Slide #DMS 199 [Eye, monkey, l.s., H&E]. This is an approximately meridional section of a celloidin (nitrocellulose) embedded eye. The eye is exceptionally difficult to section; the lens is so tough it is usually torn out of the tissue block by the knife and the retina almost always detaches completely, separating the neural from the pigmented layers. However, the slides you will be looking out are exceptionally well prepared and virtually irreplaceable. Please be very careful in handling.
This is a very low power view through a section of the eye. An extraocular muscle and a portion of the optic nerve can be seen posteriorly, while anteriorly, the cornea, iris, lens (whose middle is artifactually missing), and ciliary body can all be defined. In life, the vitreous chamber would be filled with a gelatinous vitreous body, while the anterior and posterior chambers would be filled with aqueous humor.
In this low power view, one can define the outer fibrous coat of the eye, consisting of the sclera posteriorly and the cornea anteriorly. The corneoscleral junction, or limbus, would be in the vicinity of the arrows indicated by the asterisk (*). Ciliary body, iris, lens and the anterior and posterior chambers of the eye may all be defined.
A medium power view of the cornea demonstrates the stratified corneal epithelium beneath which is found a thin, somewhat clear layer known as Bowman's membrane. The collagen-rich corneal stroma makes up the bulk of the cornea, and occasional fibroblasts may be seen therein. Posteriorly, one finds the so-called endothelium of the cornea, which would be supported by Descemet's membrane (not readily visualized in this specimen).
This is a low power view showing the lateral aspect of the lens and fragments of the zonular fibers which extend from the ciliary processes of the ciliary body to the surface of the lens.
A medium power view of the lateral portion of the lens illustrates the amorphous lens capsule, the lens epithelium (which covers just the anterolateral aspect of the lens), and a region on the lateral portion of the lens where developing lens fibers (cells), may be seen (as evidenced by their nuclei which soon disappear).
This is a high power view of the lens showing its epithelium and the developing lens fibers, the thin, very elongated cells forming the bulk of the lens. Over time, these lens fibers will lose their nuclei and other organelles, the cytoplasm becoming filled with a protein called crystallin.
This low power view of the anterolateral portion of the eye shows the ciliary body and the iris, two components of the middle coat of the eye known as the vascular coat or uvea. Sclera is found external to the uvea, and the retinal layer of the eye is found internally, but is not well visualized at this magnification. Aqueous humor, produced by the retina-derived epithelium covering the ciliary body, flows from the posterior chamber of the eye to the anterior chamber through the pupil.
This low power view shows the structure of the iris, consisting of an inner, pigmented epithelial layer (derived from retinal layers), and an external connective tissue stroma. A collection of smooth muscle near the pupillary border of the iris constitutes the pupillary sphincter muscle, while radially-arranged smooth muscle fibers in the stroma act as the pupillary dilator muscle.
In this view of the anterolateral portion of the eye, one can define the three coats or layers which comprise the wall of the eye: an inner retinal layer (seen in more detail later); a middle vascular layer or uvea, here represented by the ciliary body with its ciliary processes and also the iris; and finally the outer fibrous coat, represented here by the sclera, seen here near the limbus or corneoscleral junction. The canal of Schlemm, a venous sinus running through the sclera at the limbus, is responsible for draining aqueous humor from the iridiocorneal angle of the anterior chamber of the eye.
A higher power view of the ciliary body shows the non-photosensitive layer of the retinal epithelia which lines the internal surface of the ciliary body and its processes. Within the ciliary body itself, numerous pigmented stromal melanocytes are seen in amongst the smooth muscle tissue that constitutes the ciliary muscle of accommodation.
This low power view of the anterior portion of the eye provides orientation for the location of the ora serrata, the site of transition between the photosensitive retina and its non-photosensitive portion. This junction is seen at higher power in the next image.
This medium power view of the ora serrata shows the multiple layers of the retina which typify its photosensitive portion (on the left) and the non-photosensitive retina on the right. The non-photosensitive retinal epithelia will continue forward to cover the ciliary body, its processes and the internal surface of the iris. This image also nicely demonstrates the three coats of the eyeball, the outer fibrous coat (here, the sclera), the middle vascular layer (here, the heavily pigmented choroid), and the innermost layer, the retina.
This is a high power image of the retina, showing its characteristic multiple layers: the layer of optic nerve fibers (1), the ganglion cell layer (2), the inner plexiform layer (3), the inner nuclear layer (4), the outer plexiform layer (5), the outer nuclear layer (6), belonging to the rods and cones), and the photoreceptor layer (7) containing the receptive surfaces of the rods and cones). The darkly stained retinal pigmented epithelium is also seen, as is the heavily pigmented choroid layer and a portion of the sclera. Note the blood vessels in both the choroid and retinal layers, both essential to the viability of the retina.
This is a high power view of the rods and cones of the retina. Their nuclei, constituting the outer nuclear layer of the retina, as well as the inner and outer segments of the photoreceptor cells can be seen here. The outer limiting membrane, which represents a zone of intercellular junctions, may also be seen. The retinal pigmented epithelium, which has a very intimate association with the outer segments of the rods and cones, is seen at the bottom of the image.
This is a low power view of the posterior portion of the eye where two additional feature may be seen: 1) the fovea, the site of most acute vision, and 2) the optic disc (papilla, nerve head) which is the site of congression and exit of the optic nerve fibers to form the optic nerve proper. Both of these features are seen at higher power in the next images.
This higher power view of the fovea shows the characteristic thinning of the retina where incoming light has less of a barrier to pass through before interacting with the rods and cones, thus permitting more visual acuity.
A high power view of the optic disc shows the exit of the optic nerve fibers from the retina, through the cribriform plate of the sclera, and forming the optic nerve itself. Note a section through the central artery of the retina traversing the optic nerve.