Lesson 9

Special Senses: Eyes and Ears

The special senses — vision and hearing — connect us to the world. The eye converts light into nerve impulses; the ear detects sound waves and provides balance. Ophthalmology and otolaryngology (ENT) cover conditions from glaucoma and cataracts to otitis media and sensorineural hearing loss.

50 min4 sections5 objectives

Learning Objectives

1Describe the anatomy of the eye and ear
2Identify combining forms for eye and ear structures
3Recognize common ocular and auditory conditions
4Interpret eye and ear diagnostic procedures
5Differentiate conductive from sensorineural hearing loss

1The Eye

Outer layer: Sclera (white) + Cornea (transparent anterior)

Middle layer (uvea): Choroid (posterior), Ciliary body (controls lens shape), Iris (controls pupil size)

Inner layer: Retina (contains photoreceptors: rods for dim light, cones for color)

Structures:

Lens: Biconvex; focuses light onto retina (accommodation)

Vitreous humor: Gelatinous fluid filling posterior chamber

Aqueous humor: Fluid in anterior chamber; drains via Canal of Schlemm

Macula: Area of sharpest vision; fovea centralis at center

Optic disc (blind spot): Where optic nerve exits; no photoreceptors

Conjunctiva: Mucous membrane covering anterior sclera and inner eyelids

2Eye Diseases

Glaucoma: Increased intraocular pressure (IOP) → damages optic nerve → vision loss

Open-angle (most common): Gradual, painless peripheral vision loss

Angle-closure: Acute, painful, emergency

Cataracts: Clouding of the lens → blurry vision; treated with phacoemulsification and IOL implant

Age-Related Macular Degeneration (AMD): Deterioration of macula → loss of central vision

Dry (90%): Drusen deposits; slow progression

Wet (10%): Neovascularization; more severe

Diabetic Retinopathy: Microvascular damage from diabetes; leading cause of blindness in working-age adults

Conjunctivitis (Pink Eye): Viral (most common), bacterial, or allergic inflammation of conjunctiva

Strabismus: Misalignment of eyes; amblyopia (lazy eye) can develop if untreated in children

3The Ear

Outer Ear: Auricle/pinna → External auditory canal → Tympanic membrane (eardrum)

Middle Ear: Three ossicles (malleus, incus, stapes) amplify vibrations

Eustachian tube connects middle ear to nasopharynx (equalizes pressure)

Inner Ear:

Cochlea: Snail-shaped; contains organ of Corti (hair cells) → converts vibrations to nerve impulses → auditory nerve (CN VIII)

Vestibular system: Semicircular canals (rotation), otolith organs (gravity/linear movement) → balance

4Ear Diseases and Procedures

Otitis Media (OM): Middle ear infection; most common in children

Acute OM: Bacterial or viral; antibiotics vs watchful waiting

OM with Effusion ("glue ear"): Fluid without infection

Otosclerosis: Abnormal bone growth around stapes → conductive hearing loss; treated with stapedectomy

Ménière's Disease: Excess endolymph → episodic vertigo, tinnitus, fluctuating hearing loss

Hearing Loss Types:

Conductive: Problem in outer/middle ear (cerumen impaction, OM)

Sensorineural: Problem in cochlea or CN VIII (noise-induced, presbycusis, gentamicin toxicity)

Mixed: Both types

Myringotomy with tubes: Surgical incision in eardrum + PE tube insertion; treats recurrent OM

Audiometry: Tests hearing at different frequencies and intensities

Clinical Connections

►Diabetic retinopathy affects >7.7 million Americans and is the leading cause of new blindness in adults 20–74
►Newborns receive universal hearing screening before hospital discharge
►Presbycusis (age-related sensorineural hearing loss) affects 1 in 3 adults over 65

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L8: The Nervous System

L10: The Integumentary System