Lecture 14: Retina PDF
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This document discusses the structure and function of the retina, focusing on the interface between the neural retina, RPE, and choroid, and functions of the RPE. It details the types of photoreceptors and their responses to different light conditions, plus portions of photoreceptors and a description of major retinal cell types (photoreceptors, bipolar cells, and ganglion cells).
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E arly changes in retina = diagnostic Loss of brain tissue bc of neurodegenerative disease = thinning of nerve fiber layer Correlated with reduction in peripapillary and mac nerve fibe...
E arly changes in retina = diagnostic Loss of brain tissue bc of neurodegenerative disease = thinning of nerve fiber layer Correlated with reduction in peripapillary and mac nerve fiber layer thickness ⇒ Amyloid plaques outer retinal layers on OCT Extensive loss of neurons throughout retina (ganglion cells and glial cells) Increased cup-to-disc ratio and decreased rim tissue Learning Objectives: L ecture 1: Describe the interface between the neural retina, the RPE, and the choroid. Basal aspect of RPE is adjacent to the choroid →RPEmore adherent to choroid than rest of retina; tightly adherent to Bruch’s membrane RPE-neuroretinal interface: no intercellular junction between RPE and photoreceptors Describe and apply the functions of the RPE. 1. Blood-retinal barrier → controls nutrients, metabolites and waste products going to and from retina a. ZONULA OCCLUDENS = tight junctions *prohibits unwantedmolecules from getting in (molecules have to go through RPE) b. Glucose in (amount depends on RPE), lactic acid + water (waste products) out 2. Phagocytosis of (sloughed off) photoreceptor discs 3. Metabolizes and stores vitamin A 4. Contributes to the formation of interphotoreceptor matrix (IPM) between the RPE and photoreceptors a. IPM allows photoreceptors to adhere to RPE 5. Produces growth factors →keeps choroidal BV healthy a. Secretes vascular endothelial growth factor (VEGF) = helps maintain choriocapillaris function i. VEGF stimulates BV growth; decreased VEGF stops growth of unnecessary BV b. Produces pigment epithelial derived factor (PEDF) i. Antiangiogenic = stops BV from growing 6. Absorbs light →gets rid of any excess light ontrast the types of photoreceptors, under what conditions they are stimulated, and when they are C sloughed off. Rods ○ Stimulated/activated in dim illumination ○ Sloughed off MOSTLY in the early morning Cones ○ Stimulated/activated in bright illumination ○ Sloughed off MOSTLY at the end of the day Describe the portions of the photoreceptors. Rods and cones Outer segment ○ Flattened membranous discs ○ Rods: contain rhodopsin (send neural signal when light incident on retina) ○ Cones: three pigments (blue, short - 420nm; green, medium - 531nm; red, long - 588 nm) Cilium ○ Stalk connecting inner and outer segments ⇒ Inner segment contains mitochondria and endoplasmicreticulum (produces proteins) ○ Ellipsoid Closer to photoreceptors Contain mitochondria → ENERGY ○ Myoid Father from photoreceptors (more inner) Contain endoplasmic reticulum and golgi apparatus Outer fiber Cell body → contains nucleus ⇒ Inner fiber (axons goes up to synapse) ○ Specialized nerve endings Spherule (rod) Pedicule (cone) → more invaginations = more connections with other cells ○ Secrete glutamate escribe the major retinal cell types (photoreceptors, bipolar cells, and ganglion cells) and their D connections. Photoreceptors Bipolar cells ○ Dendrite (receives info) synapses with photoreceptors and horizontal cells ○ Axons (transmits info via glutamate) synapses with ganglion and amacrine cells Secretes NT glutamate Ganglion cells ○ Dendrite synapses with bipolar cells and amacrine cells ○ Axon synapses with: Optic radiations (90% of the time) Other 10% of the time Pretectal nucleus → pupils Superior colliculus → helps with saccades (saccading to new target) *r ods pick up peripheral movement and sends signalto brain Suprachiasmic → pineal gland; regulates circadian rhythms Identify the types and functions of ganglion cells. P-cells ○ Terminate in parvocellular layers of the LGN; found in fovea (central vision) ○ Function: high-contrast detail and color resolution M-cells (parasol ganglion cells) ○ Project to the magnocellular layers of the LGN; found in peripheral vision ○ Function: movement and seeing flickering of light Koniocellular ganglion cells ○ Project to koniocellular layers of lateral genicular nucleus; low number ○ Function: sees blue-yellow color Intrinsically photosensitive ganglion cells (ipRGC) ○ Photopigment = melanopsin = sensitive ~480nm ○ Connects with suprachiasmic nucleus → melatonic synthesis; responsible for circadian rhythm ○ Connects with pretectal nucleus → pupil reflexes Analyze how the anatomy contributes to clinical conditions. Clinical correlate ○ Retinal detachment→ separation between RPE and photoreceptors Fluid enters and opens up potential space Most of us DO NOT have retinal detachment due to passive forces (forces keep RPE and photoreceptors together) IOP, osmotic pressure, vitreous, interphotoreceptor matrix (proteins, glycosaminoglycans → adhesive mechanism keeping photoreceptors next to RPE) L ecture 2: Describe the functions and connections of horizontal and amacrine cells Horizontal cells → take info horizontally along retina ○ Synapse with photoreceptors, bipolar cells, and other horizontal cells; synapse with a cone in the triad ○ Functions: Role in visual integration Modulate cone responses (likely do not influence rods) Provide inhibitory feedback to photoreceptors or inhibitory feedforward to bipolar cells Amacrine cells → in inner retina ○ Synapses with bipolar cells, ganglion cells, other amacrine cells ○ Function: modulates information that reaches ganglion cells Explain the glial cells within the retina and their functions Muller cells ⇒ ○ Extend through much of retina start in myoid portion of photoreceptors to inner retinal space ○ Functions: Provides structure to the retina Absorbs ions, NTs, and metabolic waste products Metabolize, synthesize, and store glycogen ○ MAKE UP ILM! Microglial cells ○ Function: phagocytosis → come in after inflammation or injury and clean up Astrocytes ○ Found in NFL at ON ○ Functions: Supportive → encircles nerves and retinal capillaries Contributes to ILM (ONLY at ON) escribe which anatomical components are present in each of the retinal layers and the order which D the layers are found 1. Retinal pigment epithelium (RPE) ⇒ a. 4-6 million LOTS OF PIGMENT found here 2. Photoreceptor layers a. Made up of outer and inner segment b. Projection of Muller cells 3. External limiting membrane (ELM) *not a true membrane ⇒ a. Junctions between photoreceptors and Muller cells zonula occludens 4. Outer nuclear layer (ONL) a. Has cell bodies of photoreceptors (rods and cones) ⇒ b. Thickest portion in fovea 10 layers of cones 5. Outer plexiform layer (OPL) a. Synapses i. Rods and cones synapse [here] with bipolar and horizontal cells ii. Bipolar cells and horizontal cells synapse [here] 6. Inner nuclear layer (INL) a. Has cell bodies of horizontal cells, bipolar cells, amacrine cells, Muller cells b. Has deep retinal BV c. THICKEST in fovea 7. Inner plexiform layer (IPL) a. Synapses i. Bipolar and ganglion cells ii. Amacrine and bipolar cells iii. Ganglion and amacrine cells 8. Ganglion cell layers (GCL) a. Single-layer thick; gets thicker surrounding fovea (8-10 cells thick) b. Has ganglion cell bodies and Muller cells (ELM through entire retina and forms ILM) 9. NFL a. Where glaucoma occurs/damages cell b. Thickest at superior and inferior disk (thins with glaucoma) c. Has axons of ganglion cells, Muller cells, and superficial BV 10. ILM a. Innermost boundary of retina b. Muller cells → end here and spread out throughout retina Identify each of the ten retinal layers on an OCT Identify the photoreceptor sections on an OCT Outer segment and ellipsoid zone (image above) Describe and apply the relative thicknesses of the retinal layers 1. RPE 2. Photoreceptor layers 3. ELM → not a true membrane; not really seen (appears as dashed lines) 4. ONL 5. OPL 6. INL 7. IPL 8. GCL → single-cell thick 9. NFL 10. ILM Apply how the anatomy contributes to clinical conditions and procedures Clinical correlates ○ Retinal hemorrhages Flame-shaped hemorrhages (in NFL) Dot/blot hemorrhages (in INL) → confined in tight area ○ Retinal sheen→ reflections off ILM (Muller cells) L ecture 3: Describe the functions of the macular pigments Xanthophyll pigments (lutein and zeaxanthin) ○ Functions: reduces chromatic aberration, antioxidant effect *protects against UV damage Describe the position of the macula relative to the disc 3.5mm lateral to the edge of the disc 1mm inferior to the center of the disc *15-20º from the disc escribe the anatomic differences between the fovea and the remainder of the retina, including the D relative concentration of photoreceptors and blood vessels Fovea ○ Depression in the center of the macula (wants lightto go straight through) ○ 1.5mm diameter ⇒ ○ Rod-free zone *HIGH concentration of cones rods become elongated ○ Capillary-free zone ○ INL and GCL not present ○ H enle’s fiber layer → photoreceptor axons synapse with bipolar and horizontal cells OUTSIDE of fovea Foveola ○ 0.35mm diameter; 0.13mm thick ○ DENSEST population of cones Parafoveal and parifoveal zones ○ Parafovea INL: 12 cells thick GCL: 7 cells thick LARGEST accumulation of bipolar and ganglion cells ○ Perifovea ⇒ GCL: 4 cells thick ends when GCL is 1 cell thick iscuss and identify the retinal layers that are present within the fovea, as well as therelative D thickness of the layers in the macular area Retinal layers present within fovea: ○ RPE, photoreceptor layer (PL), ELM, ONL, ILM o OPL → synapses OUTSIDE of the fovea *n Demonstrate how the retina layers are connected with the ciliary body layers Neural retina continues as inner CB epithelium RPE continuous with outer CB epithelium Ora serrata → START of CB (end of peripheral retina) Discuss and identify the retinal layers present on the optic disc NFL (axons of ganglion cells) ILM (transition from Muller cells to astrocytes) Describe the location, patterns, and structures supplied by the retinal and choroidal blood vessels Outer retinal layers ○ Associated with receptors → RPE, PL, ELM, ONL, OPL ○ Supplied by choroid (choroidal BV) Inner retinal layers ○ OPL to ILM ○ Supplies by central retinal artery *central retinal artery → splits nasally (goes “straight”)and temporally (wraps around macula) Capillary networks ○ Radial peripapillary capillary plexus: found in NFL ○ Superficial capillary plexus: found near GCL ○ Deep capillary plexus: INL → splits into inner and outer Cilioretinal artery lood supply from choroidal circulation → BV enters retina from edge of the disc ○ B temporally (towards macula) Describe how the anatomy contributes to the blood retinal barrier BFB prevents elements of blood plasma from entering retina tissue Factors involves: ○ Choriocapillaris = fenestrated ○ Zonula occludens in RPE regulates what goes through ○ Retinal vessels are NOT fenestrated and endothelium contains zonula occludens Apply how the anatomy contributes to clinical conditions and procedures Clinical correlates ○ Foveola Foveal light reflex→ created because of parabolicshape; seen = fovea is healthy Metamorphopsia→ distortion; can be seen with Amslergrid ○ Peripheral retina Peripheral cystic degeneration→ MOST COMMON peripheralretinal degeneration;can be seen in ~everyone ○ Optic disc Scleral(whiter)or choroidal(darker)crescent→shown because RPE does NOT reach disc Papilledema→ due to INCREASE in IOP *increased fluidbuildup in brain = backup of flow in OD ⇒ Information processing bipolar cells ○ Photoreceptor dark current(dark illumination → Na+pumped out of inner segment and pumped back in through the outer segment; depolarization of -40 mV) Glutamate CONTINUALLY being released Photoreceptor cell synapsed with ionotropic receptor (in bipolar cells) causes depolarization and an increase of glutamate produced Ganglion cell response = AP produced → vision! ○ Phototransduction(light stimulation → Na+ pumpedout of inner segment and unable to be pumped back in through outer segment/Na+ channels closed; hyperpolarization of -75 mV) Release of glutamate is DECREASED Photoreceptor cell synapsed with metabotropic receptor (in bipolar cells) causes depolarization and an increase of glutamate produced Ganglion cell response = AP produced → vision! escribe how photoreceptors, bipolar cells (both ionotropic and metabotropic), and ganglion cells D respond to various lighting conditions All photoreceptor cells are OFF G anglion cells that undergo depolarization are ON; cells that undergo hyperpolarization are OFF ⇒ Depolarized ganglion cells ganglion cell response = AP produced (vision stimulated) Dark illumination (photoreceptor dark current) Photoreceptor cells: OFF; depolarized; cause an increase in glutamate production Bipolar/ganglion cells: ○ Ionotropic receptor on bipolar cell = OFF; depolarized; cause an increase in gluatamate production → ganglion cell response; AP ○ Metabotropic receptor on bipolar cell = ON; hyperpolarization; cause a decrease in glutamate production → no ganglion response; no AP Light stimulation (phototransduction) Photoreceptor cells: OFF; hyperpolarized; cause a decrease in glutamate production Bipolar/ganglion cells: ○ Ionotropic receptor on bipolar cell = OFF; hyperpolarized; cause a decrease in glutamate production → no ganglion response; no AP ○ Metabotropic receptor on bipolar cell = ON; depolarization; cause an increase in glutamate production → ganglion cell response; AP S pecifically know the two conditions where light is sent to the brain (when a ganglion cell produces an action potential) ⇒ Photoreceptor dark current dark illumination ○ Depolarization of photoreceptor cell (OFF) synapses with ionotropic bipolar cell (causes depolarization) leads to increased glutamate production → ganglion cell response (AP ⇒ produced vision stimulated) ⇒ Phototransduction light stimulation ○ Hyperpolarization of photoreceptor cell (OFF) synapses with metabotropic bipolar cell (causes depolarization) leads to increased glutamate production → ganglion cell ⇒ response (AP produced vision stimulated)
