Transcript slides - Smith Lab

Ocular Anatomy
G. Wollstein, MD
Associate Professor
The eye
Diameter: 24mm
• Anterior chamber: 3mm
deep, volume of 250μL
• Posterior chamber:
60μL
• Vitreous: 6.5mL
• Diameter: 24mm
• Anterior chamber:
3mm deep, volume
of 250μL
• Posterior chamber:
60μL
• Vitreous: 6.5mL
Tear Film
• Superficial oily layer
– Made by Meibomian glands
– Function: anti-evaporative agent
• Aqueous layer
– Made by lacrimal and accessory
lacrimal glands
– Function: provides smooth optical
surface, nutrients,
immunoglobulins, oxygen
• Mucin layer
– Made by goblet cell
– Function: wetting agent
Cornea
• Oval shape
- 12 mm wide
- 11 mm high
• Varying thickness
- Center: 0.55mm
- Limbus: 1mm
• Radius of curvature:
8mm
Cornea
• Average power: 43
diopters
• Steepest centrally,
flatter peripherally
• More curved
posteriorly then
anteriorly
Corneal Layers
OCT
Histology
Epithelium
Bowman
Stroma
Descement
Endothelium
Corneal Epithelium

Constant turnover of
cells
- Stem cells located in
crypts adjacent to
limbus
- Move centripetally and
anteriorly

Anchored to basement
membrane by
hemidesmosomes
Bowman’s layer




Anterior most stroma
Thickness: 8-14μm
Randomly dispersed
collagen fibrils
Cannot regenerate
[
Stroma

Composition:
- Collagen fibers
- Ground substance
- Keratocytes
Stroma



Fibrils arranged in
oblique and parallel
lamellae
Individual fibrils run the
entire diameter of the
cornea
Spatial organization of
the fibrils allows for
transparency
Descemet’s Membrane



Basement membrane
of the corneal
endothelium
Made of type IV
collagen
Thickens with age
[
Corneal Endothelium


A monolayer of hexagonal
cells
Cell density: 3000
cells/mm2
- Decreases with age

Cannot regenerate
- Loss of cells results in
corneal edema
Anterior Chamber Angle
• Formed between the
posterior aspect of the
cornea and anterior
aspect of iris
• Opening of the drainage
system
–
–
–
–
Trabecular meshwork
Schlemm’s canal
Collector channels
Ant. ciliary v.
Uvea
• Iris
• Ciliary body
• Choroid
Iris




Anterior border layer
Stroma
Dilator muscle
Posterior pigmented layer
- Two layers of heavily
pigmented epithelial cells
- Melanin
Iris Innervation


Dilator muscle: Primarily sympathetic
autonomic system
Sphincter muscle: Parasympathetic system
Ciliary Body

Base inserts into the
sclera spur via the
longitudinal muscle
fibers
- Gives rise to the iris

Apex is bordered by the
ora serrata of the retina
Ciliary Body - Functions

Accommodation
-

Aqueous humor
formation
-

Controlling the lens
curvature through
the zonules
Ciliary body
epithelium
Trabecular and
uveoscleral outflow
Lens
• Diameter: 9-10mm
• Ant.-post. width: 6mm
• Power: 20 Diopters
- Cornea: 40D
• The actively dividing
lens epithelial cells
are located just
anterior to the
equator of the lens
• The high refractive index of
the lens results from a high
concentration of alpha,
beta and gamma crystalins
in lens fibers
Choroid



Thickness: 0.25mm
Highly vascularized
layer
Fenestrated vessels
- Primary metabolic
source for the RPE
Choroid

“Spaghetti bowl”
Choroid - Vasculature


Arterial supply: Long
and short posterior
ciliary a. and anterior
ciliary a.
Venous drainage:
Channeled toward
equator vortex veins ->
ophthalmic v.
Bruch’s Membrane
• Separating between the choroid and retina
• Created from the fusion of basement
membranes of the choriocapillaris and RPE
• Play a critical role in preventing penetration of
abnormal vasculature into the retina
Retina
• Converts light stimuli
into electrical impulse
• Clinical macula:
Bounded by the
vascular arcade
• Histological macula: >1
ganglion cell body
Retina
• Fovea: Avascular center
of the macula
• “Center of vision”
Retina

Multilevel connections
between
photoreceptors and
optic nerve
RPE



A monolayer of hexagonal cells
RPE cells in the macula are taller, thinner and contain
more and larger melanosomes
Functions include:
-
Vitamin A metabolism
Maintenance of the outer blood retina barrier
Phagocytosis of the photoreceptor outer segments
Absorption of light
Heat exchange
Formation of matrix around the photoreceptors
Active transport of materials
Photoreceptors



The outer segment
consists of discs
connected to the inner
segment by the cilium
Constant shedding of
discs as exposed to light
High concentration of
mitochondria in the inner
segment to provide the
energy requirements
Photoreceptors


Photoreceptor density is greater in the fovea
than elsewhere in the retina
The only layers of the retina present in the
fovea are the photoreceptors and Henle’s
layer (outer plexiform layer in the fovea)
Photoreceptors


Nuclei in the outer
nuclear layer
Axons (cone pedicle
and rod spherule) in
the outer plexiform
layer
Inner Nuclear Layer



Made up of the cell
bodies of the bipolar,
horizontal and
amacrine cells
Interconnect
photoreceptors with
each other and with
ganglion cells
Initial steps of image
processing
Muller cells



Extend from the
internal to external
limiting membranes
Nuclei in the inner
nuclear layer
Provide support and
structural functions
for the retina
Inner Retina

Ganglion cell layer
- Cell bodies

Inner plexiform layer
- Ganglion cells dendrites

Nerve fiber layer
- Ganglion cell axons
Retina – Blood Supply
• CRA enter the eye
through the optic
nerve and bifurcate
into 4 main branches
• Supply inner retina
down to the inner
nuclear layer
• Outer retina supplied
by the choroidal
vasculature
Cool picture!
Vitreous
• Constitutes 95% of the
eye volume
• Main component:
water (98%)
• The component that
make vitreous viscous is
hyaluronic acid
• No time to cover other important ocular and
orbital structures
• Assembly of other important slides follows
Eyelids
Extraocular Muscles
Orbit
Orbital base
Arterial Supply
Venous Drainage
Orbital Cranial Nerves
The End