fig1 illustrates an ocular globe or eye 12 which includes a lens 13 , cornea 14 , anterior chamber 15 , iris 16 , ciliary body 17 , vitreous body 18 , optic nerve 20 , retina 21 , sclera 22 and choroid 23 . an instrument 25 , the tip of which is shown in greater detail in fig2 is a surgical needle 0 . 4 to 1 . 0 mm in outside diameter formed of stainless steel which is attached to a handpiece ( not shown ) for manipulation by the surgeon . the handpiece can be connected through flexible plastic tubing ( not shown ) to both a saline solution reservoir for irrigation ( not shown ) and a pumping system for aspiration ( not shown ). the details of elements not shown are known to those with ordinary skill in the art and need not be described in detail in order to practice the invention . the instrument 25 is a known irrigation / aspiration / cutting tip and is shown in fig1 as being inserted in the vitreous 18 . suction is used to aspirate diseased tissue 30 into a side opening 31 of the instrument 25 . as shown best in fig2 the tissue is cut by a curved microguillotine blade 32 which is actuated by the surgeon and slidable in the instrument 25 . a saline solution or the like is discharged through outlets 33 , 34 , and infuses the operation site . the infusion , in combination with controlled suction through the opening 31 , helps to draw the tissue fragments 30 into the instrument 25 for removal after they are cut by the blade 32 . arrows 36 in fig2 illustrate both the discharge of saline solution and suction action mentioned above . the conventional instrument shown in fig1 and 2 , however , has no provisions for accurately measuring the local suction force used to draw the diseased tissue 30 into the instrument 25 prior to cutting . since the tissue removed by the vitrectomy procedures is usually located in the immediate vicinity of the retina 21 , the danger of inadvertent damage to the retina 21 or other healthy tissue by excessive suction force during vitrectomy is considerable . the embodiment of the invention illustrated in fig3 and 5 solves this problem by enabling the suction force to be monitored constantly . an instrument similar to the one in fig1 and 2 has been modified to measure pressure differences between the external and internal forces of its cutting / aspiration tip . the modified instrument is referred to generally by reference numeral 60 and includes an outer elongated housing 61 which surrounds an inner concentric guillotine 70 which carries a cutting blade 62 that cooperates with an opening 66 for surgically removing tissue fragments as described above . an inner bore or channel 63 operates to convey fluids and / or tissue . only the tip of such an instrument is shown in fig3 and additional features such as the discharge outlets 33 , 34 , shown in fig2 were omitted to simplify the description . a pressure transducer 65 is mounted in a chamber 65a located near aspiration inlet 66 , the chamber 65a being bounded by two parallel diaphragms 67 , 68 , formed of silicon rubber inserts that are about 1 mm in diameter . the diaphragms 67 , 68 , are connected to the instrument 60 by means of an epoxy resin . the transducer 65 is preferably mounted at the outer end 61 ( a ) of the tip of the housing 61 . pressure transducer 65 is a piezo - electric or photo - electric device known to the art which is capable of measuring intraocular pressure with the required sensitivity (± 1 mm . hg ), stability and linearity . other types of transducers , such as sensors operating in conjunction with fiber - optic light guides which transmit signals in the form of variations in light intensity caused by pressure differences moving a reflective surface , can also be used in conjunction with the invention without substantially altering the size , shape or function of the instrument . an electrical signal generated by the transducer 65 is carried through wire leads 71 to a monitor / console which is known in the art and contains a suitable power supply as well as the necessary electrical circuits for conditioning , amplifying and displaying the pressure measurement . the piezoelectric elements 65 ( b ) are attached to a cantilever beam and a rigid base 65c , which is anchored to the wall of the instrument . wire leads 71 , which carry electrical signals from the transducer 65 , are connected to the exterior surface of the instrument 60 so as to avoid interference with the action of the guillotine cutter 70 . the leads 71 are bonded to the instrument 60 so that they are part of its smooth outer surface . the vitrectomy suction instrument 60 significantly enhances safety through sensitivity to suction force and consequently intraocular pressure during surgery . as the surgeon aspirates strands of diseased tissue into the opening 66 , the local pressure difference measured between diaphragms 67 , 68 , by the transducer 65 results in a relative pressure reading that reflects the forces exerted on the tissue strands as they enter the aspiration inlet 66 . these forces fluctuate continuously because of differences in the viscoelastic properties of the manipulated tissue and the viscosity of the surrounding vitreous . the force level at any given time can fall in a range that departs considerably from the average force and the pressure in the vacuum line can be adjusted to accommodate these fluctuating force levels . by using the transducer 65 , a signal can be generated to activate momentarily a vacuum relief valve in a known way ( not shown ) when the local pressure exceeds preset levels to adjust the suction when the force level falls outside the permissible range . thus , the instrument 60 operates to reduce considerably the danger of damage to healthy tissue by preventing excessive instantaneous peaks in local suction forces . referring to fig4 and 6 , another embodiment of the invention is illustrated , this one being directed to a surgical instrument which can measure intraocular pressure while performing an irrigation or aspiration procedure . the instrument is generally designated by reference numeral 40 and is an elongated body 41 formed of surgical grade stainless steel with an outside diameter of approximately 1 mm . the body 41 is divided through substantially its entire length into two parallel channels 42 , 43 , that are separated by an internal wall 49 . channel 43 is an irrigation / aspiration channel which is connected through a handpiece ( not shown ) to either a vacuum system ( not shown ) or a saline supply reservoir . the channel 43 has an outlet 44 located near the apex 45 of the tip of the instrument 40 . a transducer 50 is mounted in the portion of the channel 42 adjacent to the tip of the instrument 40 , the channel 42 being vented to the atmosphere at a suitable site away from the operating field . the transducer 50 is of the type described above for the embodiment of fig3 and 5 and is connected to the instrument 40 through a base 55a . at the tip of the instrument 40 , the transducer channel 42 terminates at a window 46 which is located adjacent to the outlet 44 . the window 46 is approximately 1 mm in diameter and is fitted with a diaphragm 47 formed of silicon rubber . the diaphragm 47 is connected to the window 46 by means of epoxy resin . wire leads designated by reference numeral 52 carry electrical signals generated by the transducer 50 to suitable instrumentation ( such as that described below ) for translating the signals into useful information for monitoring and regulating intraocular pressure . the intraocular pressure probe 40 is suitable for the measurement and control of intraocular pressure during closed system procedures in the anterior chamber 15 as well as in the vitreous chamber 18 . the instrument 40 can be inserted at a site separate from the operating incision and remain in place throughout the entire procedure , providing to the surgeon an independent source of determining and / or controlling intraocular pressure for providing information used in tamponade , suture tension controls and final approximation of physiologic pressure at the end of wound closure . one disadvantage of placing the transducer in the portion of the probe that penetrates the eye , as done in instruments 40 and 60 ( see fig4 and 3 , respectively ), is that this configuration requires the probe to have a larger diameter than would otherwise be necessary . this problem can be eliminated without significantly affecting the accuracy or speed of the device by relocating both the pressure sensitive diaphragm and the transducer outside the eye but in a position where a significant signal can be generated in response to changes in intraocular pressure . fig7 illustrates one such alternative embodiment of the invention . the instrument , generally designated by reference numeral 95 , includes an elongated needle section 96 with an opening 97 , which can be inserted into the ocular globe . the opposite end of the needle section 96 opens into a chamber 98 that is designed to remain outside the ocular globe . a transducer 99 is mounted in the chamber 98 opposite the opening 97 . although the transducer 99 is not located inside the ocular globe , its position adjacent to the opening into the globe supplies a pressure reading nearly as accurate as one obtained through internal placement . the transducer 99 can be of the type described above for the embodiments illustrated in fig3 - 6 , or a fused silicon type such as entran model no . epil - f080 - 55 manufactured by entran devices , inc ., fairfield , n . j ., which is separated from the chamber 98 by a diaphragm 100 formed of paralyne or the like . wire leads 102 carry electrical signals generated by the transducer 99 to external instrumentation that is described in detail below . the chamber 98 is equipped with an input opening 103 that can be connected to a flexible plastic tubing 104 for supplying fluid in appropriate amounts to the ocular globe . the instruments shown in fig3 - 5 and 7 can be incorporated into any number of systems for controlling pressure within the ocular globe 12 . for example , the signal generated by the transducer can be used to control the suction level through the same probe on which the transducer is located ( fig1 and 2 ) or a second probe when the surgical procedure requires fluid to be circulated through the eye . for other surgical procedures , pressure in the eye can be maintained within a predetermined range through a single probe . the instruments described above can be used in a system of the type shown in fig8 where a pressure level within a predetermined range is maintained and controlled more accurately than in any other known system . this is accomplished through the use of a closed loop through which saline solution is continuously circulated . the loop is connected to the eye so that reaction to a change in pressure detected by the transducer , which speeds up or slows down the circulation , causing fluid to be supplied to or withdrawn from the eye , is virtually instantaneous . referring to fig8 an instrument i of the type shown in fig3 - 6 or 7 penetrates the ocular globe 12 and is connected to a fluid conduit 104 . a flow loop 110 is connected to the conduit 104 through a flow splitter connection 109 . when the system is operating , a peristaltic pump 107 continuously circulates saline solution through the loop 110 in the direction of arrows 111 . a reservoir of solution 108 is connected to the loop 110 for supplying addition solution when needed . a pressure relief value 112 can be provided at the splitter connection 109 , but it is not considered necessary for successful operation of the circuit . if the instrument 100 detects a pressure change in the ocular globe 12 , a signal is transmitted through a line 102 to a monitor / console 105 of a type known in the art , which contains a suitable power supply as well as the necessary electrical circuits for conditioning , amplifying and displaying the pressure measurements . the signal is in turn transmitted to a microprocessor controller 106 of a type known in the art , which is operatively connected to the pump 107 . the microprocessor controller is programmed to allow the pump 107 to circulate fluid through the loop 110 at a predetermined flow rate when signals received from the transducer indicate that the pressure of intraocular fluid is within a preset range . this flow rate will operate to maintain a predetermined pressure level within the ocular globe . however , if a pressure drop is detected by the instrument i , the resulting signal to the microprocessor controller operates to speed up the pump a predetermined amount for infusing additional saline solution into the eye . conversely , if a pressure increase is detected , the pump speed is reduced . the use of a flow splitter in relatively close proximity to the instrument 100 ( for example , by resting it on the forehead of the patient ) and the continuously circulating saline solution in the loop 110 provide for a much more rapid response to pressure changes in the eye than if a long fluid column were used or if a pump had to be activated in response to each pressure change . another embodiment of the invention is shown in fig9 and 10 , where a compliance chamber 120 is connected to the fluid conduit 104 , either downstream from the splitter connection 109 ( fig . ( 9 ) or at the splitter connection 109 ( fig1 ). the compliance chamber 120 operates to accommodate sudden changes in pressure in the ocular globe 12 caused by surgical manipulations such as pressing on the globe , pulling on the ocular muscles or tightening of stitches where pressure is raised or starting or enlarging an incision where pressure is lowered . such pressure fluctuations tend to be very rapid , on the order of 10 - 2 - 10 - 1 per second . the normal response time of the system shown in fig8 is not fast enough to react to many such pressure fluctuations because of inertial and frictional forces in the equipment and associated flow lines . in order to provide a quicker response time to these sudden fluctuations , the compliance chamber 120 is included in the flow line leading to the eye , in close proximity to eye . preferably , the compliance chamber 120 is located from 6 - 10 cm . from the tip of needle section 96a . the compliance chamber 120 is formed as a small , spherical chamber that is 4 - 8 cm . in diameter with highly elastic walls . the compliance chamber 120 can be completely filled with the fluid f flowing through the flow lines 102 , 104 ( fig1 ). however , the reaction time to intraocular pressure changes can be increased by initially filling the chamber 120 with air or other gas g , as shown in fig9 for more rapidly accommodating pressure changes because of the greater compressibility of the gas g . as shown in fig9 the compliance chamber 120 can be formed as part of or connected to the conduit 104 , downstream from the splitter connection 109 . in such case , the conduit 104 can be formed separately from the conduit 102 , with individual needle sections 96 , 96a , respectively , connected to the flow line 104 and instrument i as described above . alternatively , as shown in fig1 , the compliance chamber 120 can be connected to the loop 110 at the flow splitter connection 109 . the inventions embodied in the instruments and systems described above are useful in constantly monitoring and controlling both intraocular fluid pressure and suction forces during ophthalmic surgery . by allowing the surgeon the benefit of this type of equipment much of the guesswork of maintaining optimum intraocular pressure during surgery is removed , resulting in safer and more accurate surgical procedures . moreover , the control systems can automatically regulate intraocular pressure according to a predetermined set of commands more rapidly and accurately than possible before . although different embodiments of the invention may vary in detail they are still intended to be within the scope of the inventive concept described above . the details described in the foregoing preferred embodiments are intended to be illustrative and not limiting in any sense .
an ophthalmic device and system for measuring and controlling relative pressure of fluid inside an ocular globe includes a surgical instrument which is adapted to penetrate the ocular globe . a fluid pressure transducer is mounted on the instrument so that , when the instrument penetrates the ocular globe , the transducer is located adjacent to an opening that communicates with the interior of the globe so that it can react to pressure changes in the fluid therein and generate signals in response to pressure changes in the fluid . the signal is transmitted external of the instrument to a pump or other fluid transfer device which is operatively connected to the transducer for first receiving signals and then supplying or removing fluid from the ocular globe in response to the signals according to a predetermined set of instructions . the pump is connected to a closed loop in which fluid is continuously circulated . fluctuations in intraocular pressure cause the pump to speed up or slow down and then supply fluid to or remove fluid from the ocular globe through a conduit connected to the closed loop .