glasses, prescriptions, and depth of field

I have used tri-focals for the past 2 years, but I don't normally read with
my glasses on. I do need glasses to see the computer and for distance. The
lines in the tri-focals drive me crazy, especially the reading lens which is
too low for me to see through.

I don't drive. My 19" monitor is 5 feet away. My prescription is:

OD -2.25 Cylinder -1.75 axis 020 Add 1.50

OS -1.75 Cylinder -1.00 axis 170 Add 1.50



Here are my questions:

Can I get single vision glasses, one eye for distance, the other eye
corrected for the intermediate lens of the tri-focal? How successful do you
think that would be? Am I crazy or would that really work?

As an alternative, how feasable are (read, how happy would I be with)
single vision glasses, with a weak add, say -.3 or - .5?

The last option I can think of is to get bi-focals with the intermediate
prescription and distance prescription, which is what I asked the Dr. at
Lenscrafters to prescribe. When I got my glasses they were for reading and
distance, not computer and distance, so I returned them, and want to get my
lenses elsewhere. I was surprised to find you can get glasses online and
am thinking about ordering them from FramesDirect for less than half what
Lenscrafters charged. Does anyone have experience with FramesDirect.com?



Thank you for helping me with my questions!

Rob

Dear Rob,

I am an engineer -- not an OD.

If you ignore the astigmatism
"correction" it looks like your
near vision should have



don't drive. My 19" monitor is 5 feet away. My prescription is:


OD -2.25 Cylinder -1.75 axis 020 Add 1.50

OD -2.25 +1.5 = -0.75 diopters. This
sugests that you natural "mono-vision"
and can read the monitor with no
glasses. You moght check and
see if "depth of field" will "take out"
any residual blur.

OS -1.75 Cylinder -1.00 axis 170 Add 1.50

OS -1.75 and "add" 1.5 means
that your near vision is -0.25 diopters,
or that basically you could just take
your glasses off for working at
20 inches or so.

Whether you wish to wear glasses
for "close work" is up to you -- a
personal decision and judgment.

Your distant vision requires the
minus lens prescribed as you
state.

You will receive other suggestions
on this site about your choice in
this matter.

Best,

Otis

Robin, ignor this reply from Otis
Otis, your reply is incorrect and virtually illiterate.

>My 19" monitor is 5 feet away

is your computer monitor really 5 feet away? that quite a long
distance for a 19" monitor.
i would consider moving it closer (easier to see details and small
print) and getting a pair of "computer glasses" that are focused at
that distance. why not put the monitor at 2 feet?

>Can I get single vision glasses, one eye for distance, the other eye
>corrected for the intermediate lens of the tri-focal? How successful do you
>think that would be? Am I crazy or would that really work?

this is certainly possible. we call these "monovision glasses". you
would have to try it to see if it would work for you. alternatively
you could get a special pair of bifocals (not trifocals) where the top
part of the lens is set for your computer screen distance and the
bottom part for standard reading distance. they would not be focused
at all for distance so they become dedicated "computer glasses". also
you could get distance glasses with a weak bifocal add that is focused
on the computer-- the problem is that you have to tilt your head back
to use the bifocal all the time you are working on your computer and
secondly you don't have enough power for reading with these glasses on.
This is the approach you apparently tried at Lenscrafters.

i wouldn't recommend any online suppliers for bifocal glasses. the
reason is that the segment height and pupillary distance measurements
are very important for what you are trying to accomplish. this is
measured manually at the opticians office and can't be reliably
determined otherwise. also, you might need to return or exchange your
glasses if things don't work out and doing so from an online supplier
could be difficult. otherwise i don't know anything about FramesDirect.

Robin wrote:

> I have used tri-focals for the past 2 years, but I don't normally read with
> my glasses on. I do need glasses to see the computer and for distance. The
> lines in the tri-focals drive me crazy, especially the reading lens which is
> too low for me to see through.
>
> I don't drive. My 19" monitor is 5 feet away. My prescription is:
>
> OD -2.25 Cylinder -1.75 axis 020 Add 1.50
>
> OS -1.75 Cylinder -1.00 axis 170 Add 1.50
>
>

I can't remember the last time I prescribed trifocals with that low of
an add! It doesn't make sense. Get a pair of regular bifocals with say
a 1 or 1.25 add, and relatively high set segs so you'll be comfy
looking at your monitor, assuming you're completely happy with the near
vision without glasses.


>
> Here are my questions:
>
> Can I get single vision glasses, one eye for distance, the other eye
> corrected for the intermediate lens of the tri-focal? How successful do you
> think that would be? Am I crazy or would that really work?
>

You could, but it usually doesn't work in glasses (fairly successful in
contacts).

> As an alternative, how feasable are (read, how happy would I be with)
> single vision glasses, with a weak add, say -.3 or - .5?
>

I'm sure you mean + here, but this is another compromised situation.
You'd be better off with an ordinary bifocal for general wear and a pair
of computer glasses (single vision with say a + 1.00 add over your
distance refraction.

> The last option I can think of is to get bi-focals with the intermediate
> prescription and distance prescription, which is what I asked the Dr. at
> Lenscrafters to prescribe.

You were right on line with my 1st suggestion above. Stupid LC doc
didn't believe you knew what you wanted. What can I say?

When I got my glasses they were for reading and
> distance, not computer and distance, so I returned them, and want to get my
> lenses elsewhere. I was surprised to find you can get glasses online and
> am thinking about ordering them from FramesDirect for less than half what
> Lenscrafters charged. Does anyone have experience with FramesDirect.com?

Zero.

w.stacy, o.d.

(E-Mail Removed) wrote:

>>My 19" monitor is 5 feet away
>
>
> is your computer monitor really 5 feet away? that quite a long
> distance for a 19" monitor.
> i would consider moving it closer (easier to see details and small
> print) and getting a pair of "computer glasses" that are focused at
> that distance. why not put the monitor at 2 feet?

I missed that part. That IS a far distance, but unlike the above
advice, I like the idea. The farther the better in my opinion. For
that distance, you really don't even need an add. You should be able to
see it just fine with your distance Rx, or a very slight undercorrection
(your .25 or .5 add idea makes sense here) in a single vision lens.

w.stacy, o.d.

<(E-Mail Removed)> wrote in message
news:(E-Mail Removed) ups.com...
> >My 19" monitor is 5 feet away
>
> is your computer monitor really 5 feet away? that quite a long
> distance for a 19" monitor.
> i would consider moving it closer (easier to see details and small
> print) and getting a pair of "computer glasses" that are focused at
> that distance. why not put the monitor at 2 feet?


Yes, it's 5' from the keyboard, on a buffet with hutch. Recently I moved my
office to the dining room and need to hide the equipment in furniture that
opens up to reveal the monitor, printer etc. and I sit at the dining room
table with a wireless keyboard. My excellent old computer glasses won't
focus to that distance sharply.


>>Can I get single vision glasses, one eye for distance, the other eye
>>corrected for the intermediate lens of the tri-focal? How successful do
>>you
>>think that would be? Am I crazy or would that really work?
>
> this is certainly possible. we call these "monovision glasses". you
> would have to try it to see if it would work for you. alternatively
> you could get a special pair of bifocals (not trifocals) where the top
> part of the lens is set for your computer screen distance and the
> bottom part for standard reading distance. they would not be focused
> at all for distance so they become dedicated "computer glasses". also
> you could get distance glasses with a weak bifocal add that is focused
> on the computer-- the problem is that you have to tilt your head back
> to use the bifocal all the time you are working on your computer and

I didn't think of that, sounds like a pain in the neck!

Am I correct in assuming single vision distance glasses would have greater
depth of field than the distance part of a bi-focal in the same frame, due
to the lens being larger?

> secondly you don't have enough power for reading with these glasses on.
> This is the approach you apparently tried at Lenscrafters.
>

I specifically asked for computer / distance bi-focals, and was dissapointed
when I received
the reading / distance glasses. I told her I didn't use glasses for
reading. When I called her back to tell her I couldn't see the monitor at
all with them, she gave me a hard time. Very unsatisfactory experience.

The clerk at the Lenscrafter Optomertist took digital pictures of my
retina - big bright flashes - and then set me up for the Dr to do the eye
exam. I was surprised that I couldn't read anything on the eye chart - not
even the two biggest letters - without correction, and I didn't wonder until
later if being blinded by those flashes would throw off the eye test.



> i wouldn't recommend any online suppliers for bifocal glasses. the
> reason is that the segment height and pupillary distance measurements
> are very important for what you are trying to accomplish. this is
> measured manually at the opticians office and can't be reliably
> determined otherwise. also, you might need to return or exchange your
> glasses if things don't work out and doing so from an online supplier
> could be difficult. otherwise i don't know anything about FramesDirect.


Thank you for your quick and knowlegable answers.

Rob

Robin wrote:

>
> Am I correct in assuming single vision distance glasses would have greater
> depth of field than the distance part of a bi-focal in the same frame, due
> to the lens being larger?
>

No. Lens size has no effect, only lens power.

w.stacy, o.d.

"William Stacy" <(E-Mail Removed)> wrote in message
news:fY6Fe.318$(E-Mail Removed). ..
> (E-Mail Removed) wrote:
>
>>>My 19" monitor is 5 feet away
>>
>>
>> is your computer monitor really 5 feet away? that quite a long
>> distance for a 19" monitor.
>> i would consider moving it closer (easier to see details and small
>> print) and getting a pair of "computer glasses" that are focused at
>> that distance. why not put the monitor at 2 feet?
>
> I missed that part. That IS a far distance, but unlike the above advice,
> I like the idea. The farther the better in my opinion. For that
> distance, you really don't even need an add. You should be able to see it
> just fine with your distance Rx, or a very slight undercorrection (your
> .25 or .5 add idea makes sense here) in a single vision lens.
>
> w.stacy, o.d.

Thank you, Dr. Stacy.

What is the "add" for 5' .... .25 or .5 or am I on the wrong track?

Rob

Robin wrote:

>What is the "add" for 5' .... .25 or .5 or am I on the wrong track?
>
>
>
Well, mathematically, 5' is close to 2 meters, which equates to .50
diopters. With an expected depth of focus of at least .25 D., the .25 D
should theoretically be enough (the calculation simply involves adding,
algebraically, the add of +.25 or +.50 to the first number, the sphere
power, of the distance Rx, keeping all other numbers the same). However,
if you are under 50 years of age, you probably don't need any add, since
you've still got some focusing ability. If you're over 50, welcome, and
use the .50 add.

w.stacy, o.d.