The Special Senses

Prepared by Mickelder Kercy, MD - Instructor

Anatomy of the eye

Orbit : Cavity/bony socket containing the eyeball

External Structures : -Lacrimal gland (secretes tears)

-Lacrimal Canaliculi (collect

and drain the tears

-Lacrimal sac (empties the tears

into the nasolacrimal duct)

-Nasolacrimal duct (empties the

tears into the nasal cavity)

External structures : -Palpebrae (eyelids)

-Palpebrae fissure

-Canthus (corner of the eye where

the superior and inferior palpebrae meet)

-Conjunctiva (colorless and thin

mucuous membrane lining the underside of the eyelids

and covering the sclera)

Extrinsic muscles : -Levator palpebrae superior

-Superior rectus

-Inferior rectus

-Lateral rectus

-Medial rectus

-Superior oblique

-Inferior oblique

Outer Layer : -Cornea/Window of the eye (transparent)

Controls and focuses the entry of light

into the eye

-Sclera (white)

Middle Layer : - Iris (contains the eye color. Forms the

Pupil)

-Ciliary body (holds and moves the

lens. Secretes aqueous humor that provides nutrients

to the cornea lens and other tissues)

-Choroid (lines the sclera)

Innermost layer : -Lens (colorless, accomodation)

-Retina (rods and cones)

-Fovea Centralis Retinae (cones

located in the middle of the macula lutae/yellow spot)

-Optic Nerve (enters at optic disk)

Anterior cavity : -Anterior chamber (aqueous humor)

-Posterior chamber (aqueous humor)

Posterior cavity : -Vitreous humor/body

Physiology of the Eye

Light passes through the cornea, aqueous humor, lens,

then vitreous humor to reach the photoreceptors

(cones and rods). Theses photoreceptors contain

chemicals (some of them derived from Vit A) that

cause electrical impulses transmitted to the optic

nerve, which sends signals to the brain. The brain will

interpret and create visual images.

Common Refractive Disorders

Astigmatism : Blurry near or distant vision due to the

imperfection in curvature in the cornea or lens

Myopia : Nearsightedness

Presbyopia : Nearsightedness in old age

Hyperopia : Farsightedness

Strabismus : Crossed eyes/wall eyes

Disorders related to structural irregularities

Blepharoptosis : Drooping of one/both eyelids

Ectropion : Lower eyelid turns outward/everts

Entropion : Eyelid folds inward/inverts

Exophthalmos : Bulging of one/both eyeballs

Infectious Eye Disorders

Blepharitis : Inflammation of the eyelids

Conjunctivitis : Inflammation of the conjunctiva

Hordeolum : sty or pus-filled swelling at the base of

an eyelash

Age-Related Eye Disorders

Cataracts : Clouding/Opacity of the lens

Retinal Detachment : Retina detached from the

choroid

Macular Degeneration : Degeneration of the macula

Nyctalopia : Nightblindness

Amblyopia : Blurred image sent to the brain by a lazy

eye whose nerve pathway did not develop during

childhood. This confuses the brain, and the brain may

learn to ignore the image from the weaker eye

Corneal Abrasion : Lesion/abrasion on the cornea

Diplopia : Double vision

Glaucoma : Increased pressure in the eye causing the

visual field to decrease

Nystagmus : Nystaxis/involuntary repetitive eye

movement

Retinopathy : Diseases of the retina that affect the

blood vessesls. Found in diabetes and Hypertension.

Photophobia : Sensitivity to light

Slit Lamps

Anatomy of the Ear

External Ear : -Pinna/auricle

-Auditory canal/auditory meatus

(secretes cerumen/earwax)

-Tympanic membrane/eardrum

-Fundus/floor of the tympanic membrane

Middle Ear : -Malleus/hammer

-Incus/anvil

-Stapes/stirrups

Inner ear/Labyrinth : -Cochlea (bony spiral structure

containing the cochlear ducts filled with fluid/

endolymph. Contains the organ of corti that has nerve

endings transmitting sound vibrations to the 8th nerve)

-Vestibule (central part of the

labyrinth)

-Semicircular canal (filled with

endolymph/fluid and cilia that detect head motion to

maintain balance)

-Eustachian tube (links the

middle ear to the nasopharynx)

Physiology of the Ear

Sound waves enters the ear→ vibrations of the

eardrum→ bones in the middle ear move back and

forth→ movement of the fluid in the cochlea. The

hair cells in the cochlea will sense the motion

(movement) via their cilia and convert that motion to

electrical signals/impulses that will be sent to the

auditory nerve. The brain interprets the message and

create sounds.

Hearing Loss

Conductive : Damage to the auditory canal

Sensorineural : Damage to the cochlea or to the nerve

pathways

Audiometer and Tuning Fork

Common disorders associated with the outer ear

Impacted Cerumen : Earwax that has hardened

obstructing the ear canal

Ruptured tympanic membrane : Tear in the tympanic

membrane

Common Disorders associated with the Middle Ear

Otitis Media : Inflammation of the middle ear

Otosclerosis : Overgrowth of spongy bone around the

stapes

Common disorders associated with the Inner Ear

Tinnitus : Ringing or roaring in the ear

Meniere’s disease : Idiopathic, affects hearing and

balance

Presbycusis : Mostly in older adults

The Senses of Taste and Smell

Olfactory Cells : In the roof of the nasal cavity

Taste Buds : Sweet→Salty→Sour→Bitter

The End