20/20- Not Just Another Number

There of plenty of people who have heard of 20/20 vision but very few who actually know what that truly means. This is the term used to describe the normal clarity and sharpness of vision that can be seen at a measurement of 20 feet, it is also called visual acuity. If this is your vision measurement you will be able to well from all distances with in reason. Other variations in vision measurement tell if that person has near or far sightedness and to what degree. Having 20/20 vision doesn’t mean that your vision is perfect; it only tells you the clarity of your vision at a distance nothing more. Having good vision also include how good your side vision is, depth perception, focusing ability, eye coordination, and color vision.

All these skills measure how well a person's over all visual ability is. Getting routine eye exams will tell you what level your vision is at and if you need any corrective lenses to help improve it. Some people with vision problems wear corrective lenses; either glasses or contacts, while other people have only a slight problem that is corrected with sort of vision therapy to improve it. Regular exams will also let you and your doctor know if you have an eye disease that needs to be treated to prevent future vision problems.

Actual visual acuity is measured by at what angular size you can see the smallest details at a distance and is called spatial resolving power. This must be measured for such purposes as determining the appropriate prescription that allows the best visual acuity so glasses or contacts can be gotten. The patient first notices many indications of eye diseases as visual disturbances so the doctor would look at the eye to determine if it is truly a vision problem or actually an underlying illness in the eye. In order to have great everyday performance and ability to see reading material clearly and with least amount of eyestrain, one must have good visual acuity. Many people must focus on fine details everyday, whether it is at work, home, or any other place. We rely on our eyes to pick up all the detail that is around us to give us the information we are looking for. Many of the daily tasks we take for granted are inspecting things for scratches, reading labels, gauges, and dials, and many more. We need good vision acuity to drive a vehicle and be able to know where we are going, read signs, and avoid hazards on the road.

When the doctor hands you a prescription it reads as a fraction. The top number is the measured distance of 20 feet. The top number is the smallest detail you can focus on at the 20-foot distance. The higher the bottom number is the worse your visual acuity is and the closer you would have to stand to see what a 20/20 person could see at 20 feet. The smaller the bottom number is the better the vision, if the number is below 20 than you would have better than normal vision. So a person with 20/10 vision can see things at 20 feet that a normal person would have to be at 10 feet. Some of significant visual acuities are:

A)  20/20 vision is considered normal vision
B)  20/40 vision in at least one eye is the vision required to pass the driving test
C)  20/200 vision or worse is the legal definition of blindness

Vision tests are done on each eye separately to determine the acuity of each eye alone. Many people don’t have the same acuity in both eyes. You will be sat in the chair and asked to put your chin on a rest with a machine that looks like extra large glasses. This machine will help determine what your visual acuity is by reading the letters on a chart on the wall in front of you. You must be able to read 50-75% of the first 6 lines of the chart to be considered 20/20 vision. The top letter is 20200 and id a person cannot read this with the best glasses they are considered legally blind. The second line on the chart is at 20/100 and the third line is 20/50. If you range in this area you would be considered disabled for occupations that require a lot of reading or numerical work. The forth line is 20/40 and is the line you need to be able to read to pass a drivers test in order to not be restricted on your license. The most commonly believed maximum acuity is at approximately 20/15. If you can read the bottom line of the chart well, you are probably guessing.