Anatomy And Embryology Of The Eye And Ocular Adnexa Dr. Abdullah Al-Amri Ophthalmology Consultant

Contents Anatomy of The Bony Orbit Anatomy of Ocular Adnexa. Anatomy of The Eye. Embryology.

Orbital anatomy Seven bones make up the bony orbit : Frontal Zygomatic Maxilla (or maxillary bone) Ethmoid (or ethmoidal bone) Sphenoid Lacrimal Palatine

Orbital roof

Medial orbital wall

Orbital floor

Lateral orbital wall

Optic foramen and superior ophthalmic fissure

Periorbital Sinuses The periorbital sinuses have a close anatomical relationship with the orbits. The periorbital sinuses offer a route for the spread of infection. Mucoceles occasionally arise from the sinuses and can extend into the adjacent orbit.

Extraocular Muscles There are 7 extraocular muscles: Medial rectus Lateral rectus Superior rectus Inferior rectus Superior oblique Inferior oblique Levator palpebrae superioris

Origin and insertion

Eye lid The palpebral fissure is the exposed zone between the upper and lower eyelids. The upper eyelid is more mobile than the lower and can be raised I5 mm by the action of the levator muscle alone. The levator muscle is innervated by CN Ill.

Conjunctiva The palpebral conjunctiva is a transparent vascularized membrane covered by a nonkeratinized epithelium that lines the inner surface of the eyelids. Continuous with the conjunctival fornices it merges with the bulbar conjunctiva before terminating at the limbus.

The conjunctiva consists of bulbar (red), forniceal (black), and palpebral (blue) portions.

Vascular Supply of the Eyelids The blood supply of the eyelids is derived from the facial system, which arises from the external carotid artery, and the orbital system, which originates from the internal carotid artery.

The venous drainage of the eyelids can be divided into 2 portions: Superficial system which drains into the internal and external jugular veins. Deep system which flows into the cavernous sinus.

Lymphatics of the Eyelids Lymphatic vessels are found in the eyelids and conjunctiva, but neither lymphatic vessels nor nodes are present in the orbit. Swelling of the lymph nodes is a diagnostic sign of several external eye infections.

Lacrimal Gland and Excretory System The main lacrimal gland is located in a shallow depression within the orbital part of the frontal bone. The gland is divided into 2 parts. When the upper eyelid is everted, the smaller, palpebral part can be seen in the superolateral conjunctival fornix.

Vascular Supply and Drainage of the Orbit The posterior ciliary vessels supply the whole uveal tract, the cilioretinal arteries, the sclera, the margin of the cornea, and the adjacent conjunctiva. The anterior ciliary arteries supply the rectus muscles.

The vortex veins drain the venous system of the choroid, ciliary body, and iris. Venous drainage of the orbit occurs through 2 major veins, the superior and inferior ophthalmic veins.

The eye

Cornea and the tear film

The sclera The sclera, also known as the white of the eye, is the opaque, fibrous, protective, outer layer of the eye containing collagen and elastic fiber. It is of variable thickness, 1 mm around the optic nerve head and 0.3 mm just posterior to the muscle insertions.

The uvea The uvea is the vascular pigmented middle layer of the eye. It is traditionally divided into three areas, from front to back: Iris. Ciliary body. Choroid.

The iris

The ciliary body

The retina

The lens

Optic nerve and visual pathway This is formed by the axons arising from the retinal ganglion cell layer. In the orbit, the optic nerve is surrounded by a sheath formed by the dura, arachnoid and pia mater continuous with that surrounding the brain. The central retinal artery and vein enter the eye in the center of the optic nerve.

Embryology of the eye The eye begins to develop as a pair of optic vesicles on each side of the forebrain at the end of the 4th week of pregnancy.

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