Eye and Ear Microscopic Anatomy

What are the accessory structures of the eye and their main functions?

Eyebrows, eyelashes, eyelids → Block debris

Lacrimal glands → Moisten, clean, lubricate

Conjunctiva → Protective mucous membrane

Know this picture!

What is conjunctiva?

A specialized stratified columnar epithelium with goblet cells that lines the eye and eyelids

What are the two regions of the conjunctiva?

Ocular conjunctiva – covers sclera

Palpebral conjunctiva – lines eyelids

What is this?

Conjunctiva

Do the conjunctiva cover the cornea?

NO!

What are tarsal (Meibomian) glands?

Sebaceous glands in the eyelids that prevent tear evaporation and lubricate the ocular surface

What is the lacrimal apparatus responsible for?

Producing, collecting, and draining tears

• Reduce friction

• Continually cleanses and moistens

Contains lysozyme

What epithelium lines the lacrimal drainage system?

Canaliculus: stratified squamous

Lacrimal sac: pseudostratified ciliated

What is the flow of lacrimal fluid?

Lacrimal glands → Across eye → Lacrimal puncta → Lacrimal caruncle → Lacrimal canaliculi → Lacrimal sac → Nasolacrimal duct → Nasal cavity

What are the three layers of the eye wall?

Fibrous tunic → Sclera and cornea

Vascular tunic → Choroid, ciliary body, iris

Retina → Pigmented layer, neural layer

• Communities with cerebrum through optic n. (CN 2)

What are the two cavities of the eye?

Anterior cavity → Aqueous humor

Posterior cavity → Vitreous humor

• Includes the lens

What is the hyaloid canal?

Remnant of the embryonic hyaloid artery in the vitreous

What is the sclera composed of?

Dense irregular CT

• Provide shape and protection

What is the corneoscleral junction?

The limbus

• Where cornea merges with sclera

Most common site for melanoma

What is the relationship between the cornea and sclera?

Cornea → Most anterior portion of the eye

Sclera → Superficial posterior layer of the eye; The “white” of the eye

What are the components of the vascular tunic?

Choroid

Ciliary body

iris

What can be found in the vascular tunic?

Extensive array of blood vessels

Lymphatics

Intrinsic muscles of the eye

What is the function of the choroid?

Provides nutrients/oxygen to retina

Melanin absorbs stray light (melanocytes)

What are the two layers of the choroid?

Choroidocapillary lamina — Microvasculature provides nutrition for rental layers

Bruch’s membrane — Basal complex made of elastin and collagen fibers (collagen - elastin - collagen)

What is the function of the ciliary body?

Ciliary muscle → Lens accommodation

• Circular bands of smooth muscle

Ciliary processes → Secrete aqueous humor

• Folds of epithelium that line the muscle

Ciliary zonule → Suspensory ligaments extend from the ciliary body to the lends

What muscles control pupil size?

Sphincter pupillae → Constriction

Dilator pupillae → Dilation

What are the two layers of the retina?

Pigmented layer

Neural layer

What is the function of the pigmented layer?

Provide vitamin A

Transport nutrients

Remove waste

What is the fovea centralis?

Pit in the macula lutea with highest cone density → Sharpest vision

Light focus area for vision

What does the iris regulate?

The amount of light that enters the eye

List the five layers of the cornea (superficial → deep)

1. Corneal epithelium – non‑keratinized stratified squamous

2. Bowman membrane

3. thick (corneal) stroma – collagen + proteoglycans

4. Descemet membrane

5. Corneal endothelium – simple squamous

Which layer of the cornea maintains corneal transparency?

Stroma (regular collagen attachment)

What is this?

Five layers of the cornea

What is this?

Five layers of the cornea

What is this?

Layers of the vascular tunic

What histologic features identify conjunctiva?

Stratified columnar epithelium

Goblet cells

Highly vascular

What is the iris?

Colored portion of the eye

Center of iris → Pupil

What is this?

Iris

• PE - Posterior pigment epithelium

• DPM - Dilator pupillae muscle

• SPM - Sphincter pupillae muscle

What are the principal components of the lens?

Lens capsule

Lens epithelium — Simple cuboidal epithelium

Lens fibers

What is the ora serrata?

The junction between the retina and the ciliary body

What are the two photoreceptors?

Rods → Contrast dark and light tones

Cones → Color (Red, Green, Blue)

Where is the macula lutea located?

Lateral to the optic disc

What separates the two cavities of the eye?

The lens

What structures make up the external ear?

Auricle

External acoustic meatus

Tympanic membrane

What do ceruminous glands produce?

Cerumen (ear wax)

What are the boundaries of the middle ear?

Lateral: tympanic membrane

Medial: oval & round windows

Inferior tube leads to the nasopharynx via the eustachian tube

What epithelium lines the middle ear?

Non‑keratinized stratified squamous epithelium

What are the auditory ossicles?

Malleus

Incus

Stapes

What is the function of the ossicles?

Amplify sounds waves to the oval window

What muscles protect the ear from loud sounds?

Stapedius

Tensor tympani

What is the bony labryinth?

Cavities in temporal bone housing membranous labyrinth

What are the two major functional divisions of the inner ear?

Vestibular complex – balance

Cochlea – hearing

What do semicircular canals detect?

Positional changes of the head (X, Y, Z planes)

What nerve carries vestibular and auditory signals in the inner ear?

CN VIII (Vestibulocochlear nerve)

What can be found within the middle ear?

Tympanic cavity

Auditory ossicles

How much larger is the tympanic membrane compared to the oval window?

20x larger