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The equine field eye exam: a systematic sequence
The equine eye exam proceeds from distance assessment and cranial nerve testing to examination of individual structures and ophthalmic diagnostics.
A horse described in the lecture had a droopy ear and a deviated nose, with absent palpebral and menace responses. [1] The horse was nevertheless visual and had facial nerve paralysis on that side. [1]
Start at a distance, then follow the sequence
Begin with a distance exam a few feet away from the horse. [1] Retroillumination at this stage means shining a light from a few feet away toward the horse's face so it bounces back. [1] Assess pupil size and symmetry, whether the eyeballs are aligned as expected, and facial symmetry on both sides. [1] Then move in and start cranial nerve testing. [1]
- Assess the direct pupillary light reflex in the illuminated eye, then check whether the opposite eye also constricts. [1]
- That is the indirect response in the opposite eye; then back off and do the same thing on the other side. [1]
- Next, test the palpebral reflex by touching around the eye, and the menace response. [1]
- For menace testing, create a blinder or cover the opposite eye so the horse is not benefiting from peripheral vision. [1]
- Examine the orbit, adnexal tissues including the eyelids and third eyelid, and then the ocular structures from outside inward. [1]
- Usually finish with ophthalmic diagnostics, including fluorescein staining; checking intraocular pressure may also be indicated. [1]
If moving the horse indoors is not possible, you may take it to a lean-to or a darker forest area. [1] Sedation can be helpful for horses that are uncooperative because of their demeanor or eye pain. [1]
Assess each eye’s menace response independently
The menace response evaluates conscious perception of vision. [1] Cover one eye and approach the eye being tested with a menacing gesture from different visual axes to assess for deficits. [1]
If covering one eye makes the horse close the eye being tested, use a blinder instead. [1] This still permits independent assessment of one eye and may avoid triggering that blink response. [1]
Use a helper for the indirect light reflex
Pupillary light reflexes are slower in horses than in dogs or cats. [1] Removing the light and looking for rebound dilation can be easier. [1]
A helper can be lined up with retroillumination on the opposite side while the examiner shines a light on one side. [1] Have the helper watch for the indirect response and continue watching for the pupil to reopen after light removal. [1]
Use the ophthalmoscope beyond the fundus
The tiny circle beam can be used to look for aqueous flare and assess depths within the eye. [1] The slit beam can show corneal curvature when examining a corneal ulcer. [1] An epithelial defect retains normal curvature, whereas flattening or indentation indicates loss of corneal stroma. [1]
Shine the light from the side while looking from the front, and shine it from the front while looking from the medial and lateral sides. [1] Shining the light from these different angles gives a better perspective on things happening at different levels of the eye and within the eye. [1] During retroillumination, also note any opacities in the line of reflection. [1]
Related lectures
On-demand lecture
Introduction To Equine Ophthalmology
References
- Introduction to Equine Ophthalmology (lecture recording, May 8 2026) Vet On It lecture transcriptLecture source retained by Vet On It.
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