anatomy of eyeball
TRANSCRIPT
GROSS ANATOMY OFTHE EYE
•Cystic structure kept distended by the pressure inside it•Shape-oblate spheroid•Anterior and posterior poles•Equator•Dimensions AP-24mm Horizontal-23.5mm Vertical diameter-23mm Circumference-75mm Vol-6.5ml Weight-7g
SEGMENTS AND CHAMBERS
Anterior segment-crystalline lens, iris, cornea, anterior and
posterior chambers-Anterior chamber: 2.5mm deep in the center anteriorly-cornea postriorly-iris and part of ciliary body aqueous humour-0.25ml
-Posterior chamber triangular space anteriorly-iris and part of ciliary body posteriorly-lens and zonules laterally-ciliary body aqueous humour-0.06ml Posterior segment-structures posterior to the lens
THE ORBIT
Quadrilateral truncated pyramid shaped cavity
Location -above: anterior cranial fossa -below: maxillary sinuses 40 mm in height,width and depth Formed by 6 bones-Frontal,Maxilla,Zygomatic
bone,Sphenoid,Palatine,Ethmoid,Lacrimal
4 walls-superior,inferior,medial,lateral Base Apex 2 orifices -optic canal :optic nerve & ophthalmic artery - superior orbital fissure:nerves,arteries,veins
ORBITAL FASCIA Thin connective tissue membrane lining
various intra orbital structures Divided into Fascia bulbi or Tenons capsule Muscular sheath Intermuscular septa Membraneous expansions of extraocular
muscles Ligament of Lockwood
EYELIDS
In front of the eyeball Function as -shutters - spreads tear film -helps in drainage of tears Parts of the eyelid-orbital and tarsal parts Position of eyelids Canthi- at the medial and lateral angles(inner
and outer canthi)
Palpebral aperture Vertical-10-11mm Horizontal-28-30mm Lid margin -2mm broad -medial or lacrimal portion -lateral or ciliary portion -intersegmental strip-grey line-junction of skin and conjunctiva
STRUCTURE
1.Skin: elastic2.Subcutaneous areolar tissue: loose and
contains no fat3.Layer of striated muscle: orbicularis muscle which comprises of three
portions-orbital,palpebral and lacrimal Levator palpebrae superioiris
4.Submuscular areolar tissue: loose connective tissue with nerves ans vessels
5.Fibrous layer -tarsal plate: two plates of dense connective tissue shape and firmness to the eyelids Joins at the medial and lateral canthi Attached to the orbital margin by the medial and
lateral palbebral ligaments Contains Meibomian glands
-septum orbitale Thin membrane of connective tissue Attachments central-tarsal plates peripheral-periosteun of orbital margin Perforated by nerves muscles and LPS
6.Layer of non striated muscle fiberPalpebral muscle of MullerUpper lid-fibers of LPSLower lid-Prolongation of inferiorrectus muscle7.Conjunctiva-palpebral conjunctiva
CONJUNCTIVA
Translucent mucous membrane Lines posterior surface of eyelid and anterior
surface of eyeball Extends between the lid margin and the
limbus Encloses the conjunctival sac
PARTS OF THE CONJUNCTIVA
i. Palpebral conjunctiva-lines the eyelids a-Marginal conjunctiva - extension:from the lid margin for 2mm on
the back of the eyelid upto sulcus subtarsalis
-transitional zoneB-Tarsal conjunctiva -thin,transparent and highly vascular -upper eyelid: entire plate -lower eyelid: half the width of the tarsus
c-Orbital part -between the tarsal plate and fornixii. Bulbar conjunctiva-thin,transparent -can be moved easily -Tenons capsule and episcleral tissue seperates it
from anterior sclera -limbal conjunctiva-Tenons capsule+episcleral
tissue+bulbar conjunctiva
iii.Conjunctival fornix- circular cul de sac broken medially Joins bulbar and palpebral conjunctiva Subdivided-superior,inferior,medial and lateral
Plica semilunaris:-pinkish cresentic fold of conjunctiva in the medial
canthusCaruncle-small pinkish fold of skin in the inner canthus
medial to plica semilunaris
GLANDS OF CONJUNCTIVA
1. Mucin secretory glands-goblet cells-crypts of Henle-glands of Manz2. Accessory lacrimal glands-glands of Krause-glands of Wolfring
COATS OF THE EYEBALL
Fibrous coat:dense strong coati. Cornea -transparent,avascular structure -anterior 1/6 th of the fibrous coat of the
eyeball -anterior surface-elliptical -horizontal-11.7mm -vertical-11mm -posterior suface-circular - average diameter-
11.5mm
-thickness: center-0.5-0.6 mm periphery-1-1.2mm -radius of curvature anterior- 7.8mm posterior-6.5 mm -refractive index-1.376 -refractive power-45 Dii. Sclera -posterior 5/6 opaque part - covered by Tenons capsule and conjunctiva -related to choroid and suprachoroidal space
- thickest posteriorly and thin anteriorly -thinnest-insertion of extraocular muscles-lamina cribrosa-Apertures: Posterior aperture around optic nerve transmits ciliary nerves and vessels Middle apertures posterior to equator transmits four vortex viens Anterior aperture 3-4mm from the limbus transmits anterior ciliary vessels and long
ciliary nerves
Middle vascular coat - iris,ciliary body,choroid i. Iris anterior most part Circular disc shaped Pupil-aperture of 4mm diameter at the centre Forms anterior and posterior chambers Attached to the middle of the anterior surface of
ciliary body Anterior surface of eyelids Ciliary zone Pupillary zone
ii. Ciliary body-Forward continuation of choroid at ora serrata-Triangular in cross section-Iris is attached to the middle-Supraciliary space-Inner side-anteriorly pars plicata and posteriorly pars
planaiii. Choroid-posterior most part-from optic disc to ora serrata-inner surface: smooth, brown and in contact with
pigment epithellium of retina-outer surface:rough and in contact with sclera
RETINA
Thin,delicate and transparent Extends from optic disc to ora serrata Retinal equator-imaginary line considered to
lie in line with the exit of four vena verticose veins. Seperates it into
A. Posterior pole-posterior to retinal equator i. optic disc central area-all the retinal layers
terminate except nerve fibres physiological cup
ii. Macula lutea-yellow spot Fovea centralis FoveolaB. Peripheral retina posteriorly-retinal equator anteriorly- ora serrata
Ora serrata Serrated margin Retina is attached to vitreous and choroid Pars plana extends from it
LENS
Transparent,biconvex,crystalline structure Located between the iris and vitreous humor Patellar fossa-saucer shaped depression Diameter-9-10mm Thickness 3.5-5mm Two surfaces-anterior and posterior RI-1.39 Total dioptric power-18D(16-20D)
STRUCTURE
1. Lens capsule Thin, transparent hyaline membrane Thicker anteriorly Thickest at pre equatorial regions Thinnest at the posterior pole2. Anterior epithellium Single layer of cuboidal epithellial cells Columnar at the equatorial region Form new lens fibres No posterior epithellium
3. LENS FIBRESNUCLEUS AND CORTEX
4. Suspensory ligaments of lens Set of fibres passing from ciliary body to lens Holds the lens in position Ciliary muscles act on it 3 groups-anterior group -middle group -posterior group
EXTRAOCULAR MUSCLES
Rectus muscles Superior,medial,lateral,inferior Origin: Arises from Annulus of Zinn- attached
to the apex of the orbit surrounding the optic foramina and medial part of superior orbital fissure
Insertion: sclera by flat tendons at different distances from the limbus
Medial-5.5mmInferior -6.5mmLateral-6.9mmSuperior-7.7mm Oblique muscles Superior oblique muscle-origin: sphenoid by a narrow tendon above and medial to optic foramen-insertion: passes through the trochlea :upper and outer part of sclera :behind the equator
Inferior oblique muscle-origin: orbital plate of maxilla :lateral to orifice of nasolacrimal duct-insertion: lower and outer part of sclera : behind the equator
LACRIMAL GLAND