Note: Descriptions are shown in the official language in which they were submitted.
~z7sss3
METHOD FOR MAKING BIFOCAL LENS
Field of the Invention
Tha present invention relates to the prescribing and
forming of spectacle lenses having particular utility where bifocal
corrections are required. In addition, the present invention
relates to a method for manufacturing a bifocal lens and the
bifocal lens made from that p~oces~.
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~275553
Summary of the Prior Art:
At the present time, most practicing opticians, optometrists
and ophthalmologists have in stock, single vision spectacle lenses
with given curvatures and corrections. These can range from plano
to -12.00 diopters, and plan to +12.00 diopters. It is also
possible for the~e ranges to extend to higher powers, but it is
recognized that the standard operating procedure within the
ophthalmic industry is to carry only the lower power lenses as
described.
Spectacle retailers carry a range of stock lenses in
inventory having the capacity to make spectacles for normally
thirty percent of their patients. However, when other patients
re~uire a bifocal lens, the retailer must order the lens from a
wholesale grinding laboratory because his inventory of stock lenses
is only capable of filling single vision prescriptions. The prior
art necessitates the use of a grinding laboratory because it would
be impossible to carry in stock all the possible combinations of
prescriptions, in addition to all of the possible bifocal locations
resulting from each patient's particular facial measurements. The
total inventory of prior art is far beyond even the largest
retailer's capabilities including those retailers having more than
one thousand locations.
The present state of the art does not provide for eyeglass
retailers to be able to add any available color tinting to their
glass lens inventory. These lenses are sent away to special lens
coating laboratories that have extremely expensive (usually up to
~150,000) glass coating equipment.
Present practice and that of the prior art involves time and
delay in fitting the patient with the spectacles and loss of prompt
delivery of a set of glasses which are appropriate to one's
prescription. Many patients with severe corrections are forced to
carry one extra, or even two extra pairs of eyeglasses, or have
~5S~;3
them available since without them, their sight is limited and
functional capabilities are limited.
The prior art may be found in U.S. Patents Nos. 993,812;
1,267,014; 1,304,421; 1,948,63Ç; 2,033,101; 2,330,663;
2,611,294; 3,2~8,460; 3,617,166; 3,628,854; 3,702,218; 3,771,858;
3,904,281; 3,917,776; 3,877,798; and 2,209,587 and United Kingdom
Patent 338,555 and Japan Patents Nos. 52-77738 and 52-10742.
Summary of the Invention
The present invention stems from the development of an
eyeglass lens module in which two lens components are formed. The
first component is the conventional single vision stock lens having
conventional corrections in the negative or positive diopter range
and, indeed, for the patient requiring only bifocals or trifocals,
the single vision stock lens can be of zero correction. The second
overlay lens component is desirably formed of a plastic or glass
material and is as thin as practical. These overlays are in
modules containing bifocals or trifocals or vocational
modifications of a given diopter correction. They can also contain
special vocational features such as upper bifocals for airline
pilots. Once the prescription is developed according to the method
of the invention, the optical glass lens blank is then fixtured for
receiving the overlay. Prior to shipping to the optician and the
laminating or gluing procedure, a sagittal gauge is applied for
inspection by the manufacturer to the posterior surface of the
overlay and the anterior surface of the single vision stock lens,
to determine that their curvatures are nearly equal to insure a
close physical inter-fit which, in turn, will help insure an
optically acceptable bond between the two. Desirably, the lens
and the overlay are cut and edged to the configurations of the
frame which is selected. Optionally they can be cut and edged
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~27~553
before or after laminating. Once the two lens components are
secured optically and physically to each other they can then be
fitted into the spectacle frame and delivered to the patient.
Furthermore, when tinting is required, the plastic overlay can be
readily tinted by conventional dye as distinguished from the
expensive and time consuming coating process required with the
optical glass type lens.
The present invention provides the spectacle retailer with a
kit of very thin lens covers, each of which carries the particular
bifocal correction required by that individual patient. By
providing a kit o~ lens covers to be optically laminated to the
eyeglass retailer's single vision inventory, the spectacle retailer
is able to provide spectacles for at least 90~ of his patients
within one to two hours. Further, this invention permits the cover
lens to be made of any lens material.
The present invention stems from the development of an
eyeglass lens in wh;ch two lens components are formed. The first
component is a conventional single vision stock lens having
conventional correction in the negative or positive diopter range
and, indeed, for the patient requiring only bifocals, the single
vision stock lens can be o~ zero correction. The second component
is a thin lens cover overlay formed optionally of plastic or glass,
which is placed over the single vision lens.
Once ~he prescription is developed accordin~ to the method
o~ the invention, the single vision lens is then ~ixed for
receiving the lens cover overlay. The bifocal overlay must be
precisely plano in power and even, throughout the whole lens, in
thickness.
When the overlay cover lens is cast out of plastic, the
casting must be done in a precise manner. When the material is CR-
39 or equivalent, the chemical composition of the CR-39 monomer
must be mixed with several other additives so as to give stahility
and durability to the cover lens. The water content of the monomer
~;~755~3
must be functionally nonexistent so that the shrinkage o~ the CR-39
plastic is constant from batch to batchO A pre-mixing procedure to
remove water content must be done ~o thP monomer and to the
catalyst. The chemicals must be mixed thoroughly and in a clean
environment under proper thermal controls. This thermal stability
prevents warping of the cover lens. After the casting operation
has been completed, the mold assembly is deflashed, heated, then
cooled rapidly thereby forcing a thermal expansion/contraction
which separates the cover lens from the mold. Tapping the mold
assembly assists in removing the lens. The cover lens must be
within 0.0001 inches in radius to the single vision stock lens
since that is the surface to be bonded to the single vision lens.
The two lens components may be secured to each other with an
optical cemPnt or glue which is glass or plastic compatible. After
the lenses are cleaned and marked, they are then subjected to a
U.V. bulh lamp for curing. After full cure has been achieved, the
lens can be edged and tinted as any other lens and thereafter
framed and delivered to the patient.
In view of the foregoing, it is the principal object of the
present invention to provide the practiciny spectacle retailer
(usually opticians, optometrists, and ophthalmologists), with a
pre-selected number of lens cover overlays containing bifocal
corrections. The eyeglass retailer can use his present in-house
inventory of single vision glass or plastic lenses to be combined
with the lens cover overlays thus permitting extensive control over
the eyeglass manufacture to be in the hands of the parties who have
prescribed the particular correction necessary for the patient.
A further object of the present invention is to provide the
patient with eyeglasses corrected for bifocal application and also
permits customized tintings in accordance with the recommendations
of the eyeglass retailer and/or prescribin~ doctor, as we]l as the
aesthetic taste of the patient.
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A further object of the present invention is to permit
~itting the patient, requiring only a bifocal correction, with
spectacles or sunglass spectacles and in giving prompt delivery.
A further object of the present invention is to provide the
eyeglass retailer with economically competitive lens cover overlays
which, when combined with his own in-house stock of single vision
lenses, create bifocals at a very reasonable cost, and maximizing
the productivity of the single vision lens inventory. The combined
cost of the lens cover overlay and single vision lens is comparable
to the usual and customary cost o~ the same prescription when
ordered from the wholesale prescription grinding laboratory.
A further object of this invention is to provide the
consumer or patient with prompt delivery in fitting of his or her
prescription eyeglasses even when bifocals are involved and because
all the fabrication can be done on the premises of the eyeglass
retailer. The retailer in turn benefits by the improved cash flow
resulting from payment when the eyeglasses are delivered.
In accordance with one aspect of the invention there is
provided a method for assembling an eyeglass lens having two
components comprising the steps of: casting an overlay cover lens
by removing water from a plastic monomer and ~rom a catalyst
comprising an organic peroxide, thoroughly mixing said plastic
monomer and said catalyst, forming a mixed composition, said mixing
being accomplished over a five-hour period at 70 Fahrenheit, plus
or minus 5 Fahrenheit, using mixing apparatus spinning at 200 to
300 revolutions per minute ~RPM), aging said mixed composition for
two weeks at a temperature of 40 Fahrenheit, plus or minus 5
Fahrenheit, using a mold to cast said cover lens from said aged
composition, selecting a single vision lens, and thereafter
~0 optically bonding the two lenses to each other, causing a
lamination with the overlay cover lens being the exterior portion
of the lens, said optical bonding including the steps of placing
an optical bonding agent between the lenses and, thereafter curing
the bond.
SS53
srief Description of the Drawinqs
Further object and advantages of the present invention will
become apparent as the following description of an illustrative
embodiment of both the apparatus and method proceeds, taken in
conjunction with the accompanying drawings, in which:
FIG. 1 is a diagrammatic view of a typical lens with a
negative correction, and example of a cover overlay lens;
FIG. 2 is a view in the same scale as FIG. 1 illustrating
an overlay bifocal in conjunction with a lens having a positive
correction;
FIG. 3 is another view showing a different correction than
shown in FIG. 2, but utilizing a lens having posterior and anterior
curvilinearity;
FIG. 4 is a similar example showing a typical sunglass or
other eyeglass in which the principal correction is zero, with a
bifocal portion;
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FIG. 5 is a front view of a typical single vision stock
lens;
FIG. 6 is a front view of a typical single vision stock lens
with the overlay lens~
As to each of the above, typical corrections are applied at
the locations designated by the reference numerals Fl, F2, F3 and
F4; and,
FIG. 7 shows the lens having the correction in front of the
base lens with the plano lens on the ocular side with a fixed
bifocal segment.
Detailed Description of Preferred Embodiments:
Method of the Prescription:
The method of the present invention begins with the
supplying of the eyeglass retailer with optical glass or plastic
corrective single vision stock lenses. If the eyeglass retailer
already has an inventory of these stock lenses, then he may use the
ones he already has on hand.
Next, the eyeglass retailer is supplied with a pre-selected
number of overlay lens covers having the plus diopker bifocal or
trifocal corrections. The overlays are also formed with the
conventionally used special vocational features used in the
industry.
The eyeglass retailer then selects the appropriate single
vision lens from his inventory and the appropriate bifocal,
trifocal, or vocational overlay. The overlays are selected with
respect to their bifocal or trifocal power, or other extra required
features such as special vocational segment, and also with respect
to their posterior curvatures. The posterior curvature of the
overlay must be very similar ko the anterior curvature of the
single vision stock lens for a complementary close contact fit.
Optician's Procedure-
The procedure for the use of the cover lens overlay modularsystem is best described by giving some examples.
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Prescription #1: R.E. + 1.25 .75 x 90
L.E. + 1.75 .50 x 85
Add +2.50 bi~ocal, Pink #l
Frame selected: #24, size 54/18
A - 54 B - 48 ED - 59 PD = 63/60
A patient having this prescription in hand with the above lens
powers enters the optician's office. The optician realizes the
need for bifocal lenses which heretofore would have required a
telephone order to the prescription grinding laboratory and a
customary delay of three to fifteen days to acquire the lenses.
Step ~. The optician selects two single vision lenses from
his inventory: For the right eye a +1.25-.75 and for the left eye
a +1.75-.50.
Step #2. Next, the optician aligns these lenses in the
Lensometer for the axis and centration, as usual. At this point
the optician must be sure that the cylinders have been ground on
the posterior surface of each lens, so that the anterior surface i5
spherical and can be laminated to the overlay.
Step #3. Next, the optician applies the manufactured
sagittal gauged inspected lens to the anterior surface of the
single vision lenses to determine the anterior surface curvature
value in diopters.
Step #4. The next step is the selection of the overlay
covers having a comparable sagittal value ~nd a bifocal power of
+2.50D.
Step _X5- The overlays for this prescription must be
susceptible to kinting, such as CR-39 plastic, since the
prescription requires color, i.e., pink $1. The overlays are now
tinted to the desired color using the same procedure for tinting
CR-39 plastic lenses. Conversely, a glass cover could be glued to
a CR-39 base lens which is tinted.
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Step #6. The overlays are now ready ~or bench layout.
Determlninq_the 'below' and 'înset':
'Below' - The desired bifocal height is measured to be 20mm.
The B measurement of the frame is 48, and when divided by 2 gives
the vertical mechanical center of the frame which is 24mm.
Subtract 20mm. the desired bifocal height, from the vertical
mechanical center, 24. The result is the 'below' factor, i.e.,
4mm.
'Inset' - The frame P.D. is 54 + 18 = 72mm. The patient's
near P.D. is 60. Subtract 60 from 72 and divide the result by 2.
This gives the 'inset' required. In the above example, 6mm.
Step #7. The overlay should now be placed over a protractor
so that the bifocal is positioned 4mm. 'below' and 6mm. 'in' from
the mechanical center. This procedure should be repeated for the
right and left eyes respectively, as is the usual customary
procedure in these cases.
Step #8. After the cover lens has been appropriately
selected, and the base lens selected and any cylindrical correction
applied to its ocular side, the two components are ready for
lamination. Prior to lamination it is important to clean the
exterior surface of the single vision lens or underlying lens, and
the interior surface of the cover lens so that cleanliness is
preserved at the interface between the two when they are bonded.
To this end a reciprocating stroke with a lint-free cleaning pad
and cleaning solution such as acetone are applied normally from a
top to bottom direction. This is done for the cover lens as well
as the base lens. Thereafter, the base lens is positioned on a
protractor and the overlay oriented as to the proper position for
laminating. The next step is to place a predetermined amount of
optical glue or cement on the surface of the base lens. Once this
is done, the cover is positioned on top of the base lens and slowly
rocked into position. The amount of glue is sufficient to totally
wet both surfaces of the two lens components, sufficient to
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preclude voids or bubbling, and yet limited to that amount which
will not result in excessive oozing along the edges.
Thereafter, the two lens components are subjected to black
light ~U.V.) for about ten to fifteen seconds. This accomplishes a
~uick set while the two components are in the gluing fixture. Once
set, the lens components can be moved from the fixture by hand and
placed under a black light ~U.V.) for up to one hour to accomplish
a full cure.
Step #9. The thus-assembled and bonded two lens component
is edge ground and secured to the eyeglass frame in essentially
state of the art techniques.
The Lens Structure:
The single vision lens component is standard known in the
industry today. They are generally supplied by about two dozen
major manufacturers in a variety of prescription powers. These
prescription powers are generally supplied in one-quarter diopter
increments and in both simple and compound prescriptions. This
includes corrections for hyperopia, myopia, astigmatism and
aphakia. The averages of the patients are well known in the trade
and, therefore, a larger supply of the most popular corrections is
carried by eyeglass retailers.
Usually eyeglass retailers carry inventories of standard
prescription single vision lenses made from either ophthalmic crown
glass having an index of refraction of 1.523, or ophthalmic plastic
CR-39 lens material having an index of refraction of 1.497. The
present invention contemplates that there are prescriptions
specially in stronger powers, which could be made significantly
thinner, lighter and have more desirable cosmetic attractiveness by
using ophthalmic glass having higher indexes of refraction, such as
30 1.701 through 1.805. The invention herein contemplates supplying
the single vision lenses of higher index of refraction when needed.
The overlay cover lens has no prescriptive power except ~or
the special feakure which it carries including, but not limited to,
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bifocal segments, trifocal segments, and special vocational
combination segments. Since the overlay cover lens has no power of
its own, except for the special feature. This invention also
contemplates that the overlays may be mounted onto base lenses
having an increased index of refraction.
Various selections from given patient prescriptions are set
forth in the drawings commencing with the minus diopter corrections
for the near-sighted person and progressing to the plus diopter
corrections for the far-sighted person and indeed into the area of
aphakia. Contemplated also are examples of the overlay having no
distance prescription power, but which carry the bifocal, trifocal,
vocational, or aspheric components needed for the completion of the
prescription.
Method of Chemical Formulation and Processin~
of Overlay Cover Lens
The method of the present invention requires the production
of one type of overlay cover lens and thereafter laminating the
cover lens overlay onto a single vision stock lens which would be
supplied to the eyeglass. Where the eyeglass retailer already has
an inventory of these stock single vision lenses, then he may use
the ones he already has on hand.
In the method of manufacturing one type of overlay cover
lens, the mold manufacturing is extremely important because the
bifocal overlay cover lens must be precisely plano in power and
even throughout the whole lens in thickness. The plano
configuration is achieved by forming a pair of compensated matched
molds. This radius of curvature of the ocular surface is
shortened from the radius of curvature of the anterior face hy the
thickness of the plano veneer. For example, with a 7/10 millimeter
thickness plano lens, the ocular surface radius of curvature is
shortened by 7/10 millimeter. The back mold which provides the
laminating surface must be within 0.0001 inches in radius to the
12
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single vision stock lens to which it is laminated. In order for
the overlay lens to be perfectly even in thickness, the molds must
be compensated as sat forth above. The mold must be free of all
normal mold problems such as scratches, pits, gray, fused stress,
and waves, and these problems are solved by microscopic inspection
of the molds and polishing with cerium oxide having a pH of 7-8 at
temperatures less than 125F. The anterior mold is made of S-1
crown glass. The posterior mold is made of 2.0 mm thick eonite
glass. This thickness permits flexibility o~ the eonite mold to
permit uniform shrinkage of the veneer lens as it is curing. The
CR-39 monomer is preferably injected into the mold cavity by
pneumatic pressure.
The curing of the CR-39 overlay is achieved by mixing the
CR~39 monomer in quantities of five hundred pounds with the
following additives and quantities thereof so as to give stability
and durability to the cover lens:
a) catalyst lPP-isopropyl per carbonate (diisopropyl
peroxy decarbonate) mixed at ambient for three
hours as 3 by weight of CR-39 mixed thoroughly,
b) mold release agent--oil of wintergreen .00001 by
volume,
c) mix thoroughly for five hours,
d) aging of mix over two weeks before using at 40F
plus or minus 5F.
Failure to age will result in irregular shrinkage of the plastic in
the mold. The aged catalyzed monomer will last for about five
weeks if stored at 40F so that three weeks of usage can be
achieved. Thereafter, a premixing procedure is used to remove
water from the monomer and the catalyst. This procedure consists
of vacuum degassing after the catalyst is mixed. Further, the
chemicals must be mixed in a clean environment under thermal
controls at 75F plus or minus 5F for a maximum of five hours with
a 2--=300 rpm motor for optimum quality to be insured.
~Zt755~3
Since the casting operation will vary according to the
bifocal t~pe and add power, the bifocal segment thicknesses will be
different depending on lens styles and reading powers, the
following examples illustrate the variations wlth respect to
different thicknesses of the veneer wafer overlay:
In order to avoid warping the overlay lens cover, after the
lens material is within the mold, the molds are clamped with
uniform mold clamping pressure. Therea~ter the clamped molds are
placed in water and the water is heated from ambient to 50C in
about twelve hours. By experimentation, shorter cycles can be
achieved. The mold is then removed from the water and cooled to
ambient. The mold parts are then separated. The lens cover
overlay is thereafter inspected for all standard quality control
parameters such as inclusions, striae, pits, gray, waving, power,
and add and base radius. The lens inspectors use eye loupe's of 5x
magnification in an inspection booth having a black background, a
40 watt ~clear) incandescent bulb and a 40 watt fluorescent tube.
Mold inspectors use a 10x magnification microscope to insure that
the molds are perfect after each casting before reusing said mold.
Once the method for producing the overlay lens cover is
completed and the inspection of same is done, the next step in the
p~ocedure (for a bifocal lens) includes the lamination of the
overlay by the retailar onto the single vision lens. This is
accomplished by the retailer with a bonding a~ent which is an
optical cement with indexes of refraction comparable to that of the
cover and single vision lenses used. Inspection of molds and
lenses includes fluorescent visual inspection, polariscope
inspection for stress, and arc lamp for stress. Finally the lenses
are checked with a lensometer and digital spherometer to determine
the add power and the radius of curvature. The radius of the cover
lens must be within .0001 inches of the single vision lens.
Once this bonding agent combination i5 formed, the next step
in this method is to laminate the overlay cover lens onto the
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single vision lens with the desired patient prescription of the
single vision lens and the appropriate lens cover having the proper
addition power. Prior to lamination, the lenses are cleaned with a
solvent such as acetone or methylethyl ketone to insure the two
lens components are free of oil, lint, ~ust, or dirt. Wiping the
excess solvent from the lenses should be done with a lint-free
tissue, commonly Xnown under the tradename MICROWIPES or a lint-
free rag.
Next, the method incorporates "spotting ~p" the optical
center of the single vision lens and veneer wa~er overlay.
nSpotting up" is: optical centration of veneer on convex side of
lens with respect to the segment location and optical centration of
single vision lens on the concave side of the lens. The single
vision lens is spotted on the ocular or concave side of the lens.
The procedure of finding the O.C. (optical center~ of the single
vision lens with a lensometer necessitates the dotting of sports
(mostly ink) by means of three little marking pins which are part
of the lensometer machine itself. The spotting must be dona on the
concave side of the single vision lens so as not to sandwich the
spots in the middle of the component. The overlay cover lens is
spotted on the anterior or convex side of the overlay as is the
normal procedure for all lenses. Thereafter, recleaning with
acetone or methylethyl ketone is repeated.
In order to laminate, a single sheet of soft paper (lint
free) such as facial tissue is placed on a retailer's table in a
standard office environment. The single vision lens is then placed
on the table with the convex side up. Approximately lcc of the
bonding agent is then applied by means of a pipette dispenser to
the center of the single vision lens. The overlay cover lens is
then introduced onto the single vision lens by means of a manual
implementation using a side-to-side motion~ After e~amination of
the components for bubbles and bifocal height, the component is
subjected to a high intensity mercury lamp or a long wave
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7S~;~3
ultraviolet lamp for fifteen seconds. This fifteen second exposure
allows the lens to be lifted and re-checked. If all the parameters
of the prescription have been met, the lens is further cured for
twenty minutes using, again, either the mercury lamp or the long
wave ultraviolet lamp. Here it should be noted that a short wave
light can cure the gluing, but for safety reasons it is best not
used at the retail level.
After full cure has been accomplished, the lens is then
edged by means of standard edging equipment used in all reta l and
laboratory shops. There is no need for specialized equipment or
diamond wheels in order to edge these laminated lenses. The
tinting, like the edging, necessitates no additional equipment or
different dyes in order to tint the laminated lenses. Both
operations are conventionally done and known in the industry. This
product is then ready to be delivered to the patient.
Although particular embodiments of the invention have been
shown and described in full here, there is no intention to thereby
limit the invention to the details of such embodiments. On the
contrary, the intention is to cover all modifications,
alternatives, embodiments, usages, and equivalents of eyeglass lens
modules, as fall within the spirit and scope of the present
invention, specification, and appended claims.
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