Ishihara pseudoisochromatic tests

OVERVIEW

Visual impairment and blindness have remained one of the most pressing health concerns in Eastern Mediterranean countries with 40.5 million people living with vision impairment and 5 million blind people, both of whom could have been prevented with prophylactic and screening measures in some cases. The incidence and causes of vision impairment in the region were estimated by the World Health Organization(KF, 2001)

About 8% and 0.5 percent of the male and female population, respectively, have congenital color vision impairments. Pseudoisochromatic Ishihara plates have been found to be effective in detecting color vision problems early on. This widely used color vision test was designed to detect people with the red-green component of congenital color blindness, but it may also be useful in detecting acquired color vision abnormalities. Despite the importance of the Ishihara plates, their current arrangement has several flaws. The validity, liability, and repeatability of these novel plates will require more research and investigation.

History

Professor J. Stilling of Strassburg invented pseudoisochromatic plates (PICs or PIPs) in 1876, and they were initially published in 1883. They’re a short hand-held test for several types of color blindness that relies on the recognition or non-recognition of numbers or objects against a potentially misleading colored backdrop. Stilling suggested in 1889 that the practitioner should question the patient to pick out like-colored dots under various distances and lighting circumstances, rather than relying solely on the patient reading the numbers.

Oguchi Chuta devised the first pseudoisochromatic tests in Japan in 1911, but he only used them to evaluate troops in the Imperial Japanese Army and never publicized them. As a result, no replicas of them exist in our museum. Ishihara Shinobu (1879-1963), Professor of Ophthalmology at the Imperial University of Tokyo from 1922 to 1941, devised the most recognized Japanese pseudoisochromatic tests. Ishihara created three manuscript copies, one in katakana and hiragana characters and the other in Arabic numbers, all handpainted in watercolor by himself. The International Edition, originally published by the Kanahara Trading Company in 1917, evolved from this third version. In the West, copies rapidly became popular.

Five types of Ishihara charts exist 

Group 1 should be everyone, group 2 should be read differently y normal and anomalous(color blind) people. An abnormal individual for example could mistake the number 8 for the number 3. Only those with normal eyesight should be able to read group 3. Only those with color vision impairment should be able to read group 4. Protanopes and deuteranopes will be differentiated by group 5. For example, the protanopes will read 42 as 2 while the deuteranope will read it as 4. 

Ishihara exams were also offered in the form of circles, squares, and winding lines for use with children aged 4-6 years or unlettered adults. His daughter made changes to the professor’s original watercolors. The chart was provided with the soft artist paintbrush for the patient to use in tracing the curves as illiterate would not comprehend a pen (also as a nod to the drawings’ origins).(Ishihara and Other Colour Vision Tests, n.d.)What is plate test and types:

The observer must identify a colored sign embedded in a backdrop (most pseudoisochromatic plates); identify which of four colors is most close to a standard color (City University Test); or identify which circle matches a grey rectangle in a plate test (Sloan Achromatopsia Test).

Pseudoisochromatic tests come in various forms (e.g., American Optical Hardy-Rand-Rittler, Ishihara, Dvorine, Tokyo Medical College). All of them can detect congenital red-green abnormalities with high accuracy (90 to 95%). These tests are essentially a series of cards on which colorful dots of varying sizes of discs are printed to form a multicolored figure on a multicolored backdrop. The image is a letter, an Arabic numeral, or a geometric pattern that is recognizable (e.g., a circle, triangle, or cross). The only systematic difference between the figure and background dots is color: the figure is made up of one or more colors, while the backdrop is made up of dots of various hues. Variations in the size, brightness, and saturation of the dots can be used to reduce the likelihood of identifying the intended figure based on signals other than color. Observers with normal color vision may identify the hue difference between the figure and the backdrop and, as a result, can readily interpret the figures, while those with deficient color vision may be unable to differentiate between the figure and background colors.

The disappearing design, the qualitatively diagnostic plate, the transformation plate, and the concealed flaw design are four forms of pseudoisochromatic design identified by Hardy, Rand, and Rittler (1945). The disappearing design comprises a figure that can be read by a typical trichromat but not by a color-blind viewer. A qualitatively diagnostic plate is a disappearing plate that allows a proton and a deutan observer to be distinguished. Two persons may be seen in the backdrop of the transformation plate:

For normal trichromats, the plate in the concealed digit design is a vanishing plate, but the figure is visible to color-defective observers. Several pseudoisochromatic plate tests have been studied by Lakowski (1965b, 1966, 1969, 1976). The Sloan Achromatopsia Test was developed to identify achromatopsia, whereas the City University Test was designed to detect color confusions (colors that appear extremely different to a normal observer but look quite similar to a defective viewer) (i.e., the inability to differentiate any of the rainbow hues or their intermediaries other than based on lightness). (COLOR VISION TESTS – Procedures for Testing Color Vision – NCBI Bookshelf, n.d.)

Ishihara Color Test Instructions

Plates 1–17 all have a number, whereas plates 18–24 have one or two wavy lines. You must properly identify the correct number or trace the wavy lines to pass each exam.

Sit 75cm away from your display, each circle at eye level.

It’s best if you can have some natural light and no glare on your screen. The hue of the photographs might be affected by interior lighting and glare.

Within 5 seconds, try to spot the concealed number or line, then click on the image (left mouse button).

The solution, as well as an analysis describing your situation if you got it incorrect, will be displayed when you left-click.

Continue to the next Ishihara test and complete all of them to determine the degree of your color blindness.

Please pass the test on to your friends!

What happens during a color vision test?

The exam will be done by your eye doctor. You’ll be seated in a well-lit room. You’ll close one eye and examine a set of test cards with the other. A multicolor dot pattern appears on each card.

In each color pattern, there’s a number or symbol. You’ll inform the doctor whether you can figure out the number or symbol. If you have normal color vision, numbers, shapes, and symbols should stand out from their surroundings. You might not be able to see the symbols if you have a color vision problem. It’s also possible that you’re having trouble rrecognizingpatterns among the dots.

You’ll cover one eye and look at the test cards again after examining the other. The doctor could ask you to characterize the strength of color as seen through one eye versus the other. It’s possible to have a normal color vision test result yet still have color intensity decrease in one eye or other.

What do the results mean?

  • This test can assist identify a variety of color vision issues, including:
  • tritanopia: trouble distinguishing yellow from green and blue from green
  • protanopia: difficulty differentiating blue from green and red from green 
  • Achromatopsia: total color blindness deuteranopia: trouble differentiating red from purple and green from purple deuteranopia: difficulty separating red from purple and green from purple (a rare condition, in which only shades of grey are visible) 

What happens after a color vision test?

There isn’t a therapy that specifically addresses color vision issues. If your colour vision impairment is caused by a disease, such as diabetes or glaucoma, treating the ailment may help you see colors better.

Color contrasts may be easier to perceive if you use colored eyeglasses or contact lenses. However, neither a filter nor ccoloredcontacts will help you increase your natural ability to distinguish between hues.

ADVANTAGES OF TEST

Plate testing has several benefits. They may be used on naïve subjects, illiterates, and children, and they can be given quickly and simply by untrained people. They are readily accessible, very affordable, and can be used on naive subjects, illiterates, and children. Still contain some drawbacks. 

First, the spectral quality of the light source used to illuminate the plates has an impact on how the figures are read; the plates must be presented in the normal viewing circumstances for which they were created. Second, the plates’ effectiveness is largely contingent on the judicious use of perplexing hues. The finest confusion colours for diagnostic purposes are sometimes unavailable due to technical reasons. Third, even if a set of colocolorsselected, individual differences in the eye lens and the color of the rear of the eye mean that a single set of colors will is not optimum for all viewers. Finally, there are no reliable scoring standards for categorizing abnormalities based on test performance; the number of mistakes on pseudoisochromatic tests tells us little about the kind or severity of a color vision problem.

Pseudoisochromatic tests should be used only as screening tests to distinguish between normal persons and those who are color-deficient; their diagnostic use is limited. More comprehensive information regarding color coordination should be extracted with caution. Information from pseudoisochromtic plate tests should always be regarded as offering a likely but not certain diagnosis at this time. (COLOR VISION TESTS – Procedures for Testing Color Vision – NCBI Bookshelf, n.d.)

The Ishihara test was developed to assess and diagnose red-green color vision problems. However, this test isn’t exhaustive, and some people with color vision problems may be overlooked (A et al., 2006).(E, 1979).One demonstration plate and 14 screening plates comprise the Ishihara test, which features three number designs: disappearance, transformation, and concealed digits. The Ishihara test (MK & JK, 1987) is made up of transformation cards numbered 2 through 7, disappearing designs 8 through 13, and hidden cards 14 and 15.

CONCLUSION

There are a variety of color vision tests available, but each has its own set of limitations, necessitating the development of a reliable test that can be done without the use of specialized clinical facilities, costly instruments, or a highly trained operator. To determine the kind and severity of color vision impairments, this test must be rapid to give and easy to grade (A et al., 2006).  The new test’s trial subjects reported positive findings in terms of ease of use, portability, speed, and diagnostic capability.

The test’s validity is critical since it determines how effectively it can detect individuals with color abnormalities in the same way that traditional tests can (MK & JK, 1987).  It is also necessary to evaluate the new test’s capacity to classify visual color abnormalities. To be chosen as a clinical regular screening test in the aforementioned geographic region, the new test must be able to attain a high degree of sensitivity and reliability.