Disease of the posterior segment in horses

Question 1

What parts make up the posterior segment?

Answer 1

Vitreous
Retina
Choroid
Optic nerve

Question 2

How can you examine the lens and posterior segment?

Answer 2

Ophthalmoscopy
* Direct & Slit ophthamoscopy
* Requires dilation of the pupil for a complete examination
* Tropicamide or phenylephrine
* Not atropine (effect too long without uveitis).

Ultrasonography
* Trans-palpebral
* Linear probe
* Corneal opacity
* Severe myosis

Question 3

What are the things that causes linear opacities of the vitreous?

Answer 3

• Hyaloid vasculature (should regress 6-9 months from birth)
  
  • Persistent primary vitreous aka Persistent hyaloid artery
• Vitreal filaments and membrane
• Hyalitis
  
  • yellow-green discoloured vitreous, with thickened vitreal membranes

Question 4

What are the differnt types of vitreal opacites?

Answer 4

• Focal Opacities
  
  • Floaters
• Diffuse - degenerative
  
  • Syneresis (degeneration)
  • Asteroid hyalosis (Ca₃(PO₄)₂ crystals)
  • Synchysis Scintillans
• Haemorrhage
  
  • Damage to CB, retina or choroid
  • Poor prognosis

Question 5

What are the treatment of vitreal disease? what are the goals of treatment?

Answer 5

Goals:
* Maintain comfort
* Prevent inflammation
* Preserve vision

Treat underlying cause

Vitrectomy
* Posterior uveitis (ERU)
* Advanced specialised procedure
* 1/3 blind within 3 months
* Decrease in vision but also decreased recurrent

Question 6

What colours can the normal retina be?

Answer 6

red, blue, green (lots of varriation)

Question 7

What diseases affect the retina?

Answer 7

Detachment
Retinopathies
Dysplasia
Chorioretinitis
Neuropathy

Question 8

What are the cuases of chorioretinopathies?
What are the different types?
What is the effect on vision?

Answer 8

• Causes - Uveitis, Sepsis/SIRS
• Active vs Inactive
• Focal vs diffuse
• Effect of vision
  
  • Size
  • Location (central vs peripheral)
  • Vasculature - untidy vessels and haemorrhage indicate compromise

Question 9

Do these conditions affect vision?

Answer 9

Coloboma - no effect on vision
Focal retinopahty - bullet hole lesions, if there is only a few and small no effect, if several as pictured then likely to affect vision

Question 10

What are the causes of retinal detachment?

Answer 10

• Uveitis (ERU)
• Trauma
• Retina tears
• Traction
  
  • Hyalitis
  • Haemorrhage
• Glaucoma
• Congenital abnormalities
• Vitreal degeneration
• Systemic diseases
  
  • Hypertension