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Eye Anatomy

Orbit - ventral view

The eyes are essential for our daily experience, since about 70% of information we gather is by seeing. They are placed within the orbits, two cavities in the upper face, in the anterior surface of the head.

Besides the eyes, the orbits host several structures that support the eyeballs, including muscles, vessels, nerves and a gland. The orbits are specifically designed to allow these neurovascular structures to pass through its walls, from the cranium on their way to the face.

This page will discuss the anatomy of the eye and orbit.
 

Bones of the orbit

The bony orbit is made out of seven bones, which include the maxilla, zygomatic bone, frontal bone, ethmoid bone, lacrimal bone, sphenoid bone and palatine bone. The orbit appears as a pyramid, with its base opening anteriorly onto the face, while the apex is pointed posteromedially. The orbit hosts the eyeballs, extraocular muscles, optic nerve, lacrimal apparatus, fat tissue, fascia and vessels that supply these structures.

The walls of the orbit contain several fissures, openings and fossae which are important for housing the orbital structures, and for neurovascular communication of the orbital content with the central nervous system. Some of the most important openings are the superior orbital fissure and its downstairs neighbour, the inferior orbital fissure. More about them and all the other landmarks of the orbital bones can be found in the following article and quizzes.

Bones of the Orbit
Bones of the orbit
Superior and inferior orbital fissures

Eyelid anatomy

The eyelids are soft tissue structures that cover and protect the anterior surface of the eyeball. The anatomy of the eyelid may seem complex, but if we dissolve its multi-layered structure it is actually quite simple: 

  • Skin
  • Subcutaneous tissue
  • Muscle - orbital part of the orbicularis oculi muscle
  • Orbital septum - extensions of the periosteum from the orbital margin, that extends through both eyelids and supports them; 
  • Tarsus - plates of the dense connective tissue present in both eyelids. Superior tarsus is associated with muscles that raise the upper eyelid.
  • Conjunctiva - thin membrane that covers the posterior surface of the eyelid and reflects onto the anterior surface of the eyeball. 
Eyelids and tunica conjunctiva

Lacrimal gland

The lacrimal gland is a part of the lacrimal apparatus, which besides the gland consists of its numerous ducts, the lacrimal canaliculi, lacrimal sac and nasolacrimal duct. Everyone who has cried at least once, especially because of sleep deprivation that medical college brings, probably thinks that the lacrimal gland is placed in the medial part of the orbit since the tears run from there. But actually, the gland is placed in the lacrimal fossa at the upper part of the superior orbital wall, and its duct opens at the medial part of the orbit causing the tears to run down our nose when we think about how many anatomy pages we have left and it’s already 5 AM.

So, the function of the lacrimal gland is the production of tears, and it is regulated by the lacrimal nerve, a branch of the ophthalmic nerve (CN V1). Everything about the anatomy of the lacrimal gland and lacrimal apparatus can be found in these articles and quiz, we made them in a fun and approaching way, so we promise you won't cry: 

Lacrimal Gland
Lacrimal Apparatus
Lacrimal Apparatus

Eye muscles

There are two groups of eye muscles:

  • Extraocular muscles that move the eyeballs within the orbit
  • Intrinsic ocular muscles which are within the eyeball itself and control how the eyes accommodate

Six extraocular muscles move the eye: superior rectus, inferior rectus, medial rectus, lateral rectus, superior oblique and inferior oblique muscles; and one other, levator palpebrae superioris, opens the eyelid. 
 

Extraocular Muscles
Superior rectus Origin - superior part of common tendinous ring (anulus of Zinn)
Insertion - anterior half of eyeball superiorly
Innervation - oculomotor nerve (CN III)
Function - elevation, adduction, internal rotation of eyeball
Inferior rectus Origin - inferior part of common tendinous ring (anulus of Zinn)
Insertion - anterior half of eyeball inferiorly
Innervation - oculomotor nerve (CN III)
Function - depression, adduction, external rotation of eyeball
Medial rectus Origin - medial part of common tendinous ring (anulus of Zinn)
Insertion - anterior half of eyeball medially
Innervation - oculomotor nerve (CN III)
Function - adduction of eyeball
Lateral rectus Origin - lateral part of common tendinous ring (anulus of Zinn)
Insertion - anterior half of eyeball laterally
Innervation - abducens nerve (CN VI)
Function - abduction of eyeball
Superior oblique Origin - body of sphenoid bone
Insertion - superolateral aspect of eyeball (deep to rectus superior, via trochlea orbitae)
Innervation - trochlear nerve (CN IV)
Function - depression, abduction, internal rotation of eyeball
Inferior oblique Origin - orbital surface of maxilla
Insertion - inferolateral aspect of eyeball (deep to lateral rectus muscle)
Innervation - oculomotor nerve (CN III)
Function - elevation, abduction, external rotation of eyeball
Levator palpebrae superioris Origin - lesser wing of sphenoid bone
Insertion - anterior surface of tarsus, skin of upper eyelid
Innervation - oculomotor nerve (CN III)
Function - elevation of upper eyelid

Don’t understand how all these muscles work? You can find out everything about them in the following article and video tutorials:  

Extraocular muscles
Muscles of the orbit
Superior oblique muscle
Superior rectus muscle
Inferior oblique muscle
Inferior rectus muscle
Medial rectus muscle
Lateral rectus muscle

Eyeball

The eyeball is the main structure within the orbit because it enables us to see. Its importance reflects on its size, making it the largest structure in the orbit. It is something like a little camera inside our head, with all the necessary parts for capturing an image. It is round with an anteriorly convex bulge. The most superficial layer of the convexity is the cornea, which refracts and focuses the details of the image. Posterior to the cornea are the anterior chamber, lens, vitreous chamber and the retina.

You have probably noticed that there is something in the eye called ‘the lens’, which is also present inside our digital cameras. It has the same function as a digital lens, but in the eyeballs it helps in focusing the light onto the retina. Learn more about the lens anatomy with this great video tutorial and quiz:

Lens and corpus ciliare
Lens and corpus ciliare - posterior view

The wall of the eyeball is three-layered; with the sclera as the outer layer (continuous with the cornea), choroid as the middle vascular layer (continuous with the ciliary body and iris), and the retina as the innermost layer. You can study the anatomy of the eyeball in detail through these amazing articles, video tutorials and quiz:

Structure of the Eyeball
Eyeball
Retina I

Blood supply of the eye

The eye is supplied by branches of the ophthalmic artery: these are the short posterior ciliary, long posterior ciliary, anterior ciliary and the central retinal arteries. Venous blood is conveyed by the four vorticose veins that drain into the ophthalmic vein.

Read this article, watch a video tutorial and then quiz yourself about the blood vessels of the eye to learn this topic in a more fun way.
 

Blood Vessels and Nerves of the Eye
Blood vessels of the eyeball
Blood vessels of the eyeball

Nerves of the eye

The main function of the eye is sight, and the nerve that enables sight is the optic nerve (CN II). Nerves that innervate the extraocular muscles are called bulbomotors and they are the oculomotor (CN III), trochlear  (CN IV) and abducens (CN VI) nerves. The oculomotor nerve also innervates the intrinsic ocular muscles and thus regulates accommodation. The lower eyelid is innervated by the infraorbital nerve, a branch of the maxillary nerve (V3), that passes through the infraorbital foramen. The upper eyelid is supplied by the oculomotor nerve.
Take a look at these video tutorials in order to enhance your knowledge about the nerves of the eye:

Nerves of the orbit
Optic nerve
Oculomotor, trochlear and abducens nerves

Video tutorials for Eye Anatomy

Eyeball
Muscles of the orbit
Superior rectus muscle
Inferior rectus muscle
Medial rectus muscle
Lateral rectus muscle
Superior oblique muscle
Inferior oblique muscle
Lens and corpus ciliare
Blood vessels of the orbit
Blood vessels of the eyeball
Nerves of the orbit
Ophthalmic nerve
Optic nerve
Oculomotor, trochlear and abducens nerves

Eye Anatomy quizzes

Bones of the orbit
Superior and inferior orbital fissures

Muscles of the orbit
Blood vessels of the orbit
Nerves of the orbit
Optic nerve
Oculomotor, trochlear and abducens nerves
Eyeball
Lacrimal Apparatus
Eyelids and tunica conjunctiva
Lens and corpus ciliare - posterior view
Retina I

Eye Anatomy - want to learn more about it?

Our engaging videos, interactive quizzes, in-depth articles and HD atlas are here to get you top results faster.

Sign up for your free Kenhub account today and join over 1,029,446 successful anatomy students.

“I would honestly say that Kenhub cut my study time in half.” – Read more. Kim Bengochea Kim Bengochea, Regis University, Denver

Show references

Article, review and layout:

  • Jana Vaskovic
  • Nicola McLaren

Illustrators:

  • Orbit - ventral view - Johannes Reiß
© Unless stated otherwise, all content, including illustrations are exclusive property of Kenhub GmbH, and are protected by German and international copyright laws. All rights reserved.

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