Recent Advances in Vitreoretinal Technology and Technique
Recent Advances in Vitreoretinal Technology and Technique
Safer, more efficient surgeries and new options for pharmacological management are now possible.
STANISLAO RIZZO, MD · MARCO CINQUINI, MD
It is a privilege to witness a period of time so intense and so full of advancements in technology that will benefit our patients. We recently experienced a significant advancement in retinal surgery with the arrival of a comprehensive system that enables performance far superior to that of a few years ago. The CONSTELLATION® Vision System (Alcon, Fort Worth, TX) (Figure 1) combines advanced features such as a high-speed vitrector with duty cycle control, IOP control, high brightness xenon illumination, a 532 nm laser, the INFINITI® phaco technology and V-LOCITY® Efficiency Components. This is a comprehensive system which enables us to perform surgery of the anterior and/or posterior segment where high-speed cutting, a more efficient duty cycle and IOP control are of the utmost importance.
Figure 1. The CONSTELLATION® Vision System.
HIGH SPEED CUTTING AND DUTY CYCLE CONTROL
The new ULTRAVIT® probes, available in 20, 23 and 25 gauges (Figure 2) provide high-speed cutting up to 5000 cpm. High cutting speed ensures greater stability with only minor traction on the retina, which is known as port-based flow limiting, introduced by Steve Charles, MD. The vitreous is cut into minuscule pieces, resulting in controlled flow.
Figure 2. New CONSTELLATION® System probes, available in 20-, 23-, and 25-gauge.
With the standard pneumatic vitrectors currently available, the port opening time decreases as the cutting rate increases. By contrast, the ULTRAVIT® probes maintain a minimum open time of 50% at 5000 cpm, allowing high flow rates at very high speed.
|Stanislao Rizzo, MD, is Chief of the Eye Surgery Clinic at Santa Chiara Hospital, Azienda Ospedaliero-Universitaria Pisana, Pisa, Italy. He reports minimal financial support from Alcon Laboratories, Inc.|
Marco Cinquini, MD, is affiliated with the Eye Surgery Clinic at Santa Chiara Hospital, Azienda Ospedaliero-Universitaria Pisana, Pisa, Italy.
The opening and closing cycle of the vitrector port is called the duty cycle and represents one of the principal factors that influence flow rate. By optimizing the opening time, the efficiency in terms of vitreous flow in the new vitrectors is superior to the flow achieved by current vitrectors available at significantly lower cut speeds.
The CONSTELLATION® Vision System offers control of the port opening time percentage according to the demands of the surgeon, the vitreoretinal pathology or the operational stage. The settings available are:
• CORE: maximum vitrector port opening time during the duty cycle designed for the core vitrectomy, in which a higher flow rate is required.
• SHAVE: minimum vitrector port opening time during the duty cycle designed for tissue dissection and removal, a phase in which a lower flow rate is required.
• 50/50: 50% vitrector port opening time for surgeons who prefer the vitrector port opened and closed for the same interval.
To enable such a high degree of efficiency and surgeon-controlled duty cycle, the vitrectomy probe mechanism is no longer spring-operated, but utilizes a dual pneumatic drive design. This design has two lines of compressed air (without a spring mechanism) to open and close the vitrector port independently.
Combining high-speed cutting, duty cycle control with a port closer to the tip of the vitrector (Figure 3), which allows a better dissection of the membranes, we should achieve minimal traction on the retina, which in my opinion results in improved safety and efficiency.
Figure 3. Placement of the port closer to the tip of the vitrector enhances the ability to dissect membranes.
INTEGRATED PRESSURIZED INFUSION & IOP CONTROL
Another significant advantage offered by the CONSTELLATION® Vision System is the ability to set and maintain the IOP in real time to +/- 2 mmHg. The system utilizes a sensor embedded in the cassette to measure infusion flow and calculate the pressure drop through the infusion line. This means working in a stable environment, without significant pressure fluctuations. I have used lower intraocular pressures than those I routinely use with other systems, which may be an important advantage to patients who have glaucoma or chorioretinal circulation problems.
With the CONSTELLATION® system, we finally have a comprehensive system with two separate and independent infusion lines, one for the anterior and one for the posterior segment. In phaco surgeries I experienced exceptional stability and utilized the aspiration system, which is capable of controlling both vacuum and flow. This is very important for those surgeons who are used to performing combined cataract and vitrectomy surgery.
For the first time, there are numerous parameters available to control the effectiveness of the vitrectomy probe: flow control, vacuum control, control of intraocular pressure, very high cutting rates and duty cycle control. We can therefore customize our system — instead of modifying our technique — according to the pathology of the patient.
CONSTELLATION® VISION SYSTEM SUMMARY
If we then consider that the CONSTELLATION® Vision System has an advanced xenon illuminator, an embedded 532 nm laser (PUREPOINT®) with a multifunction laser footpedal and a long list of ease-of-use features (V-LOCITY® Efficiency Components), we now really have one comprehensive system in our operating theatres that delivers on both the anterior and posterior segment surgical requirements.
EARLY EVALUATION OF NEXT-GENERATION 25+ TECHNOLOGY
Although there have already been significant improvements made in the CONSTELLATION® Vision System's 25-gauge technology, we believe we will re-evaluate the role that 25-gauge surgery currently plays with the future introduction of 25+ (Figure 4). This probe produces higher aspiration flow rates due to an enlarged port, increased ID design and increased stiffness by utilizing a stiffening collar and optimizing the length of the probe.
Figure 4. The new stiffer ULTRAVIT® 25+ probe.
The advantages are clear: Having smaller-caliber (and thus less invasive) probes that feature better rigidity than older designs, combined with the flow performance improvements that make the probe equivalent to larger-gauge cutters, will certainly make us rethink the role the 25-gauge has played so far in MIVS.
In addition to the MIVS cutter enhancements, we were given the opportunity to evaluate Alcon's new EDGEPLUS™ trocar blade. These will be available in 23 and 25 gauges (Figure 5). They provided a linear incision designed to provide improved wound architecture, which I experienced, and it required less insertion force when placing the cannulas. The handle has also been redesigned to allow improved access to complete an angled incision.
Figure 5. Extending both the blade edge and the cylinder ridge sums up the EDGEPLUS® advantage.
TREATMENT FOR WET AMD
• New perspectives for the treatment of wet-type (neovascular) age-related macular degeneration (NV-AMD). Wet (neovascular) AMD is the leading cause of irreversible vision loss in the elderly. New blood vessels start growing in the layer beneath the retina and then in the retina. This rapid growth of new blood vessels is often complicated by blood and fluid leaking causing tissue edema. When this pathophysiological phenomenon affects the macula, it leads to central vision loss.
In the United States, about 200,000 people develop NV-AMD every year. The World Health Organization estimates a development of epidemic proportions of this pathology by 2030 based on the dramatic evolution of the last few years.
• Anti-VEGF. The arrival of the new intravitreal anti-VEGF drugs has led — in the majority of cases — to a stabilization of patients affected by NV-AMD and in some cases to visual recovery; however, in 30% of cases the resolution of edema did not coincide with meaningful improvement in visual acuity. However, this kind of treatment entails a serious commitment from health workers, patients and their family in light of the many injections, appointments and examinations required from each patient undergoing the treatment. Certainly all this, given the volume of injections required each year, leads to a considerable cost for the health care system.
The new challenge today is to develop a treatment that enables us to block, or at least slow down, AMD evolution while requiring fewer anti-VEGF injections. Numerous relevant studies suggest the possibility of direct drug administration into the suprachoroidal space by combining medical therapy and surgery.
SUPRACHOROIDAL DRUGS TO TREAT AMD
The suprachoroidal space is a virtual space in the eye between the sclera and the choroid. Traditionally, it is reached by surgical dissection, which makes access to the posterior pole and the macula particularly difficult.
A recently-developed ophthalmic microcatheter (iScience Interventional Corp.) can be used to reach the suprachoroidal space through a small incision on the anterior part of the eye. The microcatheter incorporates a small luminous LED on the anterior edge, enabling visualization of its passing into the choroidal space and into the macular region. The drug can then be administered in direct contact with the choroidal surface for the neovascularization treatment.
Dr. Tim Olsen has carried out studies on animals to evaluate the safety and pharmacokinetics of drug administration in the suprachoroidal space. In these studies a steroidal drug, triamcinolone acetonide, was administered through the suprachoroidal space near the macula.1 To date the results from these animal studies have clearly shown the safety of this suprachoroidal drug administration.
Further, during the study high concentrations of the drug in all ocular tissues, including the choroid and retina, were verified, for up to 120 days after drug administration. Blood levels of triamcinolone following the treatment, however, were very low in confirmation of the selectivity of the suprachoroidal and macular drug administration methodology.
At present, researchers are experimenting with this methodology in humans, in particular on patients suffering from AMD for whom the traditional cures had failed: Dr. Tom Chang (US), Professor Albert Augustin (Germany), Professor Manfred Tetz (Germany) and Professor Stanislao Rizzo (Italy).
To date 25 patients have been treated — all of them were injected with the drug in the posterior pole by inserting a microcatheter in the suprachoroidal space. Many of the initial patients treated by Dr. Chang have reported a vision stabilization or improvement.
The surgical methodology seems complication-free and to date has not shown any adverse effects that may result in vision deterioration. The first preliminary results on the safety and efficacy of the methodology are expected by mid-2009.
The new surgical technique and instrumentations for treatment of vitreoretinal pathologies are truly impressive. We do hope that all these efforts will really benefit our patients. RP
1. Olsen TW, Feng X, Wabner K, Conston SR, Sierra DH, Folden DV, Smith ME, Cameron JD. Cannulation of the suprachoroidal space: a novel drug delivery methodology to the posterior segment. Am J Ophthalmol. 2006 Nov;142(5):777-87. Epub 2006 Sep 20.
Retinal Physician, Issue: February 2009