Structure of eye

Structure Of EYEGOAT

Eye:The eye or organ of vision (Organon visus) in the

broader sense of the term comprises; The eyeball or globe of the eye (Bulbus oculi) The optic nerve Certain accessory organs associated there withThe accessory organs (Organa oculi accessoria)

are; Orbital fascise and muscles The eyelids and conjunctiva, and Upper eyelid the lacrimal apparatus

Connection with skull:The bony walls of the orbit have been

described in connection with the skull; the peri-orbita, a fibrous membrane which encloses the eyeball together with its muscles, vessels, and nerves may be appropriately included in the account of the fasciae

Eyelids or Conjunctiva:The eyelids, upper and lower (Pal-pebra

superior and inferior respectively), are movable folds of integument situated in front of the eyeball.

The upper lid more movable than the lower one, and its free interval between the lids is termed the palpebral fissure (Rima pal-pebrarum).

The ends of the fissure are the angles or canthi, and are distinguished as medial or nasal, and lateral or temporal (Angiilus oculi medialis, lateralis)

Cont...The third eyelid (Palpebra tertia) is situated

at the medial angle of the eye.It consists of a semi-lunar fold of the

conjunctiva, known as the membrana nictitans,

which covers and partly encloses a curved plate of hyaline cartilage. Its marginal part is thin and usually more or less pigmented.

The part of it which lies in the membrane is wide and thin.

The deep part is narrower and thicker and is embedded in fat at the inner side of the

eyeball

Cont...The skin of the eyelids is thin and freely

movable, except near the free edge, where it is more firmly attached.

The underlying subcutaneous tissue is destitute of fat.

The muscular layer consists chiefly of the elliptical bundles of the orbicularis oculi, with which are associated fibers of the corrugat

or supercilii in the upper lid and the malaris in the lower lid.

Cont...At the medial side there is a fibrous band, the palpebral ligament, which is attached to the lacrimal tubercle and furnishes origin to some fibers of the orbicularis.

Cont...At the medial commissure a bundle detached

from the orbicularis passes inward behind the lacrimal sac, and is known as the pars lacrimalis (Horner's muscle)

At the lateral side the fibrous layer is thicker and denser along the free edge of the lid, forming here the tarsus.

The tarsus furnishes insertion to a layer of unstriped muscle known as the tarsal muscle.

The tarsal glands (Glandulse tarsales) are partly embedded in the deep face of the tarsus.

Cont...The conjunctiva is the mucous membrane

which lines the lids as palpebral conjunctiva (C. palpebrarum), and is reflected upon the anterior part of the eyeball as bulbar conjunctiva (C. bulbi); the line of reflection is termed the fornix conjunctiva.

Lacrimal Carimcle:there is a rounded pigmented prominence

known as the lacrimal carimcle (Caruncula lacrimalis)

about the size of a small pea, and is covered modified skin, connected with that of the medial commissure, from which project a number of hairs provided with sebaceous glands.

slit-like opening, the pimctum lacrimal, which is the entrance to the lacrimal duct.

Lacrimal Apparatus:Lacrimal Gland (Glandula lacrimalis) Which secretes lacrimal fluidExcretory ducts of gland (Ductuli excretorii) The pimcta lacrimalia are the entrances to

the two lacrimal ducts.Lacrimal ducts(Ductus lacrimales)CanaliculiLacrimal sac (Saccus lacrimalis)Naso-lacrimal duct (Ductus nasolacrimalis) Which receive fluid & convey it to nostrils

Cilia or Eyelashes:The anterior margin (Limbus palpebralis

anterior) bears stiff hairs termed the cilia (eyelashes).

On the upper lid the cilia are long and numerous except at its medial third, where they are very small or absent.

On the lower lid the cilia are often scarcely distinguish-able from the ordinary hairs

Cilia

Vessels & Nerves:Sensory Nerves branches of the ophthalmic and maxillary divisions of the trigeminus.Motor Nerves Orbicularis oculi, corrugat or supercilii, and

malaris come from the facial nerve; the levator palpebrse superioris is innervated by the oculomotor nerve and the unstriped muscle of the lids by the sympathetic.

The Orbital Fascia & Ocular MusclesThe straight muscles of the eyeball and the

oblique muscles in part are enclosed in fibrous sheaths (Fasciae musculares)

Superficial fascia (Thin)Deep fascia (corneo-scleral junction)Fascia bulbi (cover the posterior part of

eyeball)Levator palpebrae superioris (thin band, above

the rectus dorsalis.Muscles of the eyeball (Mm. oculi) seven in

number—four straight, two oblique, and a retractor

Straight muscles (Mm. recti)

Cont...Retractor oculi (Surround the optic nerve)Obliquus dorsalis s. Superior (longest and

narrowest of the ocular muscles)Obliquus ventralis s. Inferior (wide and much

shorter than the recti)NERVE SUPPLY

The oculomotor nerve supplies the foregoing muscles, with the exception of the rectus lateralis and obliquus dorsalis, which are innervated by the abducens and trochlearis respectively.

Straight Muscles (Mm. Recti):Rectus dorsalis s. superiorRectus ventralis s. inferiorRectus medialisRectus lateralisThey are all band-likearise close together around the optic foramendiverge as they pass forward to the eyeball.

The Eyeball (Bulbus oculi):situated in the anterior part of the orbital

cavityprotected in front by the eyelids and

conjunctiva, and in its middle by the complete orbital ring

related behind to the fascia bulbi, fat, and ocular muscles.

form approximately of an oblate spheroid,composed of the segments of two spheres of different sizes

Cornea:forms the anterior fifth of the fibrous tunictransparentcolorlessnon-vascularoval in outlineanterior surface (Facies anterior) is convexcentral part is termed the vertex comeae.posterior surface (Facies posterior) is

concaveThe margin (Limbus corneae) joins the scleracornea is thinnest at the vertex

Cont...Cornea consists of;Epithelium corneaeLamina limitans anteriorSubstantia propriaLamina elastica posteriorEndothelium camerae anteriorisNerves (derived from the ciliary nerves)

The Retina:The retina or nervous tunic of the eyeball is a

delicate membrane which extends from the entrance of the optic nerve to the margin of the pupil.

consists of three partslarge posterior part• pars ciliaris retinae• Pars iridica retinae• optic papilla (Papilla nervi optici)area centralis retinae

Cont...pigmented epithelium (Stratum pigmenti

retinae)arteria centralis retinae anastomotic branches from the short ciliary

arteriesveins accompany the arteries except in the

capillary plexuses; their walls consist merely of a layer of endothelial cells, around which are a lymph-channel and sheath.

Chambers Of The Eye:anterior chamber (Camera oculi anterior)posterior chamber (Camera oculi posterior)The chambers are filled by the aqueous

humor (Humor aqueus)clear fluid which consists of about 98% of

water, with a little sodium chlorid and traces of albumin and extractives.

It is carried off chiefly through the spaces in the zonula ciliaris (suspensory ligament of the lens) into the plexus venosus sclerae.

Refractive Media Of The Eyeball:vitreous body (Corpus vitreum) is a semifluidtransparent substance situated between the

crystalline lens and the retinaIn front it presents a deep cavity, the fossa

hyaloidea, which fits the posterior surface of the lens

vitreous stroma (Stroma vitreum)vitreous humor (Humor vitreus)The surface is covered by a condensation of the

stroma known as the hyaloid membrane (Membrana hyaloidea)

Cont...crystalline lens (Lens crystallina) is a biconvexEquator of the lens (Equator lentis), is almost

circularAnterior surface (Facies anterior) is convexPosterior surface (Facies posterior) is much

more strongly curved than the anteriorThe central points of the surfaces are the

anterior and posterior poles (Polus anterior et posterior lentis), and the line which connects them is the axis of the lens (Axis lentis).

zonula ciliaris is suspensory ligament of the lens

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