No assignee for this patent application has been made.
News editors obtained the following quote from the background information supplied by the inventors: "The invention refers to the field of ophthalmology, specifically refractive eye diagnostic and eye surgery. For most refractive eye treatments
"(1) pre-surgery diagnostic information of the patient's eye is determined to choose the adequate procedure (e.g. implant vs. laser) and define the individual treatment steps (e.g. where to cut or how to align the implant),
"(2) the individual surgery treatment is performed inserting refraction correcting implants (e.g. IOL's, corneal inlays) or executing surgery actions (e.g. cut incisions, apply laser shot patterns) and
"(3) post-surgery diagnostic information of the patient's eye including implant and/or surgery action is determined.
"(1) and (3) are typically performed outside the operation room using diagnostic devices like keratometer, topographer, wavefront analyzer, scheimflug devices, interferometer or slit lamps. (2) is typically performed in the operation room using a general purpose surgical microscope and adequate tools to support the surgeons manual work (e.g. knifes, phaco machine) or using dedicated devices for partial or full automation of surgical steps (e.g. refractive excimer laser treatment, cataract laser treatment).
"Currently there is a wide range of diagnostic devices that measure properties of the eye. A topograph or keratometer determines the shape and curvature of the patient's cornea (e.g. Zeiss Atlas), a wavefront device determines the full refraction of the patient's eye optics (e.g. AMO Wavefront Sciences COAS), an interferometer measures the axial length of the patient's eye ball (e.g. Haag-Streit LenStar LS900), a scheimflug device measures the front-side and back-side of the corneal refraction as well as the thickness (e.g. Oculus Pentacam) and a slit lamp provides an image of the patient's front of the eye for manual examination by the doctor.
"All different diagnostic approaches and associated devices evolved to accurate tools with a high repeatability for single eye measurements and therefore are applied pre-surgery as well as post-surgery for examination to verify clinical outcome.
"There are further approaches appearing on the ophthalmology landscape for intra-surgery measurement of the eye. An intra-surgery keratometry hand tool (e.g. astigmatic ruler by STORZ) can be used to roughly measure the corneal shape and its changes during the surgery, an intra-surgery wavefront device--in principle--allows the determination of the required power and astigmatism of an artificial lens after the removal of the natural lens (e.g. Wavetec ORange). All intra-surgery refraction measurement tools suffer from the moment of taking the measurement: The moment of eye surgery.
"All named devices and tools in this section above have in common the availability of a more or less consistent intra-device coordinate system ('device-consistent' which means that the tool or device provides from a patient X measured at one moment T multiple times a consistent output) but they all lack a full process covering consistent coordinate system ('process-consistent'). With a process-consistent coordinate system every process step (measurement or treatment) where the patient's eye is visually acquired, can be matched and transformed to an initially defined reference coordinate system.
"Due to the lack of a process-consistent coordinate system, systematic errors that occur between different steps are directly impacting the overall treatment error. Some examples:
"a) Sit-to-Sit-Error: Current practice is making all diagnostic measurements with the patients head is in an upright position. The assumption of 99% of surgeons is that the gravitation keeps the eye in the exact orientation for every measurement. This way a combination of measurement results from different devices can easily be performed. Unfortunately this assumption is wrong. The eye can rotate up to 7.degree. from one sitting position to another.
"b) Marker-Error: Current practice is the use of ink markers or ink marker tools for marking axes or positions on the cornea or the limbus border. The accuracy for using ink markers is limited due to the size of the marker (e.g. can be a 5.degree. thick mark), the unknown coordinate system while the surgeon is doing the marking (see a)) as well as the accuracy of reading a marker. The errors can easily sum up to 6.degree. or more.
"c) Surgeons-Error: Till now e.g. the cataract surgeon is doing most surgery steps that require special accuracy fully manual: They position incisions or align implants based on the marks they did previously. Besides the Maker Error the mechanical precision of the surgeon fingers needs to be taken into account.
"d) Implant-Error: Depending on the type of implant different post-surgery movements of the implant are likely to occur. For example early toric IOL designs tend to move post-operatively up-to 10.degree. based on slit lamp assessment.
"Deriving guidelines, nomograms or new implant designs and tool designs from the overall clinical outcome a separation of different systematic error influences like a)-d) could not be determined or distinguished.
"With the high optical complexity of latest generation implants or latest generation laser systems this demand for more diagnostic and surgery accuracy is already present, but with existing tools only overall errors can be determined but no error propagation addressing every single diagnostic step or surgery step."
As a supplement to the background information on this patent application, VerticalNews correspondents also obtained the inventors' summary information for this patent application: "In view of the foregoing situation, according to one embodiment there is provided a process-consistent coordinate system every process step (measurement or treatment) where the patient's eye is visually acquired, can be matched and transformed to an initially defined reference coordinate system. This overcomes the disadvantages of the lack of a coherent process coordinate system over multiple sessions which may comprise pre-surgery, surgery and post surgery.
"According to one embodiment there is provided an apparatus for monitoring one or more parameters of the eye of a patient over multiple sessions which are temporally spaced apart and between which the eye of the patient can have moved, said apparatus comprising:
"a camera for taking one or more images of the eye;
"an illumination unit for illuminating the eye by a ring-shaped light pattern to generate corneal reflections, said illumination unit being preferably located such that the center of the ring is coaxial with the optical axis of the camera;
"a module for determining during a first session the location of the corneal reflections in the image of the eye;
"a module for determining during said first session based on said determined location of the corneal reflections, at least one further parameter of the eye and its coordinates in a first coordinate system based on a geometrical model representing the eye as a spherical eyeball having a spherically shaped cornea mounted thereon;
"a module for determining during a second session temporally spaced apart from said first session said location of said corneal reflections of the eye and based thereon said further eye parameter and its coordinates in a second coordinate system;
"a module for determining the eye motion in six degrees of freedom between said first and said second session and for determining a coordinate transformation based thereon;
"a module for transforming based on said determined eye motion said further eye parameter and its coordinates from said first coordinate system into said second coordinate system;
"a module for quantifying and/or visualizing the change of said further eye parameter between said first and said second session based on said further parameter and its coordinates measured during said second session and said transformed parameter and its coordinates measured during said first session.
"Such an arrangement allows to monitor eye parameters which are determined based on the corneal reflections even over multiple sessions which are temporally spaced apart.
"According to one embodiment said at least one further parameter is determined based on an eye model which represents the shape and location of the eye by a spherical eyeball and a cornea mounted thereon and having a spherical shape or the shape of an ellipsoid to thereby enable the calculation of said at least one further parameter using the measured location of said corneal reflections and said the eye model.
"This enables the determination of eye parameters which are not directly measurable but which can be determined using the aye model and which can then be monitored over time.
"According to one embodiment said at least one further eye parameter comprises one or more of the following:
"a) the k-readings which define the shape of the cornea in terms of rotation ellipsoid parameters;
"b) the line of sight as the line connecting the pupil center and a fixation point of known location;
"c) the corneal chamber depth;
"d) the visual axis of the eye;
"e) the determination whether the eye is the left eye or the right eye.
"These are examples of further eye parameters which are of interest to be monitored even over sessions which are temporally spaced apart and between which a movement of the eye has occurred which is then compensated by the proposed approach.
"According to one embodiment said module for quantifying and/or displaying the change of said further eye parameter comprises:
"A module for displaying said further parameter measured during said second session and said transformed parameter measured during said first session in the image of the eye taken during said second session; and/or
"a module for calculating the difference between said further parameter measured during said second session and said transformed parameter measured during said first session and for visualizing said difference in said image of the eye taken during said second session.
"This enables the comparison of the development of an eye parameter over time, e.g. by comparing a post-surgical change with the situation during surgery, or by comparing two different post-surgical instances in time while the eye movement between the two measurements is compensated. The eye parameter as determined at the two instances of time may be directly visualized by displaying it in the image with the eye motion being compensated, or there may be calculated a difference (like a difference in x-, y- or rotation parameters) and just the difference being displayed in the image.
"According to one embodiment said at least one further eye parameter comprises the k-readings which are measured by determining a best fit ellipse to the corneal reflections and determining the major axis, the minor axis and the orientation of the ellipse.
"This enables the determination of astigmatism including the length of the steep and flat axis of the cornea as well as the orientation of the astigmatism. The diameter of the best fit cornea sphere can be approximated by the mean of flat and steep axis.
"According to one embodiment said apparatus further comprises a fixation target at known coordinates, preferably on the optical axis of the camera, and said at least one further eye parameter comprises the visual axis which is determined as the vector connecting the cornea center and the known fixation target, where the cornea center is determined based on the location of the corneal reflections.
"This enables the determination of the visual axis.
"According to one embodiment said at least one further eye parameter comprises the angle kappa between the visual axis and the pupil axis, or said further parameter is the intersection point between the visual axis and the cornea surface, where the cornea radius is determined based on the location of said corneal reflections. This allows the determination of further parameters which are interesting for the surgeon.
"According to one embodiment said at least one further eye parameter comprises the anterior chamber depth which is determined based on determining the radius of the limbus Ri and assuming it to be a circle of latitude on the best fit cornea sphere with radius Rc which is determined based on the corneal light reflections such that the corneal chamber depth CD is derived by
"CD=Rc-sqrt(Rc 2-RI 2).
"The anterior chamber depth is an interesting information for the surgeon,
"According to one embodiment said at least one further eye parameter comprises the line of sight which is determined as the vector connecting the pupil center and said fixation point of known location, with the z-coordinate of the pupil center being determined based on a known distance between camera and the eye and the x- and y-coordinates of the pupil being determined based on measuring the pupil location in the image, and/or
"said at least one further eye parameter comprises the pupillary axis being the line going through the center of the pupil and being orthogonal to the cornea surface.
"Line of sight and pupillary axis may be determined in this way.
"According to one embodiment said at least one further eye parameter comprises the determination of whether the center of the limbus or the center of the cornea is closer to the optical axis of the camera when the patient fixates a known fixation point lying on the optical axis of the camera.
"This enables the determination whether the eye is the left eye or the right eye. It may be used as a safeguard mechanism to prevent the surgery or diagnosis being performed on the wrong eye.
"According to one embodiment said first session is a pre-surgery session and said second session is an intra surgery session or a post surgery session, or
"said first session is an intra-surgery session and said second session is a post surgery session, or
"said first session is a post-surgery session and said second session is another post surgery session performed at a later time.
"These are suitable examples of sessions at different instances of time for which the eye parameters may be compared while compensating for the eye motion between the sessions.
"According to one embodiment the apparatus further comprises: A module for measuring and recording said at least one further eye parameter during multiple sessions over time in order to record the change of said at least one further eye parameter over time.
"This enables the recording and monitoring of the development of further eye parameters and thereby of the surgical result or impact over an arbitrarily long time period in a consistent coordinate system by compensating the eye motion. In this way e.g. studies regarding the long term success or failure of surgical techniques may be carried out which so far are not possible.
"According to one embodiment said at least one further parameter comprises a surgical or implant related parameter which comprises one or more of the following:
"the position and/or orientation of an implant in the eye, and/or
"the location and/or contour of corneal or limbal or scleral incisions
"the location and/or contour of the rhexis;
"and/or the overlap between the rhexis and the implanted lens.
"Such an arrangement allows to monitor surgical parameters even after the surgery has been performed to check whether there has been any temporal change of the surgical parameters like implant-related eye parameters or the location or contour of incisions. This is an important diagnostic information for monitoring the success or failure of surgery during the post-surgical phase.
"According to one embodiment the apparatus further comprises: A module for visualizing an arbitrary combination of said at least one or more further eye parameters determined during said first session and a possibly different arbitrary combination of said at least one or more further eye parameters determined during said second session in the same image such that the eye motion between said first and second session is compensated.
"This allows the visualization of any surgical or other parameters in any combination which are of interest while compensating for the eye motion between different sessions.
DESCRIPTION OF THE DRAWINGS
"FIGS. 1 to 15 illustrate embodiments of the invention."
For additional information on this patent application, see: Kersting, Oliver;
Keywords for this news article include: Astigmatism, Eye Diseases, Medical Devices, Patents, Refractive Errors, Surgery.
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