Structures in the Orbit and Eye

Arteries

Ophthalmic – main supply of blood to the orbital contents; off the internal carotid just prior to joining the Circle of Willis

Central artery of the retina – small branch off the ophthalmic a; arises inferior to the optic nerve, runs within the dural sheath; pierces the optic nerve and runs within it to emerge at the optic disc; spreads over the retina and supplies it

Ciliary – branches of the ophthalmic that supply the sclera, choroid, ciliary body, and iris

Veins

Superior ophthalmic – anastomoses with the facial vein; no valves, so blood can flow either way, crosses superior to the optic nerve and passes through the superior orbital fissure to end in the cavernous sinus

Inferior ophthalmic – begins as a plexus on the orbital floor and ends in either the superior ophthalmic vein or the cavernous sinus. Before ending, the inferior ophthalmic vein communicates with the pterygoid plexus through the inferior orbital fissure.

Cavernous sinus – large venous sinuses located on either side of the sella turcica; they drain into the superior and inferior petrosal sinuses, eventually ending up in the internal jugular vein (directly via the inferior petrosal, or via the sigmoid sinus from superior petrosal)

the central artery and vein, branches of the ophthalmic artery and vein, run within the optic nerve and cross the extension of the subarachnoid space around the optic nerve. Increased CSF pressure can occlude the vein and lead to Papilledema

Nerves

Supraorbital (CN V₁) – one of two branches of the frontal nerve V₁ , supplies the lateral part and front of the scalp.

External nasal (CN V₁) – supplies the tip of the nose

Mental (CN V₃) – continuation of the inferior alveolar nerve as it passes through the mental foramen (on outside of chin)

supplies sensory branches to skin of chin, mucus membrane and skin of lower lip, and the labial mandibular gingivae

Trochlear (CN IV) – supplies the superior oblique

Frontal (CN V₁) – a direct continuation of V₁, divides into two branches (supraorbital and supratrochlear)

Supratrochlear (CN V₁) – supplies the middle of the forehead, branch of the frontal nerve, V₁

Oculomotor (CN III) – passes into the lateral wall of the cavernous sinus, enters orbit through superior orbital fissure.

Superior division – supplies the leavator palpbrae and superior rectus

Inferior division – supplies the medial, inferior recti, and inferior oblique

Ciliary ganglion – CN III supplies a motor parasympathetic root to the ciliary ganglion.

Nasociliary (CN V₁) – a branch of the ophthalmic nerve in the superior orbital fissure, passing through the orbit, entering the cranial cavity through the anterior ethmoidal foramen, and then the nasal cavity, through the nasal fissure; its branches are the communicating branch to the ciliary ganglion, the long ciliary nerves, the infratrochlear, and nasal branches, supplying the mucous membrane of nose, the skin of the tip of the nose, and the conjunctiva

Abducens (CN VI) – supplies the lateral rectus

Long ciliary – one of two or three branches of the nasociliary nerve, supplying the ciliary muscles, iris, and cornea

Anterior ethmoidal (CN V₁) – branch of the nasociliary nerve

Optic (CN II) – special sensory nerve, slightly longer than distance it travels to allow for free movement of eyeball; fibers arise from the ganglion cells in the neuroepithelium of the optic retina and converge toward the optic disc, where they form the optic nerve. The optic nerve passes through the optic canal and join its partner at the Optic Chiasm. From the chiasm back to the lateral geniculate bodies of the thalamus, the nerve fibers are called the optic tracts.

Ciliary – post ganglionic fibers pass in the short ciliary nerves to sphincter pupillae and cililaris muscles

Bones

Maxilla – the skeleton of the face between the mouth and the eyes, two bones united at the midline

Infraorbital groove – transmits the infraorbital nerve and vessels, located ~1 cm inferior to the infraorbital margin

Zygomatic – paired bones that make up prominences of cheeks and anterolateral as well as infraorbital margins of orbits

Frontal – in fetal skulls the halves are divided by the metopic suture; forms the thin roof of the orbits

Lacrimal fossa – a hollow in the orbital plate of the frontal bone, formed by the overhanging margin and zygomatic process, lodging the lacrimal gland

Frontal sinus – an air sinus underneath the supraciliary arch; it communicates by the ethmoidal infundibulum with the middle meatus of the nasal cavity of the same side

Lacrimal – an irregular rectangular thin plate, forming part of the medial wall of the orbit behind the frontal process of the maxilla, articulates with the inferior nasal concha, ethmoid, frontal, and maxillary bones.

Ethmoid – irregularly shaped bone lying between orbital plates of the frontal and anterior to the sphenoid bone. It consists of 2 lateral masses of thin plates enclosing air cells, attached above to a perforated horizontal lamina (cribriform plate)

Anterior and Posterior ethmoidal cells – the enclosed air cells

Anterior and Posterior ethmoidal foramina – transmit vessels and nerves of the same name, in medial orbit

Lamina papyracea – the paper thin medial wall of the orbit

Sphenoid – wedge-shaped bone; the "keystone" of the skull; has a body, greater, and lesser wings

Optic canal – transmits the optic nerve and ophthalmic artery

Superior orbital fissure – transmits the ophthalmic veins, CN III, CN V₁, CN IV, CN VI, and sympathetic fibers; separates the lateral wall from the roof of the orbit

Inferior orbital fissure – transmits the maxillary nerve, separates the floor of the orbit from the lateral wall

Ligaments

Medial palpebal ligament – connects the eyelids and their muscles to the medial margin of the orbit

Anulus tendineus – a fibrous ring that surrounds the optic canal and the medial part of the superior orbital fissure; origin of the four rectus muscles of the eye; is partially fused with the sheath of the optic nerve

Ciliary processes – see Ciliary body below

Zonular fibers – fibers that pass from the equator of the lens to the ciliary body, collectively known as the zonula ciliaris

Membrane

Optic septum

Tarsus – a dense connective tissue band that strengthens the eyelid

Periorbita – the funnel-shaped fascial sheath that encloses the orbital contents; made of periosteum that lines the bones that contribute to the orbit

External (fibrous) coat

Sclera – the white, opaque posterior 5/6^ths of the external coat

Cornea – the transparent anterior 1/6^th of the external coat

Middle (vascular) coat – heavily pigmented vascular layer

Choroid – a dark brown membrane located between the sclera and the retina; firmly attached to the retina but can be stripped from the sclera; contains capillaries and venous plexuses that supply the adjacent layers of retina

Ciliary body – connects the choroid with the circumference of the iris, continuous posteriorly with the choroid

Iris – between the cornea and lens; a contractile diaphragm that regulates the amount of light entering the lens; eye color depends on the amount and distribution of pigment containing cells (chromatophores) in the iris

Internal (retinal) coat – thin delicate membrane, 2 layers: outer pigment layer and internal light sensitive neural layer

Optic papilla (disc) – where the optic nerve enters the eyeball, "blind spot"

Miscellaneous

Tarsal glands – located in both upper and lower eyelids; produce fatty secretions that keep eyelids from sticking together

Lacrimal sac – where tears are collected and sent to the nose via the nasolacrimal duct

Nasolacrimal duct – conducts tears from the lacrimal sac to the nose

Trochlea (of superior oblique) – located in the superior medial wall of the orbit, redirects the tendon of the superior oblique

Pupil – circular orifice in the center of the iris, through which the light rays enter the eye

Lens – transparent, flexible, biconvex structure enclosed in a transparent capsule; located posterior to the iris, avascular

Aqueous humor (anterior chamber) – clear watery fluid produced by the ciliary processes provides nutrients for the avascular cornea and lens

Vitreous humor (posterior chamber) – colorless, jelly-like substance fills the eyeball posterior to the lens, transmits light, holds the retina in place, and provides support for the lens; formed during embryonic period and not exchanged

Ora serrata – the wavy border of where the light sensitive neural layer ends at the posterior edge of the ciliary body

Muscles

Orbicularis oris – sphincter muscle of the eye, supplied by the zygomatic branch of the facial nerve (CN VII)

Frontalis – no bony attachments

Origin: skin above eyebrow

Insertion: on the epicranial aponeurosis;

Innervation: CN VII

Action: elevates the eyebrows, wrinkles forehead

Levator palpebrae –

Origin: roof of the orbit, anterior to the optic canal

Insertion: the skin of the upper eyelid

Action: elevates the upper eyelid

Innervation: CN III

Ciliary body – connects the choroid with the circumference of the iris

Ciliary processes – folds on the internal surface of the ciliary body that secrete aqueous humor

Ciliary muscles – on the external surface of the ciliary body, when contracted allows the lens to bulge

The rectus muscles – arise from the Common tendinous ring and attach to the eyeball posterior to the sclero-corneal junction

Superior rectus – CN III, elevates, adducts, and rotates medially

Lateral rectus – CN VI, abducts

Inferior rectus – CN III, depresses, adducts, and rotates laterally

Medial rectus – CN III, adducts

Superior oblique – CN IV, arises from the sphenoid bone, runs anteriorly between the superior and medial recti; runs through the Trochlea, which is attached on the superiomedial angle of the orbital wall, and inserts on the sclera at the posteriosuperior aspect of the lateral side of the orbit

Inferior oblique – CN III, a thin, narrow muscle that passes from the maxilla in the floor of the orbit, passing inferior to the inferior rectus, to insert on the posterioinferior aspect of the lateral side of the orbit

"formula" to remember the innervations, SO₄(LR₆)₃ (Superior oblique CN IV, Lateral rectus CN VI, all others CN III)