Boundaries and Contents of the Orbit

(Legend: inn. - innervation)

Boundaries

• Below the anterior cranial fossa
• Anterior to the middle cranial fossa
• 4 walls (consisting of bones):
• roof (superior wall)
• medial wall
• lateral wall
• floor (inferior wall)

Contents

1. Eyeball
1. Eyelids:
   

   i. Skin, superficial fascia, thin layer of connective tissue, obicularis oculi

   ii. Orbicularis oculi: inn. facial nerve, closes eyelids

   1. palpebral part (in eyelids): medial palpebral ligament; lateral palpebral ligament

   2. orbital part: surrounds orbit

   3. lacrimal part: fibers on the medial border; attach to posterior lacrimal crest

   iii. Orbital septum: deep to palpebral part of orbicularis oculi; attaches to upper eyelid (levator palpebrae superioris) and lower eyelid (tarsus)

iv. Tarsal plates

1. large superior tarsus (upper eyelid)

2. smaller inferior tarsus (lower eyelid)

3. attaches to lateral palpebral ligament & medial palpebral ligament

4. tarsal glands: modified sebaceous glands; secrete oily substance that increase viscosity of tears and decrease rate of evaporation of tears from surface of eyeball

5. levator palpebrae superioris: raises eyelid; inserts into the anterior surface of superior tarsus; inn. oculomotor nerve

6. superior tarsal muscle: inferior surface of levator palpebrae superioris to upper edge of superior tarsus; inn. sympathetic fibres

2. conjuctiva: thin membrane covering posterior surface of each eyelid
3. glands: sebaceous & sweat glands associated with eyelash follicles
4. vessels
5. layers of the eyeball (e.g. sclera etc)
6. innervation:

i. sensory nerves: branches of trigeminal nerve

ii. motor nerves: facial nerve, oculomotor nerve, sympathetic fibers

2. Lacrimal apparatus: production, movement & drainage of fluid from surface of eyeball
1. Lacrimal gland & ducts

i. Position: anterior in the superolateral region of orbit

ii. Larger orbital part: in lacrimal fossa

iii. Smaller palebral part: inferior to levator palpebrae superioris

iv. Two parts are divided by levator palpebrae superioris

v. Ducts empty into lateral part of the superior fornix of conjunctiva (conjunctival sac)

2. Lacrimal lake: fluid then accumulates here
3. Lacrimal canaliculi: fluid drains into here (one canaliculus associated with each eyelid) via lacrimal punctum (opening)
4. Lacrimal sac: canaliculi join together to enter this sac
5. Nasolacrimal duct: each time you blink, lacrimal sac is compressed; fluid flows into this duct
6. Inferior meatus of nasal cavity: fluid ends up here
7. Innervation:

i. Sensory: lacrimal branch of ophthalmic nerve aka lacrimal nerve

ii. Parasympathetic: fibers joins the lacrimal nerve

iii. Sympathetic: follows similar path to parasympathetic except these fibers originate in the superior cervical ganglion; travel along the plexus surrounding the internal carotid artery

3. Innervations: Optic nerve (CN II), frontal nerve, lacrimal & nasociliary (V₁), oculomotor (III), Trochlear (IV), Abducent (VI), sympathetics and parasympathetics (ciliary ganglion)
4. Extraocular muscles
5. Adipose tissue and fascia
6. Specific nerves & vessels associated with each of these structures
1. Ophthalmic artery (10 branches)
2. 2 venous channels: superior & inferior ophthalmic veins