question concerning vision

[thedman]

i was wondering...
is it possible to determine someones vision from thier glasses.

for example, say they have high myopia and thier glasses is like +7 diopters. from that info can you determine what their vision is with out glasses. they have 20/? vision.

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[cpw]

it doesn't really correlate like that. Someone with high myopia would be a -7 by the way.

It's usually 0.25D for every line on the chart, but once you get over -4 you run out of chart (at least on a standard snellen)

As far as I know there's no real equation for it.

 

[rpames]

Just to clearify what CPW said: The 0.25D rule only works for myopes, not hyperopes.

 

[iiiidave]

A person?s acuity depends somewhat on variable factors. Pupil size is probably the most important, smaller the pupil the better the vision, a persons ability to discriminate blur, more importantly a persons wish to discriminate blur. If you ask a patient to read the lowest line possible on the snellen chart they will usually stop short. I think it is because most people don?t like to be wrong. Also if you have them read from right to left they always read better (99%). Those of you that have the opportunity to try this do so, it is very interesting.