If my eyeglasses percription is -4.25 diopters, what is my vision on the 20/20 scale?

Question

I have no idea what my vision works out to be if measured on the 'standard' 20/20 scale. My eye doctor never told me. It seems that there should be some sort of rough rule to tell.

Answer 1

Eyegirl gives what sounds like a good answer but having 7yrs experience working with Ophthalmologists and Optometrists I can't understand what she is saying and I don't suppose you do either.
There is no way to answer your question without being there to see just exactlly what you are seeing. . with and without your glasses.
With a prescription of -4.25 diopters I would say that your vision without glasses your vision probably is something like 20/400 which like eyegirl tells you means that you see an object at a distance of 20 ft which normal sighted persons could see at 400 ft.
When you are fitted with corrective lenses,your Opthalmologist or Optometrist is going to try their best to get you to seeing as close to 20/20 as they can but with some people's visual problems this is not always possible and I would guess that with your prescription at best you are probably only seeing the letters on the eye chart about in the middle of the chart which means you are probably seeing somewhere between 20/50 or at best 20/40.
Please be sure to keep regular with your eye exams as you vision is likely to change over the years and this change needs to be watched.

Answer 2

Actually, there is not a conversion factor to go between the two. For example, someone could have a disease process that reduces their vision on the 20/20 scale but which a glasses prescription would not help to compensate for.

Also, if astigmatism is present, it can also affect what line is read on the 20/20 scale.

With an Rx of -4.25 I would guess that you read somewhere around 20/400 (without glasses or contact lenses)- this translates into you needing to stand at 20 feet to see a letter that a person with "normal" vision could see at 400 feet.

in response to the comment below:
Having an Rx of -4.25 and otherwise healthy eyes, there is no reason you should not be able to easily be corrected to see 20/20 with your glasses.

Answer 3

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RE:
If my eyeglasses percription is -4.25 diopters, what is my vision on the 20/20 scale?
I have no idea what my vision works out to be if measured on the 'standard' 20/20 scale. My eye doctor never told me. It seems that there should be some sort of rough rule to tell.

Answer 4

-4.25 is approximately 20/1000. This is not how we usually notate it though. The previous answers are partly right but ME states something incorrectly. He says that you can see at 20 feet what a "normal" eye could see at 400 feet. Not exactly true. If you are 20/20 it means you can see a size 20 letter at twenty feet. If you are 20/40 you can see a size 40 letter at 20 feet. Next question..what the heck is a size twenty letter? It is a unique unit of measure that blah blah blah. The reason your doc didn't tell you is because it doesn't really matter that much. He/she was a lot more concerned with what you could see with correction. If you want to know for your own sake though, ask next time...I am sure they would show you. If you are really interested in the nuts and bolts of the eye chart and all its nuances check out this wesite....The rule of thumb you ask about is for each line there is approximately -0.25 of "nearsightedness" (in your case and making a few assumptions such as no astigmatism). The Big E at the top in this case is line 11. which works out to be about -2.75....not as bad as nearsighted as your vision. After 20/400 the rule tends to break down a bit.

Answer 5

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Answer 6

Diopter Scale

Answer 7

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