Do you want to know the actual size of the spot on the retina, or the area of the field of vision it occupies? I will attempt to answer both. The blind spot of the eye, also known as the optic disc, is an area in the retina where the nerve fibers of the ganglia of the retina join to form the optic nerve, and together with the veins, exit the eye. This area is located 3 mm medial and slightly above the posterior pole of the globe. It lacks rods and cones (receptor cells), hence the name "blind spot". This disc shaped area meassures about 1-2 mm in diameter. More important though is the effect it has on the field of vision. At the posterior pole there is a yellowish pigmented spot, the macula lutea. This marks the spot of the fovea centralis, which is densly packed with cones and few cells and no blood vessels overlying the receptors. It is the point where visual acuity is greatest and highly developed in man.The eyes normaly move so that light rays from an object in vision fall on the fovea. The existence of the blind spot in the field of vision can easily be demonstrated as follows. Draw a x (on the left) and a spot (5mm in diameter and 5 cm to the right of the cross). Close the left eye and hold the figure about 15 cm in front of the right eye. While looking steadely at the cross move the figure closer until the dot dissappear. This marks the spot where the image falls on the optic disc. The reason why we are normaly not aware of the blind spot is because we have binocular vision. This means tha the seperate fields of vision of each eye overlap medialy, so that the blind spot of one eye will be "covered" by the other. About 2% of the area of vision is occupied by the blind spot of each eye.