Eye and Ear

Windsor University School of MedicineBiology Premed

1

Biology Chapter 15The Special Senses (Eye and

Ear)

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Structures of the Eye(Front View)

• Sclera– White portion of eye• Tough, fibrous membrane• Maintains shape of eyeball• Serves as protective covering for eye

• Iris– Colored portion of eye

• Pupil– Opening in center of eye– Controls amount of light entering eye

Overview of the Eye• Eye acts much like a camera– Lens of eye adjusts to bring object into focus– Pupil of eye constricts to allow less light to enter

in bright setting or dilates to allow more light to enter in darker setting

– Through bending of light rays, image reaches Retina• Sensitive nerve cell layer of eye• Image is transmitted to brain for interpretation

Structures of the Eye(Front View)

• Conjunctiva– Thin mucous membrane layer that lines anterior part of

eye and inner part of eyelids• Colorless, but appears white because it covers sclera

• Lacrimal gland– Located at upper outer edge of each eye• Produces tears

• Lacrimal duct– Located at inner edge of eye• Tears drain from eye through this duct

Structures of the Eye(Front View)

Structures of the Eye(Front View)

• Eyelids– Continuous with skin and cover the eyeball– Keep surface of eyeball lubricated and protected from

dust and debris through blinking motion

• Eyelashes– Located along edges of eyelids– Help protect eyeball by preventing foreign materials

and/or insects from coming in contact with surface of eyeball

Structures of the Eye(Cross Section)

• Sclera– “White of the eye”– Thinnest over anterior surface of the eye– Thickest at the back of the eye, near opening for

optic nerve• Cornea– Continuous with anterior portion of sclera– Transparent, nonvascular layer covering colored

part of the eye or front of eye. Refracts light toward retina

Structures of the Eye(Cross Section)

• Conjunctiva– Mucous membrane lining inner surfaces of eyelids

and outer surfaces of eye• Choroid– Vascular middle layer of eye• Just beneath sclera• Contains extensive capillaries that provide blood supply

and nutrients to eye• Contains the iris, ciliary body, and suspensory

ligaments

Structures of the Eye(Cross Section)

• Iris– Colored portion of eye• Can be seen through transparent corneal layer

• Pupil– Located in center of iris• Controls amount of light entering eye

• Lens– Colorless biconvex structure that aids in focusing

images clearly on retina

Structures of the Eye(Cross Section)

• Ciliary body– Located on each side of the lens– Contains muscles responsible for adjusting lens to view

near objects

• Suspensory ligaments– Radiate from ciliary body and attach to lens– Hold lens in place– Assist in adjusting shape of lens for proper focusing of eye

Structures of the Eye(Cross Section)

• Retina– Sensitive nerve cell layer

• Changes energy of light rays into nerve impulses• Transmits nerve impulses via optic nerve to brain for

interpretation of image seen by eye

– Nerve cells of retina• Rods are responsible for vision in dim light and for peripheral

vision• Cones responsible for visualizing colors, central vision, and

vision in bright light

– Rhodospin – Visual pigment of Rods

Structures of the Eye(Cross Section)

• Retina – Macula Lutea• Oval, yellowish spot near center of retina

– Fovea Centralis• Small depression located within macula lutea• Sharpest image is obtained when image focuses

directly on fovea centralis = central vision

Structures of the Eye(Cross Section)

• Optic nerve– Receives impulses from retina and transmits

them to the brain• Images are then interpreted as vision

• Optic disc– Contains no rods or cones– Known as the “blind spot” of the eye– Center of optic disc serves as point of entry for

artery that supplies retina

Structures of the Eye(Cross Section)

Lateral Cross Section of the Eye

Structures of the Eye(Cross Section)

• Anterior cavity of the eye– Anterior chamber• Located in front of lens• Filled with clear, watery fluid called aqueous humor

– Posterior chamber• Located behind lens• Also filled with aqueous humor • Flows back and forth between both chambers

Structures of the Eye(Cross Section)

• Posterior cavity of eye– Posterior to lens– Filled with vitreous humor• Clear, jellylike substance that gives shape to the

eyeball• Not constantly reproduced• Blindness can result if vitreous humor escapes from

eye

Process of Vision• Process begins as light rays enter eye– Transmitted through cornea, aqueous humor,

pupil, lens, and vitreous humor to retina• Sensitive nerve cells of retina transmit image through

optic nerve to brain• Brain interprets image as vision

Process of Vision• Refraction– Process of bending of light rays as they pass

through the various structures of the eye to produce a clear image on the retina

• Errors of refraction – Occur when eyeball is abnormally shaped– Occur when lens has lost ability to accommodate

to near vision• Vision will be blurred• Can be adjusted with corrective lenses

PATHOLOGICAL CONDITIONS

The Eye

Astigmatism

• Pronounced– (ah-STIG-mah-tizm)

• Defined– Refractive error causing light rays entering the eye

to be focused irregularly on the retina due to an abnormally shaped cornea• Correction: contact lenses or eyeglasses to neutralize

defect

Blepharoptosis(Ptosis)

• Pronounced– (blef-ah-roh-TOH-sis)

• Defined– Occurs when eyelid partially or entirely covers the

eye as a result of a weakened muscle

Blindness

• Pronounced– (BLINDNESS)

• Defined– Absence of vision or the need for assistive devices

and/or assistance from others to accomplish daily activities due to inability to see

Monochromatism (Color Blindness) • Pronounced– (mon-oh-KROH-mah-tizm)

• Defined– Inability to sharply perceive visual colours• Daltonism

– Unable to distinguish greens from reds

• Achromatic Vision – Cannot distinguish any color; perceives only white, gray, and

black

Cataract• Pronounced– (KAT-ah-rakt)

• Defined– Lens in the eye becomes progressively cloudy

losing its normal transparency• Alters perception of images due to interference of light

transmission to retina

Conjunctivitis, Acute

• Pronounced– (kon-junk-tih-VYE-tis acute)

• Defined– Inflammation of mucous membrane lining the

eyelids and covering the front part of the eyeball– Also called “Pinkeye”

Corneal Abrasion

• Pronounced– (COR-nee-al ah-BRAY-zhun)

• Defined– Disruption of the cornea’s surface epithelium

commonly caused by an eyelash, a small foreign body, contact lenses, or a scratch from a fingernail

Diabetic Retinopathy

• Pronounced– (dye-ah-BET-ik reh-tin-OP-ah-thee)

• Defined– Condition that occurs as a consequence of an 8 to

10-year duration of diabetes mellitus in which the capillaries of retina experience scarring

Diabetic Retinopathy• Causes of retinal capillary scarring– Abnormal dilation and constriction of vessels– Hemorrhages– Microaneurysms– Abnormal formation of new vessels causing

leakage of blood into the vitreous humor• Leakage causes permanent decline in sharpness of

vision

Exophthalmia

• Pronounced– (eks-off-THAL-mee-ah)

• Defined– Abnormal protrusion of the eyeball(s) usually with

the sclera noticeable over the iris– Typically due to an expanded volume of orbital

contents

Glaucoma

• Pronounced– (glau-KOH-mah)

• Defined– Ocular disorders identified as a group due to the

increase in intraocular pressure

Glaucoma• Chronic open-angle glaucoma– Primary disorder– Breakdown in drainage system of the circulation

of aqueous humor• Gradual elevation of internal pressure leads to

decreased blood supply to optic nerve and retina• Peripheral vision is gradually lost when untreated

Glaucoma• Acute closed-angle glaucoma– Mouth of drainage system is narrow and closes

completely– Allowing no flow of aqueous humor• Rapid occurrence characterized by severe pain, blurred

vision, photophobia, redness, and seeing “halos” around light• If untreated, person can lose his or her sight within

several days

Hemianopia

• Pronounced– (hem-ee-an-NOP-ee-ah)

• Defined– Loss of vision or blindness in one-half of the visual

field

Hyperopia• Pronounced– (high-per-OH-pee-ah)

• Defined– Refractive error in which the lens of the eye

cannot focus on an image accurately– Results in blurred vision due to light rays focused

behind the retina because eyeball is shorter than normal• Also called farsightedness

HyperopiaHyperopia (Farsightedness)

Myopia

• Pronounced– (my-OH-pee-ah)

• Defined– Refractive error in which the lens of the eye

cannot focus on an image accurately– Resulting in blurred distant vision due to light rays

focused in front of retina because eyeball is longer than normal• Also known as nearsightedness

MyopiaMyopia (nearsightedness)

Nystagmus• Pronounced– (niss-TAG-mus)

• Defined– Vertical, horizontal, rotary, or mixed rhythmic

involuntary movements of the eye(s)• Caused by use of alcohol or certain drugs, lesions on

the brain or inner ear, congenital abnormalities, nerve injury at birth, or abnormal retinal development

Strabismus• Pronounced– (strah-BIZ-mus)

• Defined– Failure of eyes to gaze in same direction due to

weakness in muscles controlling position of eye• Most common type is nonparalytic strabismus• Inherited defect in which the eye position of the two

eyes has no relationship

Strabismus

• Convergent Strabismus– Also known as “Crosseye” – Also known as “Esotropia”– Affected eye turns inward• Usually develops in infancy or early childhood

Strabismus• Divergent Strabismus– Also known as “Walleye”– Also known as “Exotropia”– Affected eye turns outward

StrabismusStrabismus

(A) Convergent(B) Divergent

Trachoma

• Pronounced– (tray-KOH-mah)

• Defined– Infectious eye disease caused by Chlamydia

trachomatis– Chronic and will lead to blindness without

treatment• Early symptoms include tearing, pain, photophobia,

and inflammation

Uveitis• Pronounced– (yoo-vee-EYE-tis)

• Defined– Inflammation of all or part of middle vascular

layer of eye made up of the iris, ciliary body, and choroid• Characterized by blurred vision, pain, redness,

pupillary constriction, and intense photophobia

Ear

Structures of the Ear• External ear– Visible portion not contained within the head– Auricle or pinna

• Cartilaginous flap or ear lobe

– External auditory canal• Tube leading from auricle to the middle ear• Lined with tiny hairs called cilia to aid in transmitting sound

waves inward

– Tympanic membrane (eardrum)• Separates external ear from middle ear• Vibrates due to moving air or sound

Structures of the Ear• Middle ear– Three tiny bones known as auditory ossicles– Malleus• Resembles shape of a hammer• Connected to tympanic membrane and transmits sound

vibrations to second auditory ossicle

– Incus• Resembles shape of an anvil• Transmits sound vibrations from malleus to third

auditory ossicle

Structures of the Ear• Middle ear – Stapes• Shaped like a tiny stirrup• Transmits sound vibrations from incus to inner ear

– Eustachian tube• Connects middle ear to pharynx

– Equalizes pressure between middle ear and atmosphere

• Auditory tube

– Oval window• Separates middle ear from inner ear• Base of stapes fits into oval window

• When stapes vibrates with Oval window, it creates pressure waves in the fluid inside the cochlea

Structures of the Ear• Inner ear– Vestibule• Central portion of inner ear• Located next to stapes and between cochlea and

semicircular canals• Contains utricle and saccule-membranous pouches or

sacs that aid in maintaining balance– Cochlea• Snail-shaped bony structure• Contains endolymph and perilymph• Auditory fluids that aid in transmission of sound

vibrations

Structures of the Ear• Inner ear – Organ of Corti• True organ of hearing• Contained within the cochlea• Contains mechanoreceptors of the ear == “Hair Cells”• Here, sound vibrations are converted into nerve

impulses that are transmitted to the brain for interpretation as hearing

– Semicircular canals• Located behind the vestibule• Three bony, fluid-filled loops that help to maintain

one’s balance

Organ of Corti• Hair cells attached to the tectorial membrane• Sound waves vibrate the basilar membrane,

result in bending of hairs and depolarization of hair cells.

The Process of Hearing

Pathway of soundvibrations

Structures of the Ear

Organs of Equilibrium• Detects body movement and position in mammals

• Semicurcular canals detect turning of the head

• Utricle and Saccule perceive position with respect to gravity and acceleration

• Each of these chambers contain hair cells that project into a gelatinous material– Embedded in gel are “Otoliths” or ear stones– Otoliths press on the hairs protruding in the gel

PATHOLOGICAL CONDITIONS

The Ear

Deafness, Conductive

• Pronounced– (Deafness kon-DUK-tiv)

• Defined– Hearing loss caused by breakdown of the

transmission of sound waves through the middle and/or external ear

Deafness, Sensorineural

• Pronounced– (Deafness sen-soh-ree-NOO-ral)

• Defined– Hearing loss caused by inability of nerve stimuli

delivered to brain from inner ear due to damage in auditory nerve or cochlea

Impacted Cerumen

• Pronounced– (Impacted seh-ROO-men)

• Defined– Excessive accumulation of waxlike secretions from

glands of external ear canal

Labyrinthitis

• Pronounced– (lab-ih-rin-THIGH-tis)

• Defined– Infection or inflammation of the labyrinth or the

inner ear– Specifically, the three semicircular canals in the

inner ear– Fluid-filled chambers and control balance

Mastoiditis

• Pronounced– (mass-toyd-EYE-tis)

• Defined– Inflammation of mastoid process– Usually an acute expansion of an infection in the

middle ear – Otitis media

Ménière's Disease• Pronounced– (may-nee-ARYZ dih-ZEEZ)

• Defined– Chronic inner ear disease– Over accumulation of fluid in the labyrinth– Characterized by recurring episodes of vertigo,

hearing loss, feeling of pressure or fullness in the affected ear, and tinnitus

Otitis External (O.E.) - Swimmer’s Ear

• Pronounced– (oh-TYE-tis eks-TER-nah)

• Defined– Inflammation of outer or external ear canal• Result of growth of bacteria or fungi in external ear• Major symptom is pain, especially when the ear is

tugged on, along with a red swollen ear canal

Otitis Media , Acute (A.O.M.)

• Pronounced– (oh-TYE-tis MEE-dee-ah)

• Defined– Middle ear infection– Predominately affects infants, toddlers, and

preschoolers

Suppurative Otitis Media• Pronounced– (SOO-per-ah-tiv oh-TYE-tis MEE-dee-ah)

• Defined– Purulent collection of fluid in the middle ear– Person may experience pain (possibly severe), an

elevation in temperature, dizziness, decreased hearing, vertigo, and tinnitus

– Also called acute otitis media

Perforation of Tympanic Membrane

• Pronounced– (per-for-AY-shun of the tim-PAN-ik

membrane)

• Defined– Rupture of tympanic membrane or eardrum

DIAGNOSTIC TECHNIQUES, TREATMENTS, AND PROCEDURES

The Ear

Diagnostic Techniques, Treatments, and Procedures

• Audiometry – Process of measuring how well an individual

hears various frequencies of sound waves

• Otoscopy– Use of an otoscope to view and examine

tympanic membrane and various parts of outer ear