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Special Topics in Equine Clinical Practice > Equine Ophthalmic Exam & Orbital Diseases > Flashcards

Equine Ophthalmic Exam & Orbital Diseases Flashcards

1
Q

Horses are prey animals, what characteristics of their eyes support this?

A
  1. prominent globes that are laterally positioned and high on their head
  2. horizontal elliptical pupil
  3. granulae iridica/corpora nigra
  4. visual field = 350 degrees
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2
Q

what are the 2 blindspots of the horse?

A

below nose and forehead and behind the tail.

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3
Q

In what order should you do your initial ophthalmic exam?

A
  1. examine from afar (look at symmetry, orbit, eyelash position, pupil size, and any epiphora)
  2. examine in the stall/roundpen, etc. (eval vision and behavior)
  3. examine up-close with restraint, sedation, +/- local block
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4
Q

What do the following observations usually indicate?

  • Eyelashes point downward
  • Eyelashes point upward
A
  • Eyelashes point downward = enophthalmos
  • Eyelashes point upward = exophthalmos

normal eyelash position is perpendicular to cornea (straight out)

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5
Q

T/F: you should perform your cranial nerve evaluation after sedating the horse in order to get accurate results

A

false – perform this exam BEFORE any sedation.

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6
Q

T/F: Indirect PLRs in horses are less prominent because decussation at the chiasm is only 85%

A

true

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7
Q

Which muscle of the eye is really strong in horses and makes it necessary for us to place a local block to achieve a thorough ocular examination?

A

orbicularis oculi muscle

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8
Q

Which local block blocks motor of the orbicularis oculi muscle (mostly the upper eyelid)?

A

auriculopalpebral block

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9
Q

which local block blocks sensory input to the central-upper eyelid?

A

supraorbital or frontal block

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10
Q

What nerve is blocked with the auriculopalpebral block?

A

palpebral branch of the auricular palpebral nerve (which is a branch of the facial nerve)

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11
Q

what needle size and amount of local block is used for both the auriculopalpebral and supraorbital/frontal blocks?

A

25g needle
1 mL of lido/bupiva/mepiv

lasts for 1-2 hours

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12
Q

The landmarks described below are for which local block?
- caudal to the posterior ramus of the mandible
- dorsal to the highest point of the zygomatic arch
- on the zygomatic arch caudal to the bony process of the frontal bone

A

auriculopalpebral block

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13
Q

Which nerve is blocked by the supraorbital or frontal block?

A

ophthalmic branch of the trigeminal nerve

this blocks sensation to the central upper eyelid.

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14
Q

Which of the following blocks is described by the landmarks below?
- place thumb below dorsal orbital rim
- place middle finger in supraorbital fossa
- place index finger straight down (midway between thumb and middle finger) to locate the supraorbital foramen

A

supraorbital or frontal block

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15
Q

T/F: tear deficiencies are a common cause of KCS in horses

A

false – tear deficiencies are rare in horses.

Tear production tests are rarely done for this reason and are indicated only for CN V or VII dysfunction.
Normal STT in horses is <20 mm/min

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16
Q

What is normal intraocular pressure for horses?

A

15-30 mmHg

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17
Q

which intraocular pressure measurement tool requires the use of topical anesthetic?

A

applanation tonometry (Tonopen)

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18
Q

What does the Jones test evaluate?

A

nasolacrimal duct patency

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19
Q

What are the indications to sedate a horse and perform irrigation of the nasolacrimal duct?

A
  • epiphora
  • mucoid ocular discharge
  • nasal puncta discharge
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20
Q

If you were performing retrograde irrigation of the NLD in a horse, what size catheter would you use and hose much sterile eyewash would you infuse?

A

5 or 6 polyethylene urinary catheter
12-20 mL sterile eyewash

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21
Q

T/F: a grey line at the edge of a horses iris is considered an abnormality and can indicate iris atresia

A

false – this is a normal finding in horses and is indicative of the iridocorneal angle.

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22
Q

What does the Tyndall Effect indicate?

A

Aqueous flare – proteins in the anterior chamber which can be resulting from equine recurrent uveitis or acute uveitis.

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23
Q

What could be a cause of corpora nigra atrophy?

A

chronic inflammation (such as in ERU cases)

24
Q

What causes posterior synechia?

A

uveitis

25
Q

What drug should you use to dilate the eyes for complete examination of the intraocular structures such as the lens, etc.?

A

1% tropicamide (20 min prior to exam)

this will last for 4-6 hours

26
Q

What are the 3 differences of the equine fundus?

A

optic disc is oval, salmon-pink, and located in the non-tapetal fundus

the retina is paurangiotic (partially vascularized)

they have a fibrous tapetum which has color variation and stars of winslow (black dots that are choroid vessels)

27
Q

T/F: Direct fundoscopy provides you with an inverted and reversed image

A

false – this is true of indirect fundoscopy (the one with the handheld lightsource and lens)

indirect provides you with a wider field of view, but less magnification

28
Q

T/F: direct fundoscopy provides you with a smaller field of view and more magnification than indirect fundoscopy

A

true

29
Q

T/F: horses have an incomplete orbit which makes fractures more likely

A

false – they have a complete bony orbit comprised of frontal, lacrimal, zygomatic, and temporal bones.

30
Q

Which nerve innervates the dorsal oblique ocular muscle?

A

trochlear nerve

31
Q

which nerve innervates the retractor oculi (bulbi) muscle?

A

abducens

32
Q

which nerve innervates the lateral rectus ocular muscle?

A

abducens

33
Q

T/F: most of the extraocular muscles are innervated by the oculomotor nerve

A

true
the muscles are: levator palpebrae superioris (opens eye), the superior, medial and inferior rectus muscles, and the inferior oblique muscle.

34
Q

what are the 3 possible sources of a “sunken” appearance to the eye?

A
  1. enophthalmos
  2. microphthalmos
  3. phthisis bulbi
35
Q

_________ is recession of the globe within the orbit usually secondary to loss of the orbital contents.

A

enophthalmos

36
Q

what are 4 potential causes of enophthalmos in horses?

A
  1. orbital fractures
  2. resorption of orbital fat (weight loss or aging)
  3. dehydration in foals (+entropion)
  4. sympathetic denervation (horners)
37
Q

__________ is a congenital anomaly resulting in a small globe

A

microphthalmia

38
Q

_________ is the gradual shrinkage of the globe due to chronic inflammation and low intraocular pressure. This is a non-visual eye.

A

Phthisis bulbi

damage to the CB results in decreased aqueous humor production leading to chronically low intraocular pressure.

39
Q

what are the 2 potential sources of a bulging ocular appearance and whats the difference between them?

A
  1. buphthalmos – enlarged globe assoc. with chronically increased IOP secondary to glaucoma
  2. exophthalmos – anterior displacement of a normal-sized globe
40
Q

what causes buphthalmos?

A

chronically increased IOP (secondary to glaucoma)

look for other signs of glaucoma such as corneal edema or haab’s striae

41
Q

T/F: glaucoma carries a poor prognosis in horses

A

true horses dont usually respond well to glaucoma therapy.

42
Q

what are 3 potential causes of exophthalmos?

A
  1. retrobulbar mass
  2. orbital cellulitis / abscess
  3. trauma (reduced orbital space)

to differentiate, do digital retropulsion to see if pain is elicited. if so, more likely inflammatory/infectious. if non-painful, more likely neoplastic or cystic mass.

43
Q

which areas of the orbit are at highest risk for fracture?

A

dorsal orbital rim
zygomatic arch

44
Q

what are clinical features of orbital fractures in horses?

A
  1. facial asymmetry
  2. blepharaedema
  3. periocular laceration
  4. conjunctival hyperemia
  5. chemosis
  6. SQ emphysema
45
Q

What is the typical approach to treating orbital fractures in horses?

A
  • ensure corneal protection and lubrication
  • check visual status
  • if eyelid/skin laceration, clean and appose
  • if minor non-displaced orbital fractures, may be able to leave it alone
  • if displaced, reposition (surgery)
  • if comminuted fracture, may require repositioning and wiring or bone grafts (surgery)
46
Q

What causes orbital fat prolapse?

A

weak episcleral fascia or trauma causing the fat to herniate

47
Q

how do you treat orbital fat prolapse?

A

resect it and suture closed the conjunctival surface over the exposed area.

48
Q

what is the clinical appearance of orbital cellulitis?

A
  • exophthalmos
  • blepharaedema/ blepharitis
  • severe conjunctival swelling
  • elevated 3rd eyelid
  • mucoid ocular discharge
  • IOP normal or elevated
49
Q

what causes orbital cellulitis?

A
  1. direct trauma
  2. seeding septic emboli
  3. foreign body
  4. uncontrolled septic endophthalmitis
50
Q

what is the most important diagnostic to diagnose orbital cellulitis?

A

imaging or FNA

51
Q

how do you treat orbital cellulitis?

A

systemic antimicrobials
aggressive NSAIDs
topical lubricants
drain abscess or remove FB (if present)

enucleation if necessary

52
Q

what are the 4 most common orbital neoplasms in horses?

A
  1. neuroendocrine tumors
  2. extra-adrenal paranglioma
  3. nasal and orbital adenocarcinoma
  4. sarcoma, lymphoma, SCC
53
Q

what is the clinical appearance of a horse with an orbital neoplasm?

A

exophthalmos
3rd eyelid elevation
strabismus
anisocoria, blindness
chemosis
epistaxis

54
Q

how do you diagnose orbital neoplasia in horses?

A

advanced imaging! (CT/MRI)
+/- orbital ultrasound + guided FNA

55
Q

how do you treat orbital neoplasia in horses?

A

exenteration
radiation
chemo
or euthanasia

the prognosis is grave if advanced stage when presenting

Special Topics in Equine Clinical Practice (18 decks)

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