The extraocular muscle function test is performed to evaluate any weakness, or other defect in the extraocular muscles which results in uncontrolled eye movements. The test involves moving the eyes in eight different directions in space to evaluate the proper functioning of the extraocular muscles of the eyes.
The visual acuity test is used to determine the smallest letters you can read on a standardized chart (Snellen chart) or a card held 20 feet (6 meters) away. Special charts are used when testing at distances shorter than 20 feet (6 meters). Some Snellen charts are actually video monitors showing letters or images.
Vision screenings are not comprehensive eye exams. Screenings usually take only a few minutes and are often performed by volunteers who are not eye care professionals.
In many cases, vision screenings are nothing more than a visual acuity test where you’re asked to identify the smallest letters you can on a vision chart across the room.
Vision screenings typically are designed to only detect subnormal visual acuity and major vision problems — as quickly and cost-effectively as possible. They generally are ineffective for detecting more subtle vision problems and potentially sight-robbing eye diseases.
People who fail a vision screening (usually because their visual acuity is worse than 20/40) are made aware of this and are encouraged to visit an eye doctor so they can have their vision problem professionally diagnosed and treated with eyeglasses, contact lenses, medicine or surgery.
Eye exams, on the other hand, are performed by licensed eye doctors (an optometrist or ophthalmologist) and evaluate not only your visual acuity, but also the complete health of your eyes, from front to back — including checking for early signs of serious eye problems such as glaucoma, cataracts, macular degeneration and detached retina.
Your eye doctor also can detect early signs of serious health problems such as diabetes, high blood pressure and risk of stroke, based on the appearance of delicate blood vessels and other structures within the eye.