visual acuity testing

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When using the Snellen eye chart a person is to stand 20 feet from the chart, and the results are recorded as eg. 20/20 or 20/30 etc. I understand that the top number indicates the distance the person is standing from the chart, and that the bottom number gives the distance at which a normal eye could have read that particular line. It's straightforward when it's 20/20 - but how does the examiner know when it's 20/30, 20/40 or 20/50, etc. - how is the denominator determined?

Does the chart provide the denominator beside each line?

Thanks.

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hi again - is anyone doing visual acuity examinations?

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Specializes in Home Care, Urgent Care, ER, Med Surg.
hi again - is anyone doing visual acuity examinations?

If I remember correctly, the chart I used had the 20/30, etc by each line of letters. Do you know what I mean?

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thanks - I'll search around, that's what I was hoping.

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Specializes in ORTHOPAEDICS-CERTIFIED SINCE 89.

1240snellen.jpg

Exactly. Then you get people like me who while being very nearsighted have a 20/10 acuity closeup but can't see a darned thing at a distance without glasses.

If I remeber correctly the tiny figures on the left of the chart are the acuity, and the 1-2- 3 etc are line numbers...."read line 6 please."

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Does anyone know how many letters you are allowed to miss to get your results on the Snellen chart? I vaguely remember reading you could miss one or two letters, but I"m not for sure and cannot find it anywhere.

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Specializes in Med/Surg, Geriatrics.
Does anyone know how many letters you are allowed to miss to get your results on the Snellen chart? I vaguely remember reading you could miss one or two letters, but I"m not for sure and cannot find it anywhere.

It's usually one letter.

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Snellen chart is easy to do

yes there are denominators written to one side.

(as I age, I must get closer to read that number after the pt gets thru!)

Our ED allows missing 1 or 2 and we test each eye individually, then together.

To be done on all eye c/o, trauma or medical, to be done pre-topical analgesic gtts if at all possible. If a poor first attempt pre med, we try again after gtts

I was advised somewhere in the last 22 yrs to ask person to "Cup" hand over eye without applying pressure and gave a patient a moment to "adjust" before asking them to tell you which line number being attempted and proceeding.

(Can't give you a solid reference on that advice though)

Did that help, I hope?

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Yes it helped a lot. Thanks. I always test each eye individually but didn't know to check them together. Thanks again for the info.

Snellen chart is easy to do

yes there are denominators written to one side.

(as I age, I must get closer to read that number after the pt gets thru!)

Our ED allows missing 1 or 2 and we test each eye individually, then together.

To be done on all eye c/o, trauma or medical, to be done pre-topical analgesic gtts if at all possible. If a poor first attempt pre med, we try again after gtts

I was advised somewhere in the last 22 yrs to ask person to "Cup" hand over eye without applying pressure and gave a patient a moment to "adjust" before asking them to tell you which line number being attempted and proceeding.

(Can't give you a solid reference on that advice though)

Did that help, I hope?

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