Patent Publication Number: US-2023157880-A1

Title: Reducing retinal radiation exposure during laser surgery

Description:
TECHNICAL FIELD 
     The present disclosure relates generally to laser vitreolysis systems, and more particularly to reducing retinal radiation exposure during laser surgery. 
     BACKGROUND 
     In laser vitreolysis, a laser beam is directed into the vitreous to treat vitreous eye floaters. Eye floaters are microscopic collagen fibers that tend to clump and cast shadows on the retina, which disturb the vision of the patient. The laser beam disintegrates the floaters to improve vision. 
     BRIEF SUMMARY 
     In certain embodiments, an ophthalmic laser surgical system for treating a floater in a vitreous of an eye includes a floater detection system, a laser device, and a computer. The floater detection system determines the location of the floater in the vitreous of the eye. The laser device directs a laser beam along a laser beam path towards the floater. The computer accesses a three-dimensional scan pattern for the laser beam that yields a three-dimensional pulse pattern of laser pulses. The three-dimensional pulse pattern has a bubble shield pulse pattern at the posterior side of the three-dimensional pulse pattern. The bubble shield pulse pattern forms a bubble shield that reduces laser radiation exposure at a retina of the eye. The computer instructs the laser device to direct the laser beam towards the floater according to the three-dimensional scan pattern. 
     Embodiments may include none, one, some, or all of the following features: 
     The computer instructs the laser device to scan a posterior portion of the three-dimensional scan pattern prior to scanning an anterior region of the three-dimensional scan pattern. 
     The ophthalmic laser system includes an xy-scanner that: receives a detection beam from the floater detection system and directs the detection beam along the detection beam path towards an xy-location of the floater; and receives the laser beam from the laser device and directs the laser beam along the detection beam path towards the xy-location of the floater. 
     In certain embodiments, a method for treating a floater in a vitreous of an eye comprises determining, by a floater detection system, the location of the floater in the vitreous of the eye. A three-dimensional scan pattern for a laser beam that yields a three-dimensional pulse pattern of laser pulses is accessed by a computer. The three-dimensional pulse pattern comprises a bubble shield pulse pattern at a posterior side of the pattern. The bubble shield pulse pattern forms a bubble shield that reduces laser radiation exposure at the retina of the eye. A laser device is instructed by the computer to direct the laser beam towards the floater according to the three-dimensional scan pattern. The laser beam is directed by the laser device along a laser beam path towards the floater. 
     Embodiments may include none, one, some, or all of the following features: 
     Instructing the laser device to direct the laser beam towards the floater according to the three-dimensional scan pattern comprises instructing the laser device to scan the posterior portion of the three-dimensional scan pattern prior to scanning the anterior region of the three-dimensional scan pattern. 
     A detection beam from the floater detection system is received by an xy-scanner and directed along the detection beam path towards an xy-location of the floater. The laser beam from the laser device is received by the xy-scanner and directed along the detection beam path towards the xy-location of the floater. 
     In certain embodiments, an ophthalmic laser surgical system for treating a floater in a vitreous of an eye includes a floater detection system, a laser device, and a computer. The floater detection system determines a location of the floater in the eye. The laser device directs a laser beam along a laser beam path towards the floater. The computer: calculates a radiant exposure at a component of the eye according to a floater-to-component distance between a z-location of the floater and the component; calculates a safety factor from the radiant exposure, the safety factor describing a mathematical relationship between the radiant exposure and a maximum exposure; determines if directing the laser beam along the laser beam path towards the floater is allowable according to a predetermined boundary of the safety factor; and instructs the laser device to direct the laser beam along the laser beam path towards the floater if that is allowable. 
     Embodiments may include none, one, some, or all of the following features: 
     The safety factor is equal to the ratio of the maximum exposure and the radiant exposure. 
     The radiant exposure describes radiant exposure at a retina of the eye, and the maximum radiant exposure describes a maximum radiant exposure for a single pulse at the retina. 
     The radiant exposure describes radiant exposure at a retina of the eye, and the maximum radiant exposure describes a maximum average power at the retina. 
     The radiant exposure describes radiant exposure at a lens of the eye, and the maximum exposure describes a maximum radiant exposure at the lens. 
     The computer calculates the radiant exposure at the component of the eye according to the z-location of the floater by: determining a laser spot size of the laser beam on the component; and calculating the radiant exposure according to the laser spot size of the laser beam and the floater-to-component distance. 
     The computer calculates a closest floater-to-component distance at which the eye can be treated, given a laser pulse energy of the laser beam. 
     The computer calculates a maximum laser pulse energy at which the eye can be treated, given the floater-to-component distance. 
     If directing the laser beam along the laser beam path towards the floater is not allowable, the computer prevents the laser device from directing the laser beam towards the floater. 
     In certain embodiments, a method for treating a floater in an eye comprises determining, by a floater detection system, the location of the floater in the eye. The radiant exposure at a component of the eye is calculated by a computer according to the floater-to-component distance between the z-location of the floater and the component. A safety factor is calculated from the radiant exposure by a computer. The safety factor describes a mathematical relationship between the radiant exposure and a maximum exposure. Whether directing a laser beam along the laser beam path towards the floater is allowable according to a predetermined boundary of the safety factor is determined by the computer. A laser device is instructed by the computer to direct the laser beam along a laser beam path towards the floater if that is allowable. The laser beam is directed by the laser device along the laser beam path towards the floater. 
     Embodiments may include none, one, some, or all of the following features: 
     The safety factor is equal to the ratio of the maximum exposure and the radiant exposure. 
     The radiant exposure describes radiant exposure at a retina of the eye, and the maximum radiant exposure describes a maximum radiant exposure for a single pulse at the retina. 
     The radiant exposure describes radiant exposure at a retina of the eye, and the maximum radiant exposure describes a maximum average power at the retina. 
     The radiant exposure describes radiant exposure at a lens of the eye, and the maximum exposure describes a maximum radiant exposure at the lens. 
     Calculating the radiant exposure at the component of the eye according to the z-location of the floater comprises: determining the laser spot size of the laser beam on the component; and calculating the radiant exposure according to the laser spot size of the laser beam and the floater-to-component distance. 
     A closest floater-to-component distance at which the eye can be treated, given a laser pulse energy of the laser beam, is calculated by the computer. 
     A maximum laser pulse energy at which the eye can be treated, given the floater-to-component distance, is calculated by the computer. 
     If directing the laser beam along the laser beam path towards the floater is not allowable, the laser device is prevented from directing the laser beam towards the floater by the computer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    illustrates an example of an ophthalmic laser surgical system that may be used to treat a floater in an eye, according to certain embodiments; 
         FIG.  2    illustrates an example of a retinal image that may be generated by the system of  FIG.  1   ; 
         FIGS.  3 ,  4 A, and  4 B  illustrate an example of a three-dimensional (3D) pulse pattern that may be created by the system of  FIG.  1   , according to certain embodiments; and 
         FIG.  5    illustrates an example of a method for fragmenting a floater with a three-dimensional (3D) scan pattern 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. 
     Laser vitreolysis is performed to remove eye floaters. However, care must be taken to not overexpose the retina to laser radiation. Accordingly, an ophthalmic laser surgical system reduces exposure of the retina by creating a gas bubble shield that protects the retina from overexposure. In addition, the system uses multiple laser pulses to fragment a floater more efficiently and to reduce the likelihood of unpredictable floater movement. Furthermore, the system calculates safety factors that can be used to evaluate whether a procedure will cause too much retinal exposure. 
       FIG.  1    illustrates an example of an ophthalmic laser surgical system  10  that may be used to treat a floater in an eye, according to certain embodiments. In the embodiments, a floater detection system determines the location of a floater in an eye. A computer instructs a laser device to direct a three-dimensional (3D) pattern of laser pulses towards the floater. The pattern includes a bubble shield that reduces radiation exposure at the retina of the eye. The laser device directs a laser beam towards the floater according to the pattern. 
     As an overview, system  10  includes a floater detection system  19 , a laser device  22 , one or more shared components  24 , and a computer  26 , coupled as shown. Floater detection system  19  includes a scanning laser ophthalmoscope (SLO) device  20  and an interferometer device  21 . Laser device  22  includes an ultrashort pulse laser  30  and a z-focusing component  32 , coupled as shown. Shared components  24  include an xy-scanner  40 , an xy-encoder  41 , and optical elements (such as a mirror  42  and lenses  44  and  46 ), coupled as shown. Computer  26  includes logic  50 , a memory  52  (which stores a computer program  54 ), and a display  56 , coupled as shown. 
     As an overview of operation of system  10 , xy-scanner  40  receives an SLO beam from SLO device  20  and directs the SLO beam along an SLO beam path towards the eye. SLO device  20  generates an SLO image of the floater shadow cast by a floater onto the retina. SLO device  20  also provides the xy-location of the floater shadow, where the xy-location is related to xy-scanner  40 . Interferometer device  21  provides the z-distance of the floater from the retina (which may be referred to as the z-location). Z-focusing component  32  of laser device  22  receives the z-location of the floater from interferometer device  21  and focuses the focal point of the laser beam onto the z-location of the floater. Computer  26  instructs laser device  22  to direct a three-dimensional (3D) pattern of laser pulses towards the floater. The pattern includes a bubble shield that reduces radiation exposure at the retina of the eye. Xy-scanner  40  receives the laser beam from the laser device and directs the laser beam along the SLO beam path towards the xy-location of the floater shadow according to the 3D pattern. 
     Turning to the parts of the system, floater detection system  19  includes one or more detection devices that detect, locate, and/or image a floater and/or a floater shadow cast by the floater on the retina. To detect, locate, and/or image a floater and/or a floater shadow, a detection device directs a detection beam along a detection beam path towards the interior of the eye. The interior reflects the detection beam, and the device detects the reflected light and detects, locates, and/or images a floater and/or a floater shadow. 
     In certain embodiments, floater detection system  19  includes SLO device  20  and interferometer device  21 . SLO device  20  utilizes confocal laser scanning to generate images of the interior of the eye. In certain embodiments, SLO device  20  generates an image of the floater shadow that a floater casts on the retina and provides the xy-location of the floater shadow in encoder units. Interferometer device  21  provides the z-location of the floater relative to the retina. Interferometer device  21  has any suitable interferometer, e.g., a Fourier domain type (such as a swept source or a spectral domain type) that utilizes a fast Fourier transform (FFT). Examples of interferometer device  21  include an optical coherence tomography (OCT) device (such as a swept-source OCT device) and a swept source A-scan interferometer (SSASI) device (where a SASSI device performs only A-scans). Swept Source OCT and SSASI devices have a measuring range up to about 30 millimeters (mm) that can measure the depth (i.e., z-location relative to the retina) within the full length of the eye from the cornea to the retina. 
     Turning to laser device  22 , laser  30  may generate ultrashort laser pulses. Unlike YAG lasers currently used for laser vitreolysis, an ultrashort pulse laser may be used without harming the retina. On the one hand, YAG laser emits longer pulses with a higher pulse energy (e.g., 5 millijoules (mJ)). However, the higher pulse energy yields retinal exposure that exceeds the ANSI Retinal Maximum Permissible Exposure (MPE) at floater-to-retina distances where clinically significant floaters are typically located, around 3 mm or closer to the retina. For example, given pulse energy PE=5 mJ, laser beam numerical aperture NA=0.1, and floater-to-retina distance D=3 millimeters (mm)=0.3 centimeters (cm), the energy density ED on the retina is approximately ED=PE/(D*2NA) 2 =5 mJ/(0.3 cm*0.2) 2 =1.39 J/cm 2 . The ANSI Retinal Maximum Permissible Exposure MPE for a nanosecond pulse is MPE=0.020 J/cm 2 . Thus, the exposure with the YAG laser at distance D=3 mm exceeds the MPE at by ED/MPE=1.39/0.02≈70 times. 
     On the other hand, an ultrashort pulse laser uses a lower pulse energy to treat floaters. The threshold of the laser breakdown energy is proportional to the square root of the pulse duration. For example, a 300-femtosecond laser has 10000×0.5=100 times lower energy threshold than a 3-nanosecond laser. Thus, femtosecond lasers can treat a floater with a pulse energy of 10 to 30 microjoules (μJ), such as 15 to 20 μJ, which is about 100 times less than that of a YAG laser. The lower pulse energy yields lower retinal exposure that can satisfy the ANSI Retinal Maximum Permissible Exposure (MPE), which is MPE=0.008 J/cm 2  for a femtosecond pulse. Given pulse energy PE=20 μJ and laser beam numerical aperture NA=0.1, the floater-to-retina distance D that satisfies the MPE is D&gt;(20 μJ/(0.008 J/cm 2 *0.2 2 )) 0.5 =2.5 mm. That is, the 20 μJ femtosecond pulse satisfies the MPE up to 2.5 mm away from the retina, while at 3 mm from the retina the 5 mJ nanosecond YAG pulse exceeds the MPE at by 70 times. In addition to providing for treatment that satisfies the MPE, the lower pulse energy also allows for multi-pulse treatment, which more effectively fragments a floater, and the lower pulse energy is less likely to cause a floater to jump unpredictably. 
     In certain embodiments, laser device  22  or the optical delivery system includes adaptive optics. The adaptive optics correct phase front errors of the laser beam to minimize the spot size of the laser beam, which in turn minimizes the required pulse energy (e.g., a few microjoules (μJ) to the nanojoule (nJ) range) and radiation exposure at the retina. In certain embodiments, adaptive optics are used to optimize the laser beam prior to treatment. In the embodiments, the laser beam is directed near the floater using subthreshold energy levels. A feedback signal (e.g., a two-photon fluorescence or a second harmonic feedback signal) from the vitreous is detected. Adaptive optics (e.g., an adaptive mirror) in the laser beam path are used to maximize the intensity of the feedback signal to minimize aberrations of the eye and the optical system. 
     In certain embodiments, laser device  22  includes an optical element that forms a Bessel or Bessel-like long focal length beam, which may increase the efficiency of floater destruction. In general, as compared with Gaussian beams, Bessel beams have a 1.6× smaller spot size, longer focal length (resulting in shorter treatment time), and larger divergence (yielding a larger spot size on the retina, reducing risk of retinal damage). Examples of optical elements that form Bessel or Bessel-like long focal length beams include an axicon, circular grating, proper phase plate, spatial light modulator (SLM), and Fabry-Perot interferometer. 
     Z-focusing component  32  longitudinally directs the focal point of the laser beam to a specific location in the direction of the floater shadow. In certain embodiments, z-focusing component  32  receives the z-location of the floater from interferometer device  21  (and may receive it via computer  26 ), and directs the laser beam towards the z-location of the floater. Z-focusing component  32  may include a lens of variable refractive power, a mechanically tunable lens, an electrically tunable lens (e.g., Optotune lens), an electrically or mechanically tunable telescope. In certain embodiments, laser device  22  or the optical delivery system also includes a fast xy-scanner used in tandem with z-focusing component  32  to, e.g., create a 3D focal spot pattern. Examples of such scanners include galvo, MEMS, resonant, or acousto-optical scanners. 
     Shared components  24  direct beams from SLO device  20 , interferometer device  21 , and laser device  22  towards the eye. Because SLO, interferometer, and/or laser beams share components  24 , the beams are affected by the same optical distortions (e.g., fan distortion of scanners, barrel or pillow distortions of the scanner lens, refractive distortions from the inner eye surfaces, and other distortions). The distortions affect the beams in the same way, so the beams propagate along the same path. This allows for aiming the laser beam precisely at the floater. 
     As an overview of operation of shared components  24 , mirror  42  directs a beam (SLO, interferometer, and/or laser beam) towards xy-scanner  40 , which transversely directs the beam towards lens  44 . Lenses  44  and  46  direct the beam towards eye. Shared components  24  may also provide spectral and polarization coupling and decoupling of SLO, interferometer, and laser beams to allow the beams to share the same path. 
     Turning to the details of shared components  24 , in certain embodiments, xy-scanner  40  receives the xy-location of the floater shadow from SLO device  20 , and directs the SLO, interferometer, and/or laser beam towards the xy-location. Xy-scanner  40  may be any suitable xy-scanner that transversely directs the focal point of the beam in the x- and y-directions and changes the angle of incidence of the beam into the pupil. For example, xy-scanner  40  includes a pair of galvanometrically-actuated scanner mirrors that can be tilted about mutually perpendicular axes. As another example, xy-scanner  40  includes an acousto-optical crystal that can acousto-optically steer the beam. As another example, xy-scanner  40  includes a fast scanner (e.g., a galvo, resonant, or acousto optical scanner) that can create, e.g., a 2D matrix of laser spots. 
     Xy-encoder  41  detects the angular position of xy-scanner  40  and reports the position as the xy-location measured in angular units. For example, xy-encoder  41  detects the angular orientations of the galvanometer mirrors of xy-scanner  40  in encoder units. Xy-encoder  41  may report the position in encoder units to SLO device  20 , interferometer device  21 , laser device  22 , and/or computer  26 . Since SLO device  20 , interferometer device  21 , and laser device  22  share xy-scanner  40 , computer  26  can use the encoder units to instruct system  20  and device  22  where to aim their beams, making it unnecessary to perform the computer-intensive conversion from encoder units to a length unit such as millimeters. Xy-encoder  41  reports the positions at any suitable rate, e.g., once every 5 to 50 milliseconds (ms), such as every 10 to 30 or approximately every 20 ms. 
     Shared components  24  also include optical elements. In general, 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). In the example, optical elements include mirror  42  and lenses  44  and  46 . Mirror  42  may be a trichroic mirror. Lenses  44  and  46  may be scanning optics of an SLO device. 
     Computer  26  controls components of system  10  in accordance with computer program  54 . Examples of computer programs  54  include floater shadow imaging, floater shadow tracking, image processing, floater evaluation, retinal exposure calculation, patient education, and insurance authorization programs. For example, computer  26  controls components (e.g., floater detection system  19 , laser device  24 , and shared components  24 ) to image a floater and focus a laser beam at the floater. Computer program  54  may include instructions to create a pattern of laser pulses according to a scan pattern. Computer  26  may be separated from components or may be distributed among system  10  in any suitable manner, e.g., within floater detection system  19 , laser device  24 , and/or shared components  24 . In certain embodiments, portions of computer  26  that control floater detection system  19 , laser device  24 , and/or shared components  24  may be part of floater detection system  19 , laser device  24 , and/or shared components  24 , respectively. 
     In certain embodiments, computer  26  uses an image processing program  54  to analyze the digital information of the image to extract information from the image. In certain embodiments, image processing program  54  analyzes an image of a floater shadow to obtain information about the floater. For example, program  54  detects a floater by detecting a darker shape in an image (using, e.g., edge detection or pixel analysis) that may be the floater shadow. As another example, program  54  detects the shape and size of a floater shadow, which indicate the size and shape of the floater. As another example, program  54  detects the tone or luminance of the floater shadow, which indicates the density of the floater. In certain embodiments, computer  26  uses a tracking program  54  to track a floater shadow. 
     In certain embodiments, computer  26  determines the radiant exposure at the retina from a laser pulse directed at a particular z-location. The determination may consider any suitable factors, e.g., laser pulse energy, laser radiation wavelength, number of laser pulses, laser pulse duration, cone angle of the focused laser beam, and the focus to the retina. For example, the exposure can be calculated using the laser spot size of the laser beam and the distance between the floater and retina. The radiant exposure 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. If the radiant exposure exceeds the maximum radiant exposure of the retina, lens, and/or IOL, computer  26  may modify any suitable factor (e.g., lower the pulse energy), provide a notification to the user, and/or prevent firing of the laser beam as an important safety feature. 
     In certain embodiments, computer  26  calculates safety factors that indicate radiation exposure relative to a maximum exposure standard. For example, a safety factor SF may take the form of: SF=E/ME, where E represents the exposure at the ocular tissue (e.g., retina or lens), and ME represents the maximum exposure, which may be defined by a standard. In certain situations, a standard allows the maximum exposure to be exceeded. For example, ANSI Z80.36-2016 does not apply to radiation for treatment of ocular tissues, and the stated MPE limit is about 10 times less than the experimentally determined retinal damage threshold. A surgeon can exceed the ANSI limits if the therapeutic advantage justifies the risk of the retinal exposure. The safety factors guide the surgeon in deciding whether or not the advantage justifies the risk. 
     Computer  26  calculates safety factors from values stored at computer  26 , e.g., pulse energy, pulse duration, number of pulses in a pulse train, laser beam numerical aperture, laser beam wavelength, repetition rate, location of the laser focus (e.g., relative to the retina, lens, and/or IOL), and other parameters. Computer  26  may output the safety factors to the surgeon during surgery. If safety factor exceeds a predetermined amount (e.g., 10), computer  26  may notify the surgeon and/or prevent the surgery. 
     Examples of safety factors include: 
     (1) Retinal Safety Factor for Single Pulse RSFSP=RE/MPESP, where RE represents retinal exposure, and MPE represents a maximum exposure limit for a single pulse, e.g., the limit set by ANSI Z80.36-2016. 
     (2) Safety Factor for Average Retinal Exposure SFARE=RE/ARE where RE represents retinal exposure, and ARE represents a maximum average power at the retina per unit area. The maximum average power may be, e.g., the limit set by ANSI Z80.36-2016 or a value determined from data. For example, given data from a million Femtosecond Laser Assisted Cataract Surgery (FLACS) surgeries, 11.0 W/cm 2  power density is considered safe. 
     (3) Safety Factor for Lens SFL=LE/LMPE, where LE represents the lens exposure and LVPE represents a maximum exposure. ANSI does not set safety limits for lenses (natural and IOL), but since lenses are less sensitive to the laser radiation than the retina, values safe for the retina should also be safe for the lens. 
     Involuntary and voluntary eye movements (e.g., saccadic and micro-saccadic movements, drift, and tremor) can make laser treatment difficult. To reduce movement, the eye can be stabilized during treatment in any suitable manner to reduce movement of the eye. For example, the treated eye and/or the other eye can be stabilized using a fixation light. As another example, a patient interface or handheld surgical contact lens can be used to mechanically stabilize the eye. In addition, movement of the treated eye and/or the other eye can be tracked in any suitable manner. Any suitable portion of the eye (e.g., pupil, pupil edge, iris, blood vessels) and/or reflections from the eye (e.g., Purkinje reflections) can be tracked. 
       FIG.  2    illustrates an example of a retinal image  60  that may be generated by system  10  of  FIG.  1   . Image  60  shows the retina  62  of an eye, with a foveal region (or fovea)  64  and a parafoveal region (or parafovea)  66 . Generally, fovea  64  has a visual angle of approximately +/−one degree, and parafovea  66  has a visual angle of approximately +/−seven degrees. Image  60  also shows floater shadows  68  ( 68   a,    68   b,    68   c ) that floaters cast on retina  62 . In general, non-moving shadows are not caused by floaters, and may be caused by, e.g., corneal or lens opacities or anatomical changes of the retina, so floater treatment is not concerned with non-moving shadows. 
     A floater may be regarded as clinically significant if it can cause a visual disturbance, which can be determined from any suitable features of the floater shadow, e.g., the size and/or density of the shadow, proximity of the shadow to the fovea and/or parafovea, and/or the track of the shadow relative to the fovea and/or parafovea. As an example, a floater can cause a visual disturbance if it permanently or transiently casts a shadow  68  on fovea  64  or can cause distraction or annoyance if it permanently or transiently casts a shadow  68  on parafovea  66 . Accordingly, if a floater shadow falls within or is predicted to move within fovea  64  and/or parafovea  66 , the floater may be designated as clinically significant. As another example, floater shadow  68  can be used to estimate the size and density of the floater. Larger, denser floaters are more likely to cause a visual disturbance. Thus, a shadow  68  larger than a critical shadow size can indicate a clinically significant floater. A shadow  68  with a higher contrast relative to the background may indicate a clinically significant floater. 
       FIGS.  3 ,  4 A, and  4 B  illustrate an example of a three-dimensional (3D) pulse pattern  134  that may be created by system  10  of  FIG.  1   , according to certain embodiments.  FIG.  3    shows pulse pattern  134  within the eye.  FIG.  4 A  shows pulse pattern  134  in the enface view, and  FIG.  4 B  shows pulse pattern  134  relative to retina  138 . In certain embodiments, three-dimensional (3D) pulse pattern that may more effectively fragment floater  110  and may include a bubble shield that reduces retinal radiation exposure at the retina of the eye. 
     The laser pulses of 3D pulse pattern  134  create rapidly expanding cavitation bubbles that disintegrate floater  110 . For example, a 20 microjoules femtosecond laser pulse creates a cavitation bubble with a maximum transient diameter of approximately 400 micrometers (μm), which expands and collapses within approximately 38 milliseconds (ms). The acceleration of the bubble wall-tissue interface is approximately 107 meter/second 2  (m/s 2 ), i.e., approximately 1,000,000 G, which functions like a violent explosion that disintegrates the collagen fibers of a floater. The cavitation bubbles expand and contract several times, growing smaller with each iteration. After a few iterations, the water vapors within the bubbles condense into water and some gases (e.g., hydrogen, oxygen, CO2, and NOX) remain inside of the bubbles. After 30 seconds to a few minutes, the bubbles dissolve in the vitreous and upward forces lift the bubbles away from the visual field. While alive, posterior bubbles form a bubble shield, an opaque layer that shields the retina from exposure by subsequent anterior pulses. 
     3D pulse pattern  134  may have any suitable size and shape. In certain embodiments, pattern  134  may be a rectangular cuboid (e.g., a cube) of pulses. The sides may have any suitable dimensions (e.g., 10 to 2000 μm, such as 100 to 1500 μm) with any suitable pulse separation (e.g., 10 to 1000 μm, such as 100 to 500 μm). The posterior layer (e.g., enface layer) of pulses operates as a bubble shield  136  that protects the retina  138 . Pattern  134  may be formed in any suitable manner, e.g., starting from posterior layers to anterior layers. In some embodiments, posterior layers, e.g., the bubble shield, are formed with a lower repetition rate (e.g., 1000 to 2000 hertz (Hz), such as 1080 Hz) and/or lower pulse energy (e.g., 10 to 15 μJ) to protect the retina, and anterior layers are then formed with a higher rep rate (e.g., 2000 to 100,000 Hz, such as 15,000 to 50,000 Hz) and/or higher pulse energy (e.g., 15 to 35 μJ, such as 20 to 30 μJ). 
     Examples of pulse patterns  134  include: 
     (1) Pulse pattern  134  is a 3×3×3 matrix of pulses separated by 400 micrometers (m). The first plane of nine pulses form the bubble shield at the posterior part of the floater at a lower repetition rate (e.g., 1080 hertz (Hz)). The bubble shield shields the retina from the remaining 18 pulses, so they can be delivered at higher repetition rate (e.g., 5000 Hz). The total treatment time is approximately 12 milliseconds (ms). 
     (2) Pulse pattern  134  is a 10×10×10 matrix of pulses separated by 100 μm. The pattern may treat a 1 mm floater. The first plane 100 laser pulses form the bubble shield posterior to the floater by about 300 μm at a lower repetition rate (e.g., 541 Hz) and lower pulse energy (e.g., 10 microjoules (μJ)). The bubble shield shields the retina from the remaining 900 pulses, so they can be delivered at higher repetition rate (e.g., 5000 Hz) and/or pulse energy (e.g., 20 μJ). The total treatment time is approximately 0.365 seconds. 
     (3) Pulse pattern  134  is a 15×15×8 matrix of 1800 pulses separated by 100 μm in the x- and y-directions and 200 μm in the z-direction. The pattern may treat a 1.5 mm floater. The repetition rate is 50,000 Hz, and the laser pulse energy 10 μJ. The treatment time is approximately 0.036 seconds. 
     (4) Pulse pattern  134  is a 15×15×15=3375 3D matrix of pulses separated by 100 um. The pattern may treat a 1.5 mm floater. At a repetition rate of 50,000 Hz, treatment time is 3375/50,000=0.0675 seconds. 
     In certain embodiments, the 3D pulse pattern  134  provides safe average laser power per area (APD) of the retina. From data from millions of FLACS surgeries, the average laser power per area APD=11.0 W/cm 2  appears to be safe. A 3D pulse pattern  134  can satisfy this value. For example, given pulse energy 20 microjoules (μJ), repetition rate 1080 Hertz (Hz), floater-to-retina distance 2.5 millimeters (mm), and full angle numerical aperture 0.2, APD=1080 Hz*20 μJ/[(2.5 mm*0.2) 2 *7π/4]=˜11.0 W/cm 2 . As another example, given pulse energy 30 μJ, repetition rate 15,000 Hz, floater-to-retina distance 12 mm, and full angle numerical aperture 0.2, APD=15,000 Hz*30 μJ/[(12 mm*0.2) 2 *π/4]=˜10 W/cm 2 . 
       FIG.  5    illustrates an example of a method for fragmenting a floater with a three-dimensional (3D) scan pattern that may be performed by system  10  of  FIG.  1   , according to certain embodiments. A user such as a surgeon may use a 3D pulse pattern to fragment a floater within the vitreous of a patient eye. The 3D pulse pattern includes a bubble shield that reduces retinal radiation exposure at the retina of the eye. 
     The method starts at step  210 , where computer  26  accesses the 3D scan pattern for laser pulses. The scan pattern may be stored in memory  52 . Floater detection system  19  provides an image of the floater to the user at step  212 . The image may allow the user to locate the floater. Computer  26  calculates and outputs safety factors at step  214 . Safety factors indicate radiation exposure in the eye relative to a maximum exposure limit. They guide the user in deciding whether or not the advantage of the surgery justifies the risk of retinal radiation exposure. The treatment may be allowable at step  215 . If the treatment is allowable, the method proceeds to step  216 . If it is not, the method ends. 
     Computer  26  sends instructions to laser device  22  to direct pulses towards the eye according to the scan pattern at step  216 . Any suitable 3D scan pattern, e.g., as described herein, may be used. Laser device  22  directs laser pulses towards the eye to form bubble shield within the vitreous at step  218 . The bubble shield reduces retinal radiation exposure at the retina of the eye. Floater detection system  19  provides an image of the bubble shield to the user at step  220 . The image may allow the user to check that the bubble shield is sufficiently opaque to protect the retina. Laser device  22  directs laser pulses to form layers, from posterior to anterior layers, to fragment floater at step  222 . 
     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 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).