Dr. DIPALI T. CHAVAN INTRODUCTION : Second cranial & sensory nerve Functioning for vision Optic nerve head is distal portion of optic nerve Synonym – Optic disc, Papilla Visualised by ophthalmoscopy On visual field – Blind spot ANATOMY OF OPTIC NERVE HEAD : Extent Extends anteriorly from the retinal surface to the myelinated portion of the optic nerve that begins approximately 3 mm just behind the sclera, posterior to lamina cribrosa ONH dimensions Diameter Vertical Horizontal - 1.88 mm - 1.77 mm Area - 0.68 to 4.42 sq.mm ANATOMY OF OPTIC NERVE HEAD : ANATOMY OF OPTIC NERVE HEAD : Same plane as retina Disc is excavated by funnel shape depression called physiological cup . It is displaced slightly to temporal side. It is whiter than rest of disc. ANATOMY OF OPTIC NERVE HEAD : Divisions of optic nerve head : Four portions from anterior to posteriorA. Surface nerve fiber layer Innermost portion Contains nerve fibres of retina astrocytes B . Prelaminar region Anterior portion of lamina cribrosa Contains nerve axons astrocytes astroglial tissue ANATOMY OF OPTIC NERVE HEAD : contd C. Lamina cribrosa region Fenestated sheets of scleral connective tissue Separated by astrocytes. Fascicles of neurons leave the eye through it D. Retro laminar region Characterised by decrese in astrocytes Acquisition of myline start ANATOMY OF OPTIC NERVE HEAD : contd BLOOD SUPPLY OF OPTIC NERVE HEAD Arterial supply : Mainly by posterior cilliary artery except for nerve fiber layer – which is supplied by retinal circulation. Nerve fibre layer is mainly supplied by arterial branches of central retinal artery. prelamilar and lamilar region is supplied by posterior cilliary arteries. Retrolamilar region supplied by both cilliary and retinal circulation. Anastomosis between retinal vessels and cilliary system of vessels does exit. Arterial anastomosis between 2-4 or more short posterior cilliary arteries,which lies in sclera around optic nerve called circle of zinn-haller Abbreviations: A = arachnoid; C = choroid; CRA = central retinal artery; Col. Br. = Collateral branches; CRV = central retinal vein; D = dura; LC = lamina cribrosa; NFL = surface nerve fiber layer of the disc; OD = optic disc; ON = optic nerve; P = pia; PCA = posterior ciliary artery; PR and PLR = prelaminar region; R = retina; RA = retinal arteriole; S = sclera; SAS = subarachnoid space. BLOOD SUPPLY OF OPTIC NERVE HEAD contd BLOOD SUPPLY OF OPTIC NERVE HEAD contd capillaries: Capillaries derived from both retinal and cilliary circulations. Charecteristics include -tight junctions -abundent perysites -nonfenestrated endothelium They do not leak fluroscein and support concept of retina nerve vasculature as a continuous system with CNS BLOOD SUPPLY OF OPTIC NERVE HEAD contd Venous drainage: Mainly by central retinal vein Central retinal vein is tributary of superior ophthalmic vein ,it wil terminate in cavernous sinus. Small portion by choroidal system Applied anatomy Optic nerve head and nerve fibre layer contains regional ganglion cell axons that are most clearly associated with glaucomatous vision loss the circle of zinn (CZ) was more posteriorly located in small optic discs. This location may induce risk factors contributing to the development of ischaemic optic neuropathy. The combination of small discs, posterior placement of the CZ, and anatomical variations in the vascular pattern may predispose to ischaemic events. Applied anatomy there is vascular insufficiency in the ONH in both anterior ischemic optic neuropathy (AION) and glaucomatous optic neuropathy (GON)-two major causes of blindness or of seriously impaired vision in man. So for the management and prevention of visual loss in these two disorders, a proper understanding of the blood flow in the ONH is essential. Nocturnal arterial hypotension is imp cause of AION. Transient nonprfusion or hypopefusion or embolic lesions of ONH circulation can cause AION. THANK YOU !