suzanne d'anna1 anatomy of the eyeball. suzanne d'anna2 cavities of the eyeball separated...
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Suzanne D'Anna 1
Anatomy of the Eyeball
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Cavities of the Eyeball
separated by the lens anterior posterior
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Anterior Cavity between lens and cornea filled with aqueous humor (watery fluid) Divided into:
- anterior chamber (anterior to iris)
- posterior chamber (posterior to iris)
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Posterior Cavity between lens and retina filled with vitreous body (jelly-like
substance) also called vitreous chamber
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Lens elastic, transparent, biconcave structure separates anterior and posterior cavities
of eyeball suspended from ciliary body by
suspensory ligaments tension on suspensory ligaments
controls shape of lens
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Layers of Eyeball (tunics)
fibrous - outer
- sclera
- cornea vascular - middle
- choroid
- ciliary body
- iris retina - inner nervous
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Layers of Eyeball
pupil
cornea
ciliary body
sclera
choroid
iris
retina
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Sclera - outer fibrous
“white of the eye” outermost protects eye thick, tough connective tissue capsule that maintains shape of eye serves as point of attachment for extrinsic
muscles makes up 5/6 of sclera
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Cornea - outer fibrous
anterior 1/6 of fibrous tunic; continuous with sclera
bulges forward, forming convex surface
- refracts light rays as they enters eye transparent - allows light rays to pass lacks blood vessels receives nutrition from lymph has five layers
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Cornea - outer fibrous (cont.)
has touch and pain receptors injury causes scarring most exposed part of eye great ability to repair itself only tissue that can be transplanted
from person to person without rejection
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Scleral Venous Sinus also called canal of Schlemm junction of sclera and cornea drains aqueous humor from eyeball
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Choroid - middle vascular layer
vascular layer; blood rich contains dark pigment produced by
melanocytes
- absorbs pigment and prevents scatter of light after it passes through retina
anterior portion becomes ciliary body and iris
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Ciliary Body - middle vascular layer
thickest part of vascular tunic forms internal ring in anterior part of
eyeball within are projections or folds called ciliary
muscles
- secrete aqueous humor into anterior cavity
lens is attached via suspensory ligaments
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Iris - middle vascular layer
extends out from ciliary body anterior to lens thin diaphragm of connective tissue seen from outside as colored portion of
eye has rounded opening called pupil regulates amount of light entering
posterior cavity of eyeball through pupil
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Pupils bright light or close up - pupils constrict dim light or distance - pupils dilate
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suspensory ligaments
lens
anteriorchamber
posterior chamber
cornea
pupil
iris
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Retina - inner nervous layer
light sensitive is where light rays form an image image travels via optic nerve to cerebral
cortex if image is not focused correctly, corrective
glasses or lenses are required contains photoreceptors
- rods and cones
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Photoreceptors rods
- 20 million - recognize gray tones and dim light
cones
- 6 million - recognize primary colors together they interpret intermediary colors in moonlight only rods are functioning;
therefore we cannot see colors
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Fovea Centralis depressed area in center of macula lutea
- yellowish spot just lateral to optic axis of eyeball
has highest concentration of cones in retina
produces sharpest vision and best color perception
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Optic Disc also called blind spot medial to optic axis fibers from ganglion cells exit eyeball to
form optic nerve no photoreceptors; light striking this
area produces no image
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Color Blindness inability to distinguish colors caused by a lack or deficiency in one of
the three cone photopigments most common type is red-green color
blindness inherited condition affecting males more
often than females - sex-linked
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Intraocular Pressure caused when scleral venous sinus is
obstructed and reabsorption of aqueous humor cannot keep up with its secretion
pressure in chambers pushes lens back and puts pressure on vitreous body which in turn presses on retina which obstructs blood supply
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Intraocular Pressure (cont.)
retinal cells die and optic nerve may atrophy causing blindness (glaucoma)
symptoms usually go unnoticed until damage is irreversible
disease can be detected by use of tonometer used to measure intraocular pressure
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Glaucoma group of eye diseases characterized by an increase in
intraocular pressure pressure causes pathological changes
in optic disk and visual field defects
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Normal Flow of Intraocular Fluid
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Abnormal Flow of Intraocular Fluid
(most common type)
egress is partially blocked causing increased accumulation of fluid causing increase pressure and eventual blindness
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Acute Closed-Angle Abnormal Flow of Intraocular Fluid egress is totally
blocked causing permanent blindness suddenly
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Accessory Structures eyelids lacrimal apparatus extrinsic muscles cranial nerves
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Eyelid Composed of:
- skin covers outer surface
- conjunctiva covers inner surface of eyelid and anterior surface of eyeball (except cornea)
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Eyelid (cont.)
Composed of:
- tarsal glands
modified sebaceous gland (oil)
open at edge of each eyelid
also called Meibomian glands
- muscles
orbicularis oculi - surrounds eye
levator palpebrae - in upper eyelid
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Lacrimal Apparatus lacrimal gland superior and inferior canaliculi lacrimal sac nasolacrimal duct
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Lacrimal Gland located in upper portion of each orbit secretes constant flow of tears
- wash anterior surface of eyeball
- maintain moist and clean environment for cornea and conjunctiva
- contain antibacterial enzyme lysozyme that helps prevent eye infections
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Superior and Inferior Canaliculi collect tears after they have washed
over eyeball
Lacrimal Sac collects tears from canaliculi
Nasolacrimal Duct connects lacrimal sac to nasal cavity
where tears are swallowed
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Extrinsic Muscles arise from bones of the orbit inserted into broad tendons on sclera Six extrinsic eyeball muscles:
lateral rectus medial rectus
superior rectus inferior oblique
inferior rectus superior oblique
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superior oblique
trochlea
superior rectus
lateral rectus(cut)
inferioroblique
medial rectusinferiorrectus
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Primary Actions of the Eye Muscles abduction adduction elevation depression
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Abduction contraction of lateral rectus moves pupil
away from nose
Adduction contraction of medial rectus moves pupil
towards nose
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Elevation contraction of superior rectus or inferior
oblique muscles moves pupil upward
Depression contraction of inferior rectus or superior
oblique muscles moves the pupil downward
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Cranial Nerves of Eyeball Innervation
oculomotor (III)
- branches innervate superior rectus, medial rectus, inferior oblique, and inferior rectus
trochlear (IV)
- innervates superior oblique abducens (VI)
- innervates the lateral rectus