Clearer Vision Ahead: New Color Grading System for High-Demand Jobs
[Author : Admin | Date : 7, April 2023 | Reading time : 6 min]
While appearing for any government or private exams, there we need to follow some rules and regulations that is setup by respective firms or companies and if you are going for the medical test color vision test is one of them that we need to test to qualify the eligibility criteria.
Here in this article we will learn about new grading system which is updated by the experts to fulfill the criteria. But, beforehand we need to know what is color visions and which kinds of color blind test are there.
Color vision is best known for the perception people have of it. It creates an aspect of the vision that cannot be appreciated in any other way.
But it is an illusion of reality that arises from the interaction of millions of neurons in the darkness of our skulls, projecting us into a multicolored universe that would otherwise remain unknown. In addition to the aesthetic effect, color vision makes it easier to recognize objects in the outside world.
A color vision test tests your ability to distinguish different colors. Color blindness is the inability to distinguish the differences between certain colors. The most common form is red-green color blindness, where red and green are seen as the same color.
A new CV grading system with application within occupations
‘Normal’ trichromatic CV (CV1)
This category includes all subjects with RG and YB CAD thresholds below the upper normal limits that have been established for healthy aging.
‘Functionally normal’ trichromatic CV (CV2)
This category includes all applicants with a CAD threshold ≤2.35 CAD units. This limit is sufficient to pass all normal trichromats, irrespective of age and ~7% of the least affected deutans. The latter exhibit almost normal RG colour discrimination and ‘pass’ the HW-A lantern test ‘with zero errors’.
In terms of anomaloscope match parameters, the deutans who pass exhibit match ranges within normal limits, but require more ‘green’ in the RG mixture field to match the monochromatic yellow field.
These subjects are not likely to have any colour detection and discrimination problems when suprathreshold colours defined by both RG and YB components are employed in visual displays.
‘Safe’ trichromatic CV (CV3)
This category includes all applicants with YB CAD thresholds within the normal range and RG thresholds ≤4 CAD units that cannot be classed as CV2. The higher limit is sufficient to pass all normal trichromats and ~22% of deutan subjects.
This higher limit matches the percentage of deutans who pass the HW-A lantern (22%) when using the CIE recommended protocol for use with this lantern.
Although some of the deutans included in this group will have difficulties with small RG colour signals that are close to normal thresholds, all these subjects exhibit normal levels of visual performance when suprathreshold colours defined by both RG and YB components are employed in visual displays.
In general, these subjects will not, however, accept metameric colour matches made by normal trichromats. The least affected protan-like subjects make errors on the HW-A lantern and exhibit minimum RG colour thresholds above 4 CAD units.
As a result, few, if any, protan subjects can be included in this category. Only ~1% of protans and ~15% of deutans fall within the CV3 category (after removing those deutans that can be classed as CV2).
‘Poor’ RG CV (CV4)
This category includes all applicants with YB CAD thresholds within the normal range and RG thresholds ≤12 CAD units that cannot be classed as CV3.
Subjects in this category have normal use of YB colour signals and can make some use of large RG colour signals. Working display environments often employ chromatic saturations as large as 24 CAD units, but only rarely as large as 36 CAD units.
With chromatic signal strengths as large as 36 CAD units, the worst affected subjects within the CV4 category will still derive some benefit based on their RG CV.
The benefit will, however, be small and comparable to what a normal trichromat can achieve with chromatic saturations as small as 3 CAD units. Based on our studies, ~32% of deutans and 29% of protans fall within this category. Many of them will have thresholds ~12 CAD units (range 4–12 units).
With suprathreshold colour differences of ~24 CAD units, as frequently encountered in many display applications, the CV4 subjects benefit from significant use of colour with RG colour signals between 2 and 6 times above their corresponding threshold.
Subjects in this category will therefore be able to make use of and cope with saturated RG colours on visual displays, but they will normally take longer to complete colour-related tasks and may also be less accurate (CAA (UK) report, CAP 1429 (2016)).
When colour differences rely on both RG and YB colour signals and when the task employs large colour differences, such as the discrimination of reds and whites in the PAPI lights used in aviation, protan subjects with thresholds ≤12 CAD units perform as well as normal trichromats.
The same subjects can also carry out the less demanding, suprathreshold, colour-related tasks encountered in aviation. Since safety-critical task performance is not affected by their colour deficiency, protan subjects that fall within the CV4 category are allowed to work as commercial airline pilots.
‘Severe’ RG colour deficiency (CV5)
This category includes all applicants with YB CAD thresholds within the normal range and RG thresholds >12 CAD units. Approximately 70% of protans and 46% of deutan subjects fall into this category.
Although some of the subjects included, i.e. those with thresholds just above 12 CAD units, can still make some use of saturated RG colours, the great majority have very little use of RG colour signals and have to rely mostly on YB colour differences.
Many of these subjects will be unable to make much use of saturated RG colours in visual displays since the maximum chromatic saturations employed in many modern display applications rarely exceed 24 CAD units. There is also an additional disadvantage.
Well-designed display applications employ both luminance and colour contrast to enhance visual performance. The use of adequate luminance contrast is essential when spatially structured patterns are involved and the visual task requires detection and discrimination of fine spatial detail.
Luminance contrast is therefore an extremely important parameter, which together with stimulus colour and size, contributes significantly to the level of visual performance that can be achieved.
In addition to very limited RG colour discrimination, subjects that fall into the CV5 category also experience significant changes in luminance contrast when viewing suprathreshold, coloured objects.
Depending on the subject's class of colour deficiency and the colours involved, the luminance contrast of an object can either be enhanced or diminished when compared with that perceived by normal trichromats.
These changes can in turn affect significantly the visual performance they can achieve. Protan-like subjects that fall into the CV5 category, in particular, can also experience an additional disadvantage.
When viewed against a bright background saturated, ‘red’ objects will appear highly conspicuous and ‘dark’ simply because they are often perceived to be of high negative contrast.
When the same objects are viewed against a dark background, as is often the case with ‘red’ signal lights, they are much less conspicuous and can therefore go unnoticed.
Good design of colour-related visual tasks, together with the use of ‘pastel’ colours defined by both RG and YB colour signals, in addition to luminance contrast, can minimize many of the disadvantages CV5 subjects can experience as a result of their CCD.
‘Supernormal’ trichromatic CV (CV0)
In addition to the five categories listed above (and summarised in Table), a new category, CV0, can be defined based on the availability of reliable data that describe variability in subjects with normal trichromatic CV.
This category includes only normal trichromats with RG colour thresholds below the mean value for the corresponding age.
Only 50% of subjects with normal trichromatic CV can be included in this ‘supernormal’ category which may be useful when extremely demanding colour-related tasks are involved, particularly the naming of diffraction-limited signal lights under conditions of poor visibility.
CV Grading Categories for YB CV
Each of the six categories above assumes ‘normal’ YB CV. In practice, this is always the case when only congenital deficiencies are involved. Congenital tritanopia caused by the total absence of S-cone pigment is extremely rare.
Congenital tritanomalous CV is also non-existent since any potential shifts in the wavelength of peak S-cone spectral responsivity, in a normally functioning YB system, either because of genetic factors or pre-receptor filtering of light in the eye, have a negligible effect on YB CV.
This is simply because of the large wavelength separation which exists between S cones and M and L cones. Congenital RG dichromats tend to have marginally smaller YB thresholds when compared with normal trichromats, and this can be attributed to the narrower wavelength sampling range of either the L or the M cones when compared with the opponent signal provided by the sum of L + M cones (in normal trichromats).
In the below table Summary of the new CV categories that can be used to classify CV in normal trichromats and in subjects with congenital or/and acquired deficiency
These CV grades include the principal categories of the CP grading system used by the armed services which relies heavily on IH and the HW-A lantern protocols. The advantage of the new CV grades is that they are based on accurate measurement of the applicant's RG and YB colour thresholds.
When the subject's thresholds exceed the upper limits that describe ‘normal’ YB CV as a function of age, the probability of acquired deficiency caused by diseases of the retina (such as glaucoma) or systemic diseases that also affect the visual pathways (such as diabetes) is high.
Loss of YB CV, particularly when this loss is much greater than the corresponding RG loss, is highly indicative of retinal or systemic disease. RG thresholds significantly greater than YB thresholds with the latter well above the age-matched upper threshold limits observed in ‘normal’ vision are indicative of acquired loss in subjects that already have congenital RG deficiency.
We have observed several such subjects in our studies which also exhibit another important characteristic that remains unexplained.
In acquired color deficiency, an increased stimulus size favors the YB threshold with reduced or no effect on RG threshold. These observations suggest that three categories are sufficient to describe YB CV (see above table).
‘Supernormal’ YB CV (CV0)
This category describes subjects with better than average YB CV for the corresponding age. This categorization can easily be established by examining the mean threshold limits that describe normal YB CV as a function of age. RG dichromats tend to fall into this category because in general they have slightly smaller YB thresholds for the reasons discussed above.
‘Normal’ YB CV (CV1)
This category includes all subjects with YB CAD thresholds below the upper normal limits that have been established for healthy aging.
‘Acquired’ color deficiency
YB thresholds above the upper normal, age-matched limits together with RG thresholds that are also frequently above the corresponding threshold limits that describe normal aging provide reliable indicators of acquired loss of CV and hence the presence of disease.
Although YB color sensitivity is often affected first in age-related macular degeneration, optic neuritis and diabetes, RG CV losses soon follow. Greater loss of RG CV (when compared with YB loss) is not normally observed in acquired deficiency, except in subjects with congenital RG deficiency.
