Optic disc and nerve, eye, human, H&E 65.
The site where the optic nerve leaves the eyeball is called the optic disc (OD). It is characteristically marked by a depression, evident here. Receptor cells are not present at the optic disc, and because it is not sensitive to light stimulation, it is sometimes referred to as the blind spot.
The fibers that give rise to the optic nerve originate in the retina, more specifically, in the ganglion cell layer (see below). They traverse the sclera through a number of openings (arrows) to form the optic nerve (ON ). The region of the sclera that contains these openings is called the lamina cribrosa (LC) or cribriform plate. The optic nerve contains a central artery and vein (not seen here) that also traverse the lamina cribrosa. Branches of these blood vessels (BV ) supply the inner portion of the retina.
PLATE 105 • EYE II: RETINA
Retina, eye, human, H&E 325.
On the basis of structural features that are evident in histologic sections, the retina is divided into ten layers, from posterior to anterior, as listed below and labeled in this figure: 1. Retinal pigment epithelium (RPE ), the outermost layer of the retina 2.
Layer of rods and cones (R&C ), the photoreceptor layer of the retina 3.
External limiting membrane (ELM ), a line formed by the junctional complexes of the photoreceptor cells 4.
Outer nuclear layer (ONL), containing nuclei of rod and cone cells 5.
Outer plexiform layer (OPL), containing neural processes and synapses of rod and cone cells with bipolar, amacrine, interplexiform and horizontal cells 6.
Inner nuclear layer (INL), containing nuclei of bipolar, horizontal, interplexiform amacrine, and Mler’s cells 7.
Inner plexiform layer (IPL), containing processes and synapses of bipolar, horizontal, interplexiform amacrine, and ganglion cells 8.
Layer of ganglion cells (GC ), containing cell bodies and nuclei of ganglion cells 9.
Nerve fiber layer (NFL), containing axons of ganglion cells 10.
Internal limiting membrane (ILM ), consisting of the external (basal) lamina of Mler’s cells
This figure also shows the innermost layer of the choroid (Ch), a cell-free membrane, the lamina vitrea (LV ), also called Bruch’s membrane. Electron micrographs reveal that it corresponds to the basement membrane of the pigment epithelium. Immediately external to the lamina vitrea is the capillary layer of the choroid (lamina choriocapillaris). These vessels supply the outer part of the retina.
KEY BV, blood vessels Ch, choroid ELM, external limiting membrane GC, layer of ganglion cells ILM, internal limiting membrane INL, inner nuclear layer (nuclei of bipolar, horizontal, amacrine, and Mler’s cells) IPL, inner plexiform layer LC, lamina cribrosa LV, lamina vitrea NFL, nerve fiber layer OD, optic disc ON, optic nerve ONL, outer nuclear layer (nuclei of rod and cone cells) OPL, outer plexiform layer RPE, retinal pigment epithelium R&C, layer of rods and cones arrows, openings in sclera (lamina cribrosa)
PLATE 106 Eye III: Anterior Segment