Dr. Andrea D. Szkely THE APPLE OF EYE Tunica fibrosa et Tunica
vasculosa bulbi
Slide 2
The eye is responsible for us to detect electromagnetis
radiation as LIGHT as well as, to distinguish between BRIGHT/DARK
contrasts and to see in COLOURS The visual organ comprises - the
apple of the eye with a 3 layered structure and the accessories
-eyelids and lacrimal apparatus THE ORGAN OF VISION Composition of
the EYE -external fibrous coat (Tunica fibrosa bulbi) Sclera Cornea
(+ Conjunctiva) -middle vascular coat (Tunica vasculosa bulbi,
Uvea) Choroidea Ciliary body Iris -inner nervous coat (Tunica
nervosa bulbi) Retina
Slide 3
5. WEEK: 2 optic vesicles form in the lateral aspects of the
DIENCEPHALON, then emerge to the surface to induce the LENS
primordium the LENS will be engulfed by the optic vesicles which
turns into a double walled wine glass the external wall keeps its
single layer - transforms to pigment epithelium the internal wall
develops into the pars optica of RETINA (4/5 of the retina)
composed by 9 layers, whereas in the blind part, pars caeca (1/5 of
the retina), 2 layers will be formed the 2 layered epithelium on
the iris and the ciliary body is also part of the retina
EMBRYOLOGY
Slide 4
The sclera, or white of the eye, is the opaque (usually white),
fibrous, protective, outer layer of the eye containing collagen
(and elastic) fibers. It is derived from the neural crest. In the
elderly, slightly yellow, fatty deposits may appear. The sclera
forms the posterior 80% of the connective tissue coat of the eye.
It is continuous with the dura mater and the cornea, and maintains
the shape of the globe, offering resistance to internal and
external forces, and provides an attachment for the extraocular
muscles. The sclera is perforated by nerves and vessels passing
through the posterior scleral foramen. At the optic disk,
two-thirds of the sclera continues with the dural sheath, the other
third with some choroidal tissue forms a plate (lamina cribrosa)
across the optic nerve with perforations through which the optic
fibers (fasciculi). The thickness of the sclera varies from 1 mm at
the posterior pole to 0.3 mm just behind the rectus muscle
insertions. The main parts of the eye also include the conjunctiva.
This is a thin layer covering the sclera. TUNICA FIBROSA BULBI
Sclera
Slide 5
The cornea has unmyelinated nerve endings sensitive to touch,
temperature and chemicals; a touch of the cornea causes an
involuntary reflex to close the eyelid. Because transparency is of
prime importance the cornea does not have blood vessels; it
receives nutrients via diffusion from the tear fluid at the outside
and the aqueous humour at the inside and also from neurotrophins
supplied by nerve fibres that innervate it. In humans, the cornea
has a diameter of about 11.5 mm and a thickness of 0.50.6 mm in the
center and 0.60.8 mm at the periphery. Transparency, avascularity,
the presence of immature resident immune cells, and immunologic
privilege makes the cornea a very special tissue. The cornea has no
blood supply; it gets oxygen directly through the air. It borders
with the sclera by the corneal limbus. TUNICA FIBROSA BULBI Cornea
L S C I The cornea is the transparent front part of the eye that
covers the iris, pupil, and anterior chamber. Together with the
lens, the cornea refracts light, and as a result helps the eye to
focus, accounting for approximately two-thirds of the eye's total
optical power. In humans, the refractive power of the cornea is
approximately 43 dioptres. While the cornea contributes most of the
eye's focusing power, its focus is fixed. The curvature of the
lens, on the other hand, can be adjusted to "tune" the focus
depending upon the object's distance.
Slide 6
TUNICA FIBROSA BULBI CORNEAL LAYERS Corneal epithelium:
stratified squamous epithelium. Irregularity or edema of the
corneal epithelium disrupts the smoothness of the air-tear film
interface, the most significant component of the total refractive
power of the eye, thereby reducing visual acuity. It is continuous
with the conjunctival epithelium. Bowman's layer (anterior limiting
membrane = a condensed layer of collagen) protects the corneal
stroma, consisting of irregularly-arranged collagen fibers. 8- 14
microns thick. Corneal stroma (substantia propria) a thick,
transparent layer, consisting of regularly-arranged collagen fibers
(approx. 200 layers of type I collagen fibrils). 90% of the corneal
thickness. Descemet's membrane (posterior limiting membrane) a thin
acellular layer that serves as the modified basement membrane of
the corneal endothelium. Corneal endothelium: a simple squamous or
low cuboidal monolayer of mitochondria-rich cells responsible for
regulating fluid transport between the aqueous and corneal stromal
compartments.
Slide 7
TUNICA VASCULOSA BULBI The uvea (Lat. uva, grape), also called
the uveal layer, uveal coat, uveal tract, or vascular tunic, is the
pigmented middle of the three concentric layers that make up an
eye. The name is possibly a reference to its reddish-blue or almost
black colour, wrinkled appearance and grape-like size and shape
when stripped intact from a cadaveric eye. The uvea lyes between
the corneoscleral unit and the retina. It is traditionally divided
into 3 regions, the iris, ciliary body and choroid. These
distinctions are based on their different structures as seen under
light microscopy, and continued use of these terms is appropriate
in anatomical studies.
Slide 8
Iris (Regenbogenhaut) TUNICA VASCULOSA BULBI The anterior part
of the UVEA (acts as a diaphragm). It forms a mobile separation
between the anterior and posterior chambers of the eye. Due to its
muscular components, it may change its thickness and extension,
while the PUPIL may shrink to 1,5 mm (Miosis) or widen to 12 mm
(Mydriasis) in response to changes in illumination. The M.
sphincter pupillae lyes near to the edge of the Pupil (Margo
pupillaris iridis), it is composed of a circular layer of oriented
smooth muscle cells. They will have cholinergic innervation. The M.
dilatator pupillae setzt is also composed of smooth muscle cells,
following a radial orientation, it reaches to the ciliary margin of
IRIS. It is innervated by noradrenergic axons deriving from the
Centrum ciliospinale (via Ganglion cervicale superius).
Slide 9
the anterior surface contains an incomplete layer of
Mesothelial cells (ENDOTHELIUM CAMERAE ANTERIORIS) The Stroma
contains a wide collection of cells (Melanocytes, Mast cells,
Macrophages and Fibrocytes), as well as blood vessels and nerves,
plus two muscles (M. sphincter and dilatator pupillae). the M.
sphincter pupillae lies close to the pupil the M. dilatator
pupillae forms a lose layer The posterior surface will be covered
in 2 layers of pigment epithelium (derivative of the RETINA).
Highly vascularized and innervated tissue. Circulus arteriosus
iridis major an anastomotic ring formed by the Aa. ciliares
posteriores longae and the Aa. ciliares anteriores at the Margo
ciliaris. Circulus arteriosus iridis minor radial anastomotic
vessels connecting the Margo ciliaris to the Margo pupillaris
iridis. The IRIS does not absorb aqueous humor due to the lack of
fenestrated capillaries IRIDAL LAYERS TUNICA VASCULOSA BULBI
Slide 10
Corpus ciliare (CILIARY BODY) TUNICA VASCULOSA BULBI The
ciliary body is the circular tissue inside the eye composed of the
ciliary muscle and ciliary processes. It is triangular in
horizontal section, and is coated by a double layer, the ciliary
epithelium. The inner layer is transparent and covers the vitreous
body, and is continuous from the neural tissue of the retina. The
outer layer is highly pigmented, continuous with the retinal
pigment epithelium, and constitutes the cells of the dilator
muscle. This double membrane is often regarded to be continuous
with the retina and a rudiment of the embryological correspondent
to the retina. The inner layer is unpigmented until it reaches the
iris, where it takes on pigment. The retina ends at the ora
serrata. The function of the ciliary body is accommodation, aqueous
humor production and the production and maintenance of the lens
zonules. It extends from the ora serrata to the root of the iris.
There are three sets of ciliary muscles in the eye, the
longitudinal, radial, and circular muscles. They are near the front
of the eye, above and below the lens. They are attached to the lens
by connective tissue called the zonule of Zinn, and are responsible
for shaping the lens to focus light on the retina. When the ciliary
muscle relaxes, it flattens the lens, generally improving the focus
for farther objects. When it contracts, the lens becomes more
convex, generally improving the focus for closer objects.
Slide 11
The epithelium consists of two layers: 1. pigmented, 2.
unpigmented. It is covered in both surfaces by Basement membranes
:Membrana limitans interna and externa. The Membrana limitans
externa is continouos with the BRUCH Membrane of the Choroid. The
Stroma corporis ciliaris is similar to the Stroma iridis. The M.
ciliaris consists of 3 parts: 1. An outer meridional muscle bundles
(BRCKE muscle), 2. A middle, radial bundle (Pars obliqua), 3. An
inner, circular bundle (MLLER muscle). The muscle contraction leads
to the dilation of lens fibres therefore the lens may follow the
curvature of the bulbus (e.g. will be rounder - Accomodation). The
innervation derives from the parasympathetic cranial nuclei (EW)
Corpus ciliare Histology TUNICA VASCULOSA BULBI
Slide 12
Choroid TUNICA VASCULOSA BULBI The choroid, also known as the
choroidea or choroid coat, is the vascular layer of the eye lying
between the retina and the sclera. In humans its thickness is about
0.5 mm. The choroid provides oxygen and nourishment to the outer
layers of the retina The choroid is supplied in humans by the
posterior ciliary arteries, originating form the ophthalmic artery.
The arteries of the uveal circulation, supplying the uvea and outer
and middle layers of the retina, are branches of the ophthalmic
artery and enter the eyeball without passing alongside the optic
nerve. The retinal circulation derives from the central retinal
artery, also a branch of the ophthalmic artery, but passes together
with the optic nerve. They are branching in a segmental
distribution to the terminal arterioles and do not form
anastomoses. This is clinically significant for diseases affecting
the choroidal blood supply. The macula, responsible for central
vision, and the anterior part of the optic nerve are dependent on
choroidal blood supply.
Slide 13
1. HALLER layer (Arteries) 2. Lamina vasculosa (Arterioles) 3.
Lamina choriocapillaris (capillaries) 4. Lamina vitrea (Complexus
basalis, BRUCH Membrane) the HALLER layer is composed of the
branches of the Aa. Ciliares posteriores breves (they break through
the sclera in the vicinity of the Discus n. optici) and of an
anastomotic mesh given by the Aa. ciliares posteriores longae and
the Aa. ciliares anteriores. the capillaries establish a glomerular
composition and will open through short venous tributaries into the
4 Vv. Vorticosae. These vessel lie in the Sclera and will be
drained by the V. ophthalmica superior et inferior. The BRUCH
membrane (cca. 2 m thick collagen- elastin layer) contains 3
layers, lyes above the pigment cells of the retina.
FUNCTIONS:maintaining the internal pressure, to form the blood
retina barrier, desaccomodation CHOROIDAL LAYERS: TUNICA VASCULOSA
BULBI Macular degeneration
Slide 14
TRABECULAR MESHWORK An area around the base of the cornea, near
the ciliary body, responsible for draining the aqueous humor from
the eye via the anterior chamber The tissue is spongy (Fontana
spaces) and lined by trabeculocytes; it allows fluid to drain into
the Schlemm's canal (venous sinus) flowing into the episcleral
veins. The corneal limbus is the border of the cornea and the
sclera. (TUMORS!!)