Surgical instrument for minimally invasive aspiration of tissue

An apparatus for disruption of cataracts in lens tissue. The apparatus includes a housing; a source of pulsed laser radiation; and an optical waveguide. The optical waveguide is configured to transmit the pulsed laser radiation from the source of pulsed laser radiation, and is coupleable to the source of pulsed laser radiation at a proximal end of the optical waveguide to receive the pulsed laser radiation from the source of pulsed laser radiation. The apparatus also includes a driving mechanism coupled to the optical waveguide for controllably changing the position of the optical waveguide relative to a distal end of the housing.

FIELD

The present disclosure relates generally to an apparatus and method for use in cataract surgery. Particularly, the present disclosure relates to a surgical laser ablation device and method for disruption and aspiration of cataractous lens tissue.

BACKGROUND

Cataract surgery was developed to treat blindness caused by opacification of lens tissue in the human eye. Although most cases of cataract are related to the aging process, occasionally children can be born with the condition, or a cataract may develop after eye injuries, inflammation and some other eye diseases. Treatment for cataractous lens tissues is one of the most frequently performed surgeries.

In modern small incision cataract surgery, the eye surgeon uses a hand-held metal or diamond blade to create an incision in the area where the sclera meets the cornea. The next step for the cataract surgery is to remove the front portion of the capsule to allow access to the cataract. Once the capsule is opened an instrument can be inserted to break apart and disrupt the cataract prior to removal. Tools for breaking apart the lens include mechanical tools such as ‘chopper’ or forceps to tear the tissue apart, and more recently tools containing ultrasonic transducers have been used to emulsify tissue prior to aspiration. Various single use ultrasonic aspiration needles have been proposed e.g. U.S. Pat. No. 8,454,551 B2

Devices have been proposed that use laser radiation to break-down tissue through heating effects or acousto-optically generated ultrasonic energy (e.g. U.S. Pat. No. 6,083,192 A). Additional techniques have been adopted in which radiation from very short pulsed lasers that are not absorbed well in eye tissue are focused inside the volume of the cataractous lens to achieve photo-disruption of the tissue prior to aspiration. This latter technique suffers from the necessity of a projection system, and has not been implemented in a hand-held instrument due to a lack of effective optical waveguide beam delivery for such short pulses.

Microsecond and longer pulsed Mid-IR lasers had been used for ablation of lens tissue. A mechanism for laser ablation (impulsive heat deposition) was described in U.S. Pat. No. 8,029,501 (which is incorporated herein by reference in its entirety) in which rapid-heating by excitation of vibrational modes inside of tissue causes vaporization of the exposed tissue. This laser source required for this new mechanism is compatible with specific fiber optic beam delivery systems.

A surgical apparatus and method in which the laser mechanism described above could be used to disrupt and remove lens tissue via a handheld instrument that included a fiber optic beam delivery system for on contact tissue disruption has been proposed, see WO2016041086A1, the entirety of which is hereby incorporated by reference. In one embodiment of that disclosure, the distal end of the fiber optic was delivered to the tissue inside an aspiration needle of larger diameter.

SUMMARY

In some examples, the present disclosure describes an apparatus for disruption of cataracts in lens tissue. The apparatus includes a housing; a source of pulsed laser radiation; and an optical waveguide. The optical waveguide is at least partially housed within the housing, and includes a flexible optical fiber. The optical waveguide is configured to transmit the pulsed laser radiation for causing disruption of cataracts, and is coupleable to the source of pulsed laser radiation at a proximal end of the optical waveguide to receive the pulsed laser radiation from the source of pulsed laser radiation. The apparatus also includes a driving mechanism coupled to the optical waveguide for controllably changing the position of the optical waveguide relative to a distal end of the housing.

DESCRIPTION OF EXAMPLE EMBODIMENTS

In some examples, present disclosure provides a hand held laser phacoemulsification apparatus for disruption and removal of cataractous-lens tissue.

In some examples, the disclosure provides an apparatus that may help to provide improved aspiration rate of a surgical instrument54, compared to conventional instruments, by utilizing laser energy to disrupt tissue on contact with a fiber optic tip16. The fiber optic tip16sits collinearly within the small diameter of an aspiration channel that is suitable for manually positioning within the anterior capsule of the human eye. The fiber optic16is able to advance or retreat within the aspiration channel to enhance the rate of tissue aspiration, and also minimize the risk of disruption to unintentionally aspirated tissue.

In some examples, the disclosure integrates the control of the fluidics (means of aspiration and irrigation) and the laser disruption, with an algorithm that adjusts laser parameters such as pulse rate, envelope and positioning of the laser tip based on user inputs and sensor outputs (e.g., measuring pressure and flow rate within the aspiration and irrigation channels) to achieve faster and more precise aspiration with minimal fluidics (flow and vacuum) and minimal disruption to surrounding tissues.

In some examples, the disclosure provides a surgical instrument54in which the user control of aspiration rate is further enhanced by the addition of a moveable fiber optic16integrated into the irrigation/aspiration tip and a control system algorithm that, in response to various user inputs and sensed fluidic conditions, automatically optimizes fiber position and laser pulse rate to minimize invasive damage to surrounding tissue structures and limit changes in the pressure of the anterior capsule, as well as minimize the flow of aspiration and irrigation during the tissue removal procedure.

The present disclosure describes an apparatus including a laser probe which, on contact, and internal to the body, can efficiently drive rapid dissolution of tissue by optical excitation of selected vibrational modes inside of the tissue's molecules on timescales faster than heat diffusion to the surroundings. The laser probe uses a laser mechanism similar to that previously disclosed in WO2016041086A1, incorporated by reference herein in its entirety.

This disclosure is directed toward an example approach for efficiently disrupting hard cataract tissue while avoiding the issues of energy propagation into other tissues of the eye.

With reference toFIG. 1, an example laser ablation approach is disclosed.FIG. 1shows an illustration of laser disruption of cataractous lens tissue1. The laser disruption occurs when laser pulses of a selected duration, wavelength and pulse energy, such as that disclosed in WO2016041086A1, are coupled to an optical waveguide12, and exit from the distal end16of the optical waveguide12. The optical wavelength guide12has been inserted into the anterior chamber of the eye through an incision point7and through an opening in the capsule9, directed inside of the cataractous lens tissue1. Light is strongly absorbed by the lens cells3or intercellular regions8, that are in contact with the exit of the waveguide16or within a distance close to the optical absorption depth40of the laser light inside the tissue irradiates a volume of tissue5, resulting in disruption of the lens cells and/or the cell structure of the lens4and effective dissolution and aspiration of the disrupted fragments of the cataractous tissue6with minimal disturbance to distant parts of the eye such as the cornea2or the lens capsule9. A hollow tube or needle13provides a means for removal of the disrupted tissue, when connected to a means of vacuum pressure. An inner tip of the aspiration channel52contains the distal end of the fiber optic16and from which emerge the laser pulses. The laser pulses disrupt the tissue on contact so the resulting material can be aspirated out of the eye.

This collinear delivery of the laser energy is advantageous in the case of small fiber optics and precise laser disruption processes since the tissue is actively drawn towards the laser energy by the aspiration pressure. The on-contact tissue disruption of the current disclosure is not limited to lens tissue and can be applied to all tissue types.

Notably, in an example embodiment, a means to move or reposition the position of the fiber optic tip16, during the surgical procedure and the means to control this position based on user input and fluidic conditions within the irrigation and aspiration channel is provided, seeFIG. 2.

FIG. 2discloses an example embodiment of the disclosure in which a handheld instrument54is coupled to a source of laser pulses10. The source of laser pulses10is controlled by a signal22from a control circuit21which also controls a means for aspiration18and a means for irrigation17. The source of laser pulses10further receives inputs from one or more sensors, such as a flow rate sensor38and a pressure sensor48within the fluidic channels. The action of irrigation, aspiration pressure, aspiration flow rate and laser power, pulse rate and fiber positioning may further be controlled through the use of a user input device11such as a multifunction foot pedal and preset parameters stored within the control circuit21. Other control means may be provided. The preset parameters may include maximum flow rate and pressure limits, laser power limits and other modes of operation. The irrigation and aspiration channels52may be coupled to flexible tubing100(seeFIG. 8), further coupled to a tool assembly19, which may be detachable, re-useable or disposable. Flexible tubing100allows for insertion and control of the distal tip20of the tool assembly19inside an ocular lens1to achieve controlled micro-disruption of the cataract tissue at the tip, seeFIG. 1. In one example, a means24(e.g., driving mechanism such as a linear motor, or linear translation mechanism driven by a rotating motor, voice-coil actuator etc.) of moving the optical fiber12is provided to control relative distance of the distal fiber optic tip16to the distal end of the aspiration channel52. A sensor or encoder53(e.g., photo-acoustics sensor) to track the fiber tip position may be provided. Another sensor may also be provided to detect when there is physical contact between the optical fiber12and the tissue.

In some examples, the optical fiber12may be made of any suitable material, such as sapphire, diamond, ZBLAN or YAG. The fiber optic tip16may be straight, or have any other suitable configuration, for example curved, tapered or angled, such as described in WO2016041086A1.

A user can control the position of the fiber optic tip16in a number of different ways. In one example embodiment, an additional user input device configured to move the fiber position forwards or backwards is provided. In a further example, the fiber is advanced using a proportional pedal that is generally used in a conventional procedure to increase the flow rate/aspiration pressure. Actuation of the pedal causes higher levels of aspiration, and at the same time the proximity of the laser disruption mechanism to the aspiration tip is decreased.

In some examples, the position of the fiber tip16is automatically adjusted based on the reaction of the pressure and flow rate of the aspiration channel52to the user's demands for higher levels of aspiration, for example by sensing a degree of occlusion on the tip. In such an embodiment, the position of the fiber optic tip16may be determined directly by the surgeon, or in combination with a control algorithm that senses the fluid conditions within the aspiration channel52and identifies several conditions including occlusions and unobstructed flow. In some examples, automatic adjustment may be used in combination with direct user input to control the position of the fiber optic top16.

In a conventional cataract surgical system the user has control (e.g., via a foot pedal) of aspiration. A conventional system may include some simple automatic controls for limiting the flow if the pressure is too high. In the present disclosure, a more comprehensive control of the system is provided, in which the laser parameters are also controlled while taking into account into the pressure and flow detected, and also while controlling positioning of the optical fiber. For example, the flow may be limited because the pressure is too high, and further the system controls the laser to turn on and controls the optical fiber to move distally towards the tip as a way to decrease the pressure. Further details of such comprehensive control is described below.

With reference toFIG. 3, under unobstructed conditions, the relationship between flow and pressure inside the aspiration channel52can be approximated by considering laminar flow and a Newtonian fluid inside a circular cross section pipe, by considering laminar flow according to Poiseuilles law:

where

Q=d⁢⁢Vd⁢⁢t
is the volumetric flow rate (volume/time), Δp is the change in pressure across both ends of the pipe, R, the radius of the pipe and η is the viscosity of the fluid, and L the length of the pipe. As disclosed by Poiseuille's equation, for rising viscosity, a larger pressure difference is required to maintain a constant flow rate. To prevent catastrophic pressure changes from damaging the eye, most opthlalmological aspiration devices have a configurable pressure limit, Δpmax, often set to around 350-600 mm/hg. Above this pressure, the pump is prevented from working harder and the flow rate is thus prevented from increasing. Similarly, there is often a flow rate limit as well, Qmaxset around 20-50 cc/min for the purposes of aspirating tissue.

Given a user control signal for desired aspiration flow rate, which can vary from 0-100%, the user could expect the flow to follow the control signal up to the maximum pressure.
Q∝A(Δp) for Δp<ΔpmaxorQ∝A(Δpmax)

With limited pressure it is important to consider ways to prevent high viscosity tissues from blocking the aspiration channel52. For example, to minimize clogging downstream, the tip51of the aspiration channel52can be tapered so that the entrance diameter is smaller than the diameter of the aspiration channel52. Laser energy delivered within the aspiration channel's52entrance can then be used to prevent unwanted clogging within the aspiration channel52. It may also be advantageous to advance the fiber directly outside the channel in the unobstructed situation, where the smaller diameter fiber can be used as a sculpting or high precision disruption tool while the aspiration channel52pressure or flow is set to almost nothing. But during high flow aspiration modes, the laser is not required to disrupt tissue in the unobstructed situation and Poiseuilles law will hold. By monitoring the pressure and flow parameters and their rates of change, it is possible to determine if an occlusion has occurred, see below.

With further reference toFIG. 3, insertion of an example device is disclosed.FIG. 3illustrates the distal tip of the example instrument54in which the aspiration needle13and the optical fiber12are collinear and the entrance of the aspiration channel52is unobstructed. The pressure within the aspiration channel52is low, and the flow rate is not limited by the pressure. In this example, the fiber tip16position is not critical and can be retracted by several mm within the aspiration needle. In some examples, the fiber tip16can be retracted up to and including a range of about 5 mm distally and up to and including a range of about 10 mm proximally. Other distances may be possible according to the dimensions of the human eye, and depending on the specific application. The laser energy used in a retracted position helps further disrupt tissue fragments that are drawn by negative pressure into the aspiration channel52. In this mode the instrument54acts much like a conventional aspiration/irrigation instrument tip. Aspiration of the lens capsule is less likely to make contact with the fiber optic and can be preserved upon accidental aspiration.

It may be desirable within the surgical procedure to hold onto a piece of tissue with the aspiration needle until it is positioned appropriately within the anterior chamber for energetic disruption. Once a piece has been engaged with the aspiration pressure it may fill the entrance of the aspiration channel52and block further removal without increased pressure.

FIG. 4illustrates such an example occlusion that occurs when the fiber is retracted. A fragment of tissue81is pulled towards the aspiration channel52by negative pressure, and is too large to be aspirated and completely occludes the aspiration channel52entrance. In this example situation, the pressure inside the aspiration channel52rises as a function of the flow rate and it is advantageous to advance the laser fiber towards the entrance of the aspiration channel52to disrupt tissue causing the obstruction, rather than to attempt aspiration at higher pressures.

Further, in this example embodiment, the aspiration needle is able to hold the occlusion better if the fiber is not protruding, otherwise the fiber itself becomes either buried inside the occluding tissue fragment, or prevents any occlusion from occurring. The tissue fragment is held to the tip of the aspiration needle by a force caused by the pressure difference between the fluid around the tissue fragment and the inside of the aspiration channel52. In this case the relationship between pressure and flow rate deviates drastically from Poiseuilles law because Q approaches 0, since no volume can flow through the occlusion, assuming that R, and L are fixed.

The solution for Q=0 only occurs if Δp=0 (the pump is off and the piece cannot be held) or the viscosity effectively becomes infinite η→∞. As the pump continues to try and aspirate despite the blockage, the pressure becomes proportional to the control signal, and rises quickly to its limit.
Δp∝Afor ΔP<Δpmaxor Δp=Δpmax

The time required to reach the pressure limit is often referred to as the aspiration fluidic systems ‘rise-time’, τ.

By monitoring the pressure and flow over time, an algorithm can predict an occlusion if the flow rate is dropping while the pressure is rising. In other words, when unobstructed and below the pressure and flow limits the control signal and the aspiration rate are well defined.

Q∝A(Δp) and thus the rate of change of flow with control signal is well defined

d⁢⁢Qd⁢⁢A∝constant
and the pressure can be described by equation 1.

However, when occluded, additional demands for flow, increasing A, result in no additional flow: Q=0 and

d⁢⁢Q⁡(A)d⁢⁢A→0
becomes negligible. Subsequently the rate of change of the pressure to the control signal now becomes well defined

d⁢⁢Δ⁢⁢pd⁢⁢A=constant.
In this way the level of occlusion can be sampled by seeing how the flow rate and pressure react to changes in the control signal.

Assuming that while the occlusion occurs the control signal does not change:

d⁢⁢Ad⁢⁢t=0.
Before the occlusion the tip is unobstructed and the flow rate is fixed by the control signal, and from equation 1 Δp∝Qη∝A or

However, once the occlusion occurs, the viscosity becomes effectively infinite as the initial flow rate Q0begins to drop to zero and

d⁢⁢Qd⁢⁢t
becomes negative and Δp grows over the ‘rise time’ to Δpmax. In other words, during this time, the sign of

d⁢⁢Δ⁢⁢pd⁢⁢Q=(Δ⁢⁢pt·Δ⁢⁢p0)(0-Q0)<0
changes and becomes negative. Meanwhile, the pressure begins to rise at the following rate,

d⁢⁢Pd⁢⁢t=Δ⁢⁢pmax·Δ⁢⁢pτ.
After the rise time the pressure is at its maximum value and neither flow nor pressure can change. In this case

d⁢⁢Qd⁢⁢t=0,d⁢⁢Δ⁢⁢pd⁢⁢t=0,
but now Q=0 AND Δp=Δpmaxso the pipe must be occluded completely. In other words,

(d⁢⁢Δ⁢⁢pd⁢⁢Q)
becomes ill defined when fully occluded, but swings from positive when unobstructed, to negative during the ‘rise’ time.

In this example embodiment, a conventional phaco machine operator would begin to use higher vacuum pressures or ultrasound to disrupt the occlusion.

FIG. 5discloses a means through which the laser fiber aids the transition from occluded to unobstructed. In other words,FIG. 5discloses tissue fragment as it is disrupted and aspirated, and the occlusion is partially or completely cleared, and the laser fiber can begin to retract until another occlusion occurs. Once the occlusion begins to clear and the pressure no longer increases dramatically with the flow rate, the laser power can be reduced or the laser tip can be retracted to prevent the remaining tissue fragment from being pushed away from the tip. The greater the occlusion, the closer the fiber should be to the blocked entrance of the aspiration channel52.

In some examples, a simple control algorithm can be defined to determine the position of the fiber tip based only on the pressure as follows:

D is a distance from the fiber tip to the aspiration channel52entrance.

In some examples, the fiber position can be set by the flow rate:

In some examples, the fiber position can be determined by the relative change of pressure and flow:

In some examples, the fiber position can be simply linked to the user control signal that normally only controls the aspiration assuming that the user demand for higher aspiration will require laser assistance and hence a lower value for D.
D(t)∝1−A(t).

The above example algorithms are not meant to be limiting. Other example control algorithms may be possible.

FIG. 6discloses a situation in which an occlusion is persistent and cannot be cleared within a certain time t>>τ. In this case the fiber position can be made to oscillate longitudinally within the channel, so as to increase the effective range of the high precision laser disruption and add a mechanical enhancement to the effect (similar to wiggling the tissue). In this example case, the control algorithm can assume that if the foot pedal is fully depressed for longer than a set time much greater than the rise time and the pressure is still at max, movement of the optical fiber is changed to oscillation mode. This is because extended input to aspirate while the pressure is not decreased may indicate that the occlusion has not been cleared and more mechanical assistance is needed.

In a further example embodiment, both laser pulse rate, envelope and fiber position are used to minimize total flow and pressure changes within the anterior capsule to achieve the most minimally invasive tissue removal possible and most importantly protect unintentional disruption of the capsule, or damage to corneal endothelial cells by laser energy, mechanical forces, or fluidics. The average power of the laser pulse is a function of the pulse rate and energy per pulse. Given a certain laser intensity threshold for laser tissue disruption it is useful to maintain a constant pulse energy and attenuate the laser power through reduction of the pulse rate rather than attenuation of the laser power. In the present disclosure, enhancement of the action of the instrument54occurs when the laser pulse rate is not evenly divided, but instead there is a time period in which the laser action is modulated by a lower frequency envelope. Envelope frequencies around 5 Hz have been found to be suitable in hardened eye tissue. Pulse rate can be increased or decreased from near 0-100% pulse width modulation of the laser pulses at the envelope frequency.

It is hypothesized that the laser pulse super heats a volume of tissue/liquid at the fiber tip. Since the tip is hard and the area (about 200 μm) is much larger than the depth of absorption (about 1 μm), the irradiated matter cannot expand backwards into the solid fiber and there is a net force pushing tissue away from the fiber. This expansion force causes an increase in pressure that counter-acts the vacuum pressure of the aspiration pump. By pausing the laser for some time during an occlusion, the aspiration pump can build a higher pressure, and the pressure change caused by the laser pulses are less likely to build up enough to reverse the sign of the pressure in the aspiration channel (and cause the tissue to detach).

With reference toFIG. 7, in some examples, the distal end of the fiber16can be set inside the aspiration needle13in such a way that the aspirated fluid72can be contained within a sterilizable or single use tool assembly19, and does not contaminate some reusable portion of the fiber optic beam delivery12while allowing the non-elastic fiber optic to be moved within the aspiration channel. In some examples, this can be accomplished by means of a compressed rubber seal73within which the fiber is fixed in a moving shaft assembly74. The tool assembly19contains irrigation70and aspiration71channels that connect to the distal tip and to tubing connectors with which to flexibly attach the means of fluidics control.

With reference toFIG. 8, in some examples the instrument54comprises three separable parts: a re-useable laser delivery assembly75, (which includes a fiberoptic12and that has a fiber connector78); a detachable tip handle assembly76, (that includes a distal instrument tip20, with an output channel for irrigation51aspiration needle13and an extension fiber optic tip16that couples on its sagittal end to the re-useable delivery system's fiber connector78); and a disposable means of aspiration and irrigation100. Connection points for connecting the disposable tubing100to the tip handle assembly76may be provided or the two disposable parts may be pre-assembled.

With reference toFIG. 9, an exploded view of a replaceable handle assembly76is disclosed. A small optical fiber88is attached to a fiber connector79, which connects with the corresponding connector78of the reusable laser delivery assembly. A shaft assembly82allows the fiber optic to be sealed with a washer73that is compressed around the shaft assembly82by a threaded nut87. The threaded nut87is held captive by the shaft assembly along with a spring101that acts to retract the fiber tip when not connected to the reusable portion of the assembly. A manifold92onto which the aspiration needle13and distal irrigation sleeve51are placed is coupled to the irrigation70and aspiration channels71of the handle assembly19via a manifold extension93and sealing washers96to keep the channels separated. The fiber shaft assembly attaches to the manifold extension93by the shaft sealing nut87.

The foregoing description of the preferred embodiments of the disclosure has been presented to illustrate the principles of the disclosure and not to limit the disclosure to the particular embodiment illustrated. It is intended that the scope of the disclosure be defined by all of the embodiments encompassed within the following claims and their equivalents.