Visual Pathway PDF

Visual Pathway Karen Gil MD, MHSN Visual Pathway Consist of the series of cells and synapses that carry visual information from the environment to the brain for processing Visual Pathway Includes: – – – – – Retina Optic nerve Optic chiasm Optic tract Lateral Geniculate Nucleus (LGN) – Optic radiatio...

Visual Pathway Karen Gil MD, MHSN Visual Pathway Consist of the series of cells and synapses that carry visual information from the environment to the brain for processing Visual Pathway Includes: – – – – – Retina Optic nerve Optic chiasm Optic tract Lateral Geniculate Nucleus (LGN) – Optic radiations – Primary Visual Cortex Embryological Development The neural tube consists of three general areas: – Forebrain (two areas separated by the optic chiasm in the adult brain) Telencephalon – optic tracts, optic radiations, LGN, cerebral cortex Diencephalon – optic cup and optic stalk and optic chiasm – Midbrain or Mesencephalon midbrain – Hindbrain or Rhombencephalon – cerebellum, medulla and pons Embryological Development Optic nerve develops from the optic stalk by axons of the ganglion cells Center of the optic cup where is the optic fissure will develop the optic disc Embryological Development Myelination of the axons within the optic nerve begins shortly before birth and continues after birth Visual Pathway First cell in the pathway (special sensory cell) – The photoreceptor Convert light energy into neuronal signal that is passed to the bipolar cell and then to the ganglion cell All these cells and synapses lie within the retina Visual Pathway The axons of the ganglion cells exit the retina via the optic nerve The nasal fibers from each eye crossing in the optic chiasm and terminating in the opposite (contralateral) side of the brain Visual Pathway The optic tract carries these fibers form the chiasm to the Lateral Geniculate Nucleus (LGN) In the LGN the next synapse occur The fibers leave the LGN as the optic radiations that terminate in the visual cortex of the occipital lobe Optic Nerve Retinal nerve fibers make a 90 degree turn at the optic disc and exit as the optic nerve Consist of visual fibers – 90% terminate in the LGN – 10% project to areas controlling pupil responses or the circadian rhythm Range of nerve fibers – 1 million to 2.22 million Optic Nerve 5 to 6 cm long Extends form the eye to the optic chiasm Divided in four segments: – Intraocular (0.7 -1 mm) Prelaminal (lamina cribosa) Laminar or Retrolaminal – Intraorbital (25 – 30 mm) – Intracanalicular (6-10 mm) – Intracranial (10 - 16 mm) Optic Nerve Divisons of the Optic Nerve Head Unmyelinated axons Myelinated axons A. Histology of the optic nerve head. Longitudinal section: (A) the surface nerve fiber layer and the physiologic cup. (B) Prelaminar region. (C) Lamina cribrosa region. The nonmyelinated axons in the optic nerve head are not stained by Luxol fast blue, whereas the myelinated axons behind the lamina cribrosa are stained. Luxol fast blue, × 40. B. High magnification demonstrates the transmission of the nonmyelinated and myelinated axons, × 400. Optic Nerve Intraocular section Intermediary tissue of Kuhnt – Ring of glial tissue that separates ON fibers from the retinal layers (#5) 3 4 5 Border tissue of Jacoby – Glial tissue that separates choroid from the optic nerve fibers (#4) Marginal tissue of Elsching – A ring of collagenous tissue of scleral derivation (#3) – Lies outer to the glial sheets Fig. 40.32 The optic nerve head, showing the distribution of collagenous tissue (grey) and neuroglial nuclei (solid blue circles). 1a, retinal internal limiting membrane; 1b, inner limiting membrane of Elschnig; 2, central meniscus of Kuhnt; 3, spur of collagenous tissue separating the anterior lamina cribrosa (6) from the choroid; 4, border tissue of Jacoby; 5, intermediary tissue of Kuhnt; 7, posterior lamina cribrosa; Sep, connective tissue septa from pia mater; Gl. M, astroglial membrane; Gl. C, astrocytes and oligodendrocytes among the fibres in their fascicles; Du, Ar, Pia: dura, arachnoid and pia mater, respectively. The dotted lines represent the borders of the lamina cribrosa. (By permission from Anderson DR, Hoyt W 1969 Ultrastructure of intraorbital portion of human and monkey optic nerve. Arch Ophthalmol 82: 506–30. Optic Nerve Blood Brain-Barrier Tight junctions within the glial border tissue prevent leakage form adjacent choriocapillaris into the optic nerve head Schematic diagram of the blood–brain barrier at the optic nerve head. Entry of proteins into the retina is blocked by the presence of a series of tight junctions between the lining glial cells and the adjacent pigment epithelium. (From Tso MOM, Shih C-Y, McLean IW. Arch Ophthalmol 93:815, 1975, ) Three-dimensional drawing of the intraocular portion of the optic nerve and part of the orbital optic nerve. Where the retina terminates at the optic disc edge, the Müller cells (1a) are in continuity with the astrocytes, forming the internal limiting membrane of Elschnig (1b). In some specimens, Elschnig's membrane is thickened in the central portion of the disc to form the central meniscus of Kuhnt (2). At the posterior termination of the choroid on the temporal side, the border tissue of Elschnig (3) lies between the astrocytes surrounding the optic nerve canal (4) and the stroma of the choroid. On the nasal side, the choroidal stroma is directly adjacent to the astrocytes surrounding the nerve. This collection of astrocytes (4) surrounding the canal is known as the border tissue of Jacoby. This is continuous with a similar glial lining called the intermediary tissue of Kuhnt (5) at the termination of the retina. The nerve fibers of the retina are segregated into approximately 1000 bundles or fascicles by astrocytes (6). On reaching the lamina cribrosa (upper dotted line), the nerve fascicles (7) and their surrounding astrocytes are separated from each other by connective tissue. This connective tissue is the cribriform plate, which is an extension of scleral collagen and elastic fibers through the nerve. The external choroid also sends some connective tissue to the anterior part of the lamina. At the external part of the lamina cribrosa (lower dotted line), the nerve fibers become myelinated, and columns of oligodendrocytes and a few astrocytes are present within the nerve fascicles. The astrocytes surrounding the fascicles form a thinner layer here than in the laminar and prelaminar portion. The bundles continue to be separated by connective tissue all the way to the chiasm (Sep). This connective tissue is derived from the pia mater and is known as the septal tissue. A mantle of astrocytes (GI.M), continuous anteriorly with the border tissue of Jacoby, surrounds the nerve along its orbital course. The dura (Du), arachnoid (Ar), and pia mater (Pia) are shown. The central retinal vessels are surrounded by a perivascular connective tissue throughout its course in the nerve; this connective tissue blends with the connective tissue of the cribriform plate in the lamina cribrosa; it is called the central supporting connective tissue strand here. (Anderson D, Hoyt W: Ultrastructure of the intraorbital portion of human and monkey optic nerve. Arch Ophthalmol 82:506, 1969) Optic Nerve The ON is surrounded by three meningeal sheaths – Dura mater (outermost sheath) – Arachnoid Subarachnoid space (contains cerebrospinal fluid) – Pia mater (only sheath that continues along the intracranial ON) Cross-section of the optic nerve. (A) central retinal artery; (V) central retinal vein; (S) connective septa from the pia mater; (P) pia mater; (An) arachnoid cell nests; (D) dura mater; (N) axon bundles intermingled with glia cell nuclei. Optic Nerve ( A ) Histological section of the optic nerve head: LC, lamina cribrosa; A and V, central retinal artery and vein; SAS, subarachnoid space. ( B ) Transverse section (Loyez stain) of the orbital portion of the optic nerve revealing the arrangement of the myelinated nerve fascicles (darkly stained) separated by pial septae (PS) which penetrate as far as the central retinal artery (CRA) in the middle of the nerve. The three layers of meninges surrounding the nerve (D, dura; A, arachnoid; and P, pia mater) are clearly visible here and in C. ( C ) Cross-section (trichrome stain) of an entire optic nerve and surrounding meninges posterior to the entry of the central retinal artery. ( D ) Blood supply of the optic nerve. The four sources of vessels supplying the optic nerve include: 1, branches from the central retinal artery or its branches; 2, branches from the circle of Zinn–Haller; 3, choroidal branches; 4, pial branches. ( E ) Scanning electron microscopy of the lamina cribrosa (LC). A and Vn, apertures for the central artery and vein. Original magnifications: A , × 60; B , × 290; C , × 40. E , × 75 (Part E, courtesy of Dr A Thale) https://www.clinicalkey.com/#!/content/book/3-s2.0-B9780702055546000010?scrollTo=%23hl0002209 Optic Nerve Optic Nerve The unmyelinated retinal fibers pass though the scleral perforations of the lamina cribosa and become myelinated (by oligodendrocytes) Astrocytes – neurofibrillary processes around nerve fibers – Provide structure – Store glycogen (A) Axons are surrounded by myelinated sheath. (B) Oligodendritic cell Optic Nerve Optic Chiasm Rectangular shape Size: – 15mm horizontal – 8 mm anterior to posterior – 4mm high Surrounded by meningeal sheaths and cerebrospinal fluid Lies within the circle of Willis – anastomotic group of anterior and posterior arteries that join the anterior circulation of the internal carotid arteries with the posterior circulation of the basilar artery Optic Chiasm Optic Chiasm Above the optic chiasm is the floor of the third ventricle Approximately 1 cm below is the pituitary gland Third Ventricle Optic Tract Cylindrical, slightly flattened band of fibers Approximately 3.5 mm high and 5.1 mm long Connect the optic chiasm to the lateral geniculate visual nuclei Nerve fibers: – Magnicellular fibers – Contralateral parvicellular fibers – Ipsilateral parvicellular fibers Lateral Geniculate Nucleus Visual information is processed in the LGN and then is relayed to higher cortical centers LGN is located on the dorsolateral aspect of the thalamus Asymmetric cone shape Retinal axons terminate here Most of the fibers that leave the LGN project on the visual cortex Lateral Geniculate Nucleus Six layered structure Two magnocellular layers (1 and 2) Four parvocellular layers (3,4,5, and 6) Below each of these layers lies a koniocellular layer LGN regulates the flow of visual information, ensuring is sent to the visual cortex The axons leave the LGN as the optic radiations Optic Radiations Also name as Geniculocalcarine Tract Nerve fibers spread fanwise as they leave the LGN deep in the white matter of the cerebral hemispheres from all six layers of the LGN All fibers sweep laterally and inferiorly around the temporal horn of the lateral ventricle Optic Radiations Primary Visual Cortex (V1) Lies on the medial surface of each occipital lobe in the interhemispheric fissure Also called striate cortex or V1 Equivalent to Brodmann area 17 The calcarine fissure extends form the parietooccipital sulcus to the posterior pole, dividing the visual cortex into – Upper portion – cuneus gyrus – Lower part –lingual gyrus Primary Visual Cortex Cuneus gyrus Lingual gyrus Primary Visual Cortex Striate cortex combines and analyzes the visual information relayed form the LGN and transmits this information to the higher visual association areas (the extrastriate cortex – Brodmann areas 18 and 19) which provide further interpretation and visual processing Contain several distinct coritical areas (V2,V3,V4,V5) Blood Supply to the Visual Pathway Outer retinal layers – Choroid Inner retina –CRA Optic Nerve – circle of ZinnHaller (short posterior ciliary arteries) and peripapillary vessels – Intraorbital portion –Pial vessels (branches of the ophthalmic artery) – Intracranial optic nerve branches of the ophthalmic anterior cerebral anterior communicating and internal carotid arteries Blood Supply of the Visual Pathway Optic chiasm – arterioles from circle of Willis – Superior network – anterior cerebral and anterior communicating arteries – Inferior networkinternal carotid, posterior cerebral and posterior communicating arteries Blood Supply to the Visual Pathway Optic tract- anterior choroidal artery (branch of the internal carotid) LGN – anterior choroidal artery, lateral choroidal and posterior choroidal branches of the posterior cerebral artery Blood Supply to the Visual Pathway Relationship of the lateral geniculate nucleus to nearby structures and its blood supply. Key: AChoA = anterior choroidal artery; BC = brachium conjunctivum; CerePed = cerebral peduncles; ICA = internal carotid artery; LGN = lateral geniculate nucleus; MCA = middle cerebral artery; MGN = medial geniculate nucleus; ON = optic nerve; PCA = posterior cerebral artery; PCoA = posterior communicating artery; PLChA = posterior lateral choroidal artery; Pulv = pulvinar; RN = red nucleus; SCA = superior cerebellar artery; SCol = superior colliculus. Blood Supply to the Visual Pathway Optic radiations – Anterior radiations – anterior choroidal artery and the middle cerebral artery – Middle radiations – deep optic branch of the middle cerebral artery – Posterior radiations – posterior cerebral artery Blood Supply to the Visual Pathway Striate cortex – calcarine branch of the posterior cerebral artery Fiber Orientation and Visual Fields Visual field – Is the entire visible area an eye is able to detect around a point of regard when eye is looking straight ahead and is fixating on an object – The information of the visual field is taken by the retina and processed though the afferent visual sensory pathway – Damage in the afferent pathway will cause a defect in the visual field Fiber Orientation in the Retina Axons of the ganglion cells are arranged in three basic patterns: – Papillomacular bundle from the macula – The superior and inferior temporal fibers (separated by the horizontal retinal raphe) forming the arcuate nerve fiber pattern – The radial fibers from the nasal retina (radiating fibers) Fiber Orientation in the Retina Fiber Orientation in the Optic Disc All the axons in the nerve fiber layer come together at the Optic Disc Nasal fibers radiate directly to the nasal side The papillomacular bundle courses directly to the temporal side (take 1/3 of the disc) The superior temporal fibers enter the superior pole The inferior temporal fibers to the inferior pole Fibers from the peripheral retina are more superficial than those coming form the central retina Remember posterior in the intracanalicular and intracranial segments of the ON the papillomacular bundle migrates inward toward the core of the nerve and the nasal and temporal halves of the retina diverge and segregate, the nasal fibers lie in the lateral perimeter Fiber Orientation in the Optic Chiasm The temporal fibers remain uncrossed The nasal fibers decussate (cross): 1. Inferior peripheral nasal fibers – cross in the inferoanterior part of the chiasm and loop into the medial aspect of the opposite optic nerve called the anterior knee of von Willebrand – The fibers then course backward into the contralateral optic tract Fiber Orientation in the Optic Chiasm 2. Superior peripheral nasal fibers – Cross to the opposite optic tract in the superoposterior part of the chiasm but loop into the optic tract of the same side, called the posterior knee of von Willebrand Fiber Orientation in the Optic Tract The crossed and uncrossed fiber intermingle The superior fibers (ipsilateral superior temporal retina and contralateral superior nasal retina) move to the medial side of the tract The fibers from the inferior retina (ipsilateral inferior temporal retinal fiber and contralateral inferior nasal retinal fibers) occupy the lateral area of the tract Macular fibers are between these two groups Fiber Orientation in the Lateral Geniculate Nucleus Six layers Receives contralateral nasal retinal fibers in layers 1, 4 and 6 The ipsilateral temporal retinal fibers in layers 2, 3, and 5 The right side of the brain receives its sensory input form the left side of the visual environment The fibers course thorough the posterior limb of the internal capsule as they leave the LGN to form the optic radiations Fiber Orientation in the Optic Radiations Fibers leaving the lateral aspect of the LGN, representing the inferior retina follow an indirect route to the occipital lobe Pass into the temporal lobe and loop around the tip of the temporal horn of the lateral ventricle – forming Meyer loops – form the inferior radiations Fiber Orientation in the Optic Radiations Fibers form the medial aspect of the LGN Representing the superior retina Lie superiorly as they pass through the parietal lobe Fiber Orientation in the Striate Cortex Superior radiations terminate in the cuneus gyrus (above the calcarine fissure), receive projections form the superior retina Inferior radiations terminate in the lingual gyrus (below the calcarine fissure) receives projections form the inferior retina Fiber Orientation in the Striate Cortex Fibers of the macular area terminate in the most posterior part superior macular in the cuneus gyrus and inferior macular in the lingual gyrus Macular area occupies a large portion of the striate cortex Visual Pathway Image on the Retina 1. Central scotoma caused by inflammation of the optic disk (optic neuritis) or optic nerve (retrobulbar neuritis). 3. Bitemporal hemianopia caused by pressure exerted on the optic chiasm by a pituitary tumor. 5. Right homonymous hemianopia from a lesion of the left optic tract. 7. Right homonymous inferior quadrantanopia caused by partial involvement of the optic radiation by a lesion in the left parietal lobe. 9. Right homonymous hemianopia (with macular sparing) resulting from posterior cerebral artery occlusion. 2. Total blindness of the right eye from a complete lesion of the right optic nerve 4. Right nasal hemianopia caused by a perichiasmal lesion (eg, calcified internal carotid artery) 6. Right homonymous superior quadrantanopia caused by partial involvement of the optic radiation by a lesion in the left temporal lobe (Meyer loop). 8. Right homonymous hemianopia from a complete lesion of the left optic radiation. https://www.youtube.com/watch?v=29FVywV2j4 http://www.youtube.com/watch?v=7-da_1-M-6Q https://www.youtube.com/watch?v=29FVywV2j4