The Ishihara test, also known as the Ishihara color vision test, is used to determine any deficiencies in color vision. It was named after its creator, Dr. Shinobu Ishihara, a Japanese ophthalmologist who published his tests in 1917. The Ishihara test consists of a number of colored plates, or images, that contain colored dots which form a number or shape clearly visible to those with normal color vision, but difficult or impossible to see for those who have color vision deficiencies. This test can identify two major types of color blindness – protan defects (issues in perceiving red light) and deutan defects (issues in perceiving green light).
How the Ishihara Test Works
The Ishihara test plates are designed to test color perception based on colors that are confused by people with red-green color deficiencies. The plates contain colored dots of various sizes and hues that form a number or shape against a contrasting background. People with normal color vision can easily discern the number or shape. Those with color vision deficiencies either cannot see the number/shape at all, or see a different number/shape.
During the test, subjects are shown the plates one at a time under consistent lighting conditions and asked to identify the number or shape they see. Their responses allow the administrator to determine if the subject has normal color vision or if they have a color vision deficiency and what type it is.
Interpreting Ishihara Test Results
Based on the subject’s performance, the test administrator can categorize their color vision as:
- Normal color vision – if the subject identifies all or nearly all plates correctly
- Deutan defect – if the subject makes errors on plates containing dots detectable by normal red-green perception
- Protan defect – if the subject makes errors on plates containing dots detectable by normal green perception
- Total color blindness – if the subject cannot discern any of the hidden shapes/numbers
The specific plates missed or seen incorrectly provide clues about the type and severity of color vision deficiency.
Advantages of the Ishihara Test
Some key advantages of the Ishihara test include:
- Quick and easy to administer and interpret
- Provides specific diagnostic information
- Detects red-green color deficiencies which account for 99% of all color vision deficits
- Suitable for screening both children and literate adults
- Inexpensive to purchase the test plates
- Plates are durable and reusable
Limitations of the Ishihara Test
Some limitations of the Ishihara test are:
- Cannot detect blue-yellow color deficiencies
- Not suitable for very young children or illiterate persons
- Requires good lighting conditions to get accurate results
- Does not assess color discrimination ability
- May miss milder color deficiencies
- Does not identify the cause of the color vision issue
What Other Color Vision Tests Exist?
Some other color vision tests that can address limitations of the Ishihara test include:
- Farnsworth D-15 Test – Arrange color caps in order detects subtle color discrimination defects
- Hardy-Rand-Rittler (HRR) Test – Match colored chips, identifies blue-yellow issues
- Lanthony Desaturated D-15 Test – Subtle color discrimination test using desaturated caps
- Farnsworth Lantern Test – Matches illuminated color lights, for maritime/aviation settings
- CAD Test – Computer administered digital color vision test
- Color Vision Meter – Quantitatively measures color perception
These tests may be used in conjunction with or in place of the Ishihara test depending on the specific type of color deficiency suspected and level of assessment needed.
Who Performs the Ishihara Test?
The Ishihara test is primarily administered by:
- Ophthalmologists – Medical doctors specializing in eye care
- Optometrists – Eye care professionals
- Orthoptists – Allied health professionals trained in eye care
- School nurses – May screen children’s vision using Ishihara test
- Occupational health screening – Test color vision for specific careers
The test must be administered in person by someone trained to give the test and interpret the results. Self-assessment using the Ishihara plates is not recommended as results may be inaccurate without proper proctoring.
Who Needs Ishihara Color Vision Testing?
Ishihara color vision testing may be recommended for the following groups:
- School children – Vision screening
- Pre-employment screening – Jobs requiring normal color vision
- Driver’s license – Meeting requirements for driving privileges
- Military service – Meeting color vision standards
- Pilots – Aviation color vision standards must be met
- Railroad workers – Ensuring safety in railroad operations
- Electricians – Accurately discerning wire colors is essential
- People with family history of color blindness
- Anyone experiencing difficulty with color distinction
This screening can identify issues early on and ensure proper precautions or restrictions for careers involving color cues.
Significant Color Vision Deficiencies
The most significant types of color vision defects detectable on the Ishihara test include:
- Protanopia – Inability to perceive red light, due to missing or abnormal L cones
- Protanomaly – Reduced sensitivity to red light
- Deuteranopia – Inability to perceive green light, due to missing or abnormal M cones
- Deuteranomaly – Reduced sensitivity to green light
- Tritanopia – Rare, inability to perceive blue light, due to missing S cones
- Monochromacy – Total color blindness, only seeing shades of grey
Protan and deutan defects involving red-green perception are by far the most common. The specific plates missed on the Ishihara test can indicate which type of color blindness a person is likely to have.
Prevalence of Color Vision Deficiencies
| Type of Color Deficiency | Prevalence in Males | Prevalence in Females |
|---|---|---|
| Protan Defects | 1% | 0.01% |
| Deutan Defects | 4.9% | 0.37% |
| Tritan Defects | 0.0001% | 0.0001% |
| Total Color Blindness | 0.0002% | 0.0002% |
Color vision defects, particularly red-green deficiencies, occur much more frequently in males than females due to the genetic inheritance pattern on the X chromosome.
Occupations Requiring Normal Color Vision
There are many occupations that require normal color vision, including:
- Pilots and air traffic controllers
- Transit workers – railroad engineers, subway operators
- Maritime occupations – sailors, boat crew
- Electricians, electronics technicians
- Firefighters
- Police officers and public safety workers
- Lab technicians and scientists
- Healthcare – doctors, surgeons, nurses, EMTs
- Military service members
- Telecommunications technicians
- Food scientists, inspectors, and preparers
- Many manufacturing and construction jobs
Individuals seeking to enter these fields would require Ishihara and other specialized color vision testing to ensure they meet the color perception requirements for safe performance of duties critical to public safety.
Conclusion
In summary, the Ishihara color test is an important screening tool that can accurately and quickly identify red-green color deficiencies that affect a sizable portion of the male population. Knowing one’s color vision status has implications for career pursuits and daily activities like driving that rely on color cues. However, the Ishihara test does have some limitations in detecting blue-yellow defects and milder anomalies, so results may need to be confirmed using secondary color vision tests if color perception issues are suspected.
Research continues on developing new color vision tests and tools to enhance evaluation of color vision disorders beyond what the pioneering Ishihara test can ascertain. ButDr. Ishihara’s simple and ingenious test remains a critical instrument in both screening programs and clinical diagnosis of common color vision problems today.