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