Prism changed from one eye to the other

[k***@yahoo.com]

Hi,

For the last five years (3 checks) I have had a prism included in my
prescription (1 OUT in the LEFT eye). I have just had another
eye-check (18 months after last check) and my new prescription shows
the prism in the RIGHT eye, 1 OUT. On querying this, I have been told
that for small variations it does not matter which eyeglass has the
prism.

Is this a reasonable explanation? Also, as I always use my old glasses
for occasional use, will the continuous swapping from right to left
have any impact?

Thank you for your views

Regards Ron

[Mike Tyner]

Post by k***@yahoo.com
Is this a reasonable explanation? Also, as I always use my old glasses
for occasional use, will the continuous swapping from right to left
have any impact?

It isn't very important which lens has the prism in it. It only matters with
both eyes open, and it's only the difference between the lenses that
matters.

Prism adds thickness to one edge of the lens, so an optician might engineer
it into the thinner lens, regardless of the written prescription.

-MT

[k***@yahoo.com]

Very clear and reassuring. Thanks Mike

[William Stacy]

I slightly disagree, and tend to consider, in order of relative
importance: If there is a strong dominancy, I tend to put the prism in
the non-dominant eye. If there is a fixation disparity, I always ask
if one eye's image is displaced more than the other. If so, I put it all
in the deviating eye, if not, I split the prism equally between the two
eyes. If one eye has better best corrected visual acuity, I will put
all the prism in the less correctible eye. Finally, if one lens is
stronger than the other, I tend to put the prism in the weaker lens,
unless the prism will actually make either lens thinner.

Other than those considerations, I agree it doesn't matter. Oh, except
I would NEVER change the laterality of a prismatic correction without a
reason to do so...

w.stacy, o.d.

Post by Mike Tyner

Post by k***@yahoo.com
Is this a reasonable explanation? Also, as I always use my old glasses
for occasional use, will the continuous swapping from right to left
have any impact?

It isn't very important which lens has the prism in it. It only matters with
both eyes open, and it's only the difference between the lenses that
matters.
Prism adds thickness to one edge of the lens, so an optician might engineer
it into the thinner lens, regardless of the written prescription.
-MT