Health Assessment OUTLINE 14 Chapter 14

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Eyes External Anatomy Bony orbital cavity surrounded by cushion of fat protects eye Eyelids are like two movable shades that further protect eye from injury, strong light, and dust Upper eyelid la ... rger and more mobile Eyelashes are short hairs in double or triple rows that curve outward from lid margins, filtering out dust and dirt Palpebral fissure: elliptical open space between eyelids When closed, lid margins approximate completely When open, upper lid covers part of iris Lower lid margin, at limbus, borders between cornea and sclera Canthus: corner of eye, angle where lids meet Inner canthus: caruncle is small fleshy mass containing sebaceous glands External Anatomy of the Eye Tarsal Plates Within upper lid, they are strips of connective tissue that give it shape Contain meibomian glands, which are modified sebaceous glands that secrete an oily lubricating material onto lids This stops the tears from overflowing and helps to form an airtight seal when lids are closed Conjunctiva and Cornea Conjunctiva: transparent protective covering of exposed part of eye Palpebral conjunctiva: lines lids, is clear, with many small blood vessels Bulbar conjunctiva: overlies eyeball, with white sclera showing through At limbus, conjunctivae merge with cornea Cornea: covers and protects iris and pupil Lacrimal Gland Lacrimal gland, in upper outer corner over eye, secretes tears Tears wash across eye and drawn up evenly as lid blinks Drain into puncta, on upper and lower lids at inner canthus Then drain into nasolacrimal sac, through ½-inch-long nasolacrimal duct, and empty into inferior meatus inside nose Extraocular Muscles Six muscles attach eyeball to its orbit and direct eye to points of person’s interest Give eye both straight and rotary movement Four straight, or rectus, muscles are superior, inferior, lateral, and medial rectus muscles Two slanting, or oblique, muscles are superior and inferior muscles Each muscle is coordinated, or yoked, with one in other eye ensuring that when two eyes move, their axes always remain parallel, called conjugate movement Parallel axes are important because human brain has a binocular, single-image visual system Internal Anatomy Eye: a sphere of three concentric coats Outer fibrous sclera Middle vascular choroid Inner nervous retina Inside retina is transparent vitreous body Only parts accessible to examination are sclera anteriorly and retina through ophthalmoscope Three Concentric Coats Internal Anatomy: Outer Layer Sclera: tough, protective, white covering Continuous anteriorly with smooth, transparent cornea, which covers iris and pupil Cornea: part of refracting media of eye, bending incoming light rays so that they will be focused on inner retina Very sensitive to touch; contact with a wisp of cotton stimulates a blink in both eyes, called corneal reflex Trigeminal nerve, cranial nerve V, carries afferent sensation into brain, and facial nerve, cranial nerve VII, carries efferent message that stimulates blink Internal Anatomy: Middle Layer Choroid: has dark pigmentation to prevent light from reflecting internally and is heavily vascularized to deliver blood to retina Anteriorly is continuous with ciliary body and iris Muscles of ciliary body control thickness of lens Iris: functions as a diaphragm, varying opening at its center, the pupil Controls amount of light admitted into retina Muscle fibers of iris contract pupil in bright light and to accommodate for near vision, and dilate pupil when light is dim and for far vision Pupil: round and regular; size determined by balance between parasympathetic and sympathetic chains of autonomic nervous system Stimulation of parasympathetic branch, through cranial nerve III, causes constriction of pupil Stimulation of sympathetic branch dilates pupil and elevates eyelid Pupil size also reacts to amount of ambient light and to accommodation, or focusing an object on retina Lens: biconvex disc located just posterior to pupil Transparent, it serves as a refracting medium, keeping a viewed object in focus on retina Thickness controlled by ciliary body; lens bulges focusing on near objects; flattens for far objects Anterior and posterior chambers contain clear, watery aqueous humor produced continually by ciliary body Continuous flow of fluid serves to deliver nutrients to surrounding tissues and to drain metabolic wastes Intraocular pressure determined by balance between amount of aqueous produced and resistance to outflow Internal Anatomy: Inner Layer Retina: the visual receptive layer of eye where light waves change into nerve impulses Retinal structures viewed through ophthalmoscope are optic disc, retinal vessels, general background, and macula Optic disc: area in which fibers from retina converge to form optic nerve Located toward nasal side of retina, it has these characteristics: a color that varies from creamy yellow-orange to pink; a round or oval shape; margins that are distinct and sharply demarcated, especially on temporal side; and a physiologic cup, the smaller circular area inside disc where blood vessels exit and enter Retinal vessels: normally include a paired artery and vein extending to each quadrant Macula: located on temporal side of fundus Slightly darker pigmented region surrounding fovea centralis, area of sharpest and keenest vision Receives and transduces light from center of visual field Visual Pathways and Visual Fields Light rays are refracted through transparent media, the cornea, aqueous humor, lens, and vitreous body, striking the retina Retina transforms light stimulus into nerve impulses conducted to visual cortex Image formed on retina is upside down and reversed All retinal fibers collect to form optic nerve, but maintain same spatial arrangement At optic chiasm, fibers from both visual fields cross over [Show More]

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