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When medical therapy is withdrawn too soon, it may appear as if the inflammation returns within a short period of time (often 2-6 weeks) = pseudorecurrence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 are the environmental factors associated with prevalence of ulcerative keratomycosis ?
Season (depends on location) → spring and fall in Colorado
Wind speed → with higher wind speeds associated with greater rates of fungal involvement
Prevalence of equine ulcerative keratomycosis in Colorado and association of environmental factors: A retrospective and descriptive study (2002–2017)
eve 2021
What is the overall complication rate for subpalpebral lavage system (SPL) dorsally placed ?
Overall complication rate for SPL systems was 29.1%, with 21.2% being ocular complications and 7.9% being nonocular complications.
The authors talk about “low complication rates” but…
Dorsally placed commercially available subpalpebral lavage systems have low complication rates in horses
javma 2022
What are the etiology of glaucoma ?
Congenital, primary and secondary glaucoma
Secondary to :
* chronic uveitis (ERU ++)
* trauma
* hyphema
* intraocular neoplasia
* lens luxation
* postcataract surgery
What are the reported risk factors for the development of glaucoma ?
- Active, recurrent, and chronic/persistent uveitis
- Age > 15 yo
- Breed (Appaloosa)
What is the first line treatment of glaucoma in horses ?
- Combination of topical β-blocker 0.5% timolol and the topical CA inhibitor 2% dorzolamide used every 8-12h. The combination is more effective than when administered alone. Potential adverse effect of timolol : miosis
- Another CA inhibitor : brinzolamide
What is the best surgical treatment in a glaucomatous visual eye ?
Transcleral cyclophotocoagulation (TSCP) is considered the therapy of choice for long-term IOP control in horses. This is indicated in visual eyes.
Contraindicated in the presence of intraocular neoplasia.
Pre-existing ocular conditions, such as uveitis, should be controlled before laser therapy to minimize complications.
What are the most common bacteria isolated from ulcerative bacterial keratitis in Tennessee Vet Hospital ?
The most common bacterial genera were Streptococcus (35%), Staphylococcus (29%) and Pseudomonas (13%), with a shift towards more Staphylococcus and less Streptococcus compared to previous years.
Same susceptibility.
Monitoring trends in antimicrobial susceptibility patterns of bacterial isolates from horses with ulcerative keratitis
eve 2023
Which tonometer to choose between the rebound (TonoVet) and the applanation (TonoPen) tonometers ?
The rebound tonometer may be the preferred instrument to minimise intra-user and inter-user variation for IOP measurement in unsedated horses.
The rebound tonometer is also likely to be the preferred instrument to minimise intra-user variation in sedated horses.
If the applanation tonometer is used to perform IOP measurement in horses, it is recommended that this is performed while horses are sedated to minimise inter-user variation for this instrument.
Inter-user and intra-user variation of two tonometers in horses
evj 2020
Is there an over- or under-estimation of IOP with the use of rebound tonometer ? applanation tonometer ?
IOP should be estimated using the same tonometer over time, and the bias of the tonometer used, such as overestimation (rebound tonometer) and underestimation (applanation tonometer), should be acknowledged.
Comparison of four tonometers in the measurement of intraocular pressure in healthy horses
evj 2023
What are the clinical effects of environment (medical barn vs horse stable) on IOP and tear production measurements ?
A notable increase in IOP was observed in the medical barn compared with the horse stable, while tear production exhibited no significant variance between the two environments.
Comparing the effects of intraocular pressure and tear production measurements in horses in two different environments: Horse stable and medical barn
evj 2024
What is the impact of sedation on IOP ?
Which IV sedation protocol has the greatest impact ?
All protocols of sedation decreased IOP compared with baseline, with greatest reduction at +5 min.
A combination of detomidine and butorphanol causes greater IOP reduction 5 minutes following sedation than other commonly used sedation protocols.
IOP reduction is less pronounced when detomidine is used alone.
Intraocular pressure following four different intravenous sedation protocols in normal horses
evj 2021
What is the most common cause of dry eye or KCS in horses ?
Facial nerve damage secondary to trauma such as mandibular fracture
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 ocular lesion can be observed in Appaloosas with congenital stationary night blindness ?
Appaloosas with congenital stationary night blindness will often have a characteristic dorsomedial strabismus.
A dorsomedial rotation can also be seen with cerebellar abiotrophy in Arabian horses.
What are the clinical signs of Horner syndrom ?
And most common etiology in horses ?
Horner syndrome is the result of a loss of sympathetic innervation to the head.
Manifestations include head sweating, upper eyelid ptosis, and mild miosis.
Enophthalmos and elevation of the nictitating membrane are inconsistently found and can be subtle.
It is more commonly associated with guttural pouch disease.
What is the most frequent neoplasm of the globe and adnexa ?
SCC is the most common neoplasm of the globe and adnexa in the horse.
Clinically, SCC typically presents as a fleshy pink growth on the nictitating membrane, conjunctiva, eyelid, or limbus.
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 the development of SCC ?
- increasing age
- ultraviolet radiation
- unpigmented skin
- a genetic link with an autosomal recessive mode of inheritance has been suggested in Halflingers
What is the prognosis associated with periocular sarcoids ?
- Although good results can still be achieved for periocular sarcoids, as treatment is most successful when lesions are small it is paramount to treat with the most effective therapies available early in the course of disease.
- Due to wide, poorly defined margins, recurrence rates after surgical excision of sarcoids are high, as high as 82% in the periocular area where there is limited tissue for resection.
What are the adverse effects documented with 10 mL retrobulbar lidocain injection ?
Retrobulbar injection using 10 mL lidocaine is safe in normal eyes of adult horses, but carries risk in structurally compromised or glaucomatous eyes due to transient IOP increase.
Reversible chemosis commonly develops 2- 4h following injection, and may be severe in some horses with risk for corneal ulceration.
Retrobulbar lidocaine injection via the supraorbital fossa is safe in adult horses but produces regionally variable periocular anaesthesia
evj 2022
How to minimize adverse effects associated with retrobulbar anesthesia ?
Low-volume (5 mL) retrobulbar block was not associated with adverse effects.
In terms of efficacy, mepivacaine block showed no clinical advantage over lidocaine block. However, bupivacaine block induced comparatively rapid and sustained corneal anesthesia.
Corneal anesthesia was similar but periocular soft tissue anesthesia was not achieved with any local anesthetic drug at low volume.
(50% reduction volume improves the safety)
Comparative efficacy of low-volume retrobulbar anesthesia using three commercial local anesthetics in adult horses
javma 2024
How to evaluate pain in ocular diseases of horses ?
Refinement and revalidation of the Equine Ophthalmic Pain Scale (R-EOPS) may be an effective tool for reliably assessing the pain level in horses with ophthalmic diseases and potentially guiding pain management although it still requires large-scale application and external validation.
Another recent study also used the Horse Grimace Scale (HGS) and Behavior Pain Score (BPS) (but not validated)
Refinement and revalidation of the Equine Ophthalmic Pain Scale: R-EOPS a new scale for ocular pain assessment in horses
vet J 2024
Pain scoring systems in hospitalized horses with ocular disease
jvim 2024
What is the clinical efficacy of noninvasive diode-laser for the treatment of iris cysts ?
Which factors are associated with less satisfactory response ?
Both short- and long-term results indicate diode laser treatment is a useful and safe option for iris cyst size reduction, with a low risk of recurrence.
Factors are associated with less satisfactory response :
- polycystic eyes
- thick-walled cysts
- hyperplastic corpora nigra
Presurgical ultrasonography is recommended
Noninvasive diode laser–an effective and safe treatment of iris cysts in 46 eyes of 35 horses
evj 2023
What is the relationship between ERU and leptospirosis ?
The exact mechanism of induction of uveitis and the pathogenesis of how the bacterium is associated with the recurrences is not completely understood. Leptospira may account for the initial blood–ocular barrier disruption, which then triggers the subsequent immune reaction.
Increased intraocular antibodies compared with the serum are indicative of local intraocular antibody production (C-value), with MAT (high Se and Spe).
C-value ≧ 4 : positive, the aqueous humour Ab titre is at least four-fold higher than the Ab titre found in the serum.
C-value ∈ [1-4] : suspicious
C-value < 1 : negative
PCR results are an unreliable method of detecting the presence of Leptospira.
Equine recurrent uveitis— A review
EVE 2023
What is the suspected etiology for ERU ?
Equine recurrent uveitis is generally considered to be an autoimmune disease. The disease’s onset and severity may be associated with environmental factors and/or genetic predisposition (Appaloosa with LP allele).
It is commonly accepted that ERU develops due to blood–ocular barrier disruption following an initial bout of inflammation. Following disruption of the local immunity, CD4+ and T-lymphocytes gain access to the eye, where they remain.
Equine recurrent uveitis— A review
EVE 2023
Which Leptospira sevorars are most prevalent in Switzerland ?
The most common intraocular serovars were Leptospira interrogans grippotyphosa, pomona, and bratislava.
Intraocular antibody production was suspected in samples of 22/65 horses (c-values > 1).
Leptospiral antibody prevalence and surgical treatment outcome in horses with Equine Recurrent Uveitis (ERU) in Switzerland
vo 2020
From a retrospective study in Switzerland, which surgical technique provide the best results between pars plana vitrectomy=PPV and suprachoroidal implants=SCDI ?
PPV was performed in 21 eyes with positive leptospiral test results, SCDI in 15 eyes with negative leptospiral test results. (Not the same population compared)
Uveitis recurred less often after PPV (2/21) compared to SCDI (6/15, P = .04), but with an increased risk of retinal detachment.
Enucleation was more often warranted in horses after SCDI in this study due to a higher uveitis recurrence.
Leptospiral antibody prevalence and surgical treatment outcome in horses with Equine Recurrent Uveitis (ERU) in Switzerland
vo 2020
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 is the prevalence of uveitis in donkeys compared to horses in UK ?
The ERU prevalence in donkeys reported here (2.9%) is comparable to that reported for horses in the UK.
The prevalence of uveitis in a population of donkeys in the UK
evj 2020
In a retrospective study of North Carolina, which leptospiral test result is most strongly correlated with an unfavorable prognosis in terms of vision in horses with recurrent uveitis (ERU)?
a) A positive titre in serum for L. bratislava
b) A positive titre in aqueous humor for any leptospirosis serotype
c) A positive PCR test in aqueous humor
d) A positive titre in aqueous humor for L. pomona
Right answer :
b) A positive titre in aqueous humor for any leptospirosis serotype
The study showed that horses with a positive titer in the aqueous humor for any serotype of leptospirosis, particularly L. bratislava, were associated with a worse prognosis regarding their vision, particularly with blindness at presentation.
Role of Leptospira spp. testing and ocular examination in horses with equine recurrent uveitis: A retrospective study of 63 horses
eve 2022
What was the main conclusion of the study on the use of low-dose intravitreal gentamicin injections (IVGI) in Swedish horses with chronic uveitis?
A) The treatment led to a high success rate, with most horses experiencing complete recovery from uveitis.
B) IVGI showed limited effectiveness, with only a small proportion of horses achieving a positive outcome.
C) The study concluded that IVGI was ineffective and should no longer be used for treating uveitis in horses.
D) The treatment showed significant success, but retinal degeneration and cataracts were not observed as long-term complications.
Answer:
B) IVGI showed limited effectiveness, with only a small proportion of horses achieving a positive outcome.
A positive outcome was observed in 41% of eyes, with retinal degeneration in 22% and mature cataracts in 15% of eyes.
Enucleations were performed in 14/32 eyes, due to lack of favourable response of IVGI, or due to complications, that is, glaucoma, corneal ulceration, and/or corneal mineralisation.
Equine uveitis: Outcome and adverse effects after one or two intravitreal low-dose gentamicin injections
evj 2024
What are the proven risk factors for primary uveitis in the UK ?
- Proximity with cattle farm
- Proximity with poultry farm
- Proximity with pig farm
- Being exposed to sunlights
Being close to a pig farm (OR 27.8) and a recent history of flooding of the pasture (OR 15.43) was associated with increased risk of uveitis.
Impact on lepto exposition ?
Being in the same owner’s possession for a longer amount of time had a protective effect (OR 0.79).
Risk factors for a first episode of primary uveitis in the UK and proportion of cases that experience recurrence following this first episode
evj 2023
What is the recurrence rate after a first episode of primary uveitis in the UK ?
- about 10%
- about 20%
- about 30%
- about 50%
about 20%
Recurrence was observed in 4/23 horses (18.2%).
All first recurrent events occured within the 12 months.
Risk factors for a first episode of primary uveitis in the UK and proportion of cases that experience recurrence following this first episode
evj 2023
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
What are the common causes of retinal detachment in UK (compared to USA) ?
ERU was the most common aetiology (n = 10) followed by trauma (n = 8), like in USA
Equine retinal detachment in the United Kingdom: 23 cases (2010–2020)
eve 2023
What is not commonly associated with retinal detachment ?
- cataracts
- vitreal debris
- anterior synechiae
- posterior synechiae
Cataracts, posterior synechiae and vitreal debris were found commonly in both the ipsilateral and contralateral eye affected.
Equine retinal detachment in the United Kingdom: 23 cases (2010–2020)
eve 2023
Does the use of ocular atropine can induce colics ?
It is possible to induce mild reversible symptoms of colic through frequent administration of topical ocular atropine in normal healthy horses.
BUT the use of ocular atropine at recommended dose rates for clinical ocular disease does not increase risk of colic.
Can ocular administration of atropine cause colic?
eve 2020
Which topical corticosteroid has the shortest doping time : dexamethasone or prednisolone?
All samples tested negative (below the limit of detection of the analytical method) for dexamethasone one day and for prednisolone one week after treatment cessation.
Prefer topical dexamethasone to treat race horses
Systemic detectability of dexamethasone and prednisolone after eye drop application in horses
evj 2021
What was the main finding of the study on the penetration of topical dexamethasone and prednisolone in equine ocular fluids?
A) Both dexamethasone and prednisolone were found in high concentrations in the vitreous humour.
B) Dexamethasone and prednisolone reached effective concentrations in the aqueous humour but not in the vitreous humour.
C) Only dexamethasone reached measurable concentrations in both aqueous and vitreous humour.
D) Both corticosteroids were present in detectable levels in serum but not in ocular fluids.
Answer:
B) Dexamethasone and prednisolone reached effective concentrations in the aqueous humour but not in the vitreous humour.
Potentially effective dexamethasone and prednisolone concentrations were measured in the anterior chamber, but vitreal concentrations were negligible. Therefore, treatment with only topically administered corticosteroids is deemed insufficient in horses in cases of posterior uveitis.
Penetration of topically administered dexamethasone disodium phosphate and prednisolone acetate into the normal equine ocular fluids
evj 2022
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.
DNA test available
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 Habronema 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 progress 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 a thinner cornea and thus an increased risk of corneal ulcers, with an increased frequency of corneal opacity.
DNA test available
What are the most common causes of central blindness in horses ?
Metabolic encephalopathies (hepatic, uremic, intestinal) are the most common cause of central blindness in horses.
Less common causes of central blindness in horses include:
- postictal change;
- head trauma;
- encephalitis owing to viral, protozoal, fungal (Aspergillosis spp. associated with guttural pouch mycosis), or bacterial infection;
- leukoencephalomalacia (“moldy corn poisoning” owing to the mold Fusarium moniliforme and its mycotoxin fumonisin);
- space-occupying masses such as tumors, abscesses, granulomas;
- thiamine deficiency;
- complications from anesthesia or inadvertent intracarotid injection.
What is the silver coat color ?
Silver coat color is associated with multiple congenital ocular anomalies (MCOA), autosomal dominant mutation with incomplete penetrance.
Black horses with the silver mutation can range in phenotype from dark body with light mane and tail (A) to a light body known as light chocolate silver (B). Also note the dappling (B) that is present in some horses with the silver mutation.
(D) Chestnut horses with the silver allele only appear chestnut because silver does not dilute red pigment. Therefore, chestnut horses with or without the silver allele coat are phenotypically indistinguishable.
Breeds affected : Rocky Mountain horse, Kentucky mountain saddle horse, Kentucky mountain pleasure horse, Icelandic horse, Shetland pony, American miniature horse, Comtois, and other breeds with silver, including American quarter horse and Morgan.
A Comtois horse breeder presents his horses for sale. What are the potential eye anomalies?
Silver coat color is associated with multiple congenital ocular anomalies (MCOA), autosomal dominant mutation with incomplete penetrance.
DNA test available : silver test
Breeds affected : Rocky Mountain horse, Kentucky mountain saddle horse, Kentucky mountain pleasure horse, Icelandic horse, Shetland pony, American miniature horse, Comtois, and other breeds with silver, including American quarter horse and Morgan.
Horses heterozygous (Z/N) for the silver mutation most often have the cyst-only phenotype, whereas homozygotes (Z/Z) have multiple ocular defects.
The cysts phenotype is characterized by temporal cysts that originate from the ciliary body or the peripheral retina.
The MCOA phenotype is considered to be more severe and is characterized by ciliary or peripheral retina cysts with additional abnormalities, including iris hypoplasia, corneal globosa, megaloblepharon, retinal dysplasia, immature nuclear cataracts, and iridocorneal hypoplasia. Horses homozygous for the silver mutation (Z/Z) have impaired vision or are blind.
What is the genetic predisposition of Haflingers ?
Which European breeds are also potentially affected?
Ocular SCC can originate at the limbus, the nictitans, or the upper and lower eyelids. Haflingers are over-represented for limbal SCC, with prevalence estimated to be 35% in this breed.
An autosomal recessive mode of inheritance best explains the genetic risk for limbal SCC in the breed. Haflingers homozygous for the T allele had 5.89 times greater risk of developing limbal SCC than horses with T/C or C/C genotypes.
DNA test available : ocular SCC
The SCC genetic risk variant was also detected in 2 other closely related breeds with reported cases of ocular SCC, the Belgian and the Percheron, suggesting that it may also be an SCC risk factor in these breeds.
What are the ocular signs of this disease ?
Junctional epidermolysis bullosa (JEB) is characterized by mechanical stress–induced lesion of the skin and mucosal membranes, in draft breeds and American Saddlebreds.
This condition is a recessive disorder and carrier-to-carrier matings should be avoided. Mutations in laminin genes
cause separation of the dermis and epidermis.
Ocular manifestations : corneal ulcers
What are the inherited ocular disorders of Friesians ?
Friesian horses have several reported inherited collagen disorders, including megaesophagus, aortic rupture, dwarfism, and hydrocephalus, and these may be related to 2 corneal disorders in the breed.
- Corneal dystrophy : characterized by stromal loss that is bilateral and has a higher occurrence in males, making an inherited X-linked recessive hypothesis likely.
- Districhiasis : condition in which cilia aberrantly emerge from the meibomian gland openings, and, when pointing toward the cornea, these can cause corneal irritation or ulceration.
No DNA test available
In a 16-year-old Appaloosa with a history of recurrent uveitis presenting with unilateral corneal edema, what diagnostic steps should be taken to rule out glaucoma?
Perform a complete ophthalmic examination, including tonometry to measure IOP.
Use a consistent protocol with the horse’s head above heart level, and consider an auriculopalpebral nerve block (conflicting results).
Compare IOP between both eyes, as normal equine IOP ranges from 15-30 mmHg.
An IOP >32-35 mmHg in the affected eye, along with the clinical signs and history, would be diagnostic for glaucoma.
Vet clinic Equine glaucoma
What is the recommended initial medical management for a horse diagnosed with glaucoma secondary to equine recurrent uveitis?
The initial medical management should include a combination of the topical β-blocker 0.5% timolol and the topical carbonic anhydrase inhibitor 2% dorzolamide, used every 8 to 12 hours. This combination is more effective than when the two drugs are administered alone.
Additionally, treat the underlying uveitis with appropriate anti-inflammatory medications.
Vet clinic Equine glaucoma
In a horse with advanced glaucoma that has become blind and painful despite medical management, what surgical options should be considered?
For a blind, painful eye with glaucoma that is unresponsive to medical management, end-stage procedures should be considered.
1. Pharmacologic ciliary body ablation using intravitreal injection of gentamicin and dexamethasone
2. Enucleation (surgical removal of the eye)
3. Evisceration with placement of an intrascleral prosthesis for a more cosmetic outcome
The choice depends on factors such as the horse’s overall health, owner preferences, and potential complications associated with each procedure.
Vet clinic Equine glaucoma
list the Regional anaesthesia for the orbit & globe
- Auriculopalpebral nerve block – motor block of facial nerve (VII) – eyelid akinesia
- Supraorbital nerve block – sensory nerve block of frontal nerve (V)
- Lacrimal nerve block – sensory nerve block of lacrimal nerve (V)
- Infratrochlear nerve block – sensory nerve block of infratrochlear nerve (V)
- Zygomatic nerve block – sensory nerve block of zygomatic nerve (V)
- Retrobulbar nerve block – sensory (ophthalmic nerve V) and motor nerve (III, IV and VI) block – globe akinesia and central eye position
What are the normal values for schirmer test?
30 mm in 30 sec or 35 mm in < 1min
Which of the following statements best describes the performance of the Equine Ophthalmic Pain Scale (EOPS) in assessing ocular pain in horses?
A) The EOPS showed poor reliability and was unable to distinguish between healthy horses and those with ocular pathology
B) The EOPS demonstrated excellent reliability but low sensitivity in detecting ocular pain
C) The EOPS showed good reliability and was able to accurately distinguish between healthy horses and those with ocular pathology
D) The EOPS had high sensitivity but poor specificity in identifying horses with ocular disease
The correct answer is C) The EOPS showed good reliability and was able to accurately distinguish between healthy horses and those with ocular pathology.
Most items in the behavioral and ocular expression categories showed excellent inter- and intra-observer reliability (ICC ≥ 0.75)
At the optimal cut-off score of ≥7, the EOPS demonstrated high sensitivity (81.3%) and specificity (100.0%) in identifying horses with ocular pathology
Overall behaviour, ear movements, position inside the box à lowest reliability
Improved after exclusion of physiological parameters (HR, RR, T)
2021 Development and preliminary validation of a pain scale for ophthalmic pain
true or false : Acetaminophen readily penetrates the aqueous humour of the normal equine eye after consecutive oral dosing
true
Acetaminophen administered orally to healthy horses at 20 mg/kg
every 12 h for six doses readily penetrates the normal equine eye,
with a higher aqueous humour:serum ratio than flunixin and firocoxib
as measured 1 h after the last dose. Further studies are required to
determine if acetaminophen represents a viable addition or alternative
to traditional NSAIDs in the treatment of equine ocular pain and
inflammation, and if so, the mechanism by which this occurs.
mean ± SD aqueous humour:serum acetaminophen concentration ratio was found to be substantially higher than previously studied oral NSAIDs, flunixin meglumine, and firocoxib (44.9 ± 15.9% compared to 3.59 ± 3.32% and 11.99 ± 4.62%, respectively)
indications Electroretinography?
differentiation between retinal and central blindness
retinal function is desired but the retina cannot be viewed, such as before cataract surgery
Suspected congenital stationary night blindness,
hyphema owing to trauma,
chorioretinal lesions (owing to equine recurrent uveitis or other causes),
glaucoma are some of the common indications for ERG in
equine patients.
normal ERG can be recorded from a blind animal if the blindness has originated from lesions in deeper retinal layers, the optic nerve, or the brain
retinal lesion prognosis?
However, the greater the extent of the lesion (active or scar), the more likely it is to
cause visual impairment. In addition, lesions in the retinal area centralis may lead to
greater effect on vision than peripheral lesions. Moreover, retinal lesions that affect only the outer retina may have a lesser effect on vision compared with deeper lesions
that affect the inner retina and the nerve fiber layer, because the nerve fiber layer
carries visual input from photoreceptors in other areas of the retina. The
Focal chorioretinopathy (“bullet hole” lesions) prognosis?
The exact etiology of these lesions is unknown; however, choroidal vasculitis,
infarction, and ischemia have been proposed. An infection with equine herpesvirus
1 in utero has also been suggested as a possible etiology. A recent study has shown
that even extensive bullet hole lesions occupying most of the nontapetal fundus
(>“150 bullet holes”) did not affect retinal function, as measured by fERG, and the reported
horses did not seem to have visual deficits
peripapillary chorioretinal scar : butterfly lesion -> cause?
Any cause of uveitis with peripapillary involvement
can lead to this type of lesion, and it is not pathognomonic to equine recurrent uveitis
