Hello and thank you for your question.
I can imagine this is quite scary for you and you are probably pretty anxious to find out any information about the possible cause(s) of this.
The temporal association of vision loss only when you turn your head suggests that the cause is vascular in nature. By this I mean that there may be an obstruction in one or more of the major blood vessels that carries blood to either the front of the head (including the arteries that supply blood directly to the eye) or the back of the head (the arteries that supply blood to the posterior circulation of the brain.
The ultrasound is definitely the first diagnostic start. If that is inconclusive then a more detailed imaging study such as a magnetic resonance angiogram may be necessary to rule out other vascular causes such as aneurysms.
Assuming there is a relative vascular obstruction, it is possible to have an ischemic (lack of blood flow) event to either the eye or the part of the brain that controls vision that could cause permanent vision loss. For this reason, expediency in this workup is important. Also, your doctor may consider starting you on an aspirin if you are not already on one.
Does that help address your concerns?
I am happy to be able to help you today. If you would be so kind, please help me get credit for my efforts in answering your questions and press the ACCEPT button for this encounter. I will also be happy to answer any other questions until you have the information you need.
Any positive feedback and/or bonus you may feel prompted to provide would be welcomed and is appreciated. Thanks for your inquiry!
My opinion is solely informative and does not constitute a formal medical opinion or recommendation. For a formal medical opinion and/or recommendation you must see an eye doctor.