The 7 bones of the orbit:
<ul>
 <li>Frontal</li>
 <li>Zygoma</li>
 <li>Maxillary</li>
 <li>Sphenoid</li>
 <li>Ethmoid</li>
 <li>Palatine</li>
 <li>Lacrimal</li>
</ul>
<ul>
 <li>Volume: 30ml</li>
 <li>There are no lymphatic vessels or nodes in the orbit</li>
 <ul>
 <li>Medial periocular tissues: drain to submandibular lymph nodes</li>
 <li>Lateral periocular tissues: drain to superficial preauricular nodes</li>
 </ul>
</ul>
<ClinicalCorrelate>A blow-out fracture most commonly affects the orbital floor postero-medially, often breaking the ethmoid bone medially too.</ClinicalCorrelate>
## Osteology
<ul>
 <li>Pear-shaped</li>
 <li>Supraorbital margin formed by frontal bone</li>
 <ul>
 <li>
 Supraorbital ridge only extends over the medial &frac12; to ⅔ of the superior orbital rim
 </li>
 </ul>
 <li>Infraorbital margin formed by zygomatic and maxilla</li>
 <li>Lateral margin formed by frontal and zygomatic</li>
 <li>
 Medial margin formed by maxillary process of frontal and lacrimal crest of the frontal process
 of maxilla
 </li>
 <li>Roof: frontal and lesser wing of sphenoid</li>
 <li>Floor: zygomatic, maxilla, palatine</li>
 <li>Lateral wall (thickest): zygomatic, greater wing of sphenoid</li>
 <li>Medial wall: frontal process of maxilla, lacrimal, ethmoid, body of sphenoid</li>
 <ul>
 <li>The lamina papyracea of the ethmoid bone is the weakest part of the orbit</li>
 </ul>
</ul>
## Relations
<ul>
 <li>Nasal cavity, ethmoid air cells and sphenoid sinus medially</li>
 <li>Frontal air sinus, meninges and frontal lobe superiorly</li>
 <li>Maxillary air sinus inferiorly</li>
 <li>Temporalis muscle, middle cranial fossa and temporal lobe laterally</li>
</ul>
## Openings
Optic canal
<ul>
 <li>Optic canal within the lesser wing of the sphenoid only</li>
 <li>4-10mm long</li>
 <li>Connects to middle cranial fossa</li>
 <li>Contains optic nerve and ophthalmic artery (with surrounding sympathetic plexus)</li>
</ul>
Superior orbital fissure
<ul>
 <li>Superior orbital fissure lies between the greater and lesser wings of sphenoid</li>
 <li>Also connects to middle cranial fossa</li>
 <li>
 Common tendinous ring (formed by thickening of periorbita) overlies the medial end of the
 superior orbital fissure, attached to
 </li>
 <ul>
 <li>Lesser wing of sphenoid</li>
 <li>Greater wing of sphenoid</li>
 <li>Orbital plate of ethmoid</li>
 </ul>
 <li>
 SOF outside ring: lacrimal, frontal and trochlear nerves and superior ophthalmic vein. Inferior
 ophthalmic vein passes below ring (also outside)
 </li>
</ul>
<ClinicalCorrelate>The 4th cranial nerve (trochlear) is therefore not affected by retrobulbar anaesthesia leaving some intorsion possible.</ClinicalCorrelate>
<ul>
 <li>SOF within ring: both branches of oculomotor nerve, nasociliary and abducens nerves</li>
</ul>
Refresher note: the nasociliary, frontal and lacrimal nerves are the three branches of the first (ophthalmic) division of the trigeminal nerve

Inferior orbital fissure
<ul>
 <li>Inferior orbital fissure lies between greater wing of sphenoid and maxilla</li>
 <ul>
 <li>Connects to</li>
 <ul>
 <li>Pterygopalatine fossa</li>
 <li>Infratemporal fossa</li>
 </ul>
 <li>Contains</li>
 <ul>
 <li>Maxillary nerve which becomes infraorbital nerve on entering the orbit</li>
 <li>Zygomatic nerve (also a branch of V2)&nbsp;</li>
 <li>Inferior ophthalmic vein draining to pterygoid plexus</li>
 <li>Infraorbital artery and vein</li>
 <li>Branches of the pterygopalatine ganglion</li>
 </ul>
 <li>Covered by vestigial muscle of Muller (function unknown)</li>
 </ul>
</ul>
Ethmoidal foramina
<ul>
 <li>Found where the roof joins the medial wall</li>
 <ul>
 <li>Anterior ethmoid foramen at the junction of the frontal and ethmoid bones&nbsp;</li>
 <ul>
 <li>Connects to anterior cranial fossa&nbsp;</li>
 <li>Contains the anterior ethmoidal nerve and artery</li>
 </ul>
 <li>Posterior foramina</li>
 <ul>
 <li>Contains the posterior ethmoidal nerve and artery supplying ethmoidal sinuses</li>
 </ul>
 </ul>
</ul>
## Lateral tubercle of Whitnall
<ul>
 <li>Insertions of:</li>
 <ul>
 <li>Check ligament of eyeball</li>
 <li>Suspensory ligament of eyeball</li>
 <li>Lateral canthal tendon</li>
 <li>Aponeurosis of levator</li>
 </ul>
</ul>
## Suspensory ligament (of Lockwood)
<ul>
 <li>Thickening of the inferior part of the fascial sheath of the eyeball (Tenon&rsquo;s)</li>
 <li>Receives fascial contributions from the inferior rectus and oblique muscles</li>
 <li>Attached medially to the lacrimal bone</li>
 <li>Attached laterally to the zygomatic bone (at the tubercle of Whitnall)</li>
</ul>

<HotTopic>There are no lymphatics in the orbit! Lymphatics from the conjunctivae and lids drain medially the submandibular glands and laterally to the superficial preauricular nodes.</HotTopic>

Orbit and ocular adnexae

Orbit

Intro

FRCOphth Part 1 Study Notes

Extraocular Muscles

Orbital Blood Vessels

Paranasal Sinuses

Lacrimal Glands

Tear Film

Eyelids

Blinking

Anterior segment - ocular surface

Conjunctiva

Conjunctivitis

Sclera

Cornea

Corneal Structure And Development

Corneal Physiology

AC to Lens

Angle

Ciliary Body

Aqueous Humour Dynamics

Iris

Pupil

Lens

Posterior segment

Choroid

Vitreous

Retinal Macrostructure

Neurosensory Retina

Retinal Pigment Epithelium

Neuroanatomy

Venous Sinuses

Cerebral Ventricles

Cerebral Blood Supply

Supranuclear Gaze Pathways

Head And Neck Autonomic Nervous Supply

Head And Neck Glands

Osteology

Nerves

Muscles And Pharyngeal Arches

Extraocular Nerves

Sensory Nerves

Physiology

Physics Of Blood Flow

Neuronal Control Of Blood Vessels

Oxygen-Haemoglobin Dissociation Curve

Cytochrome p450

Pituitary Gland

Thyroid Hormone Production

Insulin

Glucagon

Parathyroid Hormone

Corticosteroids

Catecholamines

Cardiac Cycle

Renal Physiology

Fluid Balance

Acid-Base Balance

Muscle Physiology

Sensory Fibres

Cutaneous Receptors

Endocytosis

Glycosaminoglycans

Condensed Ocular Biochemistry

Eye Movements

Accomodation

Vision

Visual Cycle And Phototransuction

Visual Pathway

Visual Acuity

Colour Vision

Binocular Vision

Pathology

Collagen

Tissue Damage

Inflammation

Disease Entities

Wound Healing

Thrombosis / Atherosclerosis

Cell Growth

Neoplasia

Histopathology

Nystagmus

Free Radicals And Antioxidants

Immunology

Ocular Immunology

Microbiology

Viral Infections

Bacterial Infections

Fungal Infections

Protozoa

Nematodes

Antimicrobials

Genetics

Chromosomes

Mitosis

Meiosis

Genes

Polypeptide Synthesis

Histones

MicroRNA

Hardy-Weinberg Equilibrium

Mutations

Chromosome Defects

Autosomal Inheritance

X-Linked Inheritance

Mitochondrial Inheritance

Multifactorial Inheritance