The orbit & adnexa

What is the bony orbit ?

A protective ( pyramid shaped ) space within the skull which contains the eyeball, eye muscles, nerved and blood vessels.

How many bones make up the bony orbit ?

7

Name the bones in the bony orbit:

• frontal

• Sphenoid

• Lacrimal

• Ethmoid

• Maxilla

• Zygomatic

• Palatine

What is the ocular adnexa ?

They are the supporting and protective structures that are attached to the eyeball.

This includes:

• eyelids

• Eyelashes

• Lacrimal drainage system

The function is to protect the eye and to keep the cornea moist and clean.

The bony orbit has four walls. Name them:

• medial

• Lateral

• Floor

• Roof

Describe the structure and function of the orbital roof:

Structure:

• thin and fragile ( some parts can be absorbed in old age due to osteoporosis)

• Composed of the frontal bone

• Composed of the lesser wing of sphenoid.

Function: separates the eyeball from the frontal lobe

What are the greater and lesser wings of sphenoid and what is the difference between them ?

• they are two pairs of wings that extend from the spheniod bone.

Lesser wings= smaller, part of the roof

Greater wings= larger part of lateral wall

Describe the structure and function of the orbital floor:

Structure:

• Weakest wall ( prone to a blow out fracture)

• Composed of the maxilla, zygomatic and palatine bone

Function:

• Supports eyeball

• The inferior oblique muscle originates from the orbital floor, its crucial for eye movement.

Describe the structure and function of the medial wall:

Structure:

• Largely composed of the ethmoid bone

• Maxilla

• Sphenoid

• composed of lacrimal bone*

* smallest bone of face, located in the medial wall of each eye orbit. Contains lacrimal sac, for tears.

Describe the structure and function of the lateral wall:

Structure:

• thickest wall

• Composed of zygomatic bone

• Composed of greater wing of sphenoid

Function:

• strongest of the four orbital wall, which protects eye from external forces

• wall contains Whitnall’s tubercle which serves as an attachment site for ligaments such as the lateral recuts muscle.

What are the openings of the orbit ?

There are 6 openings which allow the passage of nerves and blood vessels to come to and from the orbit.

Name the 6 openings in the orbit:

1) optic canal

2) Superior orbital fissure

3) Inferior orbital fissure

4) Ethmoidal foremen

5) Zygomaticfacial & zygomatictemporal

6) Nasolacrimal canal

What structures are found in the orbital space ?

• muscles ( 6 extraocular & levator palpebrae superiosis)

• Nerves ( CN 2,3,4,6)

• Vessels ( ophthalmic artery and vein)

• Lacrimal system ( gland, ducts, sac)

• Connective tissues ( orbital septum and tendons capsule)

What is the ocular adnexa ?

The structures that surround and support the eye.

This includes the eyelids and lacrimal system.

Describe the eyelids and its function:

• fold of skin that covers the globe.

• Shields eye from injury

• Sustains the tear film

• Supplies oxygen to the cornea when lid is closed.

• Eyelid is also known as the palpebral fissure.

What is epicanthal folds ?

• Fold of skin at the medial/ nasal side of a persons eye.

What is lagophthalmos ?

• when the eyelid doesn’t close properly during sleep

• Can lead to eyes becoming dry

• Can cause epithelial damage of cornea and cause a loss of transparency

How many eyelid muscles are there ? And name them all:

• 4 muscles

• Orbicualris oculi

• Levator palpebral superiosis

• Mullers muscle

• Tarsal plate muscle

Describe the orbicularis oculi:

• it is an eyelid muscle

• Attached nasally and laterally by ligaments

• Causes the eyelid to close

Theres two main divisions:

Orbital part- causes the eyelid to tightly close ( force-full blinking)

Palpebral part- gently closes the eyelid ( normal blinking)

Innervated by cranial nerve 7 ( facial nerve)

Describe the levator palpebrae superiosis:

• eyelid muscle

• Causes the upper eyelid to retract and be raised.

• Innervated by cranial nerve 3 ( oculomotor nerve) * damage to CN3 - causes the upper eyelid to droop.

Describe Muller’s muscle:

• eyelid muscle

• Assists the levator palpebrae superiosis in keeping the upper eyelid elevated.

• Innervated by the sympathetic nervous system.

Describe the tarsal plate muscle:

• eyelid muscle

• Provides rigidity and structure to the lids

• Secretes lipid layer of tears- which prevents tears from evaporating.

• This is important during eyelid eversion

Describe the tarsal gland ( meibomian):

• embedded inside the tarsal plate of both the upper and lower eyelids

• Secretes lipids

• To prevent the tears from evaporating too quickly.

What are the glands of Zeis

• located near the eyelash hair follicles

• Secrets sebum ( oil) to keep the eyelashes from becoming dry and brittle.

Way to remember* - Z ( zobia)= hair follicles

Describe the glands of Moll:

• Located near the eyelash follicles

• Acts as a sweat gland by producing sweat to help the tear film.

Describe the conjunctiva:

• thin, transparent mucous membrane that keeps the eye moist and protected from microorganisms

• at the medial edge there is a condensed bit of tissue called the caruncle.

• there are three main sections to the conjunctiva:

• Palpebral conjunctiva- this lines the inner surface of the eyelids

• Bulbar conjunctiva- covers the scalera of eyeball

• Fornix- the fold where the eyelid and eyeball meet ( acts like a junction)

Describe the tear film and its 3 layers:

• covers the anterior surface of the eye

• Outermost layer = lipid layer

• Inner layer= aqueous layer

• Innermost layer= mucous layer

Lipid layer

• contains cholesterol and fatty acids- prevents the evaporation of tears. Keeps the tear surface smooth by providing lubrication for eyelid movement

Aqueous layer

• thickest layer- provides nutrients such as salts, glucose and proteins to cornea.

Mucous layer

• allows the tear film to stick to the corneal surface

Describe the lacrimal drainage system:

• the lacrimal glands which is situated above the eyelid produces tears

• The tears get drained from the upper and lower puncta.

• The upper canaliculi merge to form the common canaliculus and tears move through that passage.

• The valve of Hasner is at the beginning of the canaliculus and prevents the back flow of tears towards the eye.

• The tears then move to the lacrimal sac which is compressed when blinking.

• Tears are then drawn into the lacrimal apparatus as the sac re-expands ( lacrimal pump)

• The nasolacrimal duct connects the lower end of the lacrimal sac with inferior meatus.

• Another valve guards the opening and prevents air from entering the sac during blowing of the nose.