THE HUMAN EYE. STRUCTURE AND FUNCTION Ibodullayev Bektosh Choriqul ugli 2-grade student Samarkand State Medical Institute, Uzbekistan

Abstract: The current paper provides an overview of current knowledge on the structure and function of the eye. It describes in depth the different parts of the eye that are involved in the ocular manifestations seen in the mucopolysaccharidoses. The mucopolysaccharidoses are a group of rare inheritable lysosomal storage disorders characterized by the accumulation of glycosaminoglycans in cells and tissues all over the body, leading to widespread tissue and organ dysfunction, also tend to accumulate in several tissues of the eye, leading to various ocular manifestations affecting both the anterior (cornea, conjunctiva) and the posterior parts (retina, sclera, optic nerve) of the eye. Key words: Anatomy of eye,human body,structure of the eye, conjunctiva, cornea. The eye is one of the most complex organs of the human body. In the human eye, three layers can be distinguished . The outer region consists of the cornea and the sclera. The cornea refracts and transmits the light to the lens and the retina and protects the eye against infection and structural damage to the deeper parts. The sclera forms a connective tissue coat that protects the eye from internal and external forces and maintains its shape. The cornea and the sclera are connected at the limbos. The visible part of the sclera is covered by a transparent mucous membrane, the conjunctiva. The middle layer of the eye is composed of the iris, the colliery body and the choroid. The iris controls the size of the pupil, and thus the amount of light reaching the retina; the celery body controls the power and shape of the lens and is the site of aqueous production; and the choroid is a vascular layer that provides oxygen and nutrients to the outer retinal layers. The inner layer of the eye is the retina, a complex, layered structure of neurons that capture and process light. The three transparent structures surrounded by the ocular layers are called the aqueous, the vitreous and the lens. Schematic illustration of the structure of the eye and the ocular barriers. The primary physiologic blockage against instilled drugs is the tear film. Cornea is the main route for drug transport to the anterior chamber. The retinal pigment epithelium and the retinal capillary endothelium are the main barriers for systemically administered drugs . Intravitreal injection is an invasive strategy to reach the vitreous . The administered drugs can be carried away from the anterior chamber either by venous blood flow after diffusing across the iris surface or by the aqueous outflow . Drugs can be removed away from the vitreous through diffusion into the anterior chamber or by the blood–retinal barrier . The cornea The cornea is the most anterior part of the eye, in front of the iris and pupil. It is the most densely innervated tissue of the body, and most corneal nerves are sensory nerves, derived from the ophthalmic branch of the trigeminal nerve.mm, and a curvature that remains rather constant throughout life. mm and a vertical diameter of 10.5 The cornea of an adult human eye has an average horizontal diameter of about 11.5 mm and is located in the centre of the cornea, anterior to the pupil, in photonic conditions. The cornea is avuncular and the branches of the anterior ciliary arteries stop at the limbos where they form arcades that supply the peripheral cornea. The optic zone (pre‐papillary cornea), which provides most of the cornea's refractive function, has a diameter Therefore, the peripheral and central cornea are very distinct in terms of physiology and pathology. The eyes of most vertebrates contain two types of photoreceptors: rods and cones. In humans, rods are approximately 20 times more abundant than cones. The photoreceptors are responsible for photo transduction, the conversion of light into an electrical signal.

For this purpose, the membranes of the outer segment discs of the photoreceptors contain pigments. Cones, which are responsible for color vision, have pigments with absorption peaks in the blue, green or yellow parts of the spectrum. Pigments of the rods have an absorption peak in the blue‐green part of the spectrum. Rods are active with low light levels, and are not involved in color vision. The anatomy and function of the eye is extremely complex and pathological events can lead to a wide range of ocular disease manifestations that may occur, patients may present with a variety of ocular diseases in both the anterior and posterior components of the eye, resulting from accumulation in various tissues. The treatment of these ocular features warrants the investigation of methods to circumvent various ocular barriers that hamper drug delivery. The eye receives oxygen through the aqueous. Its function is to nourish the cornea, iris, and lens by carrying nutrients, it removes waste products excreted from the lens, and maintain intraocular pressure and thus maintains the shape of the eye. This gives the eye its shape. Sight is, arguably, our most important sense. More of the brain is dedicated to vision than to hearing, taste, touch, and smell combined. In this article, we explain the anatomy of our eyes and how they let us see. This is the dark spot in the center of the colored part of your eye, which, in turn, is called the iris. The pupil expands and shrinks in response to light, acting similarly to the aperture on a camera. In very bright conditions, the pupil constricts or shrinks to around 1 millimeter (mm) in diameter to protect the sensitive retina from damage. When it is dark, the pupil can dilate or widen up to 10 mm in diameter. This dilation allows the eye to take in as much light as possible. The conjunctiva lines the lids and then bends back over the surface of the eyeball, constituting an outer covering to the forward part of this and terminating at the transparent region of the eye, the cornea. The portion that lines the lids is called the palpebral portion of the conjunctiva; the portion covering the white of the eyeball is called the bulbar conjunctiva. Between the bulbar and the palpebral conjunctiva there are two loose, redundant portions forming recesses that project back toward the equator of the globe. These recesses are called the upper and lower furnaces, or conjunctiva sacs; it is the looseness of the conjunctiva at these points that makes movements of lids and eyeball possible. The fibrous layer, which gives the lid its mechanical stability, is made up of the thick, and relatively rigid, tarsal plates, bordering directly on the palpebral aperture, and the much thinner palpebral fascia, or sheet of connective tissue; the two together are called the septum orbitale. When the lids are closed, the whole opening of the orbit is covered by this septum. Two ligaments, the medial and lateral palpebral ligaments, attached to the orbit and to the septum orbitale, stabilize the position of the lids in relation to the globe. The medial ligament is by far the stronger. In addition to the muscles already described, other facial muscles often cooperate in the act of lid closure or opening. Thus, the corrugators supercilious muscles pull the eyebrows toward the bridge of the nose, making a projecting “roof” over the medial angle of the eye and producing characteristic furrows in the forehead; the roof is used primarily to protect the eye from the glare of the sun. The pyramidal is, or procures, muscles occupy the bridge of the nose; they arise from the lower portion of the nasal bones and are attached to the skin of the lower part of the forehead on either side of the midline; they pull the skin into transverse furrows. In lid opening, the frontals muscle, arising high on the forehead, midway between the coronal suture, a seam across the top of the skull, and the orbital margin, is attached to the skin of the eyebrows. Contraction therefore causes the eyebrows to rise and opposes the action of the orbital portion of the orbicular is; the muscle is especially used when one gazes upward. It is also brought into action when vision is rendered difficult either by distance or the absence of sufficient light. Modern studies have shown that, under normal conditions, the cornea tends to take in fluid, mainly from the aqueous humour and from the small blood vessels at the limbus, but this is counteracted by a pump that expels the fluid as fast as it enters. This pumping action depends on an adequate supply of energy, and any situation that prejudices this supply causes the cornea to swell—the pump fails, or works so slowly that it cannot keep pace with the leak. Death is one cause of the failure of the pump, but this is primarily because of the loss of temperature; place the dead eye in a warm chamber and the reserves of metabolic energy it contains in the form of sugar and glycogen are adequate to keep the cornea transparent for 24 hours or more. When it is required to store corneas for grafting, as in an eye bank, it is best to remove the cornea from the globe to prevent it from absorbing fluid from the aqueous humour. The structure responsible for the pumping action is almost certainly the endothelium, so that damage to this lining can lead to a loss of transparency with swelling.

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