Step One

When approaching transient visual loss it is important to discern on history whether it is affecting one eye, or both. Monocular visual loss is due to a lesion anterior to the optic chiasm or within the eye itself, binocular (ie homonymous) visual loss localizes to the optic radiations or the visual cortex. It is important to ask about associated symptoms such as headache - given the history of scintillations, a migraine aura is a possible cause.

It is absolutely essential to examine visual acuity in each eye for any visual complaint.

Step Two

Fundoscopic examination is always a component of investigating a complaint of visual loss, and should ideally be done before ordering neuroimaging. Although it is important to rule out temporal arteritis (an ESR alone is sufficient), it does not generally cause transient visual loss. It is also important to inquire about related symptoms such as jaw claudication and scalp tenderness.

Step Three

If this is a suspected stroke, neither an echocardiogram nor a conventional angiogram are appropriate as the next investigation. The first step would be to order an MRI with diffusion weighted sequences - if this does not reveal an ischemic lesion, further work-up can be avoided. Transthoracic echocardiography is not adequate to detect a cardiac source of embolism, so transesophageal echocardiography would be required - in any case, a better first step would be to investigate the carotid arteries (ultrasound, MRA, or CTA) as artery-to-artery embolism from the internal carotid artery is a more common cause of embolic stroke, if we are assuming this visual loss is due to occlusion of the ophthalmic artery.

Conventional angiography is expensive and carries significant risks related to contrast and arterial cannulation. It should not be ordered until an MRI of the brain has been obtained. It is not an appropriate initial investigation for carotid stenosis when less invasive modalities are available.

Step Four

It seems that the patient's transient visual loss was caused by embolism from an internal carotid artery dissection, an extremely uncommon cause of stroke. This case presentation would also be very unusual in that it entirely lacks the more common features of internal carotid dissection, which typically include contralateral motor or sensory symptoms (from hemispheric embolisms), and often an ipsilateral Horner's syndrome (from interruption of post-ganglionic sympathetic fibres to the face, which are intimately related to origin of the internal carotid artery). Often patients experiencing internal carotid dissection report pain in the neck on the side of the dissection, or headache.