"To perceive perception is a queer undertaking.
Can seeing be seen or hearing be heard?
The Senses receive no impression of their own organs.
Why don't we see, that we do not see?
As long as I do not see, that I am blind, I am blind.
But as soon as I can see I am blind, I can see."
Eyes do not see themselves, so how can we watch vision? It was Denis Diderot, who proposed a radical solution for that problem: In order to perceive perception and to really see one's own vision, we have to become monsters with two heads, both watching each other, eye to eye.
Physiological blind spots are an anatomical fact. There are no receptors (rods and cones) where the optic nerve pierces the retina. The field of vision that falls on the physiologic blind spots is not received by the retinal receptors (no receptors in the optic disc - blind spot) and therefore not perceived by the cortex. Since we are binocular beings, the field of vision that falls on the blind spot of one eye is visualized by the contralateral eye. So, we are not consciously aware that a portion of our field of vision is not seen (perceived by the cortex).
If we were monocular, the physiologic blind spot would be filled in by the brain, approximating the surrounding field.
We don't normally notice these two great big holes in our field of vision. Not only do our eyes move around so that there's no one bit of visual space we're ignoring, but the blind spots from the two eyes don't overlap, so we can use information from one eye to fill in the missing information from the other.
However, even in situations in which the other eye isn't providing useful information and when your blind spot is staying in the same place, the brain has evolved mechanisms to fill in the hole.
Caveat: The anatomical size of the physiologic blind spot, i.e. the optic disc, is not directly proportional to the size of the brain's representation of it.