Title: Method of marking ophthalmic lens by using laser radiation
Abstract: A method of marking an ophthalmic lens, including a step of irradiating the ophthalmic lens formed of a resin material with a laser radiation, such that the laser radiation is condensed at each of predetermined at least one spot within the ophthalmic lens, to form a whitened portion at the each of the predetermined at least one spot, for thereby providing the ophthalmic lens with a marking.
Patent Number: 6,997,554 Issued on 02/14/2006 to Nakada, et al.
| Inventors:
|
Nakada; Kazuhiko (Nisshin, JP);
Suzuki; Hiroaki (Toki, JP);
Ishihara; Kenichi (Kasugai, JP);
Gotou; Yuuji (Kakamigahara, JP)
|
| Assignee:
|
Menicon Co., Ltd. (Nagoya, JP)
|
| Appl. No.:
|
991842 |
| Filed:
|
November 18, 2004 |
| Current U.S. Class: |
351/177; 351/159 |
| Current Intern'l Class: |
G02C 7/02 (20060101) |
| Field of Search: |
351/51,159,160.R,160.H,161-64,166-68,174,177-8
359/440
|
References Cited [Referenced By]
U.S. Patent Documents
| 4194814 | Mar., 1980 | Fischer et al.
| |
| 5817243 | Oct., 1998 | Shaffer.
| |
| 6042230 | Mar., 2000 | Neadle et al.
| |
| 6203156 | Mar., 2001 | Wu et al.
| |
| 2002/0027638 | Mar., 2002 | Thakrar et al.
| |
| 2002/0103478 | Aug., 2002 | Gwon et al.
| |
| 2005/0007567 | Jan., 2005 | Pierrat et al.
| |
| Foreign Patent Documents |
| 62-37368 | Aug., 1987 | JP.
| |
| 64-013520 | Jan., 1989 | JP.
| |
| 5-67932 | Sep., 1993 | JP.
| |
Primary Examiner: Schwartz; Jordan M.
Assistant Examiner: Stultz; Jessica
Attorney, Agent or Firm: Burr & Brown
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATION
This application is a continuation of U.S. application Ser. No. 10/638,665,
filed Aug. 11, 2003 now U.S. Pat. No. 6,857,744, the entirety of which is incorporated
herein by reference.
Claims
What is claimed:
1. A method of marking an ophthalmic lens, comprising a step of irradiating the
ophthalmic lens formed of a resin material with a laser radiation such that the
laser radiation passes through a surface of the ophthalmic lens and is condensed
at each of at least one predetermined spot within the ophthalmic lens, to change
the optical properties of the resin material at said each of at least one said
predetermined spot, thereby providing a marking only within the ophthalmic lens.
2. A method according to claim 1, wherein said ophthalmic lens is irradiated
with said laser radiation such that said marking is located within a predetermined
thickness portion of the ophthalmic lens, wherein the predetermined thickness portion
has a thickness equal to one half of a thickness of the ophthalmic lens, said predetermined
thickness portion having a center of thickness at a center of thickness of the
ophthalmic lens.
3. A method according to claim 1, wherein said ophthalmic lens is irradiated
with said laser radiation such that said marking is located within a predetermined
thickness portion of the ophthalmic lens, wherein the predetermined thickness portion
has a thickness equal to one fourth of a thickness of the ophthalmic lens, said
predetermined thickness portion having opposite ends as seen in a direction of
thickness of the ophthalmic lens, one of said opposite ends being located at a
center of thickness of the ophthalmic lens while the other of said opposite ends
is spaced from said one of opposite ends in a direction toward a back surface of
the ophthalmic lens.
4. A method according to claim 1, wherein said ophthalmic lens is irradiated
with said laser radiation thereby providing said marking within the ophthalmic
lens which includes a plurality of markings each formed by said laser radiation
such that at least one of opposite ends of each of said markings have respective
different positions in a direction of thickness of the ophthalmic lens.
5. A method according to claim 1, wherein said ophthalmic lens is internally colored.
6. A method according to claim 4, wherein said ophthalmic lens is internally
colored with a dye.
7. A method according to claim 5, wherein said ophthalmic lens is internally
colored with at least one of a phthalocyanine compound and an azo-compound which
is included in said material of the ophthalmic lens.
8. A method according to claim 1, wherein said ophthalmic lens is formed of a
polymer obtained from a polymerizable monomer which contains a methacrylic group
or an acrylic group.
Description
This application is also based on Japanese Patent Application No. 2001-281015,
filed on Sep. 17, 2001, the contents of which are incorporated hereinto by reference.
FIELD OF THE INVENTION
The present invention relates to a method of marking an ophthalmic lens such
as a contact lens or an intraocular lens. More particularly, the present invention
relates to a method of marking the ophthalmic lens by irradiating the ophthalmic
lens with a laser radiation to thereby form, within the ophthalmic lens, a marking
in the form of characters, figures, symbols, etc.
BACKGROUND OF THE INVENTION
Conventionally, an ophthalmic lens such as a contact lens or an intraocular
lens is provided with an identifying mark in the form of characters, figures, symbols,
etc., principally for easy distinction between the front and back surfaces of the
lens or between lenses for the left and right eyes, and/or indicating the specifications
of the lens, for instance. For marking the ophthalmic lens, there are known a printing
method, a laser marking method, etc.
In the printing method, the ophthalmic lens is partially dyed or colored with
a printing liquid containing a dye or a dyeing solution (ink). In general, the
ophthalmic lens is dyed or colored by a screen printing method which uses a screen
or stencil that is patterned so as to correspond to a desired identifying mark
to be formed. The identifying mark formed by the printing method using the dye
tends to gradually disappear or peel off due to various treatments repeatedly conducted
on the lens such as cleaning of the lens by rubbing and boiling of the lens for
disinfection. In view of this, various techniques have been proposed to improve
the durability of the identifying mark of the lens under severe environments of
use. For instance, the identifying mark is formed by coloring or dyeing the lens
with the ink which permeates into the material of the lens, or the identifying
mark is fixed to an inner portion of the lens with a chemical reaction of the lens
material with the ink which has permeated into the lens material. In the above-described
printing method employed for marking the ophthalmic lens, however, the dye may
get in the polymer of the lens, and may be contained in the ophthalmic lens, causing
a problem of insufficient safety.
The printing method by which the identifying mark is directly formed using the
ink or dye as described above inevitably increases the number of process steps
for marking the ophthalmic lens and requires additional steps and devices such
as a drying step and a device for drying the ink or dye after the printing step.
In addition, the ophthalmic lens needs to be handled frequently, undesirably resulting
in a high defect or reject ratio of the ophthalmic lens. Accordingly, the cost
of manufacture of the ophthalmic lens is undesirably increased, causing a problem
of poor economy.
Examples of the laser marking method are disclosed in JP-B-62-37368 and
JP-A-64-13520 wherein an ophthalmic lens is irradiated with a laser radiation,
so that a mark is engraved in the lens surface. Another example of the laser marking
method is disclosed in JP-B-5-67932 wherein a mark in the form of recesses and
protrusions is formed, by a laser radiation, in a mold for molding a lens so that
the lens formed in the mold has a mark on its surface, which mark corresponds to
the recesses and protrusions of the mold. In the former method wherein the mark
is engraved by the laser radiation, the thickness of the engraved or marked portions
of the lens is inevitably reduced if the depth of engraving by the laser radiation
is made relatively large in an attempt to attain a high degree of clarity or visibility
of the mark. In this case, the strength of the ophthalmic lens is reduced, and
the ophthalmic lens tends to be easily broken. Further, deposits (contaminants,
stains) are likely to accumulate in the engraved or marked portions in the form
of grooves or recesses, causing undesirable troubles such as irritation of the
eye of the lens user. In the latter method wherein the mark is formed on the lens
surface corresponding to the recesses and protrusions of the mold, the mark in
the form of protrusions formed on the front surface of the ophthalmic lens is in
contact with the inner surface of the eyelid during wearing of the lens, so that
the lens user may feel uncomfortable. Even if the size of the mark and the amount
of protrusion of the mark are made relatively small, it is impossible to completely
get rid of the feeling of discomfort.
SUMMARY OF THE INVENTION
The present invention was developed in the light of the background art described
above. It is therefore an object of the present invention to provide a method of
marking an ophthalmic lens, which method is capable of providing the ophthalmic
lens with a marking that can be easily read or recognized with a high degree of
visibility or clarity, without giving a feeling of discomfort to a lens user or
causing problems such as contamination of the lens and reduction of the strength
of the lens.
The object indicated above may be achieved according to the principle of the
present invention, which provides a method of marking an ophthalmic lens, comprising
a step of irradiating the ophthalmic lens formed of a resin material with a laser
radiation of a femtosecond pulse width, such that the laser radiation is condensed
at least one predetermined spot within the ophthalmic lens, to form a whitened
portion at the at least one predetermined spot, for thereby providing the ophthalmic
lens with a marking.
The present method of marking an ophthalmic lens described above is different
from the conventional method of marking an ophthalmic lens by irradiating the surface
of the lens with a laser radiation, in that the laser radiation of the femtosecond
pulse width is condensed at least one predetermined spot within the ophthalmic
lens, to form a whitened portion at each of the at least one predetermined spot,
thereby providing the ophthalmic lens with a marking in the form of characters,
figures, symbols, etc. According to the present marking method, the marking formed
in the inner portion of the ophthalmic lens does not yield any protrusions and
recesses on its surface, thereby avoiding conventionally experienced problems of
deterioration of the lens wearing comfort due to the mark in the form of protrusions
formed on the lens surface and irritation of the eye due to the deposits accumulated
on or attached to the marks in the form of grooves or recesses formed in the lens
surface. Thus, the present method assures the lens user of high degrees of lens
wearing comfort and safety while effectively preventing a reduction of the optical
properties of the ophthalmic lens due to the deposits adhering to the lens surface.
In the present method wherein the whitened portion which provides the marking
is formed by an ultrashort pulse laser radiation of a femtosecond pulse width,
the spot within the ophthalmic lens at which the laser radiation is condensed can
be determined with high accuracy, so that only the area within the spot and the
vicinity of the spot within the ophthalmic lens can be processed by the laser radiation
without damaging the surface of the lens. In general, the marking is formed at
a peripheral portion of the ophthalmic lens to prevent its optical region (vision
correction region) from being adversely influenced by the marking. Accordingly,
the marking formed at the peripheral portion of the ophthalmic lens is extremely
small and is not recognized by naked eyes. By using the laser radiation of the
femtosecond pulse width according to the present invention, it is possible to significantly
reduce the size of the whitened portion formed at each spot in the ophthalmic lens
at which the laser radiation is condensed. According to the present method, the
marking which can be easily read or recognized with a high degree of clarity or
visibility is advantageously formed.
In one preferred form of the present invention, the ophthalmic lens is irradiated
with the laser radiation such that the marking is located within a predetermined
thickness portion of the ophthalmic lens, which predetermined thickness portion
has a thickness equal to one half of a thickness of the ophthalmic lens, the predetermined
thickness portion having a center of thickness at a center of thickness of the
ophthalmic lens. This arrangement advantageously prevents a reduction of the strength
of the ophthalmic lens.
In another preferred form of the present invention, the ophthalmic lens is irradiated
with the laser radiation such that the marking is located within a predetermined
thickness portion of the ophthalmic lens, wherein the predetermined thickness portion
has a thickness equal to one fourth of a thickness of the ophthalmic lens, the
predetermined thickness portion having opposite ends as seen in a direction of
thickness of the ophthalmic lens, one of the opposite ends being located at a center
of thickness of the ophthalmic lens while the other of the opposite ends is spaced
from the one of opposite ends in a direction toward a back surface of the ophthalmic
lens. Where the ophthalmic lens to be marked according to the present invention
is a contact lens, external physical forces tend to act on the contact lens in
a direction generally from its back surface toward its front surface during handling
of the contact lens. The present arrangement effectively prevents cracking of the
lens due to the external physical forces, at the whitened portions formed in the
inner portion of the lens, so that the ophthalmic lens is protected from being broken.
In still another preferred form of the present invention, the ophthalmic lens
is irradiated with the laser radiation such that the marking includes a plurality
of whitened portions each formed by the laser radiation such that the plurality
of whitened portions have respective different positions in a direction of thickness
of the ophthalmic lens, at least one of opposite ends of the each whitened portion.
According to this arrangement, the marking to be formed has a higher degree of visibility.
In yet another preferred form of the present invention, the ophthalmic lens is
internally colored. The ophthalmic lens according to this arrangement has a high
degree of contrast, so that the marking which is provided by the whitened portion
formed in the inner portion of the ophthalmic lens has a higher degree of clarity
or visibility, resulting in considerably easy reading or recognition of the marking.
In a further preferred form of the present invention, the ophthalmic lens is
internally
colored with a dye. For instance, the ophthalmic lens is internally colored with
at least one of a phthalocyanine compound and an azo-compound which is included
in the resin material of the ophthalmic lens.
In a yet further preferred form of the present invention, the ophthalmic lens
is formed of a polymer obtained from a polymerizable monomer which contains a methacrylic
group or an acrylic group. Preferably, the ophthalmic lens is formed of a polymer
obtained from methyl methacrylate. Where the marking is formed in the ophthalmic
lens formed of the polymer described above, each whitened portion formed by irradiation
of the lens with the laser radiation emits a fluorescent light by exposure to an
excitation light. Accordingly, the marking can be easily and clearly read or recognized,
with the fluorescent light emitted from the whitened portion formed in the ophthalmic lens.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other objects, features, advantages and technical and industrial
significance of the present invention will be better understood by reading the
following detailed description of presently preferred embodiments of the invention,
when considered in connection with the accompanying drawings, in which:
FIG. 1 is a view schematically showing a laser device used as a marking device
for marking an ophthalmic lens according to the present invention;
FIGS. 2A and 2B are fragmentary views for explaining a method of marking the
ophthalmic lens according to one embodiment of the present invention, wherein FIG.
2A is a vertical cross sectional view of the ophthalmic lens while FIG. 2B is a
top plan view of the ophthalmic lens of FIG. 2A;
FIG. 3 is a plan view showing the ophthalmic lens in which a marking is formed
according to the present invention;
FIG. 4 is a fragmentary enlarged view showing a part of the marking of FIG.
3; and
FIG. 5 is a fragmentary view showing an ophthalmic lens in vertical cross section,
for explaining a method of marking the ophthalmic lens according to another embodiment
of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
To further clarify the present invention, embodiments of the present invention
will be described in detail by reference to the drawings.
Referring first to FIG. 1, there is schematically shown a laser device
10 used for marking an ophthalmic lens according to the present invention.
The laser device
10 includes a femtosecond laser radiation source
12,
a pulse shaper
14, a reflecting mirror
16, and a condensing lens
18. The laser device
10 is arranged such that a laser radiation
20
of a femtosecond pulse width in the order between 10
-15 and 10
-13
second is condensed to be incident on a desired portion of an inner portion
26 of an ophthalmic lens to be processed, i.e., a contact lens
22
in the present embodiment.
The ophthalmic lens
22 to be marked according to the present invention
may be one of known contact lenses and intraocular lenses formed of resin materials.
For instance, the present invention is applicable to: a hard contact lens formed
of a polymer material obtained from a polymerizable composition whose major component
is, for instance, methyl methacrylate, siloxanyl methacrylate, fluoroalkyl methacrylate,
siloxanyl styrene, fluoroalkyl styrene, siloxanyl fumarate, or fluloroalkyl fumarate;
a water-absorptive soft contact lens formed of a polymer material obtained from
a polymerizable composition whose major component is, for instance, hydroxyethyl
methacrylate, N-vinyl pyrrolidone, dimethyl acrylamide, or polyvinyl alcohol; a
non-water-absorptive soft contact lens formed of a polymer material obtained from
a polymerizable composition whose major component is, for instance, butyl acrylate,
siloxanyl acrylate, or fluoroalkyl ether monomer; and an intraocular lens principally
formed of a polymer such as a methacrylate polymer. In the present embodiment,
the marking is conducted on the contact lens
22 formed of a methyl methacrylate
polymer which is obtained from a polymerizable composition whose major component
is methyl methacrylate.
For providing the contact lens
22 described above with a predetermined
marking, the contact lens
22 is initially placed on a support (not shown).
Subsequently, the laser radiation
20 of the femtosecond pulse width is emitted
from the laser radiation source
12 of the laser device
10 toward
the contact lens
22 placed on the support. In the present embodiment, the
predetermined laser radiation
20 of the femtosecond pulse width is condensed
to be focused not on its surface
24, but at each of at least one predetermined
infinitesimal portion or spot
30 in the inner portion
26 of the contact
lens
22. In the present embodiment wherein the laser radiation
20
of the femtosecond pulse width is condensed at each of at least one predetermined
infinitesimal portion or spot
30, a whitened portion
28 which appears
to be white is formed at each predetermined portion or spot
30 in the inner
portion
26 of the contact lens
22 formed of the resin material, without
damaging the surface
24 of the lens
22.
It is speculated that the whitened portion
28 is formed for the following
reasons: Multiphoton absorption which induces electron excitation is induced only
in the irradiated area in the spot
30 and in the vicinity of the spot
30
in the contact lens
22, at which the laser radiation
20 of the femtosecond
pulse width is condensed, causing a photochemical reaction, a structural change,
or a defect of the lens material, so that the optical properties (refractive index)
of the lens material are changed in the spot
30 and its vicinity to form
the whitened portion
28. Since the ultrashort pulse laser of the femtosecond
pulse width is employed for marking the contact lens
22 in the present embodiment,
the contact lens
22 is processed without substantially suffering from an
influence of heat, which would take place if a laser of a microsecond or a nanosecond
pulse width was employed. Accordingly, the whitened portion
28 can be formed
with high accuracy in the selected portion of the inner portion
26 of the
contact lens
22 without damaging the lens surface
24. In addition,
the size of the portion at which the photochemical reaction takes place can be
made smaller than the spot size of the laser radiation
20, depending upon
the distribution of the photon density within the spot
30 in the contact
lens
22. Accordingly, the present arrangement wherein the laser radiation
20 of the femtosecond pulse width is employed assures more precise or finer
processing to mark the contact lens
22, than in the case where the laser
of the microsecond or the nanosecond pulse width is employed.
In the present method of marking an ophthalmic lens, the whitened portion
28
formed at each of the at least one predetermined spot
30 in the inner portion
26 of the contact lens
22 can serve as a desired marking. According
to this arrangement, the marking yields no protrusions and recesses on or in the
lens surface
24, advantageously avoiding the deterioration of the lens wearing
comfort and the eye irritation of the lens wearer due to deposits adhering to the
protrusions and recesses, and the deterioration of the optical properties of the
ophthalmic lens arising from such deposits. Further, the present arrangement wherein
the contact lens
22 is marked by the laser radiation
20 of the femtosecond
pulse width does not use any printing liquid which includes a dye, etc., thereby
preventing the eye of the lens user from being adversely influenced by the dye.
Thus, the present arrangement assures the lens user of excellent lens wearing comfort
and a high degree of safety.
The advantages described above are obtained, as long as the whitened portion
28 which functions as the marking is formed in the inner portion
26
of the contact lens
22. Since the ophthalmic lens in the form of the contact
lens
22 to be irradiated with the laser radiation is a thin plate member,
the strength of the lens tends to be lowered by irradiation of the lens with the
laser radiation. For permitting the contact lens
22 to maintain a high degree
of strength, it is preferable that the whitened portion
28 is formed within
a predetermined thickness portion (first thickness portion) of the contact lens
22, as indicated at "A" in FIG. 2A, which first thickness portion has a
thickness equal to one half of a thickness "D" (FIG. 2A) of the contact lens
22
and has a center of thickness at a thickness center "C" (FIG. 2A) of the contact
lens
22. It is particularly preferable that the whitened portion
28
is formed within a predetermined thickness portion (second thickness portion) of
the contact lens
22, which second thickness portion has a thickness equal
to one fourth of the thickness "D" of the contact lens
22 and has opposite
ends as seen in a direction of the thickness "D" of the contact lens
22,
one of the opposite ends being located at the center "C" of the thickness of the
contact lens
22 while the other of the opposite ends is spaced from the
above-indicated one of the opposite ends in a direction toward a back surface
34
of the contact lens
22. Where the ophthalmic lens, especially the contact
lens
22 is handled or subjected to a cleaning operation, for instance, the
contact lens
22 receives external physical forces that generally act in
a direction from its back surface
34 toward its front surface
32,
due to its configuration. Accordingly, owing to the whitened portion
28
formed in the above-indicated second thickness portion on the side of the back
surface
34 of the contact lens
22, the contact lens is effectively
protected from being broken.
For forming the whitened portion
28 described above to provide the contact
lens
22 with the desired marking in the form of characters, figures, and
symbols as shown in FIG. 3 by way of example, there are employed any known methods.
For instance, the contact lens
22 or the laser device
10 is moved
along at least one of an X-axis direction, a Y-axis direction, and a Z-axis direction,
depending upon the configuration of the marking to be formed, for thereby changing
the position of the spot
30 in the inner portion
26 of the contact
lens
22 at which the laser radiation
20 is condensed. Alternatively,
the laser radiation
20 is condensed at a plurality of portions in the inner
portion
26 of the contact lens
22, for forming the desired marking.
FIG. 3 shows a typical example of the marking formed in the inner portion
26
of the contact lens
22, wherein a plurality of whitened portions
28
cooperate to indicate the specifications of the lens, production lot number, effective
term of use, and trademark.
Described more specifically, the marking shown in FIG. 3 is constituted
by a matrix of whitened portions
28 which are spaced apart from each other
by a predetermined distance, as shown in FIG. 4. Where the marking is constituted
by the matrix of whitened portions
28 as described above, the size of each
whitened portion
28 is not particularly limited, and is preferably determined
such that the maximum diameter of each whitened portion
28 indicated by
"a
1" and "a
2" in FIGS. 2A and 2B is preferably held in a
range from 0.5 μm to 3 μm. The size of the whitened portion
28
is changed by suitably adjusting the intensity of the laser radiation
20
emitted from the laser radiation source
12, for instance. If the diameter
("a
1", "a
2") of the whitened portion
28 is excessively
small, the marking to be provided by the whitened portion
28 has poor clarity
or visibility. If the diameter of the whitened portion
28 is excessively
large, the strength of the contact lens
22 is undesirably lowered, resulting
in a risk of cracking of the contact lens
22 during its handling.
The distance between the adjacent ones of the whitened portions
28 indicated
by "d
1" and "d
2" in FIGS. 2A and 2B is not particularly limited,
and is preferably held in a range from 1 μm to 100 μm, more preferably
in a range from 3 μm to 50 μm. In this respect, it is noted that adjacent
cracks which may occur in the lens tend to be easily connected together if the
distance ("d
1", "d
2") is excessively small. If the distance
is excessively large, on the other hand, a marking having a complicated configuration
may not be clearly visible.
The plurality of whitened portions
28 need not be arranged such that corresponding
ends of the plurality of whitened portions
28 as seen in the direction of
the thickness "D" of the contact lens
22 are located at the same position
in the direction of thickness of the contact lens
22, shown in FIG. 2A.
That is, the plurality of whitened portions
28 may be arranged such that
the corresponding ends (on the side of the front surface
32 and/or on the
side of the back surface
34) of the whitened portions
28 as seen
in the direction of thickness of the contact lens
22 may be located at respective
different positions in the direction of thickness of the contact lens
22,
as shown in FIG. 5. According to this arrangement, the light which passes through
the contact lens
22 can be effectively scattered, enabling the marking to
be read or recognized with a higher degree of clarity or visibility.
Even if each of the whitened portions
28 to be formed is extremely small,
the laser radiation
20 of the femtosecond pulse width can be condensed at
each spot
30 in the inner portion
26 of the contact lens
22
with high accuracy and controllability. According to the present method, the number
of the whitened portions
28 which constitute the marking, in other words,
the number of marking dots can be advantageously increased, so that the marking
formed according to the present method has a significantly higher degree of resolution
than the conventional marking. Thus, the marking formed according to the present
method can be easily recognized or identified.
According to the present method, the marking operation is performed on
the contact lens
22 formed of the methyl methacrylate polymer (PMMA) which
is obtained from the methyl methacrylate (MMA). Accordingly, if a suitable excitation
light (350 nm-380 nm) is incident on the marked portion of the contact lens
22,
the marked portion (the whitened portion
28) is excited such that a broad
emission spectrum in a wide wavelength range of 500-700 nm is detected in the marked
portion. It is speculated that the light emission from the marked portion upon
exposure to the excitation light arises from breakage of the main chain of the
PMMA by the laser radiation
20. However, the mechanism is not clear. By
utilizing the characteristics described above, the fluorescent light emitted from
the marked portion of the contact lens
22 upon exposure to the suitable
excitation light can be detected, so that the marking formed in the contact lens
22 can be easily recognized or identified.
For permitting the marking formed in the contact lens
22 to be read or
recognized with a higher degree of visibility or clarity, it is preferable that
the contact lens
22 is internally colored, in other words, the inner portion
26 of the contact lens
22 is colored, prior to the marking operation.
In this case, the whitened portion
28 has a high degree of contrast with
respect to the transparent, colored portion, whereby the marking can be read or
recognized with a high degree of visibility or clarity. Where only the surface
of the contact lens
22 is colored, the whitened portion
28 does not
have a high degree of contrast with respect to the colored portion, resulting in
insufficient visibility or clarity of the making. In view of this, it is preferable
that the contact lens
22 is internally colored. The color of the contact
lens is not limited, provided that the colored contact lens
22 is not opaque,
but is light-transparent. For example, the contact lens
22 is preferably
colored green, blue, yellow, or red, from the standpoint of the visibility of the marking.
The contact lens
22 is colored with known coloring agents such as dyes
and pigments. For coloring the contact lens
22, selected at least one of
the known coloring agent is contained in the resin material for the contact lens
22 such that the coloring agent added to the polymerization system is copolymerized.
Alternatively, the coloring agent or agents is/are added to the resin material
for the contact lens
22. As the coloring agent (dye) for coloring the contact
lens
22, at least one of a phthalocyanine compound and an azo-compound which
includes an azo pigment and an azo dye is advantageously employed, for easy recognition
of the whitened portion
28.
The contact lens
22 colored with the dye which is contained in or added
to the resin material is subjected to the marking operation such that the predetermined
laser radiation
20 is condensed at each of the at least one predetermined
spot
30 of the inner portion
26 of the contact lens
22, which
at least one spot
30 is located at a predetermined position as seen in the
direction of thickness of the contact lens
22. The thus formed marking can
be read or recognized with a high degree of visibility or clarity since the whitened
portion
28 has a higher degree of contrast with respect to the transparent
colored portion than a contact lens not colored.
The laser employed for marking the contact lens
22 according to the present
method is not particularly limited, as long as the laser has a pulse width in the
femtosecond range, i.e., in the order from 10
-15 to 10
-13 second.
There may be employed various known types of lasers such as a tunable solid-state
laser whose typical example is a Ti:sapphire laser. It is particularly preferable
to use a laser whose pulse width is held in a range from 1 fs to 500 fs. It is
possible to form the whitened portion in the inner portion
26 of the contact
lens
22 by employing the laser of the microsecond or nanosecond pulse width.
With the laser of the microsecond or nanosecond pulse width, however, the range
of energy in which a change of the optical properties (refractive index) is caused
is very small, so that it is difficult to control the energy of the laser. Further,
cracks tend to be generated, undesirably resulting in a high defect or reject ratio
of the contact lens. Even if the whitened portion is formed by using the laser
of the microsecond or nanosecond pulse width, the whitened portion formed by the
laser of the microsecond or nanosecond pulse width has a size much larger than
that formed by the laser of the femtosecond pulse width. Accordingly, it is difficult
to form a clear marking consisting of a large number of dots, in other words, a
clear marking having a high degree of resolution. In addition, there is a high
possibility that the mechanical strength of the contact lens
22 is lowered.
The oscillation wavelength of the femtosecond laser is not particularly limited,
and is suitably determined depending upon the specific type of the laser radiation
source
12 to be employed. It is preferable to use a visible light. Where
the titanium sapphire laser is employed, the oscillation wavelength is preferably
400 nm or 800 nm corresponding to the fundamental or harmonic frequency. The pulse
energy and the number of pulses of the femtosecond laser are not particularly limited,
and is suitably determined depending upon various factors such as the laser radiation
source
12, the oscillation wavelength of the laser radiation
20,
the material of the contact lens
22, and the size of the whitened portion
28 to be formed. Where the titanium sapphire laser is used, the pulse energy
is preferably held in a range of 0.01-0.1 μJ/pulse, and the number of pulses
is held in a range of 1-1000. If the pulse energy and the number of pulses of the
laser radiation
20 are excessively large, the intensity of the laser radiation
20 is excessively high, undesirably giving an adverse influence to the contact
lens
22.
While the presently preferred embodiments of this invention have been described
in detail by reference to the accompanying drawings, the invention is not limited
to the details of the foregoing description, but may be otherwise embodied.
In the illustrated embodiments, the laser radiation
20 is incident on
the
contact lens
22 in a direction from the front surface
32 toward the
back surface
34. The direction of incidence of the laser radiation
20
is not limited to that in the illustrated embodiments. The laser radiation
20
may be incident on the contact lens
22 in a direction from the back surface
34 toward the front surface
32.
In the illustrated embodiments, the specifications of the lens, the production
lot number, the effective term of use, and the trademark are marked in the ophthalmic
lens (the contact lens
22), as shown in FIG. 3. There may be formed any
other marking in the form of characters, figures, symbols, etc., for distinction
between the front and back surfaces of the lens or between lenses for the left
and right eyes.
The condensing lens
18 for condensing the laser radiation
20 at
each predetermined spot
30 in the inner portion
26 of the contact
lens
22 is not particularly limited. Various known condensing lenses may
be used.
In the illustrated embodiments, the ophthalmic lens in the form of the contact
lens
22 formed of the PMMA is marked according to the present method. Contact
lenses and intraocular lenses formed of other resin materials may be marked in
a manner similar to that employed for marking the contact lens
22 formed
of the PMMA. The laser device
10 may be otherwise arranged. For instance,
the laser device
10 may be modified such that the laser radiation emitted
from the laser radiation source
12 is split into a plurality of laser beams.
It is to be understood that the present invention may be embodied with various
changes, modifications and improvements, which may occur to those skilled in the
art, without departing from the spirit and scope of the invention defined in the
attached claims.
EXAMPLES
There will be described some examples of the present invention to further clarify
the present invention. It is to be understood, however, that the present invention
is not limited to the details of the following examples.
As the ophthalmic lens to be marked, there were prepared two plates (contact
lenses)
each having a thickness of 100 μm, by polymerizing a polymerizable composition
containing methyl methacrylate and trimethyl silylpropyl methacrylate in a proportion
of 50:50 by weight. One of the thus prepared two contact lenses was colored green
by adding copper phthalocyanine in an amount of 0.005 wt. % to the polymerizable
composition in the polymerization process. As the laser radiation source, a titanium
sapphire laser was used.
Each contact lens was positioned on a three-axis piezoelectric actuator such
that the laser radiation emitted from the laser radiation source was incident upon
a desired portion of the contact lens and such that the laser radiation was focused
at a predetermined position in the inner portion of the contact lens in the direction
of thickness thereof. A condensing lens having a magnification of ×100 was used.
A laser radiation having a pulse width of 150 fs, a center wavelength of 800
nm,
and a pulse energy of 0.05 μJ/pulse was emitted from the laser radiation
source, such that the number of pulses of the laser radiation was equal to 100.
The laser radiation emitted from the laser radiation source as described above
was condensed by the condensing lens at the predetermined portion of the inner
portion of the contact lens, as seen in the direction of thickness of the contact
lens, so that the density of the photon at that thickness portion, i.e., the spot
at which the laser radiation was condensed was increased to exceed a predetermined
threshold value. Thus, there was formed a substantially spherical whitened portion
at the spot in the inner portion of the contact lens. The operation of irradiating
the inner portion of the contact lens with the laser radiation was repeated while
the contact lens was moved, whereby fifteen whitened portions were formed in the
inner portion of the contact lens such that those whitened portions were equally
spaced apart from each other by a distance of 3 μm so as to provide the contact
lens with a marking in the form of a straight line.
In each of the contact lenses marked as described above, the marking in the form
of the straight line was formed with a high degree of visibility or clarity, and
the marking was recognized by naked eyes. Each of the whitened portions which constitute
the marking was spaced from the back surface of the contact lens by a distance
of about 32-35 μm in the direction of thickness of the contact lens, which
distance is substantially equal to one third of the thickness of the contact lens.
No recesses, no protrusions, and no cracks were observed on the surface of the
contact lens. In the transparent contact lens colored green with the dye (the phthalocyanine
compound), the marking can be easily read or recognized than that formed in the
transparent, colorless contact lens.
The transparent, colorless contact lens was irradiated with an excitation light
of 365 nm, and there was detected a light of 500-700 nm by using a CCD camera (available
from KABUSHIKI KAISHA HAMAMATSU PHOTONICS, Japan). It was confirmed that a fluorescent
light was emitted from the marked portion of the contact lens, so that the marking
could be easily read or recognized.
As is apparent from the foregoing description, according to the present method
of marking an ophthalmic lens, the laser radiation is condensed at each of the
at least one predetermined spot in the inner portion of the ophthalmic lens formed
of the resin material, to form the whitened portion at each predetermined spot,
for thereby providing the ophthalmic lens with the marking. Accordingly, the present
method assures the lens user of excellent lens wearing comfort and a high degree
of safety. Further, the present method prevents the stains and deposits from adhering
to the marked portion of the ophthalmic lens, and protects the ophthalmic lens
from being broken due to a reduction in its mechanical strength.
In the present method wherein the ultrashort pulse laser radiation of the femtosecond
pulse width is employed for marking the ophthalmic lens, the spot in the inner
portion of the ophthalmic lens at which the laser radiation is condensed can be
determined with high accuracy, and only the selected spot and its vicinity can
be processed by the laser radiation without damaging the surface of the lens. By
using the laser radiation of the femtosecond pulse width according to the present
invention, it is possible to significantly reduce the size of the whitened portion
formed at the spot in the ophthalmic lens at which the laser radiation is condensed.
Therefore, the present method advantageously permits formation of the marking which
has a high degree of resolution and which can be easily read with a high degree
of visibility or clarity.
*
