sheena the eye

8/8/2019 Sheena the Eye

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THE HEAD



THE EYE

The human eye is the organ which gives us the sense of sight, allowing us to observe

and learn more about the surrounding world than we do with any of the other foursenses.

GENERAL ANATOMY

Parts of the Eye

Lens the nearly spherical body in the eye, located behind the cornea, that focuses light raysonto the retina

Posterior chamber behind the iris and in front of the lens Anterior chamber behind the cornea and in front of the iris and lens C ornea the clear part of the eye covering the iris and pupil; it lets light into the eye, permitting

sight. Pupil the round, dark center of the eye, which opens and closes to regulate the amount of light

the retina receives. Aqueous humur clear fluid in the front of the eye, between the cornea and the iris, that

provides nutrients to the cornea and the lens. The fluid is produced by the cilliary body. *Glaucoma causes a difficulty in draining this fluid, and intraocular pressure builds up.The result is damage to the optic nerve and loss of vision.



Iris colored part of your eye surrounding the pupil. This pigmented membrane lies betweenthe cornea and the lens; it acts as a diaphragm to widen or narrow the opening called the pupil,

thereby controlling the amount of light that enters the eye. C onjuctiva mucous membrane that lines the visible part of the eye and the inner surface of the

eyelids.

S uspensory ligament also called z onule of Zin. Membrane of fibers (zonules) that holds theeye s lens in place.

C iliary body between the iris and the choroid; functions are accomodation, AH production and

holding the lens in place. Lateral rectus muscle muscle that moves the eye away from the nose S clera outer coat of the eyeball that forms the visible white of the eye and surrounds the optic

nerve at the back of the eyeball. C horoid layes of blood vessels located between the sclera and the retina; they provide

nourishment to the back area of the eye Retina the sensory membrane that lines the eye;

F orvea a depression in the retina contains only cones (not rods), and that provides acuteeyesight

Optic nerve the nerve that carries electircal impulses from photoreceptor cells in the retina tothe visual cortex in the brain

Optic nerve head also called optic disk . C ircular area where the optic nerve enters the retina,

and the location of the eye s blind spot V itreous body between the lens and the retina, contaning a clear jelly called the vitreous

humor. Medial rectus muscle muscle that moves the eye toward the nose.

EX TRAOCULAR MUSCLE



EYE MOVEMENTS

Conjugate eye movements are those that preserve the angular relationship between the right andleft eyes.

Vergence eye movements are ones where the angle between they eyes changes

Saccades or saccadic eye movements are very fast jumps from one eye position to another.

Smooth pursuit movements are just as their name implies. The eyes move smoothly instead of in jumps. They are called pursuit because this type of eye movement is made when the eyesfollow an object.

Fixed gaze movements are tiny tremors of the eyeballs when the gaze isfixated on a single point.

Ny stagmus is a result of the vestibular balance system. The vestibularsystem has a profound influence on eye movements.



Th e vestibulo-ocular reflex (VOR) is the system that generatesnystagmus. The VOR is a reflex the brain uses to maintain a steady view of an object despite the fact that the observer's head is moving and this headmovement would normally blur or disturb the clear vision of the object

Th e Optokinetic Reflex is a closely-related reflex which allows the eyes tofollow a moving target even when the head remains motionless.

GAZE MIS- AL IGN MEN TS OR STR AB ISMUS

E.Cranial N erves .

Twelves "cranial nerves" emerge from the base of the brain to innervatedifferent parts of the head and neck.



I - Olfactory II - OpticIII - Oculomotor IV - Trochlear

V - Trigeminal VI - Abducens

VII - Facial VIII - Auditory IX - Glossopharyngeal

X - VagusXI - Accessory XII - Hypoglassal

Three of these cranial nerves (III, IV, and VI) emerge from the brain andattach to the various extraocular muscles, and signalling along these nervescontrols the muscles that aim the eyeballs. The three controlling cranialnerves are the oculomotor nerve (Cranial Nerve III, Supplies four of the sixextraocular muscles of the eye and the levator palpebrae superioris muscleof the upper eyelid),



the trochlear nerve (Cranial Nerve IV, innervates the superior oblique muscleof the contralateral orbit),



and the abducens nerve (Cranial Nerve VI, innervates the lateral rectusmuscle of the ipsilateral orbit).

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