Equine Ophthalmic Exam Flashcards
What is this nerve block and what does it do?
Auriculopalpebral nerve block – blocks motor control of upper eyelid so stops blepharospasm but does NOT anaesthetise the ocular surface. Make sure you test menace response BEFORE performing this nerve block!
What is this nerve block and what does it do?
Supraorbital nerve block – blocks sensory innervation to medial 2/3 of upper eyelid (but not ocular surface) so aids examination.
What is the location of the supraorbital nerve block?
Supraorbital foramen easily palpated as a small hole on the bony orbital rim dorsal to the medial canthus of the eye. Inject 2mls local anaesthetic with a 5/8” needle through the foramen and 1ml subcutaneously as needle withdrawn.
How do you anaesthetise the ocular surface?
Topical local anaesthetic needs to be applied to the cornea (eg. Proxymetacaine, Tetracaine).
What are the 6 steps to an ocular exam?
- Distance exam
- Asses reflexes
- Gross examination
- Distant direct ophthalmoscopy
- Close direct ophthalmoscopy
- Indirect ophthalmoscopy
What do you observe in the distance exam?
Start from the front and then move to the side:
- Eyes equally open and eyelid angle (normal ~90 degrees to cornea)
- Swellings/depressions
- Any blepharospasm, ptosis (when the upper eyelid droops over the eye)
- Tearing (epiphora)
- Redness/swelling
What are the three reflex tests to do?
- Menace response
- PLR
- Dazzle response
What is the menace reponse?
Non-tactile visual threat to eye (movement of hand close to eye) causes ipsilateral eyelid closure.
Afferent arc is the visual pathway - retina, optic nerve, optic chiasm, contralateral visual cortex; efferent arc is facial nerve but also has cerebellar input.
What is the PLR?
Shine a bright light (e.g. pen torch) in each eye and note ipsilateral pupillary constriction (direct response). Swing light from one eye to the other to check consensual response – pupil already partially constricted; as direct response stronger a further brief constriction should occur.
What is the dazzle response?
Blink to bright light – best observed in dimly lit room.
What is the gross examination of?
Gross examination of adnexa and anterior chamber using bright light source (pen torch, phone torch)
- Change in colour of eye (red, cloudy etc)
- Foreign bodies
What is distant direct ophthalmoscopy?
Hold bright light source (pen torch, phone torch or direct ophthalmoscope) close to your eye and look at horse’s eye to observe reflected light from the retina – the tapetal or fundic reflex.
- Assess pupil size, symmetry, shape and response to light
- Tapetal reflectivity and symmetry
- Any opacities
What is close direct opthalmoscopy?
Rest your hand on the facial crest of the horse and start with a sense setting of 0.
- Tapetal fundus = green
- Non tapetal fundus = brown
- Optic disk = salmon pink
Start to increase settings up to +20
What can you visualise on close direct opthalmoscopy with the following lens settings:
2 to +12
+12
+15
+20
2 to +12 should focus on the vitreus
+12 should obtain the posterior lens and anterior vitreous in focus,
+15 the anterior lens capsule and iris face and,
W+20 the cornea, conjunctiva and eyelids.
What is Indirect ophthalmoscopy?
Equipment = opthalmascope and 20D lens
Stand at arm’s length from the horse with the ophthalmoscope against your eye.
Hold the 20D lens close (3-5 cm) to the horse’s eye (flat side to horse) – hold lens with thumb and first finger and rest little finger on horse’s head for stability.
Lens must be at 90° to tapetal reflection horizontally and vertically.
