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Transcript
Chapter 19
Special Senses: Vision
Fig. 19.9
Accessory Structures of the Eye
• Structures that prevent foreign objects from entering eye:
• eyebrows
• eyelashes (length ideally 1/3 width of eye opening)
• eyelids (AKA palpebrae) include
• thin layer of skin, muscle, fibrous core
Fig. 19.10
Lacrimal Apparatus
Lacrimal gland
(orbital part)
Lacrimal gland
(palpebral part)
• Produces, collects, and
drains lacrimal fluid
(tears)
• lubricates anterior
surface of eye
• cleanses and moistens
eye surface
• contains antibacterial
enzyme to help prevent
infection
Lacrimal puncta
Lacrimal caruncle
Lacrimal canaliculi
1
2
Lacrimal sac
3
4
Nasolacrimal duct
5
Nasal cavity
Nostril
Fig. 19.11a
Anatomy of the Internal Eye
• Human eye is about 2.5 cm
in diameter
• Orbital fat cushions eye against bone
• provides blood vessels and supports nerves
• Fibrous tunic is tough external layer
• Sclera is “white” of eye, made of dense,
irregular connective tissue
• Cornea is clear surface of anterior eye
• convex shape bends light coming into eye
• continuous with sclera but clear
Fibrous tunic
Sclera
Cornea
Vascular tunic
Iris
Ciliary body
Choroid
Retina
Pigmented layer
Neural layer
Fig. 19.9b
Accessory Structures of the Eye
Eyebrow
• Conjunctiva produces mucus
and (some) tears
• Palpebral conjunctiva covers
inner surface of eyelid
• Ocular conjunctiva covers sclera
Ocular conjunctiva
Palpebral conjunctiva
Superior tarsal plate
Superior eyelid
Cornea
Eyelashes
Inferior eyelid
Inferior tarsal plate
Fig. 19.9b
Accessory Structures of the Eye
• conjunctiva contains blood
vessels
• does not cover surface of
cornea so blood vessels
and nerves don’t block
vision
Eyebrow
Ocular conjunctiva
Palpebral conjunctiva
Superior tarsal plate
Superior eyelid
Cornea
Eyelashes
Inferior eyelid
Inferior tarsal plate
Fig. 19.11
Central
artery of Central
retina vein of
retina
Ciliary muscle Ciliary body
Ciliary process
Suspensory ligaments
Limbus
CN II (optic)
Lens
Iris
Cornea
Pupil
Optic disc
Fovea centralis
Posterior
cavity
Retina
Choroid
Sclera
(b)
Sphincter pupillae
Dilator pupillae
Anterior chamber
Posterior chamber
Anterior
cavity
Fig. 19.11a
Anatomy of the Internal Eye
• Vasclar tunic (AKA uvea)
• 3 regions
• Iris is colored portion of eye
• black hole at center is pupil
• two layers of pigment-forming
cells give eye color
• contains two groups of smooth muscle
fibers, controls size of pupil
Fibrous tunic
Sclera
Cornea
Vascular tunic
Iris
Ciliary body
Choroid
Retina
Pigmented layer
Neural layer
Fig. 19.11
• Within iris, two layers of
muscles
• sphincter pupillae is in
concentric circles, constricts
pupil
• dilator pupillae extends in
radial pattern, dilates pupil
Lens
Iris
Cornea
Pupil
Sphincter pupillae
Dilator pupillae
Fig. 19.11a
Anatomy of the Internal Eye
• Vascular tunic (AKA uvea)
• 3 regions
• Ciliary body is continuous with iris
• composed of ciliary muscles and
ciliary processes that cover
muscles
• suspensory ligaments extend to
lens, focus eye by contracting or
relaxing
Fibrous tunic
Sclera
Cornea
Vascular tunic
Iris
Ciliary body
Choroid
Retina
Pigmented layer
Neural layer
Fig. 19.11
Ciliary muscles in
ciliary body
Suspensory ligaments
Lens
Fig. 19.11a
Anatomy of the Internal Eye
• Vascular tunic (AKA uvea)
• 3 regions
• Choroid is most posterior region,
black color
• prevents reflection of excess light
back into retina
• in cats, cows, etc., choroid
covered with tapetum lucidum
that reflects light
Fibrous tunic
Sclera
Cornea
Vascular tunic
Iris
Ciliary body
Choroid
Retina
Pigmented layer
Neural layer
14
Fig. 19.11a
Anatomy of the Internal Eye
• Retina is most internal layer
• composed of 2 layers
• pigmented layer is
attached to choroid
• provides Vitamin A for
photoreceptor cells
• transports nutrients and oxygen
to photoreceptor cells, removes waste
• neural layer is internal to pigmented layer
• houses photoreceptors and other neurons
involved in receiving and processing light signals
• not attached to other layers, except at optic nerve
Fibrous tunic
Sclera
Cornea
Vascular tunic
Iris
Ciliary body
Choroid
Retina
Pigmented layer
Neural layer
Tapetum
lucidum
Cow eye
Human eye
Organization of the Retina
Retina
• Blood vessels and neurons leave
eye through optic disc, travel
through center of optic nerve out
back of eye
Sclera
Choroid
Optic disc
– optic disk creates blind spot
Optic
nerve
Fovea centralis
Fig. 19.13a & b
Organization of the Retina
Choroid
Retina
Sclera
Choroid
Optic disc
Optic
nerve
Rod
Photoreceptor
Cone cells
Pigmented
layer
Horizontal cell
Bipolar cells
Retina
• Light travels
through neural
layer and is
received by
photoreceptor
cells on deepest
layer of retina
Neural
layer
Incoming light
Nerve signal
Amacrine cell
Ganglion cells
Axons of ganglion
cells to optic nerve
Fig. 19.13a & b
Organization of the Retina
• Photoreceptor cells
– rods are most sensitive in
dim light, process black
and white, most numerous
outside fovea centralis
– cones process color, are
most sensitive in highintensity light, most
numerous within fovea
centralis
Choroid
Rod
Photoreceptor
Cone cells
Horizontal cell
Bipolar cells
Amacrine cell
Ganglion cells
Axons of ganglion
cells to optic nerve
Fig. 19.11
Choroid
Pigmented
layer
Retina
Rods and cones
Bipolar cells
Neural
layer
Ganglion cells
LM 250x
Axons of ganglion cells
Posterior cavity
Fig. 19.13a, 19.14
Organization of the Retina
• Area around fovea centralis is
macula lutea
• Contains numerous rods and
cones, no bipolar or ganglion cells
• Light doesn’t have to pass
through other cells to get to rods
and cones
Optic disc
Optic
nerve
Macula lutea
– produces crispest vision
Fovea centralis
Macula lutea
Lateral
Fovea
centralis
Blood
vessels
Optic disc
Medial
Macular Degeneration
(a) Normal vision
(b) As viewed by a person
with macular degeneration
• Loss of photoreceptors and thinning
of pigmented layer in macula
• May also involve bleeding, capillary
proliferation, scar tissue formation
• Major cause of blindness
– caused by diabetes, infection, smoking,
hypertension, trauma to the eye
• Laser surgery can slow
degeneration, but not restore lost
sight
(c) Amsler grid, seen with
normal vision
(d) Amsler grid, as viewed
by a person with macular
degeneration
• Space between lens and
cornea is anterior cavity
• divided into anterior chamber
between iris and cornea, and
posterior chamber between iris
and lens
• filled with aqueous humor
(clear liquid)
24
• Space behind lens is
posterior cavity
• filled with vitreous humor
• clear, jelly-like substance
• helps maintain eye shape
25
Fig. 19.11
Central
artery of Central
retina vein of
retina
Ciliary muscle Ciliary body
Ciliary process
Suspensory ligaments
Limbus
CN II (optic)
Lens
Iris
Cornea
Pupil
Optic disc
Fovea centralis
Posterior
cavity
Retina
Choroid
Sclera
(b)
Sphincter pupillae
Dilator pupillae
Anterior chamber
Posterior chamber
Anterior
cavity
How do these structures work
together to produce vision?
• Cornea bends light as it enters eye
• Light passes through aqueous
humor without bending
• Iris controls amount of light entering eye
• Lens further bends light
• Light is focused on fovea centralis
Fovea
centralis