Patent Publication Number: US-2022225874-A1

Title: Evaluating measurements using information from multiple measuring devices

Description:
TECHNICAL FIELD 
     The present disclosure relates generally to ophthalmic measuring devices, and more particularly to evaluating measurements using information from multiple measuring devices. 
     BACKGROUND 
     Ophthalmic measuring systems typically address a particular application. For example, a dedicated system provides measurements for calculating an intraocular lens (IOL) power for a cataract surgery. The systems generally do not have multiple devices that provide measurements for the same thing. Accordingly, measurement errors can be difficult to detect. Some doctors use measurements from multiple systems to check for errors or average the output from multiple systems to obtain a measurement. Such approaches are time-consuming and often ineffective at obtaining accurate measurements. 
     BRIEF SUMMARY 
     In certain embodiments, an ophthalmic system for measuring an eye comprises measuring devices and a computer. The measuring devices comprise an optical coherence tomography (OCT) device and an aberrometer. The OCT device directs OCT light towards the eye, and detects the OCT light reflected from the eye to measure the eye. The aberrometer directs aberrometer light towards the eye, and detects the aberrometer light reflected from the eye to measure the eye. The computer generates an ocular model of the eye according to the reflected OCT light. The ocular model comprises parameters for the eye, where each parameter is assigned a value. The computer determines an OCT-based wavefront according to the ocular model, determines an aberrometer-based wavefront according to the reflected aberrometer light, ascertains a deviation between the OCT-based wavefront and the aberrometer-based wavefront, and evaluates measurements from one or more of the measuring devices according to the deviation. 
     Embodiments may have none, one, some, or all of the following features: The computer evaluates measurements by identifying one or more problems related to the deviation. The one or more problems may be associated with a measurement condition or a measuring device. The one or more problems may be a tear film instability, an inaccurate lens topography parameter, an inadequate patient fixation, an inadequate device alignment, and/or an inadequate device calibration. 
     The computer evaluates measurements by identifying one or more measuring devices associated with the deviation. 
     The measuring devices comprise a topographer that directs topographer light towards the eye, and detects the topographer light reflected from the eye. The computer generates the ocular model of the eye by: determining an OCT-based anterior corneal surface from the ocular model, determining a topographer-based anterior corneal surface from the reflected topographer light, and checking the ocular model by comparing the OCT-based anterior corneal surface and the topographer-based anterior corneal surface. The computer may evaluate one or more measurements by: identifying one or more related problems comprising a problem selected from a group consisting of an insufficient sampling, a tear film instability, an inadequate device alignment, and an inadequate device calibration. 
     The computer ascertains the deviation between the OCT-based wavefront and the aberrometer-based wavefront by: calculating OCT-based sphere and cylinder parameters of a simulated wavefront through the ocular model, calculating aberrometer-based sphere and cylinder parameters of the aberrometer-based wavefront, and comparing the OCT-based sphere and cylinder parameters and the aberrometer-based sphere and cylinder parameters. The computer may evaluate one or more measurements by: identifying one or more related problems comprising an inaccurate axial length measurement, an inadequate patient fixation, an inadequate device alignment, and/or an inadequate device calibration. 
     The computer ascertains the deviation between the OCT-based wavefront and the aberrometer-based wavefront by: determining one or more aberrometer-based values of the aberrometer-based wavefront, determining one or more OCT-based values of the ocular model, and comparing the one or more aberrometer-based values and the OCT-based values. The one or more aberrometer-based values may comprise one or more aberrometer-based slopes of the aberrometer-based wavefront. The one or more OCT-based values may comprise one or more OCT-based slopes of one or more rays exiting the ocular model. 
     The computer adjusts one or more values assigned to one or more of the parameters by repeating the following until an adjusted OCT-based wavefront and the aberrometer-based wavefront satisfies a predefined tolerance: adjusting the one or more values to yield an adjusted ocular model, determining the adjusted OCT-based wavefront according to the adjusted ocular model, and comparing the adjusted OCT-based wavefront and the aberrometer-based wavefront to check if they satisfy the predefined tolerance. 
     The OCT device checks the ocular model by: directing next OCT light towards the eye at an angle different from an angle of the OCT light, and detecting the next OCT light reflected from the eye. The aberrometer checks the ocular model by: directing next aberrometer light towards the eye at an angle different from an angle of the aberrometer light, and detecting the next aberrometer light reflected from the eye. The computer checks the ocular model by: generating a next ocular model of the eye according to the reflected next OCT light, generating a next aberrometer-based wavefront according to the reflected next aberrometer light, determining a next OCT-based wavefront according to the next ocular model, and comparing the next OCT-based wavefront and the next aberrometer-based wavefront. 
     In certain embodiments, an ophthalmic system for measuring an eye comprises measuring devices and a computer. The measuring devices comprise an optical coherence tomography (OCT) device and a topographer. The OCT device directs OCT light towards the eye, and detects the OCT light reflected from the eye. The topographer directs topographer light towards the eye, and detects the topographer light reflected from the eye. The computer determines an OCT-based anterior corneal surface from the reflected OCT light, determines a topographer-based anterior corneal surface from the reflected topographer light, ascertains a deviation between the OCT-based anterior corneal surface and topographer-based anterior corneal surface, and evaluates the OCT-based anterior corneal surface and the topographer-based anterior corneal surface according to the deviation. 
     Embodiments may have none, one, some, or all of the following features: The computer evaluates the OCT-based anterior corneal surface and the topographer-based anterior corneal surface by identifying one or more problems related to the deviation. The one or more related problems may be associated with a measurement condition or a measuring device. The one or more related problems may comprise an insufficient sampling, an inadequate device alignment, and/or an inadequate device calibration. 
     The computer evaluates the OCT-based anterior corneal surface and the topographer-based anterior corneal surface by identifying one or more measuring devices associated with the deviation. 
     The measuring devices comprise an aberrometer that directs aberrometer light towards the eye, and detects the aberrometer light reflected from the eye. The computer generates an ocular model of the eye according to the reflected OCT light. The ocular model comprises parameters for the eye, where each parameter is assigned a value. The computer determines an OCT-based wavefront according to the ocular model, determines an aberrometer-based wavefront according to the reflected aberrometer light, compares the OCT-based wavefront and the aberrometer-based wavefront, and evaluates one or more measurements from one or more of the plurality of measuring devices according to the comparison. 
     In certain embodiments, an ophthalmic system for measuring an eye comprises measuring devices and a computer. The measuring devices comprise an optical coherence tomography (OCT) device, an aberrometer, and a topographer. The OCT device directs OCT light towards the eye, and detects the OCT light reflected from the eye to measure the eye. The aberrometer directs aberrometer light towards the eye, and detects the aberrometer light reflected from the eye to measure the eye. The topographer directs topographer light towards the eye, and detects the topographer light reflected from the eye. The computer generates an ocular model of the eye according to the reflected OCT light. The ocular model comprises parameters for the eye, where each parameter is assigned a value. The ocular model is generated by: determining an OCT-based anterior corneal surface from the ocular model, determining a topographer-based anterior corneal surface from the reflected topographer light, and checking the ocular model by comparing the OCT-based anterior corneal surface and the topographer-based anterior corneal surface. The computer determines an OCT-based wavefront according to the ocular model, determines an aberrometer-based wavefront according to the reflected aberrometer light, and ascertains a deviation between the OCT-based wavefront and the aberrometer-based wavefront. The deviation between the OCT-based wavefront and the aberrometer-based wavefront is ascertained by: calculating OCT-based sphere and cylinder parameters of a simulated wavefront through the ocular model, calculating aberrometer-based sphere and cylinder parameters of the aberrometer-based wavefront, and comparing the OCT-based sphere and cylinder parameters and the aberrometer-based sphere and cylinder parameters; and determining one or more aberrometer-based values of the aberrometer-based wavefront, determining one or more OCT-based values of the ocular model, and comparing the one or more aberrometer-based values and the OCT-based values, wherein the one or more aberrometer-based values comprise one or more aberrometer-based slopes of the aberrometer-based wavefront, and the one or more OCT-based values comprise one or more OCT-based slopes of one or more rays exiting the ocular model. The computer evaluates one or more measurements from one or more of the measuring devices according to the deviation by: identifying one or more problems related to the deviation and associated with a measurement condition or a measuring device, the one or more related problems comprising a problem selected from a group consisting of an inaccurate axial length measurement, an insufficient sampling, a tear film instability, an inaccurate lens topography parameter, an inadequate patient fixation, an inadequate device alignment, and an inadequate device calibration; and identifying one or more measuring devices associated with the deviation. The computer adjusts one or more values assigned to one or more of the parameters by repeating the following until an adjusted OCT-based wavefront and the aberrometer-based wavefront satisfies a predefined tolerance: adjusting the one or more values to yield an adjusted ocular model, determining the adjusted OCT-based wavefront according to the adjusted ocular model, and comparing the adjusted OCT-based wavefront and the aberrometer-based wavefront to check if they satisfy the predefined tolerance. The OCT device checks the ocular model by: directing next OCT light towards the eye at an angle different from an angle of the OCT light, and detecting the next OCT light reflected from the eye. The aberrometer checks the ocular model by: directing next aberrometer light towards the eye at an angle different from an angle of the aberrometer light, and detecting the next aberrometer light reflected from the eye. The computer checks the ocular model by: generating a next ocular model of the eye according to the reflected next OCT light, generating a next aberrometer-based wavefront according to the reflected next aberrometer light, determining a next OCT-based wavefront according to the next ocular model, and comparing the next OCT-based wavefront and the next aberrometer-based wavefront. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an example of a system that evaluates measurements of an eye, according to certain embodiments; 
         FIG. 2  illustrates an example of an OCT device measuring the anterior corneal surface of an eye; 
         FIG. 3  illustrates an example of a topographer measuring the anterior corneal surface of an eye; 
         FIG. 4  illustrates an example of OCT light and aberrometer light interacting with an eye; 
         FIGS. 5A and 5B  illustrate an example of applying a ray-tracing procedure to determine the locations of the anatomical interfaces of an eye in order to generate an ocular model; and 
         FIG. 6  illustrates an example of a method for evaluating measurements of an eye that may be performed by the system of  FIG. 1 , according to certain embodiments. 
     
    
    
     DESCRIPTION OF EXAMPLE EMBODIMENTS 
     Referring now to the description and drawings, example embodiments of the disclosed apparatuses, systems, and methods are shown in detail. The description and drawings are not intended to be exhaustive or otherwise limit the claims to the specific embodiments shown in the drawings and disclosed in the description. Although the drawings represent possible embodiments, the drawings are not necessarily to scale and certain features may be simplified, exaggerated, removed, or partially sectioned to better illustrate the embodiments. 
     Embodiments of the disclosed systems and methods evaluate measurements from a measuring device by comparing them with measurements from another device. In certain embodiments, the measurements are compared by comparing wavefronts derived from the measurements. 
       FIG. 1  illustrates an example of a system  10  that evaluates measurements of an eye  12 , according to certain embodiments. In the example, system  10  includes a computer  20  (which includes logic  22 , a memory  24 , and an interface  26 ), measuring devices  28 , and an optical system  36 , coupled as shown. Measuring devices  28  include an optical coherence tomography (OCT) device  30 , an aberrometer  32 , and a topographer  34 , coupled as shown. 
     According to an example of operation, computer  20  generates an ocular model of eye  12  according to measurements from OCT device  30 . Computer  20  determines an OCT-based wavefront from the ocular model and an aberrometer-based wavefront from aberrometer  32 . Computer  20  compares the OCT-based and aberrometer-based wavefronts. If there is a deviation, the computer evaluates measurements according to the deviation. 
     Turning to the parts of system  10 , measuring devices  28  include OCT device  30 , aberrometer  32 , and topographer  34 . OCT device  30  directs OCT light towards eye  12  and detects the OCT light reflected from parts of eye  12  to generate an image of the parts. OCT device  30  may be any suitable device that uses OCT to capture two- or three-dimensional images from within optical scattering media, e.g., eye tissue. OCT device  30  may use time domain, frequency domain, or other suitable spectral encoding, and may use single point, parallel, or other suitable scanning. An example of operation is described in more detail with reference to  FIG. 2 . 
       FIG. 2  illustrates an example of OCT device  30  measuring the anterior corneal surface  58  of eye  12 . In general, OCT device  30  detects reflections of light from an interface between media, e.g., between the air and eye  12  or between parts of eye  12 , such as between the cornea and aqueous humor. OCT device  30  records the optical path length of the detected light and converts the optical path lengths to physical distances. In certain embodiments, raw data from OCT device  30  is converted such that the distances to the interfaces of eye  12  is expressed “as in air”, i.e., not taking into account the refractive indices of the tissue. 
     In the illustrated example, OCT device  30  detects reflections of light from anterior corneal surface  58 , records the optical path length of the detected light, and expresses the distance to anterior corneal surface  58  “as in air”. The distances to different points of surface  58  can be used to construct surface  58  in an ocular model. OCT device  30  measures the distances to the interfaces between other parts of eye  12  in a similar manner to construct the rest of the ocular model. 
     Returning to  FIG. 1 , aberrometer  32  directs aberrometer light towards eye  12  and detects the aberrometer light reflected from eye  12 . Aberrometer  32  uses aberrometry (i.e., wavefront technology) to measure how light travels through eye  12  to retina, which reflects the light. An aberration of the eye causes the light to take on a different shape, which can be used to characterize the aberration. Aberrometer  32  generates a wavefront map (e.g., a Zernike coefficient map) from the reflected light. A Hartmann-Shack aberrometer is an example of an aberrometer  32 . 
     Reflection topographer  34  directs topographer light towards the eye, and detects the topographer light reflected from the eye to measure the shape of anterior corneal surface  58 . In certain embodiments, measurements from topographer  34  and OCT device  30  are used to construct anterior corneal surface  58  of the ocular model. An example of operation is described in more detail with reference to  FIG. 3 . 
       FIG. 3  illustrates an example of a topographer  34 , such as a reflection topographer, measuring the anterior corneal surface of eye  12 . In the example, topographer  34  includes an illumination system  60  and a sensor  62 . Illumination system  60  directs topographer light towards the eye. The light projects a pattern (e.g., concentric rings or grid of dots) onto anterior corneal surface  58 . Sensor  62  (e.g., a camera) detects the topographer light reflected from the eye and generates an image of the reflected light. The image is analyzed to determine features of the eye, e.g., the shape of surface  58 . If the surface is an ideal sphere, the reflected pattern matches the projected pattern. If the surface has aberrations, areas where the reflected portions of the pattern (e.g. rings or dots) are closer together may indicate steeper corneal curvature, and areas where the portions are farther part may indicate flatter areas. Topographer  34  may output the results in the form of a map of the surface, such as an axial, tangential, refractive power, or elevation map. 
     Returning to  FIG. 1 , measuring devices  28  may acquire measurements sequentially and/or simultaneously. To compare the measurements, the measurements should be aligned. In certain cases, the measurements may be aligned using a feature of eye  12 , e.g., the pupil or iris markings. In other cases, the measurements may be aligned using eye-tracking functions. In other cases, measuring devices  28  may take measurements along the same optical path such that eye  12  has the same alignment for the measurements. An example of measuring devices  28  making measurements along the same optical path is described with reference to  FIG. 4 . 
       FIG. 4  illustrates an example of OCT light  54  and aberrometer light  56  interacting with eye  12 . In the example, eye  12  includes ocular parts, e.g., a cornea  40 , aqueous humor  42 , an iris  44 , a lens  46 , vitreous humor  50 , and a retina  52 . In certain embodiments, one or more surfaces of and/or the interfaces between parts of eye  12  may be regarded as anatomical interfaces that may be used to generate an ocular model. For example, anatomical interfaces may include: the anterior surface of cornea  40 ; interfaces between cornea  40 , aqueous humor  42 , iris  44 , lens  46 , vitreous humor  50 , and/or retina  52 ; and retina  52 . 
     In the example, OCT beams  54  enter the cornea  40 , and aberrometer rays  56  reflect from retina  52 . If eye  12  is an ideal emmetrope (with no optical aberrations), then each OCT ray  54  has a reflecting wavefront ray  56  traveling exactly the same optical path, just in reverse. If eye  12  has optical aberrations, the aberrations cause rays  54 ,  56  from the measurement devices  28  to travel different paths through eye  12 . In the illustrated example, OCT beams  54  are parallel. However, OCT beams  54  may have any other suitable beam geometry, e.g., a single scanning OCT beam. As long as the beam geometry is known, the paths of OCT beams  54  can be determined. 
     Returning to  FIG. 1 , optical system  36  includes one or more optical elements that direct light from measuring devices  28  towards eye  12 . An optical element can act on (e.g., transmit, reflect, refract, diffract, collimate, condition, shape, focus, modulate, and/or otherwise act on) a laser beam. Examples of optical elements include a lens, prism, mirror, diffractive optical element (DOE), holographic optical element (HOE), and spatial light modulator (SLM). 
     Computer  20  controls the operation of system  10  to evaluate measurements from measuring devices  28 . In certain embodiments, computer  20  generates an ocular model of eye  12  according to measurements from OCT device  30 . Computer  20  determines an OCT-based wavefront from the ocular model and an aberrometer-based wavefront from aberrometer  32 . Computer  20  compares the OCT-based and aberrometer-based wavefronts. If there is a deviation the computer evaluates measurements according to the deviation. In certain embodiments, computer  20  may perform additional checks on the model. 
     Generating an Ocular Model: Ocular Models. An ocular model may comprise parameters that describe eye  12 , where each parameter is assigned a value. A parameter may describe a characteristic (e.g., location, dimension, shape, and/or material property such as refractive index) of a feature (e.g., a part such as the cornea of lens) of eye  12 . Parameters may describe, e.g., the following of eye  12  or a part of eye  12 : (1) wavefront of eye  12 ; (2) shape of a surface of a part of eye  12  (e.g., anterior or posterior corneal or lens surface); (3) distance (e.g., physical or optical) through or between parts of eye  12  (e.g., between posterior cornea and anterior lens, between posterior lens and retina, or through cornea, lens, vitreous, or aqueous humor); and refractive index of a part of eye  12 . The value assigned to a parameter gives the specific value for the parameter, e.g., the specific thickness of the cornea. 
     Parameter values are subject to constraints. Constraints can be harder constraints that have a higher priority to be satisfied, or softer constraints with a lower priority to be satisfied. In certain examples, the following parameter values may be certain and be considered harder constraints: (1) whole eye: wavefront; (2) cornea: shape of anterior and posterior surfaces, physical and optical distance through, and refractive index; (3) aqueous humor: physical distance through and refractive index; (4) lens: shape of anterior lens surface, optical path length through, and general refractive index profile (but without specific values); (5) vitreous: physical distance through and refractive index. In the examples, the following parameter values may be uncertain and be considered variables or softer constraints: (1) lens: shape of posterior lens surface, physical path through, and specific values of refractive index profile; (2) vitreous: beam direction through; (3) retina: location, shape of surface. 
     Generating an Ocular Model: Ray-Tracing. Computer  20  may generate the ocular model according to reflected OCT light in any suitable manner. In certain embodiments, computer  20  applies a ray-tracing procedure to generate the ocular model. Ray-tracing determines the paths of rays through eye  12 , including how interfaces between parts of eye  12  refract the ray. At tissue boundaries, refraction is calculated according to according to Snell&#39;s Law, which states the ratio of the sines of the angles θ of incidence and refraction is equivalent to the reciprocal of the ratio of the indices of refraction n: sin θ 2 /sin θ 1 =n 1 /n 2 . A ray traveling through a part of eye  12  with a uniform refractive index propagates in a constant direction, while a ray traveling in a part with a gradient refractive index travels in a curved path. As the rays travel through eye  12 , the process calculates the intersections between rays and surfaces, as well as the surface normals at those points, to determine the new direction of the ray according to Snell&#39;s Law. The points and surface normals at the points can be used to determine the shape of a surface. An example of such process is described with reference to  FIGS. 5A and 5B . 
       FIGS. 5A and 5B  illustrate an example of applying a ray-tracing procedure to determine the locations of the anatomical interfaces  56  of eye  12  in order to generate an ocular model.  FIG. 5A  illustrates anatomical interfaces  56 , which include: interface  56   a  (anterior corneal surface  58 ); interface  56   b  between aqueous humor  42  and lens  46  (anterior lens surface); interface  56   c  between lens  46  and vitreous humor  50  (posterior lens surface); and interface  56   d  (surface of retina  52 ). Distance d′ represents the physical distance to an interface  56 . 
       FIG. 5B  illustrates measurements from OCT device  30 , which records the distances d an OCT ray travels to a point of interfaces  56  as measured “as in air”. The ray travels through air to interface  56   a , so distance d 1 =d′ 1 . However, the ray travels through eye tissue to interfaces  56   b  to  56   d , which decreases the distance, such that d′ i &lt;d i , where i=b, c, and d. 
     According to an example of operation, computer  20  defines rays traveling through the anatomical interfaces of eye  12 , determines the locations of the anatomical interfaces from the rays, and generates the ocular model using the locations of the anatomical interfaces. Computer  20  defines a ray by repeating the following for each anatomical interface: determine the angle of refraction from an anatomical interface using the refractive indices of the tissue and angle of incidence; and determine the distance to the next anatomical interface from the OCT measurements. 
     In the example, OCT device  30  provides initial “in air” distances d to points of interfaces  56 . In certain embodiments, topographer  34  may provide additional measurements for the shape of interface  56   a  (anterior corneal surface  58 ). In addition, uncertain parameter values may be assigned initial values that may be adjusted in response to additional information. For example, anterior corneal surface  58  may be initially parameterized, e.g., expressed in terms of parameters with initial values assigned to the parameters. The initial values may be, e.g., average values for a population. 
     Starting from interface  56   a  (anterior corneal surface  58 ), OCT device  30  provides distances d 1 =d′ 1  to points of interface  56   a . Distances d′ 2  to points of interface  56   b  (anterior lens surface) may be calculated from the distances d 2  to the points and the refractive index of the aqueous humor. The angle of refraction at the points of interface  56   b  may be calculated from the shape of the anterior lens surface, direction of the ray, aqueous humor refractive index, and lens refractive index at the points. Distances d′ to points of the remaining interfaces  56   d  and  56   d  may be calculated in a similar matter. 
     Computer  20  constructs the ocular model from the lengths and positions of the rays. The points where rays intersect interfaces  56  and surface normals at the points can be used to determine the shape of interfaces  56 . In certain embodiments, computer  20  constructs the ocular model by modifying an existing model. In other embodiments, computer  20  constructs the ocular model from the raw data. 
     In certain cases, computer  20  may take into account additional aspects of eye  12  while generating the eye model. These additional aspects may be found, e.g., in the medical history of eye  12 . Examples of such considerations include the refractive index of the IOL of a pseudophakic patient, an atypical corneal refractive index of a previously cross-linked cornea, and an atypical corneal surface of a kerataconic cornea. 
     Generating an Ocular Model: Checking the Model. In certain embodiments, computer  20  may check the ocular model by comparing one or more parameter values of the ocular model to values of other measurements of eye  12 , e.g., measurements from measuring devices  28  of system  10  or external to system  10 . A significant deviation among values may indicate a problem. A significant deviation may be, e.g., a deviation outside of one or two standard deviations or greater than a specified percentage such as 2% or 5%. Examples of problems include a problem with: the measurement conditions (e.g., insufficient sampling, inadequate patient fixation, and/or tear film instability), the measuring device  28  (e.g. device alignment and/or calibration), or the parameters of the model (e.g., corneal parameters). In some cases, a deviation may have a particular signature that indicates the likely problem. 
     Computer  20  may respond to detecting the deviation in any suitable manner. For example, computer  20  may send a notification identifying one or more related problems, e.g., one or more problems responsible for or likely responsible for the deviation. As another example, computer  20  may provide a recommendation to redo the measurements with one or more measuring devices  28  associated with the deviation, e.g., that could be responsible for the deviation. As another example, computer  20  may identify conditions of eye  12  (e.g., from the medical history of eye  12 ) that provides context for the deviation and notify the user of the conditions. 
     Comparing Anterior Corneal Surfaces. In certain embodiments, computer  20  may compare values describing anterior corneal surface  58  of the ocular model with values from other descriptions of anterior corneal surface  58 , e.g., measurements of toric power or anterior corneal surface  58  as measured by topographer  34 . A significant deviation may indicate a problem with, e.g., insufficient sampling of surface  58  and/or inadequate device issue (e.g., inadequate device alignment or calibration). For example, computer  20  may determine that the measurements of surface  58  from OCT device  30  and/or topographer  34  are insufficient, or that the measurements of OCT device  30  and/or topographer are not aligned with other measurements. Computer  20  may send a notification identifying the problem or likely problems and/or a recommendation to redo the measurements with one or more measuring devices  28  (e.g., OCT device  30  and/or topographer  34 ) that could be responsible for the deviation. 
     Determining Wavefronts. Ocular wavefronts are typically measured at the corneal surfaces or entrance pupil plane of the eye. However, the wavefront may be calculated (using aberrometry and/or anatomic OCT data) at any suitable location, e.g., the anterior lens surface. Computer  20  may determine an OCT-based wavefront according to the ocular model in any suitable manner. In certain embodiments, computer  20  determines the OCT-based wavefront by applying a ray-tracing procedure to the ocular model. Rays originating from a spot on the retina are propagated through eye  12 , similar to what is shown in  FIG. 5A , but in the reverse direction. Computer  20  obtains the position and orientation of the rays at the selected location, and constructs the OCT-based wavefront from the position and orientation. Computer  20  determines the aberrometer-based wavefront according to the reflected aberrometer light from aberrometer  32 . In certain embodiments, aberrometer  32  generates a wavefront map, and computer  20  determines the aberrometer-based wavefront from the map. 
     Comparing Wavefronts. Computer  20  may compare the OCT-based wavefront and the aberrometer-based wavefront in any suitable manner. In certain embodiments, computer compares the wavefronts to see if they differ beyond a predefined tolerance. The predefined tolerance may be defined to accommodate known margins of error of measuring devices  28 . For example, the predefined tolerance may be the largest of the known margins of error. 
     The wavefronts may be parameterized with the same parameters, and computer  20  may compare the wavefronts by comparing the values of the parameters. According to an example of operation, computer  20  parameterizes the OCT-based wavefront with parameters, where each parameter is assigned an OCT-based value that describes the OCT-based wavefront. Computer  20  parameterizes the aberrometer-based wavefront with the parameters, where each parameter is assigned an aberrometer-based value that describes the aberrometer-based wavefront. Computer  20  then compares the OCT-based values with the aberrometer-based values. 
     Generally, comparing more parameter values may increase the time needed to make the comparison. Accordingly, the number of parameters to compare may be selected in light of expected efficiency. In certain embodiments, computer  20  may perform a faster comparison that compares fewer parameter values in order to identify major deficiencies of the ocular model, which can be addressed before performing a more extensive (yet slower) comparison that compares more parameter values. 
     According to an example of a fast comparison, computer  20  may check the ocular model by generating a less detailed simulated wavefront. For example, computer  20  may determine a toric representation of interfaces  56  and then calculate sphere and cylinder parameters of a simulated wavefront through interfaces  56 . The parameters of the simulated wavefront may be compared to the sphere and cylinder parameters of the aberrometer-based wavefront. A significant deviation may indicate a problem with, e.g., inaccurate axial length measurement, inadequate patient fixation, and/or inadequate device alignment or calibration. Computer  20  may send a notification identifying the problem or likely problems and/or a recommendation to redo the measurements with one or more measuring devices  28  (e.g., OCT device  30  and/or aberrometer  32 ) that could be responsible for the deviation. 
     According to another example of a faster comparison, computer  20  may check whether the parameters of the simulated wavefront conform to measurements from, e.g., topographer  34 . For example, computer  20  may compare anterior corneal surface  58  of ocular model with surface  58  as measured by topographer  34 . In the example, computer  20  determines a model-based anterior corneal surface from the ocular model and a topographer-based anterior corneal surface from topographer  34 . Computer  20  checks the ocular model by comparing the model-based and topographer-based anterior corneal surfaces. A significant deviation may indicate a problem with, e.g., the tear film instability and/or inadequate device alignment or calibration. Computer  20  may send a notification identifying the problem or likely problems and/or a recommendation to redo the measurements with one or more measuring devices  28  (e.g., OCT device  30  and/or topographer  34 ) that could be responsible for the deviation. 
     According to an example of a more extensive comparison, computer  20  utilizes a wavefront map (e.g., a Zernike coefficient map) that includes wavefront parameters. In the example, computer  20  checks OCT-based values of an OCT-based wavefront with aberrometer-based values of an aberrometer-based wavefront. For example, the slopes of the aberrometer-based wavefront may be compared with the slopes of the rays exiting the eye according to the OCT-based model. Any suitable number of values that reconciles the OCT-based and aberrometer-based values (e.g., slopes) may be checked, e.g., 20 to 50, 50 to 100, or more than 100. The number of values may be adjusted according to desired completeness and/or efficiency. A significant deviation in the higher-order Zernike parametrization may indicate a problem with, e.g., tear film instability, inaccurate lens topography parameters, inadequate patient fixation, and/or inadequate device alignment or calibration. Computer  20  may send a notification identifying the problem or likely problems and/or a recommendation to redo the measurements with one or more measuring devices  28  (e.g., OCT device  30  and/or aberrometer  32 ) that could be responsible for the deviation. 
     Adjusting Parameter Values. If the OCT-based wavefront and the aberrometer-based wavefront differ beyond a predefined tolerance, computer  20  adjust one or more parameter values (such as a lens parameter value) of the OCT-based wavefront until a comparison of the wavefronts satisfies the predefined tolerance. Computer  20  adjusts the values by repeating the following: adjust values to yield an adjusted ocular model; determine an adjusted OCT-based wavefront according to the adjusted ocular model; and compare the adjusted OCT-based wavefront and the aberrometer-based wavefront to see if they satisfy the predefined tolerance. 
     Computer  20  may adjust the parameter values in any suitable manner. In certain embodiments, less certain values are adjusted before more certain values. Less certain values may include values that are not directly measured (e.g., lens refractive indices or cataract grading), values from less reliable measuring devices  28 , or values given by softer constraints. More reliable values may include values supported by multiple measurements, values that are generally known in the field, or values given by harder constraints. 
     Performing Another Check. In certain embodiments, system  10  performs another check of the ocular model. In the embodiments, measuring devices  28  measure eye  12  from a different angle than was previously used to measure eye  12 , and the measurements are compared. For example, measuring device  28  may first measure eye “on-axis”, i.e., the optical axis of measuring device  28  is aligned with an axis (e.g., visual or optical) of eye  12 . To check the ocular model, measuring device  28  may measure eye “off-axis”, i.e., the axis of measuring device  28  is at an angle with the axis of eye. The angle may be, e.g., 0 to 10, and/or 10 to 20 degrees, such as approximately 3 degrees. Computer  20  uses the measurements at the different angle to generate new wavefronts to compare in order to check the ocular model. 
     For example, OCT device  30  directs OCT light towards the eye at the different angle and detects the OCT light reflected from the eye. Aberrometer  32  directs aberrometer light towards the eye at the different angle, detects the aberrometer light reflected from the eye, and generates an aberrometer-based wavefront. Computer  20  generates another ocular model of the eye according to the reflected OCT light and determines an OCT-based wavefront from the ocular model. Computer  20  then compares the wavefronts to check the ocular model. 
     Computer  20  stores the resulting ocular model in memory  24  and may output the model via interface  26 . In certain embodiments, computer  20  uses the resulting ocular model to plan an ophthalmic surgery, e.g., a cataract or refractive surgery. For example, the model may be used to size accommodative intraocular lenses (IOLs) or to predict the post-operation position of an IOL. 
       FIG. 6  illustrates an example of a method for evaluating measurements of an eye that may be performed by system  10  of  FIG. 1 , according to certain embodiments. In certain embodiments, computer  20  may perform steps of the method by sending instructions to the components of system  10 . 
     The method starts at step  110 , where OCT device  30  directs OCT light towards the eye, which reflects the light. OCT device  30  detects the reflected OCT light at step  112  to measure the eye. Aberrometer  32  directs aberrometer light towards the eye at step  116 , and detects the aberrometer light reflected from the eye at step  118  to measure the eye. Topographer  34  directs topographer light towards the eye at step  120 , and detects the aberrometer light reflected from the eye at step  122  to measure the eye. 
     Computer  20  constructs an ocular model of the eye according to the reflected OCT light at step  126 . In certain embodiments, computer  20  applies a ray-tracing procedure to generate the ocular model. Certain embodiments may include variations in generating the ocular model. For example, computer  20  may construct the anterior corneal surface of the ocular model according to measurements from OCT device  30  and topographer  34 . Computer  20  may determine an OCT-based anterior corneal surface from the ocular model, determine a topographer-based anterior corneal surface from the reflected topographer light, and check the ocular model by comparing the OCT-based and topographer-based anterior corneal surfaces. A deviation between the surfaces may indicate a problem such as an insufficient sampling, tear film instability, inadequate device alignment, and/or inadequate device calibration. If there is a deviation at this step, computer  20  may report the deviation such as at step  138 . 
     Computer  20  determines an OCT-based wavefront according to the ocular model at step  128 . Computer  20  may apply a ray-tracing process to calculate the OCT-based wavefront. Computer  20  determines an aberrometer-based wavefront according to the reflected aberrometer light at step  130 . In certain embodiments, aberrometer  32  generates a wavefront map and provides the map to computer  20 . 
     Computer  20  compares the OCT-based and aberrometer-based wavefronts and ascertains a deviation at step  132 . Computer  20  may compare the wavefronts by parameterizing the wavefronts with parameter values and comparing the wavefront values. Computer  20  evaluates one or more measurements from one or more measuring devices according to the deviation at step  136 . Computer  20  may evaluate measurements by identifying one or more problems related to the deviation. Related problems may be associated with a measurement condition or a measuring device. Examples of related problems associated with a measurement condition include a tear film instability and/or inadequate patient fixation. Examples of related problems associated with a measuring device include an inaccurate lens topography parameter, inadequate device alignment, and/or inadequate device calibration. Computer  20  may identify one or more measuring devices potentially responsible for the deviation. 
     In certain embodiments, the comparison at step  132  may inform computer  20  about the problems related to the deviation. For example, computer  20  may compare the wavefronts by: determining an OCT-based anterior corneal surface from the ocular model; determining a topographer-based anterior corneal surface from the reflected topographer light; and checking the ocular model by comparing the OCT-based and topographer-based anterior corneal surfaces. A deviation of the surfaces may indicate a problem such as an insufficient sampling, tear film instability, inadequate device alignment, and/or inadequate device calibration. 
     As another example, computer  20  may compare the wavefronts by: calculating OCT-based sphere and cylinder parameters of a simulated wavefront through the ocular model; calculating aberrometer-based sphere and cylinder parameters of the aberrometer-based wavefront; and comparing the OCT-based and aberrometer-based sphere and cylinder parameters. A deviation of the parameters may indicate a problem such as an inaccurate axial length measurement, inadequate patient fixation, inadequate device alignment, and/or inadequate device calibration. 
     As another example, computer  20  may compare the wavefronts by: determining one or more aberrometer-based values of the aberrometer-based wavefront; determining one or more OCT-based values of the ocular model; and comparing the aberrometer-based and OCT-based values. In some cases, the aberrometer-based values are aberrometer-based slopes of the aberrometer-based wavefront, and the OCT-based values are OCT-based slopes of rays exiting the ocular model. A deviation of the values may indicate a problem such as a tear film instability, inaccurate lens topography parameter, inadequate patient fixation, inadequate device alignment, and/or inadequate device calibration. 
     Computer  20  provides the results at step  138 . Computer  20  may display the results and/or use the results in any suitable manner. For example, the results may be used to plan an ophthalmic surgery (e.g., cataract or refractive). The method then ends. 
     In certain embodiments, computer  20  may check the ocular model to improve the accuracy of the ocular model, which may yield improved detection and evaluation of measurements of the eye. For example, computer  20  may adjust one or more values assigned to parameters of the ocular model by repeating the following until an adjusted OCT-based wavefront and the aberrometer-based wavefront satisfies a predefined tolerance: adjusting the values to yield an adjusted ocular model; determining the adjusted OCT-based wavefront according to the adjusted ocular model; and comparing the adjusted OCT-based and aberrometer-based wavefronts to check if they satisfy the predefined tolerance. 
     As another example, system  10  may measure the eye at a different angle, and computer  20  may use the measurements to adjust the ocular model. In the example, the OCT device directs next OCT light towards the eye at an angle different from an angle of the OCT light, and detects the next OCT light reflected from the eye. The aberrometer directs next aberrometer light towards the eye at an angle different from an angle of the aberrometer light, and detects the next aberrometer light reflected from the eye. Computer  20  checks the ocular model by: generating a next ocular model of the eye according to the reflected next OCT light; generating a next aberrometer-based wavefront according to the reflected next aberrometer light; determining a next OCT-based wavefront according to the next ocular model; and comparing the next OCT-based and next aberrometer-based wavefronts. 
     A component (such as the control computer) of the systems and apparatuses disclosed herein may include an interface, logic, and/or memory, any of which may include computer hardware and/or software. An interface can receive input to the component and/or send output from the component, and is typically used to exchange information between, e.g., software, hardware, peripheral devices, users, and combinations of these. A user interface (e.g., a Graphical User Interface (GUI)) is a type of interface that a user can utilize to interact with a computer. Examples of user interfaces include a display, touchscreen, keyboard, mouse, gesture sensor, microphone, and speakers. 
     Logic can perform operations of the component. Logic may include one or more electronic devices that process data, e.g., execute instructions to generate output from input. Examples of such an electronic device include a computer, processor, microprocessor (e.g., a Central Processing Unit (CPU)), and computer chip. Logic may include computer software that encodes instructions capable of being executed by the electronic device to perform operations. Examples of computer software include a computer program, application, and operating system. 
     A memory can store information and may comprise tangible, computer-readable, and/or computer-executable storage medium. Examples of memory include computer memory (e.g., Random Access Memory (RAM) or Read Only Memory (ROM)), mass storage media (e.g., a hard disk), removable storage media (e.g., a Compact Disk (CD) or Digital Video or Versatile Disk (DVD)), database, network storage (e.g., a server), and/or other computer-readable media. Particular embodiments may be directed to memory encoded with computer software. 
     Although this disclosure has been described in terms of certain embodiments, modifications (such as changes, substitutions, additions, omissions, and/or other modifications) of the embodiments will be apparent to those skilled in the art. Accordingly, modifications may be made to the embodiments without departing from the scope of the invention. For example, modifications may be made to the systems and apparatuses disclosed herein. The components of the systems and apparatuses may be integrated or separated, or the operations of the systems and apparatuses may be performed by more, fewer, or other components, as apparent to those skilled in the art. As another example, modifications may be made to the methods disclosed herein. The methods may include more, fewer, or other steps, and the steps may be performed in any suitable order, as apparent to those skilled in the art. 
     To aid the Patent Office and readers in interpreting the claims, Applicants note that they do not intend any of the claims or claim elements to invoke 35 U.S.C. § 112(f), unless the words “means for” or “step for” are explicitly used in the particular claim. Use of any other term (e.g., “mechanism,” “module,” “device,” “unit,” “component,” “element,” “member,” “apparatus,” “machine,” “system,” “processor,” or “controller”) within a claim is understood by the applicants to refer to structures known to those skilled in the relevant art and is not intended to invoke 35 U.S.C. § 112(f).