INTRAOCULAR PRESSURE CONTROL

Field of the Invention

The present invention generally pertains to microsurgical systems and more

particularly to controlling intraocular pressure in ophthalmic surgery.

Description of the Related Art

During small incision surgery, and particularly during ophthalmic surgery, small

probes are inserted into the operative site to cut, remove, or otherwise manipulate tissue. During these surgical procedures, fluid is typically infused into the eye, and the infusion fluid and tissue are aspirated from the surgical site.

Maintaining an optimum intraocular pressure during ophthalmic surgery is

currently problematic. When no aspiration is occurring, the pressure in the eye becomes the pressure of the fluid being infused into the eye. This pressure is typically referred to as the "dead head pressure". However, when aspiration is applied, the intraocular

pressure drops dramatically from the dead head pressure due to all the pressure losses in

the aspiration circuit associated with aspiration flow. Therefore, ophthalmic surgeons currently tolerate higher than desired dead head pressures to compensate for occasions

when aspiration would otherwise lower the intraocular pressure to soft-eye conditions. Clinically, such over-pressurizing of the eye is not ideal.

Accordingly, a need continues to exist for an improved method of controlling intraocular pressure during ophthalmic surgery.

Summary of the Invention

In one aspect, the present invention is a method of controlling intraocular pressure

with a microsurgical system. An infusion chamber containing an irrigating fluid is

provided, and a desired intraocular pressure is selected. The infusion chamber is

pressurized with a pressurized gas to provide irrigating fluid to a surgical device. A flow rate of the fluid within a fluid line fluidly coupled to the surgical device is measured. A

signal corresponding to the measured flow rate is provided to a computer. A predicted

intraocular pressure is calculated with the computer in response to the signal. A level of

the pressurized gas is adjusted in response to a second signal from the computer to

maintain the predicted intraocular pressure proximate the desired intraocular pressure.

In another aspect of the present invention, an infusion chamber is provided. The

infusion chamber has a first chamber for holding irrigating fluid and a second chamber

for holding irrigating fluid. The first chamber is not fluidly coupled to the second chamber. An irrigating fluid is provided from an infusion source to the first chamber and the second chamber. The irrigating fluid is provided to a surgical device from the first

chamber during a microsurgical procedure, and this step is ended when the level of the

irrigating fluid in the first chamber reaches a bottom limit. Upon such ending, the irrigating fluid is provided to the surgical device from the second chamber, and the first

chamber is refilled with the irrigating fluid from the infusion source.

Brief Description of the Drawings

For a more complete understanding of the present invention, and for further

objects and advantages thereof, reference is made to the following description taken in

conjunction with the accompanying drawings, in which:

Figure 1 is a schematic diagram illustrating infusion control in an ophthalmic microsurgical system; and

Figure 2 is a schematic diagram illustrating infusion control and irrigation control

in an ophthalmic microsurgical system.

Detailed Description of the Preferred Embodiments

The preferred embodiments of the present invention and their advantages are best understood by referring to Figures 1-2 of the drawings, like numerals being used for like

and corresponding parts of the various drawings. As shown in Figure 1, ophthalmic

microsurgical system 10 includes a pressure cuff 12; an infusion source 14; a dual infusion chamber 16 having a chamber 16a and a chamber 16b; fluid level sensors 18 and

20; a flow sensor 22; filters 24 and 26; a surgical device 29; a computer or

microprocessor 28; gas manifolds 30 and 32; a pressurized gas source 34; proportional

solenoid valves 36, 38, and 40; "on/off solenoid valves 42, 44, 46, 48, 50, 52, 54; actuators 56, 58, 60, and 62; and pressure transducers 64, 66, and 68. Dual infusion

chamber 16; fluid level sensors 18 and 20; portions of infusion fluid lines 70, 72, 74, 76,

78, and 80; and portions of gas lines 84 and 86 are preferably disposed in a surgical

cassette 27. Infusion source 14; dual infusion chamber 16; flow sensor 22; filters 24 and

26; and surgical device 29 are fluidly coupled via infusion fluid lines 70-80. Infusion

source 14, dual infusion chamber 16, gas manifolds 30 and 32; pressurized gas source 34;

and actuators 56, 58, 60, and 62 are fluidly coupled via gas lines 82, 84, 86, 88, 90, 92, 94, and 96. Infusion source 14; fluid level sensors 18-20; flow sensor 22; microprocessor

28; proportional solenoid valves 36-40; on/off solenoid valves 42-54; actuators 56-62; and pressure transducers 64-68 are electrically coupled via interfaces 100, 102, 104, 106,

108, 110, 112, 114, 116, 118, 120, 122, 124, 126, 128, 130, and 132.

Infusion source 14 is preferably a flexible infusion source. Fluid level sensors 18

and 20 may be any suitable device for measuring the level of fluid in infusion chambers

16a and 16b, respectively. Fluid level sensors 18 and 20 are preferably capable of

measuring the level of fluid in infusion chambers 16a and 16b in a continuous manner.

Flow sensor 22 may be any suitable device for measuring the flow rate of fluid within fluid line 80. Flow sensor 22 is preferably a non-invasive flow sensor. Filters 24 and 26 are hydrophobic micro-bacterial filters. A preferred filter is the Versapor ^® membrane

filter (0.8 micron) available from Pall Corporation of East Hills, New York.

Microprocessor 28 is capable of implementing feedback control, and preferably PID

control. Surgical device 29 may be any suitable device for providing surgical irrigating fluid to the eye but is preferably an infusion cannula, an irrigation handpiece, or and

irrigation/aspiration handpiece. In operation, fluid lines 70, 72, and 74; chambers 16a and 16b; fluid lines 76, 78,

and 80; and surgical device 29 are all primed with a surgical irrigating fluid 140 by

pressurizing infusion source 14. Surgical irrigating fluid 140 may be any surgical

irrigating fluid suitable for ophthalmic use, such as, by way of example, BSS PLUS®

intraocular irrigating solution available from Alcon Laboratories, Inc.

The pressurizing of infusion source 14 is preferably performed by pressure cuff

12. More specifically, microprocessor 28 sends a control signal to open solenoid valve

42 via interface 106 and to close solenoid valves 44 and 46 via interfaces 108 and 110,

respectively. Microprocessor 28 also sends a control signal to open proportional solenoid

valve 40 via interface 104 so that manifold 30 supplies the appropriate amount of

pressurized air to actuate pressure cuff 12. Pressure transducer 68 senses the pressure within gas line 82 and provides a corresponding signal to microprocessor 28 via interface

126. Solenoid valves 48-54 are initially open so that manifold 32 provides pressurized air

to actuate actuators 56-62 to close fluid lines 72-78. Microprocessor 28 sends control signals to close solenoid valves 48-54 via interfaces 114-120. The closing of solenoid

valves 48-54 actuates actuators 56-62 to open fluid lines 72-78. After all ¹ chambers and fluid lines are primed, microprocessor 28 closes actuators 56-62 and thus fluid lines 72-

78. Alternatively, the pressuring of infusion source 14 may be performed solely via

gravity.

After priming, a user then provides a desired intraocular pressure to microprocessor 28 via an input 134. Input 134 may be any suitable input device but is

preferably a touch screen display or physical knob. Chamber 16b is preferably the initial

active infusion chamber. Microprocessor 28 sends appropriate control signals to open

solenoid valve 44 and to open proportional solenoid valve 36 (via interface 100) to provide an appropriate level of pressurized air to chamber 16b. Pressure transducer 64

senses the pressure within gas line 84 and provides a corresponding signal to

microprocessor 28 via interface 124. Microprocessor 28 also sends an appropriate control

signal to open actuator 60 and thus fluid line 78. Chamber 16b supplies pressurized fluid

140 to the eye via fluid lines 78 and 80 and surgical device 29. Flow sensor 22 measures

the flow rate of fluid 140 and provides a corresponding signal to microprocessor 28 via

interface 132. Microprocessor 28 calculates a predicted intraocular pressure using the

signal from flow sensor 22 and empirically determined impedance information of

microsurgical system 10. Microprocessor 28 then sends an appropriate feedback control

signal to proportional solenoid valve 36 to maintain the predicted intraocular pressure at

or near the desired intraocular pressure during all portions of the surgery.

Fluid level sensor 20 continuously monitors the decrease in the level of fluid 140 in chamber 16b during surgery and provides a corresponding signal to microprocessor 28

via interface 130. Microprocessor 28 performs adjustments to the air pressure provided

to chamber 16b to accommodate for the difference in fluid head height as the level of fluid 140 decreases. When the level of fluid 140 in chamber 16b reaches a bottom limit level, microprocessor 28 closes solenoid valve 44 and actuator 60 and opens solenoid

valve 46 and actuators 58 and 62. Chamber 16a is now the active infusion chamber. Microprocessor 28 sends an appropriate control signal to proportional solenoid valve 38

via interface 102 to provide an appropriate level of pressurized air to chamber 16a.

Pressure transducer 66 senses the pressure within gas line 86 and provides a corresponding signal to microprocessor 28 via interface 122. Chamber 16a supplies

pressurized fluid 140 to the eye via fluid lines 76 and 80 and surgical device 29. Flow

sensor 22 measures the flow rate of fluid 140 and provides a corresponding signal to

microprocessor 28 via interface 132. Microprocessor 28 calculates the predicted

intraocular pressure as described above and the sends an appropriate feedback signal to

proportional solenoid valve 38 to maintain the predicted intraocular pressure at or near the desired intraocular pressure during all portions of the surgery. Microprocessor 28

closes actuator 58 and fluid line 74 once chamber 16b is refilled with fluid 140.

Fluid level sensor 18 continuously monitors the decrease in the level of fluid 140

in chamber 16a during surgery and provides a corresponding signal to microprocessor 28 via interface 128. Microprocessor 28 performs adjustments to the air pressure provided

to chamber 16a to accommodate for the difference in fluid head height as the level of

fluid 140 decreases. When the level of fluid 140 in chamber 16a reaches a bottom limit

level, microprocessor 28 switches chamber 16b to active infusion, makes chamber 16a inactive, and refills chamber 16a with fluid 140 via fluid line 72. This cycling between

chambers 16b and 16a continues throughout the surgery.

Infusion source 14 is preferably mom ^' tored via a fluid level sensor (not shown) capable of providing a signal to microprocessor 28 via interface 112 when source 14

reaches a near empty limit. Chambers 16a and 16b also preferably each have a volume that enable infusion source 14 to be exchanged, when near empty, without interrupting

the surgical procedure. More specifically, chambers 16a and 16b preferably each have a

volume of about 30 cc. Such volume allows about two minutes for a near empty infusion source 14 to be exchanged during conditions of maximum flow (e.g. core vitrectomy), hi

addition, once infusion source 14 is exchanged, all air bubbles within fluid lines 70, 72,

and 74 will be automatically "scrubbed out" as the inactive chamber 16a or 16b refills, without the need for re-priming.

In the case of failure of either of chambers 16a or 16b, microprocessor 28 can

preferably continue surgery with only one active chamber. In the case of failure of both chambers 16a and 16b, microprocessor 28 can preferably continue surgery using only

infusion source 14.

Figure 2 shows a modified ophthalmic microsurgical system 10a. Microsurgical

system 10a is similar to microsurgical system 10 except that it has an irrigation system in

addition to the infusion system described above for system 10. More specifically, system

10a is identical to system 10 except that system 10a also includes an irrigation source

200; fluid lines 202 and 206; gas lines 208 and 216; solenoid valves 210 and 218;

actuators 214 and 222; electrical interfaces 212 and 220; and a surgical device 224. As shown in Figure 2, irrigation source 200 is pressurized solely by gravity. As will be appreciated by one of ordinary skill in the art, microsurgical system 10a allows surgical

irrigating fluid 140 to be delivered to surgical device 29 via fluid line 80 (infusion), and

surgical irrigating fluid 140 to be delivered to surgical device 224 via fluid line 206 (irrigation), independently. Microprocessor 28 can calculate flow information for fluid

140 within fluid line 206 by continuously monitoring the volumetric change of fluid

inside chamber 16b, as indicated by fluid sensor 20.

From the above, it may be appreciated that the present invention provides an

improved method of controlling intraocular pressure with a microsurgical system. The present invention is illustrated herein by example, and various modifications may be

made by a person of ordinary skill in the art. For example, while the present invention is

described above relative to controlling intraocular pressure in an ophthalmic

microsurgical system, it is also applicable to controlling pressure within the operative tissue during other types of microsurgery.

It is believed that the operation and construction of the present invention will be

apparent from the foregoing description. While the apparatus and methods shown or

described above have been characterized as being preferred, various changes and

modifications may be made therein without departing from the spirit and scope of the invention as defined in the following claims