Visual Acuity Charts

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Prevention is better than cure, while myopia is incurable. 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 detect nearsightedness or myopia accurately and early.

measure optotypes on iPhone and iPad using a ruler

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

Android Devices

Requirements:

  • Minimum version: Android 4.3 
  • Required Permissions: Vibration
  • Device Types: smart phone, tablet

Content rating: 3+ with IARC Rating Certificate

Get it on Google Play

iOS Devices

Requirements:

  • Minmum version: iOS 10
  • Entitlements: None
  • Device Types: iPhone, iPad

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 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 may be defined in Settings.

Remarks

  • At exactly 20 feet’ distance from the “patient”, the topmost optotypes at decimal 0.1 like "E" should be 88.7 mm tall, because 20 feet equals 6.096 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) 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.

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 tests only shortsightedness/myopia, and 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. 

Android

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

iOS

iPhoneiPad