The development of new surgical technologies and techniques is critical for improving patient care. However, not all technologies can or should be implemented in routine clinical practice, and the rationale for adoption can be unclear. Understanding the potential role of a new technology like the ExPRESS shunt (Alcon, Fort Worth, TX) in routine clinical practice requires an examination of technological change in general. Technologies that are adopted may be broadly categorized into 2 categories: sustaining and disruptive. Disruptive technologies often begin with inferior performance but have some fundamental advantages (safer, faster, less expensive, more convenient) that allow them ultimately to displace the existing technologies as progressive advances allow them to match and then surpass their entrenched rivals. Disruptive technologies often require long adoption periods while incremental improvements are introduced. Cataract extraction by phacoemulsification is a classic example of a disruptive technology that initially had limited advantages over intracapsular or extracapsular cataract extraction, with longer surgical times, the potential for greater endothelial cell loss, and increased equipment expense. However, the fundamental advantage of phacoemulsification, namely, a much smaller incision and hence faster recovery and improved safety, ultimately led it to develop into the dominant cataract-removal technique.

Trabeculectomy was introduced as a potentially disruptive technique, with the premise that removal of a portion of the trabecular meshwork, the main site of abnormal aqueous humor outflow resistance in primary open-angle glaucoma, would restore normal outflow. Although this mechanism of action was incorrect, guarded filtration surgery was still a significant departure from the full-thickness filtration surgeries that had been performed since the beginning of the 20th century. As with many disruptive techniques and technologies, trabeculectomy faced early resistance to adoption, in this case because intraocular pressure (IOP) reduction was typically less than that which occurred with full-thickness surgery. However, full-thickness filtration surgery has a significant risk for postoperative hypotony and anterior chamber collapse. The guarded filter of trabeculectomy significantly reduced this risk compared with full-thickness surgery and eventually became the gold standard for glaucoma surgery.

In contrast to disruptive technologies, a sustaining technology is one that improves the performance of the existing technique but does not result in fundamental alterations. Sustaining technologies tend to be adopted or discarded faster than disruptive technologies, and the benefits are often more apparent. With trabeculectomy, there have been numerous sustaining improvements, notably the use of antimetabolites to reduce the incidence of episcleral fibrosis and surgical failure, but the fundamental characteristics of the surgery remain unchanged. However, there are innumerable variations on the technique, with postoperative care involving as much art as science. Reducing this variability may be an area in which sustaining technological innovations can improve filtration surgery.

In this issue of the Journal , Netland and colleagues report on a randomized, prospective trial of the ExPRESS shunt compared with standard trabeculectomy (the XVT Study). The ExPRESS shunt is a stainless steel surgical implant intended for use in glaucoma surgery. It was first introduced in the hope that it would be a disruptive technology, enabling a rapid full-thickness filter by placing it directly under the conjunctiva, with the flow rate from the anterior chamber controlled through the size of the device’s lumen. Early clinical trials revealed that this was not a viable approach because of the high rates of hypotony. It was then changed to a sustaining technology, namely, a modification of trabeculectomy in which the implant was placed under a scleral flap. The goal was to produce a more consistent surgery that would ultimately be safer and possibly have better clinical efficacy.

The key question in evaluating the ExPRESS shunt or any other new sustaining technology for adoption into routine practice is whether or not it adds clinical value to the existing technique. One approach is to define clinical value broadly as efficacy, safety, and cost in all its forms. Efficacy and safety are typically evaluated in clinical trials and are the parameters most commonly discussed by clinicians with their patients. However, cost is a parameter that should not be ignored, and assessment of cost must include far more than just the cost of the device itself.

When evaluating efficacy, it is helpful to consider short-term disease control, long-term disease control, and effect on future disease management. In the XVT Study, IOP control was used as the primary outcome measure. Netland and colleagues demonstrated that short-term and long-term IOP control was similar in the ExPRESS shunt group and the standard trabeculectomy group. The number of medications required was also similar in the 2 groups. Success rates, defined as IOP between 5 and 18 mm Hg, with or without medications, and without further glaucoma surgery, were also similar in the 2 groups. The authors also compared the visual acuity in the 2 groups and found no difference beyond the 1 month postoperative period through to 2 years of follow-up. Visual field results were not reported in this manuscript, but the study was probably too small to find small differences in visual field scores if they existed. As well, the study was too short to report on any possible beneficial or detrimental effects on future glaucoma surgeries. Overall, the study results suggest that the ExPRESS shunt does not add to the short-term or long-term efficacy of standard trabeculectomy.

Safety is obviously a critical factor in evaluating a new surgical technology. Netland and colleagues report a higher overall rate of postoperative complications in the standard trabeculectomy group compared with the ExPRESS group. However, the only individual postoperative complication that was significantly higher in the trabeculectomy group was the rate of hyphema. Because all the hyphemas resolved without treatment, it is reasonable to ask whether it should really be considered a complication. Although bleeding from iridectomies is certainly possible, sclerotomies that excise a portion of the trabecular meshwork and the Schlemm canal would be expected to result in reflux bleeding and hyphema. Some angle surgeries such as ab interno trabeculotomy have virtually universal intraoperative or postoperative hyphemas by a similar mechanism, and they clear spontaneously. It would be interesting to know whether the complication rate would still be significantly lower in the ExPRESS group if hyphemas were removed from the analysis. Nevertheless, both techniques appeared to have good safety records according to this study, with relatively low rates of severe complications requiring additional surgery.

Cost is probably the most complex factor that should be examined, but it was not evaluated as part of the XVT Study. A complete accounting of costs would have to consider 3 main perspectives: the payer, the provider, and the patient. From the payer perspective, the main cost difference would be the implant cost, with postoperative medications and subsequent procedures being similar in the 2 groups in the XVT Study. From the provider standpoint, most costs are indirect but can still be estimated using careful cost accounting. The types of costs that should be assessed include items such as opportunity costs related to surgical time and postoperative care visits (particularly in a bundled-fee model) as well as associated overhead costs. From the patient perspective, assuming coverage of the implant fee by insurance, the main costs would be related to postoperative visits and recovery, including potential lost income and transportation expenses for both the patient and any caregivers. In this study, the postoperative visits were standardized so that costs would be similar in the 2 groups, although some (but not all) previous studies have suggested that fewer postoperative visits are required with the ExPRESS shunt. One area in which the ExPRESS shunt appears to be consistently superior to standard trabeculectomy is the rate of visual recovery. In the XVT Study, the ExPRESS shunt patients had returned to baseline vision by the 1-month visit, while the standard trabeculectomy patients had not returned to baseline vision until the 3-month visit. This could be a significant factor for certain patients, such as those who are monocular or are hindered from returning to work due to poor vision in the operative eye. While the actual value of each of these factors could be assessed, they would likely vary significantly with each patient, provider, and health insurance system, making global recommendations based on cost difficult.

In conclusion, based on the results of the XVT Study, the ExPRESS shunt appears to provide efficacy similar to that of standard trabeculectomy. These results are consistent with previous studies comparing ExPRESS shunts with standard trabeculectomies. There may be a slight reduction in the number of complications with the ExPRESS, particularly in reducing the rate of hyphemas. Whether or not it should be used routinely during filtering surgery appears to depend largely on an analysis of the value of faster visual recovery versus the added cost of the implant. Other costs such as postoperative visits also need to be assessed. These factors are likely to vary with individual ophthalmologists and patients, and until further data are available, the decision of whether or not to use the ExPRESS shunt rests within the individual doctor-patient relationship.