The Ishihara test is one of the few clinical instruments that crosses the Canada-US border without changing. The plate book is the same, the instruction to name the number is the same, and the red-green deficiency it screens for is the same. What changes is the paperwork that sits behind the result: where the pass-or-fail threshold is written down, who is entitled to ask for it, and what a clinic has to hand over when an employer, a licensing body or a school programme wants evidence.
For optometry practices, occupational health services and screening programmes on either side of the border, that is the practical question. The test takes three minutes; the recording and referral steps are what consume the appointment.
What is the Ishihara test actually measuring?
The plate book is a set of pseudoisochromatic plates. The optometric description is precise about the mechanism: the American Optometric Association explains that a colour deficiency "can be diagnosed through a comprehensive eye examination," in which "the patient is shown a series of specially designed pictures composed of colored dots, called pseudoisochromatic plates," and asked to find numbers among the dots. Some plates are built so that a person with normal colour vision sees one number while a person with a deficiency sees a different one. That design is what lets a single plate distinguish a red-green deficiency from normal colour vision without the patient describing anything.
Two limits follow from that design, and both belong in the record conversation:
- The plates screen, they do not diagnose. A plate result is a screening outcome. Confirmation belongs to a full examination in which the plates are one part.
- The plate set is a book, not a page. Plate editions differ in length and in which plates are included, so "failed the Ishihara" without a plate number and a count of errors is not a result anyone can act on.
| Test | What the patient does | What the result describes | Typical setting |
|---|---|---|---|
| Ishihara plates | Names numbers in coloured dots | Red-green colour deficiency, screening | Primary care, occupational screening |
| Acuity chart | Reads or matches optotypes | Sharpness of vision at a distance | Every vision examination |
| Contrast sensitivity | Detects low-contrast targets | Performance in dim or low-contrast light | Low vision, driving assessments |
| Visual field screening | Responds to peripheral targets | Extent of the visual field | Glaucoma and neurological review |
How is a colour vision result recorded differently from an acuity result?
An acuity result is a fraction. A colour vision result is a description. That asymmetry is why the two are often recorded badly in the same chart.
A complete colour vision entry names four things: the test used, the plate set or edition, the lighting conditions, and the errors observed per eye. "Colour vision: abnormal" is not a record — it does not tell the next clinician whether the patient failed one plate or twelve, and it does not let a future examiner repeat the same test under the same conditions.
The examination itself has two parts worth separating on paper. First, the screening result. Second, the consequence, which is a conversation about the patient's occupation and about what the deficiency does and does not affect. That second part is where the Canadian and US situations start to diverge.
Do Canada and the US write colour vision into the same documents?
Not in the same place, and the difference is visible in the regulation text of each country.
In the United States, colour perception is written directly into the federal eye standard for pilots. 14 CFR 67.103 lists the eye standards for a first-class airman medical certificate, and paragraph (c) reads: "Ability to perceive those colors necessary for the safe performance of airman duties." Losing that ability is a stated ground for the standard to fail, and the standard sits in the same section as the acuity and field-of-vision clauses.
The commercial driving rule uses the same technique with a colour list. 49 CFR 391.41 requires a driver to have "the ability to recognize the colors of traffic signals and devices showing standard red, green, and amber," alongside a distant visual acuity of at least 20/40 (Snellen) in each eye and a field of vision of at least 70° in the horizontal meridian.
Canada's aviation regulation, by contrast, writes its eye requirement in metric acuity with no colour clause beside it. Section 804.26 of the Canadian Aviation Regulations (SOR/96-433) requires a distant visual acuity "of 6/12 (20/40) or better in each eye separately and binocular visual acuity of 6/9 (20/30) or better." A full-text search of that regulation for the words colour perception, colour vision and colour-blind returns no hits, while visual acuity returns the clause above (checked 2026-09-26 against the consolidated text). The colour requirement in Canadian practice therefore attaches to the medical or licensing process for the task in question rather than to a colour clause in the regulation text.
| Item | Canada | United States |
|---|---|---|
| Screening instrument | Pseudoisochromatic plates (Ishihara type) | Pseudoisochromatic plates (Ishihara type) |
| Where the colour threshold is written | With the task's medical or licensing requirement rather than in the regulation text | Written into the federal standard, e.g. 14 CFR 67.103(c) |
| Aviation eye clause | Metric acuity first: 6/12 (20/40), 6/9 (20/30) | Imperial acuity: 20/20 distant, 20/40 near at 16 inches |
| Commercial driving colour clause | Task-specific medical review | "Red, green, and amber" recognition, 49 CFR 391.41 |
| Record content | Plate number, lighting, errors by eye | Plate number, lighting, errors by eye |
| Who receives the result | Patient; employer or licensing body on consent | Patient; employer or licensing body on consent |
For a clinic, the operational difference is the direction of the request. A US employer or regulator can point at a clause. A Canadian employer or regulator points at its own medical standard, which means the clinic's job is to provide a well-documented screening result and let the receiving body apply its threshold — not to declare the patient fit or unfit for a task.
How should a colour vision screening room be set up?
Three variables decide whether a plate result is worth recording.
Light. Pseudoisochromatic plates are designed to be read under a specified illuminant, and the common failure is a room lit by a mix of cool overhead light and window light. A screening station should have one predictable light source and no direct glare on the book.
Plate condition. Fading is the slow failure mode. A book that has been left open under bright light for years gives false results, and replacing it on a schedule costs less than re-testing a cohort.
The record. One line per patient: test used, plate set, light condition, errors by eye, and whether the result is a screening outcome pending examination.
The consumables that keep that station running are unglamorous: examination gloves for any contact with the patient, cotton swabs and wipes for the plate book cover and the occluder, and exam table paper for the seat. A screening programme that runs out of gloves stops screening, whatever the plate book says.
Does a colour vision plate set need a device licence?
This is a question buyers ask when they order from outside Canada, and the honest answer is that the plate book is not the kind of product the Medical Devices Regulations (SOR/98-282) are aimed at. The Class II hook in Schedule 1, Rule 2(1) turns on a device that comes into contact with the surface of the eye, which is what captures contact lenses and lens care products. A printed plate book does not contact the eye.
The US position is the same in shape. 21 CFR part 886 classifies ophthalmic devices by intended use, and a buyer can check any specific product in the FDA classification database, the registration and listing database and the 510(k) database rather than assuming that a clinical instrument must carry a clearance.
What should a clinic tell a patient after an abnormal screening?
Three sentences, in this order. That the screening suggests a red-green colour deficiency. That confirmation requires a full examination, and the plates are one part of it. And that the practical effect depends on the task — some occupations have a written standard and some do not, so the patient should ask the body that sets the requirement before making a career decision on a screening result.
That last point is the one that saves the clinic an argument. The plates are the same in both countries; the threshold belongs to whoever owns the task.
Sources
- 14 CFR 67.103, Eye standards for a first-class airman medical certificate
- 49 CFR 391.41, Physical qualifications for drivers
- Canadian Aviation Regulations, SOR/96-433 (s. 804.26, visual acuity)
- American Optometric Association, Color vision deficiency
- American Academy of Ophthalmology, Color blindness
- American Academy of Ophthalmology, Amblyopia
- Medical Devices Regulations, SOR/98-282 (Schedule 1, Rule 2)
- 21 CFR part 886, Ophthalmic devices
- FDA, Medical device classification database
- FDA, Device registration and listing database
- FDA, Premarket notification 510(k) database
- College of Optometrists of Ontario, Standards of practice
- College of Optometrists of Ontario, Infection control
- Canadian Association of Optometrists, Eye health library
- WHO, Blindness and visual impairment fact sheet
- WHO, World report on vision
- American Academy of Ophthalmology, How to take care of contact lenses
Ordering for a clinic, occupational health service or screening programme? Wholesale and multi-site ordering covers account setup and case pricing, and the B2B wholesale collection lists the lines stocked for institutional buyers. Sites that also run an in-house sterilizer can start with the biological indicator 5-pack trial.
Related reading
- Eye Clinic Consumables: Gloves, Swabs and Tape for Optometry
- Audiology Clinics: Between-Patient Hygiene for Hearing Test Rooms
- Shared Equipment Between Exam Rooms: What Ontario IPAC Requires
Frequently Asked Questions
What does the Ishihara test check for?
The plate set screens for red-green colour deficiency. The American Optometric Association describes the mechanism: the patient is shown pseudoisochromatic plates made of coloured dots and asked to find numbers among them, and a person with a deficiency sees a different number or no number at all.
Is the Ishihara test the same in Canada and the US?
The test and the plates are the same instrument in both countries. What differs is where the pass-or-fail threshold is written: in the United States it appears in federal standards such as 14 CFR 67.103(c) and 49 CFR 391.41, while in Canada it attaches to the medical or licensing requirement for the specific task.
Can a clinic declare a patient fit or unfit for a job after a colour vision screening?
No. A plate result is a screening outcome, and confirmation belongs to a full examination. Occupational fitness is decided by the body that sets the requirement for that task, using the clinic's documented result.
What should be recorded for a colour vision test?
The test used, the plate set or edition, the lighting conditions, and the errors observed for each eye separately. A record that says only "colour vision abnormal" cannot be repeated or compared, and it gives a future examiner nothing to work from.
Does a colour vision plate book need a medical device licence in Canada?
A printed plate book is not the product family the Medical Devices Regulations target. The Class II hook in Schedule 1, Rule 2(1) turns on contact with the surface of the eye, which captures contact lenses and lens care products rather than test charts and plate books.
Why do some colour vision requirements mention red, green and amber?
That wording comes from the driving standard. 49 CFR 391.41 requires the ability to recognise the colours of traffic signals and devices showing standard red, green and amber, so the requirement is written as a task rather than as a plate score.
How often should a colour vision plate book be replaced?
Replace it when the plates show fading or colour shift, and set a review interval rather than waiting for a failure. Faded plates produce false results, and a screening programme that never audits its books is measuring the book as much as the patient.
CliniEco Medical supplies examination gloves, cotton swabs, exam table paper and the wider clinic consumable lines described in this article. Health Canada MDEL #35334. This article is written for clinic, occupational health and procurement professionals and is not clinical guidance; colour vision assessment and fitness decisions belong to the treating eye care professional and the body that sets the requirement.
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