That depends on several factors, but you need to see your eye doctor right away. If it happened suddenly, you could have had one of four conditions that are most commonly known as a stroke in the eye:
Central retinal artery occlusion or CRAO
Central retinal vein occlusion or CRVO
Branch retinal artery occlusion or BRAO
Branch retinal vein occlusion or BRVO
Typically, CRAO and BRAO cause total loss of vision, but it can be just central depending on where the occlusion is located.
You could also have a vitreous hemorrhage. If you are diabetic or on blood thinners, this is a common cause of the "ink blot" shaped loss of vision. They typically happen suddenly as well, but tend to float when you move your eye.
It could also be a severe case of wet macular degeneration that has hemorrhaged, although this typically develops gradually over time.
However, if you have noticed a sudden and severe change in your vision, you need to see your ophthalmologist right away. In the case of a CRAO, treatment needs to be administered within 90 minutes, or vision loss becomes permanent.
If you haven't already, I advise you to call your ophthalmologist right now, or walk in to their office and explain your symptoms. Never wait to see your eye doctor, it's better to be safe than sorry.