Quick facts
- An ophthalmic bar prism is a bar of fused prisms of steadily increasing strength, held in front of the eye in turn to measure latent and manifest strabismus or the power of fusion.
- In the United States it files under 21 CFR 886.1650, Ophthalmic bar prism, at Class I, product code HKW (Prism, bar, ophthalmic).
- Canada keeps no named entry. The bar is a passive, non-invasive optical device, so Rule 7(1) of Schedule 1 keeps it at Class I.
- The first near miss is Rule 10(1): the active-diagnostic rule does not reach a bar that carries no light source and sends no energy into the eye.
- The second near miss is Rule 7(2)(a): a device that acts as a calibrator, tester or quality-control support to another device is Class II, but a prism bar measures the patient, not another device.
- Entries, classes and product codes below were checked against the eCFR, the Regulations and the openFDA classification database on 2026-10-14.
An ophthalmic bar prism is the hand-held bar of increasing prism powers that a clinician holds in front of one eye and then the other while the patient looks at a target. It is the instrument behind the prism-cover test and the measurement of fusion, and it sits in the same drawer as a Maddox lens and a trial frame. The United States names it in a regulation at Class I; Canada keeps no entry for it and derives the same class from the passive-device rule. This article sets out both routes, the two rules that look as though they might apply and do not, and what the class means for the drawer a practice restocks — with the pre-perforated exam table roll that covers the chair the test is run in.
What is an ophthalmic bar prism?
It is a bar composed of fused prisms of gradually increasing strengths. The clinician holds the bar vertically or horizontally in front of one eye and moves along it, watching the patient's fixation as the prism power rises, until the deviation is neutralised or the fusion response changes. Because the powers are laid out in a known order on one bar, the reading is the position on the bar rather than a separate prism the clinician has to find and hold.
The instrument is used in the measurement of strabismus and in the assessment of fusion. It does not illuminate the eye, it does not touch the globe, and it produces no image of its own; the clinician reads the patient's response. That description is what fixes the device's family, and it is the description the classification rules read first.
Is an ophthalmic bar prism a Class I device in the United States?
It is a named entry at Class I. 21 CFR 886.1650 is titled Ophthalmic bar prism and the identification reads: \"An ophthalmic bar prism is a device that is a bar composed of fused prisms of gradually increasing strengths intended to measure latent and manifest strabismus (eye muscle deviation) or the power of fusion of a patient's eyes.\" The entry places the device at Class I (general controls), exempts it from the premarket notification procedures in subpart E of part 807 subject to the limits in section 886.9, and also exempts it from the quality management system requirements of part 820 except for the requirements on records and complaint files.
The openFDA device classification API lists product code HKW under that regulation number. The carve-out is worth reading twice, because it is more than a formality: a Class I device that is exempt from most of part 820 is still expected to keep records and to keep complaint files, and those two things are the ones a clinic is most likely to be asked about when a prism bar is in use across a whole practice.
| Item | Detail |
|---|---|
| US regulation | 21 CFR 886.1650 - Ophthalmic bar prism |
| US class | Class I (general controls) |
| Product code | HKW (Prism, bar, ophthalmic) |
| Route to market | Exempt from premarket notification under subpart E of part 807, subject to the limits of section 886.9 |
| Quality-system carve-out | Exempt from part 820 except records and complaint files |
| Contact | Held in front of the eye; no contact with the globe |
How does Canada classify an ophthalmic bar prism?
Canada keeps no named entry, so the class is derived from Schedule 1 of the Medical Devices Regulations. The first question the rules ask is whether the device is invasive. A prism bar is held in front of the eye; it does not penetrate a body orifice and it does not come into contact with the surface of the eye, so Rule 2(1) does not reach it and it is a non-invasive device. Rule 7(1) then states: \"Subject to subrule (2), all other non-invasive devices are classified as Class I.\" That is Class I, the same class the United States gives the bar.
Two rules look as though they might lift it, and neither does. Rule 10(1) places an active diagnostic device that supplies energy for imaging or for monitoring a physiological process in Class II; a fused prism bar has no lamp, no sensor and no supply, so it is a passive optical element and the rule does not capture it. Rule 7(2)(a) lifts a non-invasive device to Class II where it is intended to act as a calibrator, tester or quality-control support to another medical device; a prism bar is held in front of a patient's eye to measure that patient, so it is not a check on another device. Read together, the two near misses explain why an instrument that looks like a bench test tool stays in the Class I drawer.
| Item | Canada | United States |
|---|---|---|
| Named entry | None; classified by rule | 886.1650 - Ophthalmic bar prism |
| Class | Class I (Rule 7(1), non-invasive) | Class I (general controls) |
| Governing text | Schedule 1, Part 1, Rule 7(1) | 21 CFR 886.1650 |
| Rule 10(1) applies? | No; the bar supplies no energy | Not applicable |
| Rule 7(2)(a) applies? | No; the bar is not a tester for another device | Not applicable |
| Route to market | Class I obligations under the Regulations | Exempt from premarket notification, subject to section 886.9 |
How is a prism bar different from a Fresnel prism or a gonioscopy prism?
All three are prisms and all three sit in an eye clinic, but they are three different device families that happen to share an optical element. A bar prism is a measuring instrument held in front of the eye for the duration of a test. A Fresnel prism is a thin press-on sheet fitted to a spectacle lens or a carrier to redirect light for the patient to wear. A gonioscopy prism is a contact prism placed on the anaesthetised eye to view the drainage angle, so it does touch the globe. The class follows the intended use of each, not the name.
| Device | How it is used | Contact with the eye | Class, Canada | Class, US |
|---|---|---|---|---|
| Bar prism | Held in front of the eye to measure deviation or fusion | None | I (Rule 7(1)) | I (886.1650, HKW) |
| Fresnel press-on prism | Fitted to a lens or carrier and worn | None | I (Rule 7(1)) if passive | I (886.1655 range) |
| Gonioscopy prism | Placed on the anaesthetised globe to view the angle | Yes, on the surface of the eye | II (Rule 2(1), contact with the surface of the eye) | II (886.1660 range) |
That table is the practical reason the eye-contact question matters more than the prism question. A practice that orders one bar prism and one gonioscopy prism is ordering two devices that share an optical principle and sit in two different classes in Canada, because one touches the surface of the eye and the other does not. The supplier's stated intended use is the document that settles which is which.
It is also the reason a reprocessing routine cannot be copied from one prism to the next. A bar prism is wiped between patients according to the maker's instructions; a gonioscopy prism that contacts the globe is reprocessed to the standard the maker states for a device that touches the eye, and the record of that reprocessing belongs with the instrument, not with the patient's spectacle file.
What should a practice check before ordering a prism bar?
Three checks. First, confirm the prism range and the step between powers, because a bar that runs to 40 prism dioptres with a wide step measures quickly while a bar with a narrow step measures finely, and the two answer different clinical questions. Second, confirm the reading position convention the maker prints on the bar, since a bar whose powers run from the handle outward and one whose powers run the other way will produce readings that are not directly comparable between clinicians. Third, confirm the cleaning instructions the maker states, because the bar is handled close to the patient's face and is reused all day.
An optometry or ophthalmology practice also restocks the consumables used at the same work-up station. Clinics that stock for a whole practice can order through the wholesale programme and request a bulk quote for a standing or annual order; the pre-perforated exam table roll sits in the same catalogue. Reselling? become a distributor.
How does the class affect the records a practice keeps?
The class sets the market-entry path; it does not set the clinical record. A prism-cover work up is recorded with the target used, the distance or near condition, the prism power at which the deviation was neutralised or the fusion response changed, and the initials of the clinician who ran it. That record is what lets a second clinician repeat the measurement and compare it with the first.
Because the bar is a reused optical instrument, the routine also includes the cleaning step the maker states and, where a practice keeps an equipment file, the bar's own entry with its purchase date and range. None of that changes with the class; it is the ordinary routine of a patient-contact ophthalmic service, and the record is what shows the instrument was used as the maker intended.
Sources
- openFDA device classification API
- Medical Devices Regulations, SOR/98-282, full text and Schedule 1
- US FDA, medical device databases
- US FDA, overview of device regulation
- Health Canada, medical devices
- Health Canada, establishment licensing
- Standards Council of Canada
- CSA Group
- ISO 13485:2016, medical devices quality management
- ISO 14971:2019, application of risk management to medical devices
- ISO 15004-1:2020, ophthalmic instruments, general requirements
- ISO 17664:2017, processing of health care products, information to be provided
- Canadian Association of Optometrists
- College of Optometrists of Ontario, standards of practice
- Canadian Ophthalmological Society
- CCOHS, OSH answers
- Health Canada, medical device licence application guidance
A one-page sheet for the refraction room. A prism-cover work up is only as useful as the record beside it: date, target, distance, prism power at neutralisation and the clinician who ran it. Open the compliance log centre and print the blank sheet — no account and no sign-up, and you can take as many copies as the room needs.
Lay out the month in one pass. Enter the practice name, the instrument drawer and the test list once, and the sterilization log generator returns a dated sheet you can print or file straight into the practice quality folder.
Ask a compliance specialist. A classification question usually turns on how the device is used, not only on its name. Ask a compliance specialist — you get a written answer specific to your equipment and province, with the regulation or standard it is based on cited.
Related reading
- Ophthalmic Fresnel prisms in Canada vs the US
- Gonioscopy prisms in Canada vs the US
- Maddox lenses in Canada vs the US
CliniEco Medical supplies eye care, laboratory and dental consumables of the kind described in this article. MDEL #35334. This article is written for optometry, laboratory and dental procurement professionals and is not legal advice; the class of a device and the records a practice keeps belong to the manufacturer and to the requirements that apply to it.
Frequently Asked Questions
What class is an ophthalmic bar prism in the United States?
Class I, under 21 CFR 886.1650, Ophthalmic bar prism, product code HKW, exempt from premarket notification subject to the limits of section 886.9.
What class is it in Canada?
Class I, under Rule 7(1) of Schedule 1 of the Medical Devices Regulations, which is the default for non-invasive devices.
Does Rule 10(1) lift a prism bar to Class II?
No. Rule 10(1) covers an active diagnostic device that supplies energy for imaging or for monitoring a physiological process. A fused prism bar has no supply and sends no energy into the eye.
Does Rule 7(2)(a) lift it, because it is used in a test?
No. Rule 7(2)(a) reaches a device intended to act as a calibrator, tester or quality-control support to another device. A prism bar measures the patient's response, not another device.
What else is an ophthalmic bar prism called?
It is also written as prism bar, Berens prism bar, prism rack and prism ladder; the US regulation describes the same article as a bar of fused prisms of increasing strengths.
Does the class change how the bar is cleaned?
No. The class sets the market-entry path. Cleaning follows the maker's instructions, and the practice keeps the record that the step was done between patients.
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