Visual acuity refers to the sharpness of distance vision, the ability to discern shapes and details. Eye care professionals define 20/20 vision as the ability to see clearly at 20 feet what is considered “normal” for the average human eye. Performing a visual acuity test at home helps track changes in your sight but is not a replacement for a comprehensive eye examination.
Preparing Your Home Testing Environment
Before beginning, obtain a standard Snellen eye chart, either by printing a calibrated version or using a properly sized digital display. Ensure the chart is printed to the correct scale, often specified on the download page, so letter sizes represent standard visual angles. Affix the chart securely to a windowless wall, placing the 20/20 line at your eye level when standing.
Use a tape measure to establish the correct distance from the chart. While doctors use 20 feet, many home charts are designed for a scaled distance, such as 10 feet. Ensure the testing area is brightly and evenly lit, focusing light onto the chart itself, not behind you or directly into your eyes. If you wear glasses or contact lenses for distance vision, wear them during the test to determine your best-corrected visual acuity.
Performing the Visual Acuity Test
The test is performed one eye at a time. Stand precisely at the measured distance facing the chart and cover your left eye completely with a clean hand or an eye patch. Avoid pressing on the eyelid, as this can temporarily distort your vision when you switch eyes.
Begin reading the letters aloud from the largest line at the top, continuing downward to the smallest line you can clearly distinguish. To consider a line read correctly, you must identify more than half of the letters on that row. Note the fraction written next to the smallest line you read accurately.
Repeat the process for your other eye, covering the right eye without applying pressure. Finally, perform the test once more using both eyes together (binocular vision). Recording the results for each eye and for both eyes provides a baseline measurement of your sight.
Interpreting the Acuity Scores
The resulting score is expressed as a fraction, such as 20/40. The top number represents the distance you stood from the chart (20 feet in the standard system). The bottom number indicates the distance at which a person with 20/20 vision could read that same line. For example, 20/40 means you see at 20 feet what a person with normal vision sees clearly from 40 feet away.
If you achieve 20/20, your distance vision aligns with the standard. Scores with a smaller denominator, such as 20/15, indicate above-average vision; you see at 20 feet what the average person needs to move to 15 feet to see. Conversely, a score like 20/100 signifies reduced sharpness, meaning you must be 20 feet away to see a letter that a person with standard vision identifies from 100 feet away.
When Home Testing Is Not Enough
An at-home acuity test measures visual sharpness but is not a substitute for a professional eye examination. It only assesses one aspect of vision and cannot detect underlying eye health conditions or diseases. The test does not check for issues affecting the back of the eye, such as glaucoma, cataracts, or macular degeneration, which require specialized equipment for diagnosis.
Regardless of your home test results, certain symptoms require an immediate visit to an eye care professional. A professional exam also assesses depth perception, peripheral vision, and the coordination between your two eyes. Even if your home test indicates 20/20 vision, regular professional check-ups remain necessary to monitor overall eye health.
Symptoms Requiring Professional Attention
- Sudden or rapid changes in your vision
- Persistent eye pain
- Seeing new floaters
- Flashes of light
- A curtain-like obstruction in your visual field