NW2005 Color vision
-
Upload
nawat-watanachai -
Category
Health & Medicine
-
view
442 -
download
1
description
Transcript of NW2005 Color vision
Color Vision
ณวฒัน์ วฒันชยักิติกลุ ลีละวงค์
Visual process
light sourcelight
reflected light/color
object
eye
Electromagnetic spectrum
Visible light
normally visible light 400-700 nm
except : beta peak (380-400 nm) infant aphakic condition
color vision
how we can see all these colors?
AnaToMy
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
Rod and Cone photoreceptors
Rod and Cone photoreceptors
<400 nm400-700 nm
>700 nm
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
Rod photoreceptors
mediate vision at low illumination levels (scotopic)
108 range of illumination from near darkness to daylight
critical flicker threshold 20 Hz
Cone photoreceptors
4.6 millions (5M) highest density at
macula stable numbers, no
relationship to age Mediate best vision
at daylight levels (photopic)
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
Rods and Cones together Mesopic photopic + mesopic + scotopic = 1014 range of illumination
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
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
Gene Encoding the Human Photopigments
Rhodopsin chromosome 3
Iodopsin (SWS) chromosome 7
Iodopsin (MWS,LWS) chromosome X
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%
genes : L, M cones
- located on chromosome X- tandem array ~ 2-6 (1 LWS, >1 MWS) hybrid
protan (red-blind) deutan (green-blind)
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 ?
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
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
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
optic nerve LGB cortex/ other centers
Color vision11 basic color term
4 uniques hue : red yellow green blue3 achromatic color: blackblack white graygray
other 4 color :orange purple brownbrown pink
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
Theory of color reception
theory of trichromacy
theory of opponent color opponent cells double
opponent cells
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
W.
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
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
Colorless objects that appear colored
Blue sky : blue – easier scattered
Colorless objects that appear colored red sunset
Colorless objects that appear colored
blue water
Color Vision Defect
what is color?!?!?moo.o..o...
Color Vision Defects
Normal trichromats 92% Dyschromatopsia 8%
Classification of hereditary color defect
red green blueblueano. Trichromats Protanomal Deuteranomal TritanomalDichromats Protanope Deuteranope TritanopeMonochromats Blue cone monochromats Rod monochromatsRod monochromats
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
Congenital red-green defect most common male 8%, female 0.5% Cause
Deletion of R-G pigment gene Hybridization of R-G gene
Congenital red-green defect
Congenital red-green defect
Characteristics symmetrically binocular constant in type and severity
through out life normal VA/ fundus/ photoERG name the color correctly
HUE DISCRIMINATION DEFECT
Acquired color vision abnormality Characteristics
VA & VF defectGenerally varied in type and
severityUnstable severity
Acquired color vision abnormality
charateristics Affect one eye or asymmetrically
affect Use incorrect color name or
report that familiar color appearance has changed
Acquired color-vision abnormality
Kollner’ rule B/Y : retinal/choroid recept
or/outer plexiform R/G : neural disorder ganglio
n cell
Kollner’s ruleRetinal diseases : B/Y
Eg: RD, RP, ARMD, myopic degen, chorioretinitis, CRVO, DR, CSCR
Except : cone-dystrophy, Stargardt’s
Kollner’s ruleOptic nerve diseases : R/G
Eg: optic neuritis, ON compression, LHON, toxic optic neuropathy
Except : AD optic atrophy, glaucoma, AION, OHT
Acquired/hereditary color defect
characteristics- Color- naming- unilateral/bilateral- blue-yellow- change/ unstable- other visual symtoms
Color Discrimination
Hue Saturation (chroma) Brightness (luminance, intensity)
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
Hue Discrimination
1. HUE DISCRIMINATION
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)
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
2. SATURATION SENSITIVITY
yellow – lowest
saturation
3. Luminosityrelative brightness/lightness peak absorption photopic 555 scotopic 507 Purkinje shift (rod & blue
cone pathway?)
3. LUMINOSITY CURVE507555
Color vision tests
Color vision testsPatient selection- screening test in children, student,
worker- undiagnosed low vision- recent color disturbance- Family Hx of color defect- Occupations
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
Color vision tests1. Screening test2. Color discrimination test3. Color matching test
Color vision test 1: screening test
1.Color confusion1. Ishihara test2. FD15 test
2.Color saturation1. AO-HRR test2.TMC plate
Color vision test : Ishihara test
- Test R-G- High sensitivity
for congen R-G defect
Color vision test : AOHRR test
- 24 plates- Color
defect or not
- Assess severity (+/-)
- R-G and B-Y
Color vision : FD-15- Farnsworth D-15
- line of confusion- R/G,B/Y- separate color handicap
FD-15
FD-15
Color vision tests1. Screening test2. Color discrimination test3. Color matching test
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
Color vision test 2 : discrimination ใชเ้วลามาก อาศัยความชำานาญ ไมเ่หมาะกับ routine exam ไมเ่หมาะกับเด็กอายุน้อยกวา่ 10 ปี
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
FM 100 hue test
Goals Grading of color discrimination in
normal subjects (superior/ average/ low)
Find zone of color confusion
Farnsworth-Munsell 100 hue test
Color vision tests1. Screening test2. Color discrimination test3. Color matching test
Color vision 3 : matchingAnomaloscope1. Nagel R/G
red640 + green545 = yellow5892. Pickford-Nicolson B/Y, R/G3. Sloan’s achromatopsia test
grading severity Expense
ไมเ่ห็นรูเ้รื่องเลย...ย.........
?