- The photoreceptor layer consisting of the rods and cones is the outer
layer of the retina. - The outer limiting membrane is formed by the junctional complexes
between Müller’s cells and the membranes of photoreceptor cells. - The outer nuclear layer contains the nuclei of rod and cone cells and
the surrounding cytoplasm (perikarya). - The outer plexiform layer contains rod and cone synapses as well as the
cell processes of bipolar, horizontal, and photoreceptor cells. - The inner nuclear (bipolar) layer is composed of the nuclei and
perikarya of the bipolar and amacrine cells as well as the nuclei of
Müller’s cells. - The inner plexiform layer consists of amacrine cells dispersed between
the processes of bipolar and ganglion cells. This layer is responsible for
modulation of signals from the ganglion to the photoreceptor cells. - The ganglion cell layer contains the ganglion cells separated by the
cytoplasm of astrocyte-like glia (Müller’s cells). - The nerve fiber layer consists of axons of the ganglion cells that will
form the optic nerve. - The internal limiting membrane is located between the vitreous body
and the retina. The photoreceptors are of two types: rods and cones.
The nuclei of the rods and cones are found in the outer nuclear layer
and extend across the outer limiting membrane in one direction and
toward the outer plexiform layer in the other direction. The outer seg-
ment is the photon-sensitive portion of the rod and cone and contains
membranous disks. Rhodopsin is composed of opsin and retinal. It is
responsible for transduction of light (photons) into hyperpolarization
of the cell membrane. Rhodopsin is present in the disks of the outer
segment of the rod. The inner segment contains numerous mitochon-
dria, glycogen, and protein synthetic apparatus. Rods are responsible
for night vision, whereas the cones are responsible for color vision,
which is best resolved at the fovea. The fovea, which is the center of
the macula, is composed exclusively of cones and is the site of optimal
resolution.
The choroid is a highly vascular layer that consists of three parts:
stroma, choriocapillaris, and Bruch’s membrane. Blood supply to the retina
is derived from the choriocapillaris of the choroid. The sclera is a layer of
relatively avascular dense connective tissue.
404 Anatomy, Histology, and Cell Biology