Quick facts
- An eye chart is not one product. It is a printed or projected set of symbols in graduated sizes, used at a defined test distance under defined lighting.
- United States: the chart itself has a device entry. Under 21 CFR 886.1150 a visual acuity chart is Class I (general controls), exempt from premarket notification subject to limits.
- Canada: the Medical Devices Regulations classify by rule rather than by named entry, so a printed chart held in front of a patient is assessed against general rules and the invasive-device definition rather than a chart-specific line.
- The notation is not universal. Canadian federal aviation rules write acuity metric-first as 6/12 (20/40); the United States rules write 20/20 and 20/40 with a Snellen equivalent.
- Optotypes are standardised. ISO 8596:2017 specifies Landolt ring optotypes and a method for measuring distance acuity under photopic conditions for certification and licensing.
- The chart is the least expensive regulated device in the room and the one most often replaced with an uncalibrated substitute.
An eye chart looks like a poster and behaves like a measuring instrument. Its result depends on the size of the symbol, the distance from the patient, the contrast of the print and the light falling on it. Change any one of those and the number written in the record stops being comparable to the number written last year.
This article covers how each country treats the chart, how the acuity notation differs, and what a buyer should be able to point at when charts are ordered for a lane.
What is an eye chart, and what exactly does it measure?
An eye chart, also called a visual acuity chart, presents symbols in graduated sizes and asks the patient to identify them. The result is expressed as a fraction: the test distance over the distance at which the smallest correctly read symbol would subtend the standard angle.
The United States device identification describes it plainly. Under 21 CFR 886.1150 a visual acuity chart is a device that is a chart, such as a Snellen chart with block letters or other symbols in graduated sizes, intended for testing visual acuity.
Three variables sit behind that simple description:
- Test distance. A chart scaled for six metres is not the same chart as one scaled for three metres, and a wall-mounted chart is not interchangeable with a mirror-lane chart.
- Optotype. Block letters, tumbling E, Landolt ring, Lea symbols and numbers all measure acuity, but they are not equally readable by every patient, and they do not all have the same published specification behind them.
- Contrast and luminance. Acuity measured under photopic conditions is the reference case, and a chart read under the wrong illumination produces a number that looks valid and is not.
The American Academy of Ophthalmology's vision screening guidance and the American Optometric Association's material on vision screening in schools both make the same point from a different direction: a screening chart test answers one narrow question and is not a substitute for a full examination.
Which optotype standard applies to an eye chart?
The reference document is a standard, not a chart design. ISO 8596:2017 specifies a range of Landolt ring optotypes and describes a method for measuring distance visual acuity under photopic conditions for the purposes of certification or licensing. It also states that it is neither intended as a standard for clinical measurements nor for the certification of blindness or partial sight, and that other optotypes used for clinical investigation are described in an annex for information.
That wording matters commercially. A chart manufacturer can place a chart squarely inside ISO 8596, or outside it. Both are legitimate products, but they suit different jobs: certification and licensing work is where the Landolt ring specification belongs, while clinical examination may use letter charts whose lineage is different.
The instrument side has its own standard, ISO 15004-1:2020, which sets fundamental requirements for non-invasive, active and non-active ophthalmic instruments and for devices for enhancing low vision, and states which instrument categories it excludes. A projected chart system is an instrument; a printed card is a chart. The two standards do different work, and a supplier claiming a single standard covers both is describing one of them imprecisely.
Is an eye chart classified the same way in Canada and the United States?
No, and the practical consequence is that a Canadian buyer cannot settle a specification question by quoting a Canadian chart entry, because there is none.
In the United States, the chart is a named entry: 21 CFR 886.1150, Class I (general controls), exempt from the premarket notification procedures of subpart E of part 807 subject to the limitations in § 886.9. The same part carries entries for the rest of the acuity toolkit, including the color vision tester and the anomaloscope, both Class I.
In Canada, the Medical Devices Regulations, SOR/98-282 work from definitions and rules. An invasive device is defined as one intended to come into contact with the surface of the eye or to penetrate the body, and Rule 2(1) of Schedule 1 places devices meeting that description in Class II. A printed chart on a wall does not meet that definition, so it is not swept into Class II by the eye-contact route, and it is not given a named entry either.
| Item | Canada | United States |
|---|---|---|
| Chart classification route | Rules in Schedule 1 applied to device definitions | Named entry, 21 CFR 886.1150 |
| Chart class | Falls to the general rules; a printed wall chart does not contact the eye | Class I (general controls) |
| Pre-market route | By class and licence application | Exempt from premarket notification, subject to § 886.9 |
| Optotype specification | ISO 8596:2017 available as the specification of record | ISO 8596:2017, plus the device entry above |
| Colour vision tooling | General rules; no chart-specific entry | Own entries: colour vision tester and anomaloscope, both Class I |
| Acuity notation in law | Metric first, with the imperial figure in brackets | Imperial, with a Snellen equivalent where a near figure is given |
The boundary between a chart and an instrument is worth watching, because a projector or a digital acuity system moves the product from the chart family into the instrument family. That is where ISO 15004-1:2020 starts to apply, and it is also where a Canadian supplier's classification work gets harder.
Do Canada and the United States write visual acuity the same way?
No, and the difference is visible in the statutes rather than in clinical convention.
The United States eye standards for a first-class airman medical certificate require distant visual acuity of 20/20 or better in each eye separately, with or without corrective lenses, and near vision of 20/40 or better, Snellen equivalent, at 16 inches in each eye separately, with a second near distance added from age 50. The commercial driver physical qualification standard sets a separate vision limb for drivers.
The Canadian aviation rule expresses the same kind of requirement in metres. Under SOR/96-433 the standard is written as a distant visual acuity of 6/12 (20/40) or better in each eye separately, with binocular visual acuity of 6/9 (20/30) or better.
For a chart buyer, the consequence is concrete: a chart printed for a six metre lane and a chart printed for a twenty foot lane are describing the same measurement in different units, and the record has to say which one was used. Mixing a metric chart with an imperial record is not a style question, it is a traceability problem.
| Item | Canada | United States |
|---|---|---|
| Standard acuity test distance | Six metres in the metric convention | Twenty feet in the imperial convention |
| Notation form | 6/12 with 20/40 in brackets | 20/20, 20/40 with a Snellen equivalent |
| Near vision distance | Expressed in the same metric family | Stated as 16 inches, with 32 inches from age 50 |
| Colour requirement | Not written into the aviation acuity clause | Written into the airman and driver rules |
| Optotype for licensing work | ISO 8596:2017 Landolt ring | ISO 8596:2017 Landolt ring |
Which consumables does an acuity lane actually go through?
Charts are a capital purchase with a long life. The consumables around them are the recurring cost, and each one has a specification.
- Examination room paper. A lane consumes paper at the chair and at the instrument table on every patient. Smooth examination table paper is bought by width and length, and the width has to match the chair.
- Occluders and eye masks. Acuity is tested monocularly, so an occluder is used on every acuity measurement. Eye masks sit in the same order in clinics that also run dry-eye and post-procedure routines.
- Ophthalmic sponges and wipes. In the United States the ophthalmic sponge is a Class II device entry, and sterile gauze sponges are stocked for the same reason: the lane uses them constantly.
- Cleaning and disinfection supplies. Whatever touches the face or the forehead rest needs a defined cleaning step, and where chemicals are handled the employer duty on eye and face protection applies.
- Record forms. The acuity notation, the test distance and the chart used are all part of the record. In Ontario the framework for insured optometric services runs through the Health Insurance Act, R.S.O. 1990, c. H.6 and R.R.O. 1990, Regulation 552.
The College of Optometrists of Ontario is the provincial regulator, and the eye-health library is the patient-facing counterpart. Background on why the follow-up matters more than any single measurement is set out in the World Health Organization's blindness and visual impairment fact sheet.
For a practice buying lane consumables together, the ordering route is worth setting up once.
Sources
- 21 CFR 886.1150, visual acuity chart
- 21 CFR 886.1170, colour vision tester
- 21 CFR 886.1070, anomaloscope
- 21 CFR 886.4790, ophthalmic sponge
- 21 CFR 886.1850, slitlamp biomicroscope
- ISO 8596:2017, optotypes
- ISO 15004-1:2020
- 14 CFR 67.103
- 49 CFR 391.41
- Canadian Aviation Regulations, SOR/96-433
- Medical Devices Regulations, SOR/98-282
- AAO, vision screening
- AAO, children's vision development
- AAO, amblyopia
- AAO, cataracts
- AOA, vision screening in schools
- AOA, eye examinations
- College of Optometrists of Ontario
- Ontario eye-health library
- Health Insurance Act, R.S.O. 1990, c. H.6
- R.R.O. 1990, Reg. 552
- WHO, blindness fact sheet
- OSHA 29 CFR 1910.132
Ordering for a clinic, lab or care home? Wholesale and multi-site ordering covers account setup and case pricing, and the B2B wholesale collection lists the lines stocked for institutional buyers. Clinics that also run an in-house sterilizer can start with the biological indicator 5-pack trial.
Related reading
- Snellen chart and eye test charts in Canada vs the US: which scale
- Eye clinic consumables: gloves, swabs and tape for optometry
- Eye wash stations in Canada vs the US: ANSI Z358.1
- Heated eye masks for digital eye strain: 3 temperature options
- Hearing and vision assistance devices for Canadian seniors
Frequently Asked Questions
Is an eye chart regulated differently in Canada than in the United States?
Yes. The United States gives the chart a named device entry, 21 CFR 886.1150, classifying a visual acuity chart as Class I (general controls) and exempting it from premarket notification subject to limits. Canada classifies devices by the rules in Schedule 1 of the Medical Devices Regulations applied to device definitions, so a printed chart that does not contact the eye has no chart-specific entry to quote.
Which standard defines the optotypes on an eye chart?
ISO 8596:2017 specifies a range of Landolt ring optotypes and a method for measuring distance visual acuity under photopic conditions for certification or licensing. It states that it is not a standard for clinical measurements and not a route to certifying blindness, and that clinical optotypes are described in an annex for information. ISO 15004-1:2020 covers instruments rather than printed charts.
Do Canada and the United States measure acuity in the same units?
No. Canadian aviation rules write the requirement metric first, as 6/12 (20/40) or better separately in each eye with binocular acuity of 6/9 (20/30) or better. United States rules write 20/20 or better separately in each eye and 20/40 or better near vision, Snellen equivalent, at 16 inches, with a second near distance from age 50.
Does an eye chart have to be a printed chart?
No, and the distinction changes the specification. A printed card is a chart; a projector or a digital acuity system is an instrument, which brings ISO 15004-1:2020 into the conversation. A supplier who cites one standard for both is describing one of them imprecisely.
Why does the test distance matter so much?
Because the acuity fraction is a ratio of the test distance to the distance at which the symbol would subtend the standard angle. A chart scaled for six metres read at three metres, or the reverse, produces a figure that looks like a measurement and is not comparable with the previous visit.
What consumables does an acuity lane use most?
Examination room paper at the chair and instrument table, occluders or eye masks for monocular testing, ophthalmic sponges and gauze used at the slit lamp, and the cleaning supplies tied to the forehead rest. Clinics that handle disinfectants add eye and face protection as part of the hazard assessment.
CliniEco Medical supplies lane consumables, eye-care lines and the wider clinic catalogue described in this article. Health Canada MDEL #35334. This article is written for clinic, laboratory and procurement professionals and is not clinical guidance; acuity measurements and diagnostic decisions belong to the treating practitioner.
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