Ishihara test: Difference between revisions

{{shortShort description|Color perception test}}

| Caption = Example of an Ishihara color test plate. The number "74" should be clearly visible to viewers with normal color vision. Viewers with [[red-greenred–green color blindness]] will read it as "21",<ref>{{cite book |last1=Bonewit-West |first1=Kathy |last2=Hunt |first2=Sue |last3=Applegate |first3=Edith |title=Today's Medical Assistant - E-Book: Clinical & Administrative Procedures |date=18 June 2014 |publisher=Elsevier Health Sciences |isbn=978-0-323-29180-4 |url=https://books.google.com/books?id=Xc7sAwAAQBAJ&dq=Ishihara+chart+%2274%22+%2221%22&pg=PA389 |language=en}}</ref> and viewers with [[monochromacy]] may see nothing.

The '''Ishihara test''' is a [[color vision test]] for detection of red-greenred–green [[color blindness|color deficiencies]]. It was named after its designer, [[Shinobu Ishihara]], a professor at the [[University of Tokyo]], who first published his tests in 1917.<ref name="ishihara1917">S. Ishihara, Tests for color-blindness (Handaya, Tokyo, Hongo Harukicho, 1917).</ref>

The test consists of a number of '''Ishihara plates''', which are a type of [[pseudoisochromatic plate]]. Each plate depicts a solid circle of colored dots appearing randomized in color and size.<ref>{{cite web|last=Kindel|first=Eric|title=Ishihara|url=http://www.eyemagazine.com/feature/article/ishihara|work=Eye Magazine|access-date=3 December 2013}}</ref> Within the pattern are dots which form a number or shape clearly visible to those with normal color vision, and invisible, or difficult to see, to those with a red-greenred–green color vision defect. Other plates are intentionally designed to reveal numbers only to those with a red-greenred–green color vision deficiency, and be invisible to those with normal red-greenred–green color vision. The full test consists of 38 plates, but the existence of a severe deficiency is usually apparent after only a few plates. There are also Ishihara tests consisting of 10, 14 or 24 test plates, and plates in some versions ask the viewer to trace a line rather than read a number.<ref name="ishihara">{{cite book |last1=Ishihara |first1=Shinobu |title=Tests for Colour-Blindness |date=1972 |publisher=Kanehara Shuppan |url=http://www.dfisica.ubi.pt/~hgil/p.v.2/Ishihara/Ishihara.24.Plate.TEST.Book.pdf |access-date=17 June 2020 |archive-date=8 December 2020 |archive-url=https://web.archive.org/web/20201208160704/http://www.dfisica.ubi.pt/~hgil/p.v.2/Ishihara/Ishihara.24.Plate.TEST.Book.pdf |url-status=dead }}</ref>

File:Ishihara 19.PNG|Ishihara Plate No. 29{{efn|name=plate29}} (a line can be traced by many of those with red-greenred–green color blindness, but not by those with normal color vision){{Improve caption|reason=The caption is outdated, the image has since been updated|date=April 2024}}

Being a printed plate, the accuracy of the test depends on using the proper lighting to illuminate the page. A "daylight" bulb illuminator is required to give the most accurate results, of around 6000–7000&nbsp;K [[color temperature|temperature]] (ideal: 6500&nbsp;K, Color Rendering Index (CRI) >90), and is required for military color vision screening policy. [[Fluorescent bulb]]s are often used in school testing, but the color of fluorescent bulbs and their CRI can vary widely. Fluorescent lighting showed better results and faster recognition speed compared to CFL and LED luminance in trichromats.{{citation needed|date=September 2020}} [[Incandescent bulb]]s should not be used, as their low temperature (yellow-color) gives highly inaccurate results, allowing some color vision deficient persons to pass.

Proper testing technique is to give only three seconds per plate for an answer, and not allow coaching, touching or tracing of the numbers by the subject. The test is best given in random sequence, if possible, to reduce the effectiveness of prior memorization of the answers by subjects. Some pseudo-isochromatic plate books have the pages in binders, so the plates may be rearranged periodically to give a random order to the test.

Since its creation, the Ishihara Color Blindness Test has become commonly used worldwide because of its easy use and high accuracy. In recent years, the Ishihara test has become available online in addition to its original paper version.<ref name= >ChallengeTBIshihara{{citationcite neededweb|dateurl=Januaryhttps://www.challengetb.org/publications/tools/country/Ishihara_Tests.pdf|title=Ishihara Charts|website=www.challengetb.org|publisher=USAID|accessdate=26 October 2023}}</ref> Though both media use the same plates, they require different methods for an accurate diagnosis.

The [[United States Navy]] uses the Ishihara plates (and alternatives) for color vision screening. The current passing score is 1210 correct of 14 red/green test plates (not including the demonstration plate).{{cn|date=January 2024}}

Research has shown that scores below twelve indicate color vision deficiency, and twelve or more correct indicate normal color vision, with 97% [[Sensitivity and specificity#Sensitivity|sensitivity]] and 100% [[Sensitivity and specificity#Specificity|specificity]]. The sensitivity of the Ishihara test varies by the number of plates allowed to pass, which can vary by institutional policy. Sensitivity also may be influenced by test administration (strength of lighting, time allowed to answer) and testing errors (coaching by administrators, smudges or marks made upon the plates).

*[https://www.college-optometristsmuseyeum.org/the-college/museum/online-exhibitions/virtual-colour-vision-gallery/ishihara-and-other-colour-vision-testsresults.htmlphp?module=objects&type=browse&id=18&term=COLOUR+VISION+TESTS&page=1 The College of OptometristOptometrists - ''Ishihara and other colour vision tests'']