Eye Anatomyanatomi

8/12/2019 Eye Anatomyanatomi

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EYE ANATOMYSMF MATA 2012

Yeli Asti

I11108047


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Embriology of the eye


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Embriology of the eye


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Embriology of the eyeSurface ectoderm Neural crest

Neural ectoderm Mesoderm

lens, the lacrimal

gland, the epithelium

of the cornea,

conjunctiva, and

adnexal glands,

epidermis of theeyelids

corneal keratocytes,

the endothelium of

the cornea and the

trabecular

meshwork, the

stroma of the iris andchoroid, the ciliary

muscle, the

fibroblasts of the

sclera, the vitreous,

and the optic nerve

meninges, orbital

cartilage and bone,

the orbital connective

tissues and nerves,

the extraocular

muscles, and the

subepidermal layers

of the eyelids.

optic vesicle and

optic cup

pigmented and

nonpigmented layers

of ciliary epithelium,

the posteriorepithelium, the dilator

and sphincter

muscles of the iris,

and the optic nerve

fibers and glia

vitreous, extraocular

and lid muscles, and

the orbital and ocular

vascular endothelium


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Embryology of Specific

Structures1. Lids & Lacrimal Apparatus The lid buds are first seen at 6 weeksgrowing in front of the eye, where they meet and fuse by 8 weeks.

2. Sclera & Extraocular Muscles identifiable by 7 weeks.Development of these structures is well advanced by the fourthmonth. Tenon's capsule appears about the insertions of the rectusmuscles at 12 weeks and is complete at 5 months

3. Anterior Segment The anterior chamber of the eye first appears at 7weeks and remains very shallow until birth

4. Lens Soon after the lens vesicle lies free in the rim of the optic cup (6weeks), the cells of its posterior wall elongate, encroach on the emptycavity, and finally fill it in (7 weeks).At about 6 weeks, a hyalinecapsule is secreted by the lens cells.

5. Ciliary Body & Choroid At 3 weeks, a network of capillaries

encircles the optic cup and develops into the choroid. By the thirdmonth, the intermediate and large venous channels of the choroid aredeveloped and drain into the vortex veins to exit from the eye.

6. Retina The outer layer of the optic cup remains as a single layer andbecomes the pigment epithelium of the retina. Pigmentation begins at5 weeks. Secretion of the inner layer of Bruch's membrane occurs by 6weeks.


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Bony orbit and orbital walls

Seven bones make up the

bony orbit:

Frontal

Zygomatic

Maxillary Ethmoidal

Sphenoid

Lacrimal

Palatine


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EYE BALL

Source: Saladin. Anatomy & Physiology. Mc Graw Hill

Companies. 2003.


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Fibrous Tunic

Sclera Fibrous outer protective coating

of the eye

Composed of type collagen 1fibers and fibroblasts

The sclera covers the entire

eyeball except the cornea Sclera gives shape to the

eyeball

Margins:

- anterior: episclera

- Posterior: lamina cribosa

Nerve: ciliary nerves Blood supply: ciliary arteries

Junction between sclera andcornea: canal of schlemm (drainaqueous humor into sinus)


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Fibrous tunic

Cornea Transparent, avascular

Covers the iris

Helps focus light into retina

outer surface : nonkeratinizedstratified squamous epithelium

The middle coat of the cornea :collagen fibers and fibroblasts,and the inner surface: simplesquamous epithelium

Sources of nutrition for thecornea are the vessels of thelimbus, the aqueous, and thetears.

The superficial cornea also getsmost of its oxygen from theatmosphere.

Nerve: N V (III)


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Vascular Tunic

Located in posterior, highly vascular, darkly pigmented choroidadhering to the sclera and retina.

Intermediate between the choroid and iris is the ciliary body and its

smooth ciliary muscle attached by suspensory ligaments to the lens.

The anteriorly placed, disc-shaped iris contains two separate smooth

muscles that regulate the aperture of the pupil in the iris.


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Uveal tract


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Uveal tract

Iris Anterior extension of the ciliary body

lies in contiguity with the anterior surface of the lens, dividing the

anterior chamber from the posterior chamber, each of which

contains aqueous humor

Consists of melanocytes and circular and radial smooth muscle

fibers

Function: controls the amount of light entering the eyeball through

the pupil

Blood supply: major circle of the iris

Nerve: cilliary nerve

When bright light stimulates the eye, parasympathetic fibers of the

oculomotor (III) nerve stimulate the circular muscles (sphincter

pupillae) of the iris to contract, causing a decrease in the size of the

pupil (constriction). In dim light, sympathetic neurons stimulate the

radial muscles (dilator pupillae) of the iris to contract, causingan increase in the u ils size dilation .


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The amount of light that enters the eye through the pupil is

proportional to the areaof the pupil or to the square of the diameter

of the pupil. The pupil of the human eye can become as small as

about 1.5 millimeters and as large as 8 millimeters in diameter.

The quantity of light entering the eye can change about 30-fold as

a result of changes in pupillary aperture.


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Uveal tract

Cilliar body ciliary body (extends from the ora serrata (the jagged anterior

margin of the retina), to a point just posterior to the junction of

the sclera and cornea

contains melanin-producing melanocytes the ciliary body consists of ciliary processes and ciliary muscle.

the ciliary processes are protrusions or folds on the internal

surface of the ciliary body. they contain blood capillaries that

secrete aqueous humor. extending from the ciliary process are

zonular fibers (suspensory ligaments) that attach to the lens.


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the ciliary muscle is a circular

band of smooth muscle.

contraction or relaxation of the

ciliary muscle changes the

tightness of the zonular fibers,

which alters the shape of the

lens, adapting it for near or far

vision

blood supply: major circle of the

iris. Nerve: ciliary nerves.


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Choroid Posterior segment of the uveal

tract, between the retina andthe sclera.

The deeper the vessels are

placed in the choroid, thewider their lumens

The internal portion of thechoroid vessels is known asthe choriocapillaris

Anteriorly, the choroid joins

with the ciliary body The aggregate of choroidal

blood vessels serves tonourish the outer portion ofthe underlying retina


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Aqueous humor

Aqueous humor is produced bythe ciliary body

Posterior chamber pupil

anterior chamber trabecular

meshwork in the anterior chamber

angle. During this period, there is some

differential exchange of

components with the blood in the

iris.

Functions:

1. Its helps maintain shape of

eyeball

2. supplies oxygen and nutrients to

lens and cornea


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Outflow of Aqueous

The trabecular meshwork is composed of beams of collagen andelastic tissue covered by trabecular cells that form a filter with a

decreasing pore size as the canal of Schlemm is approached.

Contraction of the ciliary muscle through its insertion into the

trabecular meshwork increases pore size in the meshwork and

hence the rate of aqueous drainage.

Passage of aqueous into Schlemm's canal depends on cyclic

formation of transcellular channels in the endothelial lining. Efferent

channels from Schlemm's canal (about 30 collector channels and 12

aqueous veins) conduct the fluid directly into the venous system.

Some aqueous passes between the bundles of the ciliary muscle

into the suprachoroidal space and then into the venous system ofthe ciliary body, choroid, and sclera (uveoscleral flow)


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Oculi chamber


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Vitreus body

The vitreous fills the spacebetween the lens and the

retina and consists of a three-

dimensional collagen fiber

matrix and a hyaluronic acid

gel

The vitreous is 98% water.

The outer surface of the

vitreous, known as the cortex,

is in contact with the lens

(anterior vitreous cortex) and

adherent in varying degrees tothe surface of the retina

(posterior vitreous cortex)

The vitreous cortex is adherent tothe lens and especially to the retinal

surface to varying degrees


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Vitreus body


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Neural tunic

Lens biconvex, avascular, colorless,

and almost completelytransparent structure, about 4mm thick and 9 mm in diameter.

It is suspended behind the irisby the zonule, which connects itwith the ciliary body

Containing mostly type IVcollagen and glycoprotein thatcovers the epithelial cells andenvelops the entire lens

Margins: anterior: aqueous,posterior: the vitreous

lens helps focus images on theretina to facilitate clear vision.


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Lens capsule: semipermeable membranes zonule of Zinn: suspensory ligament, composed of numerous fibrils

that arise from the surface of the ciliary body and insert into the lens

equator.

The lens nucleus is harder than the cortex.

With age, subepithelial lamellar fibers are continuously produced the lens gradually becomes larger and less elastic throughout life


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Neural tunic

Retina thin, semitransparent, multilayered sheet of neural tissue that lines

the inner aspect of the posterior two-thirds of the wall of the globe.

The optic disk,located on the posterior wall of the orb, is the exit

site of the optic nerve. Because it contains no photoreceptor cells, it

is insensitive to light and is therefore called the "blind spot"of the

retina. Approximately 2.5 mm lateral to the optic diskis a yellow-

pigmented zone in the retinal wall called the macula lutea(yellow

spot). Located in the center of this spot is an oval depression, the

fovea centralis,where visual acuity is greatest


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Functions of retina:Receives light and converts it into receptor potentials and nerve

impulses. Output to brain is via axons of ganglion cells, which form

the optic (II) nerve.

Blood supply:

1. choriocapillaris immediately outside Bruch's membrane, whichsupplies the outer third of the retina, including the outer plexiform

and outer nuclear layers, the photoreceptors, and the retinal

pigment epithelium;

2. branches of the central retinal artery, which supply the inner two-

thirds

Layers of retina from inners to


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Layers of retina from inners to

outers:

1) internal limiting membrane; (2) nerve fiber layer, containing the ganglion cell axons passing to

the optic nerve;

(3) ganglion cell layer;

(4) inner plexiform layer, containing the connections of theganglion cells with the amacrine and bipolar cells;

(5) inner nuclear layer of bipolar, amacrine, and horizontal cellbodies;

(6) outer plexiform layer, containing the connections of the bipolarand horizontal cells with the photoreceptors;

(7) outer nuclear layer of photoreceptor cell nuclei;

(8) external limiting membrane;

(9) photoreceptor layer of rod and cone inner and outersegments; and

(10) retinal pigment epithelium .The inner layer of Bruch'smembrane is actually the basement membrane of the retinalpigment epithelium.


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Layers of retina


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Layers of retina


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Layers of retina

Pigment Epithelium The pigment epithelium, derived from the outer layer of the optic

cup, is composed of cuboidal to columnar cells (14 mwide and 10

to 14 mtall) whose nuclei are located basally

The cells are attached to Bruch's membrane, which is located

between the choroid and the pigment cells Functions:

1. Absorb light after it has passed through and stimulated the

photoreceptors, thus preventing reflections from the tunics, which

would impair focus.

2.Continually phagocytose spent membranous disks from the tips ofthe photoreceptor rods.

3. Esterifying vitamin Aderivatives in their SER (smooth endoplasmic

reticulum)


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Layers of retina

Layers of Rod and cone Both rods and cells are polaarized cells

whose apical portions, known as theouter segments,are specializeddendrites

The outer segments of the rods andcones are surrounded by pigmentedepithelial cells The bases of the rod andcone cells form synapses with theunderlying cells of the bipolar layer.

There are approximately 100 to 120million rods and 6 million cones. Rodsare specialized receptors forperceiving objects in dim light,

whereas cones are specializedreceptors for perceiving objects inbright light reception. Cones arefurther adapted for color vision, whereasrods perceive only light. Rods and conesare unevenly distributed in the retina, inthat cones are highly concentrated in thefovea; thus, this is the area of the retinawhere high-acuity vision occurs.


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Rods Cones

Activated in dim light only, areso sensitive that they can

produce a signal from a singlephoton of light

The outer segment of the rod,its dendritic end, presents severalhundred flattened membranouslamellae

The membranes containrhodopsin (visual purple),alight-sensitive pigment

rods contain more rhodopsin,respond more slowly thancones, and have the capacity to

collectively summate thereception.

inner segment of the rodisseparated from the outer segmentby a constriction called theconnecting stalk.

Activated in bright light and

produce greater visual acuity

compared with rods.There arethree types of cones, each

containing a different variety of

the photopigment iodopsin.Each

variety of iodopsin has a

maximum sensitivity to one of

three colors of the spectrum-red, green, and blue-and the

difference resides in the opsins

rather than in the 11-cisretinal.

Cones are elongated cells (60 m

long by 1.5 min diameter),being longer and narrower at the

fovea centralis


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Structure of cones: Their apical terminal (outer segment) is shaped more like a cone

than a rod.

The disks of cones, although composed of lamellae of the

plasmalemma, are attached to the plasma membrane, unlike thelamellae of the rods, which are separated from the plasma

membrane.

Protein produced in the inner segment of cones is inserted into

the disks throughout the entire outer segment; in the rods, it is

concentrated in the most distal region of the outer segment.

Unlike rods, cones are sensitive to color and provide greater

visual acuity.

Recycling of the cone photopigment does not require the retina

pigment cells for the processing.


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Layers of retina

External (Outer) LimitingMembrane

this structure is not amembrane. Instead, electronmicrographs have revealed thatthis "layer" is a region of

zonulae adherentes betweenMller cells (modifiedneuroglial cells) and thephotoreceptors. Distal to this,microvilli of the Mller cellsproject into the intersticesbetween the inner segments of

the rods and cones.

Outer Nuclear Layer consists of a zone occupied

mainly by the nuclei of the rodsand cones

Outer Plexiform Layer

Axodendritic synapsesbetween the photoreceptor cellsand dendrites of bipolar andhorizontal cells are located inthe outer plexiform layer.

Located within this invaginated

synaptic region is a ribbon-likelamella (synaptic ribbon)containing neurotransmitter. It isbelieved that this structurecaptures and assists indistributing the neurotransmitter.


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Layers of retina

Inner Nuclear Layer1. Bipolar neurons: summation

of the signals, which isespecially useful in low lightintensity

2. Horizontal cell function: to

modulate the synaptic activity.

3. Amacrine cells: as a feedbackmechanism by transferringneuronal information derivedfrom the bipolar cell-ganglionsynaptic complex to

interplexiform cells, whoseaxons communicate withbipolar and horizontal cells.

4. Mller cells: supporting cellsfor the neural retina.

Inner Plexiform Layer1. Ganglion Cell Layer:

Cell bodies of large multipolarneurons of the ganglion cells,up to 30 min diameter, arelocated in the ganglion cell

layer.

The axons of these neuronspass to the brain.Hyperpolarization of the rodsand cones activates theseganglion cells, which then

generate an action potentialthat is passed by their axonsto the brain via the visualrelay system


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2. Optic Nerve Fiber Layer: are formed of unmyelinated axons of theganglion cells in the optic nerve fiber layer. These axons become

myelinated as the nerve pierces the sclera

3. Inner Limiting Membrane:

Basal laminae of the Mller cells compose the inner limiting

membrane


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Processing Visual Input in the

Retina

Neural organization of the retina: peripheralarea to the left, foveal area to the right.


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Processing Visual Input in the

Retina

Rods and cones cells

Bipolar cell Horizontal cell

Increase the

sensitivity and

the sharper of

vision

Enhance contrast in

visual scene, assist in

the diferentiation of

various color

Amacrine cell

Ganglion cell

Optic nerve

Lateral

inhibiton

W, X, Y cells

M h i f


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Mechanism of

"Accommodation"


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lens ligaments to the eyeball is the ciliary muscle,which itself has

two separate sets of smooth muscle fibers:

1. The meridional fibers: extend from the peripheral ends of the

suspensory ligaments to the corneoscleral junction. When these

muscle fibers contract, theperipheral insertionsof the lens

ligaments are pulled medially toward the edges of the cornea,

thereby releasing the ligaments' tension on the lens.

2. The circular fibers: are arranged circularly all the way around

the ligament attachments so that when they contract, a

sphincter-like action occurs, decreasing the diameter of the

circle of ligament attachments; this also allows the ligaments to

pull less on the lens capsule.


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The ciliary muscle is controlled almost entirely by parasympatheticnerve signals transmitted to the eye through the third cranial nerve

from the third nerve nucleus in the brain stem

Stimulation of the parasympathetic nerves contracts both sets of

ciliary muscle fibers, which relaxes the lens ligaments, thus allowing

the lens to become thicker and increase its refractive power. With

this increased refractive power, the eye focuses on objects nearerthan when the eye has less refractive power.

Consequently, as a distant object moves toward the eye, the number

of parasympathetic impulses impinging on the ciliary muscle must be

progressively increased for the eye to keep the object constantly in

focus.


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Visual aquity

The average diameter of the cones in the foveaof the retina-thecentral part of the retina, where vision is most highly developed-is

about 1.5 micrometers

The normal visual acuity of the human eye for discriminating

between point sources of light is about 25 seconds of arc

The fovea is less than 0.5 millimeter (


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Autonomic Control ofAccommodation and Pupillary

Aperture


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The parasympathetic preganglionic fibers arise in the Edinger-Westphal nucleus(the visceral nucleus portion of the third cranial

nerve) and then pass in the third nerveto the ciliary ganglion, which

lies immediately behind the eye.

There, the preganglionic fibers synapse with postganglionic

parasympathetic neurons, which in turn send fibers through ciliary

nervesinto the eyeball. These nerves excite (1) the ciliary musclethat controls focusing of the eye lens and (2) the sphincter of the iris

that constricts the pupil.


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Brain pathway and visual field


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1. The axons of all retinal ganglion cells in one eye exit theeyeball at the optic disc and form the optic nerve on that

side.

2. At the optic chiasm, axons from the temporal half of each

retina do not cross but continue directly to the lateral

geniculate nucleus of the thalamus on the same side.3. In contrast, axons from the nasal half of each retina

cross the optic chiasm and continue to the opposite

thalamus.

4. Each optic tract consists of crossed and uncrossed

axons that project from the optic chiasm to the thalamus onone side.


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5. Axon collaterals (branches) of the retinal ganglion cells

project to the midbrain, where they participate in neural circuits that

govern constriction of the pupils in response to light and coordination of

head and eye movements. Collaterals also extend to the

suprachiasmatic nucleus of the hypothalamus, which establishes

patterns of sleep and other activities that occur on a circadian or daily

schedule in response to intervals of light and darkness.

6. The axons of thalamic neurons form the optic radiations as they

project from the thalamus to the primary visual area of the cortex on

the same side.


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Internal carotid artery

Arterial system

Ophthalmic artery

Central retinal A

Short post ciliary A

Long post ciliary A

Anterior ciliary A

Lacrimal A

Superior muscular A

Inferior muscular A

Posterior ethmoidal A

Anterior ethmoidal A

Supraorbital ASupratrochlear A


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Venous system

Central retinal V

Superior vortex V

Superior episcleral plexus

Inferior vortex V

Inferior episcleral plexus

Pterygoid plexus

Superior

ophthalmic V

Cavernous

sinus

Jugular v

Accessory Structures of the


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EyeEyelid /palpebraeFrom superficial to deep, each eyelid consists of epidermis,dermis, subcutaneous tissue, fibers of the orbicularis oculi

muscle,a tarsal plate, tarsal glands, and conjunctiva

Meibomian

glands



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Eye

Skin: thin, loose, elastic, no subcutaneus fat, few hair follicles Orbicularis oculi muscle: close the lids, innervated by facial nerve

Levator palpebrae muscle:

Areolar tissue: deep orbicularis oculi muscle communicates with

subaponeurotic of the scalp

Tarsal plate: dense fibrous tissue layer with small amount of elasticlayer

Palpebra conjungtiva: adheres firmly with tarsal plate

Lid margins:

Anterior: eyelash, glands of zeis, glands of mol

Posterior: meibomians gland


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Eye

Modified sweat (sebaceus) glands, called glands of Moll,form asimple spiral before opening into the eyelash follicles

located in the tarsus of each lid, open on the free edge of the lids

The oily substance secreted by these glands becomes incorporated

into the tear film and impedes evaporation of the tears

Eyelashes and Eyebrows

protect the eyeballs from foreign objects, perspiration, and the direct

rays of the sun.

Sebaceous ciliary glands: sebaceous glands at the base of the

hair follicles of the eyelashes release a lubricating fluid into the

follicles



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Eye Conjungtiva Thin, tranparent mucus membrane

Covers posterior surface of the lids

Continous with the skin at the lid margin (a mucocutaneous junction)

and with the corneal epithelium at the limbus.

Palpebral conjunctiva:

lines the posterior surface of the lids and is firmly adherent to the

tarsus, reflected posteriorly (at the superior and inferior fornices) and

covers the episcleral tissue to become the bulbar conjunctiva

Bulbar conjunctiva: loosely attached to the orbital septum in thefornices and is folded many times



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Eye The Lacr imal Apparatus Functions: produces and drains lacrimal fluid or tears.

The lacrimal glands: size and shape of an almond, secrete

lacrimal fluid, which drains into 612 excretory lacrimal ducts that

empty tears onto the surface of the conjunctiva of the upper lid

The lacrimal fluid: produced by these glands is a watery solution

containing salts, some mucus, and lysozyme, a protective

bactericidal enzyme.

Functions of fluid: protects, cleans, lubricates, and moistens the

eyeball.

Nerve: parasympathetic fibers of the facial (VII) nerves.

Blood supply: lacrimal artery. The vein that drains the gland joins

the ophthalmic vein.

The lymphatic drainagejoins with the conjunctival lymphatics to

drain into the preauricular lymph nodes


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After being secreted from the lacrimal

gland, lacrimal fluid is spread medially

over the surface of the eyeball by theblinking of the eyelids. Each gland

produces about 1 mL of lacrimal fluid

per day.


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the meibomian glands, which secrete the outer lipid layer; the

main and accessory lacrimal glands, as well as the

conjunctival and corneal epithelia, which secrete the middle

aqueous layer; and the conjunctival goblet cells, which secrete

the inner mucous layer.



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EyeExtr insic Eye MusclesExtend from the walls of the bony orbit to the sclera (white) of

the eye and are surrounded in the orbit by a significant quantity

of periorbital fat.



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Eye

All th t l l h th d b f i


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All the extraocular muscles are ensheathed by fascia.

The fascia is continuous with Tenon's capsule, and fascial

condensations to adjacent orbital structures (check ligaments) act as

the functional origins of the extraocular muscles

Blood supply: branches of the ophthalmic artery


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Eye Anatomyanatomi