How do you use the snellen chart?

[velove]

I know how to grade the chart, how far away the chart should be and all that, but the one lone fact I can't figure out is... how many letters can the pt get right to count the line? Do they have to read all the letters on the line? Or just half? I've tried googling it and get both answers.

Thanks!

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[Blondiechick919]

I know how to grade the chart, how far away the chart should be and all that, but the one lone fact I can't figure out is... how many letters can the pt get right to count the line? Do they have to read all the letters on the line? Or just half? I've tried googling it and get both answers.

Thanks!

chart is supposed to be at optical infinity (20 feet) but some exam lanes are not exactly, so the projector compensates. If the person gets one letter wrong on the 20/30 line, you record it as 20/30 -1. If they get all but one or two on a line wrong, list it as 20/xx +1, etc.

 

[4Eyes]

I would add that if, for example, a pt gets 20/40-2 but also reads 20/30-2, they still technically only get credit for the 20/40-2. (In the real world, though, I may jot down if they get some of the 20/30 letters too.)

 

[velove]

chart is supposed to be at optical infinity (20 feet) but some exam lanes are not exactly, so the projector compensates. If the person gets one letter wrong on the 20/30 line, you record it as 20/30 -1. If they get all but one or two on a line wrong, list it as 20/xx +1, etc.

So then even if they only read one letter on a line, you give them that line?
But if they only read one letter on two lines, you give them the worse vision?

I am doing a psychology research study where I need pts with 20/20 vision- so really it's just a simple screen, so we don't need to record vision as 20/30 -2.

 

[jc328]

For your purpose, if your patient can read half of the 20/20 line correctly, then you can record 20/20. If they can only read 1 or 2 letters of the 20/20 line correctly, then they are not 20/20.

 

[syma]

If you want them to read 20/20 then you need them to read all the letters on the line with the chart placed at 6 metres (20 feet)