Neural signals from the rods and cones undergo processing by other neurons, whose output takes the form of action potentials in retinal ganglion cells whose axons form the optic nerve. Several important features of visual perception can be traced to the retinal encoding and processing of light. In vertebrate embryonic development, the retina and the optic nerve originate as outgrowths of the developing brain, specifically the embryonic diencephalon; thus, the retina is considered part of the central nervous system (CNS) and is actually brain tissue. It is the only part of the CNS that can be visualized non-invasively. Much like the rest of the brain is isolated from the vasular system via the Blood-brain barrier, the retina is similarly protected by the Blood-retinal barrier. Structure
Inverted versus non-inverted retina
The vertebrate retina is inverted in the sense that the light sensing cells are in the back of the retina, so that light has to pass through layers of neurons and capillaries before it reaches the photosensitive sections of the rods and cones. The ganglion cells, whose axons form the optic nerve, are at the front of the retina; therefore the optic nerve must cross through the retina en route to the brain. In this region there are no photoreceptors, giving rise to the blind spot. In contrast, in the cephalopod retina the photoreceptors are in front, with processing neurons and capillaries behind them. Because of this, cephalopods do not have a blind spot.
Carac may refer to

a trade name of the drug Fluorouracil
a sweet pie specialty of Swiss origin, see Carac (pastry)