Eye Exam Charts
An eye exam chart is an important kit for your eye improvement process.
If you have seen a eye exam chart before, you may be curious about how the eye chart was invented. The eye chart was first designed by a Dutch ophthalmologist, Herman Snellen in 1860s. At first, the purpose was to determine distance acuity (i.e. the sharpness or clarity of vision).
How to use an eye chart?
Our eyes are designed for distant vision. At 20 feet, the light rays that enter our eyes are parallel. There is no need for our eye to bend the light rays to focus them on the retina.
The 20/20 line in the eye chart indicates the size of print a person with normal vision could read when he stands 20 feet away.
Although we use foot as the unit of measurement in above illustration, we can also express it in metre. This is best illustrated in the table below. The 20/20 vision is equivalent to 6/6.
A visual acuity score of 20/20 is considered as normal vision. Visual acuity scores of 20/32 or 20/40 (i.e. 6/9 or 6/12 in metre terms) indicates the presence of significant but low-power refractive errors. Visual acuity of between 20/63 and 20/200 (i.e. 6/18 and 6/60 in metre terms) is moderate refractive errors. Those with severe myopia will not be able to see 20/200 (i.e. 6/60 in metre terms) without glasses. A person with worse than 6/60 visual acuity despite the best glasses correction, is considered as legally blind.
On the other hand, if you have 20/15 vision (i.e. you can read at 20 feet the letters that can only be seen by someone who meets the standard measure of normal eyesight), you are said to have good vision. A fortunate 5% of the population have 6/5 or 6/4 vision which is sometimes termed “eagle” vision.