Recurrent Uveitis and Equine Vision Loss

Question 1

What are the 3 components of the uvea?

Answer 1

Choroid, iris, ciliary body
-contains all of the blood vessels that the eye receives

Iris and ciliary body make up anterior uvea, choroid makes up posterior uvea

Question 2

What can atrophy of the corpora nigra indicate?

Answer 2

Chronic inflammation of the eye
-also may be incidental

Question 3

What are the clinical signs associated with acute vs chronic anterior uveitis?

Answer 3

Acute: blepharospasm/epiphora, miosis, aqueous flare/hypopeon/hyphema

Chronic: all acute signs are possible, cataracts (from inflamed aqueous- lens cant get nutrition), retinal detachment, secondary glaucoma (accumulation of debris at drainage angle), phthisis bulbi

Question 4

What are the main causes of acute anterior uveitis?

Answer 4

Keratitis (ulcer/abscess)
Trauma
Sepsis (neonatal)

Question 5

What are some synonyms for equine recurrent uveitis?

Answer 5

ERU, Moon blindness, periodic ophthalmia

Question 6

What are the causes of equine recurrent uveitis?

Answer 6

Relatively unknown
-can be due to leptospirosis, onchocerca cervicalis, immune mediated/hypersensitivity and many others

Question 7

What is the main breed predisposed to ERU?

Answer 7

Appaloosas
- can change depending on geography

Question 8

What are the main clinical findings associated with ERU?

Answer 8

-can be unilateral or bilateral (usually starts unilateral)
-symptoms can be intermittently severe (classic) or chronic low grade/insidious (often associated with slow vision loss and horses are non painful)
-this is a very common cause of blindness in horses
-anterior segment: can see miosis, aqueous flare and posterior synechiae
-posterior segment: can see vitreal debris/liquefaction (green appearance to vitreous), chorioretinitis, and retinal detachment
-chronic changes: cataracts, posterior synechia, retinal detachment, hyperpigmentation of iris, secondary glaucoma and phthisis bulbi

Question 9

What is deposition of inflammatory tissue on the corneal endothelium also known as?

Answer 9

Keratic precipitates

Question 10

What is the “classic butterfly lesion” seen on the fundus in cases of ERU?

Answer 10

Peripapillary retinal scarring (around the optic nerve) associated with active retinal inflammation

Question 11

What are the primary diagnostics you should use in cases of ERU?

Answer 11

-CBC/Chem (rarely useful or specific)
-serology (lepto titers)
-conjunctival biopsy (look for onchocerca larvae)
-ocular ultrasound

Question 12

What are the main goals of ERU therapy?

Answer 12

-control ocular inflammation (to preserve vision and maintain comfort)
-eliminate the primary problem (rarely definitively identifiable)

Question 13

What are the main medical therapies used in ERU cases?

Answer 13

-systemic NSAIDs (banamine best as it crosses the blood aqueous barrier)- check renal values over time, consider adding omeprazole
-topical corticosteroids (stain the eyes before using)
-topical atropine (test IOP before using- glaucoma risk)
-can add in systemic antibiotics if indicated (lepto cases)- use penicillin, doxycycline or enrofloxacin

*Treat aggressively until symptoms are controlled- tapering meds gradually may help minimize relapse

Question 14

What are the 3 functions of atropine?

Answer 14

-cycloplegia (paralysis of ciliary body)
-dilation of pupil and decrease possibility of posterior synechiae formation
-stabilization of the blood aqueous barrier

*Some think horses on long term atropine may have increased risk of colic- but definitely need it in ERU cases

Question 15

What are the surgical options for treatment of ERU?

Answer 15

1. Cyclosporine implants
   - allow for long term uveitis control (80-90% success rate)
   -placed suprachoroidal (different than the trt for dry eye)
   -never a standing procedure- movement can cause whole eye to fill with blood
   -lasts for 3 years
2. Vitrectomy
   - reduces inflammation
   - high incidence of cataract formation (can change dynamic of the lens)
   - for posterior segment disease (more used in europe)
3. Intravitreal gentamycin
   - anecdotal but promising
   -can result in cataract formation
   -horses can go over a year before requiring secondary infection

Question 16

What can be changed in terms of management to help prevent against flare ups of ERU?

Answer 16

• environmental management: change pasture/stable, change bedding type, decrease dust exposure
  -general health maintenance: anthelminthics/vaccinations, hoof and dental care. Dont vaccinate if horses are actively inflamed (or can give banamine at the same time to prevent flare ups)

Question 17

What is the long term prognosis for ERU?

Answer 17

-long term prognosis for vision retention is poor (50-60% lose vision)
-blindness due to secondary cataract, glacuoma and/or retinal detachment is common

Question 18

What is the main cause of uveal cysts?

Answer 18

Most common and problematic is idiopathic cystic corpora nigra
-can arise from any portion of the uveal tract
-can cause visual disturbance, can laser treatment can be effective
-do not treat if not causing visual impairment

Question 19

How can you distinguish uveal cysts from melanoma?

Answer 19

Cysts transilluminate unlike melanoma
- fluid filled- light can pass through

Question 20

Describe the normal equine fundus

Answer 20

-paurangiotic retina: 50-80 short vessels surroud the optic nerve
-optic nerve is in the non-tapetal retina
-color of tapetum varies with coat color
-stars of Winslow common (end on vessels)

Question 21

What is chorioretinitis and what can cause it?

Answer 21

It is inflammation of the choroid and retina
- can be caused by ERU, EHV, trauma and others
- no specific treatment available

Question 22

What is a classic presentation of a horse eye affected by equine herpes virus 1?

Answer 22

Bullet hole chorioretinopathy
<20 multifocal lesions, they aren’t likely to have visual deficits

Question 23

What are the congenital causes of equine vision loss?

Answer 23

Cataracts, optic nerve coloboma (missing piece of optic nerve) or congenital stationary night blindness

Question 24

Describe some of the features of Congenital Stationary Night Blindness

Answer 24

-normal daytime vision, but blindness in dark or dim lighting
-retina appears normal (electroretinogram required for diagnosis)
-miscommunication between rods and bipolar cells of the optic nerve
-appaloosas are most commonly affected (heritable)
-no treatment, but this is non progressive

Question 25

What are the main causes of acquired vision losses in horses?

Answer 25

-ERU leading to cataracts, retinal detachment or glaucoma
-glaucoma
-traumatic optic neuropathy
-exudative optic neuropathy