Post by LFS
Are progressive lenses the same as varifocals?
For many years I wore reading glasses which I was always losing so I
bought half frames so I could wear them all the time but look over the
top when not needing magnification (also good for intimidating students).
Eventually the optician who then looked after my eyes suggested that it
was time for something more, particularly when driving, and he proposed
bifocals. I wore them for a time but found the line across the lens
distracting so he suggested varifocals. My husband had had some
difficulty in adjusting to varifocals so I was apprehensive but I had no
problems adjusting to them. I have been wearing them for about fifteen
years with no change in the prescription needed.
Recently I have had some vision problems and my new optometrist tells me
that I need new lenses which can't be fitted into my old frames - which
is a costly nuisance. She has also recommended that I get a cheap pair
of reading glasses because these will provide a bigger lens area for
reading than the varifocals do.
I now feel slightly baffled and have the sense that I have come full
But hearing aids are *much* more problematic...
Laura, let's talk a bit about eye examinations and so forth.
The trained talent that works in the field has three titles.
Ophthalmologist: Has MD training, and can prescribe drugs and perform
surgery, in addition to conducting vision examinations. Many limit
their practice to the high end.
Optometrist: Trained to conduct vision examinations, including methods
for detecting various vision diseases. Many OD's are tops in their
ability to solve problems; however, they cannot prescribe drugs or
Optician: A technologist who makes eyeglasses. Does not conduct vision
In addition, many practices employ semi-skilled assistants to conduct
basic tests, using equipment that doesn't require skill or high risk.
The prescription: You can look up several on-line articles that will
tell you what the prescription is telling you and how to interpret it.
Basically, OD is "opter dexter," or "right eye." OS is "opter
sinister," or "left eye." Spherical grind is overall correction;
cylindrical is at an angle and is astigmatic correction. Both are
specified in "diopters." One diopter focusses parallel light at one
meter. Prismatic correction is a tilt correction that is specified in
"prism diopters," which is an angular measurement. This is for problems
with double vision, where the two eyes do not converge on a common
point. Specified as a diopter value and "base" (widest part) position.
PD is "pupillary distance", measured either from the bridge of the nose
to either eye (2 measurements) or between the centers of the pupils of
the two eyes (1 measurement). Important because a corrective lens that
is not centered directly in front of the eye will distort the image and
give an unwanted "prism" effect. Values are in millimeters.
"Add" is for near vision correction. It is in diopters, the number to
add to the distance vision spherical correction. It is NOT the absolute
value of the near vision correction that needs to be in your reading
One important number that is not on the prescription is your eyeball
pressure. Major problem is with high pressure causing glaucoma.
Typical "good" pressures are around 12-20 millimeters of mercury. That
is like barometric pressure, except the numbers are much smaller.
The basic tools used nowadays to get a specification for distance vision
are the autorefractor and phoropter. An autorefractor is a fancy
electronic device that operates like a camera autofocus to do a "rough
cut" on the spherical and cylindrical corrections needed. This is
relatively modern technology, but they seem to do a pretty good job.
The phoropter is the classic device used to put corrective lenses
manually in front of an eye to determine the correction needed. Even
with a good autorefractor printout, a good examination includes
phoropter work to verify and home in on the final specification.
The phoropter also is used to conduct the two-eye tests for vertical and
Tonometry is used to determine eyeball pressure.
Those are just some of the basics.
When it comes to fitting lenses to frames, traditionally lenses were
made as large round lenses which were ground down to the size and shape
needed to fit the frame. Nowadays it seems that lenses for popular
current frames are available that need only grinding to set the PD
I buy my glasses from Zenni Optical.
I got "calibrated" by several high-tech people who know more about
optics than I do on Zenni some years ago. At something like $30 a
pair, I can have three sets with different spherical values for various
distances, and they are "expendables" at those prices.
For sunglasses, I have Noir UVshield 21's (lighter) and 22's (darker), also
cheap expendables. They double as protective glasses, and can be worn over
I think if you are talking about relensing 15-year-old frames, you
should consider new frames. Things like the temple hinge pins tend
to wear out, and other parts get bent up with time.