I had a stroke (a blood clot) in the right branch vein in my left eye.

It created a hemorrhage into the retina, which in daylight was a purple shadow, and at night was an actual hole in my night vision.

I also had an aching pain with it. This happened at a work situation that lasted 8hrs of intense stress and elevated blood pressure.

I had to have angiograms in both eyes, which after the fact showed normal blood flow returning to that eye. It took about 6 months for it to recover, and now I am normal again.

This should be seen by an ophthalmologist ASAP. Another possibility is a retinal detachment, or inflammation of the eye called uveitis:
http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0002000/

The blood vessels in the eye, can be affected by homocysteine levels that are too high. Checking B12 levels would be a good idea and if you are low, taking a supplement to boost them would possibly prevent further issues. If you have autoimmune disease like a friend of ours, the uveitis will be ongoing, and require treatment.