Mrs. Amany Ahmed Niazy Opto 435 Lecture 2. Eyeball The eyeball lies in a pyramid-shaped bony cavity...
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- Slide 1
- Mrs. Amany Ahmed Niazy Opto 435 Lecture 2
- Slide 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.
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- Three Tunics Outer Tunic: Cornea transparent part Sclera opaque
part. Intermediate Tunic: Choroid cord Ciliary body Iris Innermost
Tunic: Retina optic nerve
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- Anatomy of the Eye
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- 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.
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- Sclera "the white of the eye." Its the white, tough wall of the
eye. Along with the internal fluid pressure it keeps the eyes shape
and protects its delicate internal part.
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- Three Tunics Outer Tunic: Cornea transparent part Sclera opaque
part. Intermediate Tunic: Choroid cord Ciliary body Iris Innermost
Tunic: Retina optic nerve
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- Anatomy of the Eye
- Slide 9
- 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.
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- 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.
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- Iris Its 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.
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- Pupil Is the hole in the center of the iris, that light passes
through.
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- Three Tunics Outer Tunic: Cornea transparent part Sclera opaque
part. Intermediate Tunic: Choroid cord Ciliary body Iris Innermost
Tunic: Retina optic nerve
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- Anatomy of the Eye
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- 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.
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- Structure of the Retina Nerve cells Photoreceptors Choroid
Light
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- Optic Nerve
- Slide 18
- 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.
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- Eye lens
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- 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).
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- 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.
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- Vitreous The Vitreous is the clear liquid between the lens and
the retina. The space that it fills is called the vitreous
body.
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- 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
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- 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
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- 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.
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- Normal Flora of the Eye Following vaginal birth, the infants
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.
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- Normal Flora of the Eyes
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- Ocular Defense Mechanisms Nonspecific Ocular DefensesSpecific
Ocular Defenses EyelidsEye-associated lymphoid tissue
TearsLangerhans Cells Ocular EpitheliumImmunoglobulins Normal
Ocular Bacterial FloraT-lymphocytes MucinB-lymphocytes
Antibacterial Factors Macrophages & Natural Killer Cells
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- 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
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- 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.
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- Tear
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- The Tear Film ComponentFunction Flushing actionMechanical
removal of pathogens Mucin Prevents pathogen binding to ocular
surface. Traps microbes for removal via lacrimal drainage.
LactoferrinIron-binding protein B-LysinAttacks bacterial membrane
LysozymeHydrolyzes bacterial cell wall CytokinesRegulation of
immune responses. Immunoglobulins Opsonization of pathogens. Block
pathogen binding to ocular surface. Neutralization of toxins.
DefensinsInhibits pathogen growth.
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- 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
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- 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.
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- 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.
- Slide 36
- Antibacterial Factors - Lysozyme Its 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.
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- 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.
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- 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.
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- 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.
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- 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):
662685.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 Stephen A. Klotz,1,2,* Christopher C. Penn,3
Gerald J. Negvesky,4 and Salim I. Butrus4Author information
Copyright and License information