Snellen Chart

Prevention is better than cure. Designed for children older than 6, parents with young children, and general practitioners, this app displays optically precise optotypes of Snellen Chart for you to measure distant visual acuity accurately in order to detect nearsightedness or myopia and early, so you can take preventive measures and seek help from medical professional early to prevent pseudomyopia from becoming myopia, or prevent nearsightedness from getting worse.

Predefined Test Distances:

* 6, 5, 4, 3, and 2 meters

* 20, 15, 12, 10, 6 feet

At exactly 6 meters away from the “patient”, the optotypes on the 6/6 line (Decimal 1.0 or LogMar 0.0) shall subtend 5 minutes of arc, which means that the chart should be sized such that these optotypes are 8.73mm tall, and the topmost (Snellen Fraction 6/60, Decimal 0.1, or LogMar 1.0) optotypes should be 87.3 mm tall. At exactly 20 feet away from the “patient”, the topmost optotypes should be 88.7 mm tall, because 20 feet equals 6.096 meters.

Scenarios:

1. "Doctor" and "Patient".

2. Self-diagnosis with a mirror.

3. Self-diagnosis with a Bluetooth keyboard.

4. Self-diagnosis within arm's reach.

Notations：

1. Decimal (0.50)

2. Fraction (20/40)

3. LogMAR (0.30)

4. Fraction (5/10)

5. Fraction (6/12)

6. MAR (2)

7. VAS or VAR (85)

Test Modes:

1. Autoplay

2. Manual

In Autoplay, the app calculates the score. For LogMAR notation, the score is (LogMAR value of the best line read) + 0.02 x (number of optotypes missed). And the maximum missed is 3. For VAS notation, the score is an inversion of the logMAR scale, based on VAS=100-50xlogMAR. For other notations, the score is the notation value of the best line read and optionally minus number of optotypes missed, and the maximum missed is 2.

By default, setting "Play Interval Until Next Optotype" is none. Available intervals in second: 2, 4, 6, 8, and 10. If the "patient" could not recognize the optotype within the interval, this counts a miss.

Through enabling “Record Scores” in Settings, you can keep track of the progression of your visual acuity. Visual acuity scores of multiple testees could be recorded. Visual Acuity Score (VAS) is an inversion of the logMAR scale, based on VAS=100-50xlogMAR. It is more intuitive since higher values indicate better visual acuity.

In the scores review, score 100 in blue indicates the reference standard, scores above 100 in green indicates no myopia, while scores below 100 in red may indicate myopia.

Testing for myopia takes several procedures and the first step is often to check distant visual acuity through a visual acuity chart. And the decrement of visual acuity may indicate the development of myopia.

Disclaimer:

While this app may replace Snellen Chart in print, however it cannot replace doctors and optometrists who carry out comprehensive tests for your eyes. Please visit optometrists regularly and seek help from medical professional at early signs of visual acuity problems.