how do I find out my visual acuity based on my eyeglass prescription?

Question

I just recently got new glasses and have a copy of my prescription. It gives me numbers for both my left and right eye and was wondering how I figure out me visual acuity (20/20, 20/50, etc.) from this prescription. It says SPH -4.00 and -4.50, CYL -2.00 and -1.25, and Axis 007 and 170 for my right and left eyes, respectively. Can anyone help me figure this out? Or at least give me a link to a website that can calculate it. Thanks!

Answer 1

You can't calculate your VA from your prescription, as it does not depend upon it. Corrected VA depends upon the health of your eyes. You could be legally blind and not need glasses at all or have perfectly normal vision with a prescription of -15.00,

Call your doctor and ask. He/she would have recorded your visual acuity with the new prescription. Don't be surprised if your visual acutiy without glasses (I suspect this is the number you want) was not measured; it is not a standard thing to measure.

Answer 2

Better answer:
https://en.wikipedia.org/wiki/Eyeglass_prescription#Cylindrical_lenses_and_cylindrical_correction
All perfectly explained. Adjust your Rx (SPH+CYL) to your axis (90˚ =1.00) and then you get your unmodified Rx.
Take that, and apply the Snellen chart.
Literal version:
—.50 D 20/50
—1.00 D 20/100
—2.00 D 20/200
—3.00 D 20/300
—4.00 D 20/400
—5.00 D 20/500
—6.00 D 20/600
—7.00 D 20/700
—8.00 D 20/800
—9.00 D 20/900
—10.00 D 20/1000
A modified probably more accurate version I found online:
20/30 0.50
20/40 0.75
20/50 1.00
20/70 1.25
20/100 1.50
20/150 2.00
20/200 2.50
20/250 3.00
20/300 3.50
20/400 4.50
Anyway:
That will give you your rough vision.
Like I have astigmatism lenses, -5.75, and then I have -1.00, which would mean a total of -6.75, but the axis is 45/135, bother of which are 45˚ off of straight, so that means +0.50, so my literal Rx would be 6.25 w/o astigmatism correction.
So my unmodified vision would be 20/650 or so.

My qualifications, none. I ve worn glasses all my life, and pay attn. because we have an optical engineer in the family who made the machines with the little red dot, so I pick these things up.

Also I get sick of the intentionally ignorant "you can t tell" responses, and the "i want to save my job so i ll tell you it s impossible" reponses. Nonsense. I own a bookstore, I know my job is obsolete. To be the last guy standing, you just have to do a better job. If you don t want people buying a DIY machine for $250 and then $10 a pair from an online import house, then make it worth your while.

My last visit to the optometrist was two weeks ago. He didn t even examine my eyes, just added 0.25 to each Sphere. I could have done that, in fact, I already had. If you re an optometrist: Don t be that guy. Make added value. Don t go spreading myths on the internet.

Of course a random internet user can use wikipedia and a snellen chart to find out what their vision is based on his Rx. Maybe it won t be exact, but it beats someone telling him or her that "It s magic!"

Answer 3

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Another simple way to put it is that if you are seeing 20/100 on the chart , it in no way tells the Dr. WHY you are only seeing 20/100 , it could be any one of several reasons., and it doesn't tell him what correction you need to regain 20/20 either. A refraction is needed to find out the reason why the vision is less than normal. All the chart tells is that you can determine with a certain sharpness, black letters on a white background. People who are worse than 20/300 can't even see the chart without a correction to start with , so the chart is of little use except to determine when they are able to see 20/20 again. So, in other words, the chart is used to determine how good a vision is possible with a given correction rather than how much of a correction is needed. So it stands to reason, the powers needed are not based on what lines can be read. In the lower powers, we can make an educated guess as to what the uncorrected VA might be based on the average of those who wear that similar prescription. But if there is astigmatism involved, or even hyperopia, then even an educated guess could be way off.

Answer 4

You basically can't calculate your visual acuity based on your prescription-your glasses where prescribed to help you getting best corrected visual acuity but the only way to know about your BCVA would have been asking your specialist while you where examined.It has nothing to do with your prescription-there are people who are emmetrope that means their glasses are equal to zero-but there visual acuity is not even nearly 20/20

Answer 5

Here is my understanding of visual acuity and how it is measured. if you scored 20/50 I believe this means that the smallest letter the respective person can see at 20 feet could be seen at 50 feet for normal eyesight. For more information check out this link.
http://www.mdsupport.org/library/acuity.html

This article does not give any comparison between a prescription above -2.00 and its respective visual acuity. Infact the link above states that anything above -2.50 (approximately) is considered legal blindness. I am not sure if the informaiotn in the site above will help better understand visual acuity but I hope it does.

*Please do not quote me on this information I am not a eye care provider and the information I relayed is found within the mentioned link above).

Answer 6

What Is My Visual Acuity

Answer 7

There's no direct correlation.
Someone with eye disease could have almost no Rx, say -0.50, but have 20/200.

With your Rx, healthy eyes and most importantly a normal pupil size, your unaided vision will be about 20/300.
The aim of the Rx, whatever its numbers, is to focus your eyes to the best they are capable of. Like tuning a radio: it's the right spot, not more is better. Go too far and it gets worse, not better.
With the right correction, most young adults with healthy eyes can get slightly better than 20/20. 20/18 perhaps.

Why pupil size? Make a 1mm hole in a piece of paper , hold it to your eye *without* glasses and look in the distance. You'll see a lot better with the pinhole than without, but there's no Rx change, or lens.

Answer 8

Learn How To Improve Eyesight!

Answer 9

1

Answer 10

agreed with pedestal (like i do most of the time!)

no direct linear relationship between Rx and acuity. its never as easy as it seems.