20/20 is often associated with vision and since we are now in the year 2020, we felt that it was an appropriate time to discuss what these numbers actually mean in the world of eye care.
Having 20/20 vision is often perceived as perfect vision. But, is your eyesight superior to others whose vision does not match those specific numbers? When someone has 20/20 vision, it simply means normal vision, and that what is meant to be seen at a distance of 20 feet is seen normally at that distance. In fact, there are variations on this number. A person can have 20/60 vision which would mean that the person needs to be as close as 20 feet to see what a person with normal vision can see at 60 feet. The first number corresponds to the distance the person being tested is standing to an object and the second number is the distance a person with normal vision would be standing at, to see the same object.
How are these numbers determined? Optometrists evaluate your vision during a comprehensive eye exam which includes a few different tests. With these tests, the optometrist can determine whether you require glasses and then they can provide a prescription that corresponds to your specific eyesight. Here is a list of tests used by the optometrist to assess your vision.
Visual Acuity Test
Using eye charts, this test measures how sharp your vision is. Generally, a projected eye chart placed at a specific distance measures your visual acuity for things and objects at a distance and a smaller hand-held chart to determine your near vision.
Colour Blindness Test
People who are colour blind, have a deficiency in distinguishing colours. To determine this, an optometrist will use an Ishihara test. This test consists of an image made of a sequence of circles in random shapes and colours which form a number or shape in the centre. If the person cannot see the number or shape, then they are most likely colour blind.
Cover Test
During this test, the eye doctor will ask you to focus on an object across the room and then cover your eyes alternately to test each one. This will be repeated with an object that is near.
This test will check if your eyes work together or if you have strabismus, amblyopia or any other condition that can cause eye strain.
Ocular Motility Test
This test is done to verify how well your eyes move. Typically, the eye doctor will hold a little light in front of you and ask you to follow it with only your eyes. If your eyes make saccade movements or are too slow to follow an object, this can eventually cause eye strain and can also affect certain skills, like reading.
Stereopsis Test
This test checks your depth perception and how you perceive 3-dimensional objects. The optometrist will ask you to wear 3D glasses through which you have to look at a series of patterns. Each pattern has four circles and you need to point out which circle looks the closest to you.
Retinoscopy
This test is performed to obtain your prescription. To perform this test, the lights are dimmed and you will be asked to focus on a large target, like the E in the eye chart, then the eye doctor will flip lenses in a machine in front of your eyes. The lenses have different powers that will estimate which lens will correct your vision.
Refraction
This test determines your level of hyperopia, myopia, astigmatism and presbyopia. If you need corrective lenses, a phoropter is placed in front of your eyes and as you look through you will be asked which lenses let you see the clearest.
Slit Light Exam
This magnifying instrument looks like a binocular microscope that is used to examine the structure of your eyes. During this test, you will need to place your chin and forehead against the instrument and your eye doctor will then examine the interior and exterior of your eyes. This helps the optometrist see your retina and optic nerve. This is essential since eye conditions and diseases can often affect the back of the eye before any symptoms are felt or seen as in the case of age-related macular degeneration, cataracts, diabetic retinopathy etc.
Glaucoma Test
This test measures the pressure in your eye. A small puff of air is burst directly into your eye. The machine calculates your intraocular pressure which is based on the eye’s resistance to this puff of air. If the numbers are high, you may be at risk for or have glaucoma.
Visual Field Test
This test is performed to check for possible blind spots. Blind spots can be a sign of diseases such as glaucoma or a result of a stroke or tumour.
In some cases, a more in-depth look into your eye may be needed so your eye doctor may recommend that you see a specialist for more specialized testing.
Make your appointment with IRIS today for your comprehensive eye exam.
