Eyes

• eyelids - protect the eye from foreign bodies and limit the amount of light entering the eye
• The upper eyelid is larger, more mobile, and contains tarsal plates made up of connective tissue.
• Tarsal plates - plates contain the meibomian glands,
• meibomian glands - secrete an oily substance that lubricates the eyelid
• The eyelids join at two points: the lateral (outer) canthus and medial (inner) canthus
• The medial canthus contains the puncta, two small openings that allow drainage of tears into the lacrimal system
• The medial canthus contains caruncle, a small, fleshy mass that contains sebaceous glands.
• The white space between open eyelids is called the palpebral fissure.
• Eyelashes - are projections of stiff hair curving outward along the margins of the eyelids that filter dust and dirt from air entering the eye.
• conjunctiva is a thin, transparent, continuous membrane that is divided into two portions: a palpebral and a bulbar portion
• palpebral conjunctiva - lines the inside of the eyelids
• bulbar conjunctiva - covers most of the anterior eye, merging with the cornea at the limbus.
• lacrimal apparatus - consists of glands and ducts that lubricate the eye
• lacrimal gland - located in the upper outer corner of the orbital cavity just above the eye, produces tears
• The extraocular muscles - are the six muscles attached to the outer surface of each eyeball
• Innervation for extraocular muscles is supplied by three cranial nerves: the oculomotor (III), trochlear (IV), and abducens (VI)
• eyeball - is composed of three separate coats or layers
• Sclera - a dense, protective, white covering that physically supports the internal structures of the eye.
• cornea - permits the entrance of light, which passes through the lens to the retina. It is well supplied with nerve endings, making it responsive to pain and touch
• iris - is a circular disc of muscle containing pigments that determine eye color.
• The central aperture of the iris is called the pupil
• lens - is a biconvex, transparent, avascular, encapsulated structure located immediately posterior to the iris
• choroid layer - contains the vascularity necessary to provide nourishment to the inner aspect of the eye and prevents light from reflecting internally.
• retina - consists of numerous layers of nerve cells, including the cells commonly called rods and cones.
• optic disc - is a cream-colored, circular area located on the retina toward the medial or nasal side of the eye
• physiologic cup - this area is approximately one-third the size of the entire optic disc and appears somewhat lighter/whiter than the disc borders.
• A retinal depression known as the fovea centralis is located adjacent to the optic disc in the temporal section of the fundus.
• eyeball contains several chambers that maintain structure, protect against injury, and transmit light rays.
• anterior chamber - is located between the cornea and the iris
• posterior chamber is the area between the iris and the lens
• anterior and posterior chamber - are filled with aqueous humor, a clear liquid substance produced by the ciliary body
• Aqueous humor helps cleanse and nourish the cornea and lens as well as maintain intraocular pressure (IOP)
• vitreous chamber - largest of the chambers and is filled with a vitreous humor that is clear and gelatinous, located behind the lens to retina
• A visual field refers to what a person sees with one eye.
• binocular vision - two-eyed vision in which the visual cortex fuses the two slightly different images and provides depth perception, or three-dimensional vision.
• Visual perception - occurs as light rays strike the retina, where they are transformed into nerve impulses, conducted to the brain through the optic nerve, and interpreted.
• Accommodation is a functional reflex allowing the eyes to focus on near objects. This is accomplished through movement of the ciliary muscles, causing an increase in the curvature of the lens.