# Visual acuity to Diopter conversion

Posted , 5 users are following.

I have found a chart that converts visual acuity to diopter.

From all the defocus charts I found that a monofocal set for distance has visual acuity drop below 20/32 from 33" to 0". Specifically from this post

https://patient.info/forums/discuss/monofocals-set-for-distance-806866

Specifically its around 20/100 at 12"

which is a diopter of -2.0

I have a LeftEye of -2.0 . So does that mean that from 12" to 33" I will be able to see things as blurred as my left eye uncorrected vision? That would be an acceptable loss of focus for me with the monofocal lens.

Please let me know if I have accurately determined the loss of focus I would experience. Are there any errors in my calculation?

0 likes, 4 replies

## 4 Replies

• Edited

1. Are you looking at the image attached to the first response on that thread?
2. Are you looking at the dashed line? I think the dashed line is for somebody set to 4 meters-- about -0.25D, but that is close enough to plano for this purpose.

Your 20/100 vision level conclusion seems to be in the ballpark. To read a newspaper or the ingredient list on food, etc, that 20/100 is not going to get the job done.

• Edited

I got the 20/100 figure from this conversion chart

• Posted

Not quite understand what you are asking. But I know (heard) there's a rule of thumb to estimate the focal point FP (sharpest distance) for myopia.

FP = 100 / Sphere (no minus sign) in cm. Example: For -2.0, FP = 100/2 = 50 cm; for -1, 100 cm or 1 m etc. It seems to make sense. In my case, mine is (-8/-9), so I can see things most sharply at 100/8-9 or about 11-12 cm away from my nose. Hope it helps.

• Edited

A defocus curve is established by taking a large group of people that have vision fully corrected for distance, and then putting a series of + power lenses in front of them, while measuring their visual acuity with the lens in place. When you put a + 1.0 D lens in from of an eye with corrected vision at distance, they will become -1.0 D myopic. A + 2.0 D makes the eye -2.0 D myopic. As you make the eye more and more myopic the distance vision decreases. The curve is derived by plotting visual acuity vs lens power. However at the same time near vision improves. You can calculate that distance by dividing 1 meter by the diopter value. A diopter of 2.0 works out to be 1/2 a meter or about 19". The peak vision for someone with -2.0 D myopia is at about 19" or so.

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"I have a LeftEye of -2.0 . So does that mean that from 12" to 33" I will be able to see things as blurred as my left eye uncorrected vision?"

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If you look at that curves at the link I posted in that thread you will see that at 0.5 meter the visual acuity of a distance set eye is about 20/63. Then if you look at the 2.0 D curve you will see that visual acuity when you are -2.0 D myopic is about 20/63 at just over 2 meters or about 7 feet. So you could roughly estimate your vision with distance set IOLs by looking at an eye chart with your myopic eye now when you set the eye chart at a distance of about 7 feet.

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Kind of convoluted, but that is the way I think it works.

#### Thanks for your help!

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