Visual Acuity is the first eye test on the iPhone platform developed by vision scientists and dedicated to the measurement of visual acuity. It is the perfect complementary tool for the optometrists and other vision care specialists. Visual Acuity uses a computerized and modern method (logMAR) which is becoming the preferred visual acuity test in many eye clinics, and is effectively replacing the imperfect Snellen chart. Two kinds of test are available: a 'single letter' test and an interactive 'chart' test.
The single letter test follows an adaptive procedure that computes an acuity score similar to the tests performed in clinical environment. This test uses C or E letters presented at decreasing size until the user cannot reliably see their orientation. This test is best for measuring your own Near Visual Acuity up to "20/20" when holding your device at arm length (typically 45 to 60 cm, or 18 to 24").
The second test is an interactive logMAR chart, also available as a standalone app in the App Store: "Fast Acuity". This test provides the fastest way to measure visual acuity in a precise and efficient way, and could not be easier to use:
1) set the viewing distance of the patient using the bottom slider (up to 8m),
2) adjust the vertical slider on the right to select a range of letter sizes that can be easily seen by the patient,
3) press the + and - buttons to fine tune the letters size by small steps,
4) touch the smallest line for which the patient can detect the orientation of every single letter.
Several choices are available to customize both tests: optotypes (Landolt C, Tumbling E, Sloan, HOVT, Lea), acuity units (foot: 20/*, meter: 6/*, decimal, VAR, or logMAR units), 4 or 8 orientations (8 improves the test reliability for Landolt C), black letter on white background or vice-versa. Acuity scores can be saved as function of the test condition (left, right or both eyes, optotypes, corrected or uncorrected). The acuity history also keeps notes about each measurement (eg, subject’s name) which can be used to retrieve the acuity history for a given patient. Tests history can be also emailed to yourself or others. The Tools section provides information and recommendations for the tests, a conversion tool between visual acuity units, as well as a standard Snellen chart for comparison purpose.
Why is logMAR better than Snellen? Because logMAR tests:
- use special fonts for the optotypes, in which all the lines are of equal thickness for all letters,
- present the same number of letters for each size,
- can be carried out at any distance allowing testing of very poor visual acuity,
- allow each presented letter to be scored individually to provide a more precise measurement,
- provide a logMAR score as a “real number” that can be used in calculations and statistics.
Contrarily to most other acuity charts available on the iPhone, Visual Acuity provides:
- eye charts that are randomly generated to prevent memory effects,
- support for viewing distance up to 8 meters (26 ft) in metric or imperial units,
- standard optotypes (letters or symbols) to test literate or illiterate people, and preschool children,
- support for the most common acuity units,
- and, most importantly, follows the logMAR design recommended by the National Eye Institute (NEI) and the International Council of Ophthalmology (ICO).
Version 1.4 (Oct 13, 2009):
- Improved email export of test history.
Version 1.3 (Sept 8, 2009):
- Addition of a Help section to each component.
- Addition of Sloan, HOTV and Lea interactive logMAR charts,
- Addition of a Search Bar in Test History section (applies only to Notes field),
- Improvement of single letter test with white letters on black background,
- Response controls in single letter test remain now presented all the time to speed up test,
- Redesign of Tools section (with a section dedicated to Snellen chart history, design & limitations).
Version 1.2 (July 3, 2009):
- Compatibility with iPhone OS 3.0,
- Addition of a conversion tool for acuity units in Help section,
- Addition of an interactive logMAR chart,
- Acuity results can now be reordered or deleted, and e-mailed as HTML table,
- Information about tested eye, eye correction etc. now asked after the test,
- Clearer Help section divided into Instructions, Conversion Tool, and Eye Charts subsections.
Version 1.1 (March 10, 2009):
- Minor cosmetic improvements,
- 'Stop' button now also used to stop test and provide option to save acuity score,
- Addition of VAR unit (Visual Acuity Rating),
- Addition of two new options in Settings section: choice for 4 or 8 orientations to improve reliability of the test, choice between black letter on white background or vice-versa,
- Better positioning of response buttons for those with a very low vision,
- Improved Help section,
- Addition of a standard Snellen chart in the Help section for comparison purpose (to be hold at arm length),
- Ability to provide some notes (can be used for example to specified user's name) for each test,
- Updated report with new settings in Tests History section (Notes and number of orientations and optotype aspect, for example '4BoW' to specify a test with 4 orientations and Black optotypes on White background).
Version 1.0 (February 21, 2009):
- First release on AppStore.