Equine Recurrent Uveitis

Question 1

What is the term for inflammation of the uveal tract of the eye?

Answer 1

Uveitis

Question 2

What is the leading cause of blindness in the horse?

Answer 2

Uveitis

Question 3

Is ERU a primary or secondary cause of uveitis?

Answer 3

PRIMARY (it is a primary immune-mediated process, so there does NOT have to be anything elsewhere in the eye or in the body to initiate this recurrent inflammatory condition)

Question 4

True or false: ERU is one specific disease process

Answer 4

False - it is a syndrome or group of diseases with similar manifestations

Question 5

What part of the uvea is responsible for controlling the amount of light that enters the eye?

Answer 5

Iris

Question 6

What part of the uvea is responsible for producing aqueous humor and anchoring fibers that suspend the lens (zonules)?

Answer 6

Ciliary body

Question 7

What part of the uvea provides nutrition and oxygen to the highly metabolically active retina and is sandwiched between the sclera and retina?

Answer 7

Choroid

Question 8

What type of inflammatory cells predominate when lymphocytic infiltrate begins to accumulate in the uvea and other eye tissues?

Answer 8

T cells, MHC Class II reactive

Question 9

What is a key clinical sign of uveitis?

Answer 9

Miosis (unless there is secondary glaucoma)

Question 10

What are 5 signs of acute uveitis?

Answer 10

Hypopyon, hyphema, aqueous flare, keratic precipitates, and fibrin

Question 11

What is the hallmark sign of glaucoma in the horse?

Answer 11

Corneal edema (doesn’t have to be diffuse like in a dog)

Question 12

What are Haab’s striae?

Answer 12

Breaks in descemet’s membrane (either ruptured or thinned) that become fibrotic

Question 13

What is Phthisis bulbi?

Answer 13

The globe shrinks from chronic inflammation, and is considered end-stage for the disease process! This is an acquired condition (vs. microphthalmia which is congenital)

Question 14

How do you diagnose ERU?

Answer 14

Rule out other primary causes of inflammation and use your history + clinical signs

Question 15

What is the most likely pathogenesis of ERU?

Answer 15

Dysregulation of T-cell response with recurrent episodes due to epitope spreading (body is recognizing self as foreign)

Question 16

True or false: Uveitis relapses can occur even in blind and phthisical eyes

Answer 16

True because of the persistence of auto-antigenic proteins (expression of ocular proteins continues to be impaired)

Question 17

Are insidious uveitis cases bilaterally or unilaterally affected?

Answer 17

> 80% are bilaterally affected

Question 18

A 5 year old Appaloosa mare comes to your clinic for a pre-purchase exam. The owner reports that the mare has never shown any signs of ocular pain, etc. On ophthalmic examination, you notice that the eyes are slightly red, and there is hyperpigmentation and posterior synechia along the iris. What are you concerned about in this mare?

Answer 18

Insidious uveitis (ERU) - these horses never have overt episodes and the casual observer may not notice a deterioration.

Question 19

How many times more likely are Appaloosas to suffer from uveitis than other breeds?

Answer 19

8.3 times!

Question 20

What infectious agent is a significant cause of uveitis worldwide?

Answer 20

Leptospirosis

Question 21

What is the pathogenesis of Leptospira induced ERU?

Answer 21

Exact mechanism unknown but molecular mimicry highly suspected

Question 22

How much more likely is an Appaloosa with a history of leptospirosis likely to lose vision?

Answer 22

3.8 times

Question 23

What percent of horses with uveitis suffer corneal ulcers over time and why is this a concern?

Answer 23

> 25% - This is a concern because owners try to self treat (due to burnout and $$$) and may end up administering a steroid treatment in the presence of an undiagnosed ulcer!

Question 24

What are the main goals for treatment of classic acute episodes of uveitis?

Answer 24

Dilate the pupil, control pain and inflammation

Question 25

What topical medical therapies can be used in ERU cases?

Answer 25

Mydriatics, corticosteroids (prednisolone acetate or dex), NSAIDs, or cyclosporine

Question 26

How long would you want to administer topical corticosteroids in a case of ERU?

Answer 26

Treat with corticosteroids at least 30 days past resolution of clinical signs! Don’t want to keep them on this forever because it causes immunosuppression of the cornea and predisposes to ulcers.

Question 27

When is a vitrectomy contraindicated?

Answer 27

If there is extensive posterior synechia

Question 28

What would you be concerned about if you saw a horse that had focal iris depigmentation and pigmented keratic precipitates?

Answer 28

Heterochromic Iridocyclitis (still an immune-mediated uveitis)

Question 29

What breeds are overrepresented with HIK?

Answer 29

Warmbloods

Question 30

A 10 year old Warmblood gelding presents to your clinic for corneal opacification and blepharospasm of the left eye. On your ophthalmic exam you find pigmented keratic precipitates, corneal edema, iris depigmentation, and retrocorneal membranes. What is the BEST differential diagnosis for this patient?

Answer 30

Heterochromic Iridocyclitis

Question 31

A 10 year old Warmblood gelding presents to your clinic for corneal opacification and blepharospasm of the left eye. On your ophthalmic exam you find pigmented keratic precipitates, corneal edema, iris depigmentation, and retrocorneal membranes. You diagnose this patient with HIK, what are the medical treatment options for this patient?

Answer 31

Topical corticosteroids or NSAIDs + systemic NSAIDs