-3.50, what should be my V.A?

Question

I mean, what lines should I be able to see from the chart with that approx. prescription?

Answer 1

It doesn't correspond with precision, but with a normal pupil size, about 20/300 (6/90)
Most test charts will have a 20/200 (6/60) top letter, so you wouldn't be able to see that at the normal test distance.
By moving closer to the chart until the top test letter is visible, an acuity can be registered: 16/200, for example, for someone who has to move four ft. nearer.

But: if you look through a 1mm pinhole in a piece of thin card held close to the eye, suddenly your vision will be a lot better.
This is why "squeezing" the eyes, (actually holding the lids half-shut, producing an artifical small aperture) seems to help the eyesight for a moment.

Answer 2

Do you mean with or without glasses on? You need to ask your doctor what acuity you have with your glasses on, it doesn't depend upon your prescription and needs to be measured.

It isn't possible to calculate glasses off VA from your prescription, but an estimate for your vision would be between 20/200 and 20/400 at far, assuming you have at least 20/20 with glasses on. Depending on the acuity chart that you are using (there are many different kinds) you may not read any lines or may see the top one or the top two with glasses off.

Answer 3

Normal eyes are focused at infinity. Near sighted people are focused closer than that. That's because their lens system is too strong for their eye.

P = 1/d where d is in meters.

If your eyes are +1.00 too strong, they are focused at 1 meter in front of you. Your doc would give you a -1.00 to move that focal point back out to infinity.
If your eyes were +2.00 too strong, you'd be focused at a half meter in front of you, you'd need a -2.00 lens.

If you were focused at a third of a meter in front of you, that'd be +3.00 too strong, you'd get a -3.00 lens.

quater of a meter, need a -4.00
fifth of a meter, -5.00
one seventh of a meter, -7.00

You are already focused at between a third of a meter and a fourth of a meter in front of you. So they give you a -3.50 to Rx your myopia.

How well do you see when you have your Rx on? THAT'S the measure of your vision, not the power of the lens that corrects your near vision to distance....

How well you see is two lines separated by a same width space, and you can still see that there are two lines and not one fuzzy one. Usually that's measured in degrees such as seen in an E. The E is 5 degrees high or one degree per line or space. When the lines get smaller and the spaces smaller, we can't make out the letter.

When you have your Rx, you should see 20/20.
How poorly you see without your Rx doesn't really count. Can't say take a picture with this camera, but don't focus it. If it's a close up lens on that camera, and you take a picture of the mountain over there and it comes out fuzzy, is it a bad camera? NO, it's just not focused at that distance. It would do just fine for the flowers over on the table close up.