Ophthalmosurgical Measuring Device

Abstract

An ophthalmosurgical measuring device (100) has an irrigation line (4) through which irrigation fluid (3) can be transported and an aspiration line (7) through which aspiration fluid can be transported to a suction pump (8). The ophthalmosurgical measuring device also includes a sensor (10) with which a differential pressure between irrigation line (4) and aspiration line (7) can be detected.

Description

FIELD OF THE INVENTION

The invention relates to an ophthalmosurgical measuring device, an ophthalmosurgical system having such a measuring device, and a method for operating such a measuring device.

BACKGROUND OF THE INVENTION

There are several ophthalmosurgical techniques for treating a clouded lens of the human eye. The most widely used technique is phacoemulsification, in which a thin tip is introduced into the diseased lens and is excited with ultrasound vibrations. In its immediate environment, the vibrating tip emulsifies the lens in such a way that the resulting lens fragments can be sucked through a line by a pump. When the lens has been completely emulsified, a new and artificial lens can be inserted into the empty capsular bag, such that a patient treated in this way can recover good visual acuity.

In phacoemulsification, a device is used that generally has a vibratable tip in a handpiece, a flushing line (irrigation line) for conveying irrigation fluid to the lens to be treated, and a suction line (aspiration line) for transporting emulsified lens fragments into a collecting vessel. During transport into the collecting vessel, it can happen that a lens fragment blocks the inlet area of the handpiece tip. With a suction pump running continuously, an underpressure therefore builds up downstream in the aspiration line. The lens fragment can be broken into smaller segments, for example by continued ultrasound vibrations of the tip, as a result of which the blockage (occlusion) is ended abruptly. The underpressure that has built up in the aspiration line has the effect that, when such an occlusion has been broken through, a relatively large amount of fluid is sucked out of the eye in a very short time. This may result in a collapse of the anterior chamber of the eye. It is then possible that the capsular bag will be drawn toward the tip of the handpiece and be punctured by the tip. With such damage to the capsular bag, it is also possible for a tip that has penetrated too deeply to cause damage to the vitreous body lying behind the capsular bag.

It is therefore important to avoid a collapse of the anterior chamber of the eye when an occlusion is broken through. A precondition for this is that the break-through of the occlusion is identified quickly. One possibility is to precisely detect the pressure profile in the aspiration line. If the underpressure quickly decreases, this is an indication that an occlusion has been broken through. Such information can be used to change the vibrations of the tip of the handpiece or to change the volumetric flow in the irrigation line or aspiration line. In the prior art, this is described, for example, in U.S. Pat. No. 5,700,240.

A disadvantage of measuring the pressure in the aspiration line is that the onset of the occlusion and the end of an occlusion are only detected relatively late. If a blockage of the needle occurs, a relatively high underpressure in the aspiration line builds up only slowly, depending on the efficiency of the suction pump. Although the high underpressure in the aspiration line decreases relatively quickly when an occlusion is broken through, a much quicker change in pressure takes place in the irrigation line, with the result that valuable time is lost before the break-through of an occlusion can be reliably detected. In this “dead time”, there is a great danger of the above-described problems occurring, namely damage to the capsular bag or to the vitreous body lying behind the latter. A sensor for pressure measurement could now likewise be placed in the irrigation line. However, a disadvantage of such a solution is that, on the one hand, two pressure sensors would have to be used, which would result in a very expensive design, and, on the other hand, the signals from two pressure sensors with unavoidably different time constants would have to be processed, and this would result in a relatively high outlay in terms of control elements.

SUMMARY OF THE INVENTION

It is an object of the invention to make available an ophthalmosurgical measuring device with which the onset and break-through of an occlusion can be detected very quickly, very precisely, inexpensively and with minimal outlay in terms of control elements. It is also an object to make available an ophthalmosurgical system having such a measuring device, and a method for operating such a measuring device.

The ophthalmosurgical measuring device according to the invention includes: an irrigation line through which irrigation fluid can be transported, an aspiration line through which aspiration fluid can be transported to a suction pump, and a sensor with which a differential pressure between the irrigation line and aspiration line can be detected.

In such a measuring device, the pressure in the aspiration line or the pressure in the irrigation line is not detected directly. Instead of using two sensors, which always have different time constants and whose signals are therefore difficult to process together, only one sensor is used according to the invention. With this sensor, it is not possible to detect the relative pressure in the aspiration line or irrigation line, for example in relation to atmospheric pressure. Rather, the two pressures are compared with each other and the difference is formed. A reference point, which for example can be the ambient pressure in the case of a relative pressure sensor, is not available in the measuring device according to the invention with the sensor measuring the differential pressure. The advantages are, on the one hand, that only a single sensor is needed, as a result of which an inexpensive solution is achieved. On the other hand, the rapid change of pressure in the irrigation line can be used to be able to detect the onset and end of an occlusion more quickly. Moreover, it is not necessary to evaluate two sensors with different time constants in a control device.

According to one embodiment of the invention, the irrigation line has an irrigation valve which, seen in the direction of flow, is arranged upstream of a handpiece for ophthalmosurgical treatment with a vibrating needle tip.

By suitable actuation of such an irrigation valve, it is possible to quickly terminate or resume the supply of an irrigation fluid. Moreover, the sensor can be arranged such that it can be acted upon by a pressure in the irrigation line, which pressure, seen in the direction of flow, is present upstream of the irrigation valve. This has the effect that it is possible to detect a fault condition of the ophthalmosurgical system in which the irrigation valve is closed and at the same time a suction pump is activated, which poses a danger to the eye. In this fault condition, the underpressure building up in the aspiration line is continued through the eye into the area of the irrigation line located between eye and irrigation valve. The entire eye is thus exposed to a dangerous underpressure. However, in the area of the irrigation line located upstream of the irrigation valve, as seen in the direction of flow, a normally high hydrostatic pressure is still present depending on the position of the irrigation fluid container, such that the sensor for detecting the differential pressure between irrigation line and aspiration line can detect a marked difference from the underpressure present in the aspiration line.

The device preferably has a venting valve in a venting line, which connects the irrigation line directly to the aspiration line. If, for example after an occlusion has been broken through, the vacuum pressure in the aspiration line increases again in the direction of the normal suction pressure, the venting line can be suitably opened by means of the venting valve, such that a rapid pressure compensation is possible and a drop in the suction pressure to too high a value is avoided.

According to another embodiment of the invention, the ophthalmosurgical measuring device has a control unit, wherein the sensor generates a signal that is associated with the differential pressure and that can be delivered to the control unit, which is able to control the flow of fluid in the irrigation line and/or aspiration line and/or an ultrasound energy for the handpiece. For example, the control unit, at the onset of an occlusion on the handpiece, can increase the ultrasound energy delivered for operating the handpiece and, at the end of the occlusion, can reduce the delivered ultrasound energy. By means of the increased ultrasound energy, a particle causing the blockage can be set particularly intensively into vibration, such that there is an increased probability of this particle being broken up. When this has finally been achieved, the ultrasound energy can be reduced after the end of the occlusion, in order to minimize the danger of damage to the capsular bag.

The sensor of the measuring device according to the invention preferably has a bidirectionally movable element, such as a membrane, a spring tongue or a bar, whose position can be changed as a function of the differential pressure between the irrigation line and aspiration line, or whose force exerted on a force sensor can be detected as a function of the differential pressure between the irrigation line and aspiration line. Such a sensor with a high degree of sensitivity and a short response time can be produced. The sensor preferably has a time constant of T≧10 ms at a pressure resolution of less than 666 kg/(ms²) (5 mmHg). To allow a noninvasive measurement, the measuring device can be designed such that the bend position of the bidirectionally movable element can be detected by a contactless path sensor.

The invention further relates to an ophthalmosurgical system with an ophthalmosurgical measuring device as described above, an irrigation fluid container, a handpiece, and a suction pump for aspiration of aspiration fluid.

The invention further relates to a method for operating an ophthalmosurgical measuring device as described above, wherein the differential pressure between irrigation line and aspiration line is detected by the sensor. The time gradient of the differential pressure profile is preferably determined. In this way, the change in pressure at the onset and at the end of an occlusion can be detected even more quickly. According to one embodiment of the invention, the signal of the gradient of the differential pressure profile is used to control the flow of fluid and/or the suction pump and/or the ultrasound energy delivered to the handpiece.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described with reference to the drawings wherein:

FIG. 1 is a schematic of an ophthalmosurgical system according to the invention with an ophthalmosurgical measuring device according to the invention;

FIG. 2 is a schematic of the pressure profiles in an aspiration line and irrigation line of the system according to the invention, and of the pressure profiles in a suction pump and an irrigation valve;

FIG. 3 is a schematic of the differential pressure as a function of time at the pressure profiles shown in FIG. 2;

FIG. 4A is a schematic of the control-technology relationships of a measuring device with two individual pressure sensors;

FIG. 4B is a schematic of the control-technology relationships in the measuring device according to the invention;

FIG. 5 is a schematic of the pressure profiles as a function of time when an occlusion is broken through; and,

FIG. 6 is a schematic of the profile of the differential pressure as a function of time during use of the measuring device according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

FIG. 1 is a schematic of an embodiment of the ophthalmosurgical system 1 according to the invention. An irrigation fluid container 2 contains an irrigation fluid 3 that can flow through an irrigation line 4 to a handpiece 5 having a tip 6. The tip 6 is designed in such a way that it is able, with the aid of a needle set in vibration by ultrasound, to break up a clouded and relatively hard lens of an eye into small fragments. The fluid located in the anterior chamber of the eye and the fragmented particles are guided through an aspiration line 7 to a suction pump 8, which discharges the fluid and the particles into a container 9. A sensor 10 is arranged between the irrigation line 4 and the aspiration line 7.

In this embodiment, the sensor is connected by way of a first line 11 to the irrigation line 4, and by way of a second line 12 to the aspiration line 7. It is thus possible for the sensor to detect a differential pressure between the irrigation line 4 and the aspiration line 7. However, the sensor can also be designed in such a way that a first line 11 and a second line 12 are not present, such that the sensor 10 is connected directly to the irrigation line 4 and the aspiration line 7. At least part of the irrigation line 4, the differential pressure sensor 10 and at least part of the aspiration line 7 conjointly define an ophthalmosurgical measuring device 100. A venting line 13, which is provided with a venting valve 14, can be connected in parallel with this measuring device 100.

If the differential pressure measurement by means of the sensor 10 indicates that the occlusion has been broken through, the venting valve 14 can be activated in such a way that irrigation fluid 3 from the irrigation line 4 can pass through the venting line 13 into the aspiration line 7, in order to quickly lower the underpressure in the aspiration line 7.

The sensor 10, which generates a signal related to the differential pressure, can supply the signal to the control unit 200 via the line 201. In dependence upon this signal, the control unit 200 can control the fluid flow in the irrigation line 4 via a line 202. The control unit can also control the fluid flow in the aspiration line 7 via the line 203. Alternatively or additionally, the control unit can control the ultrasound energy for the handpiece 5 in that it, via a line 204, controls a power unit 210 which is connected to the handpiece 5 via a line 211 and can thus supply ultrasonic energy to the handpiece 5.

FIG. 1 shows a sensor 10 which has a first chamber 101 and a second chamber 102. The first chamber 101 can be connected to the irrigation line via a line 11 and the second chamber 102 can be connected to the aspiration line via the line 12. It is, however, also possible that no line 11 or line 12 is present so that the sensor 10 is connected directly to the irrigation line 4 with its first chamber 101 and connected directly to the aspiration line 7 with its second chamber 102. The sensor 10 has an element 103 which can move bidirectionally such as a membrane, a flexible tongue, or a bar whose position can be shifted in dependence upon the differential pressure between the irrigation line and the aspiration line. In the embodiment shown in FIG. 1, the element 103 is aligned horizontally. This indicates that the pressure in the second chamber 102 is equal to the pressure in the first chamber 101.

FIG. 2 shows, in the upper area, the pressure profiles in an aspiration line and an irrigation line as a function of time. The upper curve 20 describes the profile of the irrigation pressure, while the curve 30 below this represents the profile of the aspiration pressure. It is assumed that, prior to the operation of a suction pump, the hydrostatic pressure in the irrigation line is ca. 10666 kg/(ms²) (=80 mmHg), and the aspiration pressure is 0 kg/(ms²) (=0 mmHg), in connection with which it will be noted that these figures, and the figures given hereinbelow, serve only as examples, and higher or lower values are also possible. With the start-up of a suction pump (see reference sign 41 in FIG. 1), the suction pressure in the aspiration line rises (see reference numeral 32) to a stationary value 33. At the same time, the pressure in the irrigation line decreases (see reference numeral 22) and likewise reaches a stationary value 23. At these stationary values 23 and 33, the suction pump works, for example, with a delivery volume of 60 milliliters per minute (see reference numeral 42).

If an occlusion occurs (see reference numerals 24 and 34), the pressures in the irrigation line and aspiration line change. In the irrigation line, the pressure rises quickly again to the hydrostatic pressure (see reference numeral 25), while the underpressure in the aspiration line rises relatively slowly, until it has reached a maximum level of, for example, −79993 kg/(ms²) (=−600 mmHg) (see reference numeral 35). The suction pump can then be switched off (see reference numeral 43). If the occlusion is broken through (see reference numerals 26 and 36), the pressure in the irrigation line and aspiration line changes. In the irrigation line, there is a very rapid drop in pressure, shortly after which the pressure rises rapidly again and assumes the hydrostatic pressure (see reference numeral 27). The underpressure in the aspiration line drops relatively quickly from the very high level of −79993 kg/(ms²) (=−600 mmHg) (see reference numeral 37) and reaches the hydrostatic pressure (see reference numeral 38). When the suction pump is returned to its previous suction capacity (see reference numerals 44 and 45), the pressures in the irrigation line and aspiration line fall again to the levels prior to the occlusion (see reference numerals 28 and 39). Throughout the cycle, an irrigation valve was at all times open in the irrigation line, such that the irrigation fluid was permanently available (see reference numeral 50 in FIG. 2).

FIG. 3 shows a profile 60 of the differential pressure between the irrigation line and the aspiration line analogously to the situation shown in FIG. 2. Before the suction pump is switched on, the differential pressure has a relatively low value. With the suction pump switched on (see reference numeral 61), the differential pressure between the irrigation line and the aspiration line rises. If the needle at the tip 6 of the handpiece 5 is blocked, the differential pressure rises quickly to a high value (see reference numeral 62). When a particle is broken through and an occlusion ended (see reference numerals 26 and 36 in FIG. 2), the differential pressure drops very quickly (see reference numeral 63 in FIG. 3). After the suction pump is switched on, the differential pressure again reaches the level that existed prior to the occlusion (see reference numeral 64).

The profile of the differential pressure in FIG. 3 makes clear that the respective pressure in the irrigation line and aspiration line is not known. Neither a pressure in the aspiration line nor a pressure in the irrigation line is separately measured. Thus, no component of the ophthalmosurgicai system is controlled on the basis of a separately measured irrigation pressure or aspiration pressure. The only available signal for controlling a system component originates from the differential pressure sensor. It is not possible to tell from the curve how this pressure profile determined by the differential pressure sensor is composed of the irrigation pressure and aspiration pressure. A reference to atmospheric pressure is not known. To evaluate this profile, it is possible to use either the directly measured differential pressure (see curve 60 in FIG. 3) or a time gradient of the curve profile. The start and end of an occlusion in the needle of a handpiece can be identified very clearly and unambiguously from the curve 60. Such a profile can be used such that the needle of the handpiece can be set in vibration only when the differential pressure does not exceed a predetermined amount.

FIG. 4A is a schematic of the control technology relationship for a measuring device in which a pressure in the irrigation line and aspiration line is recorded separately. FIG. 4B is a schematic representation of the control technology relationship for the measuring device according to the invention in which a differential pressure between irrigation line and aspiration line is recorded. As can be seen from FIG. 4A, a first-order delay element with the time constant T_IRR is assumed for the transfer function G₁(s) of the sensor for measuring the pressure in the irrigation line. A first-order delay element with the time constant T_ASP is assumed for the transfer function G₂(s) for the sensor of the pressure in the aspiration line. The processing of both signals yields a pressure p3. In the transfer functions, “s” stands for the complex variable. In the diagram shown in FIG. 4B, the pressure in the irrigation line and the pressure in the aspiration line are fed to a differential pressure sensor, which determines from these a differential pressure Δp. The transfer function of this differential pressure sensor is assumed by a first-order delay element with the time constant T_Δp. The behavior in the differential pressure measurement can thus be detected with only one transfer function and one time constant.

FIG. 5 shows the time profile of the pressure curve 20 for the irrigation line and of the pressure curve 30 for the aspiration line. This is a small segment of the situation shown in FIG. 2 at the end of an occlusion (see reference sign 26 for the pressure in the irrigation line and reference sign 36 for the pressure in the aspiration line). If the pressure profiles are detected separately with individual pressure sensors, that is, with a pressure sensor for the irrigation line and a pressure sensor for the aspiration line, a pressure profile can be measured that is shown in each case by a broken line in FIG. 5. The broken line 71 shows the pressure profile for the irrigation line, while the broken line 72 shows the pressure profile for the aspiration line.

The pressure sensor that records the pressure in the irrigation line has a relatively large time constant at the level of T_IRR=50 ms. This is due to the fact that, in the prior art, if a pressure sensor is indeed present at all in the irrigation line, it is used to detect the hydrostatic pressure of the irrigation fluid, such that the vertical position of the irrigation fluid container can be changed, if so required. Such a pressure sensor is relatively slow. It can be inferred from the profile of the curve 71 that the sharp drop in the irrigation pressure when the occlusion is broken through is barely detected, on account of the long time constant of the irrigation pressure sensor, with the result that the curve is “smudged”. By contrast, the pressure sensor for the aspiration line is intended to be able to detect the pressure fluctuations relatively quickly, with the result that in most cases such a pressure sensor has a time constant with a relatively low value in the region of, for example, T_ASP=10 ms. The profile of the curve 72 shows that the pressure profile in the aspiration line can be readily detected and, as a result, there not so much “smudging”. Addition of the pressure values shown by the curves 71 and 72 according to the signal processing shown in FIG. 4A results in the sum profile shown by reference numeral 73 (see FIG. 6). If the irrigation pressure sensor is omitted, and only the relatively quickly responding aspiration pressure sensor is used for the evaluation, a break-through of an occlusion cannot be detected quickly enough, because the aspiration pressure changes only relatively slowly.

If the differential pressure sensor according to the invention is used with signal processing according to FIG. 4B, wherein the sensor has a time constant of T_ΔP=10 ms, this results in the curve profile indicated by reference numeral 80 (see FIG. 6). A comparison between the curves 73 and 80 shows that, with the curve 80, a change in the differential pressure of 33331 kg/(ms²) (=250 mmHg) can be detected after only about 40% of the time that is needed when using two conventional pressure sensors. The measurement with the measuring device according to the invention is therefore much quicker, such that control of the flow characteristics and/or of the ultrasound energy for the handpiece can be initiated more quickly. The very rapid change in the irrigation pressure can be better detected by the differential pressure sensor, with the overall result that a more rapid reaction is possible to an occlusion being broken through.

It is understood that the foregoing description is that of the preferred embodiments of the invention and that various changes and modifications may be made thereto without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

1. An ophthalmosurgical measuring device comprising: an irrigation line for transporting irrigation fluid therethrough;a suction pump;an aspiration line for transporting aspiration fluid therethrough to said suction pump;a sensor for detecting a differential pressure between said irrigation line and said aspiration line;said sensor including a first chamber and a second chamber separated from said first chamber; and,said first chamber being directly connected to said irrigation line and said second chamber being directly connected to said aspiration line.

2. The ophthalmosurgical measuring device of claim 1, further comprising: a handpiece for ophthalmosurgical treatment and said handpiece being operatively connected to said irrigation line and said aspiration line; and,an irrigation valve mounted in said irrigation line which, seen in the direction of flow, is arranged upstream of said handpiece.

3. The ophthalmosurgical measuring device of claim 2, wherein said sensor is arranged so as to be acted upon by pressure in said irrigation line, which pressure, seen in the direction of flow, is present upstream of said irrigation valve.

4. The ophthalmosurgical measuring device of claim 3, further comprising a venting line connecting said irrigation line directly to said aspiration line; and, a venting valve mounted in said venting line.

5. The ophthalmosurgical measuring device of claim 4, wherein said sensor generates a signal associated with said differentiated pressure; and, wherein said device further comprises a control unit for receiving said signal to control the flow of fluid in said irrigation line and/or said aspiration line and/or an ultrasonic energy for said handpiece.

6. The ophthalmosurgical measuring device of claim 5, wherein said control unit, at the onset of an occlusion on said handpiece, increases the ultrasound delivered for operating said handpiece and, at the end of the occlusion, reduces the delivered ultrasound energy.

7. The ophthalmosurgical measuring device of claim 6, wherein said sensor has a bidirectionally movable element whose position changes as a function of the differential pressure between the irrigation line and aspiration line, or whose force exerted on a force sensor can be detected as a function of the differential pressure between said irrigation line and said aspiration line.

8. The ophthalmosurgical measuring device of claim 7, wherein said movable element is one of a membrane, spring tongue and a bar.

9. The ophthalmosurgical measuring device of claim 7, wherein said sensor has a time constant T≧10 ms at a pressure resolution of less than 666 kg/(ms2).

10. The ophthalmosurgical measuring device of claim 9, wherein the bend position of the element can be detected by a contactless path sensor.

11. An ophthalmosurgical system comprising: an irrigation fluid container;an irrigation line for transporting irrigation fluid therethrough;a suction pump for aspirating fluid;an aspiration line for transporting aspiration fluid therethrough to said suction pump;a sensor for detecting a differential pressure between said irrigation line and said aspiration line;said sensor including a first chamber and a second chamber separated from said first chamber;said first chamber being directly connected to said irrigation line and said second chamber being directly connected to said aspiration line; and,a handpiece for ophthalmosurgical treatment and said handpiece being operatively connected to said irrigation line and said aspiration line.