U.S. patent application number 16/713139 was filed with the patent office on 2020-04-16 for apparatus for modelling ocular structures.
The applicant listed for this patent is Novartis AG. Invention is credited to Daniel Boss, Michael Mrochen, Andrew Nolan, Pav Zakharov.
Application Number | 20200113430 16/713139 |
Document ID | / |
Family ID | 52946378 |
Filed Date | 2020-04-16 |
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United States Patent
Application |
20200113430 |
Kind Code |
A1 |
Boss; Daniel ; et
al. |
April 16, 2020 |
APPARATUS FOR MODELLING OCULAR STRUCTURES
Abstract
An apparatus for motion compensated modelling of a parameter of
an eye, comprising: a first measuring means for measuring a
plurality of position parameters of the eye with respect to an
optical reference coordinate system of the apparatus; a second
measuring means for measuring an interference signal at a plurality
of optical reference coordinates, wherein the measurement of the
plurality of position parameters and measurement of the
interference signal are time synchronised; means for correcting the
interference signal to account for a displacements of a parameter
of the plurality of position parameters; and means for modelling
the eye parameter based at least in part on the corrected
interference signal.
Inventors: |
Boss; Daniel; (Zurich,
CH) ; Mrochen; Michael; (Eglisau, CH) ; Nolan;
Andrew; (Louth, IE) ; Zakharov; Pav;
(Volketswil, CH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Novartis AG |
Basel |
|
CH |
|
|
Family ID: |
52946378 |
Appl. No.: |
16/713139 |
Filed: |
December 13, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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16030104 |
Jul 9, 2018 |
10568501 |
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16713139 |
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15091615 |
Apr 6, 2016 |
10016125 |
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16030104 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61B 3/0025 20130101;
A61B 3/113 20130101; A61B 3/102 20130101; G01B 9/02091 20130101;
A61B 3/103 20130101 |
International
Class: |
A61B 3/00 20060101
A61B003/00; G01B 9/02 20060101 G01B009/02; A61B 3/103 20060101
A61B003/103; A61B 3/113 20060101 A61B003/113; A61B 3/10 20060101
A61B003/10 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 15, 2015 |
EP |
15163726.1 |
Claims
1. An apparatus for motion compensated modelling of a parameter of
an eye, comprising: a first measuring means for measuring a
plurality of position parameters of the eye with respect to an
optical reference coordinate system of the apparatus; a second
measuring means for measuring an interference signal at a plurality
of optical reference coordinates, wherein the measurement of the
plurality of position parameters and measurement of the
interference signal are time synchronised; means for correcting the
interference signal to account for a displacements of a parameter
of the plurality of position parameters; and means for modelling
the eye parameter based at least in part on the corrected
interference signal.
2. The apparatus according to claim 1 wherein the plurality of
position parameters include lateral displacement along an x axis of
the optical reference coordinate system, lateral displacement along
a y axis of the optical reference coordinate system and axial
displacement along a z axis of the optical reference coordinate
system.
3. The apparatus according to claim 1 wherein the plurality of
position parameters include cyclorotation around the z-axis.
4. The apparatus according to claim 1 wherein the plurality of
position parameters include rotation around the x axis and rotation
around the y axis.
5. The apparatus according to claim 1 wherein means for determining
a displacement comprises means for interpolating between
measurements of the plurality of position parameters.
6. The apparatus according to claim 1 further comprising means for
determining a reference location of the second measuring device and
means for correcting said reference location based on the measured
position parameters.
7. The apparatus according to claim 1 wherein the means for
correcting further comprises means for correcting an optical path
length based on a difference in an optical path length between an
off-axis ray-traced path length and a path length along the z axis
of the optical reference coordinate system.
8. The apparatus according to claim 1 wherein the first measuring
device further comprises means for measuring a position parameter
based on a retinal reflex.
9. The apparatus according to claim 7 further comprising means for
iteratively correcting the optical path length.
10. The apparatus according to claim 1 wherein the first measuring
device comprises means for illuminating a targeted ocular surface
(116-120) with a least one incident light beam and means for direct
at least two light beams returning from the illuminated ocular
surface to an image forming device (110).
11. The apparatus according to claim 10 wherein the ocular surface
includes an anterior corneal surface, a posterior corneal surface,
an anterior lens surface, a posterior lens surface or a retinal
surface.
12. The apparatus according to claim 1 wherein the first measuring
means is selected from a list including a Purkinje Mirror Imaging
device, an Optical coherence Tomography Device or a Scheimpflug
Imaging System and the second measuring means comprises an optical
coherence device.
13. The apparatus according to claim 11 further comprising means
for determining refraction at the ocular surface and correcting the
modelled eye parameter based on the determined refraction.
14. An method for motion compensated modelling of a parameter of an
eye, comprising: measuring a plurality of position parameters of
the eye with respect to an optical reference coordinate system of
the apparatus; measuring an interference signal at a plurality of
optical reference coordinates, wherein the measurement of the
plurality of position parameters and measurement of the
interference signal are time synchronised; correcting the
interference signal to account for a displacements of a parameter
of the plurality of position parameters; and modelling the eye
parameter based at least in part on the corrected interference
signal.
15. A computer readable programmable medium carrying a computer
program stored thereon which when executed by a processing module
implements the method according claim 14.
Description
TECHNICAL FIELD
[0001] The technology described herein relates to ocular modelling
and in particular motion compensated modelling of a parameter of an
eye.
BACKGROUND ART
[0002] Ocular procedures often modify one or more structures of the
eye, such as the cornea, lens or retina. Some procedures involve
removing or replacing one or more structures of the eye, or adding
an implant. For example, lens replacement surgery involves removing
a patient's existing lens and replacing it with a new lens. Some
procedures, such as laser vision correction surgery, do not remove
or replace existing structures of a patient's eye, or add an
implant to the eye, but rather reshape existing structures.
Regardless of the type of modification being made (e.g. removal,
replacement, insertion, or alteration), the optical performance of
the eye is altered by adjustments made to the structures of the
eye. Therefore in order to accurately model the structure of any
eye, it is necessary to determine the ocular parameters of that
eye. These parameters include shape, thickness and refractive index
of ocular structures such as the cornea, the lens, the retina, or
any other structure of interest.
[0003] Measuring parameters such as curvatures, or shapes of
surfaces, or thickness of elements within a patient's eye is
traditionally carried out using variations of ultrasound Optical
Coherence Tomography (OCT) or Optical Low Coherence Reflectometry
(OLCR), Purkinje or Scheimpflug imaging systems.
[0004] With living subjects and taking into account the precision
of the measurements required it is necessary to introduce a level
of movement compensation. Solutions for movement compensation are
introduced in US 2012140175 A (CARL ZEISS MEDITEC, INC) 24 Jan.
2012, US 2013188140 A (CARL ZEISS, MEDITEC, INC) 17 Jan. 2013, US
2011267340 A (UNIV FRIEDRICH ALEXANDER ER [DE]; MASSACHUSETTS INST
TECHNOLOGY [US]) 29 Apr. 2011, EP 2198771 A (OPTOPOL TECHNOLOGY,
SA) Feb. 12, 2012, and WO 2010/101162 A (CANON KK [JP]; NUMAJIRI
YASUYUKI [JP]; YAMADA KAZURO [JP]; HIROSE FUTOSHI [JP) 24 Feb.
2010. Additionally, US 2012249956 A (NARASIMHA-IYER HARIHAR [US];
EVERETT MATTHEW J [US]; ZEISS CARL MEDITEC INC [US]), WO
2010/149420 A (SIEMENS AG [DE]; KLEINFELD JENS [DE]; KLUGE ANDRE
[DE]; MEISL JUERGEN [DE]; TUESCHEN SABINE [DE]; WO) 26 Mar. 2009 US
2013195336 A (UCHIDA HIROKI [JP]; CANON KK [JP) 30 Aug. 2012 apply
additional data processing and scan patterns to movement
compensation to account for movement of the subject/patient's head.
US 2009091766 A (CANON KK [JP]) 30 Aug. 2008 and DE 102009022958 A
(ZEISS CARL MEDITEC AG [DE]) 28 May 2009 also acquire simultaneous
fundus images in order to track eye movement and thus compensate
for same in order to improve the determination of optical
parameters.
[0005] To further improve the determination and accuracy of optical
measurements using OCT/OLCR, attempts have been made to combine
measurements made using these systems with additional
measurement/movement detection to correct motion artefacts.
Advances have been made in corneal vertex position detection
through the use of additional measuring modality to provide
accurate axial length measurement.
[0006] U.S. Pat. No. 5,387,951 B (TOPCON CORP) Jul. 3, 1995
discloses an apparatus for intraocular length measurements which
avoids errors in measurement caused by the movement of a subjects
head. By concurrently measuring the axial movement of the eye
during the measurement process, the actual eye length can be
calculated by adjusting the apparent length by the amount of axial
movement. A disadvantage of this system is that motion correction
applies only to axial length measurement.
[0007] US 2007076217 (CARL ZEISS MEDITEC, INC) May 10, 2005 is
directed to the use of optical coherence tomography for eye length
measurement. A second OCT device is used to correct measurements
made by the first OCT device. As with U.S. Pat. No. 5,387,951 this
disclosure is only directed to axial length correction rather than
a total A-scan. Furthermore, only z-axis displacement is accounted
for in measurements and corrections.
[0008] US 2010014051 A (SIS AG SURGICAL INSTR SYSTEMS) 24 Jul. 2008
combined interferometric techniques to determine a relative
position of the retina of the eye and uses a second
non-interferometric technique to determine a relative position of
the cornea and uses these measurements to determine the axial
length of the eye. As previously, only z-axis displacement is
accounted for. No motion compensation A-scan measurements are
possible.
[0009] WO 2014/043517 A (UNIV JOHNS HOPKINS [US]) 13 Sep. 2013 is
also directed to a motion compensated OCT and feedback system which
provides for correction of deviation based on cross correlation of
adjacent scans. However, this document does not provide for
absolute motion tracking.
[0010] WO 2010/010116 A (BIOGASOL IPR APS [DK]; MIKKELSEN MARIE
JUST [DK]; YAO SHUO [DK) 29 Jul. 2009 implements the Scheimpflug
principles in corneal vertex position detection with additional
measuring modality. This document provides a means for measuring
corneal vertex position (x, y, z) however, provides only for axial
eye motion, i.e. z-axis compensation.
[0011] WO 2009/149953 A (ZEISS CARL MEDITEC AG [DE]; BUBLITZ DANIEL
[DE]; KRAMPERT GERHARD [DE]; HACKER MARTIN [DE]) Dec. 6, 2009 uses
first and second OCT measurements to compensate for a complete
A-scan OCT, but again only provides for active eye motion
compensation, is z-axis compensation.
[0012] It is therefore an object of the present invention to
implement an improved compensation system and method for eye
movement compensated measurements of multiple ocular surface
locations. In systems such as those described above where two
methods of measurement are implemented compensation is only for
axial length measurements and compensation is for z-axis
displacement. It is an object of the present invention to provide a
more accurate system and namely a measurement system that is not
influenced by eye motions.
SUMMARY OF INVENTION
[0013] It should be appreciated that all combinations of the
foregoing concepts and additional concepts discussed in greater
detail below (provided such concepts are not mutually inconsistent)
are contemplated as being part of the inventive subject matter
disclosed herein. In particular, all combinations of claimed
subject matter appearing at the end of this disclosure are
contemplated as being part of the inventive subject matter
disclosed herein. It should also be appreciated that terminology
explicitly employed herein that also may appear in any disclosure
incorporated by reference should be accorded a meaning consistent
with the particular concepts disclosed herein.
[0014] The invention as described herein includes an apparatus for
motion compensated modelling of a parameter of an eye, comprising:
[0015] a first measuring means for measuring a plurality of
position parameters of the eye with respect to an optical reference
coordinate system of the apparatus; [0016] a second measuring means
for measuring an interference signal at a plurality of optical
reference coordinates, wherein the measurement of the plurality of
position parameters and measurement of the interference signal are
time synchronised; [0017] means for correcting the interference
signal to account for a displacements of a parameter of the
plurality of position parameters; and [0018] means for modelling
the eye parameter based at least in part on the corrected
interference signal.
[0019] This integrated measurement system for ocular modelling
allows for measurements of the eye that are independent of eye
motions of a patient or are not influenced by eye motions. The
first measuring means provides instantaneous measurement of eye
position parameters, while the second measuring means provides
measurements of optical path length differences.
[0020] The plurality of position parameters may include lateral
displacement along an x axis of the optical reference coordinate
system, lateral displacement along a y axis of the optical
reference coordinate system and axial displacement along a z axis
of the optical reference coordinate system.
[0021] The plurality of position parameters may include
cyclorotation around the z-axis.
[0022] The plurality of position parameters may include rotation
around the x axis and rotation around the y axis.
[0023] The provision of instantaneous measurements of the eye
position in a plurality of planes facilitates accurate motion
compensation as eye roll is taken into account. The combination of
the position parameters for eye parameter/ocular modelling provides
for more accurate eye parameter reconstruction. For example where
the second measuring means is an OCT system providing a time domain
A-scan, and the first measuring means is a Purkinje imaging system
or other ocular coherence tomography or Scheimpflug imaging system,
the apparatus as claimed allows for the whole A-scan to be
compensated, and not only the OPD between two surfaces as in a dual
beam OLCR implementation. The motion compensated A-scan takes into
account lateral eye movement and also axial displacement. The
combination of the features allows for a relaxation in scanning.
For example if the second measuring means is an OCT system, a
slower scanner can be used as it is not essential that the patient
stay still as the OCT measurements can be motion compensated.
[0024] The modelled eye parameter may comprise a shape, thickness,
distance, or position of the eye.
[0025] Means for determining a displacement may comprise means for
interpolating between measurements of the plurality of position
parameters.
[0026] The embodied apparatus may further comprise means for
determining a reference location of the second measuring device and
means for correcting said reference location based on the measured
position parameters.
[0027] The means for correcting may further comprise means for
correcting an optical path length based on a difference in an
optical path length between an off-axis ray-traced path length and
a path length along the z axis of the optical reference coordinate
system.
[0028] The first measuring device may further comprise means for
measuring a position parameter based on a retinal reflex.
[0029] The optical path length may be iteratively corrected.
[0030] The first measuring device may comprise means for
illuminating a targeted ocular surface with a least one incident
light beam and means for direct at least two light beams returning
from the illuminated ocular surface to an image forming device.
[0031] The ocular surface may include an anterior corneal surface,
a posterior corneal surface, an anterior lens surface, a posterior
lens surface or a retinal surface.
[0032] The first measuring means may be selected from a list
including a Purkinje Mirror Imaging device, an Optical coherence
Tomography Device or a Scheimpflug Imaging System and the second
measuring means comprises an optical coherence device. The second
measuring means may be selected from a list including a Purkinje
Mirror Imaging device, an Optical coherence Tomography Device or a
Scheimpflug Imaging System.
[0033] The apparatus may further comprise means for determining
refraction at the ocular surface and correcting the modelled eye
parameter based on the determined refraction.
[0034] A further embodiment of the invention includes a method for
motion compensated modelling of a parameter of an eye, comprising:
[0035] measuring a plurality of position parameters of the eye with
respect to an optical reference coordinate system of the apparatus;
[0036] measuring an interference signal at a plurality of optical
reference coordinates, wherein the measurement of the plurality of
position parameters and measurement of the interference signal are
time synchronised; [0037] correcting the interference signal to
account for a displacements of a parameter of the plurality of
position parameters; and [0038] modelling the eye parameter based
at least in part on the corrected interference signal.
[0039] The plurality of position parameters may include lateral
displacement along an x axis of the optical reference coordinate
system, lateral displacement along a y axis of the optical
reference coordinate system and axial displacement along a z axis
of the optical reference coordinate system.
[0040] The plurality of position parameters may include
cyclorotation around the z-axis.
[0041] The plurality of position parameters may include rotation
around the x axis and rotation around the y axis.
[0042] The modelled eye parameter may comprise a shape, thickness,
distance, or position of the eye.
[0043] Determining a displacement may comprise interpolating
between measurements of the plurality of position parameters.
[0044] The embodied method may further comprise determining a
reference location of the second measuring device and correcting
said reference location based on the measured position
parameters.
[0045] Correcting may further comprise correcting an optical path
length based on a difference in an optical path length between an
off-axis ray-traced path length and a path length along the z axis
of the optical reference coordinate system.
[0046] The method may further comprise measuring a position
parameter based on a retinal reflex.
[0047] The optical path length may be iteratively corrected.
[0048] The method may further comprise illuminating a targeted
ocular surface with a least one incident light beam and means for
direct at least two light beams returning from the illuminated
ocular surface to an image forming device.
[0049] The ocular surface may include an anterior corneal surface,
a posterior corneal surface, an anterior lens surface, a posterior
lens surface or a retinal surface.
[0050] The method may further comprise determining refraction at
the ocular surface and correcting the modelled eye parameter based
on the determined refraction.
[0051] A further embodiment of the invention includes a system
comprising the apparatus according to any of claims 1 to 14 and
further comprising a camera.
[0052] There is also provided a computer program comprising program
instructions for causing a computer program to carry out the above
method which may be embodied on a record medium, carrier signal or
read-only memory.
BRIEF DESCRIPTION OF DRAWINGS
[0053] Various non-limiting embodiments of the technology described
herein will not be described with specific reference to the
following figures. It should be appreciated that the figures are
not necessarily drawn to scale.
[0054] FIG. 1 depicts a configuration of an optical system
combining a Purkinje Mirror Imaging modality (PMI) and an OLCR
measurement apparatus for ocular measurements in accordance with an
embodiment of the present intervention.
[0055] FIG. 2 depicts features in illumination channels for
extraction in accordance with the present invention.
[0056] FIG. 3 illustrates translational eye position measurement
from P1 spot locations
[0057] FIG. 4 is illustrative of the range of eye movements
measurable with PMI in accordance with the present invention,
namely 3 translational and 3 rotational degrees of freedom of eye
motion.
[0058] FIG. 5 shows scanning measurement principles used in OCT
[0059] FIG. 6 depicts axial motion compensation in OCT-A scans
using PMI tracked eye position.
[0060] FIG. 7 illustrates registration applied to align multiple
A-scans obtained at single measurement point within the eye
coordinate system in accordance with the present invention.
[0061] FIG. 8 shows off axis compensation in OLCR A scans for eye
length measurements
[0062] FIG. 9 demonstrates reconstruction of ocular surfaces based
on a combination of PMI with multiple OCT measurement points within
the eye coordinate system.
[0063] FIG. 10 illustrates the reconstruction of eye parameters
taking into account refraction of the OLCR measuring beam within
the subject eye in accordance with the present invention.
[0064] FIG. 11 shows an iterative process for reconstruction of
ocular surface in accordance with the present invention
DESCRIPTION OF EMBODIMENTS
[0065] The aspects of the technology mentioned above, as well as
additional aspects, will now be described in greater detail. The
aspects may be used individually, all together or in any
combination of two or more, as the technology is not limited in
this respect.
[0066] The system shown in FIG. 1 illustrates a configuration of an
optical system combining a Purkinje Mirror Imaging (PMI) Modality
100 and an Optical Low Coherence Reflectometry (OCLR) 200 for
ocular measurements of structures of interest in accordance with
the present invention. A structure of interest may be a complete
structure (e.g., a lens) or a surface (e.g. the front of the lens)
and a parameter may be the shape, thickness or refractive index of
the structure of interest. Any of these parameters may be of
interest either as an ultimate result or a means for determining
other parameters or for both purposes. For example, the shape of
the cornea may be of interest as an end result for modelling the
cornea, but may also facilitate the determination of the refractive
index of the cornea.
[0067] The Purkinje Mirror Imaging Modality 100 comprises light
source(s) and optics 101 which are arranged to emit collimated
light. The collimated light illuminates the surface of interest.
Illumination of the surfaces can be done with any wavelength beam
of any type, be that coherent laser light, partially coherent LED
light or an incoherent broadband source. In a preferred embodiment,
wavelengths are chosen such that water and tissue absorption in the
eye are minimized. Wavelengths in the range of 400 to 1300 nm
(broad) and preferably 700-900 nm are optimal.
[0068] A beam splitter 102 reflects illuminating light into at
least two illumination channels. Light paths 111, shown in FIG. 1,
are illustrative of illumination through an illumination channel
consisting of outer and inner mirror 103, 104. These mirrors are
arranged to direct illuminating beams 111 onto an eye 115 at a
fixed illumination angle .alpha.1 with respect to an optical
reference coordinate system 113 (x, y, z) as shown in FIG. 1. These
mirrors may be rod mirrors for example. However, it will be
appreciated that they are not restricted as such and may also
include any reflective element including a combination of prisms
with or without mirrors or glass cones.
[0069] When the illuminating beams fall on the mirrors they are
directed to ocular surfaces 116, 117, 118, 119, 120 from which they
are then reflected. As will be appreciated ocular surfaces include
an anterior corneal surface 116, posterior corneal surface 117
anterior lens surface 118, posterior lens surface 119 and retinal
surface 120.
[0070] Light reflected from the ocular surfaces is collected by at
least two imaging channels onto at least one image forming device
110.
[0071] An example of such an imaging channel is shown by light path
112 which illustrates the image formation through an imaging
channel. Reflected light from the anterior corneal surface 116 is
collected by an outer mirror 105 and an inner mirror 106. This
reflected and collected light is then transmitted through the beam
splitter 102.
[0072] To achieve a telecentric image formation on the image
forming device 110 of the reflections from the ocular surfaces
(Purkinje reflections) a pin hole 108 placed at a focal points of
two lenses 107 and 109. In this imaging channel, image formation
occurs for reflected rays making a fixed angle .alpha.2 with
respect to the optical system coordinate system 113.
[0073] Illuminating channels used to illuminate the eye with
collimated beams at a fixed angle .alpha.1 are used at the same
time as imaging channels to transmit light reflected at a fixed
angle .alpha.2 onto the image forming device 110.
[0074] A suitable configuration for such a PMI unit is described in
WO 2012/130818 A (NAT DIGITAL RES CT [IE]) 26 Mar. 2012 which is
incorporated herein by reference in its entirety. The system
described therein is referred to as a "Mirricon" system. In the
Mirricon system an illuminating beam from a collimated source is
injected into the system to illuminate mirrors located on the
optical axis. When rays from the source fall on the mirrors these
rays are then reflected to a system of meridional flat mirrors. The
Mirricon system is configured both for the illumination of the eye
with collimated beams off axis and also for imaging the Purkinje
reflections. The returning light passes back to the imaging forming
device as described herein.
[0075] In combination with the PMI unit 100, an OCT imaging
modality unit/Eye scanning unit 200 is provided. This unit
incorporates a light source 201, photodetector 202, light coupler
203, reference light beam with reference mirror 204, and an object
light beam 205. It will be appreciated that OCT imaging modality
may be time domain OCT, optical coherence reflectometry, OLCR, or
Spectral Domain OCT using a broadband source or swept source.
Unless specifically mentioned herein OCT may refer to any of these
systems.
[0076] In accordance with the system of FIG. 1 the imaging forming
device 110 captures and stores images which contain information on
the spatial locations of Purkinje reflections from illuminating
beans in the at least two illuminating channels and images through
the at least two imaging channels. It will be appreciated that
generally at least four Purkinje images reflected from incident
light of an illumination channel and transmitted through an imaging
channel are usually visible, for example the first Purkinje image
(P1) is the reflection from the anterior corneal surface. The
second Purkinje image (P2) is the reflection from the posterior
corneal surface. The third Purkinje image (P3) is the reflection
from the anterior lens surface. The fourth Purkinje image (P4) is
the reflection from the posterior lens surface
[0077] Further, the image forming device 110 captures light
emanating from an illumination channel that is retro-reflected at
the retinal surface 120 and is transmitted back through the
illumination channel onto the image forming device 110. As shown in
FIG. 2, the boundaries of the areas of the retinal reflex is
indicative of the pupil boundary imaged through the imaging channel
onto the image forming device. The images shown in FIG. 2 are
illustrative of the pupil boundaries without and with retinal
retroflex. The levels of illumination for the p1 images differ in
both cases.
[0078] Parameters of the eye may include shape, thickness,
distances, position of the eye and refractive index of the ocular
structures of the eye. While some of the parameters listed above
are intrinsic to the eye it will be appreciated that measurements
such as position of the eye are derived from measurements of other
parameters. Measurement of any one of shape, thickness and/or
refractive index of an ocular structure of interest may depend to
some extent on the directional changes which light employed by the
measurement technique undergoes while passing through any ocular
structures preceding the structure of interest. Thus, according to
one aspect of the technology, measurements of shape thickness,
and/or refractive index of ocular structures may be corrected to
account for the dependence of the measured values of other
parameters for that structure, as well as on any of the parameters
of the preceding structures.
[0079] To reconstruct any of the eye parameters, the information
collected and stored at the image forming device 110 is used to
determine features including Purkinje image locations and pupil
boundary locations based on the PMI Image Acquisition containing
images of at least two image channels collecting reflections from
the at least two illumination channels.
[0080] Reconstruction of any parameter of the eye may be performed
using reverse ray-tracing through the modelled optical system. In
such a system, rays are traced back from the detected locations of
a detected feature on the image forming device 110 through the
image channel onto the ocular surface containing the particular
feature where it is reflected back at a certain angle. It will be
appreciated that this angle must coincide with the angle of
illumination al shown in FIG. 1. If these angles do not coincide,
the initial parameter of the modelled subject eye is altered until
the angle of the reference plane matches the illumination angle
.alpha.1. Accordingly, an angle constraint is obtained for each
detected Purkinje location. The difference between the known angle
of illumination al and the reconstructed angle enters a merit
function, i.e., the merit function is constructed from the multiple
angle constraints from each detected Purkinje image. The optical
path differences (OPD) between the ocular surfaces obtained from
optical coherence peak positions is used as an additional
constraint that can enter the merit function. In a preferred
embodiment reconstruction is performed using an iterative
optimization method. Parameters of the subject eye are altered
until a minimum of the merit function is achieved. Examples of
optimization methods include a damped least squares algorithm (DLS)
or an Orthogonal Descent (OD) algorithm. The DLS algorithm for
example uses numerically computed derivatives to determine a
direction in solution space which produces an optimal configuration
with a lower merit function. OD in contrast, uses an
ortho-normalization of the variables and discrete sampling of
solution space to reduce the merit function. The OD algorithm does
not compute numerical derivatives of the merit function.
[0081] For parameters, such as anterior corneal parameters,
including eye position, reconstruction is also possible based on
matching ray positions from opposing spots. For example, given two
channels A and B where both are simultaneously illuminated B, in a
first step A is illuminated and B is imaged and in a second step B
is illuminated and A is imaged. Based on an assumption that the
beams take the same path in opposite directions positions of the
rays can be matched to forma a merit function. It will be
appreciated that such a configuration is suitable for anterior
cornea or eye position reconstructions. If the sequential
illuminations are sufficiently fast to be considered instantaneous
then the above described method is also applicable to the anterior
cornea. Eye position for example, may be determined with respect to
the optical system reference axis. The system reference axis may be
the central axis of the OCT system or any other defined reference
axis, such as reference axis 113.
[0082] In an additional or alternative embodiment, eye position
measurements may be determined directly from detected features. It
will be appreciated that this is without an optimization procedure.
As an example, lateral and axial position changes are directly
infer-able from measured P1 spot locations. These spot locations
emanate from opposing illumination channels and imaged by opposing
imaging channels on the camera plane. FIG. 3 shows an axial
displacement .DELTA.z and a lateral displacement .DELTA.x of the
eye. This further shows the changes in spot positions in a virtual
plane conjugate to the camera plane. The displacement .DELTA.z of
the eye along the optical axis is proportional to the change in
distance between the spots in opposing illumination channels
.DELTA.d=d-d'. The displacement .DELTA.x within the x-y plane is
proportional to the displacement of the centre of gravity .DELTA.c
of the spots from opposing illumination channels. The constant
relation between .DELTA.d and .DELTA.z, and .DELTA.c and .DELTA.z
is determined by the geometry of the PMI configuration.
[0083] It will further be appreciated that P4 and the pupil centre
positions derived from the pupil boundary positions can also be
used for eye position determination.
[0084] FIG. 4 depicts the eye position parameters that can be
reconstructed from a PMI acquisition with respect to an optical
system reference axis as indicated. These eye position parameters
include lateral displacements .DELTA.x, .DELTA.y which are shown
along the x, y axis respectively. The parameters also include axial
displacement .DELTA.z which is indicated along z-axis. In addition,
cyclorotation 5 is indicated where .delta. is rotation around
z-axis. An additional parameter p shown in FIG. 2b and is
representative of rotation around x-axis (eye roll movement).
Rotation around y-axis (eye roll movement) is represented by the
symbol e. It will be appreciated that one or more or any
combination of these parameters can be reconstructed or determined.
In accordance with the present invention and as depicted in FIG. 5,
A scans or .DELTA.xial scans and B scans or transversal scans are
performed. These scans are time dependent. Geometrical
reconstruction is dependent on the displacement of the eye due to
eye motion.
[0085] The graphs of FIG. 6 are illustrative of axial motion
compensation in a TIME domain OCT/OLCR axial scan at a given
lateral position, x, y in the optical system reference axis.
[0086] The interference signal detected on the photodetector 202 of
the OCT imaging modality 200 is filtered to extract an envelope
signal I(t) as a function of time t of said interference signal as
the reference mirror 204 is displaced by a known distance
z.sub.ref(t) with respect to the optical system reference axis (cf.
FIG. 6A)
[0087] For example, with an OCT scan in accordance with the present
invention, for each measurement of an eye, 32 interferograms may be
acquired. 32 is given herein as an example only. Envelope signals
are reconstructed from the interferogram signals. In an example,
the envelope of an interferogram may be reconstructed by filtering
the raw interferogam with a Gabor filter. Such a filter is defined
by two parameters, namely: the width of the Gaussian envelope and
the frequency of sinusoidal modulation. The modulation frequency of
the filter has to be matched with the frequency of the
interferogram, f, which is defined by the speed of the scanner v,
and the wavelength of the source .lamda.:
f=2*v/.lamda.
[0088] As an alternative, the envelope may be obtained by taking
the absolute value of the complex analytic signal obtained from
Hilbert transform of a Fourier filtered interferogram.
[0089] During the scanning period, the PMI modality 100 acquires
images on the image forming device 110. Optionally these images may
be obtained at a fixed temporal interval .DELTA.t. Where a fixed
temporal interval is chosen it will be appreciated that this
interval is chosen so that the acquisition frequency is higher than
typical temporal frequencies of eye movements. Alternatively, a
higher frequency may be chosen, such as for example, during an
anterior chamber scan.
[0090] In the embodiment shown in FIG. 6, the acquisition of the
PMI images is time synchronized with the measurement of the
interference signal detected on the photodetector. This ensures
that a PMI image acquisition corresponds to a known time point of
the envelope signal I(t).
[0091] For example, from the measured PMI images the axial
displacement .DELTA.z (.DELTA.t.sub.i) with respect to the optical
system reference axis of the anterior cornea at the position
[x',y',z']=(0,0,0) with respect to the subject eye reference axis
114 is reconstructed. Using the discrete set of axial displacement
measurements .DELTA.z(.DELTA.t.sub.i), a function .DELTA.z(t) is
obtained using an interpolation method (cf. FIG. 6B). It will be
appreciated that this interpolation method can be a linear
interpolation method, a nearest neighbour interpolation method or a
spline interpolation method or the like.
[0092] An axial scanner position can then be expressed with respect
to the subject eye coordinate system as
z'.sub.ref(t)=z.sub.ref(t)+.DELTA.z(t)
[0093] With the knowledge of the function z'.sub.ref(t), the
envelope signal I(t) can be expressed as a function I'(z') of the
axial coordinate z' of the subject eye reference axis to obtain a
compensated A-scan (cf. FIG. 6C) for axial eye displacements.
[0094] Multiple A-scans acquired sequentially at a given lateral
position x,y in the optical system reference axis can be averaged
by summing individual eye motion compensated A-scans.
[0095] If the absolute scanner position z(t) of the OCT modality is
not known with respect to the optical system coordinate axis, i.e.
only relative position changes of the scanner are known, it will be
appreciated that the multiple eye motion compensated A-scans
require re-alignment prior to averaging the multiple A-scans. This
realignment can be performed by registration algorithms. Said
registration algorithm can be based on maximizing the cross
correlation amplitude between subsequent A-scan signals I(t) as
shown in FIG. 7.
[0096] Motion compensation is further illustrated in the
embodiments shown in FIGS. 8 to 11.
[0097] In a first embodiment as shown in FIG. 8 X, Y motion
compensation or off-axis compensation for OLCR axial length
measurements is implemented. The motion compensation of a single
OCT/OLCR A-scans for eye length measurements takes into account the
lateral off-axis position (.DELTA.x, .DELTA.y) of the subject eye
reference axis with respect to the system coordinate axis
reconstructed from a PMI image acquisition. Such an embodiment is
illustrated in FIG. 8 which shows the optical system reference
axes, x, y and z with the optical measurement axis of the OCT along
the z-direction and a subject eye coordinate system centred at the
anterior corneal vertex position.
[0098] It will be appreciated that for accurate eye length
measurements it is desirable to measure OCT A-scans when the
optical system z-axis and the subject eye z'-axis are aligned.
[0099] For a laterally displaced eye coordinate system due to eye
motions, a reflection of the OLCR measuring beam at the cornea
occurs after the measuring beam travels an additional optical path
length .epsilon.(.DELTA.x,.DELTA.y) that is dependent on the
off-axis position (.DELTA.x,.DELTA.y).
[0100] To compensate for an off-axis position in the measurement of
eye length, the reconstructed measurement of the axial displacement
of the anterior cornea .DELTA.z (t) with respect to the optical
reference system is corrected as .DELTA.z.sub.corr (t)=.DELTA.z
(t)-.xi.(.DELTA.x(t), .DELTA.y (t), .DELTA.z(t)). A correction
function .xi.(x,y,z) can be derived from an average topography of
the cornea of multiple eyes or from a corneal curvature measurement
of the subject eye derived from measured PMI eye parameters.
[0101] It will be appreciated that the correction function
.xi.(x,y,z) further depends on the axial displacement of the
scanner position z(t).
[0102] For scanner positions in the vicinity of the expected retina
position the function .xi.(x,y,z) equals to 0, such that no
off-axis correction is added to the measured axial displacements
.DELTA.z(t) when the OCT signal from the retinal surface is
detected. The embodiment of the invention as shown in FIG. 9 is
illustrative of a system which combines PMI and OLCR/OCT measured
at off-axis positions XY. In this embodiment the OCT object beam
measures at multiple measurement points within the eye coordinate
system. Multiple measurements at different locations within the
subject's eye coordinate system are taken using a transversal
scanning (B-scan) of the OCT measuring beam. In an alternative,
multiple measurements are taken at different locations within the
subject eye coordinate system by allowing passive movements of the
subject eye coordinate system with respect to the optical system
coordinate. Such passive relative movements could occur due to eye
movements or movements of a handheld implementation of a PMI/OCT
measurement device.
[0103] The measuring location (x',y') of a reflection position of
the OCT object beam on an ocular surface within the eye coordinate
system can be calculated from the measuring location (x,y,z) within
the optical system coordinate axes and the measured eye position
parameters obtained from the PMI acquisition.
[0104] The axial displacement z' of said reflection position on
said ocular surface within the eye coordinate system can be
obtained either from the reconstructed eye parameters or from the
measured peak position in the OCT scan. This thus offers novel
constraints that can enter the merit function to more accurately
reconstruct the eye parameters based on multiple measurement points
within the eye coordinate system.
[0105] Iterative processes may be applied to calculate corrections
which may be due to light propagation and refraction at a known
surface point. For example, the surface of the eye may be
reconstructed based on corrected OPD/OLCR/OCT signals. Derivation
of these corrections may be implemented in an iterative
process.
[0106] FIG. 10 details X, Y and eye roll movement compensation
using the combination of PMI with OLCR whilst taking into account
refraction at the ocular surface. This iterative reconstruction is
therefore based on PMI in combination with OLCR peak positions and
light propagation/refractions within the eye.
[0107] An actual optical path 2 and an assumed optical path 1 are
shown in FIG. 10. Distances between surfaces of the eye along the
assumed path 1 are shown as d1, d2, d3 and d4, with corresponding
distances along the actual optical path shown as d1', d2', d3' and
d4'. For example the distance between surface 1 and surface 2 along
the assumed path is d1 and the corresponding distance along the
actual path is shown as d1'.
[0108] For example, surface 1 may be the front surface of the
cornea and surface 2 may be the back surface of the cornea. The
distances d1 and d1' are therefore the assumed and actual distances
between the front and back surface of the cornea. Surface 3 may be
considered the front surface of the lens of the eye and surface 4
the back surface of the lens of the eye. The cornea and the lens
are separated by a distance d2 and d2', i.e. the assumed and actual
distance from the back surface of the cornea to the front surface
of the lens. The distances d3 and d3' are between the front and
back surfaces of the lens. Surface 5 may be the retina of the eye.
Surface 5 is separated from the surface 4, or the back surface of
the lens, by a distance d4 or d4'. As shown in the graphs of FIG.
7, the first graph is indicative of the surfaces on the assumed
optical path and the second graph is indicative of the surfaces on
the actual optical path.
[0109] In a first iteration of reconstruction, eye parameters are
reconstructed using OPD values attributed to an assumed optical
path 1 along the subject eye z'-axis.
[0110] In a second iteration, the OCT measuring beam is traced
through the eye based on reconstructed eye parameters including eye
position measurements (.DELTA.x, .DELTA.y, .DELTA.z, .theta.,
.rho., .delta.).
[0111] The optical path length d.sub.n' along the actual optical
path 2 must correspond to the measured OCT distances. If it is not
the case, the eye must be reconstructed with corrected OPD
measurements d.sub.1 . . . d.sub.n-1 (assumed distances) along the
subject eye z'-axis.
[0112] An exemplary iterative process is shown in FIG. 11.
[0113] For each ocular surface, n=1, 2, 3, 4, 5 eye parameters up
to surface n are reconstructed 801 using OPD distance measurements
d.sub.1 . . . d.sub.n-1 as outlined above. In a first iteration the
on-axis OPD distance measurement corresponds to the measured OLCR
distance measurement d.sub.n-1'.
[0114] OLCR measurement beam are traced up to the relevant surface
n based on reconstructed eye up to surface and eye position
measurement (.DELTA.x, .DELTA.y, .DELTA.z, .theta., .rho., .delta.)
thus defining a position with respect to system coordinate system
at the time t that the peak of surface n as shown in FIG. 10 was
measured.
[0115] The on-axis OPD distance measurement d.sub.n-1 is then
corrected 802. This correction is according to the difference
between the traced and measured distance d.sub.n-1'. If the
difference between the traced and measured distance d.sub.n-1 is
greater than a threshold the iterative process begins again at step
801. If the difference between the distances is less than or equal
to a threshold, measurements may move to a new surface and the
process is restarted for the new surface.
[0116] In a further embodiment a non-iterative reconstruction may
also be implemented. In such an embodiment, eye reconstruction
takes into account eye movements and refraction at ocular surfaces.
In a first step the shape of the anterior cornea and the location
and incidence of OLCR/OCT beam with regard to the eye coordinate
system is reconstructed with PMI in an instantaneous fashion. PMI
allows mapping of the OLCR/OCT A-scan signal emanating from the
anterior corneal to the eye coordinate system and evaluating of the
change of the incidence of the OLCR/OCT measuring beam occurring at
the anterior corneal surface.
[0117] In a second step, posterior corneal surface is reconstructed
based on the reconstructed anterior corneal surface,
instantaneously acquired PMI P2 signals and corneal thickness OPD
at the location of the OLCR/OCT A-scan signal emanating from the
posterior corneal surface with respect to the eye coordinate
system. The reconstructed posterior corneal surface allows the
evaluation of the change of the incidence of the OLCR/OCT measuring
beam at this surface.
[0118] In a third step, the anterior lens surface is reconstructed
based on the reconstructed anterior and posterior corneal surfaces,
the instantaneously acquired P3 signals and anterior chamber depth
OPD at the locations of the OLCR/OCT A-scan signal emanating from
the anterior lens surface with respect to the eye coordinate
system. The reconstructed anterior lens surface allows the
evaluation of the change of the incidence of the OLCR/OCT measuring
beam. The posterior lens surface is similarly reconstructed.
[0119] Finally the OLCR/OCT A-scan signal emanating from the
retinal surfaces can be mapped to the eye coordinate system by
tracing the OLCR/OCT measuring beam through the reconstructed
surfaces.
[0120] The invention and embodiments thereof as described herein
provide for a combination of a PMI/OCT modality for reconstruction
of eye parameters where the PMI modality is used for (passive,
offline) movement compensation of OCT measurements. This provides
for more accurate eye parameter reconstruction.
[0121] Furthermore eye movement compensated measurements of
multiple ocular surface locations in a time-domain OCT A-scan are
provided for (i.e. whole A-scan is motion compensated, not only OPD
between two surfaces as in a dual beam OLCR implementation.
[0122] The embodiments described above also allow for motion
compensated OCT A-scan for eye length measurement taking into
account lateral eye movements (.DELTA.x, .DELTA.y) in addition to
axial displacement .DELTA.z.
[0123] The increased accuracy of correction allows a relaxation of
requirements for OCT/OLCR scanners in that a slower scanner may be
implemented. It will be appreciated that the SNR ration can be
increased since additional light is collected for each
displacement.
[0124] The embodiments described herein also facilitate iterative
reconstruction based on PMI and OLCR/OCT of eye parameters taking
into account optical path of OLCR measurement beam through
reconstructed eye.
[0125] The reconstruction of ocular surfaces based on multiple OCT
measurement points within the eye coordinate system and the
alignment of multiple scans using PMI provides for more accurate
reconstruction through the use of the detected peaks.
[0126] PMI modality also provides for time resolved measurement of
eye movements .DELTA.x, .DELTA.y, .DELTA.z, .theta., .rho.,
.delta..
[0127] It should be appreciated that various techniques described
herein may therefore be used to design lenses, for example,
including lens implants. The techniques may apply to designing
various types of lenses, including, but not limited to: plano,
convex, concave, multifocal (refractive, diffractive, etc), toric,
accommodative, prismatic, multiple lens configurations, variable
curvature (e.g. aspherical), phakic intraocular lenses, light
adjustable lenses or any combination of those listed.
[0128] Additionally one or more of the techniques described herein
may be used in the context of planning or performing various types
of surgeries. Such surgeries may include, but are not limited to,
myopic, hyperopic and presbyopic LASIK, LASEK or PRK, conductive
keratoplasty, radial keratotomy or a combination of the above.
[0129] It should be appreciated that the various aspects described
above are not limited to human eyes, but rather may be applied to
any type of eye, including human eyes or any other organism. In
addition, while various aspects have been described as relating to
the structure of the eye and implants for the eye, it should be
appreciated that the techniques may also apply to additional
elements, such as glasses, contact lenses or other elements used
for ocular purposes.
[0130] As previously mentioned, it should be appreciated that the
methods and apparatus described above may be used to form a model
of any number of structures of interest within an eye. For example,
according to some embodiments, a complete model of the eye may be
formed. In other embodiments, a model of a single structure (e.g.,
the lens, or a surface of the lens) may be formed. In still other
embodiments, the methods and/or apparatus described above may be
used to determine a single parameter of interest of a
structure.
[0131] Thus, individual acts of the methods described above may be
used for some applications, irrespective of whether the other acts
are also performed.
[0132] The above-described embodiments of the present technology
can be implemented in any of numerous ways. For example, the
embodiments may be implemented using hardware, software or a
combination thereof. When implemented in software, the software
code can be executed on any suitable processor or collection of
processors, whether provided in a single computer or distributed
among multiple computers. It should be appreciated that any
component or collection of components that perform the functions
described above can be genetically considered as one or more
controllers that control the above-discussed functions. The one or
more controllers can be implemented in numerous ways, such as with
dedicated hardware, or with general purpose hardware (e.g., one or
more processors) that is programmed using microcode or software to
perform the functions recited above. In this respect, it should be
appreciated that one implementation of the embodiments of the
present technology comprises at least one computer-readable storage
medium (e.g., a computer memory, a floppy disk, a compact disk, a
tape, a flash drive, etc.) encoded with a computer program (i.e., a
plurality of instructions), which, when executed on a processor,
performs the above-discussed functions of the embodiments of the
present technology. The computer-readable storage medium can be
transportable such that the program stored thereon can be loaded
onto any computer resource to implement the aspects of the present
technology discussed herein. In addition, it should be appreciated
that the reference to a computer program which, when executed,
performs the above-discussed functions, is not limited to an
application program running on a host computer. Rather, the term
computer program is used herein in a generic sense to reference any
type of computer code (e.g., software or microcode) that can be
employed to program a processor to implement the above-discussed
aspects of the technology.
[0133] While various inventive embodiments have been described and
illustrated herein, those of ordinary skill in the art will readily
envision a variety of other means and/or structure for performing
the function and/or obtaining the results and/or one or more of the
advantages described herein, and each of such variations and/or
modifications is deemed to be within the scope of the inventive
embodiments described herein. Those skilled in the art will
recognize, or be able to ascertain using no more than routine
experimentation, many equivalents to the specific inventive
embodiments described herein. It is, therefore, to be understood
that the foregoing embodiments are presented by way of example only
and that, within the scope of the appended claims and equivalents
thereto, inventive embodiments may be practiced otherwise than as
specifically described and claimed. Inventive embodiments of the
present technology are directed to each individual feature, system,
article, material, kit, and/or method described herein. In
addition, any combination of two or more such features, systems,
articles, materials, kits, and/or methods, if such features,
systems, articles, materials, kits, and/or methods are not mutually
inconsistence, is included within the inventive scope of the
present disclosure. All definitions, as defined and used herein,
should be understood to control over dictionary definitions,
definitions in documents incorporated by reference, and/or ordinary
meanings of the defined terms. The indefinite articles "a" and
"an," as used herein in the specification and in the claims, unless
clearly indicated to the contrary, should be understood to mean "at
least one."
[0134] The phrase "and/or," as used herein in the specification and
in the claims, should be understood to mean "either or both" of the
elements so conjoined, i.e., elements that are conjunctively
present in some cases and disjunctively present in other cases.
Multiple elements listed with "and/or" should be construed in the
same fashion, i.e., "one or more" of the elements so conjoined.
Other elements may optionally be present other than the elements
specifically identified by the "and/or" clause, whether related or
unrelated to those elements specifically identified. Thus, as a
non-limiting example, a reference to "A and/or B", when used in
conjunction with open-ended language such as "comprising" can
refer, in one embodiment, to A only (optionally including elements
other than B); in another embodiment, to B only (optionally
including elements other than A); in yet another embodiment, to
both A and B (optionally including other elements); etc. As used
herein in the specification and in the claims, "or" should be
understood to have the same meaning as "and/or" as defined above.
For example, when separating items in a list, "or" or "and/or"
shall be interpreted as being inclusive, i.e., the inclusion of at
least one, but also including more than one, of a number or list of
elements, and, optionally, additional unlisted items. Only terms
clearly indicated to the contrary, such as "only one of or "exactly
one of," or, when used in the claims, "consisting of," will refer
to the inclusion of exactly one element of a number or list of
elements. In general, the term "or" as used herein shall only be
interpreted as indicating exclusive alternative (i.e., "one or the
other but not both") when preceded by terms of exclusivity, such as
"either," "one of," "only one of," or "exactly one of." "Consisting
essentially of," when used in the claims, shall have its ordinary
meaning as used in the field of patent law. As used herein the
specification and in the claims, the phrase "at least one," in
reference to a list of one or more elements, should be understood
to mean at least one element selected from any one or more of the
elements in the list of elements, but not necessarily including at
least one of each and every element specifically listed within the
list of elements and not excluding any combinations of elements in
the list of elements. This definition also allows that elements may
optionally be present other than the elements specifically
identified within the list of elements to which the phrase "at
least one" refers, whether related or unrelated to those elements
specifically identified. Thus, as a non-limiting example, "at least
one of A and B" (or, equivalently, "at least one of A or B," or,
equivalently "at least one of A and/or B") can refer, in one
embodiment, to at least one, optionally including more than one, A,
with no B present (and optionally including elements other than B);
in another embodiment, to at least one, optionally including more
than one, B, with no A present (and optionally including elements
other than A); in yet another embodiment, to at least one,
optionally including more than one, A, and at least one, optionally
including more than, B (and optionally including other elements);
etc. It should also be understood that, unless clearly indicated to
the contrary, in any methods claimed herein that include more than
one step or act, the order of the steps or acts of the method is
not necessarily limited to the order in which the steps or acts of
the method are recited. In the claims, as well as in the
specification above, all transitional phrases such as "comprising,"
"including," "carrying," "having," "containing," "involving,"
"holding," "composed of," and the like are to be understood to be
open-ended, i.e., to mean including but not limited to. Only the
transitional phrases "consisting of and "consisting essentially of
shall be closed or semi-closed transitional phrases, respectively,
as set forth in the United States Patent Office Manual of Patent
Examining Procedures, Section 2111.03.
[0135] The words "comprises/comprising" and the words
"having/including" when used herein with reference to the present
invention are used to specify the presence of stated features,
integers, steps or components but does not preclude the presence or
addition of one or more other features, integers, steps, components
or groups thereof. It is appreciated that certain features of the
invention, which are for clarity, described in the context of
separate embodiments, may also be provided in combination in a
single embodiment. Conversely, various features of the invention
which are, for brevity described in the context of a single
embodiment, may also be provided separately or in any suitable
combination
* * * * *