Depigmented areas at 6 o’clock below optic nerve in a HORSE. Before you diagnose ERU, what else must also be present?
Must have evidence of degeneration ELSEWHERE in the eye, not this single lesion
“Sunburst”/band appearance of depigmentation/white radiating out from the optic nerve in the non-tapetal region in a HORSE is pathognomonic for…
Had previous chorioditis (from ERU) –> this lesion is from retinal folds from a detached retina that re-attached
How do you treat chorioretinitis in the horse?
Systemic meds – Banamine or steroids (dex, pred)
What are 3 signs of choroiditis in the horse?
- Bullet hole lesions in retina
- Vitreal degeneration
- Vitreal discoloration
Are bullet hole lesions pathognomonic for ERU in horses?
NO
In a horse with choroiditis, what color is the vitreous and why?
Green, because serum leaks into the vitreous
What are the “butterfly” like lesions seen around the optic nerve?
Peripapillary chorioretinal scars
If there is peripapillary scarring AND vitreal changes, what does that mean?
That when it was active, some plasma leaked into the vitreous
White or myelin appearing bleb on the edge of the optic nerve in a HORSE. What are the 5 DDx?
- Optic neuritis
- Proliferative optic neuropathy (PON, discrete)
- Optic nerve tumor
- Ectopic myelination or peripapillary ganglion cells (more diffuse)
- Coloboma of RPE (diffuse, white)
In a visual horse eye with something on the nerve, what is NOT your DDx?
Optic neuritis (horse will be blind)
What is more common: PON or an optic nerve tumor?
PON by FAR (optic nerve tumors are RARE)
What is PON in a horse?
Benign glial tumor [oligodendrocytoma]
What is the signalment for PON in a horse? What will its PLR be like?
> 15 yr old with normal PLR
What is the treatment for PON? Optic nerve tumors?
None for either, but PON isn’t a big deal usually
What is the normal color of an equine optic disc and why?
Orange/beige d/t capillaries
How does the color of the equine optic disc change with optic nerve atrophy?
Becomes lighter with atrophy
What is the normal location for vessels around an equine optic nerve?
Everywhere but 6 o’clock
What is the reticular pattern on the equine optic nerve?
The lamina cribosa
The lamina cribosa is normally hard to see on a horse. What is happening if it is easy to see?
Optic nerve atrophy (there has been DEMYELINATION, exposing it)
What are Stars of Winslow? Are they normal? Species? Appearance?
“Dots” on the TAPETAL fundus of a HORSE
They are NORMAL
These are end-on choriocapillaries in the retina
What is breed is Congenital Stationary Night Blindness seen in (CSNB) most commonly seen in? Specifically which horses?
Appaloosa (up to 1/3 of all apps!), most commonly leopard complex gene (which can also occur in POAs, Knabstruppers, Miniatures)
What are the clinical signs of CSNB? Appearance of the retina? Histologic appearance? ERG appearance?
Vision impaired in dim light, normal in bright light
Normal retina
Normal histology
ERG: all a wave (aka a “negative ERG” since no positive B wave present)
What is the cause of CSNB?
Defect in the TRPM1 gene
Transient receptor potential melatansin 1
What is the treatment for CSNB? Recommendation to breed?
No treatment; do NOT breed
Retinal hemorrhage in foal. How common? Affect on vision? Resolution?
Fairly common (~16% of TB foals)
No affect on vision
Resolve on own in 10 days
How does ischemic optic neuropathy occur in horses?
Ligation of the internal and external carotid, and the greater palatine artery, when trying to treat GP mycosis
(NOTE: the maxillary artery should be the ONLY artery occluded)
Unlike small animals, where damage to the optic chasm is usually from enucleation, when does this occur in the horse?
Trauma to the occipital region, causing both globes to move anteriorly and stretching this area
Equine Motor Neuron disease causes what changes to the retina?
A mosaic of light and dark d/t ceroid lipofusion in the pigmented area
When can you get fungal optic neuritis in horses? (2)
- Crypto meningitis
2. Guttural pouch mycosis
Retinal dysplasia in a HORSE has been associated with what process, and in what breed?
Anterior segment dysgenesis; Rocky Mountain of course
When are peripheral retinal (ciliary) cysts seen?
Silver dapple coloration associated with multiple congenital ocular abnormality syndrome
How should you advise owners of horses with peripheral retinal (ciliary) cysts?
No affect on vision, but don’t breed these horses
What do peripapillary lesions represent?
Post-inflammatory lesions
How common are bullet hole lesions?
VERY– like 80% of mature horses!
What is thought to probably cause the bullet hole lesions?
Equine herpesvirus
When are bullet hole lesions considered significant?
- When densely and widely distributed over entire pigmented fundus or when locally extensive
- distributed in a linear pattern across the circumpapillary or ventral peripapillary fundus
What is associated with distributed linear distribution of bullet hole lesions across the circumpapillary or ventral peripapillary fundus?
Behavioral issues are associated, suggesting visual deficits (unknown why this location does that)
What is the appearance of optic nerve atrophy?
Pale, granular, nonvascularized; blind in ONE eye
What usually causes optic nerve atrophy
Space occupying lesion in the optic chiasm; can progress to bilateral blindness
Describe bullet hole lesions?
Multiple small, circular focal areas of depigmentation with a central area of hyperpigmentation
Describe fibrinous traction bands
White spike-like structures that radiate from the perimeter of the optic disc
What should be your first thought if you see retinal detachment in a horse?
ERU
Where is the pigment of the RPE the least concentrated in the equine retina?
Over the visual streak
How does the pigment concentration change from the level of the visual streak?
The pigment gradually increases as the tapetum thins out
How does the shape of the optic nerve change from foal to horse?
Rounder as a foal
Where is the visual streak located?
Ventral tapetum, parallel to the edge of the bottom of the tapetum
How does the tapetum appear when observed in bright light?
As a horizontal band (as opposed to triangular/semi-circular in shape)
What is the horizontal band of tapetum thought to represent by some people?
The only functional part of the tapetum under normal (day or night) light conditions
How do the visual streak and horizontal band of tapetum relate to the pupil?
All are horizontal = horizontal visual field
Where in the eye is the optic disc?
ventrolateral
How should you visualize the the optic disc in a horse?
Stand in front, at level of eye or slightly above, and look down
What is the name for the age-related retinal changes in horses?
Senile retinopathy
What is the appearance of senile retinopathy?
Hyper pigmented (black) streaks with depigmented (white) streaks on either side, within the non-tapetal fundus, mostly ventral to optic disc. This will be bilateral.
What is the clinical significance of senile retinopathy?
None– no visual deficits
What is the DDx for senile retinopathy?
Vit E deficiency/EMND
What is the appearance for horses with Vit E deficiency and/or EMND?
Mosaic, honeycomb pattern of a dark brown to yellow-brown pigmentation in the tapetal zone, and a horizontal band of pigment at tapetal-non-tapetal junction
What is the pigment that is deposited in Vit E deficiency/EMND?
Ceroid lipofuscin