Histology of the eyeball Flashcards
what are 3 tunics of the eye
-fibrous
-vascular
-neural
what makes up the fibrous layer
-cornea
-sclera
what makes up the vascular layer
-choroid
-ciliary body
-iris
what makes up the neural layer
retina
what is the cornea
its the transparent avascular and highly innervated anterior portion of the fibrous coat
what are the layers of the cornea
-corneal epithelium
-bowman’s membrane
-stroma
-descemet’s membrane
-corneal endothelium
what is the corneal epithelium like
its non keratinized stratified squamous epithelium
the corneal epithelium has numerous what
free nerve endings
what is the bowman’s membrane
its a homogenous non cellular layer containing type 1 collagen fibrils
what is the thickest layer of the cornea
stroma
what is the stroma composed of
parallel lamellae of dense collagenous C.T (200-250 layers)
what is each lamella of the stroma composed of
parallel type 1 collagen fibers with long fibroblasts
the basement membrane of the corneal epithelium rests on what
bowman’s membrane
what does the bowman membrane (anterior limiting membrane) separate
corneal epithelium from stroma
in the corneal stroma what is located between the layers of collagen fibers
flattened fibrocytes
what accounts for the transparency of the cornea
the regular arrangement of the collagen fibers and their small diameter in the corneal stroma
what lines the posterior surface of the cornea
posterior endothelium
what does the descemets membrane (posterior limiting lamina) separate
the posterior endothelium and the corneal stroma
the lateral margins of the cornea are continuous with what
the conjunctiva and sclera
what is the descemets membrane
its a thick basement membrane
what is the corneal endothelium
its a simple squamous epithelium
what is the function of the corneal endothelium
-it forms the descemets membrane
-it keeps the stroma relatively dehydrated
whats the limbus
its the highly vascular transition zone between the cornea and sclera
what does the limbus contain
-trabecular meshwork, which is endothelium lined spaces that lead to the canal of schlemm
-canal of schlemm, which drains the aqueous humor into the venous system
what does the sclera cover
5/6 of the fibrous tunic
what does the sclera proper consist of
interlacing bundles of type 1 collagen
whats located in the deeper regions of the sclera
melanocytes
what is the choroid
its the vascular pigmented posterior portion of the middle vascular tunic
what is the choroid composed of
loose C.T with melanocytes
what separates the choroid from the retina
its Bruch’s membrane
what does the Bruch’s membrane consist of
-basal laminae of the capillaries and pigmented epithelium
-elastic and collagen layers
what is the ciliary body
it is the anterior continuation of the choroid
what does the choroid surround
the lens
what forms the ciliary body
loose vascular and pigmented C.T that contains 3 bundles of smooth muscle cells i.e. the ciliary muscle
what lines the inner surface of the ciliary body
pars ciliaris retinae ( 1 row of outer pigmented columnar cells and 1 row of inner non pigmented columnar cells)
the ciliary bodys highly folded inner surface forms what
ciliary processes
what are ciliary processes
short extensions from the inner surface of the anterior 1/3 of the ciliary body towards the lens
what covers the ciliary processes
pars ciliaris
ciliary processes give attachment to what
the lens suspensory ligaments (zonular fibers)
what do the zonula fibers do
anchor the lens and are attached to the ciliary processes
what forms the zonule of zinn
the radially oriented zonular fibers
what are the 2 components of the iris
anterior uveal/ stroma face- made of fibroblasts and melanocytes (its non epithelial)
posterior neuroepithelial surface made up of the retina
the anterior uveal face of the iris consists of what
-vascularized loose connective tissue rich in melanocytes, macrophages, fibrocytes and sphincter pupillae muscle at the tip
what are the 2 pigmented sub layers of the posterior neuroepithelial surface
-outer pigmented layer of the ciliary body, with myoepithelial cells that form the dilator pupillae muscle anterior to it
-inner highly pigmented inner layer, that is a continuation of the retina that forms the posterior epithelium
what are the 5 layers of the iris
- anterior border layer- which is an incomplete layer of fibroblasts and melanocytes
- stroma- which a poorly vascularized C.T with fibroblasts and melanocytes
- vessel layer- which is well vascularized loose C.T that centrally contains sphincter pupillae muscle
- dilator pupillae muscle layer- which contains myoepithelial cells
- posterior surface layer (pigmented epithelium layer)- which is composed of 2 rows of pigmented epithelial cells which are a continuation of the pars ciliaris retinae
the posterior part of the iris is always what colour
brown
whats the iris like in people with brown eyes
they have pigment throughout the iris
whats the iris like in people with blue eyes
the iris is clear nd the brown pigment at the back of the iris appears blue after passing through sclera/cornea
the sphincter pupillae muscle form a circle where
at pupillary margin
the sphincter pupillae is under what control
parasympathetic
the dilator pupillae muscle is under what control
sympathetic control
what mediates pupillary constriction/ miosis
sphincter pupillae muscle (circular muscles)
whats the light pathwaywhat mediates pupillary dilation/ mydriasis
dilator pupillae muscle (radial muscles)
what forms the sphincter pupillae muscle
a ring of smooth muscle
what makes the dilator pupillae muscle
myoepithelium adjacent to the pigmented double epithelium
whats the light pathway
cornea> anterior segment> pupil> lens> posterior segment> neural layer of retina> pigmented retina
where is the lens positioned
behind the iris and between the ciliary processes
the ciliary muscles are under what control
parasympathetic
whats the lens
its a transparent, biconvex elastic and avascular structure
what does the lens consist of
-lens capsule
-subcapsular epithelium
-lens substance
what does the lens not have
blood vessels or nerves
what covers the anterior side of the lens
simple epithelium/ subcapsular
Where is the basal side of the simple (subcapsular) epithelium in the lens facing and what covers it
It’s facing the anterior and is covered by the basement membrane/lens capsule
whats the apical side of the subcapsular epithelium doing
ancoring the posterior lens fibers
whats the lens capsule
a thick,elastic basal lamina
what forms the lens capsule
mitotically active cells of the subcapsular epithelium
what inserts into the lens capsule
xonule fibers
cells of the subcapsular epithelium that are mitotically active only cover what
te anterior hemisphere of the lens
what happens as the mitotically active cells of the subcapsular epithelium divide
they gradually move towards the equator of the lens were they transform into lens fibers
what proteins make up the lens
filensin and crystallin ( alpha, beta and gamma)
what do the proteins in the lens do
they are responsible for the transparency and refractive properties of the lens and account for up to 60% of the mass of the lens fibers
new lens fibers are produced when
throughout life
what is presbyopia
decreased elasticity and power of accommodation with age
whats a cataract
a loss of transparency (can be caused by infections, metabolic, hereditary, trauma, uv light)
myoepithelial cells in the outer layer of the iris is continuous with what
retina (because they have the same embryonic origin)
the layer adjacent to the stroma of the iris has what
radially oriented muscular extensions which form the dilator pupillae muscle beneath the anterior layer of the retina
the outer non-sensory retinal pigmented epithelium is derived from where
the outer layer of the optic cup
the pigmented epithelium of the retina contain many what
melanin granules
what is the outer non sensory pigmented layer of the retina like
-has cuboidal to columnar epithelium
-has apical microvilli
-has abundance of melanin granules
whats the function of the pigmented epithelium of the retina
-absorbs light
-phagocytosis of membranous discs from tips of rods
-esterification of vitamin A
what are the layers of the retina
- pigmented epithelium
- rods and cones layer
- outer limiting membrane
- outer nuclear layer
- outer plexiform layer
- inner nuclear layer
- inner plexiform layer
- ganglion cell layer
- optic nerve fiber layer
- inner limiting layer
whats the visual pigment in rods and cones
R- rhodopsin
C- photopsin
the retina is an outgrowth of
the brain
where do photoreceptors sit
on pigmented layer of choroid
the fovea centralis is in direct line with what
lens
each rod and cone has what
-dendrite
-cell body
-axon
what forms the dendrite of rods and cones
-outer segment which contains: membranous discs, rhodopsin in rods, iodopsin in cones
-connecting stalk with modified cilium
-inner segment
the axon of the rod and cones synapse with what
the dendrite of bipolar neuron of inner nuclear layer
whats the outer limiting membrane of the retina
a region of zonula adherent junctions between muller cells and photoreceptors
what does the outer nuclear layer of the retina contain
nuclei of rods and cones
what does the outer plexiform layer of the retina contain
axodendritic synapses between the photoreceptor cells and dendrites of bipolar and horizontal cells
what does the inner nuclear layer of the retina contain
nuclei of:
-bipolar neurons
-horizontal neurons
-amacrine neurons
-neuroglial cells (muller cells) that extend between the vitreous body and the inner segments of the rods and cones
what does the inner plexiform layer of the retina contain
axodendritic synapses between axons of bipolar neurons and dendrites of ganglion cells and amacrine cells
what does the ganglion cell layer of the retina contain
cells bodies of large multipolar neurons of the ganglion cells
what does the optic nerve fiber layer of the retina contain
unmyelinated axons of the ganglion cells ( NB. these axons become myelinated as the nerve pierces the sclera)
what forms the inner limiting membrane of the retina
basal laminae of the muller cells
where does the fovea centralis lie and what does it do
center of macula lutea
responsible for visual acuity
what are 4 cell groups of the sensory retina
- photoreceptor neurons- rods and cones
- conduction neurons- bipolar and ganglion cells
- association neurons- horizontal and amacrine cells
- supporting neuroglia cells- muller cells and astrocytes
what happens at the optic papilla
-the optic nerve penetrates the retinal layer and leaves the eye
- the retinal blood supply enters and exists
whats the second blood supply system of the retina
central retinal artery and vein
what is the conjunctiva
its the transparent mucous membrane lining the inner surfaces of the eyelids ( palpebral conjunctiva) and reflecting onto the sclera of the anterior surface of the eye ( bulbar conjunctiva)
whats the epithelium of the conjunctiva
stratified columnar epithelium with many goblet cells
what is the lamina propria of the conjunctiva
loose C.T
what requires an ophthalmologic exam
-retinal detachment
-iridodialysis
-opacified cornea
-dislocated lens
in an ophthalmologic exam what reveals a corneal abrasion
fluorescein
what does the bowmans membrane consist of
densely packed collagen fibrils embedded in ground substance
whats the sclera
the tough layer of dense CT (consisting of collagen fibers and elastic networks)
the sclera is distended by what
intraocular pressure
what are functions of the sclera
-maintains the shape of the eyeball
-is the site for ocular muscle attachment
-provides a point of insertion for part of the ciliary muscle
what is the choriocapillary layer
its where there are small blood vessels in the innermost part of the choroid that supply the retina with nutrients
what forms the ciliary epithelium
pars ciliaris of the retina
the outer cell layer of ciliary body is what
pigmented
the inner cell layer of the ciliary body is what
non pigmented
What do 2 of the bundles of the ciliary muscle do
they attach to the sclera and stretch the ciliary body when they contract , which regulates the tension of the zonal e fibers
What does the reduced tension in the suspensory ligaments do
It results in the thickening of the lens which focuses the lens on close objects , in a process called accommodation
The outer non sensory retinal pigmented epithelium extends how
From optic disc to ora serrata
