Patent Publication Number: US-2023157878-A1

Title: Determining radiant exposure at the retina during an ophthalmic procedure

Description:
TECHNICAL FIELD 
     The present disclosure relates generally to ophthalmic systems and methods, and more particularly to ophthalmic systems and methods for determining radiant exposure at the retina during an ophthalmic procedure. 
     BACKGROUND 
     During ophthalmic laser surgery, a surgeon may direct a laser beam into the eye to treat the eye. For example, a laser beam may be directed into the vitreous to remove eye floaters. Eye floaters are clumps of collagen proteins that form in the vitreous. These clumps disturb vision with moving shadows and distortions, and sometimes they block vision. The laser beam may be used to disintegrate the floaters, thus improving vision. However, as with any ophthalmic laser surgery, care must be taken to avoid overexposing the eye to laser radiation. 
     BRIEF SUMMARY 
     In certain embodiments, an ophthalmic laser system includes a laser device, an ophthalmic microscope, a z-direction sensor, and a controller. The laser device directs a laser beam towards a target within an eye that has a retina. An axis of the eye defines a z-axis, where a z-position is a position relative to the z-axis. The ophthalmic microscope receives light from a focal point within the eye to provide an image of an object at the focal point. The z-direction sensor determines the z-position corresponding to the focal point of the ophthalmic microscope. The controller: determines a position Z 0 , the z-position where the focal point of the ophthalmic microscope is at the retina of the eye; determines a position Z, the z-position where the focal point of the ophthalmic microscope is at the target within the eye; calculates a target-to-retina distance ΔZ according to a difference between the position Z and the position Z 0 ; and calculates a radiant exposure H e  at the retina according to the target-to-retina distance ΔZ. 
     Embodiments may include none, one, some, or all of the following features: 
     * The z-direction sensor determines the z-position corresponding to the focal point of the ophthalmic microscope by detecting the z-position of a base of the ophthalmic microscope. 
     * The controller determines the position Z 0 , the z-position where the focal point of the ophthalmic microscope is at the retina of the eye, by: autofocusing the focal point of the ophthalmic microscope at the retina of the eye; and determining, from the z-direction sensor, the z-position corresponding to the focal point. 
     * The controller determines the position Z 0 , the z-position where the focal point of the ophthalmic microscope is at the retina of the eye, by: receiving user input that the focal point of the ophthalmic microscope is at the retina of the eye; and determining, from the z-direction sensor, the z-position corresponding to the focal point. 
     * The controller determines the position Z, the z-position where the focal point of the ophthalmic microscope is at the target within the eye, by: autofocusing the focal point of the ophthalmic microscope at the target within the eye; and determining, from the z-direction sensor, the z-position corresponding to the focal point. 
     * The controller determines the position Z, the z-position where the focal point of the ophthalmic microscope is at the target within the eye, by: receiving user input that the focal point of the ophthalmic microscope is at the target within the eye; and determining, from the z-direction sensor, the z-position corresponding to the focal point. 
     * The controller calculates the radiant exposure H e  according to the target-to-retina distance ΔZ by: determining a laser spot size of the laser beam on the retina; and calculating the radiant exposure H e  according to the target-to-retina distance ΔZ and the laser spot size of the laser beam. 
     * The controller further calculates: a closest target-to-retina distance ΔZ at which the eye can be treated, given a laser pulse energy E of the laser beam; a maximum laser pulse energy E at which the eye can be treated, given the target-to-retina distance ΔZ; and/or a range of laser pulse energy E values and a range of target-to-retina distance ΔZ values at which the eye can be treated. 
     * The controller further: determines whether the radiant exposure H e  exceeds a maximum radiant exposure; if the radiant exposure H e  exceeds a maximum radiant exposure, prevents the laser device from directing the laser beam towards the target within the eye; and otherwise, allows the laser device to direct the laser beam towards the target within the eye. 
     In certain embodiments, a method directs a laser beam towards a target within an eye that has a retina. An axis of the eye defines a z-axis, where a z-position is a position relative to the z-axis. The method includes: receiving, at an ophthalmic microscope, light from a focal point within the eye to provide an image of an object at the focal point; determining, by a z-direction sensor, the z-position corresponding to the focal point of the ophthalmic microscope; determining, by a controller, a position Z 0 , the z-position where the focal point of the ophthalmic microscope is at the retina of the eye; determining a position Z, the z-position where the focal point of the ophthalmic microscope is at the target within the eye; calculating a target-to-retina distance ΔZ according to a difference between the position Z and the position Z 0 ; and calculating a radiant exposure H e  at the retina according to the target-to-retina distance ΔZ. 
     Embodiments may include none, one, some, or all of the following features: 
     * The determining, by the z-direction sensor, the z-position corresponding to the focal point of the ophthalmic microscope further comprises detecting the z-position of a base of the ophthalmic microscope. 
     * The determining, by the controller, the position Z 0 , the z-position where the focal point of the ophthalmic microscope is at the retina of the eye, further comprises: autofocusing the focal point of the ophthalmic microscope at the retina of the eye; and determining, from the z-direction sensor, the z-position corresponding to the focal point. 
     * The determining, by the controller, the position Z 0 , the z-position where the focal point of the ophthalmic microscope is at the retina of the eye, further comprises: receiving user input that the focal point of the ophthalmic microscope is at the retina of the eye; and determining, from the z-direction sensor, the z-position corresponding to the focal point. 
     * The determining the position Z, the z-position where the focal point of the ophthalmic microscope is at the target within the eye, further comprises: autofocusing the focal point of the ophthalmic microscope at the target within the eye; and determining, from the z-direction sensor, the z-position corresponding to the focal point. 
     * The determining the position Z, the z-position where the focal point of the ophthalmic microscope is at the target within the eye, further comprises: receiving user input that the focal point of the ophthalmic microscope is at the target within the eye; and determining, from the z-direction sensor, the z-position corresponding to the focal point. 
     * The calculating the radiant exposure H e  according to the target-to-retina distance ΔZ further comprises: determining a laser spot size of the laser beam on the retina; and calculating the radiant exposure H e  according to the target-to-retina distance ΔZ and the laser spot size of the laser beam. 
     * The method further comprises: calculating a closest target-to-retina distance ΔZ at which the eye can be treated, given a laser pulse energy E of the laser beam; a maximum laser pulse energy E at which the eye can be treated, given the target-to-retina distance ΔZ; and/or a range of laser pulse energy E values and a range of target-to-retina distance ΔZ values at which the eye can be treated. 
     * The method further comprises: determining whether the radiant exposure H e  exceeds a maximum radiant exposure; if the radiant exposure H e  exceeds a maximum radiant exposure, preventing the laser device from directing the laser beam towards the target within the eye; and otherwise, allowing the laser device to direct the laser beam towards the target within the eye. 
     In certain embodiments, an ophthalmic laser system includes a laser device, an ophthalmic microscope, a z-direction sensor, and a controller. The laser device directs a laser beam towards a target within an eye that has a retina. An axis of the eye defines a z-axis, where a z-position is a position relative to the z-axis. The ophthalmic microscope receives light from a focal point within the eye to provide an image of an object at the focal point. The z-direction sensor determines the z-position corresponding to the focal point of the ophthalmic microscope by detecting the z-position of a base of the ophthalmic microscope. The controller determines a position Z 0 , the z-position where the focal point of the ophthalmic microscope is at the retina of the eye by: autofocusing the focal point of the ophthalmic microscope at the retina of the eye or receiving user input that the focal point of the ophthalmic microscope is at the retina of the eye; and determining, from the z-direction sensor, the z-position corresponding to the focal point. The controller determines a position Z, the z-position where the focal point of the ophthalmic microscope is at the target within the eye, by: autofocusing the focal point of the ophthalmic microscope at the target within the eye or receiving user input that the focal point of the ophthalmic microscope is at the target within the eye; and determining, from the z-direction sensor, the z-position corresponding to the focal point. The controller calculates a target-to-retina distance ΔZ according to a difference between the position Z and the position Z 0 . The controller calculates a radiant exposure H e  at the retina according to the target-to-retina distance ΔZ by: determining a laser spot size of the laser beam on the retina; and calculating the radiant exposure H e  according to the target-to-retina distance ΔZ and the laser spot size of the laser beam. The controller also calculates: a closest target-to-retina distance ΔZ at which the eye can be treated, given a laser pulse energy E of the laser beam; a maximum laser pulse energy E at which the eye can be treated, given the target-to-retina distance ΔZ; and a range of laser pulse energy E values and a range of target-to-retina distance ΔZ values at which the eye can be treated. The controller also: determines whether the radiant exposure H e  exceeds a maximum radiant exposure; if the radiant exposure H e  exceeds a maximum radiant exposure, prevents the laser device from directing the laser beam towards the target within the eye; and otherwise, allows the laser device to direct the laser beam towards the target within the eye. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    illustrates an example of an ophthalmic laser system, according to certain embodiments; 
         FIG.  2    illustrates an example of z-direction sensor that determines the z-position corresponding to the focal point focal point of the ophthalmic microscope of the ophthalmic laser system of  FIG.  1   , according to certain embodiments; and 
         FIG.  3    illustrates an example of a method for treating an eye that may be performed by the controller of the ophthalmic laser system  10  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. 
     In certain embodiments, an ophthalmic laser system avoids overexposing the retina to laser radiation during an ophthalmic procedure. The laser system has a laser device, an ophthalmic microscope, and a z-direction sensor. The z-direction sensor measures the z-position of a base plate of the system. The z-position of the base plate indicates the z-position of the focal point of the microscope and thus the z-position of an object (e.g., a floater or the retina) on which the microscope is focused. In the embodiments, the z-direction sensor is used to determine the distance between a target (such as a floater) and the retina. The laser system calculates radiant exposure at the retina from the distance to the retina, and uses the calculated radiant exposure to take steps to avoid overexposing the retina to radiation that exceeds a maximum radiant exposure. 
       FIG.  1    illustrates an example of an ophthalmic laser system  10 , according to certain embodiments. Ophthalmic laser system  10  allows an operator (with an operator eye  12 ) to perform an ophthalmic laser procedure on a patient eye  14  of a patient. In certain situations, ophthalmic laser system  10  is used to perform laser vitreolysis to direct a laser beam to targets in the vitreous, such as vitreous floaters. Ophthalmic laser system  10  allows the operator to see floaters within the eye, and then direct a laser beam to fragment the floaters. 
     In the illustrated example, ophthalmic laser system  10  comprises oculars  20 , a laser delivery head  22 , an illuminator (such as a slit lamp  26 ), a positioning device (such as a joystick  28 ), a base  30 , a z-direction sensor  33 , and a console  32 , coupled as shown. Laser delivery head  22  includes a laser fiber  34  (with a distal end  35 ), a zoom system  36 , a collimator  38 , a mirror  40 , and an objective lens  42 , coupled as shown. Slit lamp  26  includes a light source  43 , condenser lens  44 , a variable aperture  45 , a variable slit plate  46 , a projection lens  47 , and a mirror  48 . Console  32  includes a computer (such as a controller  50 ), a laser  52 , and a user interface  54 , coupled as shown. 
     As an overview, ophthalmic laser system  10  includes a laser device  16  (e.g., laser  52 , laser fiber  34 , and laser delivery head  22 ) and an ophthalmic microscope  18  (e.g., oculars  20 , objective lens  42 , mirror  48 , and slit lamp  26 ). Operator eye  12  utilizes the optical path from oculars  20  through mirror  40 , objective lens  42 , and mirror  48  to view patient eye  14 . A laser beam follows the laser path from laser  52  through laser delivery head  22  and mirror  48  to treat patient eye  14 . 
     According to the overview, the laser device directs a laser beam towards a target within patient eye  14 . An axis of eye  14  (e.g., visual or optical) defines a z-axis. A z-position of an object is the position of the object relative to the z-axis. Ophthalmic microscope  18  receives light reflected from a focal point within eye  14  to provide an image of an object at the focal point. Z-direction sensor  33  determines the z-position corresponding to the focal point of the ophthalmic microscope. Controller  50  determines z-position Z 0 , where the focal point of the ophthalmic microscope is at the retina of eye  14 , and z-position Z, where the focal point of the ophthalmic microscope is at the target within eye  14 . Controller  50  calculates a target-to-retina distance ΔZ by calculating a difference between z-position Z and z-position Z 0 , and calculates the radiant exposure H e  at the retina according to the target-to-retina distance ΔZ. 
     In more detail, in certain embodiments, oculars  20  allow operator eye  12  to view patient eye  14 . Laser delivery head  22  delivers a laser beam from laser  52  of console  32  to patient eye  14 . Laser fiber  34  of delivery head  22  transports the laser beam from laser  52  to the distal end  35  of fiber  34 . Zoom system  36  includes optical elements that change the spot size of the laser beam that exits distal end  35  of fiber  34 . An optical element can act on (e.g., transmit, reflect, refract, diffract, collimate, condition, shape, focus, modulate, and/or otherwise act on) light. Collimator  38  collimates the laser beam, and mirror  40  directs the beam through objective lens  4 , which focuses the beam. 
     The illuminator of laser system  10  provides light that illuminates the surgical site of patient eye  14 . In certain embodiments, the illuminator comprises a slit lamp. Slit lamp  26  includes light source  43 , which emits light such as a high-intensity illumination light. Condenser lens  44  directs the light towards variable aperture  45  and variable slit plate  46 . Variable aperture  45  defines the height of the light in the y-direction, and variable slit plate  43  defines the width of the light in the x-direction to form the light into a slit shape. Projection lens  47  directs the light towards prism mirror, which directs the slit of light into patient eye  14 . 
     Base  30  supports laser delivery head  22  and slit lamp  24 . Joystick  28  moves base  30  in the x- and z-directions. Console  32  includes components that support the operation of system  10 . Controller  50  of console  32  is a computer that controls of the operation of components of system  10 , e.g., joystick  28 , base  30 , laser delivery head  22 , slit lamp  26 , laser  52 , and/or user interface  54 . For example, in response to instructions from joystick  28 , controller  50  moves the laser delivery head  22 , according to the instructions. Laser  52  supplies the laser beam that has a cone-shaped energy profile that focuses energy onto a point. Any suitable laser  30  may be used, e.g., a femtosecond or nanosecond laser with any suitable crystal (e.g., Nd:YAG, Erbium:YAG, Ti: Sapphire, or ruby). The laser beam may have any suitable wavelength, e.g., in a range from 500 nm to 1200 nm. User interface  54  communicates information between the operator and system  10 . 
     Z-direction sensor  33  determines the z-position corresponding to the focal point of ophthalmic microscope  18  by detecting movement of base  30 . Z-direction sensor  33  may be any suitable sensor that can detect movement of base  30 . Examples of such sensors include linear, capacitive, inductive, Hall-effect based, magnetic, magneto-resistive, optical, ultrasound, interferometric, grating based, and/or image-based sensors. In some examples, the sensor may be a rotary sensor that detects movement of the rack and pinion of slit lamp  26 . 
       FIG.  2    illustrates an example of z-direction sensor  33  that determines the z-position corresponding to the focal point focal point  62  ( 62   a ,  62   b ) of the ophthalmic microscope  60  ( 60   a ,  60   b ) of ophthalmic laser system  10  of  FIG.  1   , according to certain embodiments. In certain embodiments, z-direction sensor  33  determines the z-position corresponding to the focal point within eye  14  by detecting the z-position of a base  30  ( 30   a ,  30   b ) of the ophthalmic microscope. Base  30  moves one or more components (e.g., the objective lens  42 ) of ophthalmic microscope  16  that determine the focal point of microscope  16 , such that the movement of base  30  indicates movement of the focal point of microscope  16 . 
     In the illustrated example, eye  14  has an axis (e.g., visual or optical) that defines a z-axis  58 . In the example, base  30  is at a particular z-position when a specific point of base  30  is at the z-position. For example, base  30   a  is at z-position z 1  because a point of base  30  is at z-position z 1 , and base  30   b  is at z-position z 2  because that point of base  30  is at z-position z 2 . Z-direction sensor  33  records the z-position of base  30 . 
     The z-position of base  30  indicates the z-position of the focal point  62  of the ophthalmic microscope  60 . For example, base  30   a  at z-position z 1  indicates that focal point  62   a  is at z-position z′ 1 , and base  30   b  at z-position z 2  indicates that focal point  62   b  is at z-position z′ 2 . Accordingly, the z-position z of base  30  also indicates the z-position z′ of an object on which microscope  60  is focused. An object may be a feature of the eye (e.g., the retina) or a target (e.g., a floater) within the eye. Moreover, the difference between the z-positions z 1 -z 2  of base  30  may be at least proportional to or equivalent to the difference between the z-positions z′ 1 -z′ 2  of focal points  62  or objects on which microscope  60  is focused. 
     In certain embodiments, controller  50  uses the z-position of base  30  from z-direction sensor  33  as an indicator of the z-position z′ of an object within the eye. For example, controller  50  receives user input that ophthalmic microscope  60  is focused on an object within the eye (e.g., the retina or a floater), i.e., the object is in focus and the focal point is at the object. In response, controller  50  determines the corresponding z-position z of base  30  using z-direction sensor  33 . As another example, controller  50  receives input from ophthalmic microscope  60  that is has autofocused on an object, and in response controller  50  determines the corresponding z-position z of base  30  using z-direction sensor  33 . 
       FIG.  3    illustrates an example of a method for treating an eye that may be performed by controller  50  of ophthalmic laser system  10  of  FIG.  1   , according to certain embodiments. As an overview of the method, ophthalmic laser system  10  measures the distance of a target to the retina, determines the radiant exposure on the retina according to the distance, and provides information via a user interface and/or adjusts treatment in accordance with the radiant exposure to avoid overexposing the retina. 
     The method starts at step  110 , where controller  50  determines z-position Z 0  where the focal point of the ophthalmic microscope is at the retina of the eye. In certain embodiments, controller  50  determines z-position Z 0  by autofocusing the focal point of the ophthalmic microscope at the retina of the eye, and determining, using the z-direction sensor, the z-position corresponding to the focal point. In other embodiments, controller  50  determines z-position Z 0  by receiving user input that the focal point of the ophthalmic microscope is at the retina of the eye, and determining, using the z-direction sensor, the z-position corresponding to the focal point. 
     Controller  50  determines z-position Z where the focal point is at the target at step  112 . In certain embodiments, controller  50  determines z-position Z by autofocusing the focal point of the ophthalmic microscope at the target within the eye, and determining, using the z-direction sensor, the z-position corresponding to the focal point. In other embodiments, controller  50  determines z-position Z by receiving user input that the focal point of the ophthalmic microscope is at the target within the eye, and determining, using the z-direction sensor, the z-position corresponding to the focal point. 
     The target-to-retina distance ΔZ is calculated at step  114 . Controller  50  calculates the target-to-retina distance ΔZ from the difference between positions Z and Z 0 . The radiant exposure H e  at the retina is calculated at step  116 . Controller  50  calculates the radiant exposure H e  by determining a laser spot size of the laser beam on the retina and calculating the radiant exposure H e  according to the target-to-retina distance ΔZ and the laser spot size on the retina. For example, the laser spot diameter Θ may be calculated according to Θ=2*ΔZ*tan α, where a represents the known half angle of the cone of the laser beam. The radiant exposure H e  may be calculated according to: 
         H   e =4* E/Θ   2 *π=4* E /(2*Δ Z *tan α) 2 π  (1)
 
     where E is the energy of the laser pulse. 
     Controller  50  may optionally perform steps  120 ,  122 , and/or  124  to calculate values at which the eye can be safely treated, given the calculated radiant exposure H e . The radiant exposure H e  should be less than a maximum radiant exposure, which may be determined in accordance with accepted standards. For example, the maximum radiant exposure may be set in accordance with ANSI Z80.36-2016. 
     Given laser pulse energy E, the closest target-to-retina distance ΔZ may be calculated at step  120  according to Equation (1). For example, given radiant exposure H e  and laser pulse energy E, the minimum target-to-retina distance ΔZ such that H e =4*E/(2*ΔZ*tan α) 2 π is less than the maximum radiant exposure may be determined. 
     Given target-to-retina distance ΔZ, the maximum laser energy E may be calculated at step  122  according to Equation (1). For example, given radiant exposure H e  and target-to-retina distance ΔZ, the maximum laser pulse energy E such that H e =4*E/(2*ΔZ*tan α) 2 π is less than the maximum radiant exposure may be determined. 
     More generally, laser pulse energy E values and target-to-retina distance ΔZ, values at which the eye can be treated may be calculated at step  124 . For example, given radiant exposure H e  and a range of laser pulse energies E, a range of target-to-retina distances ΔZ, such that H e =4*E/(2*ΔZ*tan α) 2  is less than the maximum radiant exposure may be determined. As another example, given radiant exposure H e  and a range of suitable target-to-retina distances ΔZ, a range of maximum laser pulse energies E such that H e =4*E/(2*ΔZ*tan α) 2 π is less than the maximum radiant exposure may be determined. 
     In certain embodiments, controller  50  may output the calculated radiant exposure H e  and/or calculated values from steps  120 ,  122 , and/or  124  to the operator via a user interface. In the embodiments, controller  50  may also receive user input from the operator selecting a calculated value and adjusting system  10  according to the selected value. 
     Controller  50  may determine that the radiant exposure H e  exceeds a maximum radiant exposure at step  130 . If the radiant exposure H e  exceeds the maximum radiant exposure, controller  50  moves to step  132  to prevent the laser device from directing the laser beam towards the target. Additionally or alternatively, controller  50  may provide a warning (e.g., audio and/or visual) via a user interface. If the radiant exposure H e  does not exceed the maximum radiant exposure, controller  50  moves to step  134  to allow the laser device to direct the laser beam towards the target. The method then ends. 
     A component (such as controller  50 ) 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 is a type of interface that a user can utilize to communicate with (e.g., send input to and/or receive output from) a computer. Examples of user interfaces include a display, Graphical User Interface (GUI), 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 an 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).