Chapter 11: Senses of the Eye and Ear
Professions:
1. Ophthalmologists: specialize in the diagnosis and treatment of
diseases of the eye
2. Optometrists: skilled in the measurement of vision and maintaining
eye health
3. Otologists: specialize in diseases of the ear
4. Otorhinolaryngologist: ENTS; specialize in diseases of the ear, nose,
and throat
5. Audiologists: evaluate hearing function
Accessory Structures:
Eyebrows: keep sweat from running into the eyes and are used in
nonverbal communication to see how you’re feeling
Eyelids: protect eyes from foreign objects
Eyelashes: strong hairs that keep debris out of the eyes
Conjunctiva: a transparent mucus membrane that lines the inside of
both eyelids; keeps eyeball moist; sensitive and easily irritated
Lacrimal apparatus: secretes tears and carry them to the
conjunctiva’s surface
Nasolacrimal duct: carries tears into the nose where they will be
eventually swallowed
Tears:
o Clean and lubricate eyes
o Deliver nutrients and oxygen to the conjunctiva
o Prevent infection through bacterial-killing enzymes
The cornea protects the eye and provides 60% focusing power
Iris controls the amount of light entering into the eye
The lens changes shape to focus rays of light on the retina
Extrinsic Muscles of the Eye
Eyes work together to give 3D perception (stereopsis)
There are 6 extrinsic eye muscles in each eye that are attached to
the inner wall of the orbit and outer surface of the eyeball
o They keep the eyes aligned
o Moves the eyes in all directions
The Eyeball
, Adjusts the amount of light to reach the retina
Focuses on near and distant objects
Produces images of those objects and instantly transmits them to the
brain
Three layers of the eyeball:
o Outer fibrous Layer: sclera (white, protects inner eyes
structures) and cornea (transparent, bends light rays)
o Middle vascular layer (aka the uvea): iris (colored part,
controls pupil size), ciliary body (bends the lens), and choroid
(absorbs light)
o Inner layer: retina (neural layer, absorbs light)
Iris dilates in dark rooms to allow more light and constricts in bright
rooms to allow less light in the eye
The lens is avascular and contains no nerves and loses elasticity with
age
The Retina
Small, has ten layers of cells, located at back of the eye
Final destination for light rays
Has 130 million rods that only perceive light NOT color
6.5 million light and color activated cones – only perceive red, blue, or
green light
Optic nerve: bundle of more than 1 million nerve fibers; transmits
impulses to brain
Optic disc: where the optic nerve and retina connect; also called
“blind spot”
Disorders of the Eye
Professions:
1. Ophthalmologists: specialize in the diagnosis and treatment of
diseases of the eye
2. Optometrists: skilled in the measurement of vision and maintaining
eye health
3. Otologists: specialize in diseases of the ear
4. Otorhinolaryngologist: ENTS; specialize in diseases of the ear, nose,
and throat
5. Audiologists: evaluate hearing function
Accessory Structures:
Eyebrows: keep sweat from running into the eyes and are used in
nonverbal communication to see how you’re feeling
Eyelids: protect eyes from foreign objects
Eyelashes: strong hairs that keep debris out of the eyes
Conjunctiva: a transparent mucus membrane that lines the inside of
both eyelids; keeps eyeball moist; sensitive and easily irritated
Lacrimal apparatus: secretes tears and carry them to the
conjunctiva’s surface
Nasolacrimal duct: carries tears into the nose where they will be
eventually swallowed
Tears:
o Clean and lubricate eyes
o Deliver nutrients and oxygen to the conjunctiva
o Prevent infection through bacterial-killing enzymes
The cornea protects the eye and provides 60% focusing power
Iris controls the amount of light entering into the eye
The lens changes shape to focus rays of light on the retina
Extrinsic Muscles of the Eye
Eyes work together to give 3D perception (stereopsis)
There are 6 extrinsic eye muscles in each eye that are attached to
the inner wall of the orbit and outer surface of the eyeball
o They keep the eyes aligned
o Moves the eyes in all directions
The Eyeball
, Adjusts the amount of light to reach the retina
Focuses on near and distant objects
Produces images of those objects and instantly transmits them to the
brain
Three layers of the eyeball:
o Outer fibrous Layer: sclera (white, protects inner eyes
structures) and cornea (transparent, bends light rays)
o Middle vascular layer (aka the uvea): iris (colored part,
controls pupil size), ciliary body (bends the lens), and choroid
(absorbs light)
o Inner layer: retina (neural layer, absorbs light)
Iris dilates in dark rooms to allow more light and constricts in bright
rooms to allow less light in the eye
The lens is avascular and contains no nerves and loses elasticity with
age
The Retina
Small, has ten layers of cells, located at back of the eye
Final destination for light rays
Has 130 million rods that only perceive light NOT color
6.5 million light and color activated cones – only perceive red, blue, or
green light
Optic nerve: bundle of more than 1 million nerve fibers; transmits
impulses to brain
Optic disc: where the optic nerve and retina connect; also called
“blind spot”
Disorders of the Eye
