1. Sensory Systems
The Eye

3. The Cornea

4. Histology of the front of the Eye

5. Ciliary Body and Processes

6. The Iris

7. The Lens

8. The Retina
Ganglion Cells
Bipolar Cells
Rods and Cones
Pigmented Retina

9. Rods and Cones
Pigmented Retina

10. Rod
Cone

11. EYE & SEEING/VISION
The eyes are paired for security, a wider field of view,
and to aid distance perception and other apects of
seeing. However, ‘seeing double’ spells trouble!
The eyes contain the receptors for light, provide
mechanisms for influencing the light falling on the
photoreceptors, and are constructed to hold their shape,
and have transparent regions
Although connected to the brain by the optic nerve, the
eye has muscle attachments for movement, and needs
blood vessels
Other accessory structures, in and around the bony orbit
housing the eye, comprise the ocular adnexa, e.g., tear
glands & eyelids

12. GLOBE’S LAYERS & CHAMBERS
outer tunic
SCLERA
&
CORNEA
sagittal
view
UVEA middle tunic
RETINA
inner
LENS
ANTERIOR
CHAMBER
POSTERIOR
not
CHAMBER Note: Posterior chamber isdoes
posterior in the globe, but
lie behind the anterior chamber
VITREOUS
CAVITY

13. GLOBE’S ANTERIOR STRUCTURES
SCLERA
CILIARY BODY
CORNEA
IRIS
PUPIL
LENS
ZONULE
ANTERIOR
CHAMBER
POSTERIOR
CHAMBER
Chambers filled with aqueous
ZONULE suspends
and pulls on the lens

14. GLOBE’S ANTERIOR STRUCTURES: LIMBUS
SCLERA
LIMBUS is where
the cornea
meets the sclera
CILIARY BODY
CORNEA
PUPIL
LENS
ZONULE
IRIS
ANTERIOR
CHAMBER
POSTERIOR
CHAMBER
LIMBUS = corneoscleral junction
LIMBAL epithelium is the sole source of cells, by mitosis & migration, for
turnover & repair of the corneal epitheium

15. OPTICAL ASPECTS I
CILIARY BODY includes the muscle to
relax the lens shape for more focusing
dark UVEA prevents
light reflecting
around inside & is
vascular
Transparent CORNEA’S
extra curvature focuses light
IRIS controls the
amount of light
reaching the retina
PUPIL size reflects
iris muscles’ activity
Vitreous body (a
jelly) lets light
LENS
through, and keeps
the layers attached
Chambers are filled with the
aqueous humor which provides
tranparency, and its pressure holds
the eye in shape
‘White of the eye’ is dense scleral
connective tissue for strength, and to
keep light out, aided by dark inner uvea
posterior/neural RETINA
is sensitive to light

16. OPTICAL ASPECTS I (Tabular)
Transparent CORNEA’S
extra curvature focuses light
Chambers are filled with the
aqueous humor which provides
tranparency, and its pressure holds
the eye in shape
‘White of the eye’ is dense
scleral connective tissue for
strength, and to keep light out,
aided by dark inner uvea
Dark UVEA prevents light
reflecting around inside
& is vascular
IRIS controls the
PUPIL size
amount of light
reflects iris
reaching the retina muscles’ activity
LENS adds focusing
Vitreous body (a jelly) lets
light through, and keeps
the layers attached
Posterior/neural RETINA
is sensitive to light
CILIARY BODY includes
the muscle to relax the lens
shape for more focusing
Anterior ‘RETINA’ is a
double-layered epithelium
unresponsive to light

17. OPTICAL ASPECTS II: Focusing
CILIARY BODY includes the muscle to
relax the lens shape for more focusing
On neural RETINA is a tiny
REAL INVERTED
IMAGE of object
Transparent CORNEA’S
extra curvature focuses light
OBJECT
Visual axis
Elongated lens focuses light
further onto the retina
LENS
Vitreous jelly lets light
through, and keeps the
layers attached

18. OPTICAL ASPECTS III: Near-vision Focusing
CILIARY MUSCLE contracts; tension in
zonule decreases; the lens’ elasticity
changes it into a rounder shape
Close
OBJECT
Visual axis
LENS
Rounder lens focuses light
more onto the retina
The older lens loses this elastic ability
to change shape, so that one cannot
clearly see close objects - presbyopia
NEURAL RETINA

19. OPTICAL ASPECTS IV: Near-vision Focusing 2
CILIARY MUSCLE contracts; tension in zonule decreases; the lens’
elasticity changes it into a rounder shape
At first hearing, these sound to be contradictory
Under parasympathetic control the CILIARY MUSCLE contracts;
tension in zonule decreases; the
len capsule’s elasticity changes
CILIARY MUSCLE
lens into a rounder shape
ZONULE
LENS
LENS
LENS
A-P view
CILIARY MUSCLE - within the
eye - is an intra-ocular muscle
LENS

20. OPTICAL ASPECTS V: Central vision
NEURAL RETINA
The eyes are moved by the
extra-ocular muscles
to bring the object of
attention onto the visual axis
OBJECT
Visual axis
On the visual axis, the
LENS
MACULA/FOVEA is the region of
retina for precise central vision

21. OPTICAL ASPECTS VI: Peripheral vision
OBJECT
Visual axis
LENS
This part of the anterior nonneural retina is the PARS PLANA
Outside the macula, the remainder of the
neural retina is responsible for peripheral
vision - for things off the visual axis
MACULA for
central vision
Can all of the neural retina see things? No

22. OPTICAL ASPECTS VII: NerveHead & Blind spot
The neural retina contains
not only the
photoreceptors, but nerve
and glial cells for the
initial processing of the
signals. The result is
patterns of firing in
retinal ganglion neurons
whose axons leave the
eye, at one place, to
become the optic nerve
LENS
The place is the Nerve
head/ optic disc/ optic
papilla Also where vessels
OPTIC
NERVE
The optic nerve leaves on the
nasa/ medial side to the macula
enter

23. OPTICAL ASPECTS VIII: Blind spot
LENS
The neural retina contains not only
the photoreceptors, but nerve and
glial cells for the initial processing
of the signals. The result is
patterns of firing in retinal
ganglion neurons whose axons
leave the eye, at one place, to
become the optic nerve
LENS
LENS
LENS
OPTIC
NERVE
OPTIC
UNSEEN
OBJEC T
CHIASMA
Nerve head/ optic
disc/papilla has no
photoreceptorshence is blind
The optic nerves leave on the nasa/ medial side to the macula, so that they
can connect at the midline OPTIC CHIASMA: the starting device for binocular
integration - seeing one object with two eyes and two sides to the brain

24. OPTICAL ASPECTS IX: Experiencing the Blind spot
Place a small bright coin on a dark
table, e.g., a quarter
L
Place another bright coin, e.g. a dime,
to the right of the first coin
LENS
R
LENS
Cover your left eye with your left hand
Fixate your right eye on the first coin
Move the second coin to right & left
with your right-hand forefinger, but
not obscuring your view
At about 17 cm separation, the
second coin should disappear from
view as its image falls on the right
eye’s blind spot/ nerve head
10
25
[Reverse the side of second to first
coin for testing the left eye]

25. OPTICAL ASPECTS X: Retinal layers
LENS
The neural retina contains not only
the photoreceptors, but nerve and
glial cells for the initial processing
of the signals.
These cells are arranged in layers
with the photorecptors next to
the uvea, and
Vitreous
the retinal ganglion output
neurons innermost, close to
the vitreous
Thus, for peripheral vision, the light
has to pass through all the retinal
layers to reach the photoreceptors
OPTIC
NERVE
For precise central vision, the nerve and
glial cells lie as an annular hump
around a depression - fovea - where
the cone photoreceptors can respond to
the unimpeded light

26. Retinal layers I: Cells simplified
RETINAL GANGLION NEURONS
:
MULLER CELLS (glial)
Between neurons and
stretched across the layers
BIPOLAR NEURONS
PHOTORECEPTORS
PIGMENT CELLS
BRUCH’S MEMBRANE

27. Retinal layers II: Connection layers
RETINAL GANGLION NEURONS
Inner* Zone of Synapsing processes
BIPOLAR NEURONS
Outer Zone of Synapsing processes
PHOTORECEPTORS
:
MULLER CELLS
PIGMENT CELLS
* Reference point
for inner & outer is
interior of the eye
BRUCH’S MEMBRANE

28. Retinal layers III: Orientation
* Reference point for inner &
outer is interior of the eye
GANGLION NEURONS
Inner* Zone of
Synapsing processes
BIPOLAR NEURONS
Outer Zone of
Synapsing
processes
PHOTORECEPTORS
PIGMENT CELLS
The presence of a major
basement membrane outside
the pigment cells, here, is
NOT the starting point for
orientation. The reference
point instead is opposite inside the eye , where there
is an inconspicuous basal
lamina around the vitreous
BRUCH’S MEMBRANE is a
substantial basement membrane

29. :
Retinal layers IV: Terminology
MULLER CELLS
INNER LIMITING MEMBRANE
NERVE FIBER LAYER
RETINAL GANGLION NEURONS
GANGLION CELL LAYER
Inner* Zone of Synapsing processes
INNER PLEXIFORM LAYER
BIPOLAR NEURONS
INNER NUCLEAR LAYER
Outer Zone of Synapsing processes
OUTER PLEXIFORM LAYER
PHOTORECEPTORS
OUTER NUCLEAR LAYER
OUTER LIMITING MEMBRANE
PHOTORECEPTOR LAYER
PIGMENT CELLS
BRUCH’S MEMBRANE
PIGMENT CELL LAYER

30. INNER LIMITING MEMBRANE
Glial cell layer
NERVE FIBER LAYER
GANGLION CELL LAYER
INNER PLEXIFORM LAYER
INNER NUCLEAR LAYER
OUTER PLEXIFORM LAYER
OUTER NUCLEAR LAYER
PHOTORECEPTOR LAYER
PIGMENT CELL LAYER
OUTER LIMITING MEMBRANE
RETINAL GANGLION NEURONS
Inner* Zone of Synapsing processes
BIPOLAR NEURONS’ BODIES
Outer Zone of Synapsing processes
PHOTORECEPTOR BODIES
PHOTORECEPTOR CONES & RODS
RETINAL PIGMENT CELLS

31. INNER LIMITING MEMBRANE
NERVE FIBER LAYER
GANGLION CELL LAYER
INNER PLEXIFORM LAYER
INNER NUCLEAR LAYER
OUTER PLEXIFORM LAYER
OUTER NUCLEAR LAYER
PHOTORECEPTOR LAYER
PIGMENT CELL LAYER
Retinal layers V: H&E stained

32. Retinal layers V: H&E stained
NERVE FIBER LAYER
GANGLION CELL LAYER
INNER PLEXIFORM LAYER
INNER NUCLEAR LAYER
OUTER PLEXIFORM LAYER
OUTER NUCLEAR LAYER
PHOTORECEPTOR LAYER
PIGMENT CELL LAYER

33. Retinal layers VI: More cell types?
GANGLION NEURONS
Why not have the photoreceptors directly
stimulate action potentials in the ganglion
cells?
BIPOLAR NEURONS
The light causes changes in photoreceptor
membrane potentials, but it takes STEPS to
achieve actual ganglion-cell firing
The synaptic arrangement shown transmits
‘signals’ just inwards
Additional synapses and cell types provide
for integrative influence and interactions
across the retina
PHOTORECEPTORS
Two types of photoreceptor - rods & cones have somewhat different connection patterns
& very different light sensitivities
PIGMENT CELLS

34. Retinal layers VII: More cells 2
GANGLION NEURONS
Both provide for crosswise connections, and
need more investigation
AMACRINE CELL
BIPOLAR NEURONS
HORIZONTAL CELL
ROD For low light & black-grey perception
CONE For daylight & color perception
Provides the visual acuity of the fovea
PIGMENT CELLS
BRUCH’S MEMBRANE

35. PHOTORECEPTOR STRUCTURE I
INNER
FIBER
CONE
PEDICLE
ROD
:
MULLER
CELLS
:
Attachment
of Muller cell
INNER FIBER
INNER SEGMENT
INNER
SEGMENT
MITOCHONDRIA
OUTER SEGMENT
CILIUM
connecting segments
for transport
OUTER
SEGMENT
Stacked BILAMINAR
DISCS with
photopigment
Photopigment - iodopsin(s) absorbs in red, green or blue
regions of light spectrum

36. CONE
ROD
PHOTORECEPTOR STRUCTURE II
CONES:
are larger than rods
are far fewer, except in the fovea
have a differently shaped outer segment
have different photopigments - NOT
rhodopsin - and responsiveness to light
their synaptic end - pedicle - is much larger
than the rod’s spherule
do not shed discs for phagocytosis by
pigment cells

37. Signal transduction & Electrical activity I
GANGLION
NEURONS
L
I
G
H
T
AMACRINE CELL
BIPOLAR NEURONS
HORIZONTAL CELL
ROD
CONE
Outer segments
Light passes through the retina
to be absorbed by the
photopigment stacked in the
rod/cone outer segments
The light has to alter electrical
activity: in photoreceptors, the
light stimulus counteracts an
existing depolarized state from
cyclic nucleotide-gated ion
channels - so reduced, that a
hyperpolarization occurs,
causing
the receptor to stop releasing +
transmitter from vesicles in its
spherule, so changing
membrane potentials in the
bipolar cells, which signal to
the ganglion cell that it should
produce an action potential for
its optic-nerve fiber
L
I
G
H
T

38. Signal transduction & Electrical activity II
In the DARK
SODIUM CHANNEL - held open by
bound
cGMP
allows Na to leave,
DEPOLARIZING the cell
+
Na+
Na+
cGMP
L
I
G
H
T
In the LIGHT
SODIUM CHANNEL - closes because
cGMP
cGMP
Na+
cGMP
dissociates
With rising intracellular Na+
a hyperpolarization occurs
Why the dissociation?
cGMPphosphodiesterase
hydrolyzes cGMP, so
lowering its intracellular level
cGMP
But what activates the enzyme?

39. L
I
G
H
T
In the LIGHT
Signal transduction & Electrical activity III
1
RHODOPSIN
L
I
G
H
T
RHODOPSIN
OPSIN
2
Photon
isomerizes
retinal
11-cis-RETINAL
to
Light is absorbed
by the photopigment
stacked in the rod
outer segment
OPSIN
3
all-transRETINAL
TRANSDUCIN
- a G protein
Changed shape of
retinal forces OPSIN
molecule to alter its
conformation 4
OPSIN
6 α 1 subunit activates
7
cGMP
cGMPphosphodiesterase,
which hydrolyzes cGMP, so
lowering its intracellular level
8
5 Altered OPSIN binds
TRANSDUCIN,
releasing α 1 subunit
resulting in a cGMP dissociation from the Sodium channel

40. Signal transduction IV: Recovery & adaptation
In the DARK
SODIUM CHANNEL - held open by
bound
cGMP
Ca2+
also allows Ca2+ to enter
cGMP
In the LIGHT
Ca2+
SODIUM CHANNEL - closes because cGMP dissociates
Falling Ca2+
unbinds
inactivating
Ca2+
Ca 2+ from
RECOVERIN
which can
then stimulate
Guanylyl cyclase
to make more cGMP
Ca2+
entry is blocked
Intracelllular Ca2+ falls
cGMP
Recovery? With cGMP restored,
it can quickly associate again
with the sodium channnels

41. RHODOPSIN
OPSIN
TRANSDUCIN
- a G protein
retinal
The G-protein cascade allows
amplification of the signal initially
detected by the retinal

42. Signal transduction & Electrical activity V
GANGLION
NEURONS
L
I
G
H
T
AMACRINE CELL
BIPOLAR NEURONS
HORIZONTAL CELL
Pattern of ganglion-cell firing
alters
Bipolar cells’ GABA or glycine
then inhibits ganglion activity less
In response, bipolar cells
hyperpolarize
Receptor reduces the release of
glutamate + transmitter from
vesicles in its spherule
ROD
CONE
Outer segments
Simplified sample
sequence
The light stimulus causes a
hyperpolarization
Light passes through the retina to be absorbed
by the photopigment stacked in the rod/cone
outer segments

43. Signal transduction & Electrical activity VI
COMPLICATING aspects include:
As in the CNS, inhibition is used extensively
L
I
G
H
T
There are many subtypes of ganglion, amacrine
, horizontal & even bipolar cells
The GABA interplexiform is an additional type
Amacrine cells use electrical (nexus) synapses in
addition to chemical, e.g., dopaminergic, ones
ON cells respond to a stimulus brighter than
background, OFF to one darker than surround
Great convergence of connections
characterizes the rod system
Arrangements for color & movement signal
processing are elaborate

44. OPTIC NERVE
Nerve fibers acquire myelin
as they leave the eye
NERVE-FIBER LAYER
LAMINA CRIBROSA
un-myelinated
Holes in the sclera
for the nerve fibers
A weak spot
RETINA
SCLERA
DURA
ARACHNOID
& PIA
DURA

45. RETINA in OPHTHALMOSCOPY
All this transparency to let light in means that, when the interior of the
eye is illuminated, one can look in, with magnification, at the inside of
the back of the eye - the fundus
NORMAL VIEW
FUNDUS
MACULA
OPTIC DISK
VESSELS
Macula lies circa two Disk Diameters
(2 DD) temporally to the optic disc

46. SOME RETINA QUESTIONS in OPHTHALMOSCOPY
FUNDUS - Correct color for
race? Any spots? No
unevenness?
NORMAL VIEW
MACULA - Any vessels
over it? Too red?
OPTIC DISK - Not too pale? No
bulge, or excessive excavation?
VESSELS - Right size?
Not bent? Correct course?
Engorged veins?

47. SCLERA & regional specializations
LENS
Dense irregular connective tissue
Some vessels by
limbus & ciliary body
Insertions of
extraocular muscles
Vitreous
RETINA
Lamina
fusca
LAMINA CRIBROSA
OPTIC
NERVE
exits
Melanocytes
Loose
episcleral CT
SCLERA
proper

48. UVEA Components
outer
sagittal view
UVEA middle tunic
SCLERA
RETINA
inner
LENS
1
IRIS
2
CILIARY BODY
3
CHOROID

49. Sphincter constrictor
muscle
Anterior
IRIS
Posterior
No
epithelium
LENS
Melanocytes
More stromal
melanocytes,
browner eyes
Pigmented cuboidal
epithelium
Myoepithelial dilator cells modified deeper epithelial cells
IRIDIAL STROMA of loose connective tissue

50. INTRAOCULAR MUSCLES
Separate
parasympathetic IIIrd
cranial nerve controls
CILIARY MUSCLE contracts;
tension in zonule decreases;
the lens’ elasticity changes it
into a rounder shape
Sphincter constrictor
muscle
IRIS
Pupil
Weak dilator effect from
LENS
sympathetics
A-P views
IRIS constrictor & dilator and CILIARY MUSCLES are intra-ocular muscles

51. ZONULE or SUSPENSORY LIGAMENT OF LENS
CILIARY MUSCLE contracts;
tension in zonule decreases;
the lens’ elasticity changes it
into a rounder shape
LENS
A-P view
ZONULE comprsises many
coated fibers, running from
the ciliary body to the lens
capsule
COMPOSITION of the zonule
shares many characteristics
with basal-lamina materials, e.g.

52. ORA SERRATA
PARS PLANA
Posterior-to-Ant. view
CILIARY MUSCLE
LENS
The junction
between the neural
retina and the
double cuboidal
epithelium on the
plars plana and the
ciliary body is very
irregular - creating
a serrated ‘mouth’
NEURAL RETINA

53. UVEA: Choroid
The structure of the iris
conveys much of the
ROD structure of the choroid
CONE
IRIS
PIGMENT CELLS
BRUCH’S
CHOROID
loose vascular
connective tissue
MEMBRANE
CHORIOCAPILLARIS
Wide fenestrated capillaries
to nourish the retina
Melanocytes

54. ANGLE OF ANTERIOR CHAMBER & Aqueous Humor
Corner of ant chamber
between cornea & iris,
where sclera starts
ANTERIOR
CHAMBER
PUPIL LENS
POSTERIOR CHAMBER
Chambers filled
with aqueous
humor
SCLERAL ANGLE
is another name
Epithelium of CILIARY PROCESSES makes AH

55. ANGLE of ANTERIOR CHAMBER
Corner of ant chamber between
cornea & iris, where sclera starts
CORNEA
Canal of Schlemm
Trabecular
meshwork
ANTERIOR
CHAMBER
Spaces of Fontana in
the meshwork
SCLERA
IRIS
POSTERIOR CHAMBER
CILIARY
PROCESSES make aqueous humor
CILIARY MUSCLE
Uveoscleral outflow is another drainage route

56. AQUEOUS HUMOR: Production & Flow I
Canal of Schlemm
Trabecular
meshwork
ANTERIOR
CHAMBER
Chambers filled
with aqueous
humor
PUPIL
LENS
POSTERIOR CHAMBER
SCLERAL ANGLE
Corner of ant chamber
between cornea & iris,
where sclera starts
epithelium of CILIARY PROCESSES makes AH

57. AQUEOUS HUMOR: Production & Flow II
Epithelium of CILIARY PROCESSES makes Aqueous Humor
6
POSTERIOR CHAMBER
PUPIL
3
PUPIL
SCLERAL ANGLE with
Canal of Schlemm
2
4
ANTERIOR CHAMBER
Trabecular meshwork
1
5
Uveoscleral
outflow
LENS

58. AQUEOUS HUMOR: Glaucoma
Epithelium of CILIARY PROCESSES makes AH
POSTERIOR CHAMBER
PUPIL
6
5
4
1
2
3
ANTERIOR CHAMBER
PUPIL
LENS
SCLERAL ANGLE with
Trabecular meshwork
Canal of Schlemm
Blocked drainage/venous return of
AH raises intra-ocular pressure,
damaging vessels & the retina

59. CORNEA I: Layers
CORNEAL EPITHELIUM
Bowman’s
membrane
No vessels
STROMA
Keratocyte
Descemet’s membrane
Anterior chamber
ENDOTHELIUM

60. CORNEA II: Layer constituents
CORNEAL EPITHELIUM
EPITHELIUM is stratified
squamous, with nerve fibers
Thin basal lamina
Bowman’s membrane
of dense fibrillar collagen
STROMA
No vessels anywhere
of collagen fibers in very
orderly lamellae, with regular
alternating fiber orientations
& much special proteoglycan
Keratocytes are fibroblasts
of the corneal stroma
Descemet’s membrane
- a thick basal lamina
ENDOTHELIUM
Not a vascular endothelium, but pumps water out of stroma
Transparency factors Bowman’s membrane is modified stroma, not the basal lamina

61. CORNEA II: Layer constituents
CORNEAL EPITHELIUM is stratified squamous, with nerve fibers
Thin basal lamina
Bowman’s membrane of dense fibrillar collagen
STROMA of collagen fibers in very orderly lamellae,
with
regular alternating fiber orientations & much special
proteoglycan
Keratocytes are fibroblasts of the corneal stroma
No vessels are present
Bowman’s membrane is modified stroma, not the basal lamina
Descemet’s membrane - a thick basal lamina
ENDOTHELIUM
Not a vascular endothelium, but
pumps water out of the stroma
Transparency factors, & not present in the sclera

62. CORNEA III: Tear-film constituents
oily/lipid layer - eyelid glands
aqueous phase - Lacrimal
Mucin layer
From conjunctival & tearduct goblet cells
CORNEAL EPITHELIUM
TEARS:
Protect the conjunctival & corneal surfaces
Nourish the avascular cornea
Wash out discrepancies to ‘corner’ of the eye
Kill & restrain microorganisms
Smooth corneal-surface optics

63. LACRIMAL/LACHRYMAL GLAND & PASSAGES
LACHRYMAL GLAND
LACHRYMAL DUCTS
LACHRYMAL SAC
NASOLACRIMAL DUCT
Gland is superior and
temporal to the eye
facilitating the spread of
tears across the eye to
the collection points - the
lacrimal puncta medially
at the eyelids’ margin

64. LACRIMAL GLAND II
Gland is superior and temporal to the eye
facilitating the spread of tears across the eye to the collection points the lacrimal puncta medially at the eyelids’ medial/nasal margins
evaporation is slowed by surface film of lipid from Meibomian
glands
LACRIMAL GLAND
compound tubulo-alveolar
gland with myoepithelial cells
LACRIMAL DUCTS
From eyelids
LACRYMAL SAC
with valves
NASOLACRIMAL DUCT
continuation of the sac to drain into
lower nasal cavity

65. LACRIMAL GLAND III
LACRIMAL GLAND
Compound tubulo-alveolar gland
Alveoli lined by pale columnar/cuboidal serous cells
with myoepithelial cells
Secretion - tears - comprises
water
antimicrobials - lysozyme, defensins, antibodies
electrolytes - plasma-like (tears taste salty)
Innervation - Parasympathetic in CN VII via
Pterygopalatine ganglion
Blinking - eyelid movement - is necessary to spread tears

66. UPPER EYELID I
Palpebral part of
Orbicularis oculi
Muscle
EYELID SKIN
Dense connective-tissue
TARSAL PLATE
with
Meibomian
glands
EYELASH
LID MARGIN
PALPEBRAL
CONJUNCTIVA
Levator palpebrae
superior. Muscle
BULBAR
CONJUNCTIVA

67. UPPER EYELID II
Palpebral part of
Orbicularis oculi
Muscle
Levator palpebrae
superior. Muscle
Inserts into Tarsus, etc
EYELID SKIN
BULBAR
CONJUNCTIVA
Dense connective-tissue
TARSAL PLATE
with embedded
Meibomian
glands
By the eyelash
follicle are other
small glands
EYELASH
fornix
PALPEBRAL CONJUNCTIVA
Stratified cuboidal epithelium with
some goblet cells on loose CT
LID MARGIN
Where secretion of Meibomian modified
sebaceous glands emerges

68. LENS EQUATOR & AXIS
EQUATOR
Anterior
AXIS
LENS
Posterior pole
Lateral view
Posterior--Anterior view
Lens shape is not quite as depicted: the anterior part is an
ellipsoid; the posterior bulges back more as a parabyloid

69. LENS PARTS
LENS
CAPSULE
Subcapsular epithelium
(cuboidal)
becomes elongated
LENS FIBERS (cells)
at the LENS BOW
by filling themselves
with crystallins the proteins that
confer long-lasting
transparency
ZONULE
FIBERS

70. CATARACT - Lens becomes opaque
LENS
CAPSULE
Common in old age
UV radiation is an
accelerating factor
Naphthalene (in mothballs) is
another agent, as is
Overheating with infrared
radiation from furnaces
e.g., in glassblowers, &
Traumatic damage to the
lens capsule and epithelium
Lentectomy, and replacement with
an artificial lens usually cure
Posterior-capsule opacification is one risk
ZONULE
FIBERS

71. EYE DEVELOPMENT I: Some specifications
The eye comprises many tissues, structures, and layers
that require contributions from three main sources
Using multiple sources needs tight coordination of
signals and controls
The body’s covering has to have a transparent region
For optics, the lens needs to be roundish, the eye almost
spherical, with the retina precisely hemispherical
Spaces - chambers and cavity - have to be created inside
Blood vessels have to be introduced early into the soonto-be-enclosed round eye
Nerves (afferent & efferent) to & from the brain are needed
External & internal muscles & other auxilliary structueres
are needed

72. DEVELOPMENT of the EYE I from CNS
35 days pc
3 brain ‘vesicles’ are subdividing
Mesencephalon
Rhombencephalon
BRAIN
Diencephalon
now four, then Rhombencephalon
divides into Met- & Melencephalons
Cephalic flexure/bend
Cervical flexure
start the folding
Telencephalon
Surface
ECTODERM
MESENCHYM
E
Neural
RETINA
ECTODERM
Already before 35d pc, on
each side of the ‘head’,
interactions have started
between surface
ECTODERM, a bulge of
the FOREBRAIN & the
MESENCHYME

73. EYE PARTS’ EMBRYONIC SOURCES
Surface
ECTODERM
MESENCHYME
UVEA
LENS
SCLERA
CORNEAL
EPITHELIUM
CORNEAL
STROMA
Connective tissue &
muscle (& vessels) come
from cranial mesenchyme
LENS
Neural
RETINA
ECTODERM
RETINA
OPTIC
NERVE
VITREOUS
Two ectoderms
drive events
and shaping

74. ANTERIOR EYE PARTS’ EMBRYONIC SOURCES
Surface
ECTODERM
LENS
CORNEAL
EPITHELIUM
How does a surface layer produce
two separate structures?
In much the same way as an
endocrine gland is produced: by a
downgrowth of cells that then
break off the surface connection
Here the downgrowth makes the
lens vesicle, conferring a roundish
shape from early on
Mesenchyme
To have enough cells for the
future cornea and for the lens
vesicle, the surface ectoderm first
thickens to form a lens placode
over the brain-derived optic vesicle

75. LENS & OPTIC CUP DEVELOPMENT I
While still growing, both placode and
end of the optic vesicle invaginate
optic
vesicle
Mesenchyme
Intraretinal
space
lens placode
Double wall of optic cup is starting to form
Optic vesicle precedes the lens vesicle and is a distinct structure

76. OPTIC CUP DEVELOPMENT II: Choroid fissure
Mesenchyme
Blood vessels have to be introduced early
into the soon to be enclosed round eye
Together with the invagination
centrally at the end of the optic
cup,
an invagination along the
cup & stalk’s inferior
surface occurs, to create
the choroid fissure
in which runs the
hyaloid artery

77. OPTIC CUP DEVELOPMENT II: Coloboma
Mesenchyme
Blood vessels have to be introduced early
into the soon to be enclosed round eye
Together with the invagination
centrally at the end of the optic
cup,
an invagination along the cup &
stalk’s inferior surface occurs,
to create the choroid fissure
in which runs the
hyaloid artery
Also, an annular vessel
runs around the
outside of the
Imagine a penis in which the urethra near & into the
optic cup
glans is still open on its underside - the condition
of hypospadias - (but now contains an artery)
Defects in the eye from failure of the choroid
fissure to close are colobomas

78. OPTIC DEVELOPMENT III: Lens vesicle
Mesenchyme
LENS VESICLE
Mesenchyme
l
e
n
s
Inner wall thickens
p
l
a
c
o
d
e
Deeper part of Placode sinks into
mesenchyme & makes a vesicle
Optic cup becomes deeper
Attachment to surface ectoderm will be broken
so that surface ectoderm can become corneal
epithelium & intervening mesenchyme can form
the corneal stroma

79. OPTIC DEVELOPMENT IV: Lens differentiation
Mesenchyme
Attachment to surface ectoderm lost
Mesenchyme
Anterior vesicle cells become
subcapsular epithelium
Basal lamina becomes lens capsule
Posterior vesicle cells
become elongated lens cells
Posterior vesicle cells form the nucleus of the lens.
Subsequent lens cells derive from the subcapsular
epithelium

80. OPTIC DEVELOPMENT IV: Lens differentiation
Mesenchyme
Anterior-vesicle cells become
subcapsular epithelium
Basal lamina becomes
lens capsule
Lumen obliterated
Posterior-vesicle cells
elongate to lens cells
LENS

81. OPTIC DEVELOPMENT V: Retina differentiation I
Mesenchyme
Outer layer of cup stays thin
and beomes pigment cell
layer
Intra-retinal space occluded
Inner layer of cup thickens
and becomes Neural layer
Hyaloid artery reaches inside cup
After a while, the lens and vitreous no
longer need it, and it atrophies. Only
the neural retina continues to depend
on it, but under another name - central
artery of the retina

82. OPTIC DEVELOPMENT VI: Retina differentiation II
Mesenchyme
Inner layer of cup thickens
and becomes Neural layer
Where cells multiply, form
layers and differentiate to
the several cell types of the
neural retina
Outer layer of cup stays thin
and beomes pigment cell layer