eyes

• Eye


  Organ that transmits visual stimuli to the brain for interpretation
• Eyeball


  • Located in the eye orbit
  • Surrounded by a cushion of fat in the orbit
  • Bony orbit and fat cushion protect the eyeball
• Thorough assessment of the eye

  1. Understand external structures of the eye

  2. Understand internal structures of the eye

  3. Understand visual fields and pathways

  4. Understand visual reflexes
• Eyelids


  • Two movable structures (upper and lower)
  • Composed of skin and two types of muscle: striated and smooth
  • Protect the eye from foreign bodies
  • Limit the amount of light entering the eye
  • Distribute tears that lubricate the surface of the eye
• Upper eyelid


  • Larger and more mobile than lower eyelid
  • Contains tarsal plates made up of connective tissue
  • Tarsal plates contain meibomian glands that secrete an oily substance to lubricate the eyelid
• Eyelids


  Join at two points: the lateral (outer) canthus and medial (inner) canthus
• Medial canthus


  • Contains the puncta, two small openings that allow drainage of tears into the lacrimal system
  • Contains the caruncle, a small, fleshy mass that contains sebaceous glands
• Palpebral fissure


  The white space between open eyelids
• Eyelids

  • When closed, should touch
  • When open, the upper lid position should be between the upper margin of the iris and the upper margin of the pupil
  • The lower lid should rest on the lower border of the iris
  • No sclera should be seen above or below the limbus (the point where the sclera meets the cornea)
• Eyelashes


  Projections of stiff hair curving outward along the margins of the eyelids that filter dust and dirt from air entering the eye
• Conjunctiva


  • A thin, transparent, continuous membrane that is divided into two portions: a palpebral and a bulbar portion
  • The palpebral conjunctiva lines the inside of the eyelids
  • The bulbar conjunctiva covers most of the anterior eye, merging with the cornea at the limbus
  • The point at which the palpebral and bulbar conjunctivae meet creates a folded recess that allows movement of the eyeball
  • This transparent membrane allows for inspection of underlying tissue and protects the eye from foreign bodies
• Lacrimal apparatus


  Consists of glands and ducts that lubricate the eye
• Lacrimal apparatus


  1. Lacrimal gland produces tears

  2. Tears wash across the eye and then drain into the puncta

  3. Tears empty into the lacrimal canals and are then channeled into the nasolacrimal sac through the nasolacrimal duct

  4. Tears drain into the nasal meatus
• Extraocular muscles


  • Six muscles attached to the outer surface of each eyeball
  • Control six different directions of eye movement
  • Four rectus muscles (superior, inferior, lateral, and medial) and two oblique muscles (superior and inferior) are responsible for moving the eye in the direction controlled by that muscle
  • Each muscle coordinates with a muscle in the opposite eye, allowing for parallel movement of the eyes and thus the binocular vision characteristic of humans
• Innervation for extraocular muscles


  Supplied by three cranial nerves: the oculomotor (III), trochlear (IV), and abducens (VI)
• Extraocular muscles


  Control the direction of eye movement
• Internal Structures of the Eye

  • The eyeball is composed of three separate coats or layers
• External layer

  • Consists of the sclera and cornea
  • The sclera is a dense, protective, white covering that physically supports the internal structures of the eye
  • The cornea permits the entrance of light, which passes through the lens to the retina
  • The cornea is well supplied with nerve endings, making it responsive to pain and touch
• Middle layer

  • Contains both an anterior portion, which includes the iris and the ciliary body, and a posterior layer, which includes the choroid
  • The ciliary body consists of muscle tissue that controls the thickness of the lens, which must be adapted to focus on objects near and far away
  • The iris is a circular disc of muscle containing pigments that determine eye color
  • The central aperture of the iris is called the pupil
  • Muscles in the iris adjust to control the pupil's size, which controls the amount of light entering the eye
  • The muscle fibers of the iris also decrease the size of the pupil to accommodate for near vision and dilate the pupil when far vision is needed
• Lens

  • Biconvex, transparent, avascular, encapsulated structure
  • Located immediately posterior to the iris
  • Suspensory ligaments attached to the ciliary body support the position of the lens
• Lens function

  Refract (bend) light rays onto the retina
• Adjustments in lens refraction

  1. Depending on the distance of the object being viewed

  2. Refractive ability of the lens can be changed by a change in shape of the lens (which is controlled by the ciliary body)

  3. Lens bulges to focus on close objects and flattens to focus on far objects
• Choroid layer


  • Contains the vascularity necessary to provide nourishment to the inner aspect of the eye
  • Prevents light from reflecting internally
  • Continuous with the ciliary body and the iris anteriorly
• Retina

  • Extends only to the ciliary body anteriorly
  • Receives visual stimuli and sends it to the brain
  • Consists of numerous layers of nerve cells, including rods and cones (photoreceptors)
• Rods

  Highly sensitive to light, regulate black-and-white vision, and function in dim light
• Cones


  Function in bright light and are sensitive to color
• Optic disc


  • Cream-colored, circular area located on the retina toward the medial or nasal side of the eye
  • Where the optic nerve enters the eyeball
  • Normally round or oval in shape, with distinct margins
  • Physiologic cup is a smaller circular area that appears slightly depressed
• Retinal vessels

  • Four sets of arterioles and venules travel through the optic disc, bifurcate, and extend to the periphery of the fundus
  • Venules are dark red and grow progressively narrower as they extend out to the peripheral areas
  • Arterioles carry oxygenated blood and appear brighter red and narrower than the veins
• Fundus


  • General background varies in color, depending on skin color
  • Retinal depression known as the fovea centralis is located adjacent to the optic disc in the temporal section
  • Fovea centralis and macular area are highly concentrated with cones and form the area of highest visual resolution and color vision
• Anterior chamber


  • Located between the cornea and the iris
  • Filled with aqueous humor, a clear liquid substance produced by the ciliary body
• Posterior chamber


  • Area between the iris and the lens
  • Filled with aqueous humor
• Aqueous humor


  • Helps cleanse and nourish the cornea and lens as well as maintain intraocular pressure (IOP)
  • Filters out of the eye from the posterior to the anterior chamber and then into the canal of Schlemm through a filtering site called the trabecular meshwork
• Vitreous chamber


  • Located in the area behind the lens to the retina
  • Filled with a vitreous humor that is clear and gelatinous
• Visual field


  What a person sees with one eye
• Quadrants of the visual field

  • Upper temporal
  • Lower temporal
  • Upper nasal
  • Lower nasal
• The temporal quadrants of each visual field extend farther than the nasal quadrants
• Each eye sees a slightly different view, but their visual fields overlap quite a bit
• Binocular vision


  "Two-eyed" vision in which the visual cortex fuses the two slightly different images and provides depth perception, or three-dimensional vision
• Visual perception

  1. Light rays strike the retina

  2. Transformed into nerve impulses

  3. Conducted to the brain through the optic nerve

  4. Interpreted
• Eye components that refract light

  • Cornea
  • Lens