Anatomy of the Eye - PowerPoint Presentation

Slide1

Anatomy of the Eye

Mrs.

Amany

Ahmed

Niazy

Opto

435

Lecture

2

Slide2

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. Slide3

Three Tunics

Outer Tunic:

Cornea

 transparent partSclera  opaque part. Intermediate Tunic:Choroid cordCiliary body

Iris

Innermost Tunic:

Retina  optic nerveSlide4

Anatomy of the EyeSlide5

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. Slide6

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. Slide7

Three Tunics

Outer Tunic:

Cornea

 transparent partSclera  opaque part. Intermediate Tunic:Choroid cordCiliary body

Iris

Innermost Tunic:

Retina  optic nerveSlide8

Anatomy of the EyeSlide9

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.

Slide10

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. Slide11

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. Slide12

Pupil

Is the hole in the center of the iris, that light passes through. Slide13

Three Tunics

Outer Tunic:

Cornea

 transparent partSclera  opaque part. Intermediate Tunic:Choroid cordCiliary body

Iris

Innermost Tunic:

Retina  optic nerveSlide14

Anatomy of the EyeSlide15

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.

Slide16

Structure of the Retina

← Nerve cells

← Photoreceptors

← Choroid

LightSlide17

Optic NerveSlide18

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. Slide19

Eye lensSlide20

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). Slide21

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. Slide22

Vitreous

The

Vitreous

is the clear liquid between the lens and the retina. The space that it fills is called the vitreous body. Slide23

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 floraSlide24

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 Slide25

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. Slide26

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.Slide27

Normal Flora of the EyesSlide28

Ocular Defense Mechanisms

Nonspecific Ocular Defenses

Specific Ocular Defenses

EyelidsEye-associated lymphoid tissueTears

Langerhan’s

Cells

Ocular Epithelium

Immunoglobulins

Normal Ocular Bacterial Flora

T-lymphocytes

Mucin

B-lymphocytes

Antibacterial Factors

Macrophages

& Natural Killer CellsSlide29

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 systemSlide30

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. Slide31

TearSlide32

The Tear Film

Component

Function

Flushing actionMechanical 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. Slide33

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 microbesSlide34

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. Slide35

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. Slide36

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. Slide37

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. Slide38

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 pathogenskilling of ingested pathogens. recruitment of additional immune cells via secretion of cytokines. Slide39

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. Slide40

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: PMC88956

Fungal and Parasitic Infections of the

Eye

Stephen

A. Klotz,1,2,*

Christopher C. Penn,3

Gerald J. Negvesky,4 and

Salim I. Butrus4Author information ► Copyright and License information ►