Abstract:
A laser eye surgery system that has a patient interface between the eye and the laser system relying on suction to hold the interface to the eye, the patient interface using liquid used as a transmission medium for the laser. During a laser procedure sensors monitor the level of liquid within the patient interface and send a signal to control electronics if the level drops below a threshold value. The sensor may be mounted on the inside of the patient interface, within a fluid chamber. Alternatively, a gas flow meter may be added to a suction circuit for the patient interface that detects abnormal suction levels indicating low fluid level.

Description:
RELATED APPLICATIONS 
       [0001]    This application is a non-provisional application and claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Application Ser. No. 62/094,788, filed Dec. 19, 2014, which is incorporated herein in its entirety by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present application pertains to laser-assisted eye surgery using a liquid optical interface and, more particularly, to systems and methods for monitoring and reacting to insufficient liquid within the interface. 
       BACKGROUND 
       [0003]    A cataract is formed by opacification of the crystalline lens or its envelope—the lens capsule—of the eye. The cataract obstructs passage of light through the lens. A cataract can vary in degree from slight to complete opacity. Early in the development of an age-related cataract, the power of the lens may be increased, causing near-sightedness (myopia). Gradual yellowing and opacification of the lens may reduce the perception of blue colors as those wavelengths are absorbed and scattered within the crystalline lens. Cataract formation typically progresses slowly resulting in progressive vision loss. If left untreated, cataracts may cause blindness. 
         [0004]    A common cataract treatment involves replacing the opaque crystalline lens with an artificial intraocular lens (IOL). Every year, an estimated 15 million cataract surgeries are performed worldwide. Traditionally, cataract surgery has been typically performed using a technique called phacoemulsification in which an ultrasonic tip with associated irrigation and aspiration ports is used to sculpt the relatively hard nucleus of the lens to facilitate removal through an opening made in the anterior lens capsule. Access to the lens nucleus can be provided by performing an anterior capsulotomy in which a small round hole is formed in the anterior side of the lens capsule using a surgical. Access to the lens nucleus can also be provided by performing a manual continuous curvilinear capsulorhexis (CCC) procedure. After removal of the lens nucleus, a synthetic foldable intraocular lens (IOL) can be inserted into the remaining lens capsule of the eye. 
         [0005]    One of the most technically challenging and critical steps in the cataract extraction procedure is providing access to the lens nucleus for removal of the cataract by phacoemulsification. The desired outcome is to provide a smooth continuous circular opening through which phacoemulsification of the nucleus can be performed safely and easily, and also through which an intraocular lens may be easily inserted. Because of the criticality of this step, some surgeons prefer a surgical laser beam over manual tools like microkeratomes and forceps since the laser beam can be focused precisely on extremely small amounts of eye tissue, thereby enhancing the accuracy and reliability of the capsulotomy procedure. 
         [0006]    Several commercial laser-assisted eye surgery systems are available to facilitate cataract removal and astigmatism correction. The CATALYS Precision Laser System from Abbott Medical Optics is indicated for anterior capsulotomy, phacofragmentation, and the creation of single plane and multi-plane arc cuts/incisions in the cornea to correct astigmatism. The CATALYS System uses a two-piece liquid-filled interface that docks with the patient&#39;s eye with the liquid providing a transmission medium for the laser, thus avoiding distortion of the eye from contact with an applanation lens. The liquid provides a clear optical path for real-time video, OCT imaging, and laser treatment. Aspects of the CATALYS System are disclosed in U.S. Pat. No. 8,394,084, U.S. Pat. No. 8,500,724, U.S. Pat. No. 8,425,497, U.S. Patent Publication 2014/0163534, U.S. patent application Ser. No. 14/256,307, filed Apr. 18, 2014, and U.S. Patent Publication No. 2014/0343541, filed Apr. 17, 2014, the contents of all of which are incorporated herein by reference as if fully set forth. Other systems for laser cataract surgery are the LenSx Laser from Alcon Laboratories, Inc., the LENSAR Laser System from LENSAR, Inc., and the VICTUS Femtosecond Laser Platform from TECHNOLAS Perfect Vision GmbH a Bausch+Lomb Company. 
         [0007]    The interstitial layer of fluid has a strong influence on the delivery of a high fidelity laser spot in the correct location. One drawback with current systems that use liquid-filled optical interfaces is loss of liquid. Most docking interfaces rely on suction to hold the interface to the eye, and sometimes to hold separate pieces of the interface together. If during a laser procedure the interface shifts so that the liquid-filled chamber comes in fluid communication with the suction in any of these couplings, the level of liquid in the interface may be reduced to be replaced with air which has a different index of refraction and would affect the laser optics. If this happens during laser treatment, it is important to shut off delivery of the laser energy before any mistreatment, or even injury, can occur. 
         [0008]    Accordingly, there is a need for systems that detect loss of liquid in the optical interface. 
       SUMMARY 
       [0009]    Improved laser eye surgery systems, and related methods, are provided. The laser eye surgery systems use a laser to form precise incisions in the cornea, in the lens capsule, and/or in the crystalline lens nucleus. In a preferred embodiment, a laser eye surgery system includes a laser cutting subsystem to produce a laser pulse treatment beam to incise tissue within the eye. A liquid transmissive media is used between a patient interface lens and the eye to avoid imparting undesirable forces to the patient&#39;s eye. The present application provides a number of solutions for monitoring the liquid level within the patient interface. 
         [0010]    One particular embodiment of a liquid monitor includes one or more sensors positioned within the patient interface and in communication with the liquid therein. The sensors may be conductive pads which conduct current therebetween through the liquid until the liquid level drops too low. Alternatively, a light source may be shone down onto the liquid within the patient interface and light refracted through the liquid monitored for changes in the liquid level. Still further, a matched pair of acoustic emitter and sensor may be integrated into the patient interface which produce different signals when the liquid levels are high and low. Another solution is to incorporate an extremely small diameter orifice in the side of the liquid chamber and pull a very low vacuum on the orifice. If the liquid is covering the orifice, surface tension will prevent aspiration of the fluid, but when the liquid level drops air can be pulled through the orifice which is detected by an external sensor in the vacuum line. Finally, a gas flow meter may be installed within a vacuum supply circuit for a suction ring on the patient interface. The gas flow meter detects major suction losses as well as slow leaks by utilizing a sensor of high sensitivity. 
       INCORPORATION BY REFERENCE 
       [0011]    All publications, patents, and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent, or patent application was specifically and individually indicated to be incorporated by reference. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The novel features of the invention are set forth with particularity in the appended claims. A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the invention are utilized, and the accompanying drawings of which: 
           [0013]      FIG. 1  is a side view of a patient positioned under a patient interface of a laser-assisted eye surgery system; 
           [0014]      FIG. 2  is a simplified block diagram showing a top level view of the configuration of a laser eye surgery system having a patient interface in accordance with the present application; 
           [0015]      FIGS. 3A-3D  are perspective, elevational, plan and sectional views, respectively, of an eye-contacting member of an exemplary patient interface of the present application; 
           [0016]      FIG. 4  is a sectional view through an assembled patient interface with the eye-contacting member docked against an upper member that has an object lens for laser delivery; 
           [0017]      FIGS. 5A and 5B  are sectional views through the assembled patient interface taken along a section line perpendicular to that of  FIG. 4  and showing a first solution for monitoring a fluid level within the interface comprising conductive pads mounted to an inner wall of the eye-contacting member with the fluid level both high and low, respectively; 
           [0018]      FIGS. 6A and 6B  are sectional views through the assembled patient interface showing another solution for monitoring the fluid level including a light source and refracted light position detector integrated into the interface; 
           [0019]      FIGS. 7A and 7B  are sectional views through the assembled patient interface showing a still further solution for monitoring the fluid level including a matched pair of acoustic emitter and sensor integrated within the interface; 
           [0020]      FIGS. 8A and 8B  are sectional views through the assembled patient interface showing yet another solution for monitoring a fluid level including a small orifice through the wall of the interface connected to a vacuum line; and 
           [0021]      FIG. 9  is a schematic of suction circuits connected to the patient interface and showing a still further solution for monitoring a fluid level within the patient interface. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    Methods and systems related to laser eye surgery are disclosed. A laser is used to form precise incisions in the cornea, in the lens capsule, and/or in the crystalline lens nucleus. In a preferred embodiment, a laser eye surgery system includes a laser cutting subsystem to produce a laser pulse treatment beam to incise tissue within the eye, a ranging subsystem to measure the spatial disposition of external and internal structures of the eye in which incisions can be formed, an alignment subsystem, and shared optics operable to scan the treatment beam, a ranging subsystem beam, and/or an alignment beam relative to the laser eye surgery system. The alignment subsystem can include a video subsystem that can be used to, for example, provide images of the eye during docking of the eye to the laser eye surgery system and also provide images of the eye once the docking process is complete. In a preferred embodiment, a liquid interface is used between a patient interface lens and the eye. The use of the liquid interface avoids imparting undesirable forces to the patient&#39;s eye. 
         [0023]    Laser System Configuration 
         [0024]      FIG. 1  shows a laser eye surgery system  20 , in accordance with the present application, operable to form precise incisions in the cornea, in the lens capsule, and/or in the crystalline lens nucleus. The system  20  includes a diagnostic and interventional unit  22  under which the patient lies on a patient chair  24  that may be elevated up and down. A patient interface  26  is shown between the eye E of the patient and the diagnostic and interventional unit  22 , the attributes of which will be described below. 
         [0025]    The diagnostic and interventional unit  22  houses a number of subsystems which are not illustrated herein. For example, the unit  22  may provide a touch-screen control panel, patient interface vacuum connections, a docking control keypad, a patient interface radio frequency identification (RFID) reader, external connections (e.g., network, video output, one or more foot switches, USB port, door interlock, and AC power), a laser emission indicator, an emergency laser stop button, key switch, and USB data ports. These subsystems are shown and described in U.S. Patent Publication No. 2014/012821, filed Oct. 31, 2013, the contents of which are expressly incorporated herein by reference. 
         [0026]    The patient chair  24  includes a headrest  28  and a patient chair joystick control  30  for a chair positioning mechanism (internal, not shown). The patient chair  24  is configured to be adjusted and oriented in three axes (x, y, and z) using the patient chair joystick control  30 . The headrest  28  and a restrain system (not shown, e.g., a restraint strap engaging the patient&#39;s forehead) stabilize the patient&#39;s head during the procedure. The headrest  28  desirably includes an adjustable neck support to provide patient comfort and to reduce patient head movement. The headrest  28  is configured to be vertically adjustable to enable adjustment of the patient head position to provide patient comfort and to accommodate variation in patient head size. 
         [0027]    The patient chair  24  allows for tilt articulation of the patient&#39;s legs, torso, and head using manual adjustments. The patient chair  24  accommodates a patient load position, a suction ring capture position, and a patient treat position. In the patient load position, the chair  24  is rotated out from under the diagnostic and interventional unit  22  with the patient chair back in an upright position and patient footrest in a lowered position. In the suction ring capture position, the chair is rotated out from under the diagnostic and interventional unit  22  with the patient chair back in reclined position and patient footrest in raised position. In the patient treat position, the chair is rotated under the diagnostic and interventional unit  22  with the patient chair back in reclined position and patient footrest in raised position. 
         [0028]      FIG. 2  shows a simplified block diagram of the system  20  coupled with a patient eye E. The patient eye E comprises a cornea, a lens, and an iris. The iris defines a pupil of the eye E that may be used for alignment of eye E with system  20 . The system  20  includes a cutting laser subsystem  44 , an OCT imaging system  46 , an alignment guidance system  48 , a video camera  49 , shared optics  50 , the patient interface  26 , control electronics  54 , a control panel/GUI  56 , user interface devices  58 , and communication paths  60 . The control electronics  54  are operatively coupled via the communication paths  60  with the cutting laser subsystem  44 , the OCT imaging system  46 , the alignment guidance subsystem  48 , the video camera  49 , the shared optics  50 , the patient interface  26 , the control panel/GUI  56 , and the user interface devices  58 . Again, further details of these aspects are shown and described in U.S. Patent Publication No. 2014/012821, to Gooding, previously incorporated herein by reference. 
         [0029]    In a preferred embodiment, the cutting laser subsystem  44  incorporates femtosecond (FS) laser technology. By using femtosecond laser technology, a short duration (e.g., approximately 10 −13  seconds in duration) laser pulse (with energy level in the micro joule range) can be delivered to a tightly focused point to disrupt tissue, thereby substantially lowering the energy level required as compared to the level required for ultrasound fragmentation of the lens nucleus and as compared to laser pulses having longer durations. The cutting laser subsystem  44  can produce laser pulses having a wavelength suitable to the configuration of the system  20 . As a non-limiting example, the system  20  can be configured to use a cutting laser subsystem  44  that produces laser pulses having a wavelength from 1020 nm to 1050 nm. For example, the cutting laser subsystem  44  can have a diode-pumped solid-state configuration with a 1030 (+/−5) nm center wavelength. 
         [0030]    Patient Interfaces 
         [0031]    The patient interface  26  is used to restrain the position of the patient&#39;s eye E relative to the system  20 . In a preferred embodiment, the patient interface  26  employs a suction ring that attaches to the patient&#39;s eye E using a vacuum line. The suction ring is then coupled with the patient interface  26 , for example, using vacuum to secure the suction ring to the patient interface  26 . In a preferred embodiment, the patient interface  26  includes an optically transmissive structure (lens) having a posterior surface that is displaced vertically from the anterior surface of the patient&#39;s cornea and a region of a suitable liquid (e.g., a sterile buffered saline solution (BSS)) is disposed between and in contact with the posterior surface and the patient&#39;s cornea to form part of a transmission path between the shared optics  50  and the patient&#39;s eye E. The optically transmissive structure may comprise a lens  62  (see  FIG. 4 ) having one or more curved surfaces. Alternatively, the patient interface  26  may comprise an optically transmissive structure having one or more substantially flat surfaces such as a parallel plate or wedge. In a preferred embodiment, the patient interface lens is disposable and is replaced before each eye treatment. 
         [0032]      FIGS. 3A-3D  depict an eye-contacting member  70  of the exemplary patient interface  26  used in the laser eye surgery systems described herein. As mentioned above, an exemplary patient interface  26  incorporates a suction ring  72  for coupling with the eye E, for example, using vacuum. More specifically, a lower or distal end of the patient interface  26  is placed in contact with the cornea of the eye E and suction drawn through a first suction conduit  74   a  coupled to the suction ring. The first suction conduit  74   a  extends from the suction ring  72  to a plurality of components including a vacuum source, as will be described with reference to  FIG. 9 . 
         [0033]    The patient interface  26  comprises a two-part assembly with an upper member  76  (see  FIG. 4 ) having features configured to be removably coupled to the diagnostic and interventional unit  22 , such as that described above in reference to  FIG. 1 . The upper member  76  is also removably coupled to the eye-contacting member  70  via suction, as will be described. In an exemplary procedure, the patient chair  24  is rotated out from under the diagnostic and interventional unit  22  to the suction ring capture position. A physician or technician can then easily engage the eye-contacting member  70  of the interface  26  to the patient&#39;s eyes E using the suction ring  72 . The chair  24  is then rotated to the patient treat position under the diagnostic and interventional unit  22 , and the eye-contacting member  70  and upper member  76  are coupled together, such as shown in  FIG. 1 . The system  20  is then ready for a laser-assisted ophthalmic procedure. 
         [0034]    It should be noted that the patient interface  26  may comprise separable components such as the eye-contacting member  70  and upper member  76 , or can be provided together as a single inseparable unit. Further details of exemplary liquid-filled patient interfaces are disclosed in U.S. Patent Publication 2013/0102922, filed Oct. 21, 2011, the contents of which are expressly incorporated herein by reference. 
         [0035]    With reference again to  FIGS. 3A-3D , the eye-contacting member  70  of the patient interface  26  in this embodiment comprises a generally frustoconical body  80  having an upper cylindrical rim  82 . The rigid, preferably molded, body  80  has a generally annular cross-section and defines therein a throughbore  84  as seen best in  FIG. 3D . A small radially-projecting handle  88  permits a physician or technician to easily manipulate the member  70 , and a trio of fluid conduits  74   a ,  74   b  and  90  extend radially away in the same direction. 
         [0036]      FIG. 3D  best shows an internal structure of the eye-contact member  70 . The body  80  receives an annular elastomeric seal  92  in a circular groove to provide a seal for mating with the upper member  76 . The upper fluid conduit  74   b  attaches to a corresponding nipple  94   b  having a lumen that is in fluid communication with an annular space  96  defined within two walls of the seal  92 . As is shown in  FIG. 4 , a vacuum pulled through the conduit  74   b  creates a suction within the seal  92  which pulls a lower surface of the upper member  76  into contact with the seal, thus effectively holding together the two parts of the patient interface  26 . 
         [0037]    On the bottom end of the frustoconical body  80 , the elastomeric suction ring  72  also defines a pair of annular walls (not numbered) that define a space  98  therebetween. The lower fluid conduit  74   a  attaches to a corresponding nipple  94   a  having a lumen that is in fluid communication with the space  98 . When a vacuum is pulled through the conduit  74   a , the suction ring  72  can be secured to the generally spherical surface of the eye E. 
         [0038]    The assembly of the eye-contacting member  70  coupled to the eye E, with the upper member  76  held by suction to the elastomeric seal  92 , is shown in  FIG. 4 . As mentioned above, the upper member  76  mounts within the upper cylindrical rim  82  of the frustoconical body  80  of the eye-contacting member  70 . The upper member  76  includes a generally frustoconical wall  100  having a small circular flange  102  projecting downward therefrom that fits within the annular space  96  ( FIG. 3D ) defined within the two walls of the elastomeric seal  92 . This helps center the two components. A vacuum through the upper fluid conduit  74   b  pulls the frustoconical wall  100  against the blades of the elastomeric seal  92 , thus securing the upper member  76  to the eye-contacting member  70 . 
         [0039]    The optical lens  62  is thus held securely centered within the patient interface  26 , and above the eye E. More specifically, the posterior surface of the optical lens  62  is spaced vertically from the anterior surface of the patient&#39;s cornea across a region of a suitable liquid  110  (e.g., a sterile buffered saline solution (BSS)) within a transmissive fluid chamber  112 . The chamber  112  includes that portion of the throughbore  84  within the eye-contacting member  70  below the lens  62  and within a conical field of view  114  (shown in dashed line) of the optical instruments of the laser-assisted system described above. However, the chamber  112  also extends outward from the field of view  114  which provides space for the liquid level sensing instruments described herein. Although not shown, inlet and outlet ports to the chamber  112  are provided in the eye-contacting member  70  for supplying and draining liquid as needed, in particular for maintaining a pressure equilibrium. 
         [0040]    Liquid Level Detection Solutions 
         [0041]      FIGS. 5A and 5B  are sectional views through the assembled patient interface  26  taken along a section line perpendicular to that of  FIG. 4 . A first solution for monitoring the fluid level within the interface  26  comprises a pair of conductive pads  120  mounted to an inner wall of the eye-contacting member  70 , such as diametrically across from one another (of course, the conductors could be mounted at other locations). Circuitry associated with the conducting pads  120  is not shown but would include a current sensor for detecting any current passing between the pads  120 .  FIG. 5A  shows the liquid  110  filling the chamber  112 . In this configuration, which is preferred for normal laser operation, a current may be passed through the liquid between the conducting pads  120 , thus closing the associated circuit. On the other hand, when the level of the liquid  110  drops in the chamber  112 , as seen in  FIG. 5B , an air gap exists between the conducting pads  120 , thus preventing current flow between the pads. Consequently, the current sensor communicates with the control electronics  54  and if the laser is in use, shuts it down. A pair of spaced conducting pads  120  may be mounted at the same level as shown, or two or more pairs and associated circuits may be included to provide indicators for multiple fluid levels. In an alternative configuration, the sensing pads  120  may be calibrated to measure capacitance which is altered when the fluid drops low enough to lose contact with the pads. 
         [0042]      FIGS. 6A and 6B  illustrate a second solution for optically monitoring the fluid level within the patient interface  26 . More particularly, a light emitting source  130  is provided within the patient interface  26  or above it so that it shines downward at an angle through the lens  62  and into the liquid  110  in the chamber  112 . When the light from the source  130  hits the surface of the liquid  110 , it refracts as shown. A position detector  132  mounted to the inner wall of the eye-contacting member  70  senses the position of the refractive light. For a high liquid level, as seen in  FIG. 6A , the angle of refraction causes the light to hit the position detector  132  relatively high up. On the other hand, when the liquid level drops, as seen in  FIG. 6B , the angle of refraction is altered such that the light reaches the position detector  132  lower down, thus indicating an unacceptable loss of liquid. At some point the position detector  132  communicates with the control electronics  54  and if the laser is in use, shuts it down. The light position detector  132  could be either a continuous position detector to sense all fluid levels continuously, or may be constructed with discrete detectors to monitor specific levels (e.g., normal and low). 
         [0043]      FIGS. 7A and 7B  illustrate the patient interface  26  with a matched pair of acoustic emitter  140  and sensor  142  integrated therein. In particular, the emitter  140  and sensor  142  are mounted to the inner wall of the frustoconical body  80  diametrically across from one another. When the liquid  110  is at a high level in the chamber  112 , acoustic signals from the emitter  140  are received by the sensor  142  through the fluid therebetween. After the liquid level drops, as seen in  FIG. 7B , the sound waves from the emitter  140  take on a much different character passing through the air gap to the sensor  142 . Fluid loss may also be detected by the changing character of the acoustic signature induced by a changing fluid volume, even before the level of the liquid descends below either the emitter  140  or the sensor  142 . The emitter  140  and sensor  142  may be integrated into the frustoconical body  80  of the eye-contact member  70 , or may be provided as separate components either mounted to the body or introduced into the liquid  110  from above. 
         [0044]      FIGS. 8A and 8B  shows the patient interface  26  having a small orifice  150  through the wall of the body  80 . A nipple (not numbered) leading from the orifice  150  connects to a vacuum line  152 . A slight vacuum can be applied through the vacuum line  152  and thus to the orifice  150 . When the orifice  150  is covered by fluid, such as seen in  FIG. 8A , surface tension will prevent the fluid from passing through the orifice, which results in a full vacuum. The magnitude of the vacuum pressure is sensed and a full vacuum means there is sufficient fluid in the chamber  112 . Alternatively, when the level of the liquid  110  drops below the orifice  150 , the slight vacuum will pull any residual fluid and air through the orifice  150 , thus significantly lowering the magnitude of the vacuum or negative pressure from loss of resistance. If the laser is operating it is then shut off. The diameter of the orifice  150  is extremely small such that surface tension of the liquid prevents aspiration through the orifice when a low vacuum is applied, but allows free flow of air when the fluid level drops below the orifice. A number of orifices  150  can be provided in various positions around the body  80  to reduce false-negative conditions and/or provide sensing at multiple fluid levels. 
         [0045]    Finally, an indirect method for monitoring the fluid level  110  within the patient interface may be incorporated into the patient interface suction system.  FIG. 9  is a schematic of suction circuits connected to the patient interface  26 , and illustrates the eye E below the patient interface including the upper member  76  and eye-contacting member  70 . 
         [0046]    The patient interface  26  couples to the first suction conduit  74   a  and second suction conduit  74   b . The first suction conduit  74   a  extends from the suction ring  72  (see  FIG. 4 ) to a vacuum source such as an eye retention structure vacuum pump  200 . The suction conduit  74   a  couples the first fluid collector  202  to the patient interface  26  to receive fluid therefrom. A first fluid stop  204  couples to an outlet of the first collector  202  and includes a float valve or porous structure to pass a gas such as air and inhibit flow of a liquid or viscous material so as to stop substantially the flow of the liquid or viscous. A suction vacuum regulator  206  along first suction conduit  74   a  provides a regulated amount of pressure to eye E with the suction ring, for example suction pressure between about 300 and 500 mm Hg (millimeters Mercury), for example. The outlet of the suction vacuum regulator  206  is coupled to the vacuum pump  200  which is coupled to control electronics  54  with communication paths  60 . 
         [0047]    The second suction conduit  74   b  extends from the patient interface  26  to a vacuum source such as dock vacuum pump  210 . The second suction conduit  74   b  provides suction to the interface between the upper member  76  and the eye-contacting member  70 , and clamps the two together. Suction conduit  74   b  extends to a second fluid collector  212  and then to a second fluid stop  214  which contains a porous structure or float valve to inhibit flow of a liquid or viscous material and substantially stop the flow therethrough. The components within dashed area  216  form a liquid optics interface (LOI). The second fluid stop  214  couples to a dock monitor  215 , which can be positioned along second suction conduit  74   b  in order to monitor suction for coupling upper member  76  to eye-contacting member  70 . Suction monitor  215  comprising a pressure sensor is positioned along the second suction conduit  74   b  downstream of the second fluid stop  214  and a dock solenoid valve  216 . The pressure sensor  215  can be coupled to control electronics  54  via the communication paths  60 , as described herein. The pressure sensor  215  preferably comprises a transducer responsive to pressure of the suction conduit  74   b . The suction solenoid valve  216  is coupled to control electronics  54 , and the second suction conduit  74   b  may include another suction line monitor  217  to monitor suction downstream of suction solenoid valve  216 . The suction line monitor  217  preferably couples to an inlet of the vacuum pump  210 , which is also connected to the control electronics  54 . 
         [0048]    The third conduit  90  connected to the patient interface  26  (see  FIG. 4 ) leads to a suction monitor  220  and then to a suction solenoid valve  222 . The suction monitor  220  keeps track of the section level within the suction ring  72  and is coupled to control electronics  54  via the communication paths  60 . 
         [0049]    To indirectly sense liquid loss, a flow sensor  230  is introduced in the first suction conduit  74   a  in series between a suction solenoid valve  232  and the vacuum regulator  206 . The flow sensor  230 , which may be a gas flow meter, monitors gas flow within the first suction conduit  74   a , and provides an alternative method for detecting major suction loss as well as slow leaks by utilizing a sensor of high sensitivity. A loss of liquid in the patient interface  26  may be caused by displacement between the interface and the patient&#39;s eye, which suddenly alters the gas flow into the suction ring  72 . That is, when the suction ring  72  is engaged with the eye there is very little gas flow, while a disconnect suddenly allows air to be sucked into the suction conduit  74   a . This can be sensed by the flow sensor  230  which is in communication with control electronics  54  which may shut the system down if the laser is operational. A high enough flow sensitivity also will detect small leaks which could ultimately lead to a major liquid loss. 
         [0050]    The coupling lines as described herein may comprise lines for fluidic coupling known to a person of ordinary skill in the art and may comprise one or more of tubing, flexible tubing, rigid tubing, plastic tubing, metal tubing or manifolds, for example. The containers as described herein may comprise similar materials and can be constructed by a person of ordinary skill in the art based on the teachings provided herein. 
         [0051]    A preferred laser cataract surgery using the aforementioned system is done by connecting the patient&#39;s eye with the laser system via a liquid-filled patient interface. The lower part of the patient interface attaches to the patient&#39;s eye by applying a vacuum over a ring-shaped area. The patient interface is then filled with a suitable sterile liquid (e.g., a sterile buffered saline solution (BSS)) interior to this ring, so that the sterile liquid is in direct contact with the patient&#39;s cornea. The patient is then moved with the chair to a position where the top part of the patient interface can be attached to an overhanging laser system by pulling vacuum over a second area, also with the shape of a ring. The sterile liquid is also in direct contact with the laser system&#39;s optics and the becomes part of the optical system of the instrument, interfacing the optical hardware with the patient&#39;s eye. 
         [0052]    During treatment, the laser energy is transmitted into the patient&#39;s eye thought the sterile liquid contained in the patient interface. Precise positioning of the laser beam in the human eye is very important and the system optics, interface liquid and eye media are taken into consideration by the system software. 
         [0053]    If during treatment, the liquid level within the interface to the patient were to decrease, the optics for the laser would be affected because air has a smaller index of refraction, perhaps causing harm to the patient. This situation could be caused by patient movement displacing the patient interface components such that sterile liquid enters the various vacuum conduits. Thus, the various techniques for detecting liquid loss within the patient interface  26  alert the physician/technician or system electronics to a possible catastrophic situation and corrective action can be quickly taken. 
         [0054]    While preferred embodiments of the present invention have been shown and described herein, it will be obvious to those skilled in the art that such embodiments are provided by way of example only. Numerous variations, changes, and substitutions will now occur to those skilled in the art without departing from the invention. It should be understood that various alternatives to the embodiments of the invention described herein may be employed in practicing the invention. It is intended that the following claims define the scope of the invention and that methods and structures within the scope of these claims and their equivalents be covered thereby.