Test For CVD

TEST’S FOR CVD


Different test forms

1.Pseudoisochromatic plates


Pseudoisochromatic plates are the most famous type of colour vision deficiency test. Most people know them under the name Ishihara plates test, because Dr. Shinobu Ishihara was one of the first persons who designed a very reliable plate test, introduced in 1917. He produced many different test sets and Ishihara plates are widely used all around the world. The copunctual points build the source for this type of colour vision test. The fact that colour vision deficient people can’t distinguish colours along the confusion lines is used to build a pattern of differently coloured dots. If you are colour vision deficient you won’t spot the dots which are shifted along the confusion lines and therefore numbers, letters, lines or anything else can be hidden from you.

Ishihara plate –Transformation design

There exist four different types of plates:

  • Vanishing design: Only people with good colour vision can see the sign. If you are CVD you won’t see anything.
  • Transformation design: Colour vision deficient (CVD) people will see a different sign than people with normal colour vision .
  • Hidden digit design: Only CVD people are able to spot the sign. If you have perfect colour vision, you won’t be able to see it.
  • Classification design: This is used to differentiate between protan and deutan defects. The vanishing design is used on either side of the plate, one side for deutan defects and the other for protans.


Dr.Shinobu Ishihara

Why can colour vision deficient (CVD) people see something which is not visible for people with perfect color vision?

If you are CVD you are not distracted by hue differences along the confusion lines. You will be more focused on lightness differences. These two different facts are used to design the hidden or invisible plates.

Besides the most famous Ishihara plates in a standard version of 38 plates, there exists a shorter version of 24 plates and a concise test containing 14 plates. Ishihara plates can only be used to classify red-green color vision deficiencies. Tritan defects cannot be tested by these tests.

The other well known pseudoisochromatic test plates are the 24 HRR plates by Hardy, Rand and Ritter. This test was first produced in 1954 and can be used to classify all three different forms of color vision deficiency. There also exist a lot more of such tests but none of them is widely used. Even some electronic vision test equipments include certain pseudoisochromatic plates as a quick color vision test. But none of them is very accurate to get a concise test result.


Drawbacks of Ishihara as a screening/testing tool :

It’s known that Ishihara is the most widely used test and it exists from 1917. The Medical Board, Government of India advices eye care practitioners across the nation to use this for screening and testing in hospitals, clinics, camps and in selection process of many careers. It’s been more than 100 years and the pattern of Ishihara still remains the same and thereby it includes these major disadvantages as follows:

  • Same pattern existing for over 100 years, many CVD candidates entering into the selection process in many careers just memorize the set pattern and play a ‘foul’ game risking their entire career. And to the surprise, this ‘foul’ practice is unnoticed by many selection committee members.
  • The same ‘memorization of set patterns’ happens in community activities such as school vision screening.
  • To add another surprise, there are many unethical firms who make people memorize the Ishihara booklet and make money out of it.
  • The material of the booklet cannot withstand massive wear and tear which usually happens in community screening.
  • The print on the material doesn’t last long, loses its property with time.
  • As the test material is expensive, many clinicians across the nation do not replace the booklet even after certain degradation in print and the material, thus making the test worthless.
  • Many duplicate versions of Ishihara is available in the ophthalmic market whereas using such things is never reliable (i.e.people who are CVD could read the pattern inside which shouldn’t be possible)

DALTON’S PIP - A NEW EFFECTIVE CVD SCREENING TOOL

Based on the drawbacks seen in Ishihara and the poor reliability of colour displays we at colourvision.org.in have designed and developed a new effective colour vision deficiency (CVD) screening tool which overcomes all the odds faced by the existing pseudo isochromatic plate’s and display units.

Dalton’s PIP is a patented product which is effective, affordable and provides simple yet precise test results in minimal time.A unique first of its kind screening stratergy is implemented in Dalton’s PIP. It took more than a year for our team which comprises Optometrists and vision researchers to design, validate and do test trials and achieve significant results.

We are happy to introduce such effective product to our community. We wish every eye care practitioner to purchase and use it to create awareness on careers, and saving emotions of many children who have CVD.
Click here to know more



2. Arrangement tests

Arrangement tests are also based on the theory of copunctual points(COLOUR CONFUSION LINES IN LIGHT WAVELENGHT SPECTRUM). In contrast to the static pseudo-isochromatic plates where you have to spot a path or number, an arrangement test is dynamic. Every such test consists of a certain number of coloured discs or plates which have to be arranged in the correct order starting from a pilot plate. The colours are chosen around the white point and because CVD people cannot distinguish colours along certain lines through the white point, CVD people will arrange the discs completely different compared to somebody with normal colour vision. The most well-known test was introduced by Fransworth in the forties of the last century and called Farnsworth D-15 arrangement test. As the names suggests this test includes 15 coloured plates which have to be arranged in the correct order.
Some other well-known tests in this category are the Lanthony desaturated D-15 test, which is used in case of milder forms of CVD and the Farnsworth-Munsell 100 hue test. This test includes 100 different plates which have to be arranged in batches of 20 plates.At the back of each solid colour plate will be the correct sequence number. The analysis of the results takes place in a software.


D 15 TEST


FM 100 HUE TEST - scoring tool(software)

FM 100 HUE TEST


3. Anomaloscope



ANOMALOSCOPE
The anomaloscope provides the most accurate possibility to test the severity of colour vision deficiency and distinguish between dichromats and anomalous trichromats.

It is based on the Rayleigh match: A mixture of red and green light sources has to be matched with a yellow light source. Through the matching range it is possible to discover all different types of red-green colour vision deficiency. Some of the anomaloscopes also include the Moreland match (blue-green) to test for tritan defects.

If you are a dichromat you will be able to make a match for all red-green mixture ratios. Anomalous trichromats don’t accept the normal match and the distance of their match indicates the severity of their deficiency. On the other side, if you suffer a protan vision deficiency you will use much more red to match the colours compared to people with a deutan defect, which use more green in their mixture.

In 1907 the Nagel anomaloscope was introduced and is still known as one of the best. Unfortunately it is not produced anymore. Other well known instruments are the Neitz anomaloscope, the HMC (Heidelberg Multi Color) anomaloscope or the Pickford-Nicolson anomaloscope.


4. Lanterns

The last well known type of tests was introduced by railway companies which found out, that some of their employees couldn’t distinguish certain signal lights. Lantern tests are specially designed to simulate signals and are therefore most often used as vocational tests. Compared to the other tests with lanterns you are testing the required ability directly, are robust and have a high practical value. On the other side you can’t reveal much of the nature and severity of the colour vision defect. Indian Railways use Lantern test for selecting people with normal colour vision.


FALANT LANTERN
  • Holmes-Wright lanterns: This lantern includes two different green, two red and a white light. Lights are shown in pairs of two, low or high brightness, either vertically or horizontally aligned. The test person is asked to name the colours.
  • Farnsworth lantern (Falant): This is the standard test in the US. It is comparable to the Holmes-Wright lantern but is specially designed to pass people with a mild form of colour vision deficiency.
  • Beyne lantern
  • Giles-Archer lanterns
  • Edridge-Green lantern
  • Martin – Lantern

The future of colour vision testing

Today in our digital world one might think, why don‟t we have some simple computer based CVD test. Unfortunately this is not as simple as it looks like. There are two main issues:

1. Many Computer displays just make use of three main colours red, green and blue (RGB). Every other color gets mixed from those three colours.

2. Every computer display has a different colour range it covers, little differences in light sources, different brightness, battery usage and more. This causes different test results. Only calibrated computers can be used to perform such computer based tests.



DALTON’S PIP - A NEW EFFECTIVE CVD SCREENING TOOL

Based on the drawbacks seen in Ishihara and the poor reliability of colour displays we at colourvision.org.in have designed and developed a new effective colour vision deficiency (CVD) screening tool which overcomes all the odds faced by the existing pseudo isochromatic plate’s and display units.

Dalton’s PIP is a patented product which is effective, affordable and provides simple yet precise test results in minimal time.A unique first of its kind screening stratergy is implemented in Dalton’s PIP. It took more than a year for our team which comprises Optometrists and vision researchers to design, validate and do test trials and achieve significant results.

We are happy to introduce such effective product to our community. We wish every eye care practitioner to purchase and use it to create awareness on careers, and saving emotions of many children who have CVD.
Click here to know more


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