What is 20/10 vision exactly?!

What is 20/10 vision exactly?

1) And frankly is there really a lot of people with 20/20 vision? Are they generally young people?
2) How about those who is farsighted (ie. need reading glass), do they have something like 20/20 chart too?

1 week ago
i thank you for your kind explanations! :=)

Princeidoc has given you a good answer. Let me see if I can add my two cents. He is right in that 20/20 is not "perfect" vision. It is called "standard visual acuity". Many humans are capable of seeing better than standard visual acuity.

As he said, 20/20 means a person is able to see the standard 5 minute arc letter at a distance of 20 feet. Now, let's say a person has 20/10. 20 divided by 10 equals 2. Therefore a person with 20/10 visual acuity would be able to stand 2X as far from the chart to see the 20/20 line as a person who has only 20/20 acuity. So a person with 20/10 would be able to see the 20/20 line at 40 feet from the chart. How about a person with 20/40 acuity? 20 divided by 40 equals 1/2. So a person with 20/40 visual acuity would have to stand 1/2 the distance to the chart (10 feet away) in order to see the same line as a 20/20 person. A 20/80 person would have to stand 5 feet from the chart to see the 20/20 line and so on.

As to age, most patients are capable of seeing 20/20 at distance into their 60's. As we age, though, cataracts become a common age related condition that can cause a drop in visual acuity below 20/20 standard acuity. After cataract surgery, though, almost all can again achieve 20/20 distance visual acuity.

We need to now discuss what farsightedness is. It is commonly wrongly believed that farsightedness means one has to wear reading glasses. Farsightedness simply means that in order for a person to see clearly at DISTANCE they must focus their eyes to some degree. Because young people (those below 45 or so) have the capability to adjust the focus of their eyes, those who are slightly or even moderately farsighted many time don't need to wear reading glasses. It isn't until they reach the age of 40 to 45 and develop PRESBYOPIA that reading glasses become necessary. It is the age related loss in focusing (presbyopia) that necessitates the use of reading glasses. It is true, though, that patients who are farsighted do tend to start wearing reading glasses a little earlier than others because since they are already exerting a significant amount of focusing just to see at distance, it doesn't take as much of a presbyopic loss in focusing to cause symptoms.

As far as 20/20 for farsighted people goes, if a patient has only a small amount of farsightedness they may maintain the ability to see 20/20 at DISTANCE without glasses their entire life. Of course, they will see a decrease in near visual acuity associated with the development of presbyopia.

WHEW! That was a mouthful! Hope I didn't totally confuse you. Hope this helped.