Quick facts
- A coverslip is a thin glass sheet placed over a specimen so that the optical path has a defined, uniform thickness. It is a consumable, and it is also an optical component.
- Specification: ISO 8255-1:2017 specifies requirements for dimensional tolerances, thickness and optical properties for microscope cover glasses used for transmitted light microscopy in the visible spectral range of 400 nm to 760 nm.
- United States: there is no named coverslip entry. The nearest entries are 21 CFR 864.3600 for microscopes and accessories, 21 CFR 864.3010 for tissue processing equipment used in mounting specimens on microscope slides, and 21 CFR 862.2050 for general purpose laboratory equipment labelled or promoted for a specific medical use. All three are Class I.
- Canada: Schedule 1 to the Medical Devices Regulations, SOR/98-282 contains no named coverslip entry either. A non-invasive consumable falls under Rule 7(1) as Class I.
- The grade matters more than the class. Coverslip designations follow the thickness tolerances in ISO 8255-1, and a catalogue range for the commonly stocked No. 1 grade is 0.13 mm to 0.16 mm.
- Canadian regulation text used here is current to 2026-09-21 and last amended 2026-06-17, as stated on the official consolidation.
A coverslip is bought by the box and treated as a commodity, and that is why the interesting question about it is not the class but the specification. A glass sold as a coverslip has a thickness tolerance, an optical property and a dimensional tolerance, and a laboratory that has never opened the standard has been buying one of those three on trust. This article sets out the specification, the device routes in both countries, the neighbouring entries in the American code, and what a laboratory should keep on file.
What does a coverslip do to the image?
A coverslip is not a protective sheet. It is part of the optical path, and its two jobs are mechanical and optical.
Mechanically, it flattens the specimen into a uniform layer so that everything in the field is at a comparable depth, and it keeps the specimen from contacting the objective. Optically, it introduces a defined thickness of glass between the specimen and the objective, and every corrected objective is designed to look through a glass layer of an assumed thickness.
That is why the thickness is a specification and not a preference. An objective corrected for one coverslip thickness, used through a coverslip of a different thickness, is being used outside the condition it was corrected for. The effect is a loss of image quality rather than a mechanical failure, which is why the problem can persist unnoticed.
The scope of ISO 8255-1:2017 is precise about what it covers: requirements for dimensional tolerances, thickness and optical properties for microscope cover glasses used for transmitted light microscopy in the visible spectral range, 400 nm to 760 nm. The standard also has a companion part, and the series is what a purchase order should reference when the specification has to be checkable.
How does a coverslip differ between Canada and the United States?
Neither country names the coverslip, so both reach the class by a general route.
| Item | Canada | United States |
|---|---|---|
| Named coverslip entry | None in Schedule 1 | None in the CFR |
| Class of the coverslip as such | Rule 7(1), Class I | Not separately classified; nearest general entry is 862.2050, Class I |
| Labelled for a specific medical use | Rule 7(1); Rule 7(2)(a) can lift to Class II where the device is a calibrator, tester or quality control support to another device | 862.2050 applies specifically because the device is labelled or promoted for a specific medical use |
| Optical specification | ISO 8255-1:2017 | ISO 8255-1:2017 |
| Premarket notification | No exemption list, because there is no named entry | Exempt where the 862.2050 identification is met, subject to 21 CFR 862.9 |
| Quality system relief | Not a Canadian mechanism | Exempt from part 820 except 820.180 and 820.198, where the 862.2050 identification is met |
The structural asymmetry is visible in the third row. The American section 862.2050 is defined by labelling: it reaches a device that is intended to prepare or examine specimens from the human body and that is labelled or promoted for a specific medical use. A coverslip sold to a research laboratory carries no medical promotion and sits outside that identification. The same coverslip sold for clinical histology carries the promotion and sits inside it.
Canada has no equivalent trigger. The device is non-invasive, so Rule 7(1) applies and the class is Class I. The class only moves under Rule 7(2), and both limbs are about a role: acting as a calibrator, tester or quality control support to another medical device, or being connected to an active device classified as Class II, III or IV. A coverslip does neither.
Which bench items sit nearest a coverslip in each code?
The neighbouring entries are the ones a histology laboratory buys in the same order, and each has its own class.
| Bench item | United States | Canada |
|---|---|---|
| Microscope and its optical accessories | 864.3600, Class I | Rule 7(1), Class I; Rule 10(1) where the microscope is an active diagnostic device |
| Tissue processing equipment, including mounting on microscope slides | 864.3010, Class I | Rule 7(1), Class I |
| Coverslip | No named entry; nearest general entry is 862.2050, Class I | Rule 7(1), Class I |
| Microscope slide | No named entry in the two sections above; the slide is the surface the specimen is mounted on | Rule 7(1), Class I |
| Slide stain or reagent | Classification follows the reagent's intended use | Classification follows the reagent's intended use |
Section 864.3600 describes microscopes and accessories as optical instruments used to enlarge images of specimens, preparations and cultures for medical purposes, and then lists variations by light source, including the phase contrast microscope for unstained preparations and the fluorescence microscope for specimens stained with fluorochromes. Section 864.3010 describes tissue processing equipment as devices used to prepare human tissue specimens for diagnostic histological examination by processing specimens through the stages of decalcifying, infiltrating, sectioning and mounting on microscope slides.
Read against those two identification paragraphs, a coverslip is neither an optical instrument nor tissue processing equipment. It is the consumable that closes the mount, and its American classification therefore depends on how it is labelled and promoted rather than on a section that names it.
What should a laboratory specify when it buys coverslips?
Six items, and a purchase order that omits the first three is buying on trust.
- The thickness grade and its tolerance. The designation used in supplier catalogues follows the thickness requirements in ISO 8255-1. One manufacturer's catalogue range for the commonly stocked No. 1 grade is 0.13 mm to 0.16 mm, and the grade has to match the correction of the objectives in use.
- The material and its optical class. The glass type determines the optical properties and the chemical resistance, and the standard covers optical properties for the visible range from 400 nm to 760 nm.
- The dimensional tolerance. Length, width and squareness, since an oversized or undersized coverslip changes how the mount sits.
- The cleanliness grade. Whether the coverslip is supplied pre-cleaned for the application, because a residue on the surface is inside the optical path.
- The packaging. How the coverslips are supplied and protected, since the supplier packs the product in a hinged lid box or an ounce pack and the packaging protects against damage and contamination.
- The specification reference. The standard number and part, so that a substitute can be assessed against a document rather than against a description.
Which consumables does a histology laboratory restock alongside its coverslips?
A laboratory restocks specimen containers, transport packaging, and bench consumables on the same cycle as its processing equipment. For laboratories buying at case level, the wholesale ordering page sets out account and case terms, and the B2B wholesale collection lists the lines held for institutional buyers. The specimen cups cover the collection step, the sterile centrifuge tubes cover the processing step, and a laboratory that wants the monitoring and consumable lines together can start with the sterilization monitoring collection or the biological indicator 5-pack trial.
Sources
- ISO 8255-1:2017, microscopes, cover glasses, dimensional tolerances, thickness and optical properties
- 21 CFR 864.3600, microscopes and accessories
- 21 CFR 864.3010, tissue processing equipment
- 21 CFR 862.2050, general purpose laboratory equipment
- 21 CFR 862.9, limitations of exemptions
- Medical Devices Regulations, SOR/98-282, full text and Schedule 1
- openFDA device classification API
- FDA device classification database
- ISO 15189:2022, medical laboratories, requirements for quality and competence
- ISO/IEC 17025:2017, competence of testing and calibration laboratories
- ISO 11607-1:2019, packaging for terminally sterilized medical devices
- CLSI standards and products
- Public Health Ontario, laboratory services test information index
- Public Health Ontario, infectious diseases
- Ontario Laboratory Medicine Act, R.S.O. 1990, c. L.1
- College of Medical Laboratory Technologists of Ontario
- WHO laboratory quality management system handbook
- Canadian Centre for Occupational Health and Safety, OSH answers
- US OSHA bloodborne pathogens standard, 1910.1030
- Health Canada, medical devices
Related reading
- Microscope Slides in Canada vs the US: Which Size and Finish Applies
- Stage Micrometers in Canada vs the US: Which Device Class Applies
- Phase Contrast Microscopes in Canada vs the US: Which Rules Apply
CliniEco Medical supplies eye care, laboratory and clinic consumables of the kind described in this article. MDEL #35334. This article is written for laboratory, procurement and quality professionals and is not clinical or metrological guidance; the choice of objective, the mounting method and the acceptance criteria for an image belong to the laboratory's own procedures and to the requirements that apply to it.
Frequently Asked Questions
Is a coverslip classified as a medical device?
It depends on the country and, in the United States, on the labelling. The CFR has no named coverslip entry. In the United States the nearest general entry is 21 CFR 862.2050, which reaches a device labelled or promoted for a specific medical use; a coverslip sold without that promotion sits outside it. In Canada a coverslip is a non-invasive device and falls under Rule 7(1) of Schedule 1 as Class I.
What does ISO 8255-1 actually cover?
The scope of ISO 8255-1:2017 states that it specifies requirements for dimensional tolerances, thickness and optical properties for microscope cover glasses used for transmitted light microscopy in the visible spectral range, 400 nm to 760 nm. The standard also notes that it is a third edition that cancels and replaces the second edition of 2011.
Why does the thickness of a coverslip matter?
Because a corrected objective is designed to look through a glass layer of an assumed thickness. Using a coverslip of a different thickness puts the objective outside the condition it was corrected for, and the effect appears as a loss of image quality rather than as a mechanical failure.
What thickness is a No. 1 coverslip?
One manufacturer's catalogue states that its No. 1 coverslips are made in compliance with the standard and gives the thickness as 0.13 mm to 0.16 mm. The designation follows the thickness requirements in ISO 8255-1, so a purchase order should reference the standard part and the grade rather than a supplier description.
Does Canada classify coverslips at a different class from the United States?
Both reach Class I, by different routes. The United States reaches it through a general purpose laboratory equipment entry when the product is promoted for a specific medical use, and Canada reaches it through Rule 7(1) for non-invasive devices. The Canadian class rises only if Rule 7(2) captures the device, which requires it to act as a calibrator, tester or quality control support to another device, or to connect to a Class II, III or IV active device.
What should a coverslip purchase order state?
The standard and part, the thickness grade and its tolerance, the material and optical class, the dimensional tolerance, the cleanliness grade and the packaging format. The thickness grade has to match the correction of the objectives the laboratory is using, which is the item most often left off.
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