The Anatomy of the Eye and the Physiology of the Vision

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  • Topic: Eye, Retina, Visual system
  • Pages : 9 (3532 words )
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  • Published : February 15, 2011
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Imagine a camera that is composed with 2 million working parts, and stored up to 24 million images around you throughout life span. This incredible amazing camera is our eyes. The human eyes are one of the most interesting medical field that are being studied, as well as one of the most complex organs that has many features. The eyes are the organs of sight and one of our special senses. Vision is our one of our dominant sense: 70% of all the sensory receptors in the body are in the eyes, and almost half of the cerebral cortex is involved in some aspect of the visual processing. Only the anterior one sixth of the eye is visible. (Martini, 2009) The accessory structures of the eye include the eyebrows, eyelid, conjuctiva, lacrimal apparatus, and extrinsic eye muscles. The eyebrows are short, coarse hair over the supraoribital. In the deep area to the skin of the eyebrow are parts of the orbicularis oculi and corrugator muscles. Contraction of the orbicularis muscles depresses the eyebrow, and the corrugator muscles moves the eyebrow medially (Marieb 2004). Each eye is set within a recession in the skull known as the orbit and is covered by the protective fold of the eyelid, or palpebrae. (Wingerd, 2011). The eyelids are separated by the palperbral fissure and meet at the lateral and medial canthi. In the medial canthus the lacrimal caruncle, which is a flashy elevation, is found. It contains whitish, oily secretion that will usually collect in the medial canthus during sleep (Martini 2009). Eyelids are thin, skin covered folds supported internally by connective tissue sheets called Tarasl plates. The Tarsal plates also attach the orbicularis oculi and levator palperbrae superioris muscles that run within the eyelid. The muscles that encircle the eye are Orbicularis oculi muscles, and when they contracts, the eye closes. Out of the two eyelids, the larger upper one is much more mobile, because of the levator palpebrae superioris muscle; this muscle raises the eyelid to open the eye. The eyelid muscles are activated reflexively to cause the eye to blink every 3-7 second, and the reason is to protect the eye from foreign objects, as well as to prevent drying of the eye, because each time we blink accessory structures secretions (oil, mucus, and saline solution) are spread across the eyeball surface (Marieb, 2004). In addition to the eye accessory structures, we find in free margin of each eyelid the eyelashes. The follicles of the eyelash hairs are richly innervated by nerve endings, which are hair follicles receptors, and anything that touches the eyelashes, even puff of air, will result in a reflex blinking. There are several types of glands that are associated with the eyelid. The Tarsal, or Meibomian, glands are embedded in the tarsal plates; their ducts open at the eyelid edge just posterior to the eyelashes. As a result, these sebaceous glands produce an oily secretion that lubricates the eyelid and the eye and prevents the eyelid from sticking together. Most sebaceous and modified sweat glands called ciliary glands lie between the hair follicles. (Marieb 2004). Since the eyes are very important it must be protected. Therefore, the eye receives additional protection from a thin sheet of cells that covers the anterior surface of the eye and the inner surface of the eyelid, this protection thin sheet is known as conjunctiva, means to bind together. The conjunctiva is kept moistened by watery secretion from the large lacrimal glands, which secrete tears. It covers only the iris and the pupil, not the cornea. The ocular conjunctiva is very thin, and blood vessels are visible beneath it. Conjunctival sac is where contact lenses lies; also eye medications are applied to its inferior recess. It major function is to produce mucus that prevents the eyes from drying out. (Martini 2009) Next accessory structure of the eye is the lacrimal Apparatus, which produces, distributes, and removes tears. Each eye consists of lacrimal gland...
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