Equine ophthalmic exam Flashcards
What are the most common ophthalmic conditions in horses?
- ulcers
- neoplasia
- uveitis
- cysts
- cataracts
What ophthalmic disease clinical signs are often noticed by owners?
Owner only notice visible signs
* Blepharospasm
* Swelling
* Epiphora
Locate the third eyelid, corpora nigra, limbus, sclera and pectinate ligament
What is the corpora nigra also known as?
Corpora Nigra aka granula iridica
What are the layers of the cornea?
Locate the tapetum, non tapetal fundus and optic disc
Tapetum
* Green/yellow/red/blue
* Reflective
Non-tapetal fundus (NTF)
Brown, red
Optic disc
* Large
* In non-tapetal fundus
* ~60 fine blood vessels (no vessels between 5 and 7 o’clock)
What should you check from afar in your ophthalmic exam?
- Blepharospasm
- Swelling
- Ptosis
- Conjunctival inflammation
- Epiphora/ocular discharge
- From the front and side
What response and reflexes should you test in your ophthalmic exam?
Response
- Menace
Reflexes
* PLR
* Dazzle
* Palpebral/corneal
Describe the pupil size in these pictures?
Top - miosis
Bottom - midriasis
What environment should you be in to perform your ophthalmic exam? What restraint can you use?
- Quiet and dark environment
- Sedation - prevent horse moving its head
- Nerve blocks - auriculopalpebral, palpebral and supraorbital
- ± topical anaesthesia - if you are planning on touching the cornea
How is the auriculopalpebral nerve block performed?
3 sites where it can be blocked
1. caudal to the posterior ramus of the mandible
1. dorsal to the highest point of the zygomatic arch
1. where it lies on the zygomatic arch caudal to the bony process of the frontal bone
Inject 1ml, massage the area and wait 3-5 minutes
What are the non routine nerve blocks? How are they undertaken?
LACRIMAL NB
* Needle subcutaneously just dorsal to the lateral canthus
* Direct medially across the dorsal orbital rim during injection
INFRATROCHLEAR NB
* Insert needle at medial canthus
* Needle directed along the bony notch on the dorsal rim of the orbit (toward the medial canthus)
* Desensitisation of medial eyelid
ZYGOMATIC NB
* Desensitisation of the remainder of the lower lid
* Local anaesthetic along the ventral and lateral aspect of the bony orbit
* near the junction where the orbit begins to curve upward
When would you use the colourful colour beams on an ophthalmoscope?
stain eye for ulcers - defects on cornea
* blue light - highlights orange (fluorescin)
* green - highlights red (rose bengal)
What structures have been highlighted by slit ophthalmoscopy? What would a flare indicate?
- red - cornea
- yellow - anterior surface (capsule)
- pink - posterior surface
mostly useful for anterior segment
helps highlight depth of lesions
Flare indicates uveitis
What will slit opthalmoscopy help differentiate in this case?
Melting ulcer (ulcer that is about to burst) &
bullous keratopathy
Why would you use mydriatics? What drugs can you use? How long does it last? Why should you not use atropine?
You may need to dilate the pupil for a thorough examination of the posterior segment
Tropicamide/Phenylephrine
Require >20-30 min to dilate pupil
Effect lasts 4-6 hours
Atropine NOT (!!!) an option for a non painful eye,
lasts up to 2 weeks
side effects (LC impactions)
When would you use indirect ophthalmoscopy?
Only for Fundic exam – peripheral lesions
What is normal IOP in horses? Is sedation needed for tonometry? Where do you take your mesaures?
Normal IOP ~14-22mmHg
Sedation needed for tonopen but not for tonovet
Perpendicular to central corneal
What can you use for topical anaesthesia?
- Tetracaine
- Proxymetacaine (aka proparacaine)
What could cause low or high IOP?
Low IOP
* Leakage
* Sedation
* Xylazine: IOP drops by 23%
* ACP also
* Xylazine and ketamine: no effect
High IOP
* Glaucoma
* Fibrosis, oedema (False elevation)
* Higher without palpebral NB
* 24-32mmHg
* Low head position (even with sedation)
Get used to same protocol (sedation, head position, etc)
What are normal results for schirmer tear test?
- Wait 60 seconds
- Normal wetting >10mm + clinical signs
What do fluorescin and rose bengal highlight?
fluorescin - exposed trauma
rose bengal - superficial lesions (tear film or epithelial layer)
What layers are on the ultrasound image of the eye?
- retinochoroid unit
- optic nerve head
- ciliary artery
- extraocular muscles
- retrobulbar fat
What steps of the ophthalmic exam are done in first opinion practice vs referral?
Routinely used
* Naked eye examination
* Nerve blocks
* Fluoroscein/ Rose Bengal dye
* Focal light source
* Pen torch or transilluminator
* Direct ophthalmoscopy
Not routinely done
* Indirect ophthalmoscopy
* Transpalpebral ultrasound
* Slit lamp evaluation of cornea/anterior chamber
* Tonometry
What common pathology occurs in the anterior and posterior segments?
Anterior Segment
* Oedema
* Bullae - fluid filled
* Synechiae (anterior/posterior) - adhesions
* Cataracts
* Iris cysts
* Tumours (SCC!)
Posterior segment
* Retinopathies
* Vitral floaters
* Retinal detachments
What can you see here?
ulcer
