Colour Vision PDF

CVD Lec2-Congenital · Visual Processing of Colour...

CVD Lec2-Congenital · Visual Processing of Colour · Frequency of X-linked CVD · Protan Characteristics it as red) Trichromatic processing Protans red darker I don't really see Receptoral 'Capture see. = and response 8% M = 1/12 0 4% F 1/200 Range of colours reduced. Cones = responsive to green (m) blue (s) < are 3 wavelengths; red (L). , , confusion lines intersect. OpponentProcessing I Post-receptoral processing · Terminology Copunctual point : where the colour for a dichromate >3 receptor complexes with opposing actions ; R-G , B-Y B-W ,. · Deutan Characteristics Principle Once Deutans luminosity similar; negligible differences in brightness. of Univariance A single cone is activated by the rate of absorption of photons from light. absorbed , the activated and outputs signal proportional Range of colours reduced - cone is a to this rate of absorption. particular cluster of their opsin photo pigment Deutan co-punctual point intersects point in colour > Cones respond best to a wavelengths based on. at an imaginary space. > This means they only need a small intensity of energy from their peak wavelength OR a stronger signal from other wavelengths. oTritan Characteristics dimmer further from peak with same intensity Characteristics of X-linked CVD Brightness. appears · - May see blue darker of at least 2 cones is required for colour perception Predictable and classical of colours reduced comparative input Range. lones do not independently code color - - , whole eye both eyes , - Blue isn't seen as too differently as MBL cones in the Shorter overlap Stable wavelength region ; gives a pink-red B blue dichotomy -. - All other functions appear normal X-linked : Protan B Deutan AD, ARB X-linked : Tritan CVD ec 3-Acquired · Acquired CVD Characteristics AR : Rod, blue or cone monochromat. Prevalence unknown , but I with age. 1931 ClE · Terminology Chromaticity Diagram · Maybe part eye - Colour matches from a mixture of 3 primary colours. - Dyschromatopsia-Congenital and acquired CVD. - Eyes often unequally affected A Chromatopsia Truly colour blind Variable - day to. day and person to person - - Chromatopsias - Condition of coloured vision. Colour naming problems only late - very stage ↳ Erythropsia-Red ↳ Chloropsia-Green ↳ Cyanopsia-Blue ↳ Xanthopsia- Yellow ↳ lanthinopsia-violet · Acquired CVDs Physiological - yellowing lens · Monochromacy Pathological > - disease Inherit only one cone type monochromacy =. - Neurologic - pathology of VI Inherit no cones = rod monochromacy. · Von Kries Classification Spectrum reduced toluminance only. 3 patterns of abnormal colour matching :. Increased 1 matching range (d colour discrimination SRod achromatopsia No AR monochromacy or Cones 0 07-0 003 %; total colour blindness, Shifted caused by absorption System (pre-receptoral) - 2 match , acuity , central scotoma, hystagmus. poor. ,... S Cone incomplete achromatopsia 3 Shifted match caused by alteration System (photopigments) or one functioning blue photopigment, AR, 0 OT-0 003 %; -. essentially. cone colour blind, limited colour in.. mesopic conditions only , same visual functions affected as achromatopsia. · Kollner's Rule Outer retinal diseases - B-Y deficiency Protanopia Missing Erythrolabe (Red , L) come pigment, X-linked , I M.. 0 01 %. F, Spectrum reduced to blue and yellow hues. ↳ > Deuteranopia-Missing Chlorolabe (Green, M) cone pigment, X-linked, 1 % M. 0 01 % F , reduced to blue and yellow. Spectrum hues. > Tritan opia - Missing Cyanolabe (Blue, 5) come pigment , AD , AR or X-linked , 0 007-0 003 %; Spectrum reduced to.. blue and red hues. · Anomalous Trichromacy 3 functioning cones but one has a hybrid/variant gene with altered sensitivity. S All other visual functions unaffected. 6% M : 0. 4% F , caucasian population. Protanomaly replaced by hybrid L-M (Chlorolabe) Cone B-Y usually early damage BR-G with progression Missing erythrolabe (Red, L) > X-linked , 1 %. M match Spectral requires. 0 03 % F ; red - - cone, , :. more for R+ G = Y ↳ more visual disturbance.. (most Common Cup) Acquired CVD (after Verriest, 1965) Deuteranomaly Missing/inactivated (Green, m) · > Chlorolabe Come, replaced by hybrid M-LC erythrolabe) Come X-linked, 5 % M : 0 35 % F ; - , Spectral match requires more green for R+G = Y.. > Tritanomaly - Reported cases most likely to be incomplete tritanopia , 0 007-0 003 %;.. Spectral match requires more blue for B+G = Egant white. WR5 · Protanope : M-cone Sensitivity and Matching R-G Lec1-Spectral Equations Matches that satisfy the M-cone /has only functioning m-cone ; L-cone absent) : and R Y > Accepts G = Y = · Lord Rayleigh and Anomaloscopy > Y setting significantly reduces shift from G to R , slope decreases. of univariance , matching only by brightness. The yellow By law they are be low (dark) at 73 (red) range because protanopes red darker setting will see. · Generic Specification + 540-555nm = 590nm 2640nm between vision test that can accurately distinguish Rayleigh's equation) only is the colour The anomaloscope I based on > Dichromacy B anomalous trichromacy · Anomalous Trichromats for their respective dichromat 7 Anomalous trichromacy normal The brightness setting will act the same as families as they are still missing a certain cone type. · Metameric Colours Matching range reduced as they can distinguish a change between green/red. the same but have different spectral distributions. Metamers-colours that appear identical to dichromatic source > A monochromatic source in the yellow region will appear a that emits appropriate intensities of 560nm (green) $200nm (red). and have the spectral distributions Isomers Colours that appear the same same. - · Rayleigh Equation Anomaloscope matches and metameric. Employs principle of univariance each half of field. · Deuteranomaly Controls for Matches that Satisfy 2 L-Cones (M-Cone absent/not functioning) : Match for colour and brightness. 72 different pigments - L-cone. Upper field R + G Does accept GFY RE Y. > NOT and. Lower field Y. below 42 (more green side) Matches require more green , match usually - can vary;. > Shift from G to R Normal Matching > Y setting does not reduce with. · Recall : S-cone not relevant for Rayleigh equation. · protanomaly absent) : Normal : Matches that satisfy the LBM-cone: Matches that satisfy 2 M-cones (L-cone > Has both Land M cones. 'Chimeric' both 'Chimeric > 2 different M-cone pigments Cone or R + G Only accepts ; Y = > > Does NOT accept G + Y and RFY. Matchesrequiremoreredrangemyvara from G tom ; decreasing slope. · Deuteranope : L-Lone Sensitivity and Matching absent not functioning) : the L-cone has L-cone ; M-come Matches that Satisfy only functioning > Accepts G = Y and R = Y shift from G to R- brightness not impacted. does not reduce the Y setting not relevant, they are essentially 9 monochromat (law of univariance) , matching only by brightness. but as S-cone is They can match all brightness Lec2-Spectral Equations B - Y · Improved Classification (Retinal/ON Disorders For tritans, equations necessarily involves cone types (trichromatic). of the L-cones tritan confusion lines due to the broad spectrums. Difficult to locate on · Instruments Used Why So Many ? (Rayleigh Equation) · : colour needs Neitz OT desaturated and the match The mixture is in pre-receptoral filtering > Uses interference filters desaturating. Wide variation lens but improved macular pigment, yellow. > Acts same as the Nagel , of short wavelength light : Plate is external > Trendelenberg Macular pigment absorbs the wavelengths of the mixture Heidelberg MRI : macular pigment dependent. unequally ; match is > Uses push buttons , not knobs · Moreland Equation Evolution > Digital display , not rotary dials > Adaptation built in and occurs automatically every 10s (Trendelenberg plate is internal). Oculus Heidelberg : > Computerised interface effect of macular pigment and lens optical density on trendelenberg plate Internal primaries selected to minimise > mid-matching point (MMP) , but meant that equation shifted away from tritan confusion lines. > Rayleigh B Moreland 2 equations Used with Rayleigh equation to assess acquired CVD-called 2-equation method - through > Digital display & Knobs comparison of matching range (MR) B MMP. > Adaptation built in 1 automatic OS(AR/Medmont C-100 · Macular Pigment · A different matching test to distinguish protans : Moreland (1971) absorbed. OSCAR Netherlands ↳ pair of wavelengths equally > - Choose a Medmont C-100 - Australian copy (Cheaper) equal. > matter how much is present the absorption is always > No macular pigment , 16 Hz = Dual red-green LED alternated at. Set minimum flicker Moreland (1983) 3 Equal luminance ↳ Modify to lie closer to tritan confusion line. deutan = Identifies Changes in V(2) especially protan vs. Minimise effects of yellow crystalline lens. longer commercially available. > Both tests no perception of flicker > Absorption of the crystalline lens continues to rise with decreasing Changing luminance can affect. wavelength , so the same manoeuvre is not possible. for distinguishining protan and not protan. - Excellent have a CVD i e. w/Ishihara test. certify if they. to Deficiences Can be used if there's anomaloscope but need of defect Acquired no and severity -. setting · of correlation between magnitude Affect R-G and B-Y so a test method is needed. - Protan will make setting 3-1 ; no Any other scores not protan = exist : - Four possibilities Non-examinable Examples > Rayleigh :. Shift in match 1 point. Increase in match 2 range > Moreland :. Shift 3 in match point. Increase in match range 4 · Two-Equation Method the permits classification of CVDs measured with an anomaloscope, following Verriest classification of acquired dyschromatopsia. Wk] of Colour Vision Lec 1-Clinical Examination Demonstration/Malingerer a · Significant luminance ce colour not , needed to see digit. · Confusion Line Characteristics Involves Cognitive, perceptual and colour vision abilities. reds appear darker/brownish loss) Deficiency in long-wavelength (red) sensitivity ;. Protan (L-cone : Identifies if someone is faking (malingerer). medium-wavelength (green) sensitivity ; greens Breds look similar Deutan (M-cone loss) : Deficiency in (yellowish-brown) muted , yellows shift toward pinkish shades Screening : Disappearing/Vanishing · Plate in short-wavelength (blue) sensitivity ; blues appear. Tritan (S-cone loss) : Deficiency Ishihara : · severity > Figure and background lie on or close to confusion lines Dichromats : all severe > Difficulty for a CVD Anomalous trichromacy : mild, moderate, severe. Disappearing/Vanishing Plates : letters, symbols Ellipses show where colours become indistinguishable. < Figures , confuse red and green confuse green, protanopia design. mild cases and > Most common orange pale/ dark red may or protanomaly may green eg.. see , affect Disappearing B > Unintentional luminance Cues validity colour confusions depend on : severity , illumination, colour intensity , object size , viewing time. vanishing plates fire · Alteration Plates embarrassment, safety hazard , employment issues (pilots , air traffic controllers, police, armed forces, railways , services) Impacts :. confusion line Normal BCVD see a different digit/symbol Traffic lights problematic if they lie on a colour. can be Usually designed for protan and deutan by Solutions to yellow-green region colours in red · choosing. line. - Choose colours not on the confusion Use Symbols greyscale, high contrast brightness. PIC Tests