Patent Publication Number: US-2023157540-A1

Title: Evaluating and treating eye floaters

Description:
TECHNICAL FIELD 
     The present disclosure relates generally to ophthalmic laser surgical systems, and more particularly to evaluating and treating eye floaters. 
     BACKGROUND 
     In ophthalmic laser surgery, a surgeon may direct a laser beam into the eye to treat the eye. For example, in laser vitreolysis, a laser beam is directed into the vitreous to treat eye floaters. Eye floaters are clumps of collagen proteins that form in the vitreous. These clumps can disturb vision with moving shadows and distortions. The laser beam fragments the floaters to improve vision. 
     BRIEF SUMMARY 
     In certain embodiments, an ophthalmic laser surgical system for treating a floater in an eye comprises a scanning laser ophthalmoscope (SLO) device, an interferometer device, a laser device, and an xy-scanner. The SLO device generates an SLO image of a floater shadow cast by the floater onto a retina of the eye, and provides an xy-location of the floater shadow, where the xy-location is related to the xy-scanner. The interferometer device provides a z-location of the floater, where the z-location is relative to the retina. The laser device generates a laser beam and includes a z-focusing component that focuses a focal point of the laser beam onto the z-location of the floater. The xy-scanner: receives an SLO beam from the SLO device and directs the SLO beam along an SLO beam path towards the xy-location of the floater shadow; and 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. 
     Embodiments may include none, one, some, or all of the following features: 
     The interferometer device comprises an optical coherence tomography (OCT) device.   The interferometer device comprises a swept source A-scan interferometer (SSASI) device.   The interferometer device comprises multiple reference arms, where each arm corresponds to a z-range of multiple z-ranges within the vitreous, where a z-range is relative to the retina.   The ophthalmic laser surgical system includes an xy-encoder that: detects an angular position of the xy-scanner, where the angular position corresponds to an xy-location expressed in encoder units; and reports the xy-location expressed in encoder units.   The laser device includes adaptive optics that minimize a spot size of the laser beam.   The laser device includes adaptive optics that maximize a feedback signal to optimize the laser beam.   The laser device includes an optical element that form the laser beam as a Bessel or Bessel-like long focal length beam.   The computer: performs image processing on the SLO image of the floater shadow cast onto the retina; evaluates the floater shadow to determine if the floater can cause a visual disturbance; and outputs results of the evaluation. The computer may determine if the floater shadow is cast onto a foveal region or a parafoveal region of the eye. The computer may determine if the floater shadow is larger than a critical shadow size. The computer may generate and output a report comprising the SLO image of the floater shadow cast onto the retina and educational information about the floater or a recommended treatment for the floater.   

     In certain embodiments, a method for treating a floater in an eye comprises generating, by a scanning laser ophthalmoscope (SLO) device, an SLO image of the floater shadow cast by the floater onto the retina of the eye. The xy-location of the floater shadow, where the xy-location is related to an xy-scanner, is provided by the SLO device. The z-location of the floater, where the z-location is relative to the retina, is provided by an interferometer device. A laser beam is generated by a laser device. The focal point of the laser beam is focused onto the z-location of the floater by a z-focusing component of the laser device. An SLO beam is received by the xy-scanner from the SLO device and directed along an SLO beam path towards the xy-location of the floater shadow. The laser beam is received by the xy-scanner from the laser device and directed along the SLO beam path towards the xy-location of the floater shadow. 
     Embodiments may include none, one, some, or all of the following features: 
     The interferometer device comprises an optical coherence tomography (OCT) device.   The interferometer device comprises a swept source A-scan interferometer (SSASI) device.   The angular position of the xy-scanner, where the angular position corresponds to an xy-location expressed in encoder units, is detected by an xy-encoder. The xy-location expressed in encoder units is reported by the xy-encoder.   Image processing of the SLO image of the floater shadow cast onto the retina is performed by the computer. The floater shadow is evaluated to determine if the floater can cause a visual disturbance. Results of the evaluation are output by the computer. The floater shadow may be evaluated by determining if the floater shadow is cast onto a foveal region or a parafoveal region of the eye or by determining if the floater shadow is larger than a critical shadow size.   A report is generated by the computer. The report includes the SLO image of the floater shadow cast onto the retina, and educational information about the floater or a recommended treatment for the floater.   

    
    
     
       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   ; 
         FIG.  3    illustrates an example of an SLO device that may be used in the system of  FIG.  1   ; 
         FIG.  4 A  illustrates examples of a depth measurement that may be performed by an interferometer device; 
         FIG.  4 B  illustrates an example of multiple A-scans forming a B-scan; 
         FIG.  5    illustrates an example of interferometer device that may be used in the system of  FIG.  1   ; 
         FIG.  6    is a graph illustrating an example of tracking and predicting the xy-location of a floater shadow, which may be performed by the system of  FIG.  1   , according to certain embodiments; 
         FIG.  7    illustrates an example of a method for treating a floater in an eye, which may be performed by the system of  FIG.  1   , according to certain embodiments; and 
         FIG.  8    illustrates an example of a method for evaluating floaters, which 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. 
     In laser vitreolysis surgery, a laser beam should be accurately and precisely directed at a floater in order to treat the floater safely and effectively. However, floaters are extremely difficult to visualize with known laser vitreolysis systems. Light reflected from the floaters and background typically does not yield images with enough contrast to clearly distinguish the floaters from the background. Thus, accurately determining the location of the floater is challenging. Moreover, known laser vitreolysis systems cannot provide satisfactory image guidance for the laser beam. In these systems, the imaging beam for generating images and the laser beam for treating the floater are often not aligned, resulting in inaccurate laser beam guidance. 
     Certain embodiments of ophthalmic laser surgical systems described herein address these problems. For example, a scanning laser ophthalmoscope (SLO) device generates an image of the retina that shows the floater shadow cast by a floater onto the retina. The floater shadow yields an image with a higher contrast, and thus can be used to gather accurate information about the size, density, location, and clinical significance of the floater. 
     As another example, the SLO device provides xy-locations in encoder units of an xy-scanner. The encoder units represent the angular orientation of the mirrors of the xy-scanner. Providing locations in encoder units is easier than converting encoder information into linear distances (e.g., millimeter distances) on the retina because the SLO beam propagates through several curved optical surfaces (e.g., surfaces of the cornea, natural lens, and/or intraocular lens). 
     As yet another example, embodiments include an interferometer device (e.g., a swept source full depth optical coherence tomography (SSFD OCT) devices or a swept source A-scan interferometer (SSASI) device) that provides the z-location of the floater relative to the retina. As yet another example, the treatment laser beam shares an xy-scanner with the SLO and interferometric beams, allowing the laser beam to co-propagate with the SLO and interferometric beams. Since the SLO, interferometric, and laser devices use the same xy-scanner, the floater can be treated with high spatial accuracy. 
       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. As an overview, system  10  includes a scanning laser ophthalmoscope (SLO) device  20 , an interferometer device  21 , a laser device  22 , one or more shared components  24 , and a computer  26 , coupled as shown. 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 , 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 is designed to focus the focal point of the laser beam onto the z-location of the floater. Xy-scanner  40  receives an SLO beam from the SLO device and in response to a command from computer  26  can direct the SLO beam along an SLO beam path towards the xy-location of the floater shadow. Xy-scanner  40  also 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. 
     As an example of aiming the laser beam, an image of the eye includes a reticle, which is a graphical overlay (e.g., crosshairs) that indicates where the beam is currently aimed in the xy-plane. The user or computer  26  places the reticle over the floater shadow in the image to aim the beam at the floater. Xy-encoder  41  detects the position of xy-scanner  40  to determine the xy-location of the reticle (in encoder units) centered at the floater shadow. 
     Turning to the parts of the system, 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. An example of SLO device  20  is described in more detail with reference to  FIG.  3   . 
     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. An example of an interferometer device  21  with multiple reference arms is described in more detail with reference to  FIG.  5   . 
     As an example of operation of interferometer device  21 , a splitter splits the light into measurement light and reference light. The reference light is directed to a reference arm system. The measurement light is directed through shared components  24  towards the eye and is reflected by surfaces and/or objects within the eye (e.g., the anterior and posterior surfaces of the cornea and natural or intraocular lens, the retina, and floaters). An interferometer combines the reflected measurement and reference light, which creates interference that in turn causes spectral modulation of the intensity. The frequency of the modulation is used to determine the depth at which the light was reflected, and the amplitude of the modulation carries information about the intensity of the back-reflected beam. The calculations may involve, e.g., Fourier analysis. 
     A measurement made along one direction of the xy-scanner is an A-scan. An example of an A-scan is described in more detail with reference to  FIG.  4 A . Multiple A-scans made with the movement of a scanner mirror of the xy-scanner is a B-scan. A B-scan may be used to visualize a side view of a slice of the eye. An example of a B-scan is described in more detail with reference to  FIG.  4 B . Multiple B-scans may be used to generate a 3D image of the eye. 
     The OCT images may be used to identify the location of the surfaces (e.g., the anterior and/or posterior surfaces) of a floater, the lens (natural or intraocular lens (IOL)), and/or the retina. Accordingly, the OCT images can indicate the z-location and thickness of the floater in the z-direction. 
     Turning to laser device  22 , ultrashort pulse laser  30  generates a laser beam with any suitable wavelength, e.g., in a range from 400 nm to 2000 nm. Laser device  22  delivers laser pulses at any suitable repetition rate (e.g., a single pulse to 200 megahertz (MHz)). A laser pulse has any suitable pulse duration (e.g., 20 femtoseconds (fs) to 1000 nanoseconds (ns)), any suitable pulse energy (e.g., 1 nanojoule (nJ) to 10 millijoule (mJ)), and a focal point of any suitable size (e.g., 1 to 30 microns (µm)). In a particular embodiment, the laser is a picosecond or femtosecond laser with a repetition rate that exceeds 100 pulses per second (pps). 
     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 (uJ) 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 1.6x 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 , respectively, 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  (e.g., SLO device  20 , interferometer device  21 , laser device  24 , and/or shared components  24 ) in accordance with a computer program  54 . Computer  26  may be separated from components or may be distributed among system  10  in any suitable manner, e.g., within SLO device  20 , interferometer device  21 , laser device  24 , and/or shared components  24 . In certain embodiments, portions of computer  26  that control SLO device  20 , interferometer device  21 , laser device  24 , and/or shared components  24  may be part of SLO device  20 , interferometer device  21 , laser device  24 , and/or shared components  24 , respectively. 
     Computer  26  controls the components of system  10  in accordance with a 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  uses a computer program  54  to instruct SLO device  20 , interferometer device  21 , laser device  24 , and/or shared components  24  to image a floater shadow and focus a laser beam at the floater. 
     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, as described in more detail with reference to  FIG.  6   . 
     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. 
     System  10  may be used as a diagnostic tool and/or a treatment device, which can save space in an ophthalmic office. In certain embodiments, system  10  can be used as a diagnostic tool. In the embodiments, the laser is not activated, and system  10  can display images of the floater shadows, which can help many people over the age of 50 who have vitreous floaters. In most cases, floaters do not affect the visual acuity or visual performance of the patients. However, moving floaters attract the visual attention of the patients, annoying them. Showing images of floater shadows moving on the fovea to patients and explaining that floaters do not cause blindness and the visual effects are similar to that in movie theaters may calm down many patients. The patients may decide to not to treat the floaters, but accept them as an age-related benign condition. 
     In the embodiments where system  10  is used as a diagnostic tool, certain computer programs may be appropriate. In certain embodiments, computer  26  uses a floater evaluation and diagnosis program  54  to evaluate a floater to determine if the floater is clinically significant, i.e., affects vision. In certain embodiments, display  56  of computer  26  displays images (such as a video) of a floater shadow so a user can evaluate the floater as described in more detail with reference to  FIGS.  2  and  8   . In other embodiments, computer  26  uses image processing to evaluate the floater shadow as described in more detail with reference to  FIGS.  2  and  8   . 
     In certain embodiments, a patient education program  54  generates a patient education report describing floater shadows found within a patient’s eye. The report may include, e.g., images (such as a video) of a floater shadow found within a patent’s eye; educational information about vitreous floaters; images of the vitreous pre- and post-treatment show the effectiveness of treatment; and/or other information to be provided to a patient. Computer  26  may output the report in any suitable manner. For example, computer  26  may store the report in memory  52 , display the report in display  56 , or send the report to, e.g., the user or patient. 
     In certain embodiments, a health insurance authorization program  54  generates an authorization report to obtain approval to treat floaters found within a patient’s eye. The report may include, e.g., images (such as a video) of a floater shadow found within a patent’s eye; patient information (e.g., identifying information, medical records); a recommended treatment; and/or other information required to obtain approval for treatment. Computer  26  may output the report in any suitable manner. For example, computer  26  may store the report in memory  52 , display the report in display  56 , or send the report to, e.g., the user, patient, or insurance company. 
     Involuntary and voluntary eye movements (e.g., saccadic and microsaccadic 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. 
     In some cases, a clinically significant floater may not be in a position to be safely treated. For example, floater shadow  68  may be too close to fovea  64 , large blood vessels, the optic nerve head, or other sensitive area to be treated. In certain embodiments, computer  26  uses image processing to determine if a floater is in a position to be safely treated, and provides a notification if it is not, as described in more detail with reference to  FIG.  1   . 
     In certain embodiments, a user such as a surgeon may determine significance from the displayed images (such as a video) of the floater shadow. An image processing program can assist the user in making the decision. In other embodiments, the computer can use image processing and target evaluation computer programs to determine significance from the image, as described in more detail with reference to  FIG.  8   . 
       FIG.  3    illustrates an example of SLO device  20  that may be used in system  10  of  FIG.  1   . In an example of operation, laser beam is focused onto the retina and scanned over an angular range (e.g., a 20 to 40 degree angular range) by a 2D xy-scanner (e.g., a galvo scanner). The light reflected from the retina is focused by a lens onto a pinhole. The pinhole is optically conjugated to the retinal surface such that only the light reflected from the retina is detected by a detector (e.g., a sensitive high-speed detector) and the other light is filtered out. The intensity of the back-reflected light is displayed as a 2D enface image, where the x- and y- axes of the image represent readings of an angular encoder of the xy-scanner. The xy-scanner and detector may be sufficiently fast to display the enface image as a video with any suitable frame rate (e.g., up to about 100 frames per second). 
     The SLO image displays the local intensity of the back-reflected light from the retina, which shows the anatomical features of the retina (e.g., vasculature, optic nerve head, and certain retinal decease). The image also shows shadows cast by floaters. Floaters are opaque objects that attenuate an incident laser beam, causing shadows on the retina. Floaters move with the partially liquified vitreous, so they cause moving shadows. The movement distinguishes floater shadows from static images of, e.g., anatomical objects of the retina or other parts of the eye. 
       FIG.  4 A  illustrates examples of a depth measurement  72  that may be performed by an interferometer device, such as an optical coherence tomography (OCT) device (such as a swept-source OCT device) or a swept source A-scan interferometer (SSASI) device. Depth measurement  72  may comprise an A-scan that extends from the cornea through the lens and floater  76  to the retina. The signal  74  from the A-scan indicates reflections from the cornea, lens, floater, and retina, which can used to determine the z-locations of these features relative to the retina. 
       FIG.  4 B  illustrates an example of multiple A-scans forming a B-scan. Multiple A-scans made with the movement of a scanner mirror of the xy-scanner (or other movement that yields a plane of A-scans) is a B-scan. A B-scan may be used to visualize a side view of a slice of the eye. 
       FIG.  5    illustrates an example of interferometer device  21  that may be used in system  10  of  FIG.  1   . Interferometer device  21  may be an optical coherence tomography (OCT) device (such as a swept-source OCT device) or a swept source A-scan interferometer (SSASI) device. In the example, interferometer device  21  includes reference optical system  142  (with arms  150  ( 150   a  to  150   d ) and mirror  152 ), light source  130 , and detector  140 , coupled as shown. Light source  130  provides light for the interferometer beam. Examples of light source  130  include a super-luminescent or swept-source diode, such as a super-luminescent diode. Detector  140  detects the interference signal light. Examples of detector  140  include a high-resolution spectrometer or fast diode. 
     Reference optical system  142  includes any suitable number of reference arms  150  ( 150   a  to  150   d ) and galvo mirror  152 . Each reference arm  150  is used for a different z-range  154  of the eye. For example, arm  150   a  is used for z-range  154   a , arm  150   b  is used for z-range  154   b , arm  150   c  is used for z-range  154   c , and arm  150   d  is used for z-range  154   d . In certain embodiments, the z-ranges  154  may overlap slightly, e.g., 1 mm or less. In the example, each z-range  154  corresponds to approximately 6 mm of vitreous, yielding coverage of approximately 24 mm. Galvo mirror  152  is used to direct the beam to the arm  150  for a particular z-range  154 , and may switch between arms in, e.g., less than 5 ms, such as approximately one ms. Floaters have limited movement in the z-direction, so once an arm  150  for a z-range is selected, there may be little need to switch to a different arm  150 . Computer  26  can join together images from different z-ranges  154  to yield an image of the length of the eye. In certain embodiments, interferometric devices, such as a swept source OCT device or a swept source A-scan interferometer (SSASI) device, may have measurement range as large as 35 mm, so they do not need multiple reference arms. 
       FIG.  6    is a graph  180  illustrating an example of tracking and predicting the xy-location of a floater shadow, which may be performed by system  10  of  FIG.  1   , according to certain embodiments. In the embodiments, a computer uses a tracking program to track and/or predict the movement of a floater shadow. For example, the computer performs image analysis of retinal images to track the movement of the floater shadow to track the floater. As discussed with reference to  FIG.  2   , floater treatment is concerned with moving shadows. 
     In the example, the xy-location is given in encoder units (which may be provided by encoder  41 ). Variable t represents time t = -3, -2, -1, 0, 1, 2, where t = 0 is the current time, t = -3, -2, -1 is the past time, and t = 0, 1, 2 is the future time. Yt represents the y-location in encoder units at time t, and Xt represents the x-location in encoder units at time. The tracking program predicts the future xy-locations by extrapolating from past xy-locations. 
     In the example, the interferometer device measures the z-location position of the floater at the xy-location (x1, y1) at time t = 1, shown at reference number  182 . The measurement may be performed a few milliseconds prior to firing the laser. At the xy-location (x2, y2) at time t = 2, shown at reference number  184 , the laser device fires a laser beam comprising laser pulses. The laser beam is directed by the xy-scanner to the xy-location (x2, y2) and is focused by the z-focusing component at the z-location. In general, floaters do not move much in the z-direction, so the z-location measured at t = 1 may be sufficiently close to the z-location at t = 2. 
       FIG.  7    illustrates an example of a method for treating a floater in an eye, which may be performed by system  10  of  FIG.  1   , according to certain embodiments. The method starts at step  208 , where an SLO device sends an SLO beam through an xy-scanner towards the eye. During an initial viewing, the SLO device scans a larger angular range in order to identify a region with a floater shadow. For example, the larger angular range may be 20 to 60 degrees, such as 30 to 50 degrees, e.g., approximately 40 degrees, with a frame rate of, e.g., over 40 or over 50 frames/s. The SLO device receives the SLO beam reflected from the retina at step  210 . In the SLO device, the reflected light goes through a confocal filter that transmits light from the retina and blocks the other reflected light. A display displays images (e.g., a video) at step  212  that show the floater shadow on the retina. 
     The floater shadow is tracked at step  214  using the SLO image to determine the xy-location of the shadow, as described in more detail with reference to  FIG.  6   . The angular scanning range may be changed at step  216 . The image may show a region with the floater shadow, and a smaller angular range (e.g., be 2 to 10 degrees, such as approximately 5 degrees) may be used to narrow the angular scanning to that region. Since the angular scanning range is smaller, a higher frame rate may be used, e.g., over 100 frames/s. If the angular scanning is to be changed at step  216 , the method returns to steps  210  and  214  to scan the different angular range and display the resulting image. If the angular scanning range is not to be changed at step  216 , the method proceeds to step  218  to determine whether the floater is clinically significant. 
     The floater may be clinically significant, i.e., may be expected to cause a visual disturbance, at step  218 . The floater shadow may be evaluated to determine the clinical significance of the floater, as described in more detail with reference to  FIGS.  2  and  8   . If the floater is not clinically significant at step  218 , the method proceeds to step  220  to check the next floater shadow. If the floater is clinically significant at step  218 , the method proceeds to step  224 . 
     The interferometer device determines the z-location and sends the z-location to the laser device at step  224 , so that the laser device can aim the focal point of the laser beam at the z-location, as described in more detail with reference to  FIG.  6   . The interferometer device may aim the interferometer beam at the xy-location of the floater shadow tracked by a tracking computer program to perform an A-scan in this direction. For example, a SSASI device may perform an A-scan in this direction, or an OCT device may perform A-scans in a small angular range (e.g., +/- two degrees) centered in this direction. The interferometer device may perform any suitable number of scans, e.g., a value in a range of 1 to 100, or 5 to 50, or 10 to 20 scans. In certain embodiments, the computer determines whether the expected radiance energy at the retina from a laser beam aimed at the z-location is safe, as described in more detail with reference to  FIG.  1   . 
     Via steps  212  and  224 , the surgical system determines the xy-location of the floater shadow and z-location of the floater, as described in more detail with reference to  FIG.  6   . In certain embodiments, the xy-location is the location predicted for when the laser fires. The laser device directs the laser beam through the xy-scanner to the z-location of the floater at step  226 . The xy-scanner directs the laser beam to the xy-location determined by the tracking at step  222 . The method then proceeds to step  220  to check whether there is a next floater shadow. If there is a next floater shadow, the method returns to step  210 , where the SLO device sends the SLO beam through the xy-scanner towards the next floater shadow. If there is no next floater shadow, the method ends. 
     In certain embodiments, laser device  22  is optimized 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. 
       FIG.  8    illustrates an example of a method for evaluating floaters, which may be performed by system  10  of  FIG.  1   , according to certain embodiments. In the example, the method generates a retinal image of an eye and analyzes floater shadows of the image to evaluate floaters in the eye. The method starts at step  310 , where an SLO device generates a retinal image of an eye. A computer displays the image on a display at step  312 . The computer performs image processing on the image at step  314 . An image processing program may detect the edges of a floater shadow indicating the presence of a floater. In certain embodiments, the computer overlays a graphical element onto the image that point out the shadow to a user, e.g., a circle that surrounds the shadow, an arrow that points to the shadow, or a border that outlines the shadow. 
     A shadow is selected to be analyzed at step  316 . The user or the computer may select the shadow. Steps  318   a ,  318   b , and  318   c  describe analyzing the shadow to determine if the floater is clinically significant, as described in more detail with respect to  FIG.  2   . The proximity of the shadow to the fovea or parafovea is analyzed at step  318   a . For example, a shadow on or passing over the fovea or parafovea may indicate a clinically significant floater. The size of the shadow is analyzed at step  318   b . For example, a shadow larger than a critical size may indicate a clinically significant floater. The density of the shadow is analyzed at step  318   b . For example, a shadow with a higher contrast relative to the background may indicate a clinically significant floater. 
     The method may include steps  318   a ,  318   b , and/or  318   c , i.e., the method need not include all the steps. In addition, the user and/or computer performs any or all of the included steps. In some cases, the user may decide to perform one or more steps, and then instruct the computer to perform other steps. Also, if the outcome of one step indicates that a floater is significant, the method may omit the remaining steps. For example, if steps  318   a  and  318   b  indicate the floater shadow is in the foveal region and is critically large, the method may omit step  318   c . Alternatively, if the outcome of one step indicates that a floater is not significant, the method may omit the remaining steps. For example, if step  318   a  indicates the floater shadow is far from the parafoveal region, the method may omit steps  318   b  and  318   c . 
     The floater may be designated as clinically significant at step  320  in response to the analyses performed at steps  318   a ,  318   b , and/or  318   c . The user and/or computer may make this decision. If the floater is significant, the method proceeds to steps  322  and/or  324 , where reports are generated, as described in more detail with reference to  FIG.  1   . The computer generates a patient report at step  322 . For example, the patient report can be used to educate the patient about their condition. The computer generates an authorization report at step  324 . For example, the authorization report can be used to obtain approval for treatment. In other embodiments of the method, the laser device may treat the floater, as described in more detail with respect to  FIGS.  6  and  7   , in addition to or as an alternative to generating reports. If the floater is not significant, the method proceeds directly to step  326 . 
     There may be a next shadow in the image at step  326 . If there is a next shadow, the method returns to step  316  to select the next shadow. If there are no more shadows, the method ends. 
     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).