Altai State Medical University

Department of Eye Diseases

Abstract on the topic

Pathology of the choroid and retina.

Barnaul 2015.

1. Vascular tract of the eye.

The vascular tract, consisting of the iris, ciliary body and choroid, is located medially from the outer shell of the eye. It is separated from the latter by the suprachoroidal space, which is formed in the first months of children’s lives.

The iris (the anterior part of the vascular tract) forms a vertically standing diaphragm with a hole in the center - the pupil, which regulates the amount of light entering the retina. The vascular network of the iris is formed by the branches of the posterior long and anterior ciliary arteries and has two circulation circles.

The iris can have different colors: from blue to black. Its color depends on the amount of melanin pigment it contains: the more pigment in the stroma, the darker the iris; in the absence or small amount of pigment, this shell has a blue or gray color. Children have little pigment in the iris, so in newborns and children of the first year of life it is bluish-grayish. The color of the iris is formed by the age of ten or twelve. On its anterior surface two parts can be distinguished: narrow, located near the pupil (the so-called pupillary), and wide, bordering the ciliary body (ciliary). The boundary between them is the pulmonary circulation of the iris. There are two muscles in the iris that are antagonists. One is placed in the pupillary area, its fibers are located concentrically with the pupil, and when they contract, the pupil narrows. Another muscle is represented by radially running muscle fibers in the ciliary part, with the contraction of which the pupil dilates.

The ciliary body consists of a flat and thickened coronal part. The thickened coronal part is made up of 70 to 80 ciliary processes, each of which has vessels and nerves. The ciliary body contains the ciliary, or accommodative, muscle. The ciliary body is dark in color and covered with retinal pigment epithelium. In the interprocess areas, the ligaments of Zinn of the lens are woven into it. The ciliary body is involved in the formation of intraocular fluid, which nourishes the avascular structures of the eye. The vessels of the ciliary body arise from the large arterial circle of the iris, formed from the posterior long and anterior ciliary arteries. Sensitive innervation is carried out by long ciliary fibers, motor innervation - by parasympathetic fibers of the oculomotor nerve and sympathetic branches.

The choroid, or the choroid itself, is composed mainly of the posterior short ciliary vessels. With age, the number of pigment cells - chromatophores - increases in it, due to which the choroid forms a dark chamber that prevents the reflection of rays entering through the pupil. The basis of the choroid is a thin connective tissue stroma with elastic fibers. Due to the fact that the choriocapillary layer of the choroid is adjacent to the retinal pigment epithelium, a photochemical process takes place in the latter.

2. Uveitis.

Uveitis is an inflammation of the choroid (uveal tract) of the eye. There are anterior and posterior sections of the eyeball. Iridocyclitis, or anterior uveitis, is an inflammation of the anterior part of the iris and ciliary body, and choroiditis, or posterior uveitis, is an inflammation of the posterior part, or choroid. Inflammation of the entire vascular tract of the eye is called iridocyclochoroiditis, or panuveitis.

The main cause of the disease is infection. The infection penetrates from the external environment in case of eye injuries and perforated ulcers of the cornea and from internal foci in general diseases.

The defenses of the human body play an important role in the mechanism of development of uveitis. Depending on the reaction of the choroid, atopic uveitis is distinguished, associated with the action of environmental allergens (pollen, food products, etc.); anaphylactic uveitis caused by the development of an allergic reaction to the introduction of immune serum into the body; autoallergic uveitis, in which the allergen is the pigment of the choroid or lens protein; microbial-allergic uveitis, developing in the presence of a focal infection in the body.

The most severe form of uveitis is panuveitis (iridocyclochoroiditis). It can occur in acute and chronic forms.

Acute panuveitis develops due to the introduction of microbes into the capillary network of the choroid or retina and is manifested by severe pain in the eye, as well as decreased vision. The process involves the iris and ciliary body, and sometimes the vitreous body and all the membranes of the eyeball.

Chronic panuveitis develops as a result of exposure to brucellosis and tuberculosis infections or herpes viruses, and occurs in sarcoidosis and Vogt-Koyanagi syndrome. The disease lasts a long time, with frequent exacerbations. Most often, both eyes are affected, resulting in decreased vision.

When uveitis is combined with sarcoidosis, lymphadenitis of the cervical, axillary and inguinal lymph glands is observed, and the mucous membrane of the respiratory tract is affected.

Peripheral uveitis affects people twenty to thirty-five years of age, and the lesion is usually bilateral. The disease begins with decreased vision and photophobia. With peripheral uveitis, the following complications are possible: cataracts, secondary glaucoma, secondary retinal degeneration in the macular area, papilledema. The basis for diagnosing uveitis and its complications is eye biomicroscopy. Conventional research methods are also used.

Treatment. To treat acute uveitis, it is necessary to administer antibiotics: intramuscularly, under the conjunctiva, retrobulbar, into the anterior chamber of the eye and the vitreous body. Provide rest to the organ and apply a bandage to the eye.

In case of chronic uveitis, along with specific therapy, hyposensitizing drugs and immunosuppressants are prescribed, and according to indications, excision of vitreous adhesions is performed.

Ophthalmic artery(a. ophthalmica)- a branch of the internal carotid artery - is the main collector of supply to the eye and orbit. Penetrating into the orbit through the optic nerve canal, the ophthalmic artery lies between the trunk of the optic nerve, the external rectus muscle, then turns inwards, forms an arch, bypassing the optic nerve from above, sometimes from below, and on the inner wall of the orbit it breaks up into terminal branches, which, perforating the orbital septum , extend beyond the orbit.

The blood supply to the eyeball is carried out by the following branches of the ophthalmic artery:

1) central retinal artery;

2) posterior - long and short ciliary arteries;

3) anterior ciliary arteries - the terminal branches of the muscular arteries.

Separating from the arch of the ophthalmic artery, the central retinal artery runs along the optic nerve. At a distance of 10 - 12 mm from the eyeball, it penetrates through the nerve sheath into its thickness, where it runs along its axis and enters the eye in the center of the optic nerve head. At the disc, the artery is divided into two branches - superior and inferior, which, in turn, are divided into nasal and temporal branches (Figure 1.18, see inset).

The arteries going to the temporal side arc around the area of the macula. The trunks of the central retinal artery run in the nerve fiber layer. Small branches and capillaries branch to the outer reticular layer. The central artery that supplies the retina belongs to the system of terminal arteries that do not give anastomoses to neighboring branches.

The orbital portion of the optic nerve receives its blood supply from two groups of vessels.

In the posterior half of the optic nerve, directly from the ophthalmic artery, 6 to 12 small vessels branch off through the dura mater of the nerve to its soft shell. The first group of vessels consists of several branches extending from the central retinal artery at the site of its introduction into the nerve. One of the larger vessels goes along with the central retinal artery to the lamina cribrosa.

Throughout the entire length of the optic nerve, small arterial branches widely anastomose with each other, which significantly prevents the development of foci of softening due to vascular obstruction.

The posterior short and long ciliary arteries arise from the trunk of the ophthalmic artery and in the posterior part of the eyeball, around the optic nerve, penetrate into the eye through the posterior emissaries (Figure 1.19, see inset). Here short ciliary arteries (there are 6-12 of them) form the choroid itself. The posterior long ciliary arteries in the form of two trunks pass in the suprachoroidal space from the nasal and temporal sides and are directed anteriorly. In the region of the anterior surface of the ciliary body, each of the arteries is divided into two branches, which bend in an arcuate manner and, merging, form a large arterial circle of the iris (Figure 1.20, see inset). The anterior ciliary arteries, which are the terminal branches of the muscular arteries, take part in the formation of the large circle. The branches of the greater arterial circle supply blood to the ciliary body with its processes and the iris. In the iris, the branches have a radial direction up to the pupillary edge.

From the anterior and long posterior ciliary arteries (even before their fusion), recurrent branches are separated, which are directed posteriorly and anastomose with the branches of the short posterior ciliary arteries. Thus, the choroid receives blood from the posterior short ciliary arteries, and the iris and ciliary body from the anterior and long posterior ciliary arteries.

Different blood circulation in the anterior (iris and ciliary body) and posterior (choroid itself) parts of the vascular tract causes their isolated damage (iridocyclitis, choroiditis). At the same time, the presence of recurrent branches does not exclude the occurrence of disease of the entire choroid at the same time (uveitis).

It should be emphasized that the posterior and anterior ciliary arteries take part in the blood supply not only to the vascular tract, but also to the sclera. At the posterior pole of the eye, the branches of the posterior ciliary arteries, anastomosing with each other and with the branches of the central retinal artery, form a corolla around the optic nerve, the branches of which nourish the part of the optic nerve adjacent to the eye and the sclera around it.

Muscular arteries penetrate into the muscles. After the rectus muscles attach to the sclera, the vessels leave the muscles and, in the form of the anterior ciliary arteries at the limbus, pass into the eye, where they take part in the formation of a large circle of blood supply to the iris.

The anterior ciliary arteries provide vessels to the limbus, episclera and conjunctiva

around the limb. The limbal vessels form a marginal looping network of two layers - superficial and deep. The superficial layer supplies blood to the episclera and conjunctiva, the deep layer nourishes the sclera. Both networks take part in feeding the corresponding layers of the cornea.

Extraocular arteries that do not participate in the blood supply to the eyeball include the terminal branches of the ophthalmic artery: the supratrochlear artery and the artery of the nasal dorsum, as well as the lacrimal, supraorbital artery, anterior and posterior ethmoidal arteries.

The supratrochlear artery goes along with the trochlear nerve, enters the skin of the forehead and supplies the medial parts of the skin and muscles of the forehead. Its branches anastomose with the branches of the artery of the same name on the opposite side. The artery of the dorsum of the nose, emerging from the orbit, lies under the internal commissure of the eyelids, giving off a branch to the lacrimal sac and the dorsum of the nose. Here it connects with a. angularis, forming an anastomosis between the internal and external carotid artery systems.

The supraorbital artery passes under the roof of the orbit above the muscle that lifts the upper eyelid, bends around the supraorbital margin in the area of the supraorbital notch, goes to the skin of the forehead and gives off branches to the orbicularis muscle.

The lacrimal artery arises from the initial arch of the ophthalmic artery, passes between the external and superior rectus muscles of the eye, supplies blood to the lacrimal gland and gives off branches to the outer parts of the upper and lower eyelids. The branches of the ethmoidal artery bring blood to the internal parts of the upper and lower eyelids.

Thus, the eyelids are supplied with blood from the temporal side by branches coming from the lacrimal artery, and from the nasal side - from the ethmoid artery. Walking towards each other along the free edges of the eyelids, they form subcutaneous arterial arches. The conjunctiva is rich in blood vessels. Branches extend from the arterial arches of the upper and lower eyelids, supplying blood to the conjunctiva of the eyelids and transitional folds, which then pass to the conjunctiva of the eyeball and form its superficial vessels. The perilimbal part of the conjunctiva of the sclera is supplied with blood from the anterior ciliary arteries, which are a continuation of the muscle vessels. From the same system, a dense network of capillaries is formed, located in the episclera around the cornea - a marginal looped network that nourishes the cornea.

Venous circulation is carried out by two ophthalmic veins - v. ophthalmica superior et v. ophthalmica inferior. From the iris and ciliary body, venous blood flows mainly into the anterior ciliary veins. The outflow of venous blood from the choroid proper occurs through the vorticose veins. Forming a bizarre system, the vorticose veins end in main trunks that leave the eye through oblique scleral canals behind the equator on the sides of the vertical meridian. There are four vorticose veins, sometimes their number reaches six. The superior ophthalmic vein is formed by the confluence of all the veins accompanying the arteries, the central retinal vein, the anterior ciliary veins, the episcleral veins and the two superior vorticose veins. Through the angular vein, the superior ophthalmic vein anastomoses with the cutaneous veins of the face, leaves the orbit through the superior orbital fissure and carries blood into the cranial cavity, into the venous cavernous sinus. The inferior ophthalmic vein consists of two inferior vorticose veins and some anterior ciliary veins. Often the inferior ophthalmic vein connects with the superior ophthalmic vein into one trunk. In some cases, it exits through the inferior orbital fissure and flows into the deep vein of the face (v. facialis profunda). The veins of the orbit do not have valves. The absence of valves in the presence of anastomoses between the veins of the orbit and face, sinuses and pterygopalatine fossa creates conditions for the outflow of blood in three directions: into the cavernous sinus, pterygopalatine fossa and to the veins of the face. This creates the possibility of infection spreading from the skin of the face, from the sinuses to the orbit and cavernous sinus.

The choroid, also called the vascular or uveal tract, provides nutrition to the eye. It is divided into three sections: the iris, the ciliary body and the choroid itself.

The iris is the anterior part of the choroid. The horizontal diameter of the iris is approximately 12.5 mm, vertical - 12 mm. In the center of the iris there is a round hole - the pupil (pupilla), thanks to which the amount of light entering the eye is regulated. The average pupil diameter is 3 mm, largest - 8 mm, smallest - 1 mm. There are two layers in the iris: the anterior (mesodermal), which includes the stroma of the iris, and the posterior (ectodermal), which contains a pigment layer that determines the color of the iris. There are two smooth muscles in the iris - the constrictor and the dilator of the pupil. The first is innervated by the parasympathetic nerve, the second by the sympathetic.

The ciliary, or ciliary, body (corpus ciliare) is located between the iris and the choroid itself. It is a closed ring 6-8 wide mm. The posterior border of the ciliary body runs along the so-called dentate line (ora serrata). The anterior part of the ciliary body - the ciliary crown (corona ciliaris), has 70-80 processes in the form of elevations, to which the fibers of the ciliary belt, or zinc ligament (zonula ciliaris), going to the lens, are attached. The ciliary body contains the ciliary, or accommodative, muscle, which regulates the curvature of the lens. It consists of smooth muscle cells located in the meridian, radial and circular directions, innervated by parasympathetic fibers. The ciliary body produces aqueous humor - intraocular fluid.

The actual choroid of the eye, or choroid (chorioidea), makes up the posterior, most extensive part of the choroid. Its thickness is 0.2-0.4 mm. It consists almost exclusively of vessels of various sizes, mainly veins. The largest of them are located closer to the sclera, the layer of capillaries faces towards the retina adjacent to it from the inside. In the area where the optic nerve exits, the choroid itself is tightly connected to the sclera.

The structure of the retina.

The retina (retina), lining the inner surface of the choroid, is the most functionally important part of the organ of vision. The posterior two-thirds of it (the optical part of the retina) perceive light stimulation. The anterior part of the retina, covering the posterior surface of the iris and ciliary body, does not contain photosensitive elements.

The optical part of the retina is represented by a chain of three neurons: the outer - photoreceptor, the middle - associative and the inner - ganglion. Together, they form 10 layers, arranged (from the outside to the inside) in the following order: the pigment part, consisting of one row of pigment cells shaped like hexagonal prisms, the processes of which penetrate into the layer of rod-shaped and cone-shaped visual cells - rods and cones; photosensory layer, consisting of neuroepithelium containing rods and cones, providing light and color perception, respectively (cones, in addition, provide object, or shaped, vision): outer boundary layer (membrane) - supporting glial tissue of the retina, having the appearance of a network with numerous holes for the passage of fibers of rods and cones; outer nuclear layer containing the nuclei of visual cells; the outer reticular layer, in which the central processes of the visual cells contact the processes of deeper located neurocytes; the inner nuclear layer, consisting of horizontal, amacrine and bipolar neurocytes, as well as the nuclei of ray gliocytes (the first neuron ends in it and the second neuron of the retina begins); the inner retinal layer, represented by fibers and cells of the previous layer (the second retinal neuron ends in it); ganglion layer, represented by multipolar neuropits; layer of nerve fibers containing the central processes of anglionic neurocytes and subsequently forming the trunk of the optic nerve , the inner boundary layer (membrane) separating the retina from the vitreous. Between the structural elements of the retina there is a colloidal interstitial substance. Retina. The human retina belongs to the type of inverted membranes - the light-receiving elements (rods and cones) make up the deepest layer of the retina and are covered by its other layers. In the posterior pole of the eye. the spot of the retina (macula macula) is located - the place that provides the highest visual acuity . It has an oval shape elongated in the horizontal direction and a depression in the center - the central fossa, containing only one cones. Inward from the macula is the optic disc, in the area of which there are no light-sensitive elements.

The inner shell of the eyeball - the retina - is formed by fibers of the optic nerve and three layers of light-sensitive cells. Its perceiving elements are light receptors: rod-shaped and cone-shaped cells (“rods” and “cones”). “Rods” provide twilight and night vision, cones provide visual perception of the entire palette of colors in the daytime (up to 16 shades). An adult has about 110-125 million “rods” and about 6-7 million “cones” (ratio 1:18). At the back of the retina there is a small yellow spot. This is the point of best vision, since the largest number of “cones” are concentrated in this place, and light rays are focused here. At a distance of 3-4 mm from it there is a “blind” spot inside, which is devoid of receptors. This is the point of convergence and exit of the optic nerve fibers. Six eye muscles provide mobility of the eyeball in all directions.

According to modern concepts, the perception of color is based on complex physical and chemical processes in visual receptors. There are three types of “cones” that exhibit the greatest sensitivity to the three primary colors of the visible spectrum: red-orange, green and blue

Retinal fixation.

The visual part of the retina is connected to the underlying tissues in two places - at the serratus margin and around the optic nerve. The rest of the retina is adjacent to the choroid, held in place by the pressure of the vitreous body and the connection between the rods and cones and the processes of the cells of the pigment layer.

Optical apparatus of the eye

The optical apparatus of the eye consists of transparent light-refracting media: the vitreous body, the lens and the aqueous humor that fills the eye chambers.

The lens is a transparent light-refracting elastic formation in the shape of a biconvex lens, located in the frontal plane behind the iris. It distinguishes between the equator and two poles - anterior and posterior. The diameter of the lens is 9-10 mm, the anteroposterior size is 3.7-5 mm. The lens consists of a capsule (bag) and substance. The inner surface of the anterior part of the capsule is covered with epithelium, the cells of which are hexagonal in shape. At the equator they stretch out and turn into lens fibers. Fiber formation occurs throughout life. At the same time, in the center of the lens, the fibers gradually become denser, which leads to the formation of a dense core - the nucleus of the lens. The areas located closer to the capsule are called the lens cortex. There are no vessels or nerves in the lens. A ciliary band is attached to the lens capsule, extending from the ciliary body. Different degrees of tension in the ciliary girdle lead to changes in the curvature of the lens, which is observed during accommodation.

The iris can have different colors: from blue to black. Its color depends on the amount of melanin pigment it contains: the more pigment in the stroma, the darker the iris; in the absence or small amount of pigment, this shell has a blue or gray color. Children have little pigment in the iris, so in newborns and children of the first year of life it is bluish-grayish. The color of the iris is formed by the age of ten to twelve. On its anterior surface two parts can be distinguished: narrow, located near the pupil (the so-called pupillary), and wide, bordering the ciliary body (ciliary). The boundary between them is the pulmonary circulation of the iris. There are two muscles in the iris that are antagonists. One is placed in the pupillary area, its fibers are located concentrically with the pupil, and when they contract, the pupil narrows. Another muscle is represented by radially running muscle fibers in the ciliary part, with the contraction of which the pupil dilates.

The ciliary body consists of a flat and thickened coronal part. The thickened coronal part is made up of 70 to 80 ciliary processes, each of which has vessels and nerves. The ciliary body contains the ciliary, or accommodative, muscle. The ciliary body is dark in color and covered with retinal pigment epithelium. In the interprocess areas, the ligaments of Zinn of the lens are woven into it. The ciliary body is involved in the formation of intraocular fluid, which nourishes the avascular structures of the eye. The vessels of the ciliary body arise from the large arterial circle of the iris, formed from the posterior long and anterior ciliary arteries. Sensitive innervation is carried out by long ciliary fibers, motor innervation is carried out by parasympathetic fibers of the oculomotor nerve and sympathetic branches.

Vascular tract, consisting of the iris, ciliary body and choroid, located medially from the outer shell eyes.

Vascular tract eyes. Vascular tract, consisting of the iris, ciliary body and choroid, located medially from the outer... more details ".

Iridocyclitis is an inflammation of the anterior vascular shell eyes(irises. Detection of pathology vascular tract eyes.

Vascular tract eyes. Vascular tract

Vascular tract eyes. Vascular tract, consisting of the iris, ciliary body and choroid, located medially from the nar.

Both are often affected eyes. A jelly-like exudate and a lot of easily ruptured posterior synechiae are found in the anterior chamber.
First of all it is amazed vascular tract.

Vascular tract of the eye. Uvea

A) Anatomy of the uveal tract (choroid) of the eye. The uveal tract is formed by the iris, ciliary body and choroid. The iris stroma is formed by pigmented and non-pigmented cells, collagen fibers and a matrix consisting of hyaluronic acid. Crypts vary in size, shape and depth; their surface is covered with a heterogeneous layer of connective tissue cells fused with the ciliary body.

The different colors are determined by the pigmentation of the anterior border layer and deep stroma: the stroma of blue irises is much less pigmented than that of brown irises.

The ciliary body performs the functions of producing aqueous humor, accommodating the lens, and forming the trabecular and uveoscleral outflow tracts. It extends 6 mm from the root of the iris to the anterior zone of the choroid, the anterior section (2 mm) bears the ciliary processes, the flatter and more even posterior part (4 mm) is the pars plana. The ciliary body is covered with an outer pigmented and inner non-pigmented epithelial layer.

The ciliary muscle consists of longitudinal, radial and circular portions. The ciliary processes are formed mainly from coarsely fenestrated capillaries through which fluorescein leaks and veins that drain into the vorticose veins.

The choroid lies between the retina and sclera. It is formed by blood vessels and is bounded internally by Bruch's membrane and the avascular suprachoroidal space externally. It has a thickness of 0.25 mm and consists of three vascular layers receiving blood supply from the short and long posterior and anterior ciliary arteries. The choriocapillaris layer is the innermost layer, the middle layer is the layer of small vessels, the outer layer is the layer of large vessels. The vessels of the middle and outer layers of the choroid are not fenestrated.

The choriocapillary layer is a continuous layer of large capillaries, it lies under the retinal pigment epithelium and nourishes the outer parts of the retina; The capillary endothelium is fenestrated and fluorescein leaks through it. Bruch's membrane consists of three layers: the outer elastic layer, the middle collagen layer, and the inner circular layer, the latter being the basement membrane of the retinal pigment epithelium. The choroid is tightly fixed to the edges, extends forward to the dentate line and connects with the ciliary body.

b) Embryology of the uveal tract. The uveal tract develops from neuroectoderm, neural crest and mesoderm. The sphincter, dilator and posterior epithelium of the iris develop from the neuroectoderm. Pigment differentiation and migration continues in the second and third trimester. The smooth muscles of the iris, choroidal stroma, and ciliary body develop from the neural crest. The formation of the iris begins with the closure of the fetal cleft on the 35th day of gestation. The sphincter muscle appears at the edge of the optic cup at the tenth week of gestation, myofibrils are formed at 10-12 weeks.

The dilator is formed at 24 weeks of gestation. The neuroectoderm differentiates into both pigmented and non-pigmented epithelium of the ciliary body at 10-12 weeks of gestation. Smooth muscle of the ciliary body is already present in the fourth month of gestation even before the formation of the iris stroma; it joins the ciliary groove in the fifth month. The formation of choroidal pigment cells from neural crest cells is completed at birth. Blood vessels develop from the mesoderm and neural crest. The choroidal vasculature differentiates from mesenchymal elements in the second week of gestation and develops over the next 3-4 months.

The pupillary membrane disappears shortly before term birth. At birth the pupil is narrow, but as the dilator muscle develops, it widens. The role of the ciliary muscle in accommodation increases between the third and sixth months of life. By the age of two years, the length of the ciliary body reaches three quarters of the length of the adult ciliary body. In representatives of all races, pigmentation is complete by the age of one; During the first year of life, the irises become darker, and never lighter.

(A) Structure of a normal eye. Please note that the surface of the iris is very prominent due to crypts and folds.
(B) Diagram of the normal flow of aqueous humor. The aqueous humor formed in the posterior chamber flows through the pupil into the anterior chamber.
The main route of outflow of aqueous humor is through the trabecular meshwork into Schlemm's canal.
Only a small amount of aqueous humor flows through additional pathways (uveoscleral and through the iris - both not shown).

(A) Formation of the optic vesicle on the lateral wall of the diencephalon. The optic stalk connects the optic vesicle with the forebrain. (9.5 days of mouse gestation, equivalent to 26 days of human gestation).
(B) Invagination of the optic vesicle and formation of the lens vesicle (onset at 10.5 days of mouse gestation, corresponding to 28 days of human gestation).
(B) Invagination of the lens fossa, formation of a two-layer optic cup from the invaginated optic vesicle (end of 10.5 days of mouse gestation, corresponds to 32 days of human gestation).
(D) Closure of the embryonic choroidal fissure, formation of the lens vesicle and primary vitreous body (12.5 days of mouse gestation, corresponding to 44 days of human gestation).
(E) Formation of the nerve fiber layer, migration of neural crest cells, and formation of the nuclear belt of the lens (14.5 days of mouse gestation, corresponding to 56-60 days of human gestation).
(E) Eye at the end of the organogenesis stage. The cornea, the iris beginning to form, the rudiments of the extraocular muscles and the lacrimal gland are clearly visible.
Arrows indicate the pupillary membrane (16.5 days of mouse gestation corresponds to >60 days of human gestation).