Endocapsular vortex emulsification shows promise in experimental cataract removal

EVE is a one-step, easy-to-perform, true endocapsular procedure. Animal and eye bank work suggests it may be a viable alternative to phaco.

Endocapsular vortex emulsification (EVE) is a new technology in which the cataract is emulsified by a high-speed rotary impeller. Optex Ophthalmologics and Richard P. Kratz, MD, first presented it at the 1998 meeting of the American Society of Cataract and Refractive Surgery under the name Catarex. The future trade name has yet to be determined, so subsequent references to the procedure here use the acronym EVE.

As an enabling technology, EVE may provide additional stimulus for future development of injectable accommodating lenses. Until then EVE potentially offers an important alternative to ultrasound phacoemulsification. EVE appears to be less challenging to learn and less difficult to perform; animal studies suggest it may provide several safety advantages and clinical benefits compared to ultrasound phaco.

Distinct differences

EVE and ultrasound phaco share certain similarities. Both technologies deliver energy to the eye via a probe that emulsifies the lens and cortex for removal by aspiration. Both systems are software driven and include touch screen panels that enable preset parameters and active feedback throughout the procedure.

There are some distinct differences, though, that clearly set EVE apart from current cataract removal technology. EVE is a true endocapsular procedure. Following a standard clear corneal incision, the nucleus and cortex are removed through a 1-mm capsulotomy in a single-handed, one-step process that takes place entirely within the capsular bag, which remains functionally intact. There is no sculpting, cracking or chopping and very little movement of the probe within the bag.

Ultrasound phaco typically depends on carefully choreographed movements and procedures, as well as the complex balance and interplay among flow, vacuum and power to attract, hold and then emulsify the cataract.

In contrast, EVE creates two separate and distinct flows and does not rely on tip occlusion and vacuum holding force. The first flow type, called endocapsular vortex flow, recirculates within the bag and draws the cataract to the probe tip where it is reduced by the mechanical action of a high-speed impeller. This vortex flow also keeps the bag fully inflated and hydrodissects the cortex from the capsule.

The second type is a typical irrigation and aspiration (I&A) flow, but unlike in phaco, in EVE I&A do not function to attract lens material to the tip. The sole purpose of EVE I&A flow is to gently remove the emulsified cataract from the eye. Although the speed of endocapsular vortex flow is greater than conventional I&A flow in phaco, the I&A flow rate for EVE is significantly less — approximately 5 cc/min. This reduced I&A flow requires less vacuum and lower bottle heights, drastically reducing the potential for post-occlusion surge. In animal studies, no significant movement of the anterior or posterior capsule has been observed.

Compared to ultrasound phaco, the capsular bag not only appears more stable but also confines most of the energy needed to remove the cataract, effectively isolating it from the anterior chamber. This may protect the corneal endothelium and trabecular meshwork from high flow, cataract debris and radiated energy typical of ultrasound phaco. Animal studies and Miyake view observations also suggest that the EVE procedure may exert less stress on the capsule and zonules because the bag remains totally inflated and vacuum is not used to “pull” on nucleus or cortex. Also, in a controlled simulation the EVE procedure was shown to pose no significant thermal risk, even with I&A turned off.

Complex design, simple use

---EVE creates two separate and distinct flows and does not rely on tip occlusion and vacuum holding force.

The core mechanical component of the EVE technology is the single-use hand piece that contains a 1.37-mm-diameter impeller-tipped probe. Fluid, vacuum and pneumatic lines attach to modular units on the main console (Bausch & Lomb Millennium) and supply irrigation, aspiration and pneumatic power to the turbine-driven hand piece.

The stainless steel impeller is contained within a translucent protective sleeve and is deployed or retracted using the foot pedal. The pneumatic turbine spins the impeller at speeds between 20,000 and 100,000 rpm. It is similar to the turbine systems that power dental drills except they typically run above 400,000 rpm and do not function smoothly at slower speeds. EVE engineers have developed a proprietary means of controlling pneumatic input pressure that assures true smooth operation throughout the entire speed range.

The high-speed impeller has three struts, which radiate from the shaft like spokes of a wheel. Each strut has a horizontal and vertical component. The horizontal struts are pitched like a propeller and create the endocapsular vortex flow. This vortex flow brings the nucleus to the impeller where the vertical struts emulsify it. The impeller is partially shielded by a beveled protective sleeve that also includes the irrigation ports.

Procedure

One key to performing true endocapsular surgery is the ability to produce a round capsulotomy of 1 mm or less. This is now easily and reproducibly accomplished with a proprietary electrosurgical device that uses a differential current density to produce a 1-mm capsulotomy. A disposable 21-gauge circular tip is affixed to a reusable shielded probe and is then placed on the lens capsule through a clear corneal incision. The capsulotomy is usually placed tangentially to allow for a carousel type movement of the nucleus. A dispersive pad placed in contact with the patient’s skin completes the necessary circuit. Power is engaged by means of the foot pedal for approximately 1 or 2 seconds and the resulting edges are consistently round and smooth.

In multiple wet labs, there have been no occurrences of the radial tears that sometimes can occur with a larger capsulorrhexis produced by hand.

Bausch & Lomb is currently developing the disposable version of the probe featuring the proprietary technology patented by Optex. A bipolar version may be available in the future.

Hydrodissection is performed using a specially sized curved cannula that fits over the capsulorrhexis and generally requires only a single, gentle infusion to produce a complete fluid wave.

The surgical probe is then inserted through the clear corneal incision (a scleral or limbal incision is also suitable) and approximately 1 mm into the capsular bag, slightly stretching the capsulotomy. The surgeon must visually confirm that the irrigation ports of the probe are within the capsular bag. The beveled tip of the probe is then angled slightly toward the anterior lens capsule, but no more than 45° relative to the iris plane. The impeller is then advanced using the foot pedal.

Once the impeller is activated, a vortex flow builds within the bag, which provides a slight but very stable centrifugal pressurization of the capsular bag, hydrodissects the cortex from the capsule and draws the nucleus and cortical material to the probe tip. The direction of the vortex fluid movement within the capsular bag is determined, in part, by the bevel of the protective sleeve and the peripheral placement of the hand piece tip relative to the center of the capsular bag. Vortex fluid discharges from the bevel toward the capsular walls, where it recirculates back to the probe.

This explains why there is very little movement of the EVE hand piece in the eye. The sculpting type movements commonly used with phaco would be counterproductive and interfere with the creation of the recirculating vortex flow essential to the EVE process. Only slight rotations of the bevel and changes in the impeller speed are usually needed to control followability.

Unlike ultrasound phaco, the nucleus and lens cortex are usually removed in a single step in the EVE procedure. The vortex action may also reduce the incidence of retained nuclear fragments for two reasons.

First, all lens particles remain within the capsular bag and cannot become lodged behind the iris, where they would be hidden from the surgeon’s view. The endocapsular procedure should also reduce the risk of debris in the trabecular meshwork.

Second, in working with human eye bank eyes, 3+ nuclear cataracts were easily emulsified and, in contrast to traditional ultrasound phaco, there were no nucleus chips created. Instead, the emulsified lens material was extremely fine, taking on a “dust cloud” appearance.

Once the lens and cortex have been removed, the surgeon can perfectly visualize the capsular bag and a bright red reflex facilitates the secondary capsulorrhexis before insertion of the IOL. It may well be that the “empty bag” secondary capsulorrhexis is less prone to uncontrolled tears or extensions because all tension has been removed from the anterior capsule.

Possible benefits

There is virtually no learning curve when it comes to using the capsulotomy device. Once the surgeon depresses the foot pedal the software initiates a preprogrammed pause, then activates the device up to a maximum preset time limit. The surgeon then simply removes the deactivated probe from the eye, taking care not to depress the foot pedal again.

When compared to ultrasound phaco, the EVE procedures are easier to learn. Experienced phaco surgeons, though, may at first find the rotation and relative lack of movement of the hand piece tip a bit counterintuitive. Certain surgeons may be tempted to “do phaco in the bag,” moving the tip toward a piece of nuclear material or cortex they want to attract. With EVE, however, “followability” is produced by the vortex flow, not the I&A flow, so rotating the bevel away from the nucleus and varying the revolutions per minute will often attract the nucleus more efficiently.

When the impeller is first activated, it takes a few seconds for the vortex flow to develop and this may be perceived as a “lag time” where nothing happens. In fact, the vortex is separating the cataract from the capsule and overcoming inertia. With the probe held stationary, the lens will soon begin to spiral within the bag and be conveyed to the tip for emulsification. Surgeons learn very quickly to let the vortex develop and bring the nucleus toward the hand piece tip. Although it may seem to take a while for the emulsification of the lens to begin, the entire process is generally completed in 1 to 3 minutes and has proven effective in lab tests on human eye bank cataracts from 1+ to 3+ nuclear sclerosis. So far 4+ nuclear sclerotic cataracts have not been tested.

Compared to ultrasound phacoemulsification, the entire EVE procedure appears more controlled and less variable from case to case. Ultrasound phaco uses the opposing forces of flow and ultrasonic power that must be carefully balanced with the vacuum through complex technology and surgeon control. Failing to do so can result in post-occlusion surge, chamber collapse and torn capsules. While EVE must also maintain fluidic balance, the vortex flow works in harmony with the impeller’s power to emulsify the lens and serves to inflate the capsular bag rather than impose a risk of collapse. Extremely low I&A flow and vacuum further reduce the risk of capsule movement. There is little hand piece movement, fewer steps, reduced bottle heights and the efficient transfer of energy into the creation of a single vortex flow — all contained within the lens capsular bag.

The final result may eventually be a viable alternative means of removing cataracts that potentially may be as safe or safer than traditional ultrasound phaco. EVE may well provide enhanced protection for the corneal endothelium, reduced risk of capsular rupture and no chance of thermal injury.

For Your Information:

• Terence M. Devine, MD, is chief of ophthalmology at Guthrie Medical Center in Sayre, Pa., and a clinical assistant professor at SUNY. He can be reached at 1 Guthrie Square, Sayre, PA 18840; (570) 888-5858; fax: (570) 882-3236. Dr. Devine is principal investigator for Catarex. He is a paid consultant for Bausch & Lomb.

• Others involved in the EVE project include its developers, John Sorensen, ScD; Michael Mittelstein, PhD; and Soheila Mirhashemi, PhD; the principal and ongoing advisor, Richard P. Kratz, MD; and investigators/study group members David Brown, MD; I. Howard Fine, MD; Richard L. Lindstrom, MD; and Barry S. Seibel, MD.