eyes anf ears

8/13/2019 Eyes Anf Ears

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EYE


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Orbits are pair of eye eponings containing the

the eyeball,their associated muscles,nerves,

vessels,fat and lacrimal apparatuses

the orbital o[pening is gaurded by eyelids


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Eyelids are movable curtains which protect the

eye from foreign bodies and bright light

They keep the cornea clean nad moist The upper eyelid is larger and more movable

than the lower one due to the levator

palpebra superioris The space between the 2 eyelids in known as

palpebral fissure

The 2 lids are fused togethor to form medialand lateral angles(canthi) of the eye


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At the inner canthus there is small traingularspace,the lacus lacrimalis with an elevated

lacrimal caruncle,made up of modified skinand skin glands,lateral to the caruncle the thebulbar conjunctiva is pinched up to form avertical fold called plica semilunaris

Each eyelid is atached to the margins of theorbital opening its free edge has outerlip andsharp inner lip,the outer lip presents 2 or

more rows of eyelashes at the point where theeyelashes cease there is a lacrimal pappilawith lacrimal puncta at its summit


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The innner lip has a row of tarsal glandsopeninin at its free edge

Each lid has the folllowing layers

1-skin its thin ans easily distensible by oedemaor fluid ,the sebacious glands are large to formthe Zeisglands,thesweat glands are also

present at the edge and form the Mollsglands and its ducts open into the Zeisglandsor hair follicles


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2-the superficial fascia contains the palpebral

part of the orbicularis occuli

3-the palpebral fascia of the 2 lids forms orbital

septum its thickening forms the tarsal plates in

the lids and palpebral ligament at the angles

The upper tarsus forms 2 tendinous insertions

from levator palpebra superioris 4- the conjunctiva lines the posterior surface of

the tarsus


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Arterial supply

Superior and inferior palpebral branch of the

inferior ophthalmic artery

Lateral palpebral branch of lacrimal artery

Venous drainage

inferior ophthalmic vein and lacrimal vein Nerve supply by supratrochlear and

supraorbital nerve and also infraorbital nerve


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Lacrimal apparatus

They are concerned with the secretion anddrainage of lacrimal fluid(tear)

Its a serous gland situated in the lacrimal fossa(anterolateral part of the roof of the orbit)andpartly in the upper eyelid

Its a J shaped and has

An orbital part larger and deeper

And palpebral part smaller and superficial About 12 of its ducts open into the conjunctival

sac


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Its supplied by parasympathetic nerve which is

secretomotor derived from the lacrimal

nucleus of the facial nerve and sympathetic

postganglionic nerve fibers


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Conjuctival sac

Its a mucosa membrane lined by stratifed

squamous epiothelium

It lines the deeper surface of the

eyelids(palpebral Conjuctival) and front of the

eye ball (bulbar Conjuctival)

The potential space between the palpebral

and bulbar is the Conjuctival sac


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Lacrimal puncta and canaliculi

Each Lacrimal canaliculus begins at the

Lacrimal punctum and is 10mm long ,its

vertical part is 2mm long while its horizontal is

8mm in length ,both canaliculi open in the

lateral part of the lacrimal sac

The canaliculi are lined by stratifed squamous

epiothelium


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the lacrimal sac

Its 12mm long and 5 mm wide situated in the

lacrimal groove behind the medial palpebral

ligament

The upper end is blind and lower end is

continous to the nasolacrimal duct


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the nasolacrimal duct

the nasolacrimal duct is a membranous

passage of 1.3cm in long ,it begins at the

lower part of the lacrimal sac and runs

downwards,backwards and laterally and openinto the inferior meatus of the nose

the nasolacrimal duct and the lacrimal sac are

lined by a superficial columnar with gobletcells and deep layer of flattened cells


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EYE

The eyeball consists of 3 coaits

Outer fibrous coat

Middle vascular layer Inner nervous coat


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Outer fibrous coat

Its made up of a posterior opaque part thesclera and anterior transparent part thecornea

Sclera

Basically, this is the white of the eye. Attachedto the sclera are six exterior muscles, which

enable us to look left, right, up and down. Atthe front of the eye, the sclera forms thecornea


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Sclera is composed of dense connectivetissue,posteriorly is peirced by optic nerve

The lamina cribrosa is the area of the sclera

that is peirced by the optic nerve and itsrealtively a weak area which can be made tobulge into the eyeball

If theres is arise of intarocular pressure Thelamina cribrosa will bulge outward producinga cupped disk


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Sclera is also peirced by ciliary arteries and

their veins

Its continous anteriorly with the cornea at the

sclerocorneal junction or limbus

The cornea

Its s responsible for the refraction of light

entering the eye its contact posteriorly with

the aqueous humour


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The part of the sclera in front of the colored

part of the eye is called the cornea. Unlike the

rest of the sclera, which is white, the cornea is

transparent, or completely clear, which letslight travel through it. The cornea helps the

eye focus as light makes its way through. It is a

very important part of the eye, but you canhardly see it because it's made of clear tissue.

Like clear glass,


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Middle vascular layer

(uveal tract)

The vascular pigmented coat consists from

behind forwards,of the choroid,cliary body

and the iris

Choroid its a thin pigmented layer which

separates the posterior part of sclera from the

retina it ends anteriorly at ora serrata by

merging with the ciliary body.


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ciliary body

Its continous posteriorly with the choroid and

anteriorly it lies behind the peripheral margin

of the iris its composed of Ciliary ring ,Ciliary

process and Ciliary muscle

Ciliary ring is the posterior part of the body

Ciliary process are radilay arranged folds to

the posterior surface of which are connected

to the suspensary ligament of the lens


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Ciliary muscle is composed radial and circular muscleswhich focus the lens for near vision

The radial fibers relax the suspensary ligament of lensso the lens bulge and become more convex for the

near vision

The circular fibers are atached to the anterior part ofthe radial fibers their contraction diminishes thecircumference of suspensary ligament so they are

relaxed and the lens become more convex both partsare supplied by the parasympathetic nerve throughthe 3rdnerve


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Iris and pupil

Iris is thin contractile diaphragm with a central

aperture,the pupil. its suspended in the

aqueous humor between the cornea and the

lens

The periphery of the iris is atached to the

anterior surface of the ciliary body

It divided the space between cornea and the

lens into anterior and posterior chamber


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The muscle fibers of the iris are involuntary andconsists of circular and radial fibers

circular fibers form the sphinter pupillea and are

arranged around the pupil radial fibers form the dilator pupillea and they lie

close to the posterior surface

Nerve supply sphinter pupillea is supplied by the

parasympathetic nerve from the the 3rdnervewhile the dilator pupillea is supplied by thesympathetic nerve


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The pupil is the black circle in the center of

the iris, and it lets light enter the eye. The

pupils will get smaller when a light shines near

them and they'll open wider when the light isgone.


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retina

The retina may be described as the "screen"on which an image is formed by light that haspassed into the eye via the cornea, aqueous

humour, pupil, lens, then the hyaloid andfinally the vitreous humour before reachingthe retina.The retina contains photosensitive elements(called rodsand cones) that convert the lightthey detect into nerve impulses that are thensent onto the brain along the optic nerve
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Its outer surface is in contact with choroid andinner surface is in contact with the virous body

The posterior 3/4thof the retina is the receptor

organ its anterior edge forms the a wavy ring theora serrata

At the centre of the posterior part of the retinathere is an oval yellowish area macula latea its

the area of the retina for the most distinct vision It has a central depression called the fovea

centralis


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The optic nerve leaves the retina about 3mm to

the medial side of the macula lutea

The optic disc is depressed at its centre to form

the physiological cup and its peirced by the

central artery of the retina and it has no rods and

cones in the optic disc and its insensitive to lightand its known as physiological blind spot

Opthalmoscopic examination the retina is pale

The retina is supplied by the central artery in theoptic disc it divides into upper and lower

branches


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Aqueous humor

Aqueous humor its a clear fluid which filles thespace between the cornea infront and the lendbehind ,the space is divided into anterior andposterior chambers by the iris whichcommunicate with each other through the pupil

Its a secretion or transudate from the cliaryprocess which inters the posterior chammber and

then flows into the anterior chamber through thepupil and is drained away into the space ate theiridocorneal angle into the canal of the Schlemm


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Obstruction to the drainage of the Aqueoushumor results in in a rise of intraocularpressure called the glaucoma

The function of the Aqueous humor is tosupport the wall of the eyeball by exerting aninternal pressure to maintain the opticalshape,it also nourishes the cornea and the

lens and removes the products of themetabolism


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Vitrous body

Vitrous body fills the space behind the lens

Its a clourless jelly like transparent mass whichfills the posterior segment

(posterior4/5th) of the eyeball its enclosed by thehyloid membrane

the hyloid canal is a narrow chanel that runs theVitrous body from the optic disc to the posterior

surface of the lens

It contributes to the magnification power of the eye


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lens

Lens is a transparent bioconvex body enclosedin a transparent capsule

Its situated behind the iris and infront of the

vitrous body and is encircled by the ciliaryprocess

It consists of

1-Elastic capsule which covers the structure 2-cuboidal epithelium which is confined to the

anterior surface of the lens


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3- lens fibers which make up the bulk of the

lens


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histology

The Fibrous Tunic: Cornea and Sclera

Sclera

The sclera is a tough layer of dense connective

tissue consisting of collagenous fibres andnetworks of elastic fibres., the sclera maintainsthe shape of the eyeball. It is also the site ofattachment of the ocular muscles

The sclerocorneal junction houses the canal ofSchlemm, through which the aqueous humor isdrained into ciliary veins


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Cornea

The cornea forms the anterior surface of the eye in an

area largely corresponding to the pigmented iris, whichis visible behind the cornea. The diameter of thecornea is ~11 mm; the thickness ranges from ~0.5 mmcentrally to ~1mm along the margins of the cornea.The cornea is formed by three cellular layers, which areseparated from each other by two thin, acellular layers.Blood vessels are not normally found in the cornea,and the cells are not pigmented.

he lateral margins of the cornea are continuous with

the conjunctiva (anterior corneal epithelium) andsclera (corneal stroma).


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Layers of the cornea from in to out are

Non keratinized stratified squamous epithelium

Bowmans membrane consisting of basementmembrane and thin layer of collagen fibers

Substantia propia consisting of collagen fibers

and ground substances of chondroitinsulphate and keratin sulphate

Descementsmembrane acellular layer of

elastin and basement membrane Endothelium , a single layer of cuboidal cells


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Limbus is the transition between the cornea

and sclera


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uvea

Choroid , a pigmented layer of epithelial cells restingon a basement membrane and underlying heavilypimented and vascularised connective tissue

Cliary body ,extendes from the orra serrata to the

beginning of iris,it contains pimented epithelium andvascularised connective tissue and smooth muscle cells

Iris contains pupil and adjusts its size a circularlyoriented sphinter muscle and radialy oriented dilatormuscle are present ,the cells of these muscles are

myoepithelial cells and are capable of contractions Pigment is present in the iris causing eye coloration


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retina

Pigmented epithelium The layer of rods and cones contains the outer, rod- or cone-

shaped light sensitive segements of the photoreceptive cells. Thelights sensitive part and the perikayon of the rods and cones areconnected by a narrowed bridge of cytoplasm. At the level of this

connection the rods and cones are surrounded by the processes ofa specialised type of glial cells, Mller cells, which form the

outer limiting membrane.

The outer nuclear layer contains the nuclei and perikarya of therods and cones. Their processes form part of the

outer plexiform layer, where they form synapses with theprocesses of neurones whose cell bodies are located in the


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inner nuclear layer. The cells of the inner nuclear layer areconcerned with the initial processing of the sensory input. Thethree major neurone types are horizontal, bipolar and amacrinecells. The inner nuclear layer also houses the perikarya of theMller cells.

The inner plexiform layer contains the processes of the innernuclear layer neurones which convey the sensory input to the

ganglion cell layer. Ganglion cells are not evenly distributed. Thereare few of them towards the periphery of the retina. Close to thefovea, ganglion cells form a densely packed layer. Both ganglion

cells and the cell bodies located in the inner nuclear layer whichcontact the rods and cones of the fovea are displaced towards themargins of the fovea.

Layer of optic nerve fibres. The axons of the ganglion cells travel inthis layer towards the optic disc. Towards the optic disc, thethickness of this layer increases as more and more axons are added

to it. The inner limiting membrane


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Ear

External ear

Auricle,it consists of thin plate of elastic

cartilage covered by skin it possess extrinsic

and intrinsic muscles supplied by facial nerve

External auditory meatus

outer 1/3rdby elastic cartilage

inner 2/3rdby bone (tympanic plate)


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The meatus is lined by skin and its outer 3rdis

provided with hairs and sebacious glands and

ceruminous glands which are sweat glands

that secrete yellowish brown wax the hairsand wax provide barrier that prevet the

entrance of foreign bodies


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Blood supply ,the superfical part by the superfical

temporal and posterior auricular arteries and the

deeper part by the deep auricular part of the

maxilary artery Lymphatics pass to the preauricular,postauricular

and superficial cervical lymph nodes

Nerve supply anterior half by auriculotemporalnerve and posterior part by auricular branch of

vagus nerve

T i b


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Typmanic membrane

ear drum, myringa

Its thin translucent partition between theExternal auditory meatus and the tympaniccavity

Its pearly gray in colour

Its placed obliquely facing downward,forwardand lateraly

Outer surface is concave lined by thin skin

Inner surface is convex and provides atachmentto the handle of malleus at its centre

The tip of the hand in known as umbo


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Its circular and measures about 1cm in

diameter

The circumference is thickened and is fixed to

the tympanic sulcus of the tympanic plate its

deficient superiorly where it forms a notch

,from the notch 2 bands of anterior and

posterior malleolar folds pass to the lateralprocess of malleus


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Its composed of

Outer skin layer

Middle fibrous layer

Inner cilaited columnar epithelium


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Parts

Pars flaccida or shrapnels membne

Pars tensa

Blood supply outer surface deep auricular part


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Blood supply outer surface deep auricular part

of the maxilary artery and the inner sarface by

anterior tympanic(maxilary artery ) and

posterior tympnic arater (stylomastoid branch

of posterior auricular auricular artery

Venous drainage outer surface they drain into

the facial vein and inner surface they pass to

the transverse sinus

Lymph nodes pass to the preauricular and

retrophrayngeal lymph nodes

Middl


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Middle ear

tympanic cavity

Its a narow air space between the external andinternal air within the petrous part of thetemporal bone

It looks like a match box it has 6 walls

The middle ear, separated from the external earby the eardrum, is an air-filled cavity (tympaniccavity) carved out of the temporal bone. Itconnects to the throat/nasopharynx via the

Eustachian tube. This ear-throat connectionmakes the ear susceptible to infection (otitismedia).
http://depts.washington.edu/otoweb/middle_ear.htmlhttp://www.nlm.nih.gov/medlineplus/earinfections.htmlhttp://www.nlm.nih.gov/medlineplus/earinfections.htmlhttp://www.nlm.nih.gov/medlineplus/earinfections.htmlhttp://www.nlm.nih.gov/medlineplus/earinfections.htmlhttp://www.nlm.nih.gov/medlineplus/earinfections.htmlhttp://www.nlm.nih.gov/medlineplus/earinfections.htmlhttp://depts.washington.edu/otoweb/middle_ear.html


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The eustachian tube functions to equalize air

pressure on both sides of the eardrum.

Normally the walls of the tube are collapsed.

Swallowing and chewing actions open thetube to allow air in or out, as needed for

equalization


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Contents

3 ear ossicles:malleus,incus and stapes

Two muscle :tensor tympani and stapedius

Vessels draining the middle ear

Nerves:chorda tympani and tympanic plexus

Air


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Parts

Typanic cavity which lies opposite to the

tympanic membrane

Epitympanic recess lies above the level of

tympanic membrane it contains upper half of

malleus and greater part of incus


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It transmits the sound waves from the

external to the internal air through the chain

of air ossicles and trandfroms the airborne

fibrations from the tympanic membarne tothe liquid borne vibrations in the internal ear


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Blood supply by anterior tympanic(maxilaryartery ) and posterior tympnic arater(stylomastoid branch of posterior auricular

auricular artery Venous drainage by superior petrosal sinus

and

Tympanic branch of glossopharngeal nerveand superior and inferior caroticotympanicnerves from the sympathetic plexus


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Internal ear

Bony labyrinth

Cochlea

Vestibular

Semicircular canals

Membranous labyrinth

Duct of cochlea(scala media) organ of corti

Saccule and utericle macula

Semicircular ducts crista


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Blood supply labyrinth branch of basilar

artery and stylomastoid branch of posterior

auricular artery

Labyrinth vein drains into the seperiorpetrosal vein

eyes anf ears

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