How to Test your Eyes using the Computer
Doctor's say that you should test your eyes every two years but if haven't had the chance to see a doctor all this time, you can test your vision on your computer as well.
Of course these self eye tests are no substitute for visiting your doctor but if you follow the steps well, you may get some idea about how good (or bad) your vision is.
The Snellen Eye Chart
Most of us are familiar with the Snellen Chart that has rows of alphabets of different sizes - you read these letters from a distance, usually twenty feet, and the smallest row that you can recognize accurately indicates whether you have normal vision or not.
The various eye testing tools that are available online make use of the same Snellen chart.
Test your Eyesight Online
You should start with University at Buffalo's IVAC tool. Use a physical ruler to measure the length of the line on the screen (the length will vary depending on your screen resolution). Also measure the distance of your eyes from the computer screen. Now read the row of letters on the screen and press 'smaller' to display more rows in decreasing sizes.
While performing the test, you need to cover one eye and when you have read all the characters from top-to-bottom, read them again but cover the other eye this time. When you can no longer read the letters, stop!