Final answer:
The most appropriate initial diagnostic study for amaurosis fugax is a Carotid ultrasound, which identifies possible blockages or abnormalities in the carotid arteries that may cause temporary vision loss.
Step-by-step explanation:
In a patient with amaurosis fugax, the most appropriate initial diagnostic study is D. Carotid ultrasound. Amaurosis fugax is often caused by temporary disturbances in blood flow to the retina, which can be due to carotid artery disease. A carotid ultrasound is a non-invasive test that uses sound waves to evaluate blood flow through the carotid arteries. This test can help identify any potential blockages or other abnormalities that may lead to retinal ischemia and transient vision loss.
Ophthalmoscopy can be used to directly observe the retina but wouldn't necessarily reveal the underlying vascular cause. Schiotz tonometry measures intraocular pressure and is not directly relevant to amaurosis fugax. MR angiography could provide detailed images of blood vessels, but it's generally not considered an initial test due to being more invasive, time-consuming, and less readily available than a carotid ultrasound.