Structures of Ishihara Plates

The app has respective structures and logic built in for the 38-plate edition, the 24-plate edition and the 14-plate edition. And in general you don't need to read the following during the initial screening. And the following content gives you a relatively whole picture about proper Ishihara testing.

I. Standard Test Administration Guidelines

To maintain diagnostic accuracy, clinical administrators must enforce strict environmental and testing parameters [2, 4]:

• Lighting: The test must be conducted under indirect, adequate natural daylight (at least 20 foot-candles or 200 lux) [4]. Direct sunlight, fluorescent office bulbs, and yellow incandescent lighting alter color shades and will distort the results. If natural light is unavailable, daylight-balanced bulbs designed to closely simulate natural daylight must be used.

• Distance: The book should be held exactly 75 cm (approx. 30 inches) from the subject's face [2, 4].

• Angle: The plates must be tilted so that the plane of the paper is at a right angle (90°) to the subject's line of vision.

• Monocular Testing: Each eye must be tested independently (e.g., using an eye occluder).

• Response Time Limit:

  • Numerals (Plates 1–25): The subject must state the numeral within 3 seconds [2, 4]. Verbal responses are mandatory; tracing or touching the numeral is prohibited as skin oils can degrade the pigments.

  • Winding Lines (Plates 26–38): The subject must trace the path between the two "X"s using a soft brush (never a pen, pencil, or finger) within 10 seconds [2].

II. Official 38-Plate Edition Diagnostic Key

The 38-plate test is structured into different classes of pseudo-isochromatic plates to evaluate, classify, and confirm red-green deficiencies.

1. Numeral Plates (Plates 1 to 25)

Protan vs. Deutan Numeral Classification (Plates 22 to 25)

These diagnostic plates are specifically engineered to differentiate between Protan (red-blind/weak) and Deutan (green-blind/weak) conditions and to assess their severity:

• Plate 22:

  • Normal Vision: Reads 26

  • Protanopia & Strong Protanomaly: Reads only 6 (the 6 is clearer than the 2)

  • Deuteranopia & Strong Deuteranomaly: Reads only 2 (the 2 is clearer than the 6)

  • Mild Protanomaly/Deuteranomaly: Reads both digits, but the corresponding diagnostic digit is visibly clearer [2].

• Plate 23:

  • Normal Vision: Reads 42

  • Protanopia & Strong Protanomaly: Reads only 2 (the 2 is clearer than the 4)

  • Deuteranopia & Strong Deuteranomaly: Reads only 4 (the 4 is clearer than the 2)

• Plate 24:

  • Normal Vision: Reads 35

  • Protanopia & Strong Protanomaly: Reads only 5 (the 5 is clearer than the 3)

  • Deuteranopia & Strong Deuteranomaly: Reads only 3 (the 3 is clearer than the 5)

• Plate 25:

  • Normal Vision: Reads 96

  • Protanopia & Strong Protanomaly: Reads only 6 (the 6 is clearer than the 9)

  • Deuteranopia & Strong Deuteranomaly: Reads only 9 (the 9 is clearer than the 6)

2. Winding Line Tracing Plates (Plates 26 to 38)

These plates are utilized for non-verbal subjects, pediatric screenings, or to prevent/uncover test memorization.

• Plates 26 & 27 (Diagnostic Tracing): Differentiates Protan and Deutan using tracing lines.

  • Normal: Traces both the purple and red winding lines.

  • Protan: Traces only the purple line (the red line is invisible or extremely obscure).

  • Deutan: Traces only the red line (the purple line is invisible or extremely obscure).

• Plates 28 & 29 (Hidden Tracing):

  • Normal: Cannot trace any line (or is unable to follow any path).

  • Red-Green Deficient: Easily traces a clear, continuous winding line.

• Plates 30 & 31 (Vanishing Tracing - Bluish-Green):

  • Normal: Easily traces the bluish-green winding line between the two "X"s.

  • Red-Green Deficient: Cannot trace any line or follows an incorrect, random path.

• Plates 32 & 33 (Vanishing Tracing - Orange):

  • Normal: Easily traces the orange winding line between the two "X"s.

  • Red-Green Deficient: Cannot trace any line or follows an incorrect path.

• Plates 34 & 35 (Transformation Tracing):

  • Normal: Traces the line connecting the bluish-green and yellowish-green sections.

  • Red-Green Deficient: Traces the line connecting the bluish-green and purple/violet sections.

  • Total Color Blind: Cannot trace any line.

• Plates 36 & 37 (Transformation Tracing):

  • Normal: Traces the line connecting the purple/violet and orange sections.

  • Red-Green Deficient: Traces the line connecting the purple/violet and bluish-green sections.

  • Total Color Blind: Cannot trace any line.

• Plate 38 (Control Tracing):

  • Normal, Red-Green Deficient, & Total Color Blind: Everyone can easily trace this winding line between the two "X"s (used as a validation control).

III. Interpretation and Scoring Guidelines

Depending on whether the test is administered for general clinical diagnostics or strict occupational/civil aviation licensing, different scoring thresholds apply:

A. Official Kanehara Clinical Interpretation

According to the official Kanehara guidelines [2], clinical determination of normality versus color vision deficiency relies strictly on the performance evaluated on the screening plates, Plates 1 to 21:

1. Normal Color Vision: If 17 or more plates are read/interpreted normally, the subject's color vision is clinically regarded as normal [2].

2. Deficient Color Vision: If 13 or fewer plates are read normally, the subject's color vision is clinically regarded as deficient [2].

3. The Hidden-Digit Caveat (Plates 18 to 21): Normal observers see nothing on these plates. An error is counted only if the subject reads the numbers easily and finds them easier to resolve than the corresponding numbers on Plates 14, 10, 13, and 17 [2].

4. Borderline Cases (14 to 16 normal readings): These occurrences are rare in clinical settings [2]. A definitive diagnosis in such cases requires secondary confirmation using alternative testing methods, most notably a Nagel anomaloscope or a computerized Color Assessment and Diagnosis (CAD) test [6].

B. Occupational & Civil Aviation Standards (FAA / CAA)

Military and aviation authorities use strict cut-off values for commercial and private pilots:

• FAA AME Passing Standard (United States): To pass the 38-Plate test and obtain an unrestricted medical certificate, the applicant must record 4 or fewer errors on Plates 1 to 21 (i.e., at least 17 correct) [3].

• FAA AME Failing Standard: An applicant fails if they record 5 or more errors on Plates 1 to 21 [3]. A failure results in a day-only flying restriction unless the applicant passes an alternate approved test (such as the OPTEC 900, Richmond-HRR, or a practical signal light gun test) [4].

• UK Civil Aviation Authority (CAA) Standard: Under UK rules, the applicant must record 3 or fewer errors on the full 38-plate booklet to obtain an unrestricted Class 1 or Class 2 medical certificate [6].

References

• [1] Challenge TB / USAID: Official Ishihara 38-Plate PDF Guide [1]

• [2] Scribd: Kanehara Trading Inc. Tokyo - Ishihara 38-Plate Instructions Manual [2]

• [3] Federal Aviation Administration (FAA): Acceptable Test Instruments for Color Vision Screening of ATCS [3]

• [4] Federal Aviation Administration (FAA) AME Guide: Guide for Aviation Medical Examiners: Color Vision Standards [4]

• [5] National Institutes of Health (NIH) / PubMed: Clinical Assessment & Efficiency of the Ishihara Test (City University study) [5]

• [6] UK Civil Aviation Authority (CAA): Visual Standards: Colour Vision Guidance Material [6]

• [7] Wikipedia: The Ishihara Color Vision Test History and Design [7]

24-Plate Edition Diagnostic Key

The 24-plate test is structured into different classes of pseudo-isochromatic plates to evaluate, classify, and confirm red-green deficiencies.

1. Numeral Plates (Plates 1 to 17)

Protan vs. Deutan Classification (Plates 16 and 17)

These diagnostic plates are specifically engineered to differentiate between Protan (red-blind/weak) and Deutan (green-blind/weak) conditions:

• Plate 16:

  • Normal Vision: Reads 26

  • Protanopia & Strong Protanomaly: Reads only 6 (the 6 is clearer than the 2)

  • Deuteranopia & Strong Deuteranomaly: Reads only 2 (the 2 is clearer than the 6)

  • Mild Protanomaly/Deuteranomaly: Reads both digits, but the corresponding diagnostic digit is visibly clearer [1].

• Plate 17:

  • Normal Vision: Reads 42

  • Protanopia & Strong Protanomaly: Reads only 2 (the 2 is clearer than the 4)

  • Deuteranopia & Strong Deuteranomaly: Reads only 4 (the 4 is clearer than the 2)

2. Winding Line Tracing Plates (Plates 18 to 24)

These tracing plates are primarily used for subjects who cannot read numerals (such as young children or illiterate individuals) or to confirm borderline classifications.

• Plate 18 (Diagnostic Tracing):

  • Normal: Traces both the purple and red winding lines.

  • Protan (Protanopia/strong Protanomaly): Traces only the purple line.

  • Deutan (Deuteranopia/strong Deuteranomaly): Traces only the red line.

• Plate 19 (Hidden Tracing):

  • Normal & Total Color Blind: Cannot trace any line (or is unable to follow it).

  • Red-Green Deficient: Traces a clear winding line.

• Plates 20 & 21 (Vanishing Tracing):

  • Normal: Traces a bluish-green line (Plate 20) and an orange line (Plate 21).

  • Red-Green Deficient: Cannot trace or traces a different, incorrect path.

• Plate 22 (Transformation Tracing):

  • Normal: Traces the line connecting the bluish-green and yellowish-green sections.

  • Red-Green Deficient: Traces the line connecting the bluish-green and purple sections.

  • Total Color Blind: Cannot trace any line.

• Plate 23 (Transformation Tracing):

  • Normal: Traces the line connecting the purple and orange sections.

  • Red-Green Deficient: Traces the line connecting the purple and bluish-green sections.

  • Total Color Blind: Cannot trace any line.

• Plate 24 (Control Tracing):

  • Normal & Deficient: Both can easily trace the winding line between the two X's (used as a control).

III. Interpretation and Scoring (Core Screening)

The clinical determination of normality versus color vision deficiency relies on the assessment of Plates 1 to 15 [1, 2]:

1. Normal Color Vision: If 13 or more plates are read normally, the subject's color vision is clinically regarded as normal [1, 2].

2. Deficient Color Vision: If 9 or fewer plates are read normally, the subject's color vision is clinically regarded as deficient [1, 2].

3. The Hidden-Digit Caveat (Plates 14 and 15): On these plates, a normal observer should see nothing. An abnormal reading is recorded only if the subject reads the numerals 5 and 45 easily, and finds them easier to resolve than the numbers on Plates 10 and 9 [1, 2].

4. Borderline Cases (10 to 12 normal readings): Clinically, these occurrences are rare. A definitive diagnosis in such cases requires secondary confirmation using alternative testing methods, most notably an anomaloscope [1].

References

• [1] Eyeline Optical (New Zealand Distribution): Official Ishihara 24-Plate Instructions (Kanehara Trading Inc.)

• [2] PubMed Central (PMC): Clinical Study on Color Blindness and Ishihara Guidelines (PMC6257947)

• [3] Pioneer International (Medical Equipment Providers): Ishihara Instructions Manual

• [4] MDCalc Medical Calculators: Color Vision Screening (Ishihara Test) Diagnostic Tool

• [5] Wikipedia: The Ishihara Color Vision Test Overview

14-Plate Edition Diagnostic Key

The 14-plate test is strategically structured into screening plates (Plates 1 to 11) to determine normality, and diagnostic plates (Plates 12 to 14) to classify the type of deficiency.

1. Screening Numeral Plates (Plates 1 to 10)

2. Screening Winding Line Plate (Plate 11)

Designed primarily for subjects who cannot read numerals (such as young children) or to confirm screening results.

• Plate 11 (Vanishing Tracing):

  • Normal Vision: Traces a clear bluish-green winding line between the two "X"s.

  • Red-Green Deficient: Cannot trace any line or follows an incorrect path.

  • Total Color Blind: Cannot trace any line.

3. Protan vs. Deutan Classification Plates (Plates 12 to 14)

If a color vision deficiency is detected during the screening phase (Plates 1–11), these diagnostic plates are used to classify whether the defect is Protan (red-blind/weak) or Deutan (green-blind/weak), and to assess its severity. Note: Plates 12, 13, and 14 may be omitted if the exam's sole purpose is to separate normal observers from color defectives [1].

• Plate 12 (Diagnostic Numeral):

  • Normal & Mild RG Deficient: Reads 35

  • Protanopia & Strong Protanomaly: Reads only 5 (the 5 is highly distinct; the 3 is extremely obscure or invisible)

  • Deuteranopia & Strong Deuteranomaly: Reads only 3 (the 3 is highly distinct; the 5 is extremely obscure or invisible)

• Plate 13 (Diagnostic Numeral):

  • Normal & Mild RG Deficient: Reads 96

  • Protanopia & Strong Protanomaly: Reads only 6 (the 6 is highly distinct; the 9 is extremely obscure or invisible)

  • Deuteranopia & Strong Deuteranomaly: Reads only 9 (the 9 is highly distinct; the 6 is extremely obscure or invisible)

• Plate 14 (Diagnostic Tracing):

  • Normal Vision: Easily traces both the purple and red winding lines.

  • Protanopia & Strong Protanomaly: Traces only the purple line. (In mild protanomaly, both lines are traced, but the purple line is visibly easier to follow).

  • Deuteranopia & Strong Deuteranomaly: Traces only the red line. (In mild deuteranomaly, both lines are traced, but the red line is visibly easier to follow).

III. Interpretation and Scoring Guidelines

Depending on whether the test is administered for general clinical diagnostics or strict occupational certification, different scoring thresholds apply:

A. Official Kanehara Clinical Interpretation

Clinical diagnostics rely strictly on the performance evaluated on the screening plates (Plates 1 to 11) [1]:

1. Normal Color Vision: If 10 or more plates are read/traced normally, color vision is regarded as clinically normal [1].

2. Deficient Color Vision: If 7 or fewer plates are read/traced normally, color vision is regarded as deficient [1].

3. The Hidden-Digit Caveat (Plate 9): Normal observers should see nothing on Plate 9. An error is counted only if the subject reads the numeral "2" easily, and explicitly finds it easier to resolve than the numeral "2" on the preceding Plate 8 [1].

4. Borderline Cases (8 or 9 normal readings): rare in clinical practice. A definitive diagnosis requires secondary confirmation via a Nagel anomaloscope [1].

B. Occupational & Civil Aviation Standards (FAA)

The FAA uses specific guidelines for screening commercial, private, and air traffic control candidates [3, 4]:

• FAA AME Passing Standard: To obtain an unrestricted medical certificate using the Concise 14-Plate edition, the applicant must make 5 or fewer errors on Plates 1 to 11 [3, 4].

• FAA AME Failing Standard: An applicant fails if they record 6 or more errors on Plates 1 to 11 [3, 4]. A failure results in a day-only flying restriction unless the applicant passes an alternative approved test (such as the OPTEC 900, Richmond-HRR, or a practical signal light gun test) [4].

References

• [1] Stanford University (Vista Lab): Official Ishihara 14-Plate Instructions (Kanehara & Co., Ltd. Tokyo) [1]

• [2] Stereo Optical Co. (Essilor Group): Ishihara Color Deficiency Test Instructions Manual (14-Plate Edition) [2]

• [3] Federal Aviation Administration (FAA): Acceptable Test Instruments for Color Vision Screening of ATCS and Airmen [3]

• [4] Federal Aviation Administration (FAA) AME Guide: Guide for Aviation Medical Examiners: Color Vision Standards [4]

• [5] PubMed Central (PMC): Comparison of Clinical Color Vision Tests and Optic Neuropathy Screening (PMC5145287) [5]

• [6] Wikipedia: The Ishihara Color Vision Test History and Design [6]

[Generated by Google AI Studio 2026-05-31]