my son's vision

my son's vision diagnosis was OD: -2.00 + 0.50 x 180
OS: -2.00 sph

What does this mean in general? And would this be considered a
Negative 2.5, 3.5, etc? I am looking into buying my son goggles with a
somewhat corrective lense and I am not sure what to look for to best
suit him.

THANK YOU!!

(E-Mail Removed) wrote:
> my son's vision diagnosis was OD: -2.00 + 0.50 x 180
> OS: -2.00 sph
>
> What does this mean in general? And would this be considered a
> Negative 2.5, 3.5, etc? I am looking into buying my son goggles with a
> somewhat corrective lense and I am not sure what to look for to best
> suit him.
>
> THANK YOU!!
>

This means your son is short-sighted or myopic.

If you are buying swimming goggles then the closest equivalent would be
R either -1.50 or -1.75
L -2.00

Dom

On Apr 18, 12:48 pm, "Katie via MedKB.com" <u12444@uwe> wrote:
> Dom, it looks like you've subtracted the +0.50 from the -2 to get a -1.50 or -
> 1.75.
> Does that mean then that if someone has a minus prescription with plus cyl
> that it makes it less strong than a minus prescription with minus cyl? What
> if I'm -2.50 with -0.50 and my friend is -2.50 with +0.50, whose vision is
> worse without glasses?

I join this question. I have noticed that there are 2 ways of writing
the same Rx for myopia (I am not familiar with other kinds of Rx, so
my question is limited to myopia with astigmatism). It seems to me
that the 2 following Rx examples are idintical:

#1. Sphere: -3.00 Cyl: -1.00
#2. Sphere: -4.00 Cyl: +1.00

Mathematically speaking it doesn't make much sense, since -3-1=-4,
whereas -4+1=-3, thus the prescriptions are not equal, but I believe
that in the optomeric world they are. Am I correct?

Moreover, would you say that this person refractive correction (I hope
I am using the proper term) is -3 or -4?

On Apr 18, 4:21 pm, "Mike Tyner" <mty...@mindspring.com> wrote:
> "Ms.Brainy" <mikabra...@gmail.com> wrote
>
> > #1. Sphere: -3.00 Cyl: -1.00
> > #2. Sphere: -4.00 Cyl: +1.00
>
> > Mathematically speaking it doesn't make much sense, since -3-1=-4,
> > whereas -4+1=-3, thus the prescriptions are not equal, but I believe
> > that in the optomeric world they are. Am I correct?
>
> Yes. One meridian (eg vertical) is -3.00. The other meridian (horiz)
> is -4.00.
>
> You can describe this as -300-100, or -400+100. The key is the third number
> you didn't list. If the first rx (in "minus cylinder form") says axis 90,
> the second version ("plus cyl") is axis 180. In the optometric world, 90 is
> the opposite of 180.
>
> > Moreover, would you say that this person refractive correction (I hope
> > I am using the proper term) is -3 or -4?
>
> The concept of "spherical equivalent" averages the -3 and -4 meridians to a
> spherical -3.50. That's a fair measure of how nearsighted, overall.
>
> -MT

Wow! I have a master degree in math, but this optometric math is
something else! Maybe I should consider it for a Ph.D. subject, LOL!

Anyway, you Mike, Dr Judy and the others are very helpful in clearing
up some of the confusion we common folks have. Thanks!

On Apr 18, 6:15 pm, Dave Bell <d...@TheSPAMFREEBells.net> wrote:
>
> As another non-optometrist, with some optics background, it was puzzling
> to me, too. I see the sense of it now, with the cylinder essentially
> accounting for 1/2 strength when approximated as a sphere - it only
> refracts on one axis.
> The 90/180 degree being "opposites" is strange, but again, it makes
> sense when (if I understood correctly!) you say a positive cylinder at
> 90 is similar to a negative cylinder at 180. Both would have a similar
> effect on the observed aspect ratio - squashing one axis or stretching
> the complementary one...
>

I am glad that Dave finds the sense in the "spherical equivalent", but
I am still puzzled... Adding (or subtracting, which seems to be the
same thing in optometric math) sphere and cylinder measurements appers
to me like adding (or subtracting) apples and oranges. My
understanding is that this "math" is an effort to express roughly the
refractive correction in one number. Is it?

This interests me not only from a mathematical POV, but also
personally, since I am facing a cataract surgery in my right eye (my
bad eye). I have been told that a disparity between the eyes (or the
correction? not sure) should not be more than 2D, but I have no idea
what this "2D" represents, and on the top of it I now don't even know
whether it's the "spherical equivalent" or simply the sphere. I will
present my troubling personal problem (and confusion) in a new thread,
perhaps tomorrow -- too late now.