Check your Vision on-line.
You can test your distance vision on-line using a Snellen Chart. The Snellen Chart is the eye chart most doctors use and is the industry standard. It has standard size letters and is normally viewed at a test distance of 20 feet. The on-line Snellen Chart will vary in size according to the size of your screen, therefore, the test distance will also change. You will have to calculate the proper test distance based on the size of the letter "E" at the top of the chart. Use a ruler to measure the Big "E" in inches on your screen and multiply that number by 2.838. This gives you the number of feet you must stand or sit from your screen while taking the test.
Disclaimer: This at-home test is not intended to replace an eye exam by a licensed optometrist or ophthalmologist. Visual acuity (tested here) is only one part of a complete eye exam and does not test for eye disease.