You should have your vision tested every 2 years, especially if you are over the age of 40. The most common tests assess the acuity (sharpness) of your distance vision and your ability to focus on near objects. The tests also show which corrective lenses, if any, you need. Additional tests for specific eye disorders, such as glaucoma, may be performed, depending on your age and medical history.
Wearing your usual glasses or contact lenses, if you use them, you will be asked to read very small print on a chart held at normal reading distance. This test checks your ability to focus on near objects.
Having a vision test
Lenses in the phoropter are changed until you can accurately read the letters near the bottom of the Snellen chart. This enables the optometrist to make the appropriate prescription for your corrective lenses.
The acuity of your distance vision is tested separately for each eye. The test involves noting how far down a Snellen chart you can read letters of decreasing sizes.