About 1,000 years ago,
very few people had the need, or ability to read and write. Most
of them were monks. As they grew older, reading and writing, in
not very well lighted rooms, became very difficult (due to what
we now call PRESBYOPIA). At
that time, monks were able to make "Reading Stones".
The "Reading Stones"
were a section of a spherical clear and polished natural Glass (quartz).
Imagine a ping-pong ball made of transparent and polished glass:
if you cut the ball in two equal sections, you have two reading
stones or actually what we now call, PLANO-CONVEX magnifying
By trial and error, the
monks realized that larger stones, ones with a larger spherical
radius, would give less magnification than smaller stones, and the
flat part of the stone did not have to be the middle of the sphere.
for reading have what is called Plus Power Lenses: they move the
focal point from behind the retina onto the retina itself.
Now comes an interesting
question. How did the monks made the "Reading Stones"?
I have searched and have not been able to find any information on
how this was accomplished.
Here is my best guess
on how they were made:
At that time, glass making
was in its infancy. My best guess is that the monks used quartz,
a natural glass found in nature: a piece of quartz was selected
that had some roundness shape with an appropriate radius. Next,
manually grinding the stone against some abrasive rock material,
they managed to give the stone a rough spherical shape. Lastly,
they would finely grind and polish the stone into a perfect spherical
shape. Easily accomplished in modern times, but how was it done
over 1,000 years ago?
In the manufacturing
of our i4ULENSES, we use steel convex sections that
have a perfect spherical shape and are polished to a mirror finish
to create the molds that produce our lenses. To polish the steel
Convex section, a block of a soft material (copper or brass) is
cut on a computer controlled lathe to a Concave Spherical shape,
with a radius slightly larger than the radius of the steel Convex
part to be polished. A grinding compound is added between the two
surfaces and by manually or mechanically moving one part over the
other (Lapping), the steel setion is polished to a mirror finish.
It is possible that
the monks used a similar approach. First, a clay convex plug was
created on a potters wheel (easy to make with an appropriate wood
template), and fired. Next using the clay plug, a bronze Concave
"lapping" tool was casted. By using some type of grinding
material between the lapping tool and the quartz stone, they were
able to make reading stones.
of Venice began making spectacles at the end of the 13th century.
The glasses were actually two magnifying lenses connected by hinge
or pivot mechanism (with an inverted V shape), which could be made
from wood, metal, or baleen and in later times copper wire.
Lenses" glasses were only for correcting close distance vision
(presbyopia and farsightedness). There are paintings of monks using
these eyeglasses dating to the middle of the 13th century. Also,
there is a church in Zaragoza, Spain that has statues of monks,
one having a pair of early eyeglasses (circa 1,490).
A well educated guess is that the first lenses were Plano-Convex
and were cast in a bronze mold. A clay convex "Plug" with
the radius of the lens was made on a potter wheel and fired. A Concave
bronze mold was made using this Plug.
The Concave bronze mold was polished by lapping either with the
clay convex Plug or with a bronze convex Plug (casted in a clay
The molten glass was poured in the Concave bronze mold. The lens
Convex shape could also be polished in a similar bronze Concave
mold and the lens's flat area can be polished by grinding against
another flat surface. This method is much more complicated due to
the fact that the clay shrinks during firing and by trial and error
they had to find the correct radii.
and 16th Centuries
A significant development
in the making of eyeglasses was the introduction of the concave
lenses, solving the problem of nearsightedness (distance vision).
Eyeglasses for distance vision have what is called Minus Power Lenses:
these lenses move the focal point from the front of the retina onto
the retina itself.
It is possible
that the first
Minus Power Lenses were what we now call FLAT Plano-Concave
At a later
time, lens makers got more sophisticated and created Minus lenses
of the type we now call Bent, where one surface is
convex and the other is concave with a smaller radius than the convex
One of the major problems
for the eyeglasses was how to keep them on. One solution was to
have some string or ribbons attached to the lenses and loop them
over the ears.
Finally, the side temples
were invented and have stayed with us for centuries!
Temples with sliding
extension were introduced in Europe.
Benjamin Franklin developed
the bifocal eyeglasses. He needed eyeglasses for distance and close
vision and he got tired of changing eyeglasses when he changed his
vision from distance to close or vice versa. He had the lenses cut
in halves, and mounted the distance vision half lens on the upper
part and the close vision half lens on the lower part of the eyeglasses
The Lorgnette became
very popular with people who could not wear eyeglasses.
Cylindrical lenses to
correct Astigmatism were introduced.
The monocle (one lens)
became very popular in Germany
At the end of the century,
pinch-nose (Pince-Nez) eyeglasses were well established because
of its convenience.
Early in the century,
eyeglasses frames began to be designed with fashion in mind.
By the 1945, a number
of different Contact Lenses were available: By the 1970's, with
greater improvement in the design of contact lenses (soft lenses),a
large number of people started to use them.
And finally, eye surgery:
Radial Keratotomy for Nearsightedness, and later, eye surgery using
Laser and computers became well established for solving Farsightedness,
Nearsightedness and Astigmatism (PKR and LASIK).
Some experimental techniques
are being explored to correct Presbyopia.
the first credit card size pinch nose reading glasses in the world