This is the point at which axons leave the eyeball and join the optic nerve. Also, arteries enter and veins leave the retina at the optic disk. There are no photoreceptors here, hence it is known as the 'blind spot'. It is a pinky-yellow oval, approximately 2mm in diameter, and situated in the nasal retina. The type of receptive field a particular cell has can be discovered by shining a small spot of light on the appropriate part of the retina , and recording from the cell in question.
Ganglion cells keep up a steady spontaneous firing rate in darkness or in diffuse light.
Light on the surround suppresses spontaneous firing. Light all over the receptive field will tend to cancel itself out. Rather than a simple mosaic arrangement, neighbouring ganglion cells receive their inputs from overlapping arrays of receptors, thus a single spot of light can stimulate very many ganglion cells simultaneously. The dendrites of the ganglions synapse mostly with bipolar cells, but also with amacrine and horizontal cells. Horizontal cells, like the amacrines , can thus combine messages from adjacent receptors.