The driver's license vision test typically involves a variant of the Snellen eye chart to test visual acuity and a test for peripheral vision in one or both eyes. Different jurisdictions vary in their minimum vision requirements for a driver's license for restricted or unrestricted driving.
The Snellen chart contains descending rows of smaller letters. Each successive line the person can read indicates stronger visual acuity, which is expressed as a ratio. Someone with 20/30 vision as diagnosed by test results needs to be 20 feet away to read something that someone with normal vision can read at 30 feet. One of the most common minimum requirements to receive an unrestricted license is 20/40 vision. In some cases, a restricted license can be granted at 20/60 vision or lower.
After taking the Snellen chart test, applicants are asked to indicate whether they see a flashing light in peripheral vision with the dominant eye. A 140-degree field of vision is required in most jurisdictions.
If a person is unable to pass the exam at the DMV, it's possible to obtain a visual acuity report form, take an eye exam by a licensed practitioner and have him state that the person is capable of driving safely.