Opthalmology

• • An entire female with pyometra can present with uveitis (inflammation of the uveal tract in the eye can be the first sign of a pyometra)
• The suggested routine is as follows…

  1. Hands-off exam
  2. Hands-on exam
  3. Schirmer tear test
  4. Cranial nerve tests
  5. Examine anterior segment with pen torch in dark
  6. Ophthalmoscopy: distant direct, close direct, indirect
  7. Further tests if required:

  • Fluorescein staining
  • Swabs or scrapes
  • Tonometry
• • Ocular pain can be identified via blepharospasm, discharge (which may manifest as brown tear staining down the face) and photophobia (not liking a bright light) which owners may not always identify
• The red appearance of the eye is normal in blue eyes, do not mistake this as being full of blood

  
• Ectropion is where the eyelid is inappropriately saggy which is seen on the RHS. This can be an incidental finding or can be a cause of recurrent conjunctivitis. It can also roll in on a later date which can cause further issues
• • Often a narrow palpebral fissure is due to squinting caused by pain
  • A macropalpebral fissure can be normal in brachycephalic breeds which predisposes the eye to ulcers as the eye can't blink properly
• There are many causes of third eyelid protrusion…

  • Ocular pain
  • Microphthalmos
  • Horner's syndrome
• a Schirmer tear test should be done in any eye with discharge, conjunctivitis or lacklustre cornea (the eye doesn’t look as shiny as normal). This should be done at the start of the exam, prior to the application of any drops.

  • Do not perform this test if there is a deep ulcer/risk of perforation
• a Schirmer tear test measures the aqueous part (watery part) of the tear film. to perform, position the strip in the middle to the lateral third of the eye. Be sure the strip is contacting the cornea not the third eyelid

  • Measures basal and reflex tear production
  • The eyelids can open or closed while the strip is left in place for one minute.
  • Bend while in the packet as moisture from your finger can affect the results
• STT results can be falsely elevated due to pain hence, diagnosis is made from the "normal eye" - in this case the one without the ulcer
• Ocular reflexes includes…

  • Palpebral reflex
  • Menace response
  • The absence of a menace in rabbits is normal
  • Puppies gain this response at 12-14 weeks
  • Dazzle reflex (needs a bright light source)
  • Pupillary light reflexes (needs a bright light source)
  • Vestibulo-ocular reflex - moving the head from side to side to see if the animal has a normal nystagmus
• which occur reflex is the most reliable test of vision?

  menace
• • False negative PLRs are common due to…
  • Weak light source (e.g., the ophthalmoscope) in daylight which are not strong enough to elicit PLR
  • A scared/stressed animal has a high level sympathetic tone (especially in cats)
  • Iris atrophy (an age related iris constrictor muscle atrophy)
  • A positive result is not always consistent with vision, a blind animal can still have a PLR
• fill in the blanks

  A) trigeminal

  B) oculomotor

  
• Purkinje image = reflection on the eye which indicates a smooth cornea with a suitable tear film
• fill in the blanks

  A) +20

  B) 0

  
• fill in the blank

  A) dioptre

  
• Distant direct ophthalmoscopy is essential and one of the most useful parts of routine exams. Use the 0 dioptre setting and look through the scope arm’s length away from the dog.

  • This uses the tapetal reflex to highlight visual axis.
• Nuclear sclerosis is an Age related thickening of the lens. This and a cataract can both be present with an opaque eye

  • A mature total cataract blocks the tapetal reflex
• for close direct ophthalmoscopy, use 0 dioptres, lower the rheostat, use the brow rest and get close to the patient (2-3cm)

  • Dilate pupil with tropicamide if needed
  • There is a “Key-hole” effect, this generates a small, highly magnified field of view which makes it hard to examine whole fundus
• To perform indirect opthalmoscopy, line up your eye, light source, condensing lens, and animal’s eye. Hold the pen torch at the side of your temple in line with your eye and move to pick up a tapetal reflex. Place the condensing lens with most curved side towards you (“belly to belly”), 2-4cm in front of the eye.

  • Plane of lens parallel to plane of iris
  • this allows for visualisation of the fundus
• label the image

  A) indirect

  B) direct

  
• Dyscoric = irregularly shaped pupil
• Jones test = fluorescein has appeared at both nostrils within 3-5 minutes, indicating functional nasolacrimal ducts
• Perform a Jones test in cases of tear overflow to assess nasolacrimal duct patency.

  • Positive result shows nasolacrimal ducts are functioning
  • Negative result –may be true negative but false negatives very common
  • Many dogs have accessory openings in mouth (especially brachycephalic), also dog may have licked nose, head kept too elevated, insufficient time elapsed or insufficient dye applied
• Fluorescein is an orange dye that turns green in alkaline conditions. This dye will stain the corneal stroma green but have no uptake by the intact corneal epithelium or by Descemet’s membrane. It is indicated for the majority of ophthalmic presentations and should be done towards the end of the examination as dye uptake will obscure the view for ophthalmoscopy

  • Fluorescein strips are preferable and should touch onto the bulbar conjunctiva
  • Always flush after a few blinks with water, saline or false tears to prevent any false readings
• Tonometry = a measurement of intraocular pressure (IOP)
• If there is a raised IOP, suspect glaucoma. If it is lowered, suspect uveitis.

  • Difference of more than 8mmHg between eyes is abnormal
• name 3 types of tonometry

  indentation tonometry, applanation tonometry and rebound
• Indentation tonometry (Schiotz) measures the degree of indentation of the metal rod on the cornea

  • Inexpensive (£140 approximately)
  • Cumbersome to use, needs practice, but better than not measuring IOP at all!
  • Local anaesthetic drops applied first
  • Requires conversion table to work out IOP
• Applanation tonometry (TonoPen) works on the principle of pressure = force/area. There is a small footplate which flattens (“applanates”) a given surface area of the cornea. Take 3 readings and average them out

  • Very accurate
  • Expensive (£2500 approx.)
  • Local anaesthetic drops should be applied first
  • Disposable latex tip
  • The instrument can be used at any angle
• Rebound tonometry (Tonovet) has a very small area of contact with cornea. The instrument measures the deceleration of the probe as it rebounds from the cornea from multiple readings.

  • Very accurate
  • Expensive –around £1800
  • Probably easier to use than TonoPen
  • Local anaesthetic drops not required
  • Disposable metal probe with plastic tip
  • Must be held in horizontal position
• What CN lesions causes a lack of a palpebral response?

  Trigeminal (V)
• What test should you perform to differentiate between nuclear sclerosis and cataracts?

  Distant direct
• What nerve lesion causes anisocoria?

  Oculomotor nerve (3)
• Pigmentary keratitis can cause blockages in vision or can completely obscure the vision. The cause of this is unknown but it is very common in pugs.
• fill in the blanks

  A) nuclear sclerosis

  B) cataracts

  
• key differences are…

  • Colour and Opacity: Nuclear sclerosis has a bluish haze, whereas cataracts are more opaque and white.
  • Vision Impact: Nuclear sclerosis has minimal effect on vision, while cataracts can severely impair it.
  • Age and Cause: Nuclear sclerosis is a normal aging change, while cataracts can occur due to various reasons, including systemic diseases like diabetes.
  • Ophthalmoscope Examination: you can see through nuclear sclerosis to examine the retina, but cataracts obstruct this view
• DM causes an increased glucose concentration in the lens. There is too much glucose to undergo the normal metabolism and hence there is a shunting to an alternative pathway where glucose is converted into sorbitol. The increased sorbitol concentration draws water into the lens causing the lens fibres to swell and turn white.
• Clinical signs of uveitis include…

  • Pain (blepharospasm, epiphora, photophobia)
  • Red eye (conjunctival and episcleral hyperaemia)
  • Miosis, swollen dull iris, rubeosis iridis
  • Inflammation in the anterior chamber
  • Aqueous flare, hypopyon, hyphaema, keratic precipitates
  • Corneal oedema
  • Low intraocular pressure
  • May help diagnosis!