Reducing eyeglass prescription

I wrote a few weeks ago about astigmatism. Thanks to those who helped
me understand.

Here is my new prescription:
OD: -1.00 SPH (+1.25 ADD)
OS: -0.75 +.025 080 (+1.25 ADD)

I ordered a pair of lined bifocals from Zenni, and they are great. I
was really impressed with the them! That said, I believe my
optometrist overcorrected me. Although I can see very sharply in both
eyes at distances beyond 2 to 3 feet feet, anything from 8 inches to 2
for 3 feet is blurred. My eyes struggle to try to focus around my
desk at work. So, I just take my glasses off (I can see well without
my glassses). Closeup work (less than 8 inches) is perfect with the
glasses on.

So, I want to go down 1/4 diopter in each eye (my spheres were -.75
and -.50 for many years). The right eye would go down to -.75, but
how would I reduce my left eye by 1/4 diopter? Would the +.25 cylinder
need to go down 1/4 diopter like the sphere? Or would the cyclinder
remain unchanged?

Thanks for any help,
Ed

 

Dear Ed,

I am pleased that with the advice you received you could
order your glasses from Zennioptical.com

In general, the SMALLEST measurement of astigmatism
is 1/4 diopters. If you were measured again, you
might have no astigmatism.


Here is my new prescription:


OD: -1.00 SPH (+1.25 ADD)

OS: -0.75 +.025 080 (+1.25 ADD)

Ed> So, I want to go down 1/4 diopter in each eye (my spheres were -.
75
and -.50 for many years). The right eye would go down to -.75, but
how would I reduce my left eye by 1/4 diopter?

Just convert the OD to "Spherical Equivalent".

Ed> Would the +.25 cylinder
need to go down 1/4 diopter like the sphere? Or would the cyclinder
remain unchanged?

Take 1/2 the astigmatic value (+0.25 diopters) and add it
to the "SPH", or -0.75 + 0.125 for a grand total of -0.625

So you reduce this by 1/4 diopter to: -0.375 diopters.

But they only give you 1/4 diopter increments -- so
you must "round" this value up or down to either
-0.5 diopters or -0.25 diopters.

I hope this clarifies this issue of converting LOW VALUE
astigmatism into "spherical equivalent".

Also, you might check your own Snellen, just to
make certain you pass the DMV with this
reduced lens value.

(I am an engineer, so this is just a matter of
basic math.)

You should consult with your optometrist to
see if this conversion and Zennioptical lens
is acceptable for your needs.

Always make certain you pass the DMV (20/40 line)
with this reduced lens combination.

Otis

 

Dear Ed,

Subject: Just to be safe.

If you can't get to the OD for checking, here is
a easy-to-use Snellen to verify that your
new lens calculation is OK.

Just click here:

http://www.smbs.buffalo.edu/oph/ped/IVAC/IVAC.html

Then press on "Display" to get letters. Pressing
display again will give you new random letters.

Thus you can compare your Snellen readings with
the readings provided by your OD when you get
to his office.

Enjoy,

Otis

 

wrong Scrotis.

were you really an engineer? your response is stupid. why do you
explain how to calculate spherical equivalent when all he asked is how
to reduce the prescription by -0.25? wow-- if you were a civil
engineer and actually built any bridges I'll be sure to drive
somewhere else.

perhaps you were a "sanitation" engineer.

perhaps you're getting a few brain tangles.

 

yes. the cylinder remains the same and the sphere goes down by -0.25
For example:
OS: -0.50 +.025 080

to keep the bifocal power the same as the glasses you have now then
reduce the bifocal add to +1.00 if you are going to cut the minus on
the top.

 

Thanks for the information!

Ed