CSFO Colour Vision 2023-24 Slides PDF

CSFO1 2023-24 Dr Sheila Rae 1  Around 1:20 of your patients will have a colour vision defect  Optometrists will often be the first people to identify colour vision defects when seeing children for the first time  Patients will often seek advice regarding th...

CSFO1 2023-24 Dr Sheila Rae 1  Around 1:20 of your patients will have a colour vision defect  Optometrists will often be the first people to identify colour vision defects when seeing children for the first time  Patients will often seek advice regarding their colour vision for occupational reasons 2  Revision of retinal anatomy  Trichromatic colour vision system  Spectral sensitivity of the eye  Congenital and acquired colour vision defects  Genetics and frequency of red-green colour vision defects  Screening colour vision tests  Diagnostic colour vision tests  Impact of colour deficiency 3 Related GOC Competency  3.1.4 Understands the methods of assessment of colour vision ▪ Understands classification and description of colour vision defects, and use of the different tests available for colour vision defects 4 Survival? 5 Conversation overheard on the Hatfield to Cambridge train one half term…  Brother: ‘you’re wearing a purple t-shirt’  Sister: ‘no, it’s red’  Brother: ‘it’s PURPLE’  Sister: ‘no, it’s RED’  … and so it continued for several more minutes 6 Rod and cone photoreceptors in outer retina (next to choroid)  One type of rod ▪ Rhodopsin photopigment ▪ Several rods connect to one ganglion  Three types of cone ▪ Contain different variants of opsin photopigment ▪ One cone connects to one ganglion 7 Structure and function Structure and function of of cones rods  Chromatic  Monochromatic  Good resolution  Poor resolution  Work in photopic  Work in scotopic illumination illumination  Sensitive to contrast,  Found at the foveola flicker  Absent from the  Found across the retina peripheral retina  Absent from foveola 8 9  Humans with normal colour vision are trichromats ▪ Three variants of photoreceptor (plus rod)  Most animals (except monkeys, apes and primates) are dichromats  Gene mutation in monkeys transferred a copy of one opsin gene to a different location on the genome ▪ This resulted in a third variant of the opsin gene in monkeys and their descendants 10  Greater numbers of rods as they cover a greater retinal area ▪ ~ 120 million  Fewer cones as they are concentrated in a smaller retinal area ▪ ~ 6 million  Blue-S cones fewest in number (~2%), found more away from the foveola, but seem to have enhanced responses  Red-L (~64%) and green -M (~34%) more at the centre of the foveola 11  Photopic spectral sensitivity peaks at 555nm ▪ We are most sensitive to yellowish – green light ▪ Why would this be? 12  Photopic ~ 555nm  Scotopic ~ 505 nm 13 14 net effect 15 16 Congenital Acquired  Most common  Can progress and regress  Stable through life  Due to  Inherited ▪ Pathology affecting macula  X-linked ▪ Pathology affecting optic nerve ▪ Mothers are carriers ▪ Discolouration of the lens ▪ Sons get the condition ▪ Drugs 17  May be due to drug use, retinal or optic nerve disease, discolouration of the crystalline lens  Tend to be red-green or blue-yellow confusions ▪ Colour opponency  Unlike congenital deficiencies, they can change over time ▪ Worsen or improve  Can be different in the two eyes ▪ Test suspect acquired colour deficiency monocularly 18  Gene is carried on the arm of the X chromosome that is missing on the male Y chromosome  Females need two copies of the faulty gene, for the trait to be expressed (one on each X chromosome)  Males need only one copy of the faulty gene for the trait to be expressed (on their single X chromosome)  Females with one copy of the faulty genes will be carriers  There is a 50% chance of a female carrier passing one copy of the gene to their offspring 19  A female carrier has four offspring ▪ Two females; two males  Half of the female offspring will be carriers  Half of the male offspring will have CV deficiency  The remaining two are neither carriers of affected 20  Male with colour deficiency passes the unaffected Y chromosome to each of the male offspring  They each have a 50% chance of inheriting the faulty X chromosome from a carrier mother  Therefore 50% chance of being normal and 50% chance of having a colour deficiency 21  Male with colour deficiency passes the affected X chromosome to each of the female offspring  They both inherit the faulty X chromosome from the colour deficient father  They have a 50% chance of inheriting another faulty X chromosome from the mother  Therefore one daughter will have colour deficiency, and the other will be a carrier 22 23 In rare cases, there is either  One type of cone only ▪ Blue cone monochromacy ? effects of this ▪ X-linked congenital, males ▪ ~ 1: 100 000  No cones at all (achromatopsia) ▪ Rod monochromacy ? effects of this ▪ ~ 1: 40 000, males = females ▪ Autosomal recessive inheritance 24  There are two types of colour vision deficiency, each of which can apply to the three different cones  Dichromats ▪ These individuals have only two different cones  Anomalous trichromats ▪ These individuals have three different cones, but the photopigment in one has the wrong spectral sensitivity ▪ The wrong one has sensitivity that overlaps one of the other cones, rather than having a separate distinct sensitivity 25  RED or L wavelength defects have the prefix PROTAN ▪ L deficient dichromats have protanopia ▪ L deficient anomalous trichromats have protanomaly  GREEN or M wavelength defects have the prefix DEUTAN ▪ M deficient dichromats have deuteranopia ▪ M deficient anomalous trichromats have deuteranomaly  BLUE or S wavelength defects have the prefix TRITAN ▪ L deficient dichromats have tritanopia 26  Males B 27 Commonly referred to as red-green colour deficiency  Includes red deficients ▪ Protanopia 1% of males ▪ Protanomaly 1% of males  And green deficients ▪ Deuteranopia 1% of males ▪ Deuteranomaly 5% of males  Tritanopia, blue cone monochromacy and rod monochromacy all rare conditions 28 29  All children (even quite young) ▪ Can affect education ▪ Counsel early about career choices  Males of working age  Patients in occupations with specific colour vision requirements ▪ Electricians, telecoms engineers ▪ Textiles, paints, chemicals ▪ Pilots, police, marine, train drivers ▪ Fire service, some armed forces, customs officers  Patients reporting change in colour perception  Patient’s taking certain drugs 30  R-G congenital colour vision deficiency is also known as Daltonism  John Dalton was a colour deficient 18th C scientist  Hypothesised that his vitreous was abnormally coloured blue  Bequeathed his eyes to the University of Manchester to test this theory posthumously  They still have his eyes in a jar 31  The need for colour vision tests identified in 19thC for occupational reasons  Series of railway and marine accidents attributed to inability to distinguish signal colours  Earliest forms involved identification and discrimination of small lights in signal colours ▪ Red, amber (yellow), white, green 32  Created as a system to describe colour in 1910s  Based on three parameters ▪ Hue ▪ Value (lightness) ▪ Chroma (purity) 33  International Commission on Illumination, 1931  Means of specifying colour, based on hue and saturation  Colours specified by x-y co- ordinates  Monochromatic wavelengths around edges  0.3x – 0.3y is standard illuminants E (white) 34  Ishihara  City university  D 15  Farnsworth-Munsell 100 hue 35  Some tests are able to identify patients who have a colour vision deficiency only  Some tests are able to identify patients who have a colour vision deficiency and to predict whether it is protan, deutan (or tritan)  Some tests are able to quantify the extent of a defect ▪ Useful to monitor acquired defects over time  Some tests can differentiate between dichromacy and anomalous trichromacy and differentiate between protan and deutan 36  Ishihara test first published in 1917  Based on principle of pseudoisochromatic plates ▪ Colours that will incorrectly appear the same to a colour deficient patient  Plates with patterns of coloured dots  Images appear or disappear in the pattern of dots ▪ Shapes, animals, numbers, pathways 37 38  Booklet with 24 or 38 mounted plates  Different types of plate ▪ Test ▪ Transformation ▪ Vanishing ▪ Hidden digit ▪ Classification  Viewed at 75cm, in natural daylight  Allow approximately 4 seconds per plate  Patient asked ‘if you can see a number, tell me what number you see’ 39  On some plates no number will be seen by a normal patient  On some plates no number will be seen by a colour vision deficient patient  Instruction needs to indicate that either seeing a number or not seeing a number is normal ▪ No leading questions, such as ‘is there anything there?’ 40  Should be visible to all colour deficient patients except rod and cone monochromats  An error on this plate is more likely to indicate malingering than a real defect ▪ Deliberate intention to simulate a defect ▪ Malingerers tend to give the ‘wrong’ wrong results 41  Ishihara: R-G colour deficient responses transformation test plate hidden digit vanishing classification Transformation: different Classification: one number number seen seen more clearly than the Vanishing: no number seen other Hidden: number seen 42  Ishihara: types of plate transformation vanishing classification hidden digit test plate Research suggests that the hidden digit plates are of limited value, so can be omitted Classification plate only used if a red-green defect has been identifies Using the 16 transformation and vanishing plates in the 38 plate edition, three or more errors taken as a fail 43  Ishihara identifies red-green congenital deficiencies only ▪ No good for tritan ▪ Limited use for acquired defects  Can’t ‘grade’ the defect by the number of missed plates  Attempts to differentiate between protan and deutan using the classification plate  Can’t differentiate between dichromats and anomalous trichromats 44  Designed at City university in 1980s  Derived from Farnsworth Munsell 100 hue test  1st ed. diagnostic plates only  3rd ed. introduced screening plates 45  Hold at 35-40 cm  Natural daylight  Screening plates ▪ Vertical sets of three dots ▪ Identify which dot is different  Diagnostic plates ▪ Patterns of four dots around a central dot  Identify which surround dot is most similar to central one 46  If the screening plates are correctly seen, no need to complete the diagnostic plates  If mistake(s) are made, continue with the diagnostic plates  Each of the surrounding four dots represents the response expected from ▪ Normal ▪ Protan ▪ Deutan ▪ Tritan 47  Ishihara picks up more deficiencies ▪ But, also more false positives (fails in normals)  Ishihara is reasonably good at differentiating between types of defect (protan vs. deutan)  City picks up fewer deficiencies ▪ But, passes more deficiencies (false negatives)  Also can pick up tritan defects ▪ May be useful for acquired defects  Less good at differentiating between types of defect => Depends why you need to do the test 48  D15 test ▪ Reduced ‘screening’ version of the 100 hue test, with 16 coloured caps ▪ Can confirm whether the defect is protan (red), deutan (green) or tritan (blue) ▪ Results dependent on patient’s personality 49  Empty the caps out of the box and shuffle them  Patient arranges them in the box in colour order  Close the lid, flip the box over, and record the number sequence 50  If the sequence in the box goes from 1 to 10 then 3 then 4, draw a line across from 1 to 10, then back over to 3, then 4  ‘Normal’ result is the lines goes round the numbers in sequence 51  If the patient is normal, there will be a line around the edge of the circle  If there is a defect, the lines will cross the circle  The orientation of the lines indicates whether the patient has a protan, deutan or tritan defect 52 53 Farnsworth –Munsell 100 hue test  Developed in 1940s  Four boxes of 23 or 24 coloured caps, plus reference cap from previous box  Complete one box at a time  Empty out the caps and shuffle  Px arranges in a colour sequence  Sequence recorded 54  Score plotted is the numerical difference between adjacent caps ▪ Sequence 3, 6, 4 ▪ Score would be 5  Online scoring tools readily available 55  Higher total numerical score indicates a more severe deficiency  Scores can be tracked over time ▪ Good for acquired defects  Orientation of the ‘spike’ indicates the class of defect 56 57  Various occupations require good colour vision ▪ For safety or accuracy  Level of deficiency excluded depends on the occupation  Test(s) required to be passed depends on the occupational requirements  Tend to be most stringent requirements where signal identification is required ▪ CAA (pilots), railways, marine shipping personal 58  Still definitive test for many occupations that require signal identification ▪ Railways, pilots, mariners  Various types of ‘lantern’ ▪ Holmes-Wright ▪ Fletcher 59  Shown small aperture lights in two sizes in signal colours from a distance ▪ Red, green, amber / yellow, white  Identify single light colours or differentiate between pairs  Won’t classify the type of defect, only whether a person can identify signal colours 60 Nagal anomaloscope  Only true way to differentiate anomalous trichromats and dichromats  2.5 degree bipartite field of monochromatic yellow (589nm) light observed ▪ Top half fixed ▪ Bottom half made of a mixture of red (670nm) and green (546nm) monochromatic light ▪ Patient ‘mixes’ the red and green to match the reference yellow ▪ Also can adjust the luminance of the yellow 61  Look at proportion of each colour  Protans mix in more red and deutans mix in more green  Dichromats show a wider mixing range than anomalous trichromats 62  All colour vision tests can be affected by lighting  Ideally conducted in natural ‘Northern’ daylight  CIE approved illuminants to simulate this ▪ Standard illuminant C  Fluorescent lights tend to give off spikes of colour rather than an even spectrum  ‘Artificial’ daylight fluorescent tubes are available Spectral power distribution example fluorescent tube63  Patients with colour deficiency are often well adapted to the deficiency and use other cues to differentiate between colours ▪ Contrast ▪ Objects of ‘known’ colour ▪ Comparing colours  ‘Treatments’ for colour vision deficiency are available ▪ Tinted spectacles or contact lenses worn in one eye to allow colour comparisons between eyes ▪ ‘Chromagen’ lenses 64  Can ‘guess’ traffic light colours by position in the light  Green light is a bluish green which is less likely to be confused by deutans  Red brake lights may appear duller with protanopia 65 Duochrome test  The two colours will appear more similar, or one will be appear duller  Can still use the test as it depends on how the different wavelengths are refracted (longitudinal chromatic aberration) rather than the retina’s ability to detect those wavelengths 66 67  Impact on sports and hobbies? 68  Read manufacturer instructions for 100 hue scoring  Review the scoring sheets for each test  Read the Optometry Today CET article on occupational colour vision requirements  Read the Optometry Today CET article on acquired colour vision defects 69