HUMAN EYE

 Human eye

  The human eye, in humans, is the specialized sensory organ capable of receiving visual images, which are then transmitted to the brain.

  Cross section of human eye

  The eye is protected from mechanical injury by being enclosed in a socket, or orbit, which forms a four-sided pyramid with several bone parts of the skull, the top of which points to the head.  Thus, the floor of the orbit is made up of parts of the maxilla, zygomatic and palatine bones, while the roof is made of the orbital plate of the frontal bone and behind it, the short arm of the sphenoid.  The optic pharynx, the hole through which the optic nerve goes back to the brain and enters the orbit of the large eye, is towards the nostril.  The superior orbital fissure is a large hole through which large veins and nerves pass.  These nerves can carry non-visual sensory messages - such as pain - or they can be motor nerves that control the eye muscles.  There are other cracks and canals that carry nerves and blood vessels.  The eyeball and its active muscles are surrounded by a layer of orbital fat that acts like a cushion, allowing the eyeball to rotate smoothly around a fixed point, the center of rotation.  ۔  Protosis of the eyeballs is caused by the accumulation of fluid in the orbital fatty tissue in the exophthalmic goiter.

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  Human organs

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  Eyelids

  It is important that the front surface of the eye hair, the cornea, remains moist.  This is achieved through the lashes, which regularly wipe the surface of the tear glands and other glandular secretions during waking hours and which cover the eyes during sleep and prevent evaporation.  The reflex action of the eyelids in the lids has the added function of preventing injuries from foreign bodies.  The lids are basically layers of tissue that cover the front of the orbit and leave an almond-shaped aperture when the eye is opened.  Almond points are called canthi.  Near the nose is the inner canthus, and the other is the outer canthus.  The lid can be divided into four layers: (1) the skin, which contains glands that open at the marginal surface of the lid, and the eyelids;  (2) A layer of muscle consisting primarily of the orbicularis oculi muscle, which is responsible for closing the lid.  (3) A fibrous layer that gives the lid mechanical stability, its main parts are the tarsal plates, which are directly attached to the opening between the lids, called palpebral aperture.  And (4) the innermost layer of the lid, a part of the conjunctiva.  The conjunctiva is a viscous membrane that connects the eyeball to the orbit and the lids, but allows the eyeball to rotate considerably in orbit.

  Eyelash

  Upper and lower eyelids.

  Isra SU

  conjunctiva

  Conjunctivitis lines the lids and then bends back to the surface of the hair follicles, forming an outer covering on the front of it and ending at the transparent area of ​​the eye, the cornea.  The part that lines the lids is called the palpebral part of the conjunctiva.  The part that covers the whites of the eye's hair is called the bulbar conjunctiva.  Between the bulbar and the palpebral conjunctiva are two loose, spare parts that return to the equator of the world.  These holidays are called upper and lower forensics, or conjunctival sacs.  It is the looseness of the conjunctiva in these places that makes the movement of the lids and eyeballs possible.

  Fibrous layer

  The fibrous layer, which gives the lid mechanical stability, is made up of thick, and relatively stiff, tarsal plates, which appear directly on the palpebral aperture, and a thinner palpebral fascia, or sheet of connective tissue;  Together they are called septum orbitals.  When the lids are closed, the entire septum is covered by this septum.  The two ligaments, the medial and lateral palpebral ligaments, connected to the orbit of the orbit and the septum, strengthen the position of the lids in relation to the globe.  The medial ligament is still strong.

  The muscles of the lids

  Closure of the lids is achieved by contraction of the orbicularis muscle, a single elliptical sheet of muscle extending from the forehead and facial areas and into the lids around the orbit.  It is divided into orbital and palpebral parts, and it is mainly the palpebral part, inside the lid, which causes the lid to close.  The palpebral portion passes through the lids through a ligament called the medial palpebral ligament and forms a band of fibers in a series of hemispheres to the neighboring bone of the orbit that meet outside the outer corner of the eye, the lateral kineths.  raphe.  The extra parts of the orbicularis are given different names - Horner's muscle and Revlon's muscle;  They come in close contact with the tear gas and help to drain the tears.  Revolving muscles, lying close to the edge of the lid, help keep the lids close.  The orbital part of the orbicularis is not usually associated with the eyelid, which can be done entirely through the palpebral part.  However, it has to do with closing the eyes tightly.  The skin of the forehead, temples and cheeks is then pulled towards the middle of the orbit (nose), and the rays produced by this process of the orbital part, eventually lead to the so-called well feet of the elderly.  .  It should be noted that both parts can be activated freely.  In this way, the orbital part can shrink, causing wrinkles in the eyebrows, which reduces the amount of light coming from above, while the palpebral part is relaxed and the eyes are left open.

  Opening of the eye is not only the result of inactive relaxation of the muscles of the orbicularis but also the effect of contraction of the levator palpebrae superioris muscles of the upper lid.  This muscle begins with the extravascular muscle at the top of the orbit as a narrow tendon and progresses to the upper lid as a wide tendon, the levator aponeurosis, which attaches to the anterior surface of the tarsus and covers the upper.  Skin  Lid.  Muscle contraction causes elevation of the upper eyelid.  The nerve connections to this muscle are closely related to the extracular muscles needed to lift the eye, so when the eye looks upwards, the upper eyelid converges and rises.

  The orbicularis and levator are striped muscles in voluntary control.  The lids also contain smooth (involuntary) muscle fibers that are activated by the sympathetic distribution of the autonomic system and widen the pelvic fissure (opening of the eye) by the height of the upper and the depression of the lower lid.

  In addition to the muscles described earlier, other facial muscles often assist in the process of closing or opening the lid.  Thus, the muscles of the corrugator supercilii pull the eyebrows towards the bridge of the nose, creating a characteristic trench in the forehead, forming a "roof" at the middle angle of the eye.  The roof is mainly used to protect the eye from sunlight.  The pyramid, or processor, muscles occupy the bridge of the nose.  They originate in the lower part 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 translucent skins.  When the lid is opened, the frontalis muscle rises high on the forehead, between the coronal sutures, a suture in the upper part of the skull, and the orbital border is attached to the skin of the eyebrows.  The contraction therefore causes the eyebrows to be raised and resists the action of the orbital part of the orbicularis.  Muscles are used especially when one looks upwards.  It is also practiced when vision is presented with difficulty either due to distance or lack of sufficient light.

  Quick

  The outermost layer of the lid is the skin, the characteristics of which are not very different from the skin of the rest of the body, with the possible exception of the large pigment cells, which, although found elsewhere, are very much in the skin of the lid.  Are  Cells can wander, and these are the movements of pigment cells that determine color changes in some people as health changes.  The skin contains sweat glands and hair.  As the connection between the skin and the conjunctiva develops, the hair changes its character and becomes mahram.

  Glandular device

  Moisture from the tear glands (tear glands) keeps the eye moist.  These almond-shaped glands extend inward from the outer corner of each eye under the upper lid.  Each gland has two parts.  One part of the eye socket is in a shallow depression formed by the frontal bone.  The second part projects into the back of the upper lid.  The ducts that come out of each gland, in numbers three to 12, open into the superior conjunctival pharynx, or sac.  From the pharynx, tears flow across the eye and into the pancreatic lacrimal, with small holes in the margins of each eyelid near the inner corner.  Pentacles have holes in the tear ducts.  They carry tears to the sacs, the wide upper end of the nasolabial ducts, which carry the tears to the nose.

  When tears vapor flow into the eye, the secretion of oil and mucus through other glands is largely prevented.  Thus, the meibomian, or tarsal gland, consists of a series of long glands that spread through the tarsal plates.  They release an oil that rises to the surface of the margin of the lid and acts as a barrier to tear fluid, which accumulates in the ducts between the eye hair and the lid barrier.