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?

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.

 

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.

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

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.

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

Zero.

w.stacy, o.d.

 

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.

 

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.

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?

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.

Thank you for your quick and knowlegable answers.

Rob

 

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

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

 

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.

 

Robin,

Like Otis says, he is not in the medical profession.

Please disregard his postings as he is not in the medical profession nor is
he in any position to give medical advice.

Thank you!

Allen

 

Dont understand why you need trifocals with a low add.

If the 1.5 add was set to help you read at 40cm. you would need an extra
1.00 diopter of accommodation to read at that distance.(40cm.) If half of
your accomodation is kept in reserve (Ideal case) Then through your bifocal
segment you should have a range of 66.66 cm to 28.57 cm. You will only need
to use 0 to 1.50 diopters from your available 2.00 Diopters to have a range
of infinity to 66.66 cm through your distance portion. a bifocal should
therefore offer you the range that you need. Provided of course when the
measurements were made half your accommodation at 40 cm was kept in reserve.


Roland J. Izaac

 

I don't know why they were prescribed either, since I don't need glasses to
read.
I only need them to see clearly from 1.6 meters out to infinity. Maybe I
should stop frequenting LensCrafters?

I don't follow. Where do you get the "available 2 diopters of
accomodation", is that a standard for the human eye?


Rob

 

Dear Robin,

Here is a lower-cost substitute for LensCrafters

http://zennioptical.com/cart/home.php

You need your "PD" which will be about 63mm.

Take a look.

Best,

Otis

 

Where possible, it is a good idea to keep about half of your accomodation in
reserve when reading at your prefered distance. I asumed your reading
distance to be 40cm. at 40cm you need 2.5 Diopters of accommodation. 1.5
Diopters is provided by the lower segment of your bifocal. therefore you
need to accommodate another 1.00 Diopter. If only half your accommodation
is used, then you have the other half in reserve, making two diopters.

Roland J. Izaac

 

I received my AARP invitation three years ago

So it's a straightforward .5 diopter add for 2 meters, 1 diopter for 1
meter, 1.5 diopter for 66 cm etc?

Rob

 

exactly

w.stacy, o.d.