The Amsler grid is one of the simplest yet most clinically valuable screening tools in eye care — a 10cm×10cm graph paper-like grid with a central fixation dot that reveals distortions and gaps in the central visual field corresponding to the macula. Unlike the Snellen chart, which tests resolution (acuity), the Amsler grid tests macular function specifically, making it sensitive to conditions like age-related macular degeneration, macular holes, and epiretinal membranes that may not initially reduce letter acuity.
For paraoptometrics, the Amsler grid is significant for two reasons: you may perform it in the clinic as part of a macular screening protocol, and you are responsible for teaching patients how to use it at home for self-monitoring. Both skills are tested on the CPO and CPOA exams, with emphasis on correct procedure and patient instruction.
The Amsler grid cannot diagnose disease — it only identifies that something is abnormal in the macula. The doctor then uses OCT, fundus examination, and other tools to determine the specific diagnosis. Your role is to perform and document the test accurately and to educate patients about recognizing new symptoms at home.
Step-by-Step Amsler Grid Procedure
Step 1: Near Correction
Ensure the patient is wearing their reading glasses or bifocal/progressive segment (if applicable). The Amsler grid is held at 33cm — the same distance as reading. Without reading correction, a presbyopic patient will see the grid blurred, making the test unreliable.
Step 2: Cover One Eye
Use an occluder or have the patient cover one eye with their palm. Cover completely — peeping causes false negative results. Test one eye at a time. Start with the right eye (OD) by convention, then test the left (OS).
Step 3: Proper Distance
Hold the grid at 33cm (approximately arm's length or a standard reading distance). Good ambient lighting or a backlit grid. The grid should subtend the central 10 degrees of the visual field.
Step 4: Fixation Instruction
Tell the patient: "Look ONLY at the central dot. Do not move your eye around. While looking at the dot, tell me if you can see all four corners of the grid." This ensures they are maintaining central fixation.
Patient: Look ONLY at the central dot. Do not move your eye around. While looking at the dot, tell me if you can see all four corners of the grid.
Step 5: Ask About Distortion
While the patient fixates the center: "Are any lines missing or blank?" (scotoma), "Are any lines wavy, bent, or curved?" (metamorphopsia), "Are any squares a different size?" (distortion). Ask each question separately.
Center: Are any lines missing or blank?
Step 6: Document Findings
Have the patient mark any abnormalities on a printed grid. Document which eye, the location and nature of any finding. Compare to previous recordings. Note: if grids are dated and saved, changes over time are meaningful.
Step 7: Repeat Fellow Eye
Cover the tested eye. Repeat the entire procedure for the other eye. Many conditions are bilateral (AMD is bilateral even if asymmetric) — do not skip the second eye.
Normal vs Abnormal Findings
Normal Result
All four corners visible. All lines straight and equally spaced. No missing areas or blank spots. All squares appear same size. Patient can see fixation dot clearly.
Abnormal: Metamorphopsia
Lines appear wavy, curved, bent, or irregular. Most commonly caused by AMD (subretinal fluid from choroidal neovascularization), epiretinal membrane (macular pucker), or macular hole. NEW metamorphopsia = urgent referral.
Scotoma
Missing area or blank spot in the grid. Central scotoma = foveal damage (AMD, optic neuritis, toxic maculopathy). Paracentral scotoma = parafoveal damage (early AMD, macular dystrophy). May be missed if patient unconsciously fills in the gap.
Size Distortion
Micropsia: objects appear smaller than normal (cone compression by subretinal fluid). Macropsia: objects appear larger. Size distortion occurs because photoreceptor spacing is altered — widely spaced cones produce micropsia; tightly crowded cones produce macropsia.
Practice macular screening questions for your exam
Opterio covers Amsler grid, AMD, and visual field testing with AI-powered explanations for CPO and CPOA candidates.
Patient Home Monitoring Education
Teaching AMD patients to self-monitor with the Amsler grid at home is one of the most impactful patient education tasks a paraoptometric can perform. Wet AMD can progress rapidly — patients who notice new distortion and call promptly can receive anti-VEGF injections before irreversible central vision is lost.
- Daily Testing Recommended — Patients with dry AMD should test each eye separately every morning, wearing their reading glasses, before getting out of bed or starting the day. This creates a consistent daily habit.
- Same Eye, Same Conditions Each Day — Consistency matters — same lighting, same distance, same reading correction. Variable conditions produce variable results that are hard to interpret.
- Report New Changes Immediately — Emphasize: "If you see new waves, new blank spots, or any change from your usual grid, call us the same day. Do not wait for your next scheduled appointment." — If you see new waves, new blank spots, or any change from your usual grid, call us the same day. Do not wait for your next scheduled appointment.
- Grid Should Be Dated and Saved — Give the patient printed grids to mark and save. Dated records allow comparison over time, which is valuable for monitoring slow progression.