This is what posted in Apple App Store if you are using iPhone or iPad the check the app.
"The 42-42 Promotion is being held from 2020-04-02 to 2020-05-13 lasting for 42 days. After 13th May the price is back to US$4.99. The free installation is permanent."
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 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.
Supported Eye 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. Option to have shorter middle arm.
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
Predefined Test Distances:
* 6, 5, 4, 3, and 2 meters
* 20, 15, 12, 10, 6 feet
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.
While this app may replace eye charts 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.