NW2005 Color vision

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Color Vision ณณณณณณ ณณณณณณณ ณณณณณณณ ณณณณณณณณ

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Transcript of NW2005 Color vision

Page 1: NW2005 Color vision

Color Vision

ณวฒัน์ วฒันชยักิติกลุ ลีละวงค์

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Visual process

light sourcelight

reflected light/color

object

eye

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Electromagnetic spectrum

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Visible light

normally visible light 400-700 nm

except : beta peak (380-400 nm) infant aphakic condition

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color vision

how we can see all these colors?

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AnaToMy

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Visual process light pass through

cornea/AC/lens/vit absorption by the

rod/ cone photoreceptors

retinal neural circuit horizontal cells bipolar cells ganglion cells

optic nerve higher visual centers

LGB (parvocellular portion)

Cortex

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Rod and Cone photoreceptors

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Rod and Cone photoreceptors

<400 nm400-700 nm

>700 nm

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Rod photoreceptors

92 millions (100M) no rod in central 0.25

mm of fovea peak at 5-7 mm from

foveal center decrease number with

age

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Rod photoreceptors

mediate vision at low illumination levels (scotopic)

108 range of illumination from near darkness to daylight

critical flicker threshold 20 Hz

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Cone photoreceptors

4.6 millions (5M) highest density at

macula stable numbers, no

relationship to age Mediate best vision

at daylight levels (photopic)

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Cone photoreceptors Responsible for good

visual acuity and color perception

1011 range of illumination from moonlight nights to very very bright light

critical flicker threshold 55-60 Hz

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Rods and Cones together Mesopic photopic + mesopic + scotopic = 1014 range of illumination

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no rod in central 0.25 mm of fovea, peak between 5-7 mm from foveal center, while cone has highest density at macula

this distribution means midperiphery of VF the greatest lig

ht sensitivity (night vision) fovea high acuity, good color vision

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Rod and Cone photoreceptors Rod 507 nm SWS cone (B-cone) 445 nm MWS cone(G-cone) 543 nm LWS cone (R-cone) 566 nm

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Gene Encoding the Human Photopigments

Rhodopsin chromosome 3

Iodopsin (SWS) chromosome 7

Iodopsin (MWS,LWS) chromosome X

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Cone cells L, M cones- very similar- dense hexagonal

packing- L/M ~ 2/1- all ~ 90%

S cones- longer inner segment- larger inner segment- deeper innervation- patchwork mosaic- low at fovea, peak 1

degree- all ~ 10%

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genes : L, M cones

- located on chromosome X- tandem array ~ 2-6 (1 LWS, >1 MWS) hybrid

protan (red-blind) deutan (green-blind)

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Horizontal cells1. H1 dendrite all cones-axon-rod2. H2 contact S cones avoid others3. H3 avoid S cones contact others

- local-circuit neurons- chromatic organization- opponent color coding first stage of wavelength discrimination ?

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Bipolar cellsFor rod : on-cell type (single depol.)For cone : off and on-cell type

Depolarize (on) : depol. Response to central/direct illumination

Hyperpolarize (off) : hyperpol. To center illumination and depol. To surround illumination

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Ganglion cells- Its axons form optic nerve and terminate at

LGB/ other diencephalic centers/ superior colliculus

- earliest visual neuron to generate true action potential

- neural coding in term of frequency of firing- spatial/color opponent organization- functional classification P & M

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Ganglion cellsProperty P cells M cellscolor selectivity yes noreceptive field size small large (~10 timesluminance contrast low highcell size small largeconduction velocity low highresponse time course tonic phasicfunction in scotopic no yes number of cells 1,000,000 100,000

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optic nerve LGB cortex/ other centers

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Color vision11 basic color term

4 uniques hue : red yellow green blue3 achromatic color: blackblack white graygray

other 4 color :orange purple brownbrown pink

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Basic Aspects of Color Vision

human can perceived 8000 colors at a single luminance level

at optimal cone vision (1000 luminance range) – 8,000,000 shades and tints can be distinguished

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Theory of color reception

theory of trichromacy

theory of opponent color opponent cells double

opponent cells

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Color vision : color system 1

CIE color systemCommission international del’Ecalirage specific luminance proportion x + y + z = 1 3 dimension 2 dimension spectral/non-spectral color white center

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W.

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Color vision : color system 2

Munsell color system- cylinder

- hue (spectral color) 10 x10 ( R Y G )- Circumferential

- value (lightness) up/down- chroma (whiteness) radial

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Factors that modified color vision Brightness Saturation State of dark adaptation : Perkinje effect Adjacent cone : lateral inhibition Fatique and after image Optical factors : lens, macula, chromatic

aberration, Stile-Crawford effect

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Colorless objects that appear colored

Blue sky : blue – easier scattered

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Colorless objects that appear colored red sunset

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Colorless objects that appear colored

blue water

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Color Vision Defect

what is color?!?!?moo.o..o...

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Color Vision Defects

Normal trichromats 92% Dyschromatopsia 8%

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Classification of hereditary color defect

red green blueblueano. Trichromats Protanomal Deuteranomal TritanomalDichromats Protanope Deuteranope TritanopeMonochromats Blue cone monochromats Rod monochromatsRod monochromats

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Dyschromatopsia Anomalous trichromatism

Protanomaly XR 1% Deuteranomaly XR 5% Tritanomaly AD 0.0001%

Dichromatism Protanopia XR 1% Deuteranopia XR 1% Tritanopia AD 0.0001%

Monochromatism Rod monochromatism AR 0.001% cone monochromatism XR UK

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Congenital red-green defect most common male 8%, female 0.5% Cause

Deletion of R-G pigment gene Hybridization of R-G gene

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Congenital red-green defect

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Congenital red-green defect

Characteristics symmetrically binocular constant in type and severity

through out life normal VA/ fundus/ photoERG name the color correctly

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HUE DISCRIMINATION DEFECT

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Acquired color vision abnormality Characteristics

VA & VF defectGenerally varied in type and

severityUnstable severity

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Acquired color vision abnormality

charateristics Affect one eye or asymmetrically

affect Use incorrect color name or

report that familiar color appearance has changed

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Acquired color-vision abnormality

Kollner’ rule B/Y : retinal/choroid recept

or/outer plexiform R/G : neural disorder ganglio

n cell

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Kollner’s ruleRetinal diseases : B/Y

Eg: RD, RP, ARMD, myopic degen, chorioretinitis, CRVO, DR, CSCR

Except : cone-dystrophy, Stargardt’s

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Kollner’s ruleOptic nerve diseases : R/G

Eg: optic neuritis, ON compression, LHON, toxic optic neuropathy

Except : AD optic atrophy, glaucoma, AION, OHT

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Acquired/hereditary color defect

characteristics- Color- naming- unilateral/bilateral- blue-yellow- change/ unstable- other visual symtoms

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Color Discrimination

Hue Saturation (chroma) Brightness (luminance, intensity)

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1. Hue Discrimination hue wavelength depend on proportion of cone output better in intersected sensitivity function cross point of pigment absorption

sensitivity yellow(590) red/green blue-green(490) green/blue

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Hue Discrimination

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1. HUE DISCRIMINATION

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2.Saturation

color purity fully saturated color : only 1

wavelength for visible light desaturated color : add white light perception depth of color (dark/

light blue)

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2. SaturationSaturation - how much of one hue must be add

to white to be distinguished- the more amount, the less

saturation- many variables purity, intensity,

size, time

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2. SATURATION SENSITIVITY

yellow – lowest

saturation

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3. Luminosityrelative brightness/lightness peak absorption photopic 555 scotopic 507 Purkinje shift (rod & blue

cone pathway?)

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3. LUMINOSITY CURVE507555

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Color vision tests

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Color vision testsPatient selection- screening test in children, student,

worker- undiagnosed low vision- recent color disturbance- Family Hx of color defect- Occupations

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Color vision tests Ideal color vision test

Detect the presence or absence of normal color vision

Distinguish between R-G and B-Y defect

Assess the severity of defect comfortable

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Color vision tests1. Screening test2. Color discrimination test3. Color matching test

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Color vision test 1: screening test

1.Color confusion1. Ishihara test2. FD15 test

2.Color saturation1. AO-HRR test2.TMC plate

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Color vision test : Ishihara test

- Test R-G- High sensitivity

for congen R-G defect

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Color vision test : AOHRR test

- 24 plates- Color

defect or not

- Assess severity (+/-)

- R-G and B-Y

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Color vision : FD-15- Farnsworth D-15

- line of confusion- R/G,B/Y- separate color handicap

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FD-15

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FD-15

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Color vision tests1. Screening test2. Color discrimination test3. Color matching test

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Color vision test 2 : discrimination Hue discrimination

FM-100 Farnsworth desaturated panel D-15 Lanthony new color test

Lightness discrimination Verriest’s lightness discrimination

Saturation discrimination Sahlgren’s saturation test

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Color vision test 2 : discrimination ใชเ้วลามาก อาศัยความชำานาญ ไมเ่หมาะกับ routine exam ไมเ่หมาะกับเด็กอายุน้อยกวา่ 10 ปี

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Farnsworth-Munsell 100 hue test

- 85 caps in 4 groups- hue discrimination test- serial color order within 2

min /each group- position&number of error

score

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FM 100 hue test

Goals Grading of color discrimination in

normal subjects (superior/ average/ low)

Find zone of color confusion

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Farnsworth-Munsell 100 hue test

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Color vision tests1. Screening test2. Color discrimination test3. Color matching test

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Color vision 3 : matchingAnomaloscope1. Nagel R/G

red640 + green545 = yellow5892. Pickford-Nicolson B/Y, R/G3. Sloan’s achromatopsia test

grading severity Expense

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