The orbit and ear

What are the borders of the bony orbit?

Roof: frontal bone and lesser wing of the sphenoid;

Floor: maxilla, palatine, and zygomatic bones; Medial wall: ethmoid, maxilla, lacrimal, and sphenoid bones; Lateral wall: zygomatic bone and greater wing of the sphenoid.

Optic canal - optic nerve

What is the periorbita?

A dense connective tissue membrane that covers the bones forming the orbit, thickening around the optic canal and superior orbital fissure to form the common tendinous ring.(fibrous tissue surrounding the optic nerve

and common origin of the four recti

muscles)

What structures are primarily contained within the bony orbit?

Mainly the eyeballs and their associated structures:

▪ Eyelids - cover the orbits anteriorly

▪ Muscles and Neurovascular structures

▪ Orbital fat - cushions the eye, and stabilises the extraocular

muscles

What is the function of the eyelids?

To cover and protect the anterior surface of the eyeball, keep moisture in, and help lubricate the surface of the eyes.

What are the layers of the eyelids?

Skin and subcutaneous tissue, orbicularis oculi, orbital septum, tarsal plates & levator apparatus, and conjunctiva.

What is the role of the lacrimal apparatus?

Involved in the production,

movement and drainage of fluid

from the surface of the eyeball

▪ Lacrimal glands secrete lacrimal

fluids

▪ Lacrimal fluid cleans, nourishes

and lubricates the eyes, it forms

tears when produced in excess

What is the origin and attachment and action of the levator palpebrae superioris?

Originates from the lesser wing of the sphenoid bone anterior to the optic canal and attaches to the superior tarsal plate of the upper eyelid.

Actions: Elevates the upper eyelid

What are the extra-ocular muscles?

Muscles that control eye movement, including recti muscles that originate from the common tendinous ring and oblique muscles that have an angular approach to the eyeball.

Recti Muscles

Originate from the common tendinous

ring and attach to the anterior half of the

eyeball

▪ Have a direct path from origin to

attachment

Oblique Muscles

Origin: Superior oblique (body of

sphenoid) and Inferior oblique (medial

floor of orbit posterior to rim and maxilla)

▪ Insertion: Outer posterior quadrant of the

eyeball

▪ Take an angular approach to the eyeball

What is the blood supply to the extra-ocular muscles?

Branches of the ophthalmic artery.

What is the venous drainage of the extra-ocular muscles?

Superior and inferior ophthalmic veins.

The Eyeball

Fascial sheath (Tenon's capsule)

▪ Thin layer of fascia enclosing a major part

of the eyeball

▪ Attached to the sclera, around the point it

fuses with the meninges that wrap the

optic nerve posteriorly to the corneosclera junction anteriorly.

▪ Pierced by extraocular muscles before

their insertion into the eyeball

✷Suspensory ligament - maintains and

supports the position of the eyeball in its

normal upward and forward position

within the orbit, and prevents downward

displacemen

What is the function of Tenon's capsule?

A thin layer of fascia enclosing a major part of the eyeball, providing support and maintaining its position.

What are the layers of the eyeball?

Fibrous layer (sclera and cornea), vascular layer (choroid, ciliary body, iris), and inner layer (retina).

What is the function of the sclera?

An opaque layer of dense connective tissue that provides shape to the eye and attachment for extraocular muscles.

What is the role of the cornea?

A transparent structure that refracts light entering the eye.

What is the function of the choroid?

A thin, highly vascular layer that provides nourishment to the outer layers of the retina.

What does the ciliary body do?

Controls the shape of the lens and contributes to the formation of aqueous humor.

Ciliary muscle - a collection of smooth

muscles fibres attached to the lens of the

eye by the ciliary processes; contraction

pulls the ciliary body anteriorly, loosens

of the zonular fibers of the lens (lens

shrinks and become more convex)

➢ Ciliary processes - attaching sites of the

zonular fibres of the lens

What are the functions of the iris?

A circular structure that controls the diameter of the pupil and regulates the amount of light entering the eye.

The aperture in the centre = pupil - its diameter is altered by

smooth muscle fibres within the iris

➢ Sphincter pupillae muscle - constricts the pupillary opening

➢ Dilator pupillae muscle - dilates the pupillary opening

Layers of the Eyeball : Inner / Retina

Extends from the site of exit of the optic

nerve to the posterior margin of the

ciliary body

What is the macula lutea?

The area at the center of the posterior retinal layer that contains the highest concentration of photoreceptor cells for clear vision.

What is the optic disc?

The site where the optic nerve exits the eye, known as the blind spot because it contains no photoreceptor cells.

Anterir and posteriror chambers of eye ball?

Anterior Chamber - between the cornea

and the iris

▪ Posterior Chamber - between the iris and

ciliary processes

What are the chambers of the eye filled with?

✷Both filled with aqueous humour - a clear

plasma-like fluid that nourishes and

protects the eye; secreted into the posterior

chamber, flows into anterior chamber via

the pupil and is absorbed into scleral venous

sinus (canal of Schlemm) at the junction

between the cornea and iris

What is the vitreous body?

A transparent gelatinous substance which

fills the posterior segment of the eyeball

(between the lens and retina)

✷ Cannot be replaced

▪ Three main functions:

➢ Contributes to the magnifying power

of the eye

➢ Supports the lens

➢ Holds the layers of the retina in place

Where does the eyey ball recieve blood?

Receives blood primarily via the ophthalmic artery

• Venous drainage primarily carried out by the superior

and inferior ophthalmic veins & central retinal vein

What are the components of the external ear?

Functionally and structurally divided into: Auricle (or pinna) &

External acoustic meatus

• Auricle - cartilaginous; captures and direct sound waves towards