Difference between 20/20 and 6/6 vision

Difference between 20/20 and 6/6 vision

In this article, we will unfold the term of 20/20 or 6/6 vision.

6/6 vision is measured in metres (USA). By the 6/6 vision, we mean that you see an object clearly at a distance of 6 metres while an average person can also see the same object clearly at 6 metres. The same vision measurement in feet is 20/20. So this is the average normal vision that someone sees an object clearly at 20 feet while an average person can also see the same object clearly at 20 feet. A person can have better vision as compared to 20/20, e.g. 20/16 it exhibits that you can see an object clearly at twenty feet while an average person can only see the same object clearly at 16 feet. In a similar way, if you have 20/40 vision. It shows your vision is weaker than that of an average person; what an average person sees clearly at 40 feet, you see it clearly at 20 feet.

Visual acuity

Visual acuity means how sharp your vision is. The eye specialist measures the visual acuity of a patient by his or her ability to identify letters or numbers on an eye chart from a specific distance.

What is 20/20 vision? 

Herman Snellen, the Dutch ophthalmologist, originated the visual acuity measurement system in 1862. So his measurement fractions are named after his name as a Snellen fraction.

The terms 20/20, 20/40, 20/60, etc. are visual acuity measurements and are called Snellen fractions. What do these fractions mean?

In the Snellen visual acuity system, the top number (numerator) of the Snellen fraction is the distance at which the patient sees the eye chart. 6 metres is almost equal to 20 feet. Some countries measure this distance in feet and some in metres. So it does not matter because 6 metres and 20 feet are the same distance. 

In the bottom of the eye chart, the sizes of the letters on one of the smaller lines correspond to “normal” visual acuity. This viewing distance is taken as standard. It is called the “20/20” vision line. If you can see clearly the letters on this line, your vision is normal (20/20).

In the Snellen chart, the larger letter sizes on the lines above the 20/20 line are in accordance to worse visual acuity measurements (20/40, 20/60, etc.); the lines with smaller letters below the 20/20 line on the chart are in accordance to visual acuity measurements that are even better than 20/20 vision (e.g., 20/15, 20/12, 20/10).

The visual acuity of a legally blind person is 20/200. The single big “E” at the top of the Snellen eye charts is the smallest letter size a legally blind person can identify with his or her best corrective lenses in front of eyes.

Visual acuity better than 20/20

Of course, there is a possibility of having sharper than 20/20 vision. The people with such shaper vision are usually young or have healthy eyes. They can identify at least some of the letters on the 20/15 line or even smaller letters on the Snellen chart. On the other hand, 20/10 visual acuity is twice as sharp as that of a person with normal (20/20) vision.

Use of lenses to sharpen eyesight

Nowadays the better printing methods have made it possible to print smaller letters than those on the 20/20 line of Snellen eye chart. Therefore “normal” visual acuity today is a capability to discern letters of smaller than those on the 20/20 line.

Moreover, the ageing factor affects the visual acuity of the people typically. Similarly, early cataracts do the same. Hence one has to consider the larger letters than those on the 20/20 line. The adults in their 60s or older also have the same issue with “normal” vision.

Apart from the above scenarios, suppose you have 20/20 vision, and you may think about getting sharper eyesight. Then what will be the solution?

If your 20/20 vision is not sharp enough, your eyes may have higher-order aberrations (HOAs). The regular eyeglasses or soft contact lenses cannot correct HOAs. In that case, the eye specialist will check your eye for these aberrations with wavefront technology. 

Small irregularities in the front surface of eyes can cause HOAs. In such cases, gas permeable contact lenses (GP lenses) help improve the visual acuity in a better way as compared to the eyeglasses or soft contact lenses. Being rigid, GP lenses provide a perfectly smooth, curved surface to focus light accurately.

The glasses with special high-definition lenses are usually helpful in correcting refractive errors to get sharper vision than regular eyeglass lenses. Another option for the improvement in your vision is laser surgery. The personalised laser vision correction surgery LASIK can provide better vision. 

Consulting an eye specialist

For a comprehensive eye exam, you will have to consult an eye specialist who can perform a comprehensive visual evaluation. If you want to sharpen your vision better than glasses or contacts with the help of laser vision correction could, then you need to consult an experienced LASIK surgeon.

Lastly, although your child has 20/20 vision but still has some vision problems in school, then you better consult an eye care provider who would evaluate your child’s vision for possible learning problems.

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