METHOD OF OPERATING AN INFUSION CONTROL SYSTEM
Background of the Invention
This invention relates generally to the field of cataract surgery and more particularly to an infusion control system for a phacoemulsification handpiece.
The human eye in its simplest terms functions to provide vision by transmitting light through a clear outer portion called the cornea, and focusing the image by way of the lens onto the retina. The quality of the focused image depends on many factors including the size and shape of the eye, and the transparency of the cornea and lens.
When age or disease causes the lens to become less transparent, vision deteriorates because of the diminished light which can be transmitted to the retina. This deficiency in the lens of the eye is medically known as a cataract. An accepted treatment for this condition is surgical removal of the lens and replacement of the lens function by an artificial intraocular lens (IOL). h the United States, the majority of cataractous lenses are removed by a surgical technique called phacoemulsification. During this procedure, a thin phacoemulsification cutting tip is inserted into the diseased lens and vibrated ultrasonically. The vibrating cutting tip liquefies or emulsifies the lens so that the lens may be aspirated out of the eye. The diseased lens, once removed, is replaced by an artificial lens.
A typical ultrasonic surgical device suitable for ophthalmic procedures consists of an ultrasonically driven handpiece, an attached cutting tip, and irrigating sleeve and an electronic control console. The handpiece assembly is attached to the control console by an electric cable and flexible tubings. Through the electric cable, the console varies the power level transmitted by the handpiece to the attached cutting tip and the flexible tubings supply irrigation fluid to and draw aspiration fluid from the eye through the handpiece assembly. The operative part of the handpiece is a centrally located, hollow resonating bar or horn directly attached to a set of piezoelectric crystals. The crystals supply the required ultrasonic vibration needed to drive both the horn and the attached cutting tip during phacoemulsification and are controlled by the console. The crystal/horn assembly is suspended within the hollow body or shell of the handpiece by flexible mountings. The handpiece body terminates in a reduced diameter portion or nosecone at the body's distal end. The nosecone is externally threaded to accept the irrigation sleeve. Likewise, the horn bore is internally threaded at its distal end to receive the external threads of the cutting tip. The irrigation sleeve also has an internally threaded bore that is screwed onto the external threads of the nosecone. The cutting tip is adjusted so that the tip projects only a predetermined amount past the open end of the irrigating sleeve. Ultrasonic handpieces and cutting tips are more fully described in U.S. Pat. Nos. 3,589,363; 4,223,676; 4,246,902; 4,493,694; 4,515,583; 4,589,415; 4,609,368; 4,869,715; 4,922,902; 4,989,583; 5,154,694 and 5,359,996, the entire contents of which are incorporated herein by reference.
In use, the ends of the cutting tip and irrigating sleeve are inserted into a small incision of predetermined width in the cornea, sclera, or other location. The cutting tip is ultrasonically vibrated along its longitudinal axis within the irrigating sleeve by the crystal- driven ultrasonic horn, thereby emulsifying the selected tissue in situ. The hollow bore of the cutting tip communicates with the bore in the horn that in turn communicates with the aspiration line from the handpiece to the console. A reduced pressure or vacuum source in the console draws or aspirates the emulsified tissue from the eye through the open end of the cutting tip, the cutting tip and horn bores and the aspiration line and into a collection device. The aspiration of emulsified tissue is aided by a saline flushing solution or irrigant that is injected into the surgical site through the small annular gap between the inside surface of the irrigating sleeve and the cutting tip.
The preferred surgical technique is to make the incision into the anterior chamber of the eye as small as possible in order to reduce the risk of induced astigmatism. These small incisions result in very tight wounds that squeeze the irrigating sleeve tightly against the vibrating tip. Friction between the irrigating sleeve and the vibrating tip generates heat, but the risk of the tip overheating and causing a burn to the tissue is reduces by the cooling effect of the aspirated fluid flowing inside the tip. When the tip becomes occluded with tissue or viscoelastic, this aspiration flow can be reduced or eliminated, allowing the tip to heat up. Many surgeons prefer to use a viscoelastic agent in the anterior chamber during phacoemulsification. The viscoelastic helps to protect the endothelium during surgery. As discussed above, the viscoelastic agent can block the aspiration channel and reduce the flow of cooling irrigating solution during surgery. Therefore, many surgeons recommend removing the viscoelastic agent from a pocket adjacent to the anterior capsular membrane. Prior to the present invention, this procedure was performed manually by the surgeon, who had very little indication when the pocket was formed sufficiently to continue with the surgical procedure. Therefore, a need continues to exist for an automated method of forming a viscoelastic-free surgical pocket in the anterior chamber.
Brief Summary of the Invention
The present invention improves upon the prior art by providing an automated method of forming a viscoelastic-free surgical pocket in the anterior chamber. The method constantly compares the unobstructed flow vacuum level with the current vacuum level and sounds an alert or automatically proceeds to the next step in the surgical procedure when the vacuum level approaches the unobstructed vacuum level and remains at that level for a certain duration.
Accordingly, one objective of the present invention is to provide a surgical console control system.
Another objective of the present invention is to provide a method of operating a surgical console control system having aspiration fluid pressure sensing capability.
Another objective of the present invention is to provide a method of operating a surgical console control system that provides more accurate removal of the viscoelastic agent prior to initiation of phacoemulsification.
These and other advantages and objectives of the present invention will become apparent from the detailed description and claims that follow.
Brief Description of the Drawings
FIG. 1 is a schematic illustration of an ophthalmic surgical system suitable for practicing the method of the present invention.
FIG. 2 is a block diagram of the method of the present invention. Detailed Description of the Invention
As best seen in FIG. 1, surgical system 10, suitable for practicing the method of the present invention generally contains control console 12, infusion fluid source 14, collection container 24 and handpiece 16. Control console 12 generally includes CPU 18, aspiration pump 20, handpiece power supply 22, infusion fluid valve 26, aspiration valve 28, infusion flow sensor 32 and aspiration pressure sensor 30. Information supplied to CPU 18 from sensor 30 is used to control aspiration valve 28, pump 20 and infusion fluid valve 26. CPU 18 also controls the power supplied to handpiece 16 by power supply 22. Surgical systems similar to system 10 are well-know in the art and commercially available from Alcon
Laboratories, Inc., Fort Worth, Texas under the ACCURUS® and LEGACY® trademarks. Sensor 32 may be any commercially available flow sensor, such as Models Nos. T101D or T201D available from Transonic Systems, Inc., Ithaca, New York.
As best seen in FIG. 2, upon initialization of system 10, pump 20 is run at a preset aspiration fluid flow rate (FCheck), and the aspiration fluid pressure (vacuum) (Paspcheck) is measured by sensor 30. Paspcheck is compared by CPU 18 to a predetermined expected vacuum for unobstructed flow in handpiece 16 at the preset rate for pump 20. If Paspcheck is within the allowed range, system 10 continues to the next stage of the procedure. If Paspcheck is outside the allowable range, system 10 signals an error and will not proceed to the next stage of the procedure. During this initialization step, the pressure of infusion fluid flowing from source 14 to handpiece 16 (Pin-check) is monitored by sensor 32.
The overall fluidics resistance (R) in system 10 can be approximated using the following equation:
. —■ -T irrcheck ~ " aspcheck)' Y1 check
Once R is known, the expected aspiration pressure (PaSp) for any other aspiration fluid flow rate (F) and infusion fluid pressure (Pin-) may be calculated in linear approximation using the following equation:
"asp= -t irr " -T (("irrcheck ~ "aspchec j'-t1 cheeky CPU 18 may continuously calculate an expected value of Pasp (Pthreshoid) or maybe provided a set of look-up tables so as to know continuously Pthreshoid for the instantaneous aspiration fluid flow and infusion fluid pressure conditions.
During an occluded or partially occluded condition PaSp will be greater than Pthreshoid for the instantaneous aspiration fluid flow and infusion fluid pressure conditions (indicating a higher vacuum level). As the occlusion or partial occlusion subsides, PaSp will decrease and approach Pthreshoid. CPU 18 uses this information to provide an alert to the system user that the occlusion has been removed or has subsided. Alternatively, CPU 18 may use this information to proceed automatically to the next stage of the procedure. CPU 18 may also contain a timer that can vary when the alert is sounded or when the next stage of the procedure is started.
This method is particularly useful in indicating the presence or absence of a viscoelastic agent. When handpiece 16 begins to aspirate the viscoelastic agent, the increased viscosity of the agent versus the infusion fluid causes PaSp to increase and F to decrease, thereby reducing the amount of cooling infusion fluid entering handpiece 16. These variations in Pasp can be monitored by CPU 18 in the manner described above to indicate to system 10 or to the user the presence or absence of viscoelastic agent or other obstruction at handpiece 16.
This description is given for purposes of illustration and explanation. It will be apparent to those skilled in the relevant art that changes and modifications may be made to the invention described above without departing from its scope or spirit.