U.S. patent application number 11/614518 was filed with the patent office on 2008-06-26 for corneal measurment apparatus and a method of using the same.
Invention is credited to Joseph R. Bentley, Ming Lai.
Application Number | 20080151190 11/614518 |
Document ID | / |
Family ID | 39415139 |
Filed Date | 2008-06-26 |
United States Patent
Application |
20080151190 |
Kind Code |
A1 |
Bentley; Joseph R. ; et
al. |
June 26, 2008 |
CORNEAL MEASURMENT APPARATUS AND A METHOD OF USING THE SAME
Abstract
A corneal measurement apparatus for measuring a subject's
cornea, comprising (A.) an illumination projection subsystem
comprising a light source (B.) a mask subsystem disposed in a path
of light from the light source, comprising (i) a first slit mask
defining a plurality of apertures, (ii) a second slit mask defining
a selection aperture, (iii) a translation apparatus adapted to
translate the second mask, the translation apparatus and the second
slit mask being configured and arranged such that by translating
the selection slit, portions of the light can be selectively
transmitted through each of the plurality of apertures toward the
cornea, (C.) an imaging element configured and arranged to image
the plurality of apertures onto the cornea, and (D.) an image
capture subsystem arranged to capture images of the portions of
light after the light impinges on the cornea.
Inventors: |
Bentley; Joseph R.; (West
Jordan, UT) ; Lai; Ming; (Webster, NY) |
Correspondence
Address: |
Bausch & Lomb Incorporated
One Bausch & Lomb Place
Rochester
NY
14604-2701
US
|
Family ID: |
39415139 |
Appl. No.: |
11/614518 |
Filed: |
December 21, 2006 |
Current U.S.
Class: |
351/211 |
Current CPC
Class: |
A61B 3/107 20130101;
A61B 3/135 20130101; A61B 3/1005 20130101 |
Class at
Publication: |
351/211 |
International
Class: |
A61B 3/107 20060101
A61B003/107 |
Claims
1. an apparatus for measuring a subject's cornea, comprising: (A.)
an illumination projection subsystem comprising a light source;
(B.) a mask subsystem disposed in a path of light from the light
source, comprising (i) a first slit mask defining a plurality of
apertures, (ii) a second slit mask defining a selection aperture,
(iii) a translation apparatus adapted to translate the second slit
mask, the translation apparatus and the second slit mask being
configured and arranged such that by translating the selection
aperture, portions of the light can be selectively transmitted
through ones of the plurality of apertures toward the cornea,
sequentially; (C.) an imaging element configured and arranged to
image the plurality of apertures onto the cornea; and (D.) an image
capture subsystem arranged to capture images of the portions of
light after the light impinges on the cornea.
2. The apparatus in claim 1, further comprising (E.) a second
illumination projection subsystem comprising a second light source;
(F.) a second mask subsystem disposed in a path of second light
from the second light source, comprising (i) a third slit mask
defining a second plurality of apertures, (ii) a fourth slit mask
defining a second selection aperture, (iii) a second translation
apparatus adapted to translate the fourth slit mask, the second
translation apparatus and the fourth slit mask being configured and
arranged such that by translating the second selection aperture,
portions of the second light can be selectively transmitted through
each of the second plurality of apertures toward the cornea; and
(G.) a second imaging element configured and arranged to image the
second plurality of apertures onto the cornea, the image capture
subsystem arranged to capture images of the portions of second
light after the light impinges on the cornea.
3. The apparatus in claim 1, wherein the second slit mask is
disposed upstream of the first slit mask.
4. The apparatus in claim 1, wherein the illumination projection
subsystem is configured and arranged to project light from the
light source through each of the plurality of apertures defined in
first slit mask without moving the illumination projection
subsystem.
5. The apparatus in claim 1, wherein the light source comprises at
least one LED arranged to project light in the path of light.
6. The apparatus in claim 1, further comprising a condenser lens
configured and arranged to gather light from the light source and
project the light in the path of light.
7. The apparatus in claim 6, wherein the imaging element and
condenser lens are configured and arranged to operate as a
condenser-projector system.
8. The apparatus in claim 1, wherein the imaging element and the
first slit mask are disposed in a Scheimflug arrangement to obtain
a plane of slit images the cornea.
9. The apparatus in claim 1, wherein the plurality of apertures are
disposed in a single plane.
10. The apparatus in claim 1, wherein the plurality of apertures
are formed on a single substrate.
11. The apparatus in claim 10, wherein the plurality of apertures
is defined by openings in an opaque layer deposited on the
substrate.
12. The apparatus in claim 1, further comprising an image
processing subsystem coupled to the image capture subsystem, the
image processing subsystem being adapted to convert the images into
a single representation of the cornea.
13. The apparatus in claim 1, further comprising a subject
positioning apparatus adapted to maintain the subject's cornea in a
location.
14. The apparatus in claim 5, wherein the light source comprises at
least one high power LED.
15. The apparatus in claim 5, wherein the light source consists of
a single LED.
16. A method of facilitating measurement of a subject's cornea,
comprising: (A.) providing a plurality of apertures; (B.)
projecting light toward the plurality of apertures; (C.)
translating a selection aperture while maintaining the plurality of
apertures in fixed locations to selectively transmit a portion of
the light toward the cornea, the portion of the light passing
through the selection aperture and a selected one of the plurality
of apertures; and (D.) imaging the portions of light after the
light impinges on the cornea.
17. The method of claim 16, wherein the light passes through the
selection aperture prior to passing through any of the plurality of
apertures.
18. The method of claim 16, wherein the step of projecting light
comprises projecting light from at least one LED.
19. The method of claim 16, wherein the step of imaging produces
images, and the method further comprises processing the images to
convert the images into a single representation of the cornea.
Description
FIELD OF INVENTION
[0001] The present invention relates to corneal measurement
apparatus, and a method of corneal measurement, and more
particularly to an apparatus and method for projecting a plurality
of slits of light for performing corneal measurements.
BACKGROUND OF THE INVENTION
[0002] Ophthalmologists and optometrists would like to have an
accurate representation of subjects' eye. Such representations
include, for example, one or more of a representation of a
subject's corneal anterior surface, posterior surface, and corneal
thickness and density, as well as anterior chamber profiles. This
information may be used to prescribe contact lenses and eye
glasses, and to reshape the cornea by surgical procedures or to
perform other surgical procedures. Since it is not comfortable to
measure these data with physical contact, remote sensing techniques
are preferably used to perform the measurements. A device that
measures only the front surface of a cornea is commonly referred to
as corneal topographer, a device that measures the front and back
surfaces, and the stroma of the eye is referred to as a corneal
profiler, and a device that measures anterior chamber profiles is
called an anterior chamber analyzer.
[0003] One common technique for obtaining corneal measurement
information includes projecting narrow bands of light (commonly
referred to as slits or slit beams) onto a patient's cornea at
multiple locations across a cornea. For each of the slits, after
the light in the slit has been scattered by the cornea, an image of
the light is obtained.
[0004] To project a slit of light, an aperture of appropriate shape
and size, and a lens are placed in the path of light from a light
source such that the light passing through the aperture forms a
slit of light on a subject's cornea. Typically, to project slits at
each of multiple locations across the cornea, a single aperture is
translated such that the light passing through the aperture at
selected times forms the multiple slits. One example of such a
corneal measurement apparatus is presented in U.S. Pat. No.
5,512,966 to Snook.
[0005] A problem with such apparatus is that it is difficult to
accurately position an aperture to form each of the slits, and over
time (after many patients) it is difficult to know the position of
the slits accurately so that an accurate recreation of a cornea can
be obtained.
SUMMARY
[0006] Aspects of the present invention are directed to an
apparatus for measuring a subject's cornea, comprising (A.) an
illumination projection subsystem comprising a light source, (B.) a
mask subsystem disposed in a path of light from the light source,
comprising (i) a first slit mask defining a plurality of apertures,
(ii) a second slit mask defining a selection aperture, (iii) a
translation apparatus adapted to translate the second slit mask,
the translation apparatus and the second slit mask being configured
and arranged such that by translating the selection aperture,
portions of the light can be selectively transmitted through ones
of the plurality of apertures toward the cornea, sequentially, (C.)
an imaging element configured and arranged to image the plurality
of apertures onto the cornea, and (D.) an image capture subsystem
arranged to capture images of the portions of light after the light
impinges on the cornea.
[0007] In some embodiments, the corneal measurement apparatus,
further comprises (E.) a second illumination projection subsystem
comprising a second light source, (F.) a second mask subsystem
disposed in a path of second light from the second light source,
comprising (i) a third slit mask defining a second plurality of
apertures, (ii) a fourth slit mask defining a second selection
aperture, (iii) a second translation apparatus adapted to translate
the fourth slit mask, the second translation apparatus and the
fourth slit mask being configured and arranged such that by
translating the second selection aperture, portions of the second
light can be selectively transmitted through each of the second
plurality of apertures toward the cornea, and (G.) a second imaging
element configured and arranged to image the second plurality of
apertures onto the cornea, the image capture subsystem arranged to
capture images of the portions of second light after the light
impinges on the cornea.
[0008] In some embodiments, the second slit mask is disposed
upstream of the first slit mask. In other embodiments, the
illumination projection subsystem is configured and arranged to
project light from the light source through each of the plurality
of apertures defined in first slit mask without moving the
illumination projection subsystem. The light source may comprise at
least one LED arranged to project light in the path of light. 14.
In some embodiments, the light source comprises at least one LED.
And in some embodiments, the light source consists of only a single
LED (e.g., a high power LED).
[0009] In some embodiments, the corneal measurement apparatus
further comprises a condenser lens configured and arranged to
gather light from the light source and project the light in the
path of light. The imaging element and condenser lens may
configured and arranged to operate as a condenser-projector system.
The imaging element and the first slit mask may be disposed in a
Scheimflug arrangement to obtain a plane of slit images at the
cornea.
[0010] In some embodiments, the plurality of apertures is disposed
in a single plane. The plurality of apertures may be formed on a
single substrate. The plurality of apertures may be defined by
openings in an opaque layer deposited on the substrate.
[0011] The corneal measurement apparatus may further comprise an
image processing subsystem coupled to the image capture subsystem,
the image processing subsystem being adapted to convert the images
into a single representation of the cornea. The corneal measurement
apparatus may further comprise a subject positioning apparatus
adapted to maintain the subject's cornea in a location.
[0012] Another aspect of the invention is directed to a method of
facilitating measurement of a subject's cornea, comprising (A.)
providing a plurality of apertures, (B.) projecting light toward
the plurality of apertures, (C.) translating a selection aperture
while maintaining the plurality of apertures in fixed locations to
selectively transmit a portion of the light toward the cornea, the
portion of the light passing through the selection aperture and a
selected one of the plurality of apertures and (D.) imaging the
portions of light after the light impinges on the cornea.
[0013] In some embodiments, the light passes through the selection
aperture prior to passing through any of the plurality of
apertures. In some embodiments, the step of projecting light
comprises projecting light from at least one LED. The method may
further comprise processing the images to convert the images into a
single representation of the cornea.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] Illustrative, non-limiting embodiments of the present
invention will be described by way of example with reference to the
accompanying drawings, in which the same reference number is used
to designate the same or similar components in different figures,
and in which:
[0015] FIG. 1 is a schematic plan view of an example of a corneal
measurement apparatus according to aspects of the present
invention;
[0016] FIG. 2 is an expanded plan view showing further details of
one arm of the corneal measurement apparatus of FIG. 1;
[0017] FIG. 3 is an illustration of an example of an embodiment of
a first slit mask defining a plurality of apertures viewed along
line 3-3 of FIG. 2; and
[0018] FIG. 4 is an illustration of an example of an embodiment of
a second slit mask defining a selection aperture viewed along line
4-4 of FIG. 2.
DETAILED DESCRIPTION
[0019] FIG. 1 is a schematic plan view of an embodiment of a
corneal measurement apparatus 10 according to aspects of the
present invention. The corneal measurement apparatus is adapted to
measure a subject's cornea C. The corneal measurement apparatus
comprises two illumination projection systems 13a, 13b (including
light sources 12a and 12b, respectively), two mask subsystems 100a,
100b, and an image capture subsystem 50. Mask subsystems 100a and
100b are disposed in the paths of light from illumination
projection systems 13a and 13b, respectively.
[0020] Illumination projection system 13a and mask subsystem 100a
are in a first arm 75a of the corneal measurement apparatus and
illumination projection system 13b and mask subsystem 100b are in a
second arm 75b of the corneal measurement apparatus. In the
illustrated embodiment, the first arm projects slits of light onto
one half of the cornea, and the second arm projects slits of light
onto the other half of the cornea. For example, the path of the
projects slits of light may be at a forty-five degree angle to the
visual axis of the subject's eye. Although the illustrated
embodiment of a measurement apparatus has two arms, in other
embodiments, a measurement apparatus may only have a single
arm.
[0021] Referring to FIG. 2, further details of one arm of the
corneal measurement apparatus 10 are shown. The arm comprises a
first slit mask 130 defining a plurality of apertures 132.sub.1 and
a second slit mask 120 defining a selection aperture 122. The arm
also comprises a translation apparatus 110 adapted to translate the
second mask. Second slit mask 120 is configured and arranged such
that, by appropriately positioning the second slit mask using the
translation apparatus, selection slit 122 selectively transmits
portions of the light from source 12a such that light traveling
through a selected one of the plurality of apertures 132.sub.1
impinges on cornea C. Ray R demonstrates that the selection
aperture 122 transmits light to cornea C from a selected one 132,
of the plurality of apertures, when selection aperture 122 is
appropriately aligned with the selected one 132.sub.1 of the
plurality of apertures. Subsequently, by translating second slit
mask 122, the selection aperture can be positioned such that light
from another of the plurality of apertures 132.sub.n can be
transmitted to cornea C. Such positioning of the selection aperture
can be repeated such that light from each of the plurality of
apertures or light from any suitable ones of the plurality of
apertures 132 can be transmitted to cornea C. It will be
appreciated that, on portions of the first slit mask and the second
slit mask that are outside of the apertures disposed thereon, the
slit masks are opaque or substantially opaque to light from source
12a.
[0022] It is to be appreciated that although, in the illustrated
embodiment, the second slit mask 120 (i.e., the mask including the
selection aperture)is disposed upstream (i.e., closer to source 12a
along the optical path) from first slit mask 130, in other
embodiments, the first slit mask (i.e., the mask including the
plurality of apertures) can be disposed upstream of the second slit
mask.
[0023] Referring again to FIG. 1, light sources 12a and 12b
generate the light in which a corresponding mask subsystem is
disposed. In some embodiments, the illumination projection system
projects light from the light sources in a cone of light L to
permit light to be projected through each of the apertures defined
in first slit mask 130 without moving the source or any other
component in the illumination projection system. That is to say
that, in some embodiments, only the second slit mask 120 is moved.
The movement occurs to expose a given one of the plurality of
apertures on the second mask to light from a light source. It will
be appreciated that, in such embodiments, the plurality of
apertures 132 that provide the slits of light can remain fixed in a
given location during the acquisition of the plurality of slit
images used to produce a representation of a subject's eye. An
advantage over prior art measurement apparatus, in which an
aperture is moved, is that slits of light are produced with
positions that are more accurately known, thereby providing more
accurate representations of subjects' eyes.
[0024] In some embodiments, it is advantageous if the source is
monochromatic and suitably bright. For example, an LED or a
plurality of LEDs may be used to generate the light. In some
embodiments, a high power LED has been found useful. In some
embodiments, a superluminescent LED is used. An aspect of the
invention is directed to a single high power LED configured and
arranged to be capable of illuminating the plurality of apertures
132 as the selection aperture is moved.
[0025] In some embodiments, it is advantageous that the projection
subsystem include a conventional condenser-projector system. In
FIG. 1, condenser lenses 14a, 14b gather light from sources 12a and
12b respectively, and projector lenses 18a, 18b are configured and
arranged such that the condenser lenses images sources 12a and 12b
onto the projector lenses 18a, 18b, respectively. The projector
lenses are also configured and arranged to image the apertures 132
onto cornea C. It is typically preferable that the slits of light
are not convergent or divergent between the first slit mask and the
cornea. However, some convergence or divergence may be present.
Although in the illustrated embodiment the projectors 18a, 18b are
lenses, any suitable imaging element may be used (e.g., a mirror,
holographic element).
[0026] Although in the illustrated embodiment the condenser lenses
14a, 14b are illustrated as lenses, any suitable imaging element
may be used (e.g., a mirror, holographic element). In some
embodiments, the condenser lens may be omitted. The projection
system components and first slit mask 130 may be disposed in a
Scheimflug arrangement to obtain a plane of slit images at cornea
C. Also, one or more folding mirrors 16a and 16b may be included to
direct light onto the cornea, and to achieve an appropriate package
shape for a housing (not shown) of the apparatus.
[0027] Further details of first slit mask 130 are now given with
reference to FIG. 3. Slit mask 130 includes a plurality of
apertures 132.sub.1-132.sub.n. Typically, the slits are of a same
width W and length L and are evenly spaced apart; however, aspects
of the invention are not so limited.
[0028] For example, twenty apertures may be provided on the slit
mask in first arm 75a (shown in FIG. 1) so that twenty slits of
light are projected onto a subject's cornea and twenty images are
obtained using light from the first arm 75a of the measurement
apparatus 10 (shown in FIG. 1). Accordingly, when combined with
twenty images from second arm 75b (shown in FIG. 1) a total of 40
slit images of a subject's eye are obtained. It will be appreciated
that any suitable number of apertures may be provided on the first
slit mask in each of mask subsystems 100a, 100b (shown in FIG.
1).
[0029] For example, first slit mask 130 may be formed on a
substrate 135 of soda lime glass or BK7 glass. An opaque layer may
be deposited on a surface of the substrate. For example, an opaque
metal layer may be deposited on the substrate, and the apertures
may be subsequently formed by etching a portion of the metal layer
to expose the substrate. Each of the apertures is sized and shaped
such that in a given measurement apparatus a slit of light is
projected onto a cornea in a conventional manner. Typically, the
apertures are rectangular in shape. However, any suitable shape may
be employed. In some embodiments, it may be desirable to apply and
antireflective coating to one or both of the surfaces of a
substrate. Although the plurality of apertures 132 are shown as
being formed on a single substrate (and in a single plane) any
suitable construction may be used in which the apertures are formed
at fixed locations relative to one another.
[0030] Further details of the second slit mask 120 are now given
with reference to FIG. 4. Slit mask 120 includes a single selection
aperture formed on a substrate 125. The selection aperture is sized
to permit light to pass from one of the plurality of apertures to
cornea C (shown in FIG. 1). Typically, the size of the selection
aperture is larger in width and length than any of the plurality of
apertures. The selection aperture is also typically small enough
such that light is only permitted to pass through a single one of
the plurality of apertures and onto cornea C.
[0031] In the illustrated embodiment of the second slit mask, an
aperture portion 124 (typically half the length of the selection
aperture) is also provided. The aperture portion is used for
alignment of the measurement apparatus relative to a subject's
cornea on whom a corneal measurement is to be made. The aperture
portion is aligned with one of the plurality of apertures on the
first slit mask, such that light is projected though only a portion
of the one of the plurality of apertures and a portion of a slit of
light is projected onto the middle of a subject's eye by the first
arm 75a (shown in FIG. 1) (e.g., an upper half of a slit is formed
at the middle of the subject's eye by the first arm).
[0032] Another, second slit mask 120 also having an aperture
portion is disposed in the other arm 75b (shown in FIG. 1).
Similar, to the aperture portion in the first arm, the aperture
portion in the second arm is aligned with one of the plurality of
apertures on the first slit mask of the second arm. Again, the
aperture is arranged to project light onto the middle of the
subject's cornea (e.g., a lower half of an aperture is formed at
the middle of the subject's eye). In a conventional manner, the
subject's cornea is aligned with the measurement apparatus, by
positioning either the subject or the machine such that the two
portions of the slits of light align to form a single, full-length
slit of light (e.g., the upper half of the slit of light from the
first arm aligns with the lower half of the slit of light from the
second arm) to form a single, full slit of light. The second slit
masks 120 (in the first and second arm) may be formed in a manner
similar to that described above for the first slit mask 130.
[0033] Referring again to FIG. 1, the image capture subsystem 50 is
arranged to be able to capture an image of light projected for each
of the plurality of apertures after the light impinges on the
cornea. It will be appreciated that, to capture of the images to
obtain a representation of a cornea, each of the plurality of
apertures is selected sequentially by appropriately aligning each
aperture with the selection aperture as described above. Image
capture subsystem 50 may be any suitable conventional imaging
device, such as a CCD camera.
[0034] Translation apparatus 110 may comprise any suitable
mechanism for translating the second mask 120 to project slits of
light form the plurality of apertures 132 on the first slit mask
130 to cornea C. For example, the translation apparatus may
comprise a linear translation motor capable of the moving the
second slit mask in a direction perpendicular to the length L of
the plurality of apertures 132.
[0035] Corneal measurement apparatus 10 also includes an image
processing subsystem to convert the images into a single
representation of the cornea. Techniques for reconstructing a
representation of a subject's cornea once the slit images are
obtained are well known and are not described further here.
Projection systems as described herein may be used with cornea
topographers, cornea profiler apparatus and anterior chamber
analyzers.
[0036] Corneal measurement apparatus 10 includes a subject
positioning apparatus 60 adapted to maintain a subject's cornea in
a location. For example, the apparatus may be provided with a chin
rest and/or a forehead rest which will fix the location of the
subject's head.
[0037] Having thus described the inventive concepts and a number of
exemplary embodiments, it will be apparent to those skilled in the
art that the invention may be implemented in various ways, and that
modifications and improvements will readily occur to such persons.
Thus, the embodiments are not intended to be limiting and presented
by way of example only. The invention is limited only as required
by the following claims and equivalents thereto.
* * * * *