Written and maintained by CASRAI Editorial Board
Published · Last updated
On this page
Short answer: a visual field machine is usually a perimeter, a device that maps how far out to the side, up and down a person can see while looking straight ahead. In US regulation a perimeter and a tangent screen are two separate Class I device types, and this page sets them side by side.
This page describes products and general use; it is not medical advice.
Who uses it: eye-care clinics and ophthalmology practices run these devices; clinic staff and buyers use this page to tell the device types apart, and students use it as a plain-language reference.
What is a visual field machine?
The phrase “visual field machine” is a common search term, not a regulatory name. The device it most often points to is the perimeter. Under 21 CFR 886.1605, a perimeter is “an AC-powered or manual device intended to determine the extent of the peripheral visual field of a patient.” Its purpose is a map of the visual field, not a measure of sharpness of vision.
The American Academy of Ophthalmology explains the measurement this way: visual field tests measure how wide your field of vision is, counted in degrees from the center, and a larger number means the person sees farther from the center. The National Eye Institute lists visual field testing as part of the exam used in glaucoma diagnosis, to check side vision.
How is it built?
FDA’s definition describes the working principle of a perimeter: the device projects light on various points of a curved surface, and the patient indicates whether he or she sees the light. Two details matter for anyone comparing equipment:
- The regulation covers both AC-powered and manual perimeters, so “machine” is looser than the legal definition.
- The curved surface is the defining feature. A device that maps the field on a flat surface falls under a different regulation (see the next section).
Perimeter vs tangent screen
People searching for a “visual field machine” sometimes mean a tangent screen test, which also maps the visual field but on a flat chart. FDA lists them as separate device types.
| Type | What FDA says it is | Key difference | Source |
|---|---|---|---|
| Perimeter (21 CFR 886.1605) | AC-powered or manual device that determines the extent of the peripheral visual field; projects light on points of a curved surface and the patient indicates whether the light is seen | Curved surface; peripheral field | eCFR, checked 2026-10-30 |
| Tangent screen or campimeter (21 CFR 886.1810) | AC-powered or battery-powered device that is a large square cloth chart with a central fixation mark, intended to map the central 30 degrees of the visual field on a flat surface | Flat cloth chart; central 30 degrees | eCFR, checked 2026-10-30 |
The tangent screen generic type includes projection tangent screens, target tangent screens and targets, felt tangent screens and stereo campimeters.
Regulatory class: what a buyer can verify
- Both device types are Class I (general controls).
- A perimeter is exempt from premarket notification (510(k)), subject to the limitations in 21 CFR 886.9. It is also exempt from the quality management system regulation (part 820) except for records and complaint-file requirements.
- A tangent screen, AC-powered or battery-powered, is exempt from 510(k) under the same limitations. The QMS exemption (again except records and complaint files) is stated for the battery-powered device.
An exemption from 510(k) is not a statement about how any particular product performs. For a specific product, use the manufacturer’s instructions for use.
Common mistakes
- Confusing the Goldmann perimeter with the Goldmann tonometer. A tonometer is a different instrument from a perimeter; the optometry equipment list in our optometry clinic supply checklist names the visual field analyzer (perimeter) as its own item.
- Treating a visual field test as a sharpness test. It measures the width of the field, not how clearly a person reads letters.
- Using “machine” for every type. FDA’s tangent screen definition is a cloth chart, so the machine label fits perimeters better than campimeters.
Related reading
For a home-screening grid of a different kind, see the Amsler grid test. For the specialty that uses these devices, see what is ophthalmology. Clinics that equip an eye-exam room can browse diagnostic, monitoring and imaging equipment categories.
FAQ
What is a goldmann perimeter?
It is a perimeter, a device of the type FDA defines in 21 CFR 886.1605 as one that maps the peripheral visual field using light points on a curved surface. Not to be confused with the Goldmann applanation tonometer.
What is a tangent screen test?
A tangent screen (campimeter) is, per 21 CFR 886.1810, a large square cloth chart with a central fixation mark that maps the central 30 degrees of a patient’s visual field on a flat surface.
What does a visual field test measure?
According to the American Academy of Ophthalmology, it measures how wide your field of vision is, in degrees counted from the center.
Sources
- 21 CFR 886.1605, Perimeter. eCFR. Date checked: 2026-10-30.
- 21 CFR 886.1810, Tangent screen (campimeter). eCFR. Date checked: 2026-10-30.
- American Academy of Ophthalmology, “What do visual field test measurements for glaucoma mean?” aao.org. Date checked: 2026-10-30.
- National Eye Institute, Glaucoma. nei.nih.gov. Date checked: 2026-10-30.
