EYE

• The eyes are essential for our daily experience, as about 70% of information we gather is by seeing.
• The eyes are located in the orbits, two cavities in the upper face, on the anterior surface of the head.
• The orbits host several structures that support the eyeballs, including muscles, vessels, nerves and a gland.
• The orbits are designed to allow these neurovascular structures to pass through its walls, from the cranium on their way to the face.
• The orbit anatomy includes the bones of the orbit, the eyelid anatomy, the lacrimal gland anatomy, the eye muscles, the eyeball, the blood supply of the eye, and the nerves of the eye.
• The eyelids are soft tissue structures that cover and protect the anterior surface of the eyeball.
• The conjunctiva is a thin membrane that covers the posterior surface of the eyelid and reflects onto the anterior surface of the eyeball.
• The bony orbit is made out of seven bones: maxilla, zygomatic bone, frontal bone, ethmoid bone, lacrimal bone, sphenoid bone and palatine bone.
• 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.
• The superior orbital fissure and its downstairs neighbour, the inferior orbital fissure, are two of the most important openings in the orbit.
• 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.
• The superior tarsus is associated with muscles that raise the upper eyelid.
• 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.
• 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.
• The orbit appears as a pyramid, with its base opening anteriorly onto the face, while the apex is pointed posteromedially.
• The orbit is a bony cavity within the skull that houses the eye and its associated structures such as muscles of the eye, eyelid, periorbital fat, lacrimal apparatus.
• The orbit hosts the eyeballs, extraocular muscles, optic nerve, lacrimal apparatus, fat tissue, fascia and vessels that supply these structures.
• The lacrimal gland is located 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 tears to run down our nose when we think about how many anatomy pages we have left and it’s already 5 AM.
• The function of the lacrimal gland is the production of tears, which is regulated by the lacrimal nerve, a branch of the ophthalmic nerve (CN V1).
• The inferior oblique muscle originates from the orbital surface of the maxilla and inserts at the inferolateral aspect of the eyeball (deep to lateral rectus muscle), it is innervated by the oculomotor nerve (CN III) and its function is elevation, abduction, and external rotation of the eyeball.
• The lateral rectus muscle originates from the lateral part of the common tendinous ring (anulus of Zinn) and inserts at the anterior half of the eyeball laterally, it is innervated by the abducens nerve (CN VI) and its function is abduction of the eyeball.
• The anatomy of the lacrimal gland and lacrimal apparatus can be found in these learning materials, which were made in a fun and approachable way, so we promise you won't cry: Eyelids and lacrimal apparatus Explore study unit 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, le
• The levator palpebrae superioris muscle originates from the lesser wing of the sphenoid bone and inserts at the anterior surface of the tarsus, skin of the upper eyelid, it is innervated by the oculomotor nerve (CN III) and its function is elevation of the upper eyelid.
• The superior oblique muscle originates from the body of the sphenoid bone and inserts at the superolateral aspect of the eyeball (deep to rectus superior, via trochlea orbitae), it is innervated by the trochlear nerve (CN IV) and its function is depression, abduction, and internal rotation of the eyeball.
• The medial rectus muscle originates from the medial part of the common tendinous ring (anulus of Zinn) and inserts at the anterior half of the eyeball medially, it is innervated by the oculomotor nerve (CN III) and its function is adduction of the eyeball.
• The inferior rectus muscle originates from the inferior part of the common tendinous ring (anulus of Zinn) and inserts at the anterior half of the eyeball inferiorly, it is innervated by the oculomotor nerve (CN III) and its function is depression, adduction, and external rotation of the eyeball.
• The superior rectus muscle originates from the superior part of the common tendinous ring (anulus of Zinn) and inserts at the anterior half of the eyeball superiorly, it is innervated by the oculomotor nerve (CN III) and its function is elevation, adduction, and internal rotation of the eyeball.
• Venous blood is conveyed by the four vorticose veins that drain into the ophthalmic vein.
• The choroid is a pigmented layer of connective tissue and blood vessels located between the sclera and the retina, providing the other layers of the eyeball with oxygen and nutrients.
• The sclera is the tough opaque wall component of the outer layer covering the posterior five sixths of the eyeball and acts as an attachment site for extrinsic and intrinsic muscles of the eye.
• The middle (a.k.a vascular) layer of the eyeball houses the blood vessels of the eye and consists of the choroid, ciliary body and iris.
• The outer dilator pupillae muscle is radially arranged and enables the increase of the pupil diameter (dilating the pupil) via sympathetic innervation.
• The pigmented layer of the optic part of the retina is composed of a single layer of cells, attached to the choroid and strengthens the light-absorbing properties of the choroid while minimizing the scattering of surplus light in the eyeball.
• The final part of the middle layer is the iris, a pigmented circular contractile structure with a central aperture, responsible for transmitting light.
• The lens of the eye is attached to the ciliary body and contraction and relaxation of the ciliary smooth muscle will modify the lens’s thickness and focus.
• The outer (a.k.a fibrous) layer of the eyeball gives the eyeball its shape and provides resistance.
• The inner layer of the eye is formed by the retina, the eye’s light detecting component and the intraoptic part of optic nerve (cranial nerve II).
• The neural layer of the optic part of the retina contains photoreceptors responsible for detecting visual light rays.
• The lens, located in the eye, has the same function as a digital lens and helps in focusing the light onto the retina.
• The other component of the ciliary body, the ciliary processes, contributes to the formation and secretion of aqueous humor.