3.1.4 colour vision

what photopigments are responsible for mediating colour vision

short, medium, long wavelength sensitive pigments. S,M, L

what categories of congenital colour vision deficiency are there

how many photopigments are present, or if the photopigment is abnormal

what names are given to those who have 2 photopigments

dichromat

what is an anomalous trichromat

have all 3 pigment but one has abnormal sensitivity

what is L missing called

protanope

what is M missing calling

deuteranope

what is S missing called

tritanope

what is a monochrome

they lack cones or have one cone, very rare

why are men more likely to get colour vision defect

X linked

what wavelength are deuteranopes not seeing

530nm and after, detected by L cones

how can a deutranope tell differences in colour past 530nm

by their relative brightness

what environment should colour vision test be done at

illuminated 350-400 lux lamp of colour 6500k

what distance is ishihara done at

75cm

describe D15 test

caps placed in random orders one lamp

viewing distance 50cm

px ordrrs caps in box so colour appearance changes progressively

practitioner turns caps over and plots them in the numerical order

describe the city test

does at 35cm

3rd edition

First part- 3 dogs say which one is different for screening

Second part-each page has central dot and 4 dots around, report which dot looks most similar to middle. Detection

test sheet shows normal proton, deutan and triton repsonses

how do you interpret ishihara results

fail more than 3 plates

describe the plates of ishihara

2-9 are transformation plates, different number seen by proton/deutan

10-17 are vanishing plates, number not see by protan/deutan

does not detect tritanope

describe D15 results

if one or more diametric crossing are made it indicates mod/severe prtoan/deutan CCVD

up to 2 adjacent crossing allowed

can detect tritan

describe city results

one or more error made on any 10 plates indicated mod/severe proton/deutan CCVD

how do colour vision test work

make use of confusion zones to grade severity of CCVD

plotted on CIE 1931 Chromaticity diagram

what effects of CCVD are there

comparative tasks matching colours

connotative tasks, like red matched with stop

where colour used to organise display and catch attention

colour used to make a mood

what test is done if Ishihara is failed

lantern test, name coloured lights. any error is failure

what occupations can be affected

which Ishihara test is preferred and why

38 plate test, contains most efficient plates for detection

what symptoms of a rod monochromatic are there

no functioning cones

VA reduced 6/60-6/36

photophobic

nystagmus

what symptoms of cone monochromats are there

single cone response

VA reduced 6/24-6/9

photophobic

nystagmus if VA below 6/18

what X linked defects are there

protanopes/protanomalous trichromats

deuteranopes/deuteranomolous trichromats

what colours do protanopes confuse

black with dark shades of red

dark brown with dark green, dark orange and dark red

some blues with some reds, purples and dark pinks

mid greens, some oranges

what colours do deuteranopes confuse

confuse mid reds with mid greens

blue greens with grey and mid pinks

bright greens with yellows

pale pinks with light grey

mid reds with mid brown

light blues with lilac

what colours do tritanopes confuse

light blues with greys

dark purples with black

mid greens with blue

oranges with reds

how are

what are acquired defect characteristics

symptomatic

type and severity of defect can fluctuate-Kollner’s rule

unstable

monocular differences

VA reduced, VF defects, contrast sensitivity issues

equal among sexes

reversible

what is Kollners rule

disease of outer retina and media changes result in blue-yellow colour defects

diseases of inner retina, optic nerve, visual pathway and visual cortex result in red green defects

what can causes acquired colour vision defects

ocular pathology

intracranial injury

drug/toxin induced

psychological eg hysteria rare and transient defects

cataract alters colour pereception

AMD can cause triton deficiency

what is type 1 acquired defects

similar to protan

progressive cone dystrophies

macular dystrophies

loss of va

what is type 2 acquired

similar to deutan defect

optic neuritis

optic atrophies, (Leber’s)

optic nerve intoxication

what is type 3 acquired defect

blue yellow defect

cataract

CSR/AMD

rod and Cone dystrophies retinitis pigmentosa

retinal vascular disorders CRVO/CRAO/Diabetes

peripheral retinal lesion (chorioretinitis, retinal detachment)

glaucoma

vitamin A deficiency ( alcoholism, chronic liver disease).

what effects of ethyl alcohol are there

optic neuritis

optic atophy

what effects of methyl alcohol are there

red/green defect

progresses to blue/yellow defect

what effects does tobacco have

papillomacula bundle

central scotoma

red/green defect

what effect does digoxin have

type 2 defect, red/green

scintilling scotomas

episodic coloured vision

transient visual field defects

colour vision recovers after cessation of drug

what effects of ethambutol are there

type 2 defect red/green sudden onset

colour vision records after cessation

what effect does hydroxycloroquine have

type 3

type 1 at advanced stages

what other defects for examination are there

changes in VA, pupil responses changed, VF defect, amsler chart

what is an anomaloscope

colour matching technique not used

distinguished between dichromate vs anomalous trichormats

what test should be done for acquired defects

the city test done monocularly