Orbital Anatomy (Answers)

When studying ophthalmology, it can be hard to know exactly what to spend time memorizing and what to ignore.  When I asked my senior residents for advice when studying, they provided the very unhelpful advice:  "learn everything."  Of course, it took a long while to realize that to some degree they were right - every detail we remember can be extremely helpful years down the road.  At the same time, to borrow from George Orwell, "all [ophthalmology information] is equal; but some are more equal than others."

For those people who prefer to study by answering questions, these articles will list questions you can use to guide your study.  Answers will be provided separately.  Where possible, I will try to provide a few real-world reasons for knowing this information.  For those who are interested in a book that is formatted in a very similar fashion, check out Tamesis' Ophthalmology Board Review: Pearls of Wisdom.

As a disclaimer, I am not intentionally copying questions directly from Tamesis or any other review resource, nor am I attempting to reproduce questions from the OKAP or Board exams - while there will most likely be many similar questions (since the whole point is to help remember all of the important aspects of ophthalmology), the organization, phrasing, and commentary are my personal take unless otherwise cited.

Orbital Anatomy (Answers - Spoiler Alert!)

Orbital Dimensions1


What is the volume of the orbit?30 mL

What is the height of the orbit?35 mm

What is the width of the orbit?40 mm

What is the depth of the orbit?40-45 mm

Where is the maximal orbital width located?~1 cm behind the anterior orbital margin

What is the intraorbital distance?25 mm

Orbital Bones1-2


What are the bones of the orbit?


  • Sphenoid
  • Ethmoid
  • Lacrimal
  • Frontal
  • Palatine
  • Maxilla
  • Zygomatic

What bone(s) comprise the superior orbital margin?Frontal

What bone(s) comprise the medial orbital margin?Frontal

What bone(s) comprise the inferior orbital margin?Maxilla

What bone(s) comprise the lateral orbital margin?Frontal

What bone(s) comprise the orbital roof?


  • Frontal
  • Sphenoid (lesser wing)

What bone(s) comprise the lateral orbital wall?


  • Sphenoid (greater wing)
  • Zygomatic

What bone(s) comprise the orbital floor?


  • Palatine
  • Maxilla
  • Zygomatic

What bone(s) comprise the medial orbital wall?


  • Sphenoid
  • Maxilla
  • Ethmoid
  • Lacrimal

What is the lamina papyracea?The "paper-thin" medial orbital wall

Orbital Fossas

FossaBone(s) Comprising FossaStructure(s) Contained Within Fossa

Lacrimal gland fossaFrontalLacrimal gland

Lacrimal (sac) fossaLacrimal
MaxillaLacrimal sac

Trochlear fossaFrontal*Trochlea

Hypophyseal fossaSphenoidPituitary gland

Pterygopalatine fossaPalatine
Sphenoid (greater wing)Pterygopalatine ganglion
Maxillary artery
Maxillary branch of trigeminal nerve (CN V2)

*The trochlea is located approximately 4 mm posterior to the orbital margin.

Orbital "Holes":  Foramina and Fissures

ForamenBones Containing ForamenStructures Passing Through Foramen

Optic foramenSphenoid (lesser wing)Optic nerve
Ophthalmic artery
Sympathetic fibers (from carotid plexus)

Supraorbital foramen/notchFrontalSupraorbital nerve (branch of frontal nerve [V1])
Supraorbital artery
Supraorbital vein

Anterior ethmoidal foramenFrontal
EthmoidAnterior ethmoidal nerve (branch of nasociliary nerve [V1])
Anterior ethmoidal artery
Anterior ethmoidal vein

Posterior ethmoidal foramenSphenoid
EthmoidPosterior ethmoidal nerve (branch of nasociliary nerve [V1])
Posterior ethmoidal artery
Posterior ethmoidal vein

Zygomatic foramenZygomaticZygomaticofacial nerve (branch of zygomatic nerve [V2])
Zygomaticotemporal nerve (branch of zygomatic nerve [V2])
Zygomatic artery (branch of middle temporal/superficial temporal artery [ECA])

Foramen rotundumSphenoid (greater wing)Maxillary branch of trigeminal nerve (V2)

Foramen ovaleSphenoid (greater wing)


  • Otic ganglion
  • Mandibular branch of trigeminal nerve (V3)
  • Accessory meningeal artery
  • Lesser petrosal nerve
  • Emissary veins from the cavernous sinus to the pterygoid plexus

There are two major orbital fissures that we need to know intimately.  Since many clinical applications are related to knowing these anatomical structures, this would probably be an important concept to master.

FissureBone(s) Surrounding FissureStructures Passing Through Fissure

Superior orbital fissureSphenoid bone (between greater and lesser wings)

Above/outside the annulus of Zinn:  "Elevated LFT'S":

  • Lacrimal nerve (V1)
  • Frontal nerve (V1)
  • Trochlear nerve (CN IV)
  • Superior ophthalmic vein

Within annulus of Zinn:

  • Oculomotor nerve (CN III) - both superior and inferior divisions
  • Nasociliary nerve (V1)
  • Abducens nerve (CN VI)
  • Sympathetic nerves (post-ganglionic fibers passing through ciliary ganglion)

Inferior orbital fissureSphenoid
MaxillaInfraorbital nerve (V2)
Zygomatic nerve (V2)
Orbital nerve (from pterygopalatine ganglion)
Inferior ophthalmic vein*

*Inferior ophthalmic vein will occasionally pass through the superior orbital fissure, below the annulus of Zinn.

Orbital "Holes":  Ducts and Canals

CanalBone(s) Containing The CanalStructure(s) Passing Through Canal

Nasolacrimal canalLacrimal
MaxillaNasolacrimal duct

Infraorbital canalMaxillaInfraorbital nerve (V2)
Infraorbital artery

Pterygoid canalSphenoid (medial pterygoid plate)(Vidian) nerve of the pterygoid canal
(Vidian) artery of the pterygoid canal
(Vidian) vein of the pterygoid canal


SinusBones That Border Sinus





*Frontal sinus is typically not present at birth (frontal bone is membranous), and usually does not develop until age 2.

 References, Resources, and Additional Reading

  1. Basic and Clinical Science Course, Section 2:  Fundamentals and Principles of Ophthalmology, 2010-2011 Edition.  American Academy of Ophthalmology.  San Francisco:  2010.
  2. Tamesis R, ed. Ophthalmology Board Review: Pearls of Wisdom, 2nd ed. McGraw-Hill, 2005.
  3. Foramen ovale (skull).  Wikipedia.  Online.

Did I miss any structures?  Do you have other questions you think should be added to this list?  Leave a comment!