Patent Publication Number: US-2021173229-A1

Title: Method and system for measuring optical parameters

Description:
TECHNICAL FIELD 
     The present disclosure relates generally to methods and systems for measuring optical parameters of the eye and more particularly, but not by way of limitation, to a method and system for measuring optical parameters that minimizes an impact of distortions resulting from manual opening of an eyelid. 
     BACKGROUND 
     This section provides background information to facilitate a better understanding of the various aspects of the disclosure. It should be understood that the statements in this section of this document are to be read in this light, and not as admissions of prior art. 
     When performing optical measurements on patients it is often important that the patient&#39;s eyelid is sufficiently open. Such optical measurements are common, for example, when measuring topography or wavefront as part of a diagnostic exam to obtain data required for subsequent surgery, or just to characterize the eyes as part of a diagnostic workup. 
     It is quite common that a patient&#39;s eyelid does not open sufficiently to allow for data capture over the required area. This is frequently due, for example, to the patient&#39;s age or injury to the eye or the surrounding area. In these cases the device operator often manually assists the patient with opening the eyelid. Sometimes, depending upon the level of challenge and ease of access to the eye, a second operator assists. 
     When opening the eyelid manually, it is possible to inadvertently distort the globe of the eye. This can result in the ensuing measurement being incorrect. Measurements, for example, of astigmatism or higher order aberrations can be particularly impacted. Inaccurate measurements can have a negative impact on any surgical procedure including, for example, intra-ocular lens implantation or corneal refractive surgery. Operators are trained in the best technique so as to minimize potential distortions. However, there is variation between operators and manual manipulation of the eyelid can be challenging for even the most experienced operators with particularly challenging patients. Additionally, when the opening of the patient&#39;s eyelid is assisted manually or mechanically, the tear film associated with the patient&#39;s cornea often dries due to the patient being unable to blink. Drying of the tear film also leads to inaccurate ophthalmic measurements. 
     SUMMARY 
     Various aspects of the disclosure relate to a method of verifying ophthalmic measurements. The method includes obtaining, via an ophthalmic measurement device, a first measurement of at least one ophthalmic parameter over a first measurement area. The first measurement area corresponds to an unassisted visible area of a patient&#39;s eye. A second measurement of the at least one ophthalmic parameter over a second measurement area is obtained via the measurement device. The second measurement area corresponds to an assisted visible area of the patient&#39;s eye. The first measurement is compared to the second measurement. It is determined if the second measurement diverges from the first measurement. Responsive to a determination that the second measurement diverges from the first measurement, an alert that the second measurement is inaccurate is generated. Responsive to a determination that the second measurement does not diverge from the first measurement, the second measurement is accepted as accurate. First reflections associated with the first measurement and second reflections associated with the second measurement are obtained using the ophthalmic measurement device. The first reflections are compared to the second reflections. It is then determined if there are discrepancies between the first reflections and the second reflections. Responsive to a determination that discrepancies are present between the second reflections and the first reflections, generating an alert that the patient&#39;s tear film has dried. Responsive to a determination that there are no discrepancies between the second reflections and the first reflections, accepting the second measurement as accurate. 
     Various aspects of the disclosure relate to a computer-program product comprising a non-transitory computer-usable medium having computer-readable program code embodied therein. The computer-readable program code adapted to be executed to implement a method that includes receiving, from an ophthalmic measurement device, a first measurement of at least one ophthalmic parameter over a first measurement area. The first measurement area corresponds to an unassisted visible area of a patient&#39;s eye. A second measurement of the at least one ophthalmic parameter over a second measurement area is received from the measurement device. The second measurement area corresponds to an assisted visible area of the patient&#39;s eye. The first measurement is compared to the second measurement. It is determined if the second measurement diverges from the first measurement. Responsive to a determination that the second measurement diverges from the first measurement, an alert is generated that the second measurement is inaccurate. Responsive to a determination that the second measurement does not diverge from the first measurement, the second measurement is accepted as accurate. First reflections associated with the first measurement and second reflections associated with the second measurement are received from the ophthalmic measurement device. It is determined if there are discrepancies between the first reflections and the second reflections. Responsive to a determination that discrepancies are present between the second reflections and the first reflections, generating an alert that the patient&#39;s tear film has dried. Responsive to a determination that there are no discrepancies between the second reflections and the first reflections, accepting the second measurement as accurate. 
     Various aspects of the disclosure relate to a system for ophthalmic measurement. The system includes an ophthalmic measurement device. A processor is coupled to the ophthalmic measurement device. The processor is configured to receive, from an ophthalmic measurement device, a first measurement of at least one ophthalmic parameter over a first measurement area. The first measurement area corresponds to an unassisted visible area of a patient&#39;s eye. A second measurement of the at least one ophthalmic parameter over a second measurement area is received from the ophthalmic measurement device. The second measurement area corresponds to an assisted visible area of the patient&#39;s eye. The first measurement is compared to the second measurement and it is determined if the second measurement diverges from the first measurement. Responsive to a determination that the second measurement diverges from the first measurement, generate an alert that the second measurement is inaccurate. Responsive to a determination that the second measurement does not diverge from the first measurement, accept the second measurement as accurate. The processor is configured to receive, from the ophthalmic measurement device, first reflections associated with the first measurement and second reflections associated with the second measurement. It is determined if there are discrepancies between the first reflections and the second reflections. Responsive to a determination that discrepancies are present between the second reflections and the first reflections, an alert that the patient&#39;s tear film has dried is generated. Responsive to a determination that there are no discrepancies between the second reflections and the first reflections, the second measurement is accepted as accurate. 
     This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of claimed subject matter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure is best understood from the following detailed description when read with the accompanying figures. It is emphasized that, in accordance with standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of various features may be arbitrarily increased or reduced for clarity of discussion. 
         FIG. 1  is a block diagram of an ophthalmic measurement system according to aspects of the disclosure; 
         FIG. 2  is a front view of the eye with unassisted lid opening and illustrating a first measurement area; 
         FIG. 3  is a front view of the eye with assisted lid opening and illustrating a second measurement area; 
         FIG. 4  is a flow diagram of a process for verifying optical measurements according to aspects of the disclosure; and 
         FIGS. 5A-5D  are diagrams of corneal topography illustrating changes in ophthalmic measurements during different states of eyelid opening. 
     
    
    
     DETAILED DESCRIPTION 
     Various embodiments will now be described more fully with reference to the accompanying drawings. The disclosure may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. 
     Prior to medical interventions on the eye, such as for example refractive surgery, retinal surgery, or lens-replacement surgery, it is common for many ophthalmic parameters, such as for example, corneal curvature (also known as keratometry), axial length, aberrometry, corneal anterior surface measurement (also known as corneal topography), or full-thickness measurement of a corneal structure (also known as corneal tomography) to be measured. These ophthalmic parameters are typically measured with specialized equipment and require that a certain minimum surface area of the anterior portion of the eye be visible. In the particular case of lens-replacement surgery, measurement of these ophthalmic parameters dictates the optical properties of a replacement lens. Thus, inaccuracies in measurements of the ophthalmic parameters can adversely impact the efficacy of any such medical intervention on the eye. 
       FIG. 1  is a block diagram of an ophthalmic measurement system  100 . The measurement system  100  includes a measurement device  102  that is positioned to visualize a patient&#39;s eye  104 . In various embodiments, the measurement device may be any ophthalmic measurement device such as, for example, a keratometer, an ultrasound biometer, a wavefront device, a topographer, an aberrometry device, an ophthalmic optical coherence tomography (OCT) device, or any other ophthalmic measurement device. The measurement device  102  includes a processor  106  that is configured to store and compare the ophthalmic parameters obtained by the measurement device  102 . In various embodiments, the processor  106  may be integral with the measurement device  102 ; however, in other embodiments, the processor  106  may be a stand-alone device that is coupled to the measurement device  102  via, for example, a wired or wireless coupling. The processor  106  may be any microprocessor, microcontroller, programmable element, or other device or collection of devices for processing instructions for the control of the measurement device  102 . 
     In some embodiments, a data bus  109 , which in the illustrated embodiment is a serial bus, couples various components of the measurement device  102  together such that data is communicated therebetween. In a typical embodiment, the data bus  109  may include, for example, any combination of hardware, software embedded in a computer readable medium, or encoded logic incorporated in hardware or otherwise stored (e.g., firmware) to couple components of the measurement device  102  to each other. As an example and not by way of limitation, the data bus  109  may include an Accelerated Graphics Port (AGP) or other graphics bus, a Controller Area Network (CAN) bus, a front-side bus (FSB), a HYPERTRANSPORT (HT) interconnect, an INFINIBAND interconnect, a low-pin-count (LPC) bus, a memory bus, a Micro Channel Architecture (MCA) bus, a Peripheral Component Interconnect (PCI) bus, a PCI-Express (PCI-X) bus, a serial advanced technology attachment (SATA) bus, a Video Electronics Standards Association local (VLB) bus, or any other suitable bus or a combination of two or more of these. In various embodiments, the data bus  109  may include any number, type, or configuration of data buses  109 , where appropriate. 
       FIG. 2  is a front view of the eye  104  with unassisted opening of an eyelid  206  and illustrating a first measurement area  202 . In a typical embodiment the first measurement area  202  may be, for example, a small diameter around a pupil  204  or a small diameter around some other reference such as, for example, a visual axis or line of sight. Visualization of the first measurement area  202  is often possible without any manual manipulation of the eyelid  206 . 
       FIG. 3  is a front view of the eye  104  with assisted opening of the eyelid  206  and illustrating a second measurement area  302 . The second measurement area  302  is larger than, and encompasses, the first measurement area  202 . Specifically, the second measurement area  302  includes a sub-region  304  that coincides with the first measurement area  202 . Additionally, the second measurement area  302  includes regions of the eye that would be obscured during unassisted opening of the eyelid  206 . If the patient is able to open the eye fully without assistance, then aberrations such as, for example, defocus, astigmatism, or higher order aberrations over the portion of the sub-region  304  of the second measurement area  302  will be similar to the ophthalmic parameters measured over the first measurement area  202  alone. Thus, any divergence in the ophthalmic parameters measured over the second measurement area  302  and the ophthalmic parameters measured over the first measurement area  202  could be indicative of inadvertent deformation of the globe of the eye including, for example, deformation caused by manual opening of the eyelid  206 . 
     It should be noted that the first measurement area  202  and the second measurement area  302  illustrated in  FIGS. 2-3  are exemplary only. During operation, the location, size, and shape of the first measurement area  202  and the second measurement area  302  will vary depending on the ophthalmic parameter that is being measured. For example, in  FIGS. 2-3 , the first measurement area  202  and the second measurement area  302  are illustrated by way of example as being centered on the pupil  204 . In various embodiments, the first measurement area  202  and the second measurement area  302  could, for example, be offset from the pupil  204  or may be located elsewhere on the eye  104  so as to include the sclera, iris, or other regions of the eye  104 . 
     Referring to  FIGS. 1-3  collectively, during operation, a first measurement of one or more ophthalmic parameters is taken over the first measurement area  202  and transmitted to the processor  106 . The ophthalmic parameters are measured over the first measurement area  202  without assistance opening the eyelid  206  being provided to the patient. Assistance is then provided to facilitate the patient opening the eyelid  206  to a greater degree than otherwise possible without assistance. A second measurement of the same ophthalmic parameters is taken over the second measurement area  302  and transmitted to the processor  106 . The processor  106  compares the second measurement to the first measurement. In various embodiments, the processor  106  may scale up the range of the ophthalmic parameters measured over the first measurement area  202  to match the range of the second measurement area  302 . This practice is commonly known as “data scaling” or “feature scaling.” In other embodiments, the processor  106  may sample the ophthalmic parameters measured over the sub-region  304  of the second measurement area  302  and compare the ophthalmic parameters of the sub-region  304  with the ophthalmic parameters measured over the first measurement area  202  alone. This practice is commonly known as “data sampling.” In various embodiments, the processor  106  compares the second measurement to the first measurement to assess a consistency of a shape of the eye  104 . Such a comparison, in various embodiments, may be accomplished through, for example, a root-mean-square analysis of the ophthalmic parameters. In various embodiments, the processor  106  may utilize registration data in an effort to determine where on the eye  104  the ophthalmic parameters were measured. Such registration data facilitates determination of a common reference between the first measurement area  202  and the second measurement area  302 . 
     Still referring to  FIGS. 1-3 , if the processor  106  detects no divergence between the ophthalmic parameters measured over the first measurement area  202  and the ophthalmic parameters measured over the second measurement area  302 , then no action is taken and processor  106  determines that the ophthalmic parameters measured over the second measurement area  302  are accurate. If the processor  106  detects divergence between the ophthalmic parameters measured over the first measurement area  202  and the ophthalmic parameters measured over the second measurement area  302 , then the processor  106  generates an alert notifying the operator of possible deformation of the globe of the eye  104  causing the ophthalmic parameters measured over the second measurement area  302  to be inaccurate. In various embodiments, the alert may be, for example, a visual indication, a textual indication, or an auditory indication. The alert prompts the clinician to examine the assistance provided to the patient&#39;s eyelid  206  and re-measure the ophthalmic parameters over the second measurement area  302 . 
     Still referring to  FIGS. 1-3 , during operation, the ophthalmic parameters may, in various embodiments, include reflections received from the first measurement area  202  and the second measurement area  302 . The processor  106  compares reflections detected from the first measurement area  202  and reflections detected from the second measurement area  302 . Specifically, the processor determines if blurring or other changes to the reflections have occurred between the first measurement taken over the first measurement area  202  and the second measurement taken over second measurement area  302 . Such a change in reflections between the first measurement and the second measurement could be indicative of drying of the patient&#39;s tear film. In response to such a determination, the patient&#39;s eye should be irrigated or otherwise moistened to replenish the tear film in an effort to ensure accurate measurement of ophthalmic parameters. Additionally, the processor determines if there is an absence of reflections between the first measurement taken over the first measurement area  202  and the second measurement taken over the second measurement area  302 . An absence of reflections indicates obstruction or other interference with the signal from the measurement device  102 . In various embodiments, the signal may be, for example, visible light emitted from, for example, a light-emitting diode (LED). In other embodiments, the signal may be, for example, a laser emitted from, for example, an optical coherence tomography (OCT) device or a wavefront device. Such an absence of reflections could be indicative, for example, of a need to reposition the devices assisting with opening of the patient&#39;s eyelid. 
       FIG. 4  is a flow diagram of a process  400  for verifying ophthalmic measurements. The process  400  begins at step  401 . At step  402 , the ophthalmic parameters are measured over the first measurement area  202  and the measured ophthalmic parameters are transmitted to the processor  106 . During step  402 , the opening of the patient&#39;s eyelid  206  is not assisted. At step  404 , assistance is provided to open the patient&#39;s eyelid  206  thereby opening the eyelid  206  to a degree sufficient to expose the second measurement area  302 . At step  406 , the ophthalmic parameters are measured over the second measurement area  302  and the measured ophthalmic parameters are transmitted to the processor  106 . At step  408 , the processor  106  compares the ophthalmic parameters measured over the first measurement area  202  with the ophthalmic parameters measured over at least one of the second measurement area  302  or the sub-region  304  of the second measurement area  302 . In step  408 , the comparison may, in various embodiments, utilize data scaling such that the ophthalmic parameters measured over the first measurement area  202  are scaled up and compared to the ophthalmic parameters measured over the second measurement area  302 . In other embodiments, the comparison may utilize data sampling such that the sub-region  304  is sampled from the ophthalmic parameters measured over the second measurement area  302  and compared to the ophthalmic parameters measured over the first measurement area  202 . 
     Still referring to  FIG. 4 , at step  410 , it is determined if the ophthalmic parameters measured over the first measurement area  202  diverge from the ophthalmic parameters measured over the sub-region  304  of the second measurement area  302 . If, at step  410 , it is determined that there is no divergence between the ophthalmic parameters measured over the first measurement area  202  and the ophthalmic parameters measured over the sub-region  304  of the second measurement area  302 , then the process  400  proceeds to step  412 . At step  412 , the processor  106  accepts the ophthalmic parameters measured over the second measurement area  302  as accurate. From step  412 , the process  400  ends at step  413 . In various embodiments, the process  400  may be repeated, for example, with measurements of different ophthalmic parameters or on different anatomical regions of the eye  104 . 
     Still referring to  FIG. 4 , if at step  410 , it is determined that the ophthalmic parameters measured over the first measurement area  202  diverge from the ophthalmic parameters measured over the sub-region  304  of the second measurement area  302 , then the process  400  proceeds to step  414 . At step  414 , the processor  106  generates an alert that the ophthalmic parameters measured over the second measurement area  302  may be inaccurate due to, for example, deformation of the globe of the eye caused by the assistance provided to the patient&#39;s eyelid  206 . In step  414 , the alert may be, for example, a visual indication, a textual indication, or an auditory indication. At step  416 , the clinician adjusts the assistance provided to the patient&#39;s eyelid  206 . From step  416 , the process  400  returns to step  406  where the ophthalmic parameters are re-measured over the second measurement area  302 . 
       FIGS. 5A-5D  are diagrams of corneal topography illustrating changes in ophthalmic measurements during different states of opening of the eyelid  206 .  FIGS. 5A and 5B  illustrate a natural corneal topography where the eyelid  206  is partially closed. A smaller region of coverage is illustrated by box  502 ( a )-( d ).  FIG. 5C  illustrates a topography map, where the eyelid  206  is wide open as would be the case, for example, when assistance is provided to a patient when opening the eyelid  206 . The eye  104  remains in the natural state as the box  502 ( c ) in  FIGS. 5C  displays measurements similar to the box  502 ( a ) in  FIG. 5A .  FIG. 5D  illustrates corneal topography inside the box  502 ( d ) that has changed relative to the box  502 ( b ) of  FIG. 5B  indicating that the eye  104  is not in its natural state and deformation of the globe of the eye  104  may be present. 
       FIGS. 5A and 5C  illustrate a comparison where the eye  104  remains in the natural state if the eyelid  206  is being held wide open. The corneal topography region of the natural state is indicated as the box  502 ( a ). The corneal topography of the natural state is similar to the state where the eye is being held open as illustrated by the similarities between the box  502 ( a ) of  FIG. 5A  and box  502 ( c ) of  FIG. 5C .  FIGS. 5B and 5D  illustrate a case where the corneal topography is different to the natural state if the eyelid  206  is being held open as illustrated by the differences between the box  502 ( b ) and the box  502 ( d ). The eye  104  does not remain in its natural state and deformation of the globe of the eye  104  may be present. 
     Depending on the embodiment, certain acts, events, or functions of any of the algorithms described herein can be performed in a different sequence, can be added, merged, or left out altogether (e.g., not all described acts or events are necessary for the practice of the algorithms). Moreover, in certain embodiments, acts or events can be performed concurrently, e.g., through multi-threaded processing, interrupt processing, or multiple processors or processor cores or on other parallel architectures, rather than sequentially. Although certain computer-implemented tasks are described as being performed by a particular entity, other embodiments are possible in which these tasks are performed by a different entity. 
     For purposes of this patent application, the term computer-readable storage medium encompasses one or more tangible computer-readable storage media possessing structures. As an example and not by way of limitation, a computer-readable storage medium may include a semiconductor-based or other integrated circuit (IC) (such as, for example, a field-programmable gate array (FPGA) or an application-specific IC (ASIC)), a hard disk, an HDD, a hybrid hard drive (HHD), an optical disc, an optical disc drive (ODD), a magneto-optical disc, a magneto-optical drive, a floppy disk, a floppy disk drive (FDD), magnetic tape, a holographic storage medium, a solid-state drive (SSD), a RAM-drive, a SECURE DIGITAL card, a SECURE DIGITAL drive, a flash memory card, a flash memory drive, or any other suitable tangible computer-readable storage medium or a combination of two or more of these, where appropriate. 
     The term “substantially” is defined as largely but not necessarily wholly what is specified (and includes what is specified; e.g., substantially 90 degrees includes 90 degrees and substantially parallel includes parallel), as understood by a person of ordinary skill in the art. In any disclosed embodiment, the terms “substantially,” “approximately,” “generally,” and “about” may be substituted with “within [a percentage] of” what is specified. 
     Conditional language used herein, such as, among others, “can,” “might,” “may,” “e.g.,” and the like, unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments include, while other embodiments do not include, certain features, elements and/or states. Thus, such conditional language is not generally intended to imply that features, elements and/or states are in any way required for one or more embodiments or that one or more embodiments necessarily include logic for deciding, with or without author input or prompting, whether these features, elements and/or states are included or are to be performed in any particular embodiment. 
     While the above detailed description has shown, described, and pointed out novel features as applied to various embodiments, it will be understood that various omissions, substitutions, and changes in the form and details of the devices illustrated can be made without departing from the spirit of the disclosure. As will be recognized, the processes described herein can be embodied within a form that does not provide all of the features and benefits set forth herein, as some features can be used or practiced separately from others. The scope of protection is defined by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.