1. Why can eyes see things?

to understand this problem, we must first know the structure and function of the eyeball. Some people think that the eyeball is like a camera, which is true, but the eyeball is much more delicate than the camera.

The eye is the visual organ of human body, which consists of eyeball, visual path and ocular adnexa.

(1) The eyeball is slightly round, located in the orbit, with a diameter of 24 mm, and consists of the eyeball wall and eyeball contents.

Eye wall: It is composed of three layers of membranes. 1) Outer layer: fibrous membrane, including transparent cornea at the front and opaque sclera at the back, with tough tissue, which can maintain the normal shape of eyeball and protect intraocular tissues. 2) Middle layer: this layer is rich in blood vessels and pigments, and its shape is like black-purple grape skin, so it is also called uvea. Its front part is called iris, the middle part is ciliary body, and the back part is choroid. It has the functions of nourishing intraocular tissues, shielding and regulating light. 3) Inner layer: retina, mainly composed of optic cells and nerve fibers. It is an important tissue for receiving light and conducting nerve impulses.

eyeball contents: transparent tissues such as aqueous humor, lens and vitreous body, which together with cornea form the refractive system of the eye and have the function of passing and refracting light.

(2) The optic pathway is a nerve pathway for visual conduction. When the retina is stimulated by light, it produces nerve impulses, which pass through the optic nerve, optic chiasma, optic bundle and optic line to the visual center of occipital lobe of the brain to form vision.

(3) The ocular adnexa are located around the eyeball, including the eyelid, bulbar conjunctiva and palpebral conjunctiva, lacrimal apparatus, extraocular muscles and bony orbit. Among them, the extraocular muscles protect the eyeball in different ways except the eyeball.

Therefore, the eyeball with a special structure receives various different rays from foreign objects, and through a series of refractive systems of the eyes, it stimulates retinal nerve cells and produces impulses, and then directly reaches the occipital visual center of the brain through various stations in the visual path to form vision. Under normal circumstances, our eyes can see everything, and it is a subtle physiological process for our eyes to see things, such as the brightness, shape, size and color of the objects.

2. What is the anatomy and tissue structure of cornea and sclera? What are the physiological functions?

The cornea and sclera are the outermost layers of the ocular wall, which are called fibrous membranes. They are composed of dense fibrous tissues, with tough texture, which can maintain the shape of the eyeball and protect the tissues in the eye. The cornea accounts for 1/6 of the anterior part of the fibrous membrane and the sclera accounts for 5/6 of the posterior part, and the transition between them is called corneoscleral margin.

(1) The cornea is a completely transparent membrane which is approximately round, with a diameter of about 1mm, and the transverse diameter is slightly larger than the vertical diameter. The diameter of the cornea of children over three years old is close to that of adults, and the refractive radius of the anterior surface of the cornea is 7. 8 mm, vertical direction is 7. Seven millimeters. Corneal thickness varies from part to part, and the thinnest in the center is about . 5 mm, the peripheral part is about 1 mm, and the refractive index is 1. 37 is an important part of the refractive system of the eye. The cornea itself has no blood vessels, but dense sensory nerve endings, so it feels extremely acute.

There are five layers of corneal tissue from the outside to the inside: < 1 > Epithelial cell layer: there are 5-6 layers of epithelial cells, which are orderly arranged and non-keratinized, and are connected with bulbar conjunctival epithelial cells around them. After injury, it is repaired by adjacent or deep cells without leaving traces. 〈2〉 Front elastic layer: mainly composed of collagen fibers, which cannot be regenerated after injury. 〈3〉 Matrix layer: 9/1 of the total thickness of cornea is composed of many collagen fiber lamellae with the same refractive index, about 2~25 lamellae, and there are fixed cells and a few wandering cells between lamellae. This layer becomes turbid and opaque by the scar tissue with disordered structure after being damaged. 〈4〉 Back elastic layer: It is composed of extremely fine collagen microfilaments. Elastic, firm, renewable, and resistant to chemical substances and pathological damage. 〈5〉 Endothelial cell layer: composed of single hexagonal endothelial cells, about 5,. When endothelial cells are damaged, they are covered by the expansion, migration and sliding of adjacent endothelial cells.

(2) The sclera is an opalescent membrane, which is composed of dense interlaced fibers. Its thickness is . 3~1 mm, the thickness around the optic papilla is the thickest, and the attachment point of rectus muscle is the thinnest. Its outer surface is wrapped by the eyeball fascia, and the front part is covered by the bulbar conjunctiva. The three are connected near the corneal limbus, and the optic nerve cellulose passes through the back part. Here, the sclera forms a sieve structure, which is called the scleral cribriform plate. There are many holes in the sclera through which blood vessels and nerves pass, but there are few blood vessels and nerves, so its metabolism and inflammatory reaction are slow.

The sclera is divided into three layers from the inside out: < 1 > The upper layer of sclera is composed of fine collagen fibers and elastic fibers, with loose structure and many small blood vessels. 〈2〉 Scleral parenchyma: It is composed of collagen fiber bundles, fiber cells and matrix, which are arranged intricately. 〈3〉 Scleral Brown Blackboard: It is the innermost layer of the sclera and the lateral wall of the suprachoroidal space. This layer is composed of tiny collagen fiber bundles with many pigment cells and pigment-loaded macrophages.

(3) Corneal sclera margin is the junction of cornea and sclera, which is a gray translucent area with a width of about 1 mm.. Here, the cornea and sclera tissues are interlaced with each other, and the cornea is in front and the sclera is in the back, forming an inclined interface. Histologically, there are only epithelial cells and parenchyma layers, because the anterior elastic layer has not reached the limbus of cornea. The posterior elastic layer and endothelial cells migrate to the trabecular tissue in the anterior corner. Corneal margin is rich in blood vessels.

3. What parts are the pigment membrane (grape membrane) made of? What is its anatomy, physiology and tissue structure?

The uvea is the second layer of the ocular wall, which is soft and rich in pigments and blood vessels. It has a hole in front of it, namely the pupil, and then it is penetrated by the optic nerve. It not only has the function of nourishing the intraocular tissue, but also has the function of shielding the light. It can be divided into three parts from front to back, namely iris, ciliary body and choroid.

(1) The iris is a brown disc-shaped membrane, located in front of the ciliary body and the lens, with a diameter of 12mm and a thickness of . 5 mm, there are uneven recesses, radial stripes and annular folds on the iris surface, forming iris texture. There are two in the center. 5~4 mm diameter hole, namely the pupil. There are two kinds of smooth muscles in iris tissue, namely, pupil sphincter and pupil dilators. The former is annular around the pupil and is dominated by parasympathetic nerves. The latter is radial and dominated by sympathetic nerve, which can open or narrow the pupil to adjust the amount of light entering the eye. The joint between iris and ciliary body is called iris root, and the tissue is thin. Iris contains many blood vessels and sensory nerve fibers, and it feels very keen. Iris tissue structure can be divided into four layers from front to back: < 1 > front surface layer: composed of fiber cells and pigment cells; 〈2〉 Matrix and Pupillary Sphincter: The iris matrix is a framework network composed of collagen connective tissue, which contains mucopolysaccharide matrix and liquid. Sphincter is in the matrix layer of iris pupil area, sphincter cells are arranged in parallel with the pupil margin, and muscle bundle is surrounded by dense collagen fiber layer, which contains arterioles, pigment cells, sensory nerves and motor nerves. 〈3〉 The anterior epithelium and pupil dilate muscle layer: the dilate muscle extends radially from the iris root to the pupil direction and reaches the pupil margin. The posterior pigment epithelium is a layer of epithelial cells rich in pigment particles.

(2) The ciliary body is the middle part of the uvea, which is connected to the iris root in front and moved to the choroid with the serrated edge as the boundary. The outer side of the ciliary body is attached to the inner surface of the sclera, and the ciliary body around the equatorial part of the lens can be divided into two parts: the anterior part is called the ciliary body crown, and the posterior part is thinned into a flat part. There are many radial processes on the inner surface of the ciliary crown, which produce aqueous humor and nourish intraocular tissues. There are ciliary muscles on the outer side of the ciliary body, which are dominated by parasympathetic nerves and mainly play a role in regulating the refraction of the lens.

The ciliary body is divided into five layers from the outside to the inside: <; 1> Superior ciliary cavity: connective tissue lamellar zone containing pigment; < 2> Ciliary muscle: there are three kinds of muscle fibers: longitudinal, reflective and annular, all of which are smooth muscle fiber bundles; < 3> Matrix: composed of inner connective tissue layer, blood vessels and Bruch membrane; < 4> Pigmented ciliary epithelium; < 5> Pigmented ciliary epithelium; These two layers are monolayer epithelial cells.

(3) The choroid is the last part of the uvea, between the retina and the sclera, starting from the serrated edge of the retina and ending around the optic nerve, covering the posterior part of the globe. It is a brown membrane with rich blood vessels, which nourishes the outer layer of the retina. There is a potential cavity between the membrane and the sclera, and nerves and blood vessels pass through each suprachoroidal cavity.

The choroid tissue structure is divided into four layers, including suprachoroidal cavity, matrix, capillary layer and Bruch membrane from outside to inside. 〈1〉 The suprachoroidal space is located between the choroid and the sclera, and there are fibroblasts and pigment cells in the reticular collagen fibers, as well as the long and short posterior ciliary arteries and ciliary nerves. 〈2〉 Matrix: The choroidal matrix consists of loose collagen fibers, which contain blood vessels, nerves and cells. (3) Capillary layer: Arteries come from short posterior ciliary artery, long posterior ciliary artery and anterior ciliary artery. Capillaries are dense and network-like, without pigment. They are thicker in the macula and thinner in the vicinity. 〈4〉Bruch membrane: It consists of the basal membrane of retinal pigment epithelium, the inner collagen layer, the elastic layer, the outer collagen layer and the basal membrane of choroidal capillary.

4. What is the anatomy and tissue structure of retina? What are the physiological functions?

The retina is actually a part of the brain, which is formed by neuroectoderm. The optic cup develops into two layers, the outer layer develops into pigment epithelium, and the inner layer develops into photosensitive layer. The retina is lined with ciliary body without photosensitive cells. The posterior pole of retina is shallow and concave, which is called fovea, so it is called macula. There is a reddish disc on the nasal side of macula, which is called optic disc. This is the confluence of optic nerve fibers, with a diameter of 1.5 mm, where cells are ignored and a' physiological blind spot' is formed in the visual field. Retinal vessels are central retinal arteries and veins. It can also be seen that the ciliary artery of the retZINNa passes through the temporal side of the optic papilla and reaches the retina. The central retinal artery supplies five layers of tissues in the retina, while the outer five layers are supplied by choroidal capillaries. < P > The retina is mainly composed of three kinds of cells, which are photoreceptor cells, bipolar cells and ganglion cells. There are MULLER cells and astrocytes among them for connection and support. Retinal tissues are divided into ten layers from outside to inside: <: 1> Retinal pigment epithelium: it is a single layer of multilateral pigment cells, <; 2> Sight mark and cone layer: It consists of cell processes of optic cells. There are 11-125 million visual pestles and 6.3-6.8 million visual cones in the whole omentum. <; 3> Outer membrane: a reticular membrane, which is the connecting structure of rod, cone and MUIIER cells. 4> Outer nuclear layer: it is the cell body of rod and rod. 5> Outer plexiform layer: it is a loose network structure, and it is a synapse connecting the rod of photoreceptor, the terminal of cone cell, the dendrite of bipolar cell and the process of horizontal cell, which is the basic structure of visual information processing and transmission. 6> Inner nuclear layer: It consists of horizontal cells, bipolar cells, MULLER cells and cells without long process. 7> Inner plexiform layer: it is the junction between the first and second neurons of retina, and consists of axons of inner nuclear layer cells and dendrites of ganglion cells. 8> Ganglion cell layer: It is mainly composed of the cell bodies of ganglion cells. 9> Nerve fiber layer: mainly composed of axons of ganglion cells, this layer contains rich vascular system. 1> Internal limiting membrane: It is composed of basement membrane of MUIIER cells and glial cells. < P > Retina has the function of sensing light and transmitting impulses. The photoreceptor cone can sense strong light, which can distinguish vision, shape vision and color vision. Visual sense can feel weak light and dim vision. Bipolar cells and ganglion cells have the function of conducting nerve impulses. < P > 5. What are the contents of the eyeball? What are its morphological structure and physiological characteristics?

The wall of the eyeball contains the following contents: aqueous humor, lens and vitreous body. The three characters have the same characteristics, namely, transparency, no blood vessels and nerves, and a certain refractive index. Together with the cornea, it constitutes the refractive system of the eye, thus ensuring the passage of light and forming a clear object image on the retina.

< 1 > aqueous humor is a colorless water sample with a total volume of .3 ml. Aqueous humor is produced by ciliary process, enters the posterior chamber, flows into the anterior chamber through the pupil, and then is mainly discharged from the anterior chamber through trabecular meshwork and SCHLEMM tube, with a specific gravity of 1.6 and a refractive index of 1.3336. The function of aqueous humor is to provide nutrition for cornea and lens, dredge metabolites and protect intraocular pressure.

< 2 > The lens is an elastic transparent body, shaped like a concave lens, which is located between the iris and the vitreous body. The peripheral part of the lens is connected with the ciliary body through its suspensory ligament to fix its position. The lens is divided into front and back sides, with a small curvature in the front and a large curvature in the back. The centers of the two sides are called the equatorial part where the front and back poles meet. At rest, it has a diameter of 9-1 mm, a thickness of 4-5 mm, a front refractive radius of 9 mm, a back refractive index of 5.5 mm and a refractive index of 1.385-1.46. The water content of lens is 63.5% and that of protein is 34.93%. In addition, there are more vitamin C, glutathione, a small amount of lipids and inorganic salts.

The structure of the lens is as follows: 1. The crystalline capsule is a transparent and thick basement membrane with elasticity. 2. Lens epithelium: It is located in the anterior capsule and under the equator, and it is a monolayer epithelial cell on the surface of newborn lens cells. 3. Lens cells: long hexagonal strips with edges and corners, regularly arranged in rows, running through the entire cortex, and ending at the anterior cortical suture and posterior cortical suture with the same depth in the capsule. The lens cells proliferated by equatorial epithelial cells, and the old lens cells moved into the cortex. Squeezed to the center, it is a crystal nucleus, and the nuclei formed at different ages are light bands with different densities under the slit lamp. 4. Lens suspensory ligament: it is a fibrous tissue connecting the equator and the ciliary body to maintain the position of the lens.

The lens occupies a major position in the diopter of the eye. It can change the thickness of the acoustic body with the help of the contraction and relaxation of the ciliary muscle, so that objects near and far can see clearly. In addition, the lens can absorb ultraviolet rays and has a certain protective effect on the retina.

< 3 > The vitreous body is a colorless and transparent colloid, the main component of which is water, accounting for about 99%. The vitreous body fills the cavity 4/5 behind the eyeball, and there is a dish-shaped depression in front of the vitreous body to accommodate the crystal. Vitreous body includes vitreous cortex, central vitreous body and central canal. Vitreous cortex is the part of the vitreous body that is close to cilia and retina, and it is thick. The central vitreous body is in the center and thin. The central canal is located in the center of vitreous body, where the original vitreous body is located during embryonic development, and sometimes the hyaline artery remains.

The chemical composition of vitreous body is similar to aqueous humor, and there are also hyalin and mucin, thus ensuring the gel state and transparency of vitreous body. The specific gravity of vitreous body is 1.7, the refractive index is 1.3382, and the pH value is 7.2-7.5. Vitreous body has no regenerative ability and is filled with aqueous humor after it is lost. In addition to refraction, the physiological function of vitreous body is mainly to maintain a certain intraocular pressure and support the attachment of retinal inner layer to pigment epithelium.

6. Where did the tears come from?

tear is the secretion of lacrimal gland and accessory lacrimal gland, and it should also contain mucus components of conjunctival goblet cells and lipid substances of meibomian gland, so it is a mixed liquid. Under normal circumstances, every glance