Dumb Quesiton, but what do the perscription numbers mean

[Bob]

Yep, I know I should know this, but I just went and had my glasses evaluated for their perscription at Costco. What I wanted to know was what do these numbers mean in terms of was I 20/100, 20/200 or what? As I was walking away from the counter I thought I heard the lady say that I was about 20/50 in my left eye, but this can't be right because when I started I couldn't even come close to reading the 20/50 line on the Snellen chart -- though, at times, with my left eye I can now.

Anyway, here is/was my perscription . . .

Right Eye: -2.75  -1.00 X 84
Left Eye:  -1.00  -1.50 X 82

I was just wondering . . .

Thanks,

Bob

P.S. by the way, for those of you who are wondering, my daughters eye sight is noticeably improving. She's not perfect yet of course, but she's noticeably better.

[otis]

Dear Bob,

As you may have guessed -- I do not "trust" these prescriptions.  I do suggest the following:  Always check your kids vision youself.  I have an easy-to-use Snellen (Eye-chart 2) on my site to make this very, easy.

<!-- w --><a class="postlink" href="http://www.myopiafree.com">http://www.myopiafree.com</a><!-- w -->

Only when they begin to "trust" their own readings -- is preventive success possible.  (By Bates or any other method.)  You believe results only when you SEE THEM YOURSELF.

Further response:


Yep, I know I should know this, but I just went and had my glasses evaluated for their perscription at Costco. What I wanted to know was what do these numbers mean in terms of was I 20/100, 20/200 or what?

Otis> There is no exact relationship, but generally a -1 to -1.25 diopter will clear 20/70 vision to 20/20.


As I was walking away from the counter I thought I heard the lady say that I was about 20/50 in my left eye, but this can't be right because when I started I couldn't even come close to reading the 20/50 line on the Snellen chart -- though, at times, with my left eye I can now.

Otis>  Always check yourself.

Anyway, here is/was my perscription . . .

Right Eye: -2.75  -1.00 X 84

This would be about -3.25 spherical equivalent, or about
70 x 3.23 or 20/220 approximately.


Left Eye:  -1.00  -1.50 X 82

(This would be a spherical equivalent of about -1.75 diopters,
or about 20/80 vision (as my best guess.)

Reading the chart with both eyes open would give
you about 20/80  (you always see with the better eye.)

I was just wondering . . .

Thanks,

Bob

P.S. by the way, for those of you who are wondering, my daughters eye sight is noticeably improving.

She's not perfect yet of course, but she's noticeably better.

Otis> I assume you know this because she is reading the Snellen at 20/40 or better.

Best,

Otis

[Bob]

Thanks for the info Otis!

Bob

[otis]

I am always pleased to help.

I think that your checking your kids vision on the Snellen -- will enable you to exert preventive control -- far more than most parents.

Best,

Otis

[bjsilva]

P.S. by the way, for those of you who are wondering, my daughters eye sight is noticeably improving. She's not perfect yet of course, but she's noticeably better.

Awesome! It's things like this that can be a real encouragement to people doing the Bates method who may have doubts.

[js519]

Perhaps directed at Otis, or maybe anyone else who knows how to do that conversion...

So what would
Left: -3.50 sph, 2.50 cyl, 176 axis
Right: -3.00 sph, 2.00 cyl, 5 axis
mean?

Does the fact that you always see with your better eye change if my left eye is better but I am dominantly right-eyed?

[otis]

Dear Joe,

What this prescription means is that you are myopic with
a substantial amount of astigmatism.

So what would mean?

Left: -3.50 sph, 2.50 cyl, 176 axis

The spherical equivalent would be:  -2.25 diopters

This would work out (roughly) to be 70 x 2.25 or 20/160 on the Snellen.


Right: -3.00 sph, 2.00 cyl, 5 axis

The spherical equivalent would be:  -2.00 diopters, or (roughly) 20/140
on the Snellen.

(I assume the astigmatism number is positive.  You take 1/2 the value and add it to the spherical to get the spherical equivalent.

Best,

Otis

[js519]

Hm... I didn't really pay attention to whether my astigmatism was positive or negative. Thanks, though.

[otis]

Dear Joe,

Most ODs write the "astigmatism" as negative.

If that is the case then divide by 1/2 and SUBTRACT
from the spherical.

This would make your you Snellen reading worse.

Best,

Otis

[karo]

Hello

could anyone explain what is the difference betwen vision 10/10 and 20/20 i think none but i would like to see what others think.

by karo

[otis]

Dear Karo,

Subject:  Origin of the Snellen Chart.

The orginal intent of the "distant" chart was to get
the chart as far away as possible -- consistent
with office space.  (About 1864.)

This turned out to be 20 feet or 6 meters.

Thus if you could read 3/8 inch letters at 20 feet,
you had 20/20 vision.

But as a compromise, for shorter rooms, you can
measure at 10 feet.  The size of the letter would
be 1/2 the 20 foot distance.  There is some
loss of accuracy at 10 feet.

Thus the expression 20/20,  10/10,  or
6/6 or 3/3 all describe about the limit
of BEST human visual acuity or the
ability to "resolve" 5 minutes-of-angle
letters at "distance".

Best,

Otis