Visual Acuity Charts

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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.

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 eye charts 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.

measure optotypes on iPhone and iPad using a ruler

Visual Acuity Charts on Android tablet Visual Acuity Charts on Android phone

iOS Devices

Requirements:

  • Minmum version: iOS 10.3
  • Entitlements: None
  • Device Types: iPhone, iPad

Android Devices

Requirements:

  • Minimum version: Android 5 
  • Required Permissions: Vibration
  • Device Types: smart phone, tablet

Content rating: 3+ with IARC Rating Certificate

Get it on Google Play

At exactly 6 meters’ distance from the “patient”, the optotype letters 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 optotype letters are 8.73mm tall, and the topmost (Snellen Fraction 6/60, Decimal 0.1, or LogMar 1.0) "E" should be 87.3 mm tall.

Charts

  1. Snellen Chart, with C, D, E, F, H, K, N, P, R, U V and Z, as defined in BS 4274-1:2003
  2. Tumbling E Chart
  3. Landolt C Chart
  4. ETDRS Chart, with C, D, H, K, N, O, R, S, V, and Z
  5. HOTV Chart
  6. ETDRS European-wide Chart, with H, K, O, E, P, X, B, T, M and A
  7. LEA Symbols
  8. Numbers

Scenarios

  1. "Doctor" and "Patient"
  2. Self-diagnosis with Mirror
  3. Self-diagnosis with a Bluetooth keyboard
  4. Self-diagnosis within Arm's Reach

Predefined Test Distances

  • 6, 5, 4, 3, and 2 meters
  • 20, 15, 12, 10, and 6 feet

And a custom distance between 0.5m and 30m may be defined in Settings.

Remarks

  • 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.
  • Custom distance is handy for an arm-reach distance, ad-hoc distance in a GP's office, and a very long distance up to 30 meters.
  • The letters and orientations of E or C ring are randomly shuffled during startup or waking-up from sleep. This makes memorizing an eye chart and cheating a vision test impossible.

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)

All charts in any VA notation follow the LogMAR design recommended by the International Council of Ophthalmology (ICO) and BS 4274-1:2003 to address design flaws in original Snellen chart. 

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.

Disclaimer

While this app may replace Snellen Chart, E-Chart, C-Chart, ETDRS Charts and HOTV Chart in print, 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.

The app does not test strabismus, amblyopia, estropia, extropia, hyperopia and astigmatismand which are common early vision conditions.

Device Gallery

This app has been tested on various Android phones/tablets, iPhones and iPads to ensure optotype letters are printed on screens accurately. 

iOS

iPhoneiPad

Android

Google, Samsung, HTC, LG, Acer, Motorola, Sony, Huawei and Amazon Fire Tablets.