This might not pass a doctors muster, but it's pretty close:
The blob was an artifact of your night vision. Your retinas have rods and cones on their surface that allow you to see. Cones are for "day vision" as they are activated by light and allow you to see fine detail and color. Cones are predominately located in the center of your retina, so under day vision conditions, you can see with great detail what you are looking directly at. In the absence of light, your rods take over, but they see mostly black and white and less detail. Because rods are located on the periphery of your retina, you see "best" in the dark when you don't look directly at what you are trying to look at. Since this is so annoying, the best night vision technique is to move your eyes back and forth or around the thing you are trying to look at. Your brain will fill in the details and allow you to see the object as if you were looking directly at it. It will still be largely black and white and fuzzy, but at least you won't see a black hole (or blob) where your cones are failing you.
"Its better to have a gun and not need it, than to need a gun and not have it." -- Clarence Worley in True Romance