What Is the Amsler Grid?

The Amsler grid is a basic visual field test. This paper-based eye exam can easily be performed at home to monitor for disorders involving your central vision. The grid consists of 0.5 centimeters (cm) squares that form a larger square of 10 cm by 10 cm. This test evaluates 10 degrees of vision from a focal point which overall evaluates a visual acuity of 20 degrees.

A Swiss ophthalmologist named Marc Amsler first developed the grid in 1947 and is currently used to detect or continue monitoring for scotoma (blind spot) or metamorphopsia (vision distortion).

Uses and Varieties of Visual Field Tests

Visual field tests are a method an eye doctor (opthalmologist or optometrist) can use to measure how wide an area you can visualize away from a focal point. This is a common test to evaluate for scotomas and also evaluate any visual field restrictions from eyelid disorders like ptosis (droopy upper eyelid). Types of visual field tests include:

• Confrontation visual field test
• Automated perimetry test
• Kinetic visual field test
• Frequency doubling perimetry
• Electroretinography
• Amsler grid

What Can the Amsler Grid Help Diagnose?

The Amsler grid can help screen for the following conditions that cause a scotoma:

• Age-related macular degeneration (AMD)
• Central serous chorioretinopathy (CSCR)
• Acute macular neuroretinopathy

The Amsler grid can also help screen for causes of metamorphopsia related to both AMD as well as epiretinal membrane.

Types and Versions of Amsler Grids

There are seven different versions of the Amsler grid that are available for use in order to identify or further delineate metamorphopsia and scotoma.

1. Grid 1 is the basic version that is most common of the Amsler grids.
2. Grid 2 is an overlay that you can place over the basic Amsler grid with four diagonal lines. This will help for focusing on the center dot if you have a central scotoma (blindspot in the middle of your visual field).
3. Grid 3 is identical to grid 1 except there is a black background with red lines and a red dot. This grid is helpful in identifying disorders that have an associated red desaturation such as pituitary tumor causing partial blindness, toxic maculopathy, or toxic optic neuropathy.
4. Grid 4 is used to differentiate between blind spots and distortions. This grid uses a black background with a large central white dot with randomly placed smaller dots throughout the grid. There are no lines in this grid.
5. Grid 5 uses a black background with white horizontal lines with a white dot in the center. The horizontal lines can help determine distortions related to curved sections of the cornea. This can be particularly helpful if you have reading difficulties.
6. Grid 6, while similar to grid 5, has a white background and black lines. Towards the black dot in the center, the horizontal lines are closer than in grid 5. This can be helpful in identifying fine visual distortions near the center of your visual field.
7. Grid 7 is similar to grid 1 except at the center around the large central dot there is another smaller grid. This allows identification of disease in half a degree. This is helpful in identification of macular degeneration.

White or Black Backgrounds for Amsler Grid

If you search for Amsler grids online, you will typically see examples of Grid 1 except with a white background and black lines and a black central dot. Is this OK to use?

Amsler originally created this test on a black background with white lines and a white central dot. The Amsler grid on a white background is a modified version. The white background with black lines is more commonly seen, however it is unclear if they are equal in efficacy.

How the Amsler Grid Exam Is Performed at Home

Before starting this self-examination process at home, it is ideal to discuss with your eye doctor and have the first exam performed in the office to ensure proper training. Before initiating this exam, it is important to have avoided any bright lights to your eye; exposure causes photostress that could cause visual distortions that are not related to any disorder. To perform the self-administered Amsler grid test follow the following directions at least weekly.

To prepare for your home Amsler grid exam:

1. Wear any corrective glasses or contacts you normally use.
2. Hold the 10 cm by 10 cm square approximately 13 inches away from the eye you are testing.
3. Close the opposite eye of the one you are testing.

Identify these characteristics:

1. Is the white dot in the center visible?
2. Can you see the four corners and the four sides of the grid while focusing on the dot in the center?
3. Are there any blank or blurry sections of the grid while focusing on the center?
4. Are there any wavy lines (horizontal or vertical) of the grid while focusing on the center?
5. Are there any moving lines, shiny sections or vibrations noted in the grid while focusing on the center?

Ideally, all lines will appear to be parallel. If the lines appear distorted or disappear, you should mark the areas where these were noted. You can do this by noting the number of squares between the dot and the abnormality while you are doing the test.

Distorted or warped lines represent metamorphopsia, while lines that disappear represent blind spots (scotomas). Keep the marked Amsler grid for later reference, as changes in the area of distortion can represent a progressive condition, stabilized condition, or improvement in your condition.

Contraindications to Using the Amsler Grid Exam

There is not any known reason that would restrict you from using the Amsler Grid to test your vision. While there isn't a reason that would restrict the use of this test for checking for blind spots, the Amsler test is not used in determining the physiologic blind spot and is not useful in detecting early-stage visual field defects related to glaucoma.

If you are having your eyes dilated with mydriatic drops at your eye doctor's office, the Amsler grid test should be performed prior to the administration of the eye drops. If the eye drops have already been administered, you would need to reschedule the exam at a later date.

Disadvantages of the Amsler Grid Exam

While the Amsler grid is simple to use at home and monitor for the development or changes in macular degeneration, there are a few disadvantages to using the Amsler grid.

Identification of blind spots tends to have low accuracy as compared to other testing methods. Only about 50 percent of blind spots are identified using the Amsler grid. An even larger percentage of blindspots are missed by Amsler grid when the size of the blindspot is less than 6 degrees. Additionally, only about 30 percent of people using the Amsler grid detect their own abnormal results with the tool.

Alternative Eye Exams to the Amsler Grid

There are several alternatives that may be available for you to use if you do not want to use the Amsler grid to track any development or changes to blind spots or visual distortions.

• M chart (metamorphopsia chart) can be helpful in identifying both horizontal and vertical distortions. However unlike with the Amsler grid, the shape and size of the distortion are not able to be determined.
• Preferential Hyperacuity Perimeter (PHP) testing is available home medical devices to help identify age-related macular degeneration. Small studies suggest that PHP testing is more accurate in identifying age-related macular degeneration. However, PHP does tend to have a higher rate of false-positive tests in healthy individuals, which means that when tested positive, the individual actually does not have the disorder. Foresee Home is an example of a medical device that can be prescribed by your eye doctor to be used in your home.
• Shape Discrimination Hyperacuity (SDH) is an electronic method to quantify visual distortions. MyVisionTrack is one iOS app that utilizes this method to easily track signs of macular degeneration. Using smart technology, a user can test themselves at home twice a week on their phone or tablet. If the software detects any changes, the app notifies the eye doctor that prescribed the app. A prescription is required to register with apps related to SDH.