Ophtalmo Flashcards
What are the 3 categories and breed predisposition of ERU ?
- Classic : WB, Icelandic
- Insidious : Appaloosa, Draft, Knabstrupper
- Posterior : WB
Which are the best candidates for suprachoroidal cyclosporine implants ?
Horses with ERU and recurrent bouts of inflammation that are well controlled with conventional medical therapy
Which are the best candidates for pars plana vitrectomy ?
Horses with Leptospira-associated uveitis (C-value ≧ 4) and moderate to severe vitreal inflammation
Which treatment to choose for ERU horses ?
- Conservative medical management (AIS, AINS, mydriatics) is the first line of TT to stop active uveitis and to slow down or prevent recurrent bouts of inflammation.
- If reccurences occur despite appropriate medical therapy, intravitreal and suprachoroidal injections (triamcinolone, low-dose gentamicin) provide an effective alternative to surgery, and can be performed under sedation.
- If the horses does not respond favorably to conservative medical or injection therapy, suprachoroidal cyclosporine implants or pars plana vitrectomy can be made based on the indications.
What are the potential complications associated with the intravitreal injection of gentamicin (4 mg) ?
Triamcinolone ?
Intravitreal injection of gentamicin (4 mg) : cataract formation/maturation and retinal degeneration. Low complication rates, high success rate (> 90%).
NB : T. Launois used 6 mg
Triamcinolone : risk of secondary infection (fungal or bacteria) and corneal degeneration +/- glaucoma in humans. Decrease the risk of complication with suprachoroidal TA injections with micro-needles.
What are the clinical signs associated with chronic ERU ?
- Corneal vascularization
- Endothelial degeneration resulting in persistent corneal edema
- Linear corneal calcification
- Posterior synechia (occasionally anterior)
- Cataract formation (cortical)
- Alteration in iris color (hyper or hypo) and surface apperance
- Secondary glaucoma
- Phtisis bulbi
- Blindness
What is a pseudorecurrence of ERU ?
When medical therapy is withdrawn too soon, it may appear as if the inflammation returns within a short period of time (often 2-6 weeks) = pseudorecurrence
It can lead to a misdiagnosis or to progressive intraocular changes resulting in decreased vision or blindness.
How to differentiate nuclear sclerosis from a cataract ?
Retroilluminate the eye from a distance.
- Nuclear sclerosis DOES NOT block the tapetal reflection
- A cataract DOES block the tapetal reflection
What is the nuclear or lenticular sclerosis ?
With age, the continual addition of new lens fibers compresses the nucleus and changes the degree that light is bent while passing through the lens. The nucleus becomes visible as a grayish, central sphere. This normal aging change is termed nuclear or lenticular sclerosis.
What are the different location of lens opacities ?
Lesions can be axial or equatorial and further described as capsular, subcapsular, cortical, perinuclear, or nuclear
What is the multiple congenital ocular anomalies (MCOA) syndrome?
Multiple congenital ocular anomalies (MCOA) is an inherited eye disorder that is associated with the silver dilution (PMEL17 locus) and is characterized by lens subluxation and cataract formation, ocular cysts, enlargement of the cornea, abnormally formed iris/retina, and additional abnormalities, previously termed anterior segment dysgenesis.
Mode of Inheritance: Incomplete dominance
What is the clinical significance of syneresis ?
The vitreous should be examined, if possible, for liquefaction (syneresis) or collagen clumping, which can occur secondary to inflammation or as an aging change.
How cataracts can be classified ?
Cataracts can be classified based on:
- the amount of the lens that is involved (incipient, immature, mature, or hypermature) ;
- age of onset (congenital, juvenile, or senile) ;
- or cause.
Mature cataracts involve 100% of the lens, completely block the tapetal reflection, and cause blindness.
Hypermature cataracts have sparkly appearing lens material due to liquefaction and resorption of lens proteins, causing subsequent shrinking and wrinkling of the lens capsule.
Photos :
E. Incipient cataract
F. Immature cataract
A. Hypermature/resorbing cataract
B. Immature/incomplete cataract
C. Mature/complete congenital cataract
D. Mature/complete congenital cataract
Which cataracts are more likely to progress ?
- cataracts diagnosed in foals
- cataracts diagnosed in horses with ERU
- cataracts located in the most metabolically active portion of the lens (ie, the equator or the anterior cortex)
→ are more likely to progress.
Which cataracts do not progress in general ?
Nuclear and perinuclear cataracts typically do not progress and become smaller over time in relation to the rest of the lens as the lens fibers are compressed.
What is the most common congenital ocular finding in foals ?
Cataracts are the most common congenital ocular finding in foals and occur in 35% of foals with ocular lesions.
What are the etiologies of cataracts ?
Cataracts may be congenital or inherited or occur secondary to trauma or ERU.
Which breeds are predisposed to inherited cataracts ?
Cataracts are inherited as a dominant trait in certain Belgian, QH, and Thoroughbred bloodlines.
In 2024 study in US → over-representation of Standardbreds
Breed predispositions to congenital and juvenile cataracts in horses at two academic institutions
evj 2024
What is your diagnosis ?
Normal equine fundus.
Multiple dark dots can be seen in the tapetum, these are small choriocapillaries viewed end on, and are also known
as the “stars of Winslow”.
What is your diagnosis ?
Retinal folds from previous retinal detachment that reattached are seen as pale gray streaks radiating from the optic disc. The hazy view is owing the uveitis present in this eye.
What is the etiology of chorioretinal lesions ?
Chorioretinal lesions are a relatively common finding in the horse.
Any cause of uveitis can cause chorioretinitis, and some common causes of uveitis in horses include ERU, trauma, leptospirosis, bacteremia, and septicemia.
Some recent studies report an association with EHV-1 infection early in life, due to ischemic lesions.
What is the etiology of retinal detachment ?
Retinal detachment is usually caused by inflammation (uveitis) or ocular trauma.
What is senile retinopathy ?
Condition commonly seen in geriatric horses.
Bilateral, irregular, hyperpigmented lines appear in the nontapetal fundus ventral to the optic disc, and a zone of depigmentation may be seen adjacent to the hyperpigmented lines.
This is a benign age-related retinopathy, and should not be confused with the honeycomb pigment pattern seen in the fundus of horses with EMND.
What is the etiology and breed predisposition of congenital stationary night blindness (CSNB) ?
Congenital stationary night blindness (CSNB) is an inherited, non-progressive retinal disorder characterised by poor vision under low light conditions.
The only known reported genetic cause of CSNB in horses is an insertion in the TRPM1 gene that disrupts normal gene expression.
The identified equine mutation has been shown to be causal for CSNB in Appaloosas, Knabstruppers and
American Miniature Horses and was associated with leopard complex (LP), a white spotting pattern common in these breeds. Homozygosity for LP (LP/LP) is directly associated with CSNB in Appaloosa horses.
What is the suspected etiology of congenital stationary night blindness in Tennessee Walking Horses ?
We identified a likely causal recessive missense variant in GRM6.
The estimated allele frequency in Tennessee Walking Horses is 10%.
Whole-genome sequencing identifies missense mutation in GRM6 as the likely cause of congenital stationary night blindness in a Tennessee Walking Horse
evj 2020
Does transpalpebral ultrasonographic measurement of
optic nerve sheath diameter can assess intracranial pressure in horses ?
No
Evaluation of transpalpebral ultrasonographic measurement of optic nerve sheath diameter for indirect assessment of intracranial pressure in anesthetized and standing healthy adult horses
J Vet Emerg Crit Care 2021
What are the main ocular abnormalities in horses > 15 yo in UK ?
74% had anterior segment pathology (Cobs and Shetlands) → cataract (52%), mostly anterior cortical (65%)
44% had posterior segment pathology : senile retinopathy (43%)
71% were bilateral
Ocular findings in a population of geriatric equids in the United Kingdom
ejv 2024
Does amniotic membrane extract improve the healing rate of superficial corneal ulcers ?
No
Further study will be needed to determine whether amniotic membrane extract will be helpful for infected or malacic equine corneal ulcers.
Commercial amniotic membrane extract for treatment of corneal ulcers in adult horses
evj 2021
When keratomalacia does occur ?
Keratomalacia, or corneal melting, results when there is an overabundance of these enzymatic proteins elaborated by recruited inflammatory cells, activated resident host cells, and any pathogens present.
The destructive forces overwhelm the restorative responses and result in dissolution of corneal collagen and necrosis of cells.
The production of elastase and alkaline phosphatase by Pseudomonas, hyaluronidase by Staphylococcus and other extracellular proteases by fungal organisms can greatly augment this melting process.
What lesions are suggestive of keratomycosis ?
- Often, especially in corneas infected with fungi, a groove or furrow will develop at the periphery of the lesion owing to increased concentrations and activity of proteases elaborated both by host tissues and the pathogens.
- Infections that travel to the deeper layers of the cornea, especially fungal organisms that are chemoattracted to Descemet’s membrane, are more likely to result in a full-thickness rupture.
- Most cases of corneal abscesses in the horse are fungal in origin.
What are the clinical indication of amniotic membrane graft ?
Amniotic membrane transplantation for superficial wounds may provide excellent cosmetic results and minimize corneal opacity.
However, it is not recommended for reconstruction of deeper lesions or instances of fungal keratitis.
What is the neurologic significance of lateral or medial strabismus ?
CN III dysfunction results in a laterally and lightly ventral strabismus,
CN VI results in a prominent globe with a medial strabismus,
CN IV deficiency results in a dorsomedially rotated pupil.
What is the prognosis associated with ocular SCC ?
- In general, ocular SCC is locally invasive and slow to metastasize. The prognosis for the treatment of SCC is good if lesions are identified and treated when they are small.
- Surgical excision is relatively unsuccessful if performed alone, but adjunctive treatment with radiation, cryotherapy, CO2 laser ablation, photodynamic therapy, application of mitomycin C, or a combination of treatments significantly improves outcome.
- The exception seems to be SCC of the nictitating membrane, which has a good prognosis after surgical excision with a very low recurrence rate.
- Recurrence rates after excision are higher in eyelid SCC as compared with other locations
What are the risk factors for ERU in Appaloosas ?
- Age,
- coat pattern (fewspot coat pattern was significantly associated with increased risk for ERU),
-
genetics (The LP/LP genotype was at a significantly greater risk for ERU compared to lp/lp (OR = 19.4) and LP/lp (OR = 6.37)).
→ are major risk factors for the diagnosis and classification of ERU in the Appaloosa
Risk factors for equine recurrent uveitis in a population of Appaloosa horses in western Canada
vo 2020
What are the proven risk factors for insidious uveitis in Appaloosa and Knabstruppers ?
- positive serum MAT for Leptospira
- LP allele
- Pattern 1 (PATN1) allele
- Advancing age
- Being exposed to EHV-1
- Lesions of chorioretinitis (bullet holes and butterfly lesions)
- Similar to findings for Appaloosas, LP homozygotes had higher odds of uveitis compared with true solid (N/N) horses (LP/LP OR= 7.64) and age was also identified as a risk factor. After accounting for LP, the 16–20 age group had higher odds compared with the youngest group (OR= 13.36).
- Bullet hole’ and ‘butterfly’ retinal lesions were not significantly associated with ERU-affected horses. This result is similar to findings in the Appaloosa. ‘Bullet-hole’ lesions have, in fact, been shown to be a result of EHV-1 occurring between 3 weeks and 3 months post-infection likely due to ischaemic injury caused by viraemia.
- There was no significant effect of PATN1 genotype.
- Positive results for Leptospira exposure were not associated with higher odds of ERU in our sample.
Our data support genotyping for LP to assess risk of ERU in Knabstruppers.
Prevalence of insidious uveitis in this sample of Knabstruppers was 20.7%.
Risk factors for insidious uveitis in the Knabstrupper breed
evj 2023
A horse is presented for exophtalmos. The ultrasonography reveals a a round, liquid-like structure, compatible with a cyst. What is your diagnostic hypothesis?
Exophthalmos may develop secondary to retrobulbar formation of hydatid cysts owing to Echinococcus granulosus.
The definitive host for this tapeworm is the dogs and foxes.
Horses, as well as humans, serve as an intermediate host. Dogs and other canids, as the definitive hosts, harbor the intestinal stage of the tapeworm, which produces infective eggs. The intermediate hosts and human are infected by ingesting the eggs in contaminated food or water.
After oral ingestion of E granulosus eggs, cysts may develop in many anatomic sites, including the liver. Retrobulbar cyst formation may be detected via ultrasound imaging. However, definitive diagnosis is made by histopathologic identification of tissue taken after enucleation, which is often necessary for resolution of orbital disease.
An owner describes a horse at the stable with a visible “flashing” third eyelid on both eyes. The owner also reported that the horse had difficulty moving. What is your diagnostic hypothesis?
Rapid globe retraction and resulting “flashing” third eyelid elevation are 2 well-recognized ocular signs of tetanus in the horse. Hyperesthesia is also a common finding.
An owner calls you because he has just acquired an Appaloosa, which regularly shows procidence of the 3rd eyelid. The horse is being fed alfalfa and for leisure purposes. What is your diagnostic hypothesis?
Hyperkalemic periodic paralysis (HYPP) is an inherited myopathy of QH, Paint, Appaloosas, and QH crossbreds. It occurs as an autosomal-dominant trait in horses that are related to the Quarter Horse stallion Impressive.
Clinical manifestations include myotonia, muscle fasciculations and weakness, and/or paralysis. Ocular signs of HYPP include globe retraction owing to spasm of the retractor bulbi
muscle with subsequent elevation of the third eyelid, which may present as one of the early clinical signs of an episode.
Episodes of HYPP can occur during periods of increased serum potassium, including after change in feed to high potassium diets such as alfalfa or electrolyte supplementation, or with stressors.
A horse has reared back and now presents with a head tilt consistent with peripheral vestibular syndrome. What are the expected ocular lesions?
Ocular abnormalities with peripheral vestibular disease include:
- ventral strabismus of the globe on the affected side, which is often positional (noted with head elevation),
- horizontal nystagmus with the fast phase away from the affected side.
Hypothesis ?
Onchocerciasis is caused by Onchocerca cervicalis in the horse and commonly causes dermatitis as well as ocular changes, particularly in older horses.
The matured worms in the nuchal ligament produce microfilaria, which can migrate and cause clinical disease. Migrating microfilaria have shown a preference for the ventral midline and face of the horse where they can be ingested by Culicoides spp. to help complete the cycle.
Preferential microfilaria localization associated with
the ocular tissues includes the lower eyelid and lateral limbus of the eye. Depigmentation (vitiligo) of the conjunctiva around the temporal limbus is a distinguishing clinical sign.
Hypothesis ?
Habronemiasis, also known as summer sores, is caused by the nematodes Harbronema muscae, H. microstoma, and Draschia megastoma.
Ocular signs of habronemiasis include nodule formation at the site of the hypersensitivity reaction and appear as yellow, raised, caseous lesions (“sulfur granules”) most often at the medial canthus, but can also form in the conjunctiva and periocular region. The horse may develop pruritis associated with the nodules, which can prog-
ress to fistulous tracts in the medial canthus. In some cases, keratitis and corneal ulceration develop if the eyelids become irregular from nodular formation.
What are the ocular signs of HERDA ?
Hereditary equine regional dermal asthenia (HERDA) is a genetic condition, with an autosomal-recessive mode of inheritance, that has been recognized in QH, Paint and Appaloosa with QH lineage. The condition is likely present at birth; however, clinical signs are often not recognized until the horse begins preparation for riding.
Ocular signs of HERDA include an increased incidence of corneal ulcers in affected horses. The corneal thickness is decreased in multiples areas in horses with HERDA, and increased corneal curvature as well as increased frequency of corneal opacity has been described.
