Diseases of the anterior segment in horses Flashcards
What structures are located in the anterior segment?
- Cornea
- Anterior chamber
- Posterior chamber
- Iris
- Ciliary body
- Lens
What produces aqueous humour? What is the main component? How is it sampled?
Ciliary body
98% water
Sampling
* Sedation
* Topical anaesthesia
* Retrobulbar block
What are the most common aqueous humour abnormalities? How are they characterised? What causes them?
Flare - increased opacity
* ↑↑↑ [protein]/fibrin
* Uveitis
Hypopyon
* Pus in anterior chamber
* Falls to the bottom by gravity
* Uveitis
Hyphaema
* Blood in anterior chamber
* Uveitis
* Trauma
* Coagulopathy
Glaucoma
* Increase in IOP
* Mainly of Aqueous Humour
What IOP is associated with glaucoma? How does it present? What are the advanced stages?
IOP >30mmHg
Presentation
* Variable pain
* Corneal oedema
* Often zonal
* Haabs striae - linear opacity in the cornea
* DM injury
* Mydriasis/myosis - mostly myosis
* Buphthalmos
Advanced stages
* Progressive mydriasis
* Lens: luxation/cataracts
* Retinal degeneration
* Loss of vision
How is glaucoma treated?
Treat underlying disease
Medical
* Topical treatment
* Beta blockers
* 0.25% timolol TID
* Carbonic anhydrase inhibitors
* 2% dorzolamide TID
* Mydriatics
* Atropine
* Treat concurrent disease
* Uveitis -> corticosteroids
Surgical
* Laser cyclophotocoagulation - destroys part of the ciliary body to slow down AH production
* (Gonio implants - poor success)
* Enucleation
Goal - reduce IOP to 20 mmHg
What are congenital diseases affecting the iris?
- Aniridia - no iris
- Iridal hypoplasia - underdevelopment or incomplete development of the iris
- Iris coloboma - missing part of iris
- Persistent pupillary membrane
- Dysplasic pupillary membrane
- Heterochromia
- Congenital miosis
What are acquired diseases of the iris?
- Uveitis
- Secondary, ERU
- Discolouration
- Synechiae
- “Stuck” pupil - because iris is stuck to the lens
- Dyscoria
- Cysts
- Neoplasia
- Melanoma
- Rubeosis iridis/iritis - discoloaration of the iris as a consequence of inflammation
- new blood vessel formation may occur due to ischemia
- Prolapse
- with perforation
What are synechiae usually secondary to? How are they managed?
Often secondary to uveitis, may cause the pupil to be stuck in position and therefore affect vision
Treatment
* Mydriatics
* Tissue Plaminogen Activators - help break down fibrin
Where can iris cysts be located? What is a common differential? How can you differentiate? How are they treated?
Often an incidental finding, but may obscure pupil (worse in sunlight)
Location
* Granula iridica
* Pupillary margin
* Ciliary body
* Iris stroma
Melanoma is main differential - need to ultrasound to differentiate
Treatment
* Laser deflation
* Aspiration
When does iris prolapse occur? How does it present? How can you confirm it? How is it treated?
- Subsequent to globe rupture/perforation
- Brown spot on cornea indicates prolapse
- Ultrasound
- Treatment: enucleation or transposition of the cornea
What are the stuctures in the uvea? What are their functions?
Middle vascular layer of the eye -> Blood Ocular Barrier
Provides support and nourishment
Iris
- Shutter function
Ciliary body
- continuous production of AH
- Regulation of IOP via drainage at ICA
Choroid
- Provide blood supply to the retina
What is uveitis? How can i present depending on location? What structures are involved?
Inflammation of the structures part of the Uvea
Anterior
* Iris, Ciliary body
* Aqueous flare, myosis, hypopyon, hyphaema
* Also conjunctival hyperemia, episcleral injection, corneal oedema, keratic precipitates
* fibrin clots
**Posterior **
* Choroid and retina
* Vitreal cloudiness
* Retinal degeneration
* peripapillary degeneration, aka butterfly lesion
Panuveitis
* Anterior and posterior uveitis combined
What is the pathogenesis of anterior uveitis?
Acquired uveitis
* Systemic disease
* Infections, sepsis
* Neoplasia
* Trauma (blunt)
* Equine Recurrent Uveitis (ERU)
Reflex uveitis (secondary)
* Corneal ulceration
* Conjunctivitis
* Glaucoma
What drives inflammation in posterior uveitis? What can be consequences?
- Neutrophilic infiltration of iris and ciliary body, then replaced by lymphocytes, plasma cells and macrophages
- Given that the choroid is the primary vascular supply to the retina, choroidal inflammation (choroiditis) can lead to retinopathy.
Consequences
* Retinal damage
* Serofibrinous exudate in the vitreus
* Cataracts
What is equine recurrent uveitis (ERU)? What are the different steps?
Immuno-mediated, recurrent, pan-uveitis
- Leading cause of blindness in horses (2-25%)
- Acquired condition
- Breed predisposition (eg Appaloosas, WB, Draft)
- Unilateral vs bilateral (80:20)
- Easily confuse with other ocular disease
Steps
1. First episode of acquired ocular disease
1. Blood ocular barrier compromised
1. Leakage of antigens in the eye
1. Recurrent inflammatory episodes (antigen recognition by immune system)
Describe pathogenesis of ERU
- Infection bypassing BOB, leakage of antigens within the eye
- Bacteria: Leptospira, salmonella, rhodococcus,…
- Viruses: EHV, EIV, EVA, EIA, …
- Parasites: strongyles, onchocerca, toxoplasma, …
- Fungi
- Genetics (appaloosa - increased susceptibility)
- Trauma
- Immuno-mediated processes
What are the 3 forms of ERU? What clinical signs are associated?
Classical
* Alternates acute episodes with quiescent periods
* panuveitis
Insidious
* Low grade, persistent, gradual progression
* Appaloosas
Posterior
* Vitreous cloudiness
* Chorioretinopathy
* Retinal detachment
* Cataracts
* WB, draft
Clinical signs
* Pain, epiphora, blepharospasm
* Corneal oedema
* Aqueous flare, hyphaema, hypopyon
* Myosis
* Rubeosis iridis
* Corpora nigra degeneration
* Synechiae
* Cataracts
* Chorioretinopathies
* Glaucoma
- Ultimately vision loss
How is ERU treated?
Medical - Aim is to control pain and inflammation
- Mydriatics (Atropine & Phenylephrine/Tropicamide)
- Steroids - dexamethasone/prednisolone
- NSAIDs - Topical (bromfenac, flurbiprofen, etc) or Systemic (flunixin)
- ± Antimicrobials - Topical – if corneal ulceration is present or Systemic (if one suspects bacterial pathogenesis)
Surgical
* Suprachoroidal Cyclosporin A device implant
* Release medication directly into ciliary body
* Surgery performed during quiescent phase only
* Prevents recurrence for ~5 years
* Pars plana vitrectomy
* Involves removal of the vitreous
* Aims at removing vitreal particles
* Before surgery need to confirm that there are vitreal antibodies (eg against Leptospira) as success rate is better for those cases
* Enucleation
* Uncontrollable pain
* Non visual eye
What is the prognosis of ERU? What are the complications?
Guarded to poor – vision loss most likely in the long term
It is lifelong!!!
Complications
- Synechiae, fundus lesions and iris discolouration associated with poorer outcome
Early and aggressive treatment is key
Cyclosporine A implants most successful to delay progression
What is the function of the lens?
What are the clinical signs of disease of the lens?
Function:
* Refraction
* Accommodation
* Image quality
* Protection of the retina
Clinical signs:
* Changes in vision
* ± Discomfort
* Epiphora
* Blepharospasm
* Photophobia
* Changes in eye appearance
* Changes in performance
* Owner may notice an opacity in the eye
How can you evaluate the lens?
- Sedation
- Palpebral nerve block
- Mydriatics (take 30min to work)
- Tropicamide
- Phenylephrine
- Ophthalmoscopy
- Ophthalmoscope
- Slit light
- Transillumination
- Retroillumination
- Slit-lamp biomicroscopy
Ultrasonography
What diseases affect the lens?
Congenital
- Cataracts ~35% of congenital ocular defects
- Aphakia - absence of the lens.
- Coloboma - notch-like defect at the lens equator
- Ectopia lentis - disordered lens tissue in a shallow anterior chamber
- Some luxations
- Sperophakia - abnormally spherical lens.
- Lenticonus/lentiglobus - conical or globular contour
Acquired
- Cataracts
- Luxations/subluxations
- Capsular perforation
- Expansion
- Rupture
What is a suture line on the lens?
What do they look like?
A line where the growing tissue of the lens is meeting
can be y shapped, often see the posterior suture line
not abnormal
What are the causes of cataracts?
Acquired
Confenital
Age related
Acquired (secondary)
* Uveitis
* Trauma
* Glaucoma
* Intra-ocular neoplasia
* After intra-ocular surgery
Congenital
* Breed
* Belgian draft, Morgan, QH, TB), Rocky mountain horse, American saddlebred
* With other ocular disorders
* Embryonic disruption
Age related
* Senile cataracts
* Nuclear sclerosis
* Slowly progressive, >18yo
