Quick facts
- A prism bar is a named Class I device in the United States at 21 CFR 886.1650.
- A magnifier is named separately at 21 CFR 886.5540, and a low-vision telescope at 21 CFR 886.5870 — both Class I.
- Canada names none of them: each is a non-invasive device and reaches Class I through Rule 7(1) of the Medical Devices Regulations.
- A low-vision aid connected to a higher-class active device takes that class under Rule 7(2)(b).
- Diplopia is managed with occlusion or with prisms; the two use different devices and different rules.
- The regulation text cited here is current to 2026-09-21 and was last amended on 2026-06-17.
Double vision is a symptom, not a device. What the device does is either block one image or bend the light so the two images land together again. A patch, a prism, a magnifier and a telescope all sit in that space, and the two national rulebooks reach their classes in different ways.
What is a prism bar used for?
It measures and corrects the misalignment that produces double vision, and it does so by bending light rather than by touching the eye.
A prism shifts the image so that the two eyes see a single object in the same place. A prism bar holds a graded set of prisms so that the clinician can increase the power step by step until the two images merge. The same measurement is used to size a permanent prism in a pair of spectacles, and it is used in the assessment of a squint, a nerve palsy or a decompensating phoria. The bar never contacts the eye, which is exactly why its route to a class is the non-invasive route.
Occlusion works the other way. An occluder or a patch removes one image entirely, so the brain is not asked to fuse two. That is the tool used when the two images cannot be brought together, or when the aim of management is to stop the second image from competing.
How do Canada and the United States classify a prism bar?
It reaches Class I in both countries, by a named entry on one side and by rule on the other.
| Item | Canada | United States |
|---|---|---|
| Prism bar | Class I by Rule 7(1) | Class I, 21 CFR 886.1650 |
| Hand-held magnifier | Class I by Rule 7(1) | Class I, 21 CFR 886.5540 |
| Low-vision telescope | Class I by Rule 7(1) | Class I, 21 CFR 886.5870 |
| Occluder / fixation aid | Class I by Rule 7(1) | Class I, 21 CFR 886.1290 |
| Basis named in the rulebook | Rule and use | Device entry and product code |
In the United States each aid is named on its own line. The ophthalmic bar prism is Class I at 21 CFR 886.1650, the hand-held and spectacle magnifiers at 21 CFR 886.5540, the low-vision telescopes at 21 CFR 886.5870, and the fixation aid used in occlusion assessment at 21 CFR 886.1290. Each is Class I, and each carries its own product code.
In Canada none of these is named. A prism bar bends light and touches nothing, so it is a non-invasive device, and Rule 7(1) places all other non-invasive devices in Class I. A Canadian file cites the rule and the use; a US file cites the entry. The class is identical, which is why the difference is easy to overlook until a registration file is written.
Are magnifiers and low-vision telescopes classified the same way in Canada and the United States?
They are Class I on both sides, and the interesting part is how many separate US entries a single low-vision kit spans.
| Aids in a low-vision kit | US entry | US class | Canadian basis | Canadian class |
|---|---|---|---|---|
| Hand-held magnifier | 21 CFR 886.5540 | Class I | Rule 7(1) | Class I |
| Spectacle-mounted telescope | 21 CFR 886.5870 | Class I | Rule 7(1) | Class I |
| Bar prism | 21 CFR 886.1650 | Class I | Rule 7(1) | Class I |
| Fixation device | 21 CFR 886.1290 | Class I | Rule 7(1) | Class I |
A low-vision clinic that stocks a full kit is holding four different US device entries under one shelf label. That is not a problem for the clinician, but it matters for a buyer who has to describe what is being purchased. "Low-vision aid" is a working phrase, not a US device category; the category is the entry, and there are several.
What moves a low-vision aid into a higher class?
Connection, not optics. A passive aid stays where the rule puts it; an aid wired into a higher-class active device does not.
Under Rule 7(2)(b) a non-invasive device that is intended to be connected to an active device classified as Class II, III or IV is itself placed in the class of that device. A bar prism is passive and stays Class I. A low-vision aid that feeds a powered imaging or measurement system takes the class of the system it is connected to. A clinic that buys a low-vision station as a single powered unit is therefore buying a class that is set by the unit, not by the lens in front of the patient.
The same logic runs in the other direction for occlusion. A plain occluder is passive. An occluder attached to a powered perimeter or a fixation monitor is read together with that device. The question to ask is not what the aid looks like; it is what the aid is plugged into.
Which consumables does a low-vision clinic restock?
A low-vision assessment runs on the same bench supplies as any other eye room. The sterile graduated 90 mL specimen cups carry samples to the bench and the 120 mL sterile screw-cap container holds anything that has to be kept. For a warm-compress routine that runs alongside the drop regimen, the USB heated eye mask with three temperature settings is the reusable item on the same shelf. Where a clinic also runs its own sterilisation cycle, the sterilization monitoring collection pairs with the 24-hour monitoring five-pack trial. Clinics and multi-site groups ordering at case level use the wholesale ordering page, and the B2B wholesale collection lists the lines held for institutional buyers. Reselling? become a distributor.
What is the difference between an occluder and a prism in practice?
An occluder removes an image; a prism moves it. The two tools answer different questions, and a clinic that stocks both is prepared for both.
When a patient reports two images, the first question is whether the two can be brought together. A prism bar answers that question by degrees: the clinician increases the power until the two images merge, and the power at which they merge is the size of the prism the patient needs. If no power merges them, the images cannot be fused, and the occluder becomes the tool. It stops the second image from reaching the brain at all, which is the outcome the patient can live with when fusion is not possible.
That is why the two aids sit on the same shelf and belong to the same assessment, even though they are filed under different entries. On the US side the bar prism is 21 CFR 886.1650 and the fixation aid used in occlusion assessment is 21 CFR 886.1290, each Class I. On the Canadian side neither is named, and each reaches Class I through Rule 7(1) because it bends light or blocks it without touching the eye.
For a buyer the practical consequence is to size the order against the clinic's case mix. A general eye room needs the bar and a small stock of occluders. A low-vision or binocular-vision room needs the graded bar, a set of prisms for trial framing, and the magnifiers and telescopes that follow when fusion is not the goal and magnification is. Those are different products reached through different entries, and ordering one when the clinic needs the other is the most common mismatch in this category.
Sources
- 21 CFR 886.1650, ophthalmic bar prism
- 21 CFR 886.5540, low-vision magnifier
- 21 CFR 886.5870, low-vision telescope
- 21 CFR 886.1290, fixation device
- 21 CFR 886.4750, eye shield, ophthalmic
- 21 CFR 886.1150, visual acuity chart
- Medical Devices Regulations, SOR/98-282
- Opto, eye health library
- College of Optometrists of Ontario, standards of practice
- American Academy of Ophthalmology, eye health
- CCOHS, OSH answers
- ISO 15189:2022, medical laboratories
- ISO 13485:2016, quality management
- ISO 14971:2019, risk management
- Public Health Ontario, laboratory services test index
- CLSI, clinical and laboratory standards
- Canadian Paediatric Society, documents
- Canadian Dental Association
- Royal College of Dental Surgeons of Ontario
- openFDA device classification API
A prism measurement that is not written down cannot be checked at the next visit. The printable prism and low-vision assessment log is a free sheet with columns for the patient, the prism measured, the aid issued and the date, so a change in the measurement is visible rather than recalled. The assessment record generator on the same page sizes the sheet to the number of rooms a clinic runs. No account and no sign-up are needed to open either one.
The class of an aid can turn on what it is connected to. Ask a compliance specialist and you will get a written answer specific to your equipment and province, with the regulation or standard it is based on cited.
Related reading
- Eye Drops in Canada vs the US: Which Route Applies?
- Eye Shields in Canada vs the US: Which Device Rules Apply?
- Pupil Size Chart in Canada vs the US: Which Pupil Gauge Rules Apply?
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 procurement professionals and is not legal advice; the class of a device and the records kept by a clinic belong to the manufacturer and to the requirements that apply to it.
Frequently Asked Questions
Is a prism bar a Class I device in the United States?
Yes. The ophthalmic bar prism is Class I under 21 CFR 886.1650 and carries its own product code.
Does Canada name a prism bar?
No. A prism bar is a non-invasive device that contacts nothing, so Rule 7(1) of the Medical Devices Regulations places it in Class I. The Canadian schedule names very few devices, and a prism bar is not one of them.
How many US entries does a low-vision kit span?
Several. A hand-held magnifier is 21 CFR 886.5540, a low-vision telescope is 21 CFR 886.5870, a bar prism is 21 CFR 886.1650 and a fixation device is 21 CFR 886.1290, each Class I.
What raises the class of a low-vision aid?
Connection. Under Rule 7(2)(b) a non-invasive device intended to be connected to an active device classified as Class II, III or IV takes that class. A passive magnifier stays Class I; an aid that feeds a higher-class powered system does not.
Why are occlusion and prisms used for two different problems?
Occlusion removes one image so the brain is not asked to fuse two, which suits a second image that cannot be brought together. A prism bends light so the two images land on the same place, which suits a misalignment that can be measured and corrected.
What should a prism assessment record carry?
The patient, the prism measured, the aid issued and the date. Recording the measurement is what makes a change visible at the next visit.
0 commentaire