Transcript 7-2 Visual Anatomy

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
iris
sclera
cornea
pupil
choroid
ciliary body
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
anterior
chamber
lens
cornea
posterior
chamber
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
superior rectus
inferior rectus
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medial rectus
inferior oblique
superior oblique
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superior rectus
superior oblique
trochlea
inferior
oblique
lateral
rectus
(cut)
inferior
rectus
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medial rectus
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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
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