What 2 breeds of horse develop uveal cysts from anterior segment dysgenesis?
Rocky Mountain Horse (of course)
Connemara pony
What can help differentiate uveal cysts from iris melanoma?
They do not invade the iris (they are also round and smooth)
What location for cysts appear to cause more vision issues in horses?
If they are ventral
If a uveal cyst is not causing problems in a horse, why might you laser it?
They are sometimes associated with behavioral problems and can cause some vision issues, and they get harder to rupture with laser the longer you wait.
Horse with BILATERAL lesions at the limbus filled with eosinophils, what is your likely diagnosis? What if there are yellow “sulfur granules” also seen?
Eosinophils: r/o eosinophilic keratitis
Eosinophils + sulfur granules: r/o Habronema
What type of cyst is uncommon, but can cause exophthalmos in horses?
Dentigerous cysts
Big, pink fleshy lumps on the conjunctiva/limbus/cornea of a horse. What are 3 DDx, and 1 DDx that is NOT seen in horses that you would include in dogs?
1) SCC - usually older (11 yrs)
2) Lymphocytic proliferation - think this in very young horse
3) Orbital fat prolapse - this will be SOFT (vs SCC)
NOT pannus (that is a dog disease)
SCC on the third eyelid of horse– how aggressive should you get?
Remove 3rd eyelid quickly; these can grow behind the eye, and can kill the horse (note– there are other options available for ocular SCC)
What chemotherapeutic is sometimes used topically in horses with SCC?
Mitomycin C
What breeds of horses are more associated with SCC?
Haflinger! Also Appaloosa, Paint, draft (Belgian, Shire, Clydesdale)
Where can SCC originate in horses?
Cornea, conjunctiva, limbus
Although many SCC appear as nodular in horses, how can some appear (making them harder to diagnose)? How is it diagnosed?
Stromal infiltrate – keratectomy
Is SCC painful?
NO
Phenylephrine in a horse eye– when does it dilate?
Only if used with atropine
What causes anterior segment dysgenesis?
Issue with the mesoderm or the optic stalk during fetogenesis
What is the significance of anterior segment dysgenesis?
Generally no huge disruption of vision unless severe
What DDx do you need to r/o if you are concerned about anterior segment dysgenesis?
Anterior uveitis
In severe cases of anterior segment dysgenesis, what can be seen?
- Microphthalmia
- Microphakia
- Corneal opacity
What are the 4 locations you see SCC?
- Third eyelid
- Limbal
- Corneal
- Eyelid
Which SCC location is most associated with death? Why?
3rd eyelid– likes to invade into orbit
Which SCC location is most associated with loss of globe?
Limbal
Which limbus is most commonly affected?
Lateral
When should MMC NOT be used for SCC?
When there is an ulcer (so delay its use post-surgery)