MA 140 Chapter 6 Part 3 The Eye and the Sense of Sight Medical Assisting Concorde
each eyeball has
6 extrinsic eye muscles attached to it that move the eyeball superiorly, inferiorly, laterally, or medially
presbyopia
a common eye disorder that results in the loss of lens elasticity. it develops with age and causes a person to have difficulty seeing objects close up. Treatments include contact lenses, eyeglasses, and eye surgery such as conductive keratoplasty (CK)
strabismus
a misalignment of the eyes. convergent strabismus is more commonly referred to as crossed eyes. in this condition, the eyes do not focus together, and one or both eyes turn inward. in divergent strabismus, sometimes called wall eyes, one or both eyes turn outward instead of focusing together
macular degeneration
a progressive disease that usually affects people over the age of 50. it occurs when the retina no longer receives an adequate blood supply. it is the most common cause of vision loss in the United States
cones
allow vision in bright light; detect colors; detect details
rods
allow vision in dim light; detect black, white, and gray images; detect broad outlines of images
cornea
allows light to enter the eye; bends light as it enters the eye (refraction)
mucous membranes
are called this because they produce mucus that keeps the surface of the eyeballs moist
rods
are highly sensitive to light. they function in dim light but do not provide a sharp image or detect color, only black, white and shades of gray. they give us our limited "night vision" as well as peripheral vision
lacrimal glands
are located on the lateral edge of each eyeball and produce tears.
tears
are mostly water, but they also contain enzymes (lysozymes) that can destroy bacteria and viruses as part of the body's system to protect itself. tears also have an outer oily layer that prevents them from evaporating
conjunctivas
are mucous membranes that line the inner surfaces of the eyelids and cover the anterior surface of each eyeball
extrinsic eye muscles
are skeletal muscles that move the eyeball
in the anterior part of the choroid
are the iris and the cilary body
pupil
as the muscular tissue contracts and relaxes, an opening at its center grows larger or small. this opening is this
nerves cells
at the posterior of the retina sense light
accommodation
because the lens can change shape, it helps the eye focus images of objects that are near or far away
optic nerve
carries visual information (stimuli) from rods and cones toward the brain
cataracts
clouding and hardening of the lens, which often occur with aging, lead to visual changes in this condition
signs and symptoms of Macular degeneration
common symptoms include loss of central vision (may be gradual or sudden), distortions in vision (straight lines begin to look wavy, for example), and difficulty seeing details
conjunctivitis
commonly called pink eye and is highly contagious when the cause is bacterial in nature
retina
contains visual receptors
muscles in the ciliary body
control the shape of the lens - making the lens more or less curved for viewing either near or distant objects.
iris
controls the amount of light entering the eye
there are two types of nerves cells
each named for its shape, rods and cones
light reflected from an object, or produced by one
enters the eye from the outside and passes through the cornea, pupil, lens, and fluids in the eye.
lens
focuses light onto the retina (accommodation)
cones
function best in bright light. they are sensitive to color and provide sharper images. they are responsible for our ability to differentiate different tones and hues of color. deficiencies in the number or types of cones are responsible for the various types of color blindness, which is generally an inherited condition
the ability of the eye to adapt to changes in light intensities may be reduced
glare can become painful as this ability diminishes
ciliary body
holds the lens; controls the shape of the lens for focusing
vitreous humor
holds the retina in place; maintains the shape of the eyeball
the lens
is a clear, circular disk located just posterior to the iris
the eye
is a complex organ that processes light to produce images.
the cornea
is a transparent area on the front of the eye that acts as a window to let light into the eye.
the ciliary body
is a wedge-shaped thickening in the middle layer of the eyeball.
the anterior chamber
is in front of the lens and is filled with a watery fluid called aqueous humor.
glaucoma
is indicated by an increase in intraocular pressure, caused by a buildup of aqueous humor in the anterior chamber. if untreated, this excess pressure can lead to permanent damage of the optic nerves, resulting in blindness
the iris
is the colored part of the eye. it is made of muscular tissue.
the choroid
is the middle layer of the eye, which contains most of the eye's blood vessels
presbyopia
is visual impairment as a result of aging and is caused by the loss of lens elasticity, resulting in difficulty seeing items close to you
vitreous humor
keeps the retina flat and helps to maintain the shape of the eye
amblyopia
more commonly called lazy eye and occurs when a child does not use one eye regularly. a child with this disorder does not have normal depth perception and often also has concurrent strabismus, a condition in which the eyes do not focus in unison
aqueous humor
nourishes and bathes structures in the anterior eye cavity
the posterior chamber
of the eyeball is behind the lens and is filled with a very thick, jelly-like fluid called vitreous humor
cataracts
opaque structures within the lens that prevent light from going through the lens. over time, images begin to look fuzzy and, if left untreated, may cause blindness
optic chiasm
parts of the optic nerve cross at a structure called this, located at the base of the brain. the visual area in the occipital lobes of the cerebrum is responsible for interpreting vision.
sclera
protects the eye
aqueous humor
provides nutrients to and bathes the structures in the anterior chamber of the eyeball
the size of the pupil
regulates the amount of light that enters the eye.
choroid
supplies nutrients and provides a blood supply to the eye
a number of changes occur in the structure and function of the eye
the amount of fat tissue diminishes, the quality and quantity of tears decrease, the conjunctiva becomes thinner and may be drier because of a decrease in tear production, the cornea begins to appear yellow, and a ring of fat deposits may appear around it, the sclera may develop brown spots, changes in the iris cause the pupil to become smaller, limiting the amount of light entering the eye, the lens becomes denser and more rigid, yellowing of the lens causes problems in distinguishing colors, changes in the retina may make vision fuzzy, the ability of the eye to adapt to changes in light intensities may be reduces, night vision may be impaired, peripheral vision is reduced, limiting the area a person can see and reducing depth perception, the vitreous humor breaks down, producing tiny clumps of gel or cellular material that cause floaters - dark spots or lines- that appear in a person's field of vision, rubbing of the vitreous humor on the retina produces flashes of light or "sparks"
each eyeball is divided into two chambers
the anterior and the posterior
optic disk
the area where the optic nerve enters the retina is known as this. this area contains no sensory nerves itself and is referred to as the blind spot.
refraction
the cornea, lens, and fluids help focus the light onto the retina be bending it, in a process known as this
a person's visual system consists of
the eyes; the optic nerve, which connects the eye to the vision center of the brain; and several accessory structures
retina
the inner layer of the eye consists of this
tonometry
the measurement of fluid pressure in the eyeball with a machine called a tonometer, may also be the responsibility of an ophthalmic assistant
in bright light
the pupil becomes constricted (smaller).
in dim light
the pupil becomes dilated (larger).
the sclera
the white of the eye, is the tough, outermost layer of the eye. there are no blood vessels in this, however, there are numerous sense receptors to detect even the smallest particles on the surface of the eyeball
outer layer
this layer, through which light cannot pass, covers all except the front of the eye. here the sclera gives way to the cornea in an area known as the limbus or corneal scleral junction.
the lends becomes denser and more rigid
this trend reduces the amount of light that reaches the retina and makes focusing more difficult
the eye is made up of
three main layers, two chambers, and a number of specialized parts