Eye doctors use two common tests to map how wide and how sensitive your vision is. Campimetry and perimetry sound alike, yet they differ in setup, purpose, and the kind of answers they give.
Knowing which test you might face helps you prepare, ask sharper questions, and understand your results without confusion.
Core Definitions
What Is Campimetry
Campimetry checks the central 30 degrees of vision while you stare straight ahead. A small screen or tablet is placed about a foot from your eye, and tiny lights flicker on and off.
You press a button each time you see a light, building a map of any blind or weak spots. The test is quick, needs little equipment, and is often done at the clinic chair.
What Is Perimetry
Perimetry measures the entire visual field, from center to far edge, using a bowl-shaped dome or virtual-reality headset. Lights appear in many locations, and your responses draw a full 360-degree picture of vision strength.
Because it covers the periphery, perimetry can catch early loss that campimetry would miss. It takes longer and demands more focus, but gives a wider view of eye health.
How Each Test Is Done
Campimetry Setup
You rest your chin on a pad and look at a central dot on a flat screen. The room stays bright, and you can blink normally, so the setting feels relaxed.
Only one eye is tested at a time, and the whole exam often finishes in under five minutes per eye.
Perimetry Setup
You sit inside a white dome that blocks outside light, or you wear a dark headset. A patch covers one eye while the machine flashes lights of different sizes and brightness levels across the bowl.
You must keep your gaze fixed on a center target for up to fifteen minutes per eye. Any head movement or loss of focus can create false spots on the final map.
What the Results Look Like
Campimetry Maps
The printout shows a small circle with gray shades marking where you did or did not see the lights. Darker areas hint at missing vision; lighter areas show normal spots.
Doctors use this simple picture to watch changes in the macula or optic nerve over time.
Perimetry Maps
You receive a larger, half-moon chart that extends to the far edges of vision. Numbers and symbols tell how dim a light could be before you missed it, giving a depth map rather than a yes-or-no view.
Clusters of black triangles can reveal blind spots from glaucoma, stroke, or injury. Comparing yearly charts shows if the field is shrinking, staying stable, or improving after treatment.
Clinical Uses Compared
When Doctors Choose Campimetry
Campimetry suits patients who need quick checks for macular degeneration or early diabetic eye changes. It works well for people who tire easily, because the test is short and the room stays lit.
Children and anxious adults often tolerate it better than the bowl test. If the problem is expected to lie in the very center of sight, campimetry gives enough detail without extra hassle.
When Doctors Choose Perimetry
Perimetry is the go-to tool for glaucoma follow-up, because loss usually starts far out in the field. It is also used after brain injury or stroke to find missing sectors on one side.
Anyone with night-driving complaints may be sent for perimetry, since peripheral dimness is best caught by the full-field map. Surgeons may order it before cataract or retinal procedures to plan safety zones.
Accuracy and Limitations
Campimetry Strengths
The bright room reduces false errors from pupil size changes. Because the screen is close, lens prescriptions matter less and dry eye bothers the test less.
Repeating the exam on every visit is easy, so small shifts in central vision are spotted fast.
Campimetry Limits
Anything outside the central 30 degrees is invisible to this test. It can miss early glaucoma or subtle side-field loss that a patient has not yet noticed.
Tired patients may press the button late, creating artificial gaps that look like damage.
Perimetry Strengths
The dome covers nearly the full field, so doctors see the true shape of blind spots. Adjustable light levels allow tracking of very early damage long before it affects daily life.
Software can compare new results to past ones, highlighting tiny changes that might otherwise go unseen.
Perimetry Limits
Long testing time leads to fatigue, and tired eyes produce unreliable answers. The dark room can make eyelids droop, blocking part of the view and faking defects.
People with neck pain or tremor may struggle to keep the chin steady, scattering light signals across the map.
Patient Experience Tips
Preparing for Campimetry
Wear your usual reading glasses if you use them, because the screen sits near. Arrive with relaxed eyes; no need for drops or dark adaptation.
Blink normally and press the button as soon as you spot any flash, even if it seems dim.
Preparing for Perimetry
Rest well the night before, and eat a light snack to avoid low blood sugar that can blur attention. Ask if you can pause between eyes; a thirty-second break cuts fatigue errors.
Keep your forehead against the band and think of humming a quiet song to stay alert during long stretches without lights.
Cost and Accessibility
Campimetry Practicalities
Many general eye clinics already own the tablet-style device, so the test is often bundled into a routine visit fee. No dark room is needed, and a technician can supervise several patients at once.
Insurance usually covers campimetry when the doctor documents a medical reason such as blurry central vision.
Perimetry Practicalities
The dome machine is larger and sits in a separate, light-sealed room, so only specialty practices or hospitals offer it. Expect a unique billing code and sometimes a copay, because the test takes extra staff time.
Virtual-reality versions are entering smaller clinics, potentially lowering cost and space needs while keeping the wide-field advantage.
Interpreting Your Report at Home
Reading Campimetry Output
Look for a clear bull’s-eye pattern; any sudden dark patch near the center deserves a follow-up question. If the report says “fixation loss,” it means your eye moved too much, so ask if the test should be repeated.
Compare your own copies year to year; new gray spots that were not there before can guide conversations about adjusting medications or lifestyle.
Reading Perimetry Output
Focus on the shape of any shaded wedge; a nose-side defect often links to glaucoma, while a half-side gap may point to past stroke. Numbers labeled MD give a rough average of overall field strength; a more negative value means more loss.
Do not panic over single black squares; doctors look for clusters that repeat on two or more visits before acting.
Future Directions
Technology Trends in Campimetry
Phones and tablets now host apps that mimic the clinical screen, letting patients test vision at home. Data can be uploaded to the doctor’s portal, creating a cloud diary of central field changes between office visits.
Game-style flashes keep children engaged, reducing the number of false presses.
Technology Trends in Perimetry
Headset perimeters remove the need for bulky domes and allow testing in bright rooms. Eye-tracking cameras correct for tiny movements, cutting retest rates and shortening exam time to under six minutes per eye.
Artificial intelligence can now flag worsening clusters automatically, sending alerts before the doctor opens the file.