Anatomy of the Eye, Orbit & Adnexae

Actions, innervation and attachment of lateral rectus muscle.

- Abducts eyeball - Originates from the lateral part of the common tendinous ring, and attaches to the anterio-lateral aspect of the sclera. - Abducens

Actions, innervation and attachment of medial rectus muscle.

- Adducts eyeball - Originates from the medial part of the common tendinous ring, and attaches to the anterio-medial aspect of the sclera - Oculomotor

What are the ciliary bodies?

- Comprised of 2 parts; the ciliary muscle and ciliary processes. - The ciliary muscle has smooth muscle fibers that are attached to the lens of the eye by ciliary processes. - Its functions are to control the shape of the lens and to contribute to the formation of aqueous humor.

Actions, innervation and attachment of superior oblique muscle.

- Depresses, abducts and medially rotates the eyeball. - Originates from the body of the sphenoid bone. - Its tendon passes through a trochlear, and then attaches to the sclera of the eye, posterior to the superior rectus. - Trochlear

What brainstem nuclei control the muscles?

- Edinger-Westphal nucleus • Cranial nerve III (oculomotor nerve) - Trochlear nucleus • Cranial nerve IV (trochlear nerve) - Abducens nucleus • Cranial nerve VI (abducens nerve)

Actions, innervation and attachment of levator palpebrae superioris.

- Elevates the upper eyelid - Originates from the lesser wing of the sphenoid bone, immediately above the optic foramen. - It attaches to the superior tarsal plate of the upper eyelid (a thick plate of connective tissue). - Oculomotor nerve

Actions, innervation and attachment of inferior oblique muscle.

- Elevates, abducts and laterally rotates the eyeball. - Originates from the anterior aspect of the orbital floor. - Attaches to the sclera of the eye, posterior to the lateral rectus. - Oculomotor

Involuntary fixation movements?

- Holds eyes firmly on object once it has been found - Controlled by secondary visual areas in the occipital cortex, anterior to the primary visual cortex

Actions, innervation and attachment of inferior rectus muscle.

- Mainly depresses the eyeball but contributes to adduction and lateral rotation - Originates from the medial part of the common tendinous ring, and attaches to the anterio-medial aspect of the sclera. - Oculomotor

Actions, innervation and attachment of superior rectus muscle.

- Mainly elevates the eyeball but contributes to adduction and medial rotation - Originates from the inferior part of the common tendinous ring, and attaches to the inferior and anterior aspect of the sclera. - Oculomotor

Voluntary fixation movements?

- Move eyes voluntarily to find object - Controlled by premotor cortical region

Circulation of aqueous humor?

- The fluid comes from the ciliary bodies, flows through the pupil into the anterior chamber, to the lens and then angle between cornea and iris. - Then drains out the eye via a capillary network (called trabecular meshwork), which then drains into the canal of Schlemm before entering blood (extraocular veins). Glaucoma = abnormal accumulation of this fluid leading to increased intraocular pressure

Actions, innervation and attachment of superior tarsus muscle.

- Works to keep the upper eyelid raised after the LPS has raised it - This is a collection of smooth muscle fibers that originates on the underside of LPS and inserts on the superior tarsal plate of the eyelid. - Sympathetic nervous system

What is the macula?

- Yellowish in color, highly pigmented structure located at the center of the retina. - It contains a depression known as the fovea, which has a high concentration of photoreceptors. - This is the area responsible for high acuity vision.

Medial wall of the orbit?

Formed by the ethmoid, maxilla, lacrimal and sphenoid bones. The ethmoid bone separates the orbit from the ethmoid sinus.

Roof of the orbit?

Formed by the frontal bone and the lesser wing of the sphenoid. The frontal bone separates the orbit from the anterior cranial fossa.

Floor of the orbit?

Formed by the maxilla, palatine and zygomatic bones. The maxilla separates the orbit from the underlying maxillary sinus.

Lateral wall of the orbit?

Formed by the zygomatic bone and greater wing of the sphenoid.

Apex of the orbit?

Located at the opening to the optic canal, the optic foramen.

Base of the orbit?

Opens out into the face, and is bounded by the eyelids. It is also known as the orbital rim.

Accomodation of the lens?

The lens has a unique property known as "accommodation"; this basically means that its strength can be adjusted depending on the size (or angle) of its curvature. The greater the lens curvature, the more light it is able to bend. • Sympathetic stimulation causes ciliary bodies to relax which flattens the lens. This happens when you look at distant stuff. • Parasympathetic stimulation causes ciliary bodies to constrict, which makes the lens round and strong. This helps to look at things that are close-up.

what is the lacrimal apparatus?

The physiological system containing the orbital structures for tear production and drainage

What are the primary refractive structures?

The primary refractive structures → they bend incoming light and focus the image on the retina. 1. Cornea → a transparent structure positioned centrally at the front of the eye, light entering the eye is refracted by it. 2. Lens → an elastic structure consisting of transient fibers, it is located anteriorly between the vitreous humor and the pupil.

Pathways into the orbit?

There are other minor openings into the orbital cavity. The nasolacrimal canal, which drains tears from the eye to the nasal cavity, is located on the medial wall of the orbit. Other small openings include the supraorbital foramen and infraorbital canal - they carry small neurovascular structures.

What is the iris?

This is a circular structure with an aperture in the center known as the pupil (responsible for capturing the images you see). It has 2 distinct muscles that change the size of the pupil and thus control how much light enters the retina. o Sphincter muscles - parasympathetic stimulation causes them to constrict the pupil o Dilatory muscles - sympathetic stimulation causes them to dilate the pupil

What is the choroid?

a layer of connective tissue and blood vessels, providing nourishment to the outer layers of the retina

What is the optic disc?

is the area where the optic nerve enters the retina, it also contains the retinal arteries and veins. It has no photoreceptors.

Layers of the eye?

o Fibrous layer → consists of sclera (comprises the majority of this layer) and cornea, they are continuous with each other o Vascular layer → consists of the choroid, ciliary body and iris (together known as the uvea) o Inner layer → retina

Innervation to lacrimal apparatus?

o Sympathetic supply through the carotid plexus of nerves o Parasympathetic supply from the lacrimal nucleus of the facial nerve.

What does the lacrimal apparatus consist of?

o The lacrimal gland, which secretes the tears, and its excretory ducts, which convey the fluid to the surface of the human eye o The lacrimal canaliculi, the lacrimal sac, and the nasolacrimal duct, by which the fluid is conveyed into the cavity of the nose, emptying anterioinferiorly to the inferior nasal conchae from the nasolacrimal duct

What is the retina?

the inner layer of the eye, contains photoreceptors that are responsible for catching light. Images captured here travel through the optic disc via nerve fibers that form the optic nerve

What is the sclera?

this is the visible white part of the eye, and it provides attachment to extraocular muscles

Contents of the orbit?

• Eye balls • Extraocular muscles • Eyelids • Nerves → optic, oculomotor, trochlear, trigeminal and abducens • Opthalmic artery and veins • Orbital fat - cushions the eye and stabilizes the extraocular muscles • Periorbital fascia

Vasculature of the eye?

• Main arterial supply is via the ophthalmic artery o This is a branch of the internal carotid, arising immediately distal to the cavernous sinus o Gives rise to branches, which supply different components of the eye. The central artery of retina is the most important branch as it supplies the internal surface of the retina, and occlusion will quickly result in blindness. • Venous drainage is by the superior and inferior ophthalmic veins, these drain into the cavernous sinus.

Muscles of eyelid & their innervation

• Obticularis oculi is the main protractor of the eyelid, it is innervated by CNVII • The tarsal plates are thick elongated dense connective tissue located in each eyelid, contributing to its form and support. • The superior and inferior tarsal muscles receive innervation from the supratrochlear nerve and infraorbital nerve • The medial and lateral palpebral ligaments are innervated by the lacrimal nerve

Examining them...

• Superior oblique → depresses the eye when looking medially • Inferior oblique → elevates the eye when looking medially • Superior rectus → elevates the eye when looking laterally • Inferior rectus → depresses the eye when looking laterally • Medial rectus → adduction when pupil moving along horizontal plane • Lateral rectus → abduction when pupil moving along horizontal plane

Cavities of the eye?

• The eye is also divided into anterior and posterior cavities by the lens. 1) The anterior cavity of the eye is further separated by the iris into anterior and posterior chambers - The chambers contains= aqueous humor which is a fluid that carries nutrients to supply the anterior eye structures. 2) The posterior cavity contains the vitreous humor fluid.

Eyelid; general...

• The eyelid is a thin fold of skin that covers and protects the eye • It is thinner and has more pigment than other parts of the body • Features a row of eyelashes which serve to heighten the protection of the eye from dust, foreign bodies and sweat • The main function of the eyelid is to regularly spread the tears and other secretions on the eye surface to keep it moist, since the cornea must be continuously moist. They help keep the eyes from drying out when asleep, and the blink reflex protects the eye from foreign bodies. • Each eyelid is divided by a horizontal sulcus into an orbital and tarsal part • The two lids meet at the medial and lateral canthi • It is made up of several layers, from superficial to deep these are: skin, SC tissue, obticularis oculi, orbital septum, tarsal plates and palpebral conjunctiva.