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Flashcards

NAB vision keywords

Daniel Beresford English 124 cards

Cards in this deck (124)

  1. 1IlluminanceLight from a source (lux)
  2. 2LuminanceLight reflected off objects
  3. 3Relative intensity/contrastdI/I where I is the mean background and dI the increment (or decrement) in intensity
  4. 4Pointspread functionBecause of diffraction, even with a perfect lens, the image of a point source is a blurred circle. The smaller the lens the larger the diffraction limit.
  5. 5Spherical aberrationFor a spherical surface, rays towards the edge are more strongly refracted
  6. 6Chromatic aberrationDifferent colours are focused at different depths. The human eye is well focused for green, but poorly for blue light.
  7. 7GlareSmall particles in the optical media scatter light in all directions, reducing contrast of the image
  8. 8EmmetropicObject at infinity sharply focused
  9. 9AmetropicObject at infinity not sharply focused
  10. 10MyopiaShort sight (~20% of population)- predisposes retinal detachment, degeneration and glaucoma.
  11. 11HypermetropiaLong sight (~30% of population)
  12. 12FoveaReceptor spacing should be approx. half width of the PS function- in fovea adjacent cones separated by ~0.5 arc min and arranged in precise mosaic to maximise packing density
  13. 13CorneaConsists of 650um thick layer of transparent collagen fibrils (stroma) enclosed between an epithelium and an endothelium.
  14. 14LensBuilt from long ribbon-like cells packed with transparent proteins (crystalline). Oldest cells in core with greatest refractive index to deal with spherical aberration.
  15. 15CataractClouding of the lens
  16. 16Aqueous humourSecreted by epithelium of the ciliary body and drained off through the trabecular meshwork and canal of Schlemm. Cornea and lens are avascular. Reduction in outflow primary cause of glaucoma.
  17. 17Power of lengthsExpressed in Dioptres (1/focal length m)
  18. 18AccommodationLens changes its focal length to focus on objects at different distances. Brought about by suspensory ligs/ZofZ and circular ciliary m.
  19. 19PresbyopiaReduction in accommodating power due to decrease in lens elasticity- decreases until age 50 where is levels off.
  20. 20Near reflexConvergence of the two eyes to fixate on the new target
  21. 21Direct and consensual responseIllumination of one eye evokes pupil constriction in both eyes due to bilateral projection.
  22. 22Argyll-Robertson pupilCharacteristic of neurosyphilis, the pupil does not react to light but does react to accommodation.
  23. 23Retinal glial cells (Muller cells)Acts as optical waveguides to aid transmission of light
  24. 24FoveolaCentral 260um (~1 degree) of the fovea with highest activity. Avascular.
  25. 25Macular pigmentBlue absorbent in region surrounding fovea to reduce the effects of chromatic aberration
  26. 26Parafoveal regionThe area of most sensitive vision under mesopic and scotopic conditions
  27. 27Blind spotSubtends ~5 degrees at the optic disk where the optic nerve leaves the retina.
  28. 28PapilloedemaCSF in optic nerves is in continuity with the brain, therefore optic disk can appear swollen with raised intracranial pressure.
  29. 29RhodopsinVisual pigment; membrane protein with 7 transmem helices; G-couple receptor.
  30. 3011-cis retinalChromophore molecule that binds rhodopsin in a specific binding pocket
  31. 31All-trans retinalConverted from 11-cis retinal on absorption of a single photon. Photo-isomerisation leads to a catalytically active form of rhodopsin known at metarhodopsin II (R*).
  32. 32Retinal pigment epitheliumArea where bleached rhodopsin is regenerated. The cells of which encompass the apical processes of. the outer segments
  33. 33All-trans retinolRegeneration: pigment reduced to AT- retinol then transported into RPE where it's converted into 11-cis retinal. Transported back into PR where it rejoins bleached opsin to form rhodopsin. Can take 30 mins after bright light.
  34. 34Night blindnessDeficiency of Vit A. Retinal is a derivative of Vit A
  35. 35TransducinHeterotrimeric GTP-binding protein activated by R*. Transducin & R* diffuse freely in disc membrane and by random collisions R* can activate >100 transducing molecules
  36. 36PhosphodiesteraseEach transducin molecule activates one PDE enzyme. Hydrolyses cGMP (present in high concs in dark) to 5'-GMP.
  37. 37Retinitis pigmentosaHereditary retinal degeneration afflicting 1 in 3000 people. Gradual blindness onset in adolescence leading to loss of peripheral vision in adulthood and eventually total blindness. 5-10% of cases caused by rhodopsin gene mutation.
  38. 38Dark currentIn darkness, cGMP concentrations are high, many channels open, continuous circulation consisting of Na+ and Ca2+ ions flowing into the outer segment, depolarising the cell to around -30mv. K+ diffuse out of inner circuit.
  39. 39Light adaptionReduction in sensitivity at a steady light intensity. GC inhibited by Ca2+. In light, Ca2+ extruded by Na/Ca/K exchanger. More cGMP synthesised to replenish cGMP.
  40. 40Principle of univarianceCones alone provide no colour information.
  41. 41Young-Helmholz trichromacy theoryDefining of colour by the ratio of excitation in the three cone classes.
  42. 42DeuteranopiaAbsence of green gene leading to dichromacy
  43. 43ProtanopiaLoss of red pigment gene leading to dichromacy
  44. 44Anomalous trichromatsHybrids with shifted spectral sensitivities. G-R deuteranomaly, R-G protoanomaly
  45. 45TritanopiaLoss of blue pigment gene
  46. 46Foveal tritanopiaBlue cones excluded from the fovea
  47. 47Outer nuclear layerPhotoreceptor cell bodies
  48. 48Outer plexiform layerSynapses between PR's, BiP's and HZ cells
  49. 49Inner nuclear layerBipolar, HZ and amacrine cell bodies
  50. 50Inner plexiform layerSynapses between bipolar, amacrine and ganglion cells
  51. 51Ganglion cell layerCell bodies of ganglion cells
  52. 52Lateral inhibitionMediated by HZ cells which are GABA-ergic
  53. 53Presynaptic ribbonModified presynaptic density characteristic of synapses that transmit graded signals. Vesicles cluster ready to be released.
  54. 54Synaptic triadPostsynaptic targets always include processes from both bipolar and horizontal cells
  55. 55Cone pedicleCone terminals end in large synaptic swelling. There may be up to 30 synapses at each, reflecting divergence of cone signal to multiple BP cells. Cones from invaginating and flat synaptic contacts.
  56. 56Receptive fieldArea on the retina from which its activity can be influenced by light.
  57. 57Off-centre bipolar cellsHyperpolarise to a centre stimulus, depolarise to a surround. In dark, cone releases glutamate- opens BP cell ionotropic glutamate receptors. Cone illuminated- hyperpolarises- stops NT release- BP cell hyperpolarises.
  58. 58Lateral inhibition mediated by HZ cellsHyperpolarise in response to light, so when only surround stimulated the central photoreceptor will depolarise as receives less inhibition
  59. 59On-centre bipolar cellsCentre stimulus depolarises via a metabotropic glutamate receptor (mGluR6). In dark G protein cascade inhibits channels. Hyperpolarisation of PR in light decreases NT release, less stimulation of receptor, inhibition released- depolarisation.
  60. 60Invaginating contactsSign-inverting synapses- mGluR6 receptors.
  61. 61Flat contactsSign-preserving synapses- ionotropic AMPA receptors.
  62. 62Midget bipolar cellsReceive input from 1 cone, small receptive fields. Have the potential to signal the finest special detail in the image and signals are colour specific.
  63. 63Diffuse bipolar cellsLarge receptive fields, collect spatial input from 5-10 cones. Convergence means responses are more sensitive but special detail and colour signals are lost.
  64. 64Parallel streamsDifferent aspects of the image are coded by different cells with overlapping receptive fields. Message to brain consists of parallel "neural images", each specialised for a different aspect of the image- e.g. on vs off, spatial detail, colour.
  65. 65ParvocellularType- midget, Receptive field- small, Cone input- colour encoded, Response- sustained, Cond. velocity- slow, Gain/sensitivity- low, Function- form/colour
  66. 66MagnocellularType- parasol, Receptive field- large, Cone input- broadband, Response- transient, Cond. velocity- fast, Gain/sensitivity- high, Function- motion
  67. 67Amacrine cells~50 distinct classes. M ganglion cells receive more amacrine input than the P cells. Dopaminergic amacrine cell has a role in adjusting the eye for photopic and scotopic vision.
  68. 68Starburst amacrineDirection & motion
  69. 69AII amacrineRelays rod signals
  70. 70Scotopic intensity rangeColour vision lost in this range
  71. 71Purkinje shiftOverall spectral sensitivity shift from ~560nm to the rod peak sensitivity of ~500nm
  72. 72Rod AII amacrineFully dark adapted retina: Rod - "on" rod BP cell - rod AII amacrine - gap junction - "on" cone BP cell - "on ganglion cells". They also make inhibitory glycinergic synapses with "off" bipolar cells.
  73. 73MesopicRange where both rods and cones can function. Rod spherules have electrical synapses directly to cone pedicles.
  74. 74Lateral geniculate nucleus (LGN)Primary projection from the retina- found in the thalamus
  75. 75PretectumControls pupillary responses
  76. 76Suprachiasmatic Nucleus (SCN)Biological clock
  77. 77Superior colliculusInvolved in reflex eye movements
  78. 78Striate cortex/V1Primary visual cortex. Found at the occipital pole and receives information from optic radiation via the internal capsule.
  79. 79Calcarine sulcusArea of medial hemispheres where V1 is buried
  80. 80Retinotopic mapOrderly point-for-point representation of the retina in the cortex
  81. 81Cortical magnificationFovea is grossly over represented
  82. 82Parvocellular layers in the LGN4 outer layers (ICIC)
  83. 83Magnocellular layers in LGN2 layers (CI)
  84. 84Koniocellular layersLocated between layers 1-6 with small cell bodies. Receive specific input from specific ganglion cells serving blue cones.
  85. 85Spiny stellate neuronesNeurons in layer 4 of V1- receives input from the LGN. Magnocellular 4Ca. Parvocellular 4CB.
  86. 86Pyramidal neuronsOutputs to higher visual areas from layers 2&3
  87. 87Layer 6 of V1Projections back to the thalamus
  88. 88Layer 5 of V1Project to deep brain structures such as the superior colliculus.
  89. 89Orientation tunedMost cells in V1 respond optimally to bars and edges
  90. 90Simple cellsRespond only to an edge of a particular orientation in a very well-defined position. The receptive field has an inhibitory flank on one or both sides and diffuse illumination and excitation cancel. Commonest in input areas 4 (&6)
  91. 91Complex cells75% of cells. Respond to orientated bars but position not critical. Respond best to moving edges over a larger field. Often directionally selective and found mainly in layers 2, 3 & 5.
  92. 92End-stopping/End-inhibitionSome simple cells respond only to short bars, becoming inhibited when the edge reaches a critical length.
  93. 93Orientation columnsCells of similar orientation. All orientations represented over a distance of ~1mm in an orderly progression.
  94. 94Ocular dominance columnsAlternating slabs of cortex ~0.5mm wide which receive input from one or the other eye.
  95. 95Disparity detectorsNeurons which receive input from stimuli located at slightly different positions on the two retinae for detecting objects near of further from the plane of fixation.
  96. 96BlobsCircularly symmetric receptive fields which show centre-surround antagonism. Respond to particular wavelengths and are involved in the processing of colour.
  97. 97Hypercolumn1-2mm^2 regions of cortex representing a small region of visual space in which all orientations are represented, and which contains both L&R eye OD columns each with a blob for colour analysis.
  98. 98Orientation pinwheelsActual orientation of OC's which are arranged radially around a central hub. OD columns show a 'tiger-stripe' pattern.
  99. 99AmblyopiaUncorrected squint, astigmatism or wearing an eye patch in early life leads to permanent cortical function defects.
  100. 100V2Has thick and thin stripes and interstripes
  101. 101Ventral "what" pathwayV4 receives input from thin stripes within V2. Parallel systems: parvo-blob-thin stripe-V4 stream (associated with colour), par/mag-interblob-interstipe-V4 stream (edges and analysis of fine form).
  102. 102AchromatopsiaCortical colour blindness due to lesion in V4.
  103. 103Inferotemporal cortexFinal destination of par/mag stream, contains most sophisticated cells e.g. responding to faces and hands.
  104. 104ProsopagnosiaInability to recognise faces due to lesion in the IT cortex.
  105. 105Dorsal "where" pathwayMag V1-4Ca-4B-thick stripe V2-V5 & V5a (MST)-posterior parietal cortex. Pathway dominated movement detecting cells. Cells also respond to binocular depth cues.
  106. 106MSTSome output destinations include brainstem nuclei involved with controlling eye movements. A lesion in MST may lead to the inability to see movement.
  107. 107Visual streakFound in non-primate mammals that don't have a fovea, has increased photoreceptor density to image the horizon. Retinal blood vessels avoid the visual streak to minimise light scatter and preserve image quality.
  108. 108Spectral univarianceThe waveform of the cone response to light does not depend on the wavelength.
  109. 109Single opponent cellsCorrespond to P cells in the primate
  110. 110Small bistratified ganglion cellsOrigin of blue-yello opponent signals, pass to the LGN via a distinct koniocellular pathway.
  111. 111Broadband retinal ganglion cellsDriven by both red and green cones showing centre-surround antagonism without a chromatic component, encoding luminance and correspond to the M cells.
  112. 112Double opponent cellsChromatic antagonism takes place within each region of the centre-surround. Resolves ambiguity of single opponent signals. Found in the blobs of V1.
  113. 113Colour constancyNeural processing within V4, involving comparisons across large areas of the visual field. Allows the colours of objects to remain the same, irrespective of the spectral composition of the illuminating light.
  114. 114PectenSpecialised structure within the vitreous humour that supplies nutritive needs to the bird retina (as absence of blood vessels)
  115. 115Tapetum LucidumShiny layer beneath the retina and RPE that reflects light so that PR outer segments have a second chance for photon absorption.
  116. 116Photopic rangeOnly cones contribute
  117. 117Dark lightThe absolute threshold in darkness is set by an internal signal similar to background light
  118. 118Threshold contrastdeltaI/I (constant)- Webers law
  119. 119Bleaching adaptationPhotopigment used up during light exposure. Sensitivity slowly recovers in darkness in the process of dark adaption.
  120. 120Rod-cone breakDivision between fast recovering cones and slower recovering rods in dark adaptation. At this point 90% of rhodopsin regenerated but visual threshold still dramatically increased- more complicated than loss of pigment.
  121. 121Bleaching desensitisationDesensitisation of PR's due to reduced cytoplasmic Ca2+ concentration.
  122. 122Post-bleach noiseSpontaneous quantal events in each rod. Believed to result from back reactions by quenched forms of photoisomerised rhodopsin.
  123. 123A18 amacrine cellsDopamine released in light decouples gap junctions between AII amacrine cells. In dark, stronger coupling means the rod BP signals reach a larger number of cone BP cells than in the light adapted retina, summing the signals over a larger area.
  124. 124Critical fusion frequencyFrequency above which a flickering light is perceived depends on the rods, which are best stimulated by blue-green light.

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Flashcards on NAB vision keywords, created by Daniel Beresford on 28/04/2018.
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