequences of untreated inflammation?

Glaucoma

Primary lens luxation is often associated with ....

There is a torn lens capsule —> leakage of lens proteins

—> overwhelming uveitis that can lead to vision loss.

What is phacoclastic uveitis?

• posterior synechiae

• glaucoma (inflammation, synechiae, or PIFM)

• pre-iridal fibrovascular membrane, glaucoma

• Zonular breakdown, lens luxation, glaucoma

• keratitis

• retinal detachment

phacoclastic uveitis complications ?

TRUE

TF: THERE ARE NO MEDICAL TREATMENTS THAT DISSOLVE CATARACTS!!

- uveitis--> proteins leak out of lens capsule.

- More rapid = more uveitis

All cataracts are associated with some ?

surgery!

- 90-95% success for long-term vision in dogs

- highest success rate when compared to other modes of cataract management, especially when performed early in the disease process

The only way to restore vision with cataracts?

displacement of the lens from its normal position due to breakdown or rupture of the zonular fibers that suspend it.

It can be primary (inherited) or secondary (due to underlying ocular disease).

what is lens luxation?

partial displacement of the lens due to weakened or incomplete rupture of the zonular fibers, causing lens instability while remaining partially in place.

subluxation?

Hereditary zonular dysgenesis in terriers – genetic testing

Often associated with glaucoma

Primary lens luxation?

Glaucoma -> buphthalmos -> zonular breaks

Hypermature cataract à shrinking pulls on zonules and breaks them

Chronic uveitis (most common cause in cats)

Secondary lens luxation?

"Aphakic crescent"

Change in AC depth

Phacodenesis (lens movement)

Vitreous prolapse into AC

subluxation signs?

- Referral for lens removal

- May also recommend concurrent therapy for glaucoma

- Disease is usually bilateral, so discuss therapy for the second eye (early lens removal; long-term meiotic therapy to prevent anterior luxation)

What is the treatment of primary anterior lens luxation?

- Glaucoma

- Chronic uveitis

- Intraocular neoplasia

- Penetrating trauma

What are 4 secondary causes of lens luxation?

- Medical = life-long therapy with meiotic to trap lens behind the iris

- Surgical = lensectomy +/- adjunctive therapy for glaucoma

What are the treatment options for primary lens subluxation?

Lens subluxation

You see an aphakic crescent; what is the likely cause?