Quick facts
- The Amsler grid covers the central 20 degrees of the visual field, printed as a 10 cm square of 5 mm squares; each square subtends about 1 degree at the customary reading distance of 30-35 cm.
- The American Academy of Ophthalmology's patient instruction is to test one eye at a time, with reading glasses on, looking at the centre dot rather than moving the eye around the grid.
- The grid is a monitoring tool for macular disease, not a screening test for eye disease in general; the AAO's age-related macular degeneration pages place it alongside, not instead of, a dilated examination.
- A change reported on the grid is an urgent review, not next year's appointment: new distortion, a new blank area or a change in the size of the central clear zone all warrant a prompt examination.
- The programme needs three records: the instruction given, the baseline drawing, and the date of each return.
- Sources were read on 2026-10-19; both AAO pages returned HTTP 200 the same day.
An Amsler grid costs a few cents to print and is one of the few home tests that can detect a change in macular vision between appointments. Most practices hand one over at the end of a visit, and most patients use it for a fortnight and then stop, because nobody taught them what a positive result looks like. This article sets out a programme rather than a handout: how to instruct the test, what baseline to record, how to set a recall interval and what to do when a patient calls; the grid our chart set uses is part of the CliniEco Snellen and Amsler chart set, and the programme is what turns it into a monitoring tool.
What does an Amsler grid actually test?
The grid is a fixation target surrounded by a square lattice. With one eye covered, the patient looks at the centre dot and reports whether any part of the lattice is missing, distorted, blurred or discoloured. Because the grid covers the central 20 degrees, it samples the macula, which is the area responsible for reading, recognising faces and seeing detail.
The geometry is simple enough to explain to a patient. At the customary reading distance the whole grid subtends about 20 degrees and each small square about one degree, so a patient who says that three squares near the centre are wavy is describing a distortion of roughly three degrees across. That description is more useful to the clinician than "it looks a bit odd".
What the grid does not do is measure. It does not give a visual acuity, it does not quantify contrast sensitivity, and it does not image the retina. Its value is that it can be repeated at home between visits, which is exactly where a clinic-based test cannot go.
Who should be given a grid, and who should not?
The usual candidate is a patient with age-related macular degeneration who is being monitored for conversion from dry to wet disease. The AAO's AMD guidance describes the grid as a way for patients to check their own vision between examinations, and it is that monitoring role that the programme is built around.
A patient with a condition that affects the peripheral field, such as glaucoma, is not served by an Amsler grid, because the grid samples the centre. A patient who cannot fixate steadily, or who cannot see the centre dot, will produce a result that says more about the test than about the macula.
The other exclusion is practical. A patient with significant cognitive impairment, or without a family member who can help, will not run a weekly test reliably. In that case the programme should say so in the record and rely on scheduled examination instead of pretending the grid is being used.
How should the test be taught?
Teach it with the patient's own glasses on and in the lighting they will actually use at home. Show them how to cover one eye without pressing on it, how to hold the grid at the reading distance marked on the sheet, and how to look at the centre dot while noticing the rest of the grid. The common error is to scan the grid, which defeats the purpose.
Ask the patient to describe, not to judge. "Do the lines look wavy anywhere? Is any square missing? Is any area darker or blurred?" A yes is followed by "where, and which eye". The patient should be told to test each eye separately and to write the date on the sheet.
Give a frequency and a reason for it. Weekly testing is what most practices ask for, because it catches a change within a week without turning the test into a daily anxiety. The patient should also be told what to do with a positive result: call the practice the same day, not at the next appointment.
| Step | Instruction to the patient | Common error |
|---|---|---|
| 1 | Wear the reading glasses you use for close work | Testing without glasses |
| 2 | Hold the grid at the marked distance, in good light | Holding it too close or in dim light |
| 3 | Cover one eye with the palm, without pressing | Pressing on the closed eye |
| 4 | Look at the centre dot and keep looking at it | Scanning the grid with the eye |
| 5 | Note wavy, missing, blurred or dark areas and where they are | Reporting only that vision is fine |
| 6 | Repeat with the other eye and date the sheet | Testing both eyes at once |
What baseline should be recorded at the clinic?
Record the result of the test you did in the chair, not just the fact that a grid was given. That means the date, the acuity, whether the patient could see the centre dot, whether any distortion was present at baseline, and a note of any pre-existing metamorphopsia. A patient who already has distortion in one eye cannot be monitored with a rule that treats any distortion as new.
A simple drawing is worth more than a sentence. Ask the patient to mark on a copy of the grid where the distortion or missing area is, and keep that copy in the record. At the next visit, the new drawing can be compared with the old one by the patient and the clinician together.
Record the instruction given, too: who taught the test, when, and whether a family member was present. If a patient later says they were never told what to look for, the note is the answer.
How should a reported change be handled?
A new distortion, a new central or paracentral scotoma, or a change in the size of the clear central area is treated as a possible conversion or progression and reviewed promptly. The AAO's AMD guidance describes sudden changes in vision as a reason to see an eye care professional without delay, and the programme should route the call to a clinician the same day rather than to the next routine slot.
The practice needs a named route for that call. A receptionist who books the patient three weeks out because the schedule is full has converted a monitoring programme into a source of delay. Write the escalation into the programme: who takes the call, what is asked, how soon the patient is seen, and who decides if the answer is not obvious.
Document the outcome. A patient who called with a change, was seen and was found to have no conversion is a data point that supports the programme; without the note, the call disappears and the next audit cannot tell whether the programme is working.
| Patient report | Urgency | Action |
|---|---|---|
| New wavy lines in one eye | Same-day clinician review | Dilated examination; compare with baseline drawing |
| New blank or dark area near the centre | Same-day clinician review | Dilated examination; consider imaging |
| Change in the size of the clear central zone | Within days | Compare with baseline; examine and decide |
| No change, test done weekly | Routine | Record the date; continue; review at the scheduled visit |
| Cannot see the centre dot | Routine but note it | Record the limitation; the grid is not a valid monitor for that eye |
How is the programme kept alive?
A programme that depends on the patient's memory fades within weeks. A recall at three months for the first year, then at the interval the clinician sets, keeps the grid in use and gives the practice a chance to re-teach the test. A short phone or portal check between visits is enough if it asks the two questions that matter: are you still testing weekly, and has anything changed.
Give the patient a supply of sheets rather than one. A single sheet gets lost, and a patient who has to ask for another has a reason to stop. The sheet should carry the practice's phone number and the instruction to call rather than wait.
Audit the programme once a year: how many patients were given a grid, how many returned a sheet, how many calls came in, and what happened to them. The numbers are small, but they show whether the programme is a process or a stack of handouts.
A monitoring programme consumes printed grids and charts as steadily as it consumes appointment time. Order through the wholesale programme for case pricing and an account, or become a distributor for resale. The Snellen and Amsler chart set sits in the same catalogue.
Sources
- American Academy of Ophthalmology, Amsler grid: how to test your eyes at home
- American Academy of Ophthalmology, Age-related macular degeneration (AMD)
- American Academy of Ophthalmology, How to use eye drops
- Public Health Ontario, infection prevention and control
- Health Canada, medical devices
- Medical Devices Regulations, SOR/98-282
- ISO 15004-1:2020, ophthalmic instruments, general requirements
- ISO 15004-2:2007, ophthalmic instruments, light hazard protection
- ISO 13485:2016, medical devices quality management
- ISO 14971:2019, application of risk management to medical devices
- Canadian Association of Optometrists
- Canadian Ophthalmological Society
- Canadian Centre for Occupational Health and Safety, OSH answers
- CSA Group, standards catalogue
- Standards Council of Canada
- Measurement Canada
Printable patient instruction sheet. One page with the six steps, the reading distance, a box for each eye and a line for the date, plus the practice number and the instruction to call rather than wait. Print the Amsler instruction sheet - plain paper, no account and no sign-up, and the patient leaves with something they can keep on the fridge.
Recall schedule builder. Set the first review at three months and the later interval your clinicians use, and the page produces a dated recall list with a column for whether a sheet came back. Build an Amsler recall schedule so the programme has a review date instead of relying on the patient's memory.
Ask a compliance specialist. What your province expects you to record for a home monitoring programme, and how a reported change should be triaged, are questions that depend on the practice and its scope. Ask a compliance specialist - written answer specific to your equipment and province, with the regulation or standard it is based on cited.
Related reading
- Amsler grid in Canada and the US: which rules apply
- Amsler grids in Canada and the US: which class applies
- Visual field screening in Canada and the US: which perimeter 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 practice managers and is not clinical advice; the decision to monitor a patient at home, and the action to take on a reported change, belong to the clinician responsible for that patient.
Frequently Asked Questions
How much of the visual field does an Amsler grid cover?
The standard grid covers the central 20 degrees. It is printed as a 10 cm square divided into 5 mm squares, so each square subtends about one degree at the usual reading distance of 30-35 cm.
How often should a patient use an Amsler grid?
Weekly testing is what most practices ask for. It catches a change within a week without making the test a daily source of anxiety, and it is frequent enough to be useful between appointments.
Should the patient wear glasses to use the grid?
Yes, the glasses they normally use for reading, at the distance marked on the sheet. Testing without them, or holding the grid at the wrong distance, changes the size of the image on the retina.
What counts as a change worth calling about?
New wavy lines, a new blank or dark area near the centre, or a change in the size of the clear central zone. Any of these should prompt a same-day call rather than waiting for the next appointment.
Can an Amsler grid replace a dilated eye examination?
No. The grid samples the central field and does not image the retina. The AAO's AMD guidance places it alongside regular examination, not in place of it.
Is the grid useful for glaucoma?
Not for monitoring glaucoma, because glaucoma affects the peripheral field while the grid samples the centre. A visual field test is the appropriate monitor for that condition.
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