Lens disease Flashcards
What embryologically occurs to cause aphakia?
failure of contact of optic vesicle with surface ectoderm = lens placode doesn’t form
How common is aphakia?
extremely rare
If you see a microphakic lens, what other lens change is commonly present?
Spherophakia
Other than congenital disorder, what causes acquired microphakia?
Zonular disorders (insufficient traction) think about terriers...
What are the 2 types of lens colobomas? How do they get classified as such?
Typical: 6 o’clock
Atypical: anywhere else
Lens colobomas are often associated with a coloboma WHERE?
Uvea
What can occur if there is an extensive coloboma?
Lens luxation
What common lens disorder is often associated with lens colobomas (of any size)?
Cataract
What is the embryological basis of PPMs?
They are remnants of the anterior tunica vasculosa lentis
How long does the anterior pupillary membrane remain in the dog?
14 days after birth
Are PPMs generally considered hereditary?
NO
What breed are PPMs commonly considered hereditary?
Basenji
What disorder is commonly associated with PPMs?
Cataract
What finding on the SURFACE of the lens is attributed to remnants of the pupillary membrane?
Pigment
What 2 breeds commonly get pigment on their lens from pupillary membrane remnants?
Doxies, Cairn Terriers
Why is PHTVL/PHPV considered bad?
Commonly associated with cataract
How many grades of PHTVL/PHPV exist?
Six (1 being the least affected)
What is the difference btwn lenticonus and lentiglobus?
Lenticonus = cone like Lentiglobus = spherical
Where can lenticonus/globus occur on the lens? What location is most common?
Posterior cortex/capsular regions, into the vitreous body
Also can see anteriorly and axially
What is lenticonus internum?
Lens nucleus extends into posterior cortex
Review CONGENITAL abnormalities that can be associated with cataracts
- Congenital cataract (alone)
- Lens coloboma
- PHTVL/PHPV and PPMs
- Lenticonus/lentiglobus
- Multiple ocular abnormalities
- Oculoskeletal dysplasia (form of MOA)
Where are congenital cataracts usually seen? Progressive?
FETAL NUCLEUS
non-progressive, but can involve adjacent anterior/posterior cortex
What are 3 potential causes of congenital cataracts?
- Hereditary
- Toxin exposure in utero
- Infectious agent exposure in utero
How are most cataracts inherited?
Autosomal recessive
What 2 breeds of dog have incomplete dominant inheritance of cataracts?
Chesapeake Bay Retriever
GSD
What breed has autosomal DOMINANT inheritance of cataracts?
Norwegian Buhund
What 2 breeds have triangular, posterior polar cataracts?
Golden, Lab
What 2 changes are seen histologically indicating a lens rupture?
- Curled lens capsule
2. Intralenticular leukocytes
What are bladder cells? Appearance?
Swollen lens epithelial cells
Balloon-like (increased particulate matter in cytoplasm), usually in LENS BOW region
What change is often seen histologically with posterior cataract?
Migration of epithelial cells along posterior lens capsule
What are Morgagnian globules? How do they appear?
Lytic lens proteins
Basically aggregates of eosinophilic lens proteins in aggregates
Wha 3 locations are most commonly associated with incipient cataracts?
- Cortex
- Subcortical
- Y-suture
What change to the anterior/posterior capsule is commonly seen with HYPERMATURE cataracts?
Plaque formation
What age of dog most commonly develops Morgagnian cataracts?
<1 year
What is the anterior extent of Cloquet’s canal called?
Mittendorf’s dot
Punctate lens opacities have been found in what percentage of dogs?
30-40%
What is the progression of Y-suture cataracts?
Often disappear
How many breeds of dogs are THOUGHT to have hereditary cataracts?
> 160 breeds
BUT very few have been proven
What signalment is most common with hereditary cataracts?
Pure bred dog, young to middle aged
What 2 breeds get oculoskeletal dysplasia (which is associated with cataracts)
Lab, Samoyed
What 2 gene mutations are associated with oculoskeletal dysplasia?
COL9A2 and COL9A3
Describe metabolic pathway leading to diabetic cataracts
High levels of glucose in lens –> saturate hexokinase pathway –> shifted to polyol pathway –> aldose reductase turns glucose into sorbitol –> sorbitol doesn’t diffuse out of lens –> osmotically pulls water into lens –> lens fibers swell and rupture, vacuoles form, etc –> sorbitol can also be oxidized into fructose via sorbitol dehydrogenase
What happens to aldose reductose in diabetic animals (specifically, there is something different with this enzyme over normal)
Increases in amount
What percentage of diabetics will develop cataracts at 6 months? 1 year? 15 months?
50%, 75%, 80%
Spontaneous lens capsule rupture occurs most commonly in what location?
Equatorial
Multifocal punctate cataracts that are bilaterally symmetrical are associated with what electrolyte disorder (and what systemic diseases?)
Hypocalcemia
[renal failure, primary or secondary hypoparathyroidism]
Treatment of hypocalcemia– can it affect cataracts?
May prevent progression, but won’t resolve what is there
What LOCATIONS (2) is most commonly seen with TOXIC cataracts?
Anterior and posterior cortex near the EQUATOR (area of lens fiber elongation) OR at Y-suture
What appearance is usually associated with toxic cataracts?
Vacuoles
What anti fungal can cause cataracts?
Ketoconazole
What administration of ketoconazole is commonly associated with cataracts?
Chronic (>4-37 months)
What is the most common TOXIC form of cataract seen clinically?
Secondary to PRA or other types of retinal degeneration
What 3 breeds most commonly have cataracts associated with their PRA?
1) Lab
2) Mini poodle
3) Toy poodle
What is the progression of retinal degeneration-associated cataracts?
They will eventually affect the entire lens
What nutritional deficiency is associated with cataracts?
Arginine
What location is most associated with traumatic cataracts?
Anterior SUBCAPSULAR
What are other signs that the cataract may have been traumatic?
- Iris pigmentation on lens (esp if blunt trauma)
- Corneal scar over similar location
- Cataract progressively gets “deeper” as more lens fibers are added to lens
- Unilateral
If a traumatic cataract occurs over a lens suture, what is the appearance?
Stellate
Why do dogs and rabbits seal their lens rents so well?
They have a fibrinous anterior uveitis
What size rent to the lens capsule suggests it should be removed (or else risk severe phacoclastic uveitis?)
1.5 mm+
What metal is usually well tolerated if it enters the lens? What metals are not well tolerated?
Lead
ANY other metal = usually not well tolerated (esp steel and iron)
What is the risk if an oxidizing metal (steel, iron, copper, zinc, brass) are left in the eye?
Panophthalmitis
What type of cataract is associated with electrocution/lightening strike? Are they progressive?
BILATERAL anterior subcapsular
Usually PROGRESSIVE
When are cataracts usually seen with ionizing radiation?
> 6 months from initial exposure
What arbitrary ages are usually used to assign senile cataracts?
> 6 yr small breed
>10 yr large breed
What location and appearance is commonly associated with senile cataracts?
NUCLEAR, punctate to linear
What appearance (2) is commonly associated with senile cataracts OUTSIDE of the nucleus (i.e. in the cortex)?
Wedge-shaped or spoked
What is the long-term prognosis for vision with senile cataracts?
Good–usually very slow progression and never appreciably affect vision
What percentage of dogs will develop some sort of lens opacity?
ALL of them (senile cataracts eventually if live long enough)
What is the common location for uveitis-induced cataracts?
equatorial or anterior/posterior subcapsular
How bad does uveitis need to get to cause a cataract?
Moderate to severe
What percentage of dogs will develop phacolytic uveitis?
~70% (if not treated)
What is the risk of glaucoma secondary to phacolytic uveitis?
Has not been definitely documented
What are 2 common ways to develop phacoclastic uveitis?
- Intumescent cataract that ruptured
2. Traumatic lens rupture/lens implantation syndrome
What is the prognosis for phacoclastic uveitis?
POOR– generally does not respond well to anti-inflammatories
Why is phacoclastic uveitis usually worse than phacolytic?
Phacolytic: only recrystallized lens proteins
Phacoclastic: membrane-associated antigens also present
What percentage of the lens needs to be affected before demonstrable vision loss is seen?
40-50%, and usually BOTH lenses!
How long is a menace maintained with cataracts?
Usually to near completion of cataract
Why do some dogs sometimes see better in the dark if they have cataracts?
Pupil is dilated
Spontaneous resorption of a cataract is usually seen in what 4 breeds?
- Toy poodle
- Miniature poodle
- Miniature Schnauzer
- American Cocker
What 2 complications are higher with hyper mature cataracts?
- Vitreal degeneration and retinal detachment
2. Lens subluxation/luxation
With a lens luxation, if there is associated corneal edema, will it resolve?
It may, or it may be permanent
What is more likely to lead to anterior uveitis: anterior lens luxation or posterior?
Anterior
What is more likely to lead to pupil block glaucoma: anterior or posterior lens luxation?
Anterior
What gene is associated with primary lens luxation?
ADAMTS17
How is primary lens luxation inherited?
autosomal recessive
What age range is primary lens luxation seen?
3-6 yrs
What is the likelihood that blunt trauma caused a lens luxation?
Unlikely, if that is the only thing seen
In PLL dogs managed with miotics, what percentage had vision at 1 year and 2 years?
1 year: 80%
2 years: ~60%
