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10° CONGRESSO NAZIONALE MULTISALA SIVE
PERUGIA, 31 GENNAIO-1 FEBBRAIO 2004
Brian C. Gilger
DVM, MS, Dipl ACVO
Professor, Ophthalmology
Department of Clinical Sciences
North Carolina State University College
of Veterinary Medicine
4700 Hillsborough Street
Raleigh, NC USA 27606-1499
E-mail: [email protected]
Recenti acquisizioni nella terapia
delle uveiti del cavallo
Current understanding and advances
in therapy for equine recurrent uveitis
Domenica, 1 Febbraio 2004, 17.15
st
Sunday, February 1 2004, 17.15
SALA PREZZOLINI
OFTALMOLOGIA
Chairperson: Giorgio Ricardi
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Introduzione
L’uveite ricorrente degli equini (anche nota come mal della luna, iridociclite recidivante e oftalmia periodica) è una delle principali malattie oftalmiche del cavallo, nonché la più comune
causa di cecità in questa specie animale. Questa panuveite immunomediata ha un tasso di prevalenza dell’8-25% circa nei cavalli degli Stati Uniti. Fortunatamente, recenti progressi nel trattamento degli equini colpiti dalla malattia hanno consentito di affrontarla con successo. Nel presente lavoro vengono illustrati alcuni elementi importanti sull’uveite ricorrente equina, le sue
cause e le opzioni terapeutiche per i cavalli colpiti.
La malattia è caratterizzata da episodi di infiammazione intraoculare che si sviluppano a distanza di settimane o mesi dalla regressione di un episodio iniziale di uveite. Tuttavia, non tutti i casi di uveite equina iniziale evolvono nella uveite ricorrente. I cavalli possono sviluppare
questa condizione a qualsiasi età, ma il picco del momento del primo episodio di uveite si ha a
4-6 anni, quando la maggior parte di essi inizia o sta per iniziare la propria attività agonistica.
Segni clinici dell’uveite ricorrente degli equini
Nell’uveite ricorrente degli equini si osservano tre sindromi cliniche principali, quella “classica”, quella “insidiosa” e quella “posteriore”. La “uveite ricorrente degli equini classica” è più
comune ed è caratterizzata da episodi infiammatori attivi seguiti da periodi di flogosi oculare di
minima entità. La fase attiva della uveite ricorrente degli equini, acuta, comporta principalmente l’infiammazione dell’iride, del corpo ciliare e della coroide, con concomitante coinvolgimento di cornea, camera anteriore, lente, retina e corpo vitreo. Dopo il trattamento con farmaci antinfiammatori aspecifici come i corticosteroidi, i segni dell’uveite acuta attiva possono
recedere e la malattia entra in una fase quiescente o cronica. Dopo un periodo di tempo variabile, la fase quiescente viene generalmente seguita da nuovi e sempre più gravi episodi di uveite. È la natura ricorrente e progressiva della malattia ad essere responsabile dello sviluppo di cataratta, aderenze intraoculari e tisi del bulbo (occhio cicatrizzato). Nella uveite ricorrente degli
equini di tipo “insidioso”, invece, l’infiammazione non si risolve mai completamente e si ha il
perdurare di una risposta flogistica di basso grado che porta alla progressione verso i segni clinici cronici della malattia. Spesso questi cavalli non mostrano un evidente disagio oculare ed i
loro proprietari possono non rendersi conto della presenza della malattia fino a che non si forma una cataratta o l’occhio non diviene cieco. Questo tipo di uveite si osserva più comunemente
negli Appaloosa e nei cavalli da tiro. L’uveite ricorrente degli equini di tipo posteriore è caratterizzata da segni clinici localizzati interamente nel vitreo e nella retina, con scarse o assenti manifestazioni anteriori di uveite. In questa sindrome, sono presenti opacità del vitreo ed infiammazioni e degenerazioni retiniche. Si tratta del tipo meno comune di uveite e si osserva soprattutto in Europa.
I segni clinici tipici dell’uveite ricorrente degli equini attiva sono simili a quelli dell’uveite
nelle altre specie animali. Fotofobia, blefarospasmo, edema corneale, intorbidamento dell’acqueo, ipopion, miosi, annebbiamento del vitreo e corioretinite. I segni clinici dell’uveite ricorrente degli equini cronica sono rappresentati da edema corneale, fibrosi dell’iride ed iperpigmentazione, sinechie posteriori, degenerazione dei granuli dell’iride (margini lisci), miosi, formazione di cataratta, degenerazione ed alterazione di colore del vitreo e degenerazione retinica
peripapillare. Entrambi i tipi di uveite ricorrente degli equini (“classica” o “insidiosa”) possono
presentare principalmente l’interessamento del segmento anteriore (infiammazione di cornea,
iride, lente e corpo ciliare) o posteriore (infiammazione di corpo ciliare, vitreo e corioretina). In-
Proceedings of the Annual Meeting of the Italian Association of Equine Veterinarians, Perugia, Italy 2004
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fine, anche con un trattamento aggressivo, molti cavalli sviluppano una condizione di dolore
oculare cronico e cecità come conseguenza di cataratta secondaria, sinechie (aderenze intraoculari), cicatrizzazioni, glaucoma ed insorgenza della tisi del bulbo.
Diagnosi di uveite ricorrente degli equini
La diagnosi clinica dell’uveite ricorrente degli equini si basa sulla presenza delle caratteristiche manifestazioni (edema corneale, intorbidamento dell’acqueo, sinechie posteriori, atrofia dei
granuli dell’iride [corpora nigra], formazione di cataratta, degenerazione del vitreo, edema retinico o degenerazione con o senza segni di disagio oculare associato quali epifora, tumefazione perioculare e blefarospasmo) e episodi documentati di uveite ricorrente o persistente. Per formulare questa diagnosi clinica, è necessaria la presenza di entrambe queste caratteristiche, soprattutto per differenziare la condizione dalle forme di uveite diverse da quella ricorrente e da
altre cause di flogosi oculare ricorrente o persistente, come la cheratite da herpesvirus o quella
immunomediata.
Trattamento dell’uveite ricorrente equina
Gli scopi principali della terapia dell’uveite ricorrente degli equini sono preservare la visione e ridurre e controllare l’infiammazione oculare nel tentativo di limitare il danno permanente
dell’occhio. Nei cavalli in cui sia stata identificata una causa scatenante ben definita, il trattamento è volto ad eliminare il problema primario ed effettuare le indagini iniziali per isolare gli
agenti scatenanti. Questi test possono essere rappresentati da esame emocromocitometrico completo, profilo biochimico, biopsia congiuntivale e test sierologici per l’identificazione di agenti
batterici e virali. Nella maggior parte dei casi, tuttavia, non è possibile isolare una particolare
causa. In queste circostanze, la terapia è volta ad alleviare i segni clinici e ridurre l’infiammazione oculare.
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Introduction
Clinical signs of ERU
Equine recurrent uveitis (ERU) (also
known as moon blindness, iridocyclitis and
periodic ophthalmia) is a major ophthalmic
disease of the horse and is the most common
1-4
cause of blindness in this species. This immune-mediated, pan-uveitis has approximately an 8 to 25% prevalence rate in hors1,5
es in the United States.
Fortunately, recent advances in the treatment of horses with ERU have led to the
successful management of this disease. This
chapter discusses some important facts
about ERU, its causes and treatment options
for the affected horse.
ERU is characterized by episodes of intraocular inflammation that develop weeks to
months after an initial uveitis episode sub1-4,6
sides,
however, not every case of initial
equine uveitis will develop into ERU (see below in diagnosis). Horses can develop ERU
at any age, but the peak time of the initial
uveitis episode is 4-6 years, a time when
most horses are at or nearing their prime per5
formance years.
Three main clinical syndromes are observed in ERU, the “classic”, “insidious”, and
“posterior” type of ERU. “Classic” ERU is
most common and is characterized by active
inflammatory episodes in the eye followed by
periods of minimal ocular inflammation. The
acute, active phase of ERU predominantly involves inflammation of the iris, ciliary body,
and choroid, with concurrent involvement of
the cornea, anterior chamber, lens, retina, and
vitreous. Following treatment with nonspecific anti-inflammatory medications such as corticosteroids, the signs of active, acute uveitis
can recede and the disease enters a quiescent
or chronic phase. After variable periods of
time, the quiescent phase is generally followed by further and increasingly severe
episodes of uveitis. It is the recurrent, progressive nature of the disease that is responsible for development of cataract, intraocular
1-4,6
adhesions, and phthisis bulbi (Scarred eye).
In the “insidious” type of ERU, however, the
inflammation never completely resolves and a
low grade inflammatory response continues
that leads to progression to chronic clinical
signs of ERU. Frequently, these horses do not
demonstrate overt ocular discomfort and owners of these horses may not recognize the presence of disease until a cataract forms or the
eye becomes blind. This type of uveitis is
most commonly seen in Appaloosa and draft
breed horses. The posterior type of ERU has
clinical signs existing entirely in the vitreous
and retina, with little or no anterior signs of
uveitis. In this syndrome, there is vitreal opacities and retinal inflammation and degeneration. This is the least common type of uveitis
and is most commonly seen in Europe.
Typical clinical signs of active ERU are
similar to signs of uveitis in other species:
photophobia, blepharospasm, corneal edema,
aqueous flare, hypopyon, miosis, vitreous
haze, and chorioretinitis. Clinical signs of
chronic ERU include corneal edema, iris fibrosis and hyperpigmentation, posterior
synechia, corpora nigra degeneration (smooth
edges), miosis, cataract formation, vitreous
degeneration and discoloration, and peripap-
Impact of ERU on the horse
industry
The equine industry in the United States
has an estimated annual worth of 112 billion dollars and provides approximately 1.4
7
million full time jobs across the country.
Because ERU has a prevalence rate of approximately 8 to 25% across horse breeds
in the United States, the impact of this disease on the equine industry could be as
high as a billion dollars a year. ERU causes
these large economic losses in the equine
industry because it disrupts training, decreases performance, and disqualifies horses from competition (due to medication
use, etc).
Furthermore, horses with ERU have decreased value as a result of vision deficits
or blindness. Finally, treatment, veterinary
care, and personnel costs adds to the economic impact of the disease.
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illary retinal degeneration. Either type of
ERU (“classic” or “insidious”) can have either predominantly anterior (cornea, iris,
lens, and ciliary body inflammation) or posterior (ciliary body, vitreous, and chorioretinal
1,2,4,6,8-14
inflammation) segment involvement.
Ultimately, even with aggressive treatment,
many horses develop a chronically painful
eye and blindness as a result of secondary
cataract, synechia (intraocular adhesions),
scarring, glaucoma, and development of ph1-4,6
thisis bulbi.
Organisms / infectious agents
associated with initial uveitis
(and possibly ERU)
Several organisms have been associated
with the intiation of equine uveitis. In some
instances, but not all, the uveitis associated
with these systemic infections may develop
into immune-medicated uveitis, or ERU. One
of the most commonly associated systemic
diseases associated with uveitis is leptospiro11,14
sis. Roberts demonstrated that ERU can develop after primary infection (and acute
uveitis) of leptospirosis, however ERU typically did not develop until 1 year after the systemic infection. Therefore, measuring titers in
cases of documented ERU is generally not
beneficial for management of the condition
unless there is a herd or barn outbreak of the
uveitis. Onchocerciasis is another systemic
disease associated with equine uveitis. This
disease is much less common now with the
widespread use of ivermectin, however it is
still a common initiator of uveitis. The inciting cause for the uveitis is the inflammatory
reaction associated with dead and dying onchocerca larvae in the cornea after treatment
with an antihelminic. It is recommended that
affected horses be pretreated with systemic
anti-inflammatory medications (e.g., flunixin
meglumine) before use of ivermectin. Treatment with flunixin meglumine for several
days after deforming may also be needed.
Other systemic infectious causes of uveitis include Streptococcus equi infection, brucellosis, toxoplasmosis, equine herpes virus
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Table 1. Causes of Uveitis in Horses. Any injury
to a horse’s eye may result in uveitis and possible
development of the syndrome of equine recurrent
uveitis (ERU). Some examples include:
Classification
Causes
Trauma
Blunt or penetrating injury
Bacterial organisms
Leptospira
Brucella
Streptococcus
Viral organisms
Equine influenza
Equine viral arteritis
Parainfluenza type 3
Parasites
Onchocerca
Strongylus
Toxoplasma
Miscellaneous
Endotoxemia
Tooth root abscesses
Hoof abscesses
Neoplasia
(EHV-1,2), equine viral arteritis, parainfluenza type 3, and generalized septicemia, endotoxemia, neoplasia, tooth root abscess, or
trauma (Table 1).
Pathogenesis of Recurrent
episodes of uveitis
ERU is a non-specific immune-mediated
condition that results in recurrent or persistent inflammatory episodes in the eye. To diagnose the syndrome of ERU, you must differentiate it from non-ERU uveitis. As mentioned above, there is a long list of infectious
and non-infectious agents responsible for
causing acute uveitis in the horse. Although
any of these causes of uveitis may allow
horses to develop ERU, not all of these acute
uveitis cases will develop into ERU. The recurrent episodes typical of ERU are thought
to develop because of one of three patho1,2,4
geneses:
1. Incorporation of an infectious agent or
antigen into the uveal tract following the initial uveitis episode. These inciting antigens
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become established in the ocular tissues and
their continued presence causes periodic
2,4
episodes of inflammation. Recent studies
have suggested that Leptospira organisms
15,16
may be one of the sequestered antigens. In
15
16
these studies, however, only 26 to 70% of
the eyes had Leptospira detected, suggesting
that other antigens and/or organisms also play
a role.
2. Deposition of antibody: antigen complexes into the uveal tract that incites later inflammation.
3. Persistence of an immune competent
sensitized T-lymphocyte in the uveal tract
that reactivates when given a signal. T-lymphocytes have been demonstrated to be the
predominant infiltrating cell type in chronic
17
ERU eyes and cell-mediated immunity to
uveal antigens has been demonstrated in
12,18
Studies in our laboratory
ERU horses.
have revealed that T-lymphocytes from eyes
with ERU develop an immune mediated inflammation typical of a Th1 inflammatory
19
response (i.e., high IL-2, low IL-4 levels).
These results strongly suggest a T-cell mediated autoimmune response in ERU eyes.
However, what the signal is that reactivates
these T-cells has not been determined. Possibly, a systemic re-exposure to the original
antigen, exposure to a self-protein that is
similar to the original antigen (i.e., “molecular mimicry”), or a decreased immunologic
feedback down-regulation of the T-cell may
be the inciting signal for reactivation of the
T-cell and inflammation.
Diagnosis of ERU
The clinical diagnosis of ERU is based on
the presence of characteristic clinical signs
(corneal edema, aqueous flare, posterior
synechia, corpora nigra atrophy, cataract formation, vitreous degeneration, retinal edema
or degeneration with or without signs of associated ocular discomfort such as epiphora,
periocular swelling, and blepharospasm) and
history of documented recurrent or persistent
episodes of uveitis. Both features are required
to make this clinical diagnosis, especially to
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differentiate from non-ERU uveitis and other
causes of recurrent or persistent ocular inflammation, such as herpesvirus keratitis or
immune-mediated keratitis.
Histologic Features of ERU
In chronic ERU, infiltration of the uveal
tract with lymphocytes and macrophages was
most evident in the ciliary body and base of
the iris. Lymphoid follicles are occasionally
present in the base of the iris. Loss of tissue
structure/destruction was evident in the ciliary
20
processes. Dubielzig noted several histologic distinguishing features of ERU globes: a
noncellular hyaline membrane adhered to the
inner surface of the nonpigmented ciliary epithelium, linear intracytoplasmic inclusions in
21
the nonpigmented ciliary epithelium, and an
influx of lymphocytes and plasma cells into
the ciliary body. The choroid also revealed infiltration of mononuclear cells, with overlying
retinal degeneration. Previous study of ERU
eyes in our laboratory revealed infiltration of
the uveal tract with lymphocytes, plasma
cells, and macrophages are most evident in the
ciliary body and base of the iris. Loss of tissue
structure (destruction) is most evident in the
ciliary processes. Infiltrating lymphocytes
were predominantly CD 4+ T-cells (e.g., 48%
CD4+ and 18% CD8+ in the ciliary body stroma), as determined by immunohistochem19
istry. Few inflammatory cells were observed
19
in the normal eyes.
Treatment of Equine Recurrent
Uveitis
The main goals of therapy for ERU are to
preserve vision and reduce and control ocular inflammation in an attempt to limit permanent damage to the eye. In horses where a
definite inciting cause has been identified,
treatment is directed at eliminating the primary problem, and initial tests to isolate an
inciting agent are performed. These tests
may consist of a complete blood count, biochemistry profile, conjunctival biopsy, and
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serology for bacterial and viral agents. More
often, however, one particular cause cannot
be isolated. In these instances, therapy is directed at the allaying of symptoms and reducing ocular inflammation.
Practical and Stable
Management Practices to
Decrease ERU
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and hooks in the stable, removing low tree
branches in the pasture, lighten training and
show schedule, minimize trailering, and constant use of a quality fly mask. Finally, ensuring that the horse has proper hoof care, optimal vaccination and antheliminic schedule,
and proper diet may also minimize uveitis
episodes.
Medical Therapy for ERU
Practices that decrease ocular injury or
minimize the inflammatory stimuli may decrease or eliminate the development of recurrent episodes of uveitis in ERU (Table 2).
It may be possible to eliminate environmental triggers (e.g., allergens, antigens, etc) of
the recurrent episodes of uveitis by changing
the horses’ pasture, pasture mates, or stable,
increasing insect and rodent control, decrease sun exposure, or change bedding
type. Trauma to the eye(s) can also be decreased by eliminating sharp edges, nails,
Table 2. Practical and Stable Management Practices to Decrease ERU
Classification
Practice to Institute
Environmental
Change pasture/stable/
pasture mates
Increase insect and rodent
control
Decrease dust
Decrease sun exposure
Change bedding type
Health
Maintenance
Proper hoof and dental care
Optimal anthelmintic
and vaccination schedule
Proper diet / minimize weeds
in pasture
Decrease Ocular
Trauma
“Soften” stable
(Eliminate sharp objects)
Eliminate low tree branches
in pasture
Decrease training and show
schedule
Minimize trailering
Do not feed from hay nets
Use quality fly mask
Because vision loss is a common long-term
manifestation of ERU, initial therapy must be
aggressive. In acute cases, treatment in the
form of systemic and local therapy consisting
of antibiotics, corticosteroids and anti-inflammatory drugs is used, many times simultaneously (Table 3). Initial therapy is instituted for at least two weeks, and should be tapered off over an additional two weeks after
the resolution of clinical signs. In severe cases, local subconjunctival injections of corticosteroids may be indicated as an adjunct to
therapy. In most instances, a subpalpebral
lavage catheter is placed to facilitate delivery
of topical medications. Many horses respond
well to intermittent topical and/or systemic
therapy of their active episodes of ERU. Other horses, however, do not respond to traditional therapy and may experience frequent
recurrences of uveitis.
Traditional treatments used for ERU (i.e.,
corticosteroids and non-steroidal anti-inflammatory medications) are aimed at reducing
inflammation and minimizing permanent ocular damage at each active episode. They are
not effective in preventing recurrence of disease. Other medications used to prevent or
decrease severity of recurrent episodes, such
as aspirin, phenylbutazone, and various
herbal treatments have limited efficacy and
potential detrimental effects on the gastrointestinal and hematologic systems when used
chronically in the horse. There has been some
anecdotal reports of intravitreal injections of
gentamicin (4 mg) having an effect on preventing recurrent episodes. Use of this therapy is not recommended until further clinical
and experimental studies are done.
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Table 3. Medical therapy for equine recurrent uveitis
Medications
Dose
Indication
Caution
Prednisone Acetate 1%
q 1-6 hours
Potent anti-inflammatory
medication with excellent
ocular penetration
Predisposes for corneal fungal infection
Dexamethasone
HCl 0.5-1%
q 1-6 hours
Potent anti-inflammatory
medication with excellent
ocular penetration
Predisposes for corneal fungal infection
Flurbiprofen, Voltaren,
(or other topical NSAIDS)
q 1-6 hours
Anti-inflammatory medications
with good ocular penetration
Decreases corneal epithelialization
Cyclosporine A 0.02-2%
q 6-12 hours
Strong immunosuppressant
Poor eye penetration, weak
anti-inflammatory effect
Atropine HCl 1%
q 6-48 hours
Cycloplegic, mydriatics
(pain relief and minimize
synechia formation)
May decrease gut motility and
predispose to colic
Flunixan Meglumine
0.5 mg/kg po. IV, or
IM for 5 days then
0.25 mg/kg po
Potent ocular anti-inflammatory
medication
Long-term use may predispose
to gastric and renal toxicity
Phenylbutazone
4.4 mg/kg po or IV
Anti-inflammatory medication
Long-term use may predispose
to gastric and renal toxicity
Prednisone
100-300 mg/day
po or IM
Potent anti-inflammatory
medication
Frequent side effects, laminitis
formation (use with caution and only
as a last resort). Must taper off dose
Azium
5-10 mg / day po or
2.5 – 5 mg daily IM
Potent anti-inflammatory
medication
Frequent side effects, laminitis formation
(use with caution and only as a last
resort). Must taper off dose
Subconjunctival
triamcinolone
1-2 mg
Repositol, potent
anti-inflammatory medication
with a 7-10 duration of action
Severe predisposition for bacterial or
fungal keratitis, cannot remove
therapy once given
Topical Medications
Systemic Medications
Surgical Therapy for ERU
Cyclosporine A
Two recently described surgical procedures
are aimed at preventing the recurrence of
uveitis and therefore provide long-term control of the disease: Sustained release cyclosporine devices (CsA) and Core vitrectomy
(CV).
A polyvinyl alcohol / silicone-coated intravitreal CsA sustained delivery device that
has been shown previously to produce a sus22tained level of CsA in ocular tissues (rabbit)
24
was evaluated for use in horses. A CsA device was implanted into normal horse eyes for
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up to 1 year and was not associated with ocu25
lar inflammation or complications. In equine
eyes with experimentally-induced uveitis, the
CsA decreased the duration and severity of inflammation, cellular infiltration, tissue destruction, and level of transcription of pro-in26
flammatory cytokines. The 2 by 3 mm device releasing 4 µg/day of CsA is placed into
the vitreous through a full-thickness scleral
and pars plana incision, and anchored into
place by suturing the stem of the device into
the scleral incision. The estimated time that
the device will continue to deliver medication
is 5 years.
In a recent study using CsA in horses with
27
naturally occurring ERU, horses with frequent recurrence of uveitis without vision
threatening ocular changes (i.e., cataracts,
retinal degeneration) or systemic illnesses
were selected to receive the device. Few complications occurred during and after surgery.
Only 2 of 16 horses had severe complications
after surgery resulting in vision loss: one
horse with retinal detachment and one with a
mature cataract formation. Few recurrent
episodes of uveitis were noted with only 3
(19%) developing any evidence of uveitis after device implantation and vision was judged
to be normal in 14 of 16 horses (88%) at a
mean follow up of 13.8 months (range 6 – 24
27
months). Because of these complications, a
suprachoroidal device is now being studied
which has eliminated the severe complications while allowing the beneficial effect of
sustained release CsA.
Core vitrectomy
There have been few English publications
28
describing this surgical technique, but there
29,30
have been several abstracts and articles in
German veterinary journals describing this
31-33
surgery.
This surgery uses a single-port,
nearly total vitrectomy, in which an incision is
made 1 cm posterior to the dorso-lateral limbus, through the pars plana, and into the vitreous. The vitreous is removed and is replaced
by saline or balanced salt solution. Removal
of T-cells or organisms from the vitreous is
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the goal and this is thought to decrease the recurrent episodes of uveitis. In fact, the surgery
reportedly decreases ERU recurrence by
28
92%. However the goal of this surgery is to
halt the progression and recurrent episodes of
28
uveitis, not necessarily preserve vision. In
one study, approximately 1/3 of the cases
were deemed blind months after surgery and
the authors observed a decrease in vision de33
spite a decrease in recurrent episodes. This
may be due to a high percent of cataract formation after surgery. In the only English publication of this surgical technique, of animals
reexamined by the surgeons, 12/27 (45%) had
28
“significant” cataract formation. This surgical technique was recommended to help preserve vision (but not to increase vision), decrease recurrent episodes, and to avoid enu28
cleation. Studies of CV done in the United
States indicate that there are a high percentage
of cataract formation after surgery and most
horses have decreased vision, however the
a
episodes of uveitis seem decreased.
Both CsA and CV are being evaluated at
several areas in the US for long-term control
of ERU. There are numberous sites across the
United States that are currently performing
the CsA procedure, but all ophthalmologists
with facilities for equine ocular microsurgery
could perform this surgery. Fewer locations
are currently performing the CV in the US,
Selection of appropriate horses to receive
the CsA device or CV is very important for
long-term success after surgery. Chronic
uveitic changes in the eye, such as synechiae,
corneal edema, glaucoma, vitreal degeneration, and retinal atrophy, will decrease vision
in the eye and decrease the long-term success
of the CsA because these changes cannot be
reversed. Cataracts should be especially
avoided when selecting patients for implantation. In a previous study using a 2 µg/day re27
leasing CsA device in horses, cataracts involving approximately 25% of the lens or
more continued to progress despite the fact
that recurrent episodes of inflammation were
largely eliminated. Cataract formation is even
more common after CV, with nearly 45% of
cases that were followed developing signifi28
cant cataract formation.
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The goal of both CsA and CV is to prevent
further inflammatory episodes and thereby
prevent additional chronic damage to eyes.
Eyes with less chronic changes are better candidates for CsA surgery with a 4 µg/day device because these vision-threatening complications may be prevented. However, eyes
with more chronic changes and significant
cataract formation (>25% of the lens) may be
better candidates for CV. With chronic
changes in the eyes (i.e., cataract formation,
posterior synechia, retinal degeneration, etc),
CV may not return or preserve vision, but it
may decrease the number and severity of recurrent episodes of uveitis, thereby keeping
the eye comfortable and eliminating the need
for enucleation.
Cyclosporine devices (CsA) and core vitrectomy (CV) are relatively new treatments
for long-term control of equine recurrent
uveitis (ERU). CsA are indicated for eyes
with progressive ERU but minimal ocular
changes. CV is recommended for predominantly posterior ERU and in eyes with significant ocular changes (i.e., synechiae, cataract,
vitreal degeneration, and retinal atrophy) in
advanced stage ERU.
Long-term Prognosis for ERU
In general, the prognosis for eye afflicted
with ERU is poor. Most horses with the disease have multiple recurrent episodes that
eventually lead to vision deficits. Diligent observation and treatment is required by the
owner in many cases to maintain vision longterm. Some horses have progressively increase severity and frequency of their bouts of
inflammation and these horses are ones that
may benefit from surgical therapy.
Future research
Study continues to determine the cause of
recurrent uveitis and to the genetic predisposition in some horses (i.e., appaloosa). If a genetic marker is associated, then horses with
this genotype cannot be used for reproduction
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thus decreasing the prevalence of the disease.
New immunosuppressive therapies, such as
FK506, may offer hope in the medical management. Perfecting a device to deliver such a
medication may also be feasible. Studies are
also being done to determine the role of leptospirosis or other microorganisms in the initiation and pathogenesis of ERU.
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