l 01 ocular anatomy
TRANSCRIPT
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Basic Ocular Anatomy
Cornea
Iris
Vitreous humor
Macula
Canal ofSchlemm Angle
Optic nerve
Sclera
Choroid
Pigmentepithelium
Retina
Fovea
Lens
Aqueous
humor
Ciliary muscle
Features
of the eye
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VA = visual axis
AP = anterior polePP = posterior pole
Lam. = laminacrib. = cribrosa
Med. = medial
Horizontal cross
section of
the human eye.
Three Ocular Layers
A. Outer layer Sclera Cornea
B. Middle layer (uvea) Iris Ciliary body Choroid
C. Inner layer Retina
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Sclera & CorneaSclera
Consists largely of collagen. Provides support and protection, and
maintains shape of eye.
Cornea
Transparent anterior part of eye, the mostpowerful optical component of the eye.
Lacks blood vessels, gets oxygen directlyfrom the air and the aqueous humor.
Very sensitive nerve endings, respondsrapidly to injury.
Uvea: IrisUvea
Highly vascularized, provides nutritionto various elements of the eye.
Iris
The colored part of the eye. Controls pupil size -> regulates the
amount of light entering the eye.
Influences sharpness of retinal image.
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The Outer Retinais served via thechoroidal vessels
Choroid
Detail
Uvea: Ciliary Body & Choroid
Ciliary body
Produces aqueous humor (function:nourishes the cornea and lens).
Ciliary muscle plays a major role inaccommodation (change in lens shapeto focus at distance or near).
Choroid
Provides nourishment to the retina.
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Other Ocular Structures
Crystalline lens Vitreous humor Canal of Schlemm Fovea Optic Nerve
Crystalline Lens
Provides ~1/3 of the power of the eye.Accommodation: changes its shape to
focus at different distances.
Loses its ability to change shape easilywith age -> presbyopia.
With age, lens becomes lesstransparent -> cataract.
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Vitreous Humor
Consists primarily of collagen andhyaluronic acid and has a gel-like
structure.
Provides structural support to the eyeand helps nourishes the retina.
With age, may liquefy -> floaters.
Canal of Schlemm
Provides drainage for the aqueoushumor.
Located at the angle of the eye (wherethe iris inserts into the ciliary body).
Production and drainage of aqueoushumor help maintain the intraocular
pressure (IOP).
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retina
sclera
choroidfovea
optic disc
Horizontal section through
the optic nerve and macula
Optic Nerve
Axons of the ganglion cells (leaving theeye).
Optic nerve head, or optic disc: the partof the fundus where the bundle ofganglion cells exits the eye.
No photoreceptors in optic disc, thereforeno perception of light -> physiological
blind spot.
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optic disc
fovea
artery
vein
Fundus Photograph
Retinal vessels
imaged with
fluoresceinangiography
Note the absence of
blood vessels in thefovea.
fovea
From Livingston,1995
Retinal Blood Vessels
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Retina
A sheet of neural tissue, ~0.2 to 0.4 mmthick.
5 classes of neurons: photoreceptors,bipolar cells, ganglion cells, horizontal
cells and amacrine cells. Each of these
classes has subtypes, as well.
Fovea centralis
foveola
capillary freezone
perifovea
parafovea
umbo
From Gass,1997
Anatomic Subdivisions of the Macula
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photoreceptors Ext. Limit. Memb.
Outer Nuc. Layer
Inner Nuc. Layer
Ganglion Cell Layer
Outer Plexiform Lay.
Inner Plexiform Lay.
Section through the center of the fovea
(monkey fovea)
The dark regions in blue light that are absent in green light are areas of
high macular pigment density -- most dense along the fibers of Henle.
Distribution of Macular Pigment
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Fovea
Specialized area of the retina thatsubserves most acute vision. Foveal pit: neural elements of inner
retina piled up on the side of pit.
Part of the macula (area centralis). Macula contains a pigment that screens
out blue light, thus giving the macula ayellow tinge.
Vertical sectionthrough a human
retina (1.25 mmfrom the fovea).
From Dowling, 1987
pigment epith.
outer segments
inner segments
outer nuclear lay.
outer plexiform lay.
inner nuclear lay.
inner plexiform lay.
ganglion cell lay.
nerve fiber lay.
inner limiting memb.
rods & cones
outer limitingmemb.
photoreceptorterminals
Retinal Cross
Section
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Abbreviations
Rb = rod bipolarAIIa = AII amacrine
Am = amacrine cell
M = midget
gc = ganglion cell
Pa = parasol gc
on = ON
off = OFF
F = flat
I = invaginating
d = diffuse
cb = cone bipolar
Hz = horizontal cell
From Livingston,1995
Retinal
Wiring
CHOROID
L I G H T
Retinal Wiring
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Photoreceptors 2 classes of photoreceptors: rods and
cones. Rods: night-time vision, very sensitive at
dim light level, no rods in the fovea.
Cones: daytime vision, not as sensitive asrods but work well in bright light, mostdensely packed in the fovea. Three conetypes provide trichromatic (color) vision.
Simplified RetinalWiring Diagram
Photons are absorbed in
photoreceptor
Electrical potential changes in
the membrane cause a
release of neurotransmitter
into synapse
Bipolar cell communicates
signals to Ganglion Cell
Ganglion Cell generates anAction Potential that
travels up the Optic Nerve
to the brain.