Contents
An optometrist measures vision at a standard distance of 6 meters or 20 ft. And a normal vision is 6/6 or 20/20, which means you can see at 6 meters what a normal person also sees at 6 meters, likewise 20/20 means you can see at 20 feet what a person with normal vision can see at 20 feet. The only difference in 6/6 and 20/20 is in the unit of measurements. These measurements are called, ‘visual acuity standard’ according to the Snellen chart, given by the ophthalmologist, Snellen.
Snellen chart consists of 11 rows of letters that are used to measure visual acuity. The 11 rows of letters are in decreasing order with respect to the sizes of these block letters. The topmost rows have the biggest letters and the size of the letters keeps decreasing as you go down.
A person with visual acuity 20/200 is termed as “legally blind”; however different countries have different measurements to determine blindness. Many optometrists use an improved chart to measure visual acuity now.
Visual acuity refers to the clarity and sharpness of vision. An optometrist measures your visual acuity with the help of a chart of letters. It is a way to examine a person’s ability to notice the small details at distance.
If you have ever had your eyes checked up, then you must have read the chart of letters against the wall, it is your eye power and visual acuity test. The patient sits at a distance of 6 meters or 20 feet away from the eye chart. If you can read the last letter without any glasses then your visual acuity is 6/6 that is normal. But if you need glasses to read it then you have poor vision. A patient may need a different number of eye corrective, for example, a person may see normally with a diopter of 0.5 while another may need 2.5D depending on the eyesight.
Distance 6/12 vision means that you can see at a distance of 6 meters what a normal person can see at a distance of 12 meters, meaning thereby you have poor vision and need to stand closer to see the object. Similarly, 6/9 vision means a person can see at a distance of 9 meters what you see at 6 meters. You can have a better vision than 6/6, if your visual acuity test is for example 6/4 that means you can see at 4 meters what a person sees at 6 meters. However, if you have this above-average distance vision then you may find it hard to see nearer objects. Therefore, you may still need glasses for seeing near things.
Now, there is one question that arises in the patient’s mind that how much diopter lens he/she will need with 6/12 distance vision. The answer is eye power and visual acuity is two different things. You cannot determine your eye power test through this score (6/12, 6/6). Even if you have 6/6 vision that does not mean your vision is perfect. You may have other eye disorders like farsightedness and presbyopia and astigmatism. Visual acuity test only indicates if you need correction for distance vision or not.
In India, more than 60 million people acquire some kind of visual impairment. It surely affects the quality of their life. With inventions, technological advancement, visual impairments can be examined and treated for sure.
There could be several factors affecting your vision-
6/12 vision are not that bad and you can do almost everything with glasses on. But if you aspire for a profession that requires a perfect vision then you will need surgery. In a profession like a doctor, pilot, firefighters they need a perfect vision as it includes saving others’ lives. You can’t get any vision impairment to get inhe way. Even to drive you to need a normal vision. However, in countries like Australia, people with distance 6/12 vision are allowed to drive with or without glasses but many countries do not permit it. In India, 6/6 is standard vision acuity for jobs like navy, railways, and army.
Everyone’s eye power and visual acuity differ. Genetic factors also play an important role. Someone with 6/12 vision may have normal vision without eyeglasses. Although it is rare. Whereas someone with 6/6 may need eyeglasses. So 6/6 does not mean perfect vision and they may need eyeglasses. To conclude, 6/12 visual acuity does not tell anything about eye power.