iSnellen bring to the iDevices the famous Snellen's eye chart used by eye care professionals and others to measure visual acuity. Designed with friendly graphics, it respects the conventions and rules applied to regular tests.
The app is named after the Dutch ophthalmologist Hermann Snellen who developed the chart during 1862.
The iSnellen chart is randomly generated with ten lines of symbols which are formally known as "optotypes". The first line consists of one very large optotype and subsequent rows have increasing numbers of letters that decrease in size. A person taking the test covers one eye, and recognize the symbols of each row, beginning at the top. The smallest row that can be read accurately indicates the visual acuity in that eye.
iSnellen adopts 5 series of optoypes:
- Snellen Original (pre-installed)
- Tumbling E
- Landolt C
- random generated eye chart
- adjustable value for the eye-chart distance
- measurement in feet (20/20) or meters (6/6)
- positive and negative visualization
- various background images