问有眼科医学知识的妈妈? 能不能帮我解释一下这段话

[skyeye]

Vision. You must have a distant visual acuity of not less than 6/9 in metric (20/30 in feet) in each eye separately with or without the use of correcting lenses. Where the standard of visual acuity can be obtained only with correcting lenses, you may be assessed fit provided that:
1.

you wear such correcting lenses when exercising the privileges of the license or rating applied for or held;
2.

you have a visual acuity without correction in each eye separately of not less than 6/60 in metric (20/200 in feet) and the refractive error falls within the range of plus or minus five diopters (equivalent spherical error); and
3.

you have a spare pair of suitable correcting glasses available for immediate use when exercising the privileges of your license.

 

[kliu]

Sounds like what's said on the driver's license regulation. What it basically means is that your license is conditionally granted that you must be able to see clearly. The so-called perfected vision is 20/20, but they are only requiring 20/30. If you need to wear glasses to reach that 20/30, then you must either wear it or have it around and are ready to use it when needed.

 

[skyeye]

thanks

I know this means? but 20/30 is 1.0 or 1.2, the perfect is 1.5.
so I want to know 20/30 what's meaning?
thanks

 

[kliu]

20/30 means you can read a letter from 20 feet while a normal person can read it from 30 feet. So, that vision is less than a normal person, but can still see thing clearly in an acceptable distance.

I'm not sure what you mean by 1.0, 1.2, 1.5, but you can see the conversion chart at the link to find your answer.

Conversion table as below
http://www.biopticdriving.org/repository/main/VA_T1_VA_convert.pdf

If you are looking at your own prescription, here's a sample chart from a doctor for nearsightedness (approximate only)

Snellen Estimated prescription
20/10 Plano (zero)
20/15 Plano
20/20 Plano to -0.25
20/30 -0.50
20/40 -0.75
20/50 -1.00 to -1.25
20/100 -1.75 to -2.00
20/200 -2.00 to -2.50