•• The The opticoptic nervenerve (2nd (2nd pairpair of of cranialcranial nervesnerves) ) isis notnota a nervenerve in the common in the common useuse of the of the termterm, , butbut, , morphologicallymorphologically and and functionallyfunctionally, a , a diencephalicdiencephalicprojectionprojection. .

•• ItIt isis mademade up of the up of the axonsaxons of of retinalretinal ganglionganglion cellscells, , itit extendsextends fromfrom the retina the retina toto the the opticoptic chiasmchiasmenvelopedenveloped in in itsits sheathsheath, the dura , the dura matermater, , arachnoidarachnoidand pia and pia matermater, in , in continuationcontinuation withwith the the meningesmeninges..

?? The The optic nerve optic nerve originates from the eye bulb, 1 mm originates from the eye bulb, 1 mm below and 3below and 3--4 mm 4 mm mediallymedially to its posterior pole; to its posterior pole; the length considerably varies (between 35 and 55 the length considerably varies (between 35 and 55 mm) even among the two eyes of the mm) even among the two eyes of the samesameindividualindividual; in the ; in the intraorbitalintraorbital tracttract itsits diameterdiameter isis 33--4 mm and in the 4 mm and in the intracranialintracranial tracttract itit isis 44--7 mm.7 mm.

The The opticoptic nervenerve maymay bebe divideddivided in 4 in 4 partsparts::•• IntraocularIntraocular (or (or opticopticnervenerve head):head): inside the inside the wallswalls of the of the eyebulbeyebulb(1 mm);(1 mm);

••IntraorbitalIntraorbital:: (20(20--25 mm);25 mm);••Intracanalicular: Intracanalicular: in the in the opticoptic canal (4canal (4--10 mm);10 mm);••IntracranialIntracranial:: (10(10--20 mm).20 mm).

Blood supply of a normal optic disc

VascularizationVascularization of the of the opticoptic nervenerve

-- IntraocularIntraocular partpart: : -- laminarlaminar portionportion (lamina cribrosa): (lamina cribrosa): branchesbranches of the of the briefbrief posteriorposterior ciliaryciliary arteriesarteries ((ZinnZinn­­HallerHaller):): thesethesedo do notnot constituteconstitute a precise a precise anatomicalanatomical structurestructure, , butbut whenwhen presentpresent, are , are a a functionalfunctional circularcircular (incomplete) (incomplete) anastomosisanastomosis betweenbetween differentdifferentposteriorposterior ciliaryciliary arteriesarteries whichwhich enterenter the sclera and the sclera and supplysupply the the choroidchoroidand the and the opticoptic nervenerve head. head.

VascularizationVascularization of the of the opticoptic nervenerve

-- Intraorbital portionIntraorbital portion:: it may be it may be divideddivided in in anan anterioranterior and a and a posteriorposterior tracttract in relation in relation toto the the entranceentrance of the of the centralcentralretinalretinal arteryartery; the ; the anterioranterior isis doubledouble: : axialaxial ((intraneuralintraneural) ) derivedderived byby recurrentrecurrent branchesbranches of the of the centralcentral retinalretinal arteryarteryand and superficialsuperficial fromfrom branchesbranches of the of the pialpial plexusplexus; the ; the vascularizationvascularization of the of the posteriorposterior tracttract isis onlyonly of of pialpial originorigin..-- IntracanalicularIntracanalicular and and intracranialintracranial partsparts suppliedsupplied byby the the pialpialplexusplexus ((ophthalmicophthalmic arteryartery and and collateralcollateral artieriesartieries forfor the the first first partpart; ; cerebralcerebral and and anterioranterior comunicatingcomunicating arteriesarteries forfor the the secondsecond partpart). ). The The venousvenous systemsystem of the of the opticoptic nervenerve repeatsrepeats the the arteriousarterioussystem (system (venousvenous pialpial plexusplexus).).

TheThe opticoptic discdisc•• Approx. 1,5 mm Approx. 1,5 mm diameterdiameter, a round , a round contourcontour, , oftenoften

slightlyslightly ovaloval withwith greatestgreatest verticalvertical axisaxis. . •• The The smallsmall centralcentral depressiondepression due due toto the the convergenceconvergence of of

the the fibersfibers givinggiving originorigin toto the the nervenerve isis oftenoften cratercrater--likelike((physiologicalphysiological excavationexcavation),), sometimessometimes funnelfunnel--shapedshaped,,smallsmall or or slightlyslightly hintedhinted. .

•• ItIt isis oftenoften symmetricalsymmetrical in the in the twotwo eyeseyes and and tendstends totoincreaseincrease withwith ageage. .

•• The The scleralscleral canal canal maymay bebe cylindricalcylindrical, , butbut isis oftenoftenconicalconical ((posteriorposterior base); base); itsits amplitudeamplitude, in relation , in relation toto the the scleralscleral diameterdiameter, , influencesinfluences the the physiologicalphysiologicalexcavationexcavation in the in the sensesense thatthat the more the more ampleample the canal, the canal, the the greatergreater the the excavationexcavation. .

The The layerslayers of the retina and of the retina and choroidchoroid end at the end at the edgeedge of the of the opticopticdisc; disc; sometimessometimes the the pigmentedpigmented epitheliumepithelium and the and the choroidchoroid leaveleavea a whitewhite, more or , more or lessless complete complete scleralscleral ringring or a or a semilunarsemilunarformationformation withwith greatestgreatest temporaltemporal sideside

•• In In otherother casescases the the pigmentedpigmented epitheliumepithelium extendsextends beyondbeyond the the edgeedge of the of the opticopticdisc disc givinggiving rise rise toto a more or a more or lessless complete complete pigmentatedpigmentated ringring; in ; in otherother casescasesthe the pigmentedpigmented epitheliumepithelium stopsstops long long beforebefore the the choroidchoroid formingforming a a temporaltemporalsemilunarsemilunar area in area in whichwhich the the choroidchoroid isis visiblevisible

•• The optic disc has an anterior portion, formed by the sole nerveThe optic disc has an anterior portion, formed by the sole nerve fibers, which fibers, which give rise to a deviation when leaving the eyebulb, an intermediagive rise to a deviation when leaving the eyebulb, an intermediate portion in te portion in which the astrocytes form cylindrical columns for the passage ofwhich the astrocytes form cylindrical columns for the passage of the nerve the nerve fibers, and a posterior portion, constituted by the optic fibers, and a posterior portion, constituted by the optic fibersfibers and the and the lamina lamina cribrosacribrosa:: the the latterlatter isis connectiveconnective trabeculatetrabeculate, , whichwhich crossescrosses the the scleralscleral canal canal in in itsits middle or middle or posteriorposterior portionportion and and includesincludes opticoptic fibersfibers: : itit hashas a a variablevariablethicknessthickness, , betweenbetween 0.30.3--0.7 mm0.7 mm

Glial and hyaloid artery remmants on the optic nerve

Foetal fissure

Small coloboma of the optic disc

Large coloboma of the optic disc

“Morning glory” optic disc

Congenital pit of the optic nerve

Hypoplastic optic disc

Tilted optic disc

Visual field defects with tilted disc

Septo-optic dysplasia (de Morsier)

Septo-optic dysplasia: CT scan with absence of septumpellucidum

Congenital myelinating nerve fibers

Drusen of the optic disc

Drusen of the optic disc: autofluorescence and axial CT scan

Anomalous discs with congenital vascular tortuosity

Hypermetropic optic disc

Myopic optic disc

Myopic optic disc: histology