U.S. patent application number 11/471921 was filed with the patent office on 2007-01-04 for in line thickness measurement.
Invention is credited to William Jordan Hall.
Application Number | 20070002331 11/471921 |
Document ID | / |
Family ID | 35589661 |
Filed Date | 2007-01-04 |
United States Patent
Application |
20070002331 |
Kind Code |
A1 |
Hall; William Jordan |
January 4, 2007 |
In line thickness measurement
Abstract
This invention relates to an apparatus and method for measuring
the thickness of mold components and/or lenses during a
manufacturing process. In particular, the present invention uses
fiber optic interferometry to measure the center thickness of
ophthalmic lenses created by a double-sided molding process.
Inventors: |
Hall; William Jordan;
(Atlanta, GA) |
Correspondence
Address: |
CIBA VISION CORPORATION;PATENT DEPARTMENT
11460 JOHNS CREEK PARKWAY
DULUTH
GA
30097-1556
US
|
Family ID: |
35589661 |
Appl. No.: |
11/471921 |
Filed: |
June 21, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60695653 |
Jun 30, 2005 |
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Current U.S.
Class: |
356/503 ;
356/630 |
Current CPC
Class: |
B29D 11/0098 20130101;
G01B 11/0675 20130101; G01D 5/35303 20130101; B29D 11/0099
20130101 |
Class at
Publication: |
356/503 ;
356/630 |
International
Class: |
G01B 11/02 20060101
G01B011/02; G01B 11/28 20060101 G01B011/28 |
Claims
1. A method for determining the thickness of a sample having at
least one boundary which reflects light said method comprising the
steps of: providing one or more interferometers supplied with a
coherent light source and a non-coherent light source; positioning
the contact lens such that said non-coherent light source is
incident upon the sample; and obtaining measurements of the contact
lens thickness as generated by interference fringes created by said
interferometer, wherein said method occurs on a manufacturing line
and wherein said sample is a contact lens or contact lens mold.
2. The method of claim 1, further comprising analyzing said
interference fringes.
3. The method of claim 1 further comprising the step of positioning
the sample above said non-coherent light source.
4. The method of claim 1 further comprising the step of positioning
the sample below said coherent light source.
5. The method of claim 1, wherein said one or more interferometers
comprise one or more fiber-optic interferometers.
6. The method of claim 2, wherein said analyzing step further
comprises calculating distance using optical path and group
index.
7. The method of claim 1, wherein said positioning step further
comprises placing a probe within about 5 degrees normal to the
surface to be measured.
8. The method of claim 1, wherein the distance between the sensor
and the sample is substantially constant.
9. The method of claim 1, further comprising aligning said sensor
over the center of the lens lens mold prior to said positioning
step.
10. The method of claim 1, wherein said interference fringes are
generated by light reflecting off of the boundaries between: a
medium and the lower surface of a female mold; the upper surface of
the female mold and the lens material within the assembled mold;
the lens material within the assembled mold and the lower surface
of a male mold; and the upper surface of the male mold and said
medium.
11. The method of claim 10, wherein said medium is air.
12. The method of claim 10, wherein the medium is saline.
13. The method of claim 1, wherein said positioning step further
comprises aligning the interferometer probe with the center of said
sample.
14. The method of claim 1, wherein said obtaining step further
comprises converting an optical path distance to material
thickness.
15. The method of claim 14, wherein said converting the optical
path distance comprises: measuring the optical path distance; and
dividing said optical path distance by the group index of the
material.
16. An apparatus for determining the thickness of a contact lens
having at least one boundary which reflects light comprising: one
or more movement stages connected to a lens measurement system; a
means for calculation in electronic communication with, and a lens
measurement system that contains a housing that holds a sample
lens, wherein the lens measurement system is connected to said
movement stages via a support post; and wherein said lens
measurement system further comprises a light source and a
fiberoptic interferometer.
17. The apparatus of claim 16, further comprising a means for
aligning said fiber optic interferometer with said sample lens.
18. The apparatus of claim 16, wherein said means for calculation
further comprises a computer that, in conjunction with said
interferometer, is capable of determining the group index of a
material.
Description
FIELD OF THE INVENTION
[0001] This invention relates to an apparatus and method for
measuring the thickness of mold components during a manufacturing
process. In particular, the present invention uses fiber optic
interferometry to measure the center thickness of ophthalmic
lenses.
BACKGROUND OF THE INVENTION
[0002] Ophthalmic lenses may be created using a variety of methods,
one of which includes molding. In a double sided molding process,
the lenses are manufactured between two molds without subsequent
machining of the surfaces or edges. Such mold processes are
described, for example in U.S. Pat. No. 6,113,817, which is
expressly incorporated by reference as if fully set forth herein.
As such, the geometry of the lens is determined by the geometry of
the mold. Typical molding systems include cast molding, which
involves using two mold halves, and spin-casting. These methods may
also be combined with other machining techniques to create specific
lens designs. Another process involves cycling lenses through a
series of stations on a semi-continuous basis. The cyclic portion
of lens production generally involves dispensing a liquid
crosslinkable and/or polymerizable material into a female mold
half, mating a male mold half to the female mold half, irradiating
to crosslink and/or polymerize, separating the mold halves and
removing the lens, packaging the lens, cleaning the mold halves and
returning the mold halves to the dispensing position. Once a mold
is designed and fabricated it must be measured to ensure that it
meets the proper specifications. Typical molds may be spherical or
non-spherical, depending upon the type of lens to be created.
Because most molds have one or more arcuate surfaces, linear
coordinates may be unable to measure a curved surface accurately or
may only be able to accurately measure portions of the mold
geometry. Additionally, current measurement means such as Michelson
interferometers may be adapted for use in a lab but may not be
practical or efficient for use on a manufacturing line due to
vibration and other types of interference/noise that may affect
sensitive equipment.
[0003] An interferometer is a measurement instrument that utilizes
optical interference to determine various characteristics of
optical surfaces. Interferometers typically generate a precise
monochromatic wavefront, such as that of a laser, and split it
using a beam splitter. The resulting two wavefronts include a test
wavefront and a reference wavefront. These wavefronts are passed
through a sample and a reference optical system, respectively, to
create interference fringes which may then be measured. Methods for
measuring the thickness of a material using interferometers are
known in the prior art. For example, U.S. Pat. No. 3,319,515
(Flournoy) relates to the determination of thickness on the basis
of interferometric optical phase discrimination and is expressly
incorporated by reference as if fully set forth herein. U.S. Pat.
No. 5,473,432 (Sorin) and U.S. Pat. No. 5,610,716 (Sorin et al)
relate to an apparatus and method for measuring film thickness of a
moving film, employing optical reflectrometry, both of which are
expressly incorporated by reference as if fully set forth
herein.
SUMMARY OF THE INVENTION
[0004] The present invention seeks to provide a non-destructive,
non-contact method and apparatus for determining mold
thickness.
[0005] These and other aspects of the invention will become
apparent from the following description of the preferred
embodiments taken in conjunction with the following drawings. As
would be obvious to one skilled in the art, many variations and
modifications of the invention may be effected without departing
from the spirit and scope of the novel concepts of the
disclosure.
[0006] The present invention includes a method for determining the
thickness of a sample that has one or more boundaries that reflect
light. Such a method may include providing one or more
interferometers supplied with a coherent light source and a
non-coherent light source and positioning the contact lens such
that the non-coherent light source is incident upon the sample; and
obtaining measurements of the contact lens thickness as generated
by interference fringes created by the interferometer. This method
is designed to be used on a manufacturing line so that contact
lenses or contact lens mold thickness may be determined. In one
embodiment of the present invention, the method may also include
analyzing the interference fringes. In another embodiment of the
present invention, the method may include positioning the sample
above the non-coherent light source. The sample may also be
positioned below the coherent light source.
[0007] In the present invention the one or more interferometers may
be fiber-optic interferometers. In an embodiment in which
interference fringes are analyzed, the analysis may include
calculating distance using optical path and group index. In the
positioning step of the present invention, it may be desirable to
position the sample lens such that the non-coherent light source is
incident upon the sample. In still another embodiment, the
positioning step may include placing a probe within about 5 degrees
normal to the surface to be measured. Additionally, it may be
preferable to have a substantially constant distance between the
sensor and the sample. In a related embodiment, the sensor may be
aligned over the center of the lens or lens mold prior to the
positioning step.
[0008] The interference fringes of the present invention may be
generated by light reflecting off of the boundaries between: a
medium and the lower surface of a female mold; the upper surface of
the female mold and the lens material within the assembled mold;
the lens material within the assembled mold and the lower surface
of a male mold; and the upper surface of the male mold and the
medium. In related embodiments medium may be air or saline. The
present invention may also include alignment process that aligns
the interferometer probe with the center of the sample.
[0009] In the obtaining step of the present invention, the
obtaining step may include converting an optical path distance to
material thickness. Converting the optical path distance may
comprise measuring the optical path distance; and dividing the
optical path distance by the group index of the material.
[0010] The present invention may include an apparatus that is
related to the method. This apparatus may include one or more
movement stages connected to a lens measurement system; a means for
calculation, and a lens measurement system that contains a housing
that holds a sample lens, wherein the lens measurement system is
connected to the movement stages via a support post. The lens
measurement system may include a light source and a fiberoptic
interferometer. The apparatus, similar to the method, may include a
means for aligning the fiber optic interferometer with the sample
lens. In a related embodiment, the means for calculation may
include a computer that, in conjunction with the interferometer, is
capable of determining the group index of a material.
DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 depicts a typical Michelson interferometer.
[0012] FIG. 2A depicts an apparatus used in one embodiment of the
present invention.
[0013] FIG. 2B is a detail drawing of a lens measurement system
used in the apparatus of FIG. 2A.
[0014] FIG. 3 is a detail drawing of a cold mirror setup that may
be used in conjunction with the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0015] Reference now will be made in detail to the embodiments of
the invention. It will be apparent to those skilled in the art that
various modifications and variations can be made in the present
invention without departing from the scope or spirit of the
invention. For instance, features illustrated or described as part
of one embodiment, can be used on another embodiment to yield a
still further embodiment. Thus, it is intended that the present
invention cover such modifications and variations as come within
the scope of the appended claims and their equivalents. Other
objects, features and aspects of the present invention are
disclosed in or are obvious from the following detailed
description. In particular, the terms male mold and male mold half
may be used interchangeably. The terms female mold and female mold
half may also be used interchangeably. Additionally the term
"sample" refers to a lens sample and/or a mold sample. It is to be
understood by one of ordinary skill in the art that the present
discussion is a description of exemplary embodiments only, and is
not intended as limiting the broader aspects of the present
invention.
[0016] The present invention comprises an apparatus and method to
more accurately measure the thickness of a mold assembly (an
assembled male and female mold). In a preferred embodiment, the
present invention is able to measure the center thickness (CT) of
the male mold, the female mold, and/or the polymer between the
molds. The invention comprises a fiber optic sensor and related
methods and fixtures for orienting the fiber optic sensor normal to
the surfaces of interest.
[0017] The present invention uses the principle that light incident
on a translucent or semi-translucent film reflects a portion of
that light. If there are multiple surfaces, each surface interface
(boundary) will cause some amount to be reflected, dependant upon
material properties. For example, a female mold will have two
reflections--one from the lower surface and one from the upper
surface (the surface that contacts the polymer). It is important to
remember, however, that the light is not reflecting from the
surface, but rather the boundary between two areas with a change in
refractive index of over about 0.01. In an assembled mold, with or
without polymer, there will be four reflections: one from the lower
surface of the female mold half (the boundary between the air and
the lower surface of the female mold half, one from the upper
surface of the female mold half (the boundary between the upper
surface of the female mold half and the material within the
assembled mold), one from the lower surface of the male mold half
(the boundary between the material within the assembled mold and
the lower surface of the male mold half) and one from the upper
surface of the male mold half (the boundary between the upper
surface of the male mold half and the air). The reflections measure
the thickness of the mold assemblies based upon the optical
distance that the reflections have traveled. It is believed that
because the sensor is fiber optics-based, it is not easily affected
by vibration. Hence, the present invention uses the above fiber
optic interferometer technology in conjunction with specific
fixturing and manufacturing methods to reduce manufacturing noise
that affects the accuracy of interferometric measurement.
[0018] A complete description of the fiber optic sensor technology
is described in U.S. Pat. Nos. 6,038,027; 6,067,161; 5,596,409; and
5,659,392, all of which are incorporated by reference as if fully
set forth herein. A representative system that uses these
principles is made by Lumetrics, Inc. (West Henrietta, N.Y.). In
accordance with the present invention, a fiber optic interferometer
may be used to determine the thickness of a contact lens or
associated molds.
[0019] An exemplary interferometer apparatus 20 is preferably a
dual interferometer apparatus of a Michelson configuration in an
autocorrelation mode, as shown in FIG. 1. Optical probe 18 directs
a beam of light from a non-coherent light source 30 (such as
light-emitting diode (LED) toward a sample. Optical probe 18 may
include includes a Gradient Index lens (e.g., GRIN). The light is
reflected from boundaries, as described later in the present
application. In a particular embodiment, the light may be reflected
on the front F and back B surfaces of the contact lens and the
light signals may be introduced into two arms of interferometer
apparatus 20 through an optical coupler 32 and a fiber collimator
34 (shown in FIG. 3). A coherent light source 36 (such as a HeNe
laser) emits a beam of light toward a beam splitter 38. Beam
splitter 38 divides the beams of light into pairs of light beams
directed toward a pair of hollow-cube retroreflectors 40, 42 which
are mounted 90 degrees apart and move in perpendicular directions
as shown by arrows B and C. The outputs of interferometer apparatus
20 are directed to a pair of detectors 44, 46 for LED 30 and laser
36, respectively. The non-coherent light of LED 30 follows the same
light path as the coherent light path of HeNe laser 36, but in
reverse time order. A band-pass filter 48 blocks the light from
laser 36 being incident on material M. A second filter 50 prevents
light from LED 30 from interfering with the light from laser 36. As
such, the laser interferometer tracks the distance the optical path
has changed, with the laser signal providing data acquisition
trigger signals, at constant distance intervals, for collecting
interferometric data from the LED interferometer. Therefore, the
purpose of the laser interferometer is to track the distance the
optical path moves while the LED interferometer is collecting data
from the boundaries of the sample.
[0020] The above-described system measures the optical path. To
convert the optical path distance (OPD) to actual material
thickness, the measured OPD must be divided by the group index or
group velocity of the material. The group index is a material
property, is related to the refractive index, and is described at
http://www.mathpages.com/home/kmath210/kmath210.htm. The difference
in group index between materials must be approximately larger than
0.01 in order for the instrument to detect the reflection. In an
embodiment in which the sample is a lens inside of a mold, the lens
polymer would have a different group index than the polypropylene
mold halves.
[0021] The light used by the sensor may be visible, UV, IR, or any
other wavelength of radiation that will reflect off the surfaces of
interest. Due to the small tolerance on the angle of reflectance,
the sample is preferably substantially normal (about 5 degrees from
perpendicular) relative to a light emitting probe (fiber optic
interferometer) to pick up the return signal. The probe may act as
a lens focusing system that shapes the light from the fiber optic
interferometer into a useful form. Additionally, the optics of the
interferometer probe will preferably determine the distance of the
sample from the light-emitting aperture on the interferometer
probe. For example, if points other than those located near the
center are to be scanned, the sample or the interferometer probe is
preferably moved in a way that keeps the orientation of the
interferometer probe and sample constant to within the tolerance of
the instrument. Changes in the thickness profile of the sample may
further reduce the acceptable angle to receive a signal. In an
alternative embodiment, the slim tolerance of the signal acceptance
angle may be overcome by providing a plurality of interferometer
probe heads to measure specific points of interest on the mold. In
this embodiment one interferometer probe may be used for each
point. The mold surfaces may be optimized to increase the signal by
reducing loses in the transmitted light at the air/mold interface
(with an anti-reflection coating), creating an equal thickness
mold, or optimizing the curve of the mold and/or the motion of the
interferometer probe.
[0022] In a specific embodiment the measurement device may be
located above or below a contact lens or contact lens mold sample
on the manufacturing line. The present invention also allows
measurement of a hydrated lens. The measurement device is
preferably adapted to measure both the lens height and the center
thickness.
[0023] An exemplary setup is shown in FIG. 2. Specific
manufacturers and models of components of the present invention are
exemplary only and are not intended to be limiting. Referring to
FIG. 2A, an apparatus of the present invention preferably comprises
at least one linear movement stage 16. Stage 16 preferably provides
about 25 mm of total travel and is adapted to connect to a
controller. In some embodiments, two stages may be used (one for
vertical movement and one for horizontal movement). A recommended
stage is MFA-CC from Newport and a coordinated controller may be a
Newport ESP300 controller. In an embodiment with two stages, the
lower stage is preferably a LINOS mounting base with adjustable
support feet. The lens measurement system, pictured in FIG. 2B,
sits about the linear movement stages and houses the lens, the
wetcell 1 that holds the lens, and optical measurement devices and
supports. Wetcell 1 preferably has an optically clear top and
bottom (for both visible and infrared light). Beneath wetcell 1 is
a wetcell support platform 2. The backbone of the lens measurement
system is preferably a support post 3, such as, for example a LINOS
X95 rail, which is preferably about 500 mm in length. The lens
measurement devices or components are attached to support post 3 by
a carrier 4 such as a LINOS carrier 50-X95.
[0024] Light source 5 is also a component of the lens measurement
system. Light source may be a single white LED with a plurality of
collimating lenses held in an aluminum cylinder or any optical
equivalent. Bracket 6 preferably provides a physical connection
between backlight 5 and support post 4. The cold mirror 8 is
located preferably about 45 degrees to both the light source 5 and
the lens sample. Cold mirror 8 is preferably mounted to wetcell
support platform 2 via mounting adapter 7. Cold mirror 8 may be a
31.55 mm mirror, such as LINOS part no. 38-0255 035. Focus lens 9
is used to focus the beam from the interferometer probe. The beam
preferably comes through collimator 11 through focusing lens 9.
Lens 9 preferably has about a 50 mm focal length. Lens 9 is
connected to adjustable mount 10, which allows a user to move the
lens in 2 directions +/- about 1 mm. An exemplary mount is made by
LINOS, part 06-1025. Fiber optic collimator 11 collimates the beam
from the fiber optics cable, which is part of the interferometer
Referring back to FIG. 2A, a high resolution camera 12 is
preferably located at the top of support post 3. A cooling fan 13
may be located in close proximity to camera 12 to prevent camera 12
from overheating. The present invention may also include a
0.5.times. telecentric lens 14 for camera 12. Telecentric lens 14
may be mounted via mounting bracket 15. Telecentric lens 14 may be
used to measure the diameter of the lens or other sample
characteristics to detect the presence of the beam. Telecentric
lens 14 may also be used to eliminate optical errors such as
parallax.
[0025] Because the measurement of the lens is limited to surfaces
which are nearly normal to the probe, a method is needed to align
the interferometer probe with the center of the sample. This is
important for accurate CT measurement and guarantees that the read
CT value is collected from the center of the lens. One method of
aligning the probe with the center of the lens or mold is to view
the lens or mold from the top with a digital camera. In this
embodiment, shown in FIG. 3, the interferometer probe is inverted
and placed under the lens or mold and pointed upward to the sample.
The sample in wetcell 30 may be lit by a light source 36 in a way
that allows the camera to see and measure the outer diameter and
calculate the center of the sample in relation to the camera. An
example of a preferred light source is a collimated backlight. This
requires a cold mirror, depicted in FIG. 3 as element 32, which
reflects visible light but transmits IR. A cold mirror is a special
filter that reflects visible light (.about.350-700 nm) and
transmits IR light (.about.800-2500 nm). It is designed to be used
at an angle that exhibits the best transmission/reflection, which
may be about 45 degres. In an embodiment in which a 45 degree angle
is used, the backlight and the IR beam are preferably at a 45 deg
angle to the cold mirror, as shown in FIG. 3. The cold mirror
preferably allows combination of the IR and backlight beams without
the losses of a beam splitter. Element 33 is a focusing lens that
focuses light.
[0026] The backlight 36 is preferably placed perpendicular to the
beam 35 and is reflected normal to the sample by the cold mirror 32
which may be mounted approximately 45 degrees to both the light
source 36 and the sample. The direction of IR beam 35 preferably
remains constant as it passes through cold mirror 32. A computer
compares the position of the interferometer probe with the center
of the lens or mold. In an embodiment in which the interferometer
probe is attached to a motion system, the computer preferably
directs the interferometer probe to the center of the lens or mold.
An example of a possible motion system is two MFA-CC linear stages
(Newport, Inc) mounted in an XY configuration, which may be
controlled by an ESP300 Motion Controller/Motion Driver (Newport,
Inc). The ESP300 is preferably connected to a PC through an RS-232
cable.
[0027] In an embodiment in which a camera is used that is sensitive
to 1.3 micron light (IR), the beam from the interferometer probe
preferably registers on the camera sensor. An example of this type
of camera is a PL-A782 from PixeLink. Using an IR-sensitive camera
preferably allows the system to move the interferometer probe to
the center of the lens in a closed-loop feedback system. The
position of the probe is verified by the position of the beam "dot"
from the interferometer probe relative to the calculated sample
center.
[0028] In a hydrated embodiment, the center thickness (CT) of the
lens or mold may be measured directly by the reflected light. For
example, in an embodiment in which the sagittal height of the lens
is desired, a reference may be used. If the lens is placed in a
wetcell that is full of saline, the outer diameter (typically known
as the edge flat) of the lens rests on the bottom surface of the
wetcell. The light is first reflected from the top and bottom of
the wetcell surface, returning a thickness value for the wetcell
wall. The next reflecting surface is the bottom of the lens. The
difference between the bottom of the lens and the top of the
wetcell wall form a thickness which corresponds to the posterior
sagittal height (Psag) of the lens. This is critical because the
interferometer does not measure distances, only differences in
distance (thickness), as previously described. Without a reference,
it is not possible to gauge Psag. The next reflecting surface is
the top of the contact lens, which provides the CT measurement and
the anterior sagittal height (Asag). This is advantageous because
base curve equivalent (BCE) calculations rely on the Psag, which is
typically derived from the Asag and CT. BCE = - ( ( Diameter - 2
.times. .times. ( edgeflat ) 2 4 ) + Psag 2 ) 2 / Psag ##EQU1##
[0029] Now, these values can be measured directly removing an
additional source of error in the BCE calculation. In addition, the
thickness of the wetcell wall should be constant. Any change in the
value of the wetcell thickness for the same wetcell would indicate
an error in the system. Hence, the original measured wetcell
thickness serves as a reference. Additionally, this property can be
used to identify individual wetcells. The interferometer is
accurate to about 0.1 um in such a situation. The thickness of most
wetcells varies significantly more than this value.
[0030] As mentioned above, to obtain the actual lens CT in microns,
the group index of the lens material must be known. The group index
of the material may be a limitation on the accuracy of the
instrument because the lens CT is always the measured OPD/group
index. However, with the wetcell setup as mentioned above, it is
possible to measure the real thickness directly and simultaneously
calculate group index for each sample.
[0031] In a hydrated embodiment, the procedure first involves
calculating the group index (GI) of the saline. This is
accomplished by measuring a wetcell in which the gap inside of the
cell can be measured by the instrument. Because the GI of air=1,
the OPD=real thickness. The wetcell is then filled with saline and
the OPD of the gap is measured again. The OPD of the gap will be
increased due to the presence of the saline. The GI is equal to the
OPD air/OPD saline.
[0032] Once the GI of the saline is known, the lens is placed in
the cell. There will be three distances measured between the cell
walls: the gap below the lens (cell wall to bottom of the lens),
lens thickness, and the gap above the lens (top of the lens to the
top of the cell). The top and bottom gap are filled with saline, so
those thickness can be converted accurately. These two thicknesses
can be subtracted from the total wetcell gap without the lens to
calculate the lens thickness. This thickness must be divided by the
GI of the saline to calculate the real lens thickness. The measured
OPD can be divided by this value to calculate the GI for the lens
material. This means that the real center thickness measurement is
independent of the GI of the lens material. It only depends on an
accurate measurement of the GI of the saline. In this calculation,
the lens height (PSag) is solely dependent on the GI of the saline
since it is equal to the bottom gap.
[0033] It is useful to note that the OPD for each layer (cell wall,
lens thickness, PSag) is preferably calculated from the reference,
not between peaks on the interferometer. For example, the first
peak from the interferometer represents the lens CT because this is
the smallest thickness. The next peak represents the cell walls
since it is the 2.sup.nd thinnest. The third peak represents the
PSag. The OPD for the PSag is OPD from the reference peak all the
way to the third peak, rather than the distance between the
2.sup.nd and 3.sup.rd peak. For PSag, this total OPD would be
divided by the GI of the saline. The lens CT would be the OPD from
the reference to the 1.sup.st peak, divided by the GI of the lens
material, unless the thickness is calculated as described
above.
[0034] In addition, the optical setup may be changed without
affecting the function. The probe and/or camera may be placed
either above or below the sample. If the probe is placed above the
lens, the PSag is then calculated as the gap "above" the lens.
Also, the camera may be placed perpendicular to the cold mirror and
the backlight opposite to the camera and probe. Finally, the lens
may be lit in other ways such as a ring light, diffuse LED source,
or other equivalent lighting techniques. A similar technique may
also be used for measuring lens thickness.
[0035] The invention has been described in detail, with particular
reference to certain preferred embodiments, in order to enable the
reader to practice the invention without undue experimentation. A
person having ordinary skill in the art will readily recognize that
many of the previous components, compositions, and/or parameters
may be varied or modified to a reasonable extent without departing
from the scope and spirit of the invention. Furthermore, titles,
headings, example materials or the like are provided to enhance the
reader's comprehension of this document, and should not be read as
limiting the scope of the present invention. Accordingly, the
invention is defined by the following claims, and reasonable
extensions and equivalents thereof.
* * * * *
References