Transcript Anatomy of the Eye

Mrs. Amany Ahmed Niazy
Opto 435
Lecture 2
Eyeball
 The eyeball lies in a pyramid-shaped bony cavity
called orbit.
 Each eyeball is suspended by extra ocular muscles.
 A pad of fat lies behind the eyeball to provide a
protective cushion.
 30 ml Volume.
 Have an apex where nerves and vessels emerge.
Three Tunics
 Outer Tunic:


Cornea  transparent part
Sclera  opaque part.
 Intermediate Tunic:



Choroid cord
Ciliary body
Iris
 Innermost Tunic:

Retina  optic nerve
Anatomy
of the
Eye
Cornea
 Clear, dome-shaped surface that
covers the front of the eye.
 Tears that flow over it and
aqueous humor in the chamber
behind it keep it nourished.
 It allows the light to enter the
eyeball.
 It contains no blood vessels.
Sclera
"the white of the eye."
 It’s the white, tough wall of the eye.
 Along with the internal fluid pressure it keeps the eyes
shape and protects its delicate internal part.
Three Tunics
 Outer Tunic:


Cornea  transparent part
Sclera  opaque part.
 Intermediate Tunic:



Choroid cord
Ciliary body
Iris
 Innermost Tunic:

Retina  optic nerve
Anatomy
of the
Eye
Choroid
 A layer of blood vessels
between the retina and sclera.
 It connects with ciliary body in
the front of the eye and
attached to edges of the optic
nerve at the back of the eye.
Ciliary Body
 It lies just behind the iris.
 It produce aqueous fluid that
fills the front of the eye.
 It changes the shape of the
lens (accommodation).


Relaxes  flatten the lens 
distance vision.
Contracts  rounding out the
lens  close vision.
Iris
 It’s the colored part of the eye.
 It is a ring of muscle fibers
located behind the cornea and
in front of the lens.
 It contracts and expands,
opening and closing the pupil,
in response to the light.
 It help protect the retina.
Pupil
 Is the hole in the center of the iris, that light passes
through.
Three Tunics
 Outer Tunic:


Cornea  transparent part
Sclera  opaque part.
 Intermediate Tunic:



Choroid cord
Ciliary body
Iris
 Innermost Tunic:

Retina  optic nerve
Anatomy
of the
Eye
Retina
 The retina is a multi-layered
sensory tissue that lines the
back of the eye.
 It converts light rays into
electrical signals and sends
them to the brain through
the optic nerve.
Light
Structure of the Retina
← Nerve cells
← Photoreceptors
← Choroid
Optic Nerve
Eye lens
 Convex lens made of a
transparent and flexible
material like a jelly.
 Made of proteins.
 The crystalline lenses located
just behind the iris.
 Its purpose is to focus light onto
the retina.
Eye lens
Conjunctiva
The conjunctiva is a
thin transparent,
mucous membrane
that covers the inner
surface of the eyelid
and the white part of
the eyeball (the sclera).
Aqueous humor
 It is a clear fluid
between the cornea
and the iris
(anterior chamber).
 Produced by ciliary
body.
 Nourishes the
cornea and the lens
and gives the eye its
shape.
Vitreous
 The Vitreous is the
clear liquid between
the lens and the
retina.
 The space that it fills
is called the vitreous
body.
Normal Flora of the Eye
 Bacterial colonization of the eyelid margin and
conjunctiva is normal and beneficial for the eye.
Interactions between ocular surface mucosa and
resident nonpathogenic bacteria reduce opportunities
for pathogenic strains to gain a foothold.
 Clinically, the use of antibiotics or topical
corticosteroids, or a condition such as dry eye that
prevents normal tear turnover, may alter the spectrum
of eyelid and conjunctival flora
Normal Flora of the Eye
 They comprise of mainly bacteria which do not cause
infection in normal conditions but can be a main
source of infection after ocular surgery, trauma or in
immune compromised
Normal Flora of the Eye
 The composition of the normal ocular flora changes
dynamically throughout our lives, its affected by:
 Age.
 Geographic location.
 Immunosuppressioin.
 Ocular inflammation.
 Dry eye.
 Contact lens wear.
 Antibiotic use.
 Surgery.
Normal Flora of the Eye
 Following vaginal birth, the infant’s eye commonly
harbors multiple bacterial species, including:
 Staphylococcus aureus,
 S. epidermidis,
 Streptococcus spp.
 Propionibacterium spp.
 Escherichia coli.
 With increasing age, gram-negative bacteria are more
commonly isolated.
Normal
Flora of
the Eyes
Ocular Defense Mechanisms
Nonspecific Ocular Defenses
Specific Ocular Defenses
Eyelids
Eye-associated lymphoid tissue
Tears
Langerhan’s Cells
Ocular Epithelium
Immunoglobulins
Normal Ocular Bacterial Flora
T-lymphocytes
Mucin
B-lymphocytes
Antibacterial Factors
Macrophages & Natural Killer Cells
Eyelids & Eyelashes
 Eyelid, & bony orbit protect from external trauma &
airborne particles.
 Even the slightest contact with the eyelids, eyelashes,
or corneal surface stimulate the blink reflex.
 Once blink reflex is stimulated the lids sweep any
debris, microbes and allergens in the lacrimal
excretory system
Tears & Lacrimal Drainage
 It bathes the ocular surface & prevent adhesion of
pathogenic organisms.
 It lubricates the corneal surface and facilitates the washing
action of the eyelids.
 It is composed of 3 layers:
 Lipid enhancing the stability of tear film.
 Aqueous  many components (table 1)
 Mucoid  help in trapping the organisms and flushing them
out.
Tear
The Tear Film
Component
Function
Flushing action
Mechanical removal of pathogens
Mucin
•Prevents pathogen binding to ocular surface.
•Traps microbes for removal via lacrimal drainage.
Lactoferrin
Iron-binding protein
B-Lysin
Attacks bacterial membrane
Lysozyme
Hydrolyzes bacterial cell wall
Cytokines
Regulation of immune responses.
Immunoglobulins
•Opsonization of pathogens.
•Block pathogen binding to ocular surface.
•Neutralization of toxins.
Defensins
Inhibits pathogen growth.
Ocular Epithelium
 Nonkeratinized squamous epithelium of the
conjunctiva and cornea serves as an anatomic barrier
against pathogens.
 Constant epithelial cells exfoliation, aid in the removal
of microbes
Normal Ocular Flora
 Colonization of ocular surface by microorganisms is a
dynamic phenomenon.
 Most humans harbor at least some normal bacteria in
their periocular tissues (even if culture is negative).
 Delicate balance of host-parasite relationships in the
external ocular microenvironment.
Mucins
 They trap pathogenic microorganisms until they are
swept out of the ocular aria by blinking. (eg. prevents
Candida spp from adhering to contact lenses.)
 Muccin is expressed by most specialized ocular
epithelial tissues.
Antibacterial Factors - Lysozyme
 It’s a low-molecular-weight protein that demonstrates
bacteriostatic and bactericidal activity against a wide
range of primarily gram positive bacteria.
 It facilitates the breakdown of bacterial cell wall.
 It is one of the major components of tears.
Antibacterial Factors - Defensins
 It acts as an antibiotic, and produced by leukocytes.
 Defensin target is greater than lysozyme and extends
to gram positive and gram negative bacteria, fungi and
viruses.
Macrophages and Natural Killer
Cells
 Natural Killer (NK):


are important in the initial nonspecific response to most virus
infections.
once activated they secret antiviral cytokines.
 Macrophages:




they provide first line defense against bacteria fungi and parasite.
phagocytosis (ingestion) of pathogens
killing of ingested pathogens.
recruitment of additional immune cells via secretion of cytokines.
Keep in mind,
 The blood-ocular barrier prevents the free passage of most
large molecules from the bloodstream into the aqueous
and vitreous humor. As a result, levels of soluble
immunologic components within the fluid-filled spaces of
the eye are relatively low, except in cases of intraocular
infection or inflammation.
 The aqueous and vitreous humor are not normally
populated by immune cells, incases of intraocular
infection, injury or other similar diseases, it can quickly
become packed with inflammatory cells which compromise
the visual field.
In summary
The eye is well equipped with innate and specific
defense systems. Mechanical, soluble, and cellular
components work in synchronization to prevent loss
of vision from infectious organisms and from the
damaging effects of the host's own immune
response.
ocular microbiology and immunology
represents a field rich in unanswered
questions and is deserving of continued
aggressive research
Clin Microbiol Rev. Oct 2000; 13(4): 662–685.PMCID: PMC88956Fungal and Parasitic Infections of the EyeStephen A. Klotz,1,2,*
Christopher C. Penn,3 Gerald J. Negvesky,4 and Salim I. Butrus4Author information ► Copyright and License information