Neuro-ophtalmology Flashcards
What is the swinging flashlight test
The examiner shines a light into the first eye
- the normal response is for the pupil of both eye to constrict
The examiner then swings the light to the other eye
- the normal response is for the second pupil to remain constricted or to constrict even further
- the abnormal response is for the pupil to dillate upon direct light stimulation and this result constitutes a positive swinging flashlight test
- this finding is highly suggestive of a prechiasmal lesion (i.e., a lesion in the retina or proximal optic nerve or both
How frequent is idiopathic Horner’s syndrome in cats
It is less common in the cat than in the dog
It is postganglionic in nature and tends to spontaneously resolve within 6-8 weeks
How can you differentiate between second and third-order Horner’s syndrome
Pharmacological testing with a direct-acting sympathomimetic drug can help differentiate between second and third-order Horner’s syndrome
- one drop of 0.25%-1% phenylephrine is applied to the eye
- where there is a third-order (postganglionic) lesion, mydriasis will occur within 20 minutes owing to denervation hypersensitivity of the pupillary dilator muscle
- if the lesion involves the first-order (upper motor neuron) or second-order (preganglionic) neurons, pupil dilation is much slower because the dilator muscle is not hypersensitised
What would be your main differentials for anisocoria (differentiate mydriasis and miosis)
Mydriasis (unilateral)
- retinal or optic nerve (CNII) disease
- oculomotor nerve (CNIII) lesion
- congenital iris anomaly or age-related iris atrophy
- glaucoma
- pharmacological dilation
- cerebellar lesions
Miosis (unilateral)
- anterior and reflex uveitis
- Horner’s syndrome
