Cataract surgeons tend to be interventionists at one point in a patient’s life. Simplistically speaking, we diagnose a cataract, we fix it, and our work is done. However, we recently entered an era in which we are starting to think about what happens if our patients develop diabetes or another ocular condition later down the line. Could the intervention we used earlier in life be modified to provide the patient a continuum of care?
Microinvasive glaucoma surgery (MIGS) is another area in which we must think about progression, similar to how we think about meibomian gland dysfunction and atrophy of the meibomian glands. Perhaps there is atrophy of the collector channels, so we perform selective laser trabeculoplasty sooner or place a stent that allows the collector channels to remain healthy over a longer period of time. Such an approach could provide patients with a more proactive, preventative approach to benefit the health of the outflow system for intraocular pressure (IOP) control.
INTRODUCING THE HYDRUS MICROSTENT
The Hydrus Microstent (Ivantis) is a MIGS device made from a super-elastic biocompatible alloy called nitinol. Roughly the size of an eyelash (Figure 1), the Hydrus Microstent measures 8 mm in size and spans 3 clock hours. The device is designed to be inserted into Schlemm canal and open the channel to allow blocked fluid to flow more freely, reducing IOP. The Hydrus Microstent provides a trimodal mechanism of action: The device opens a bypass through the trabecular meshwork, dilates and scaffolds Schlemm canal to augment outflow, and spans 90° of the canal to provide expanded access to the eye’s fluid collector channels.
THE DEVICE IN ACTION
The Hydrus Microstent has a little lip on the edge where it incises the trabecular meshwork. It has three windows, each of which is slowly delivered into the correct space. The surgeon leaves the proximal collar of the device out of the trabecular meshwork, which is what provides the bypass stent portion. The three windows and supporting scaffold stent open Schlemm canal and improve access to the collector channels.
Inserting the Hydrus is an elegant procedure. It provides verified confirmation that you are in the right tissue and that the device is placed properly and can do the job it is expected to do. It has an intuitive delivery system that is easy to learn. I have had the opportunity to take the Hydrus Microstent on mission trips, where I am operating under less-than-ideal circumstances, and I have found the procedure to remain quite straightforward and successful.
The Hydrus Microstent received the CE Mark in 2017 and TGA approval in Australia in 2013. Multiple clinical trials evaluating the device are currently underway, spanning the spectrum of mild, to moderate, to advanced disease.
The Horizon trial is an investigational device exemption (IDE) clinical trial of the Hydrus Microstent. According to the company, it is the largest MIGS study to date, including a total of 558 patients with mild to moderate primary-open angle glaucoma.
The Hydrus II was a randomized controlled trial conducted in Europe to evaluate the device in 100 glaucoma patients undergoing cataract surgery. The study data, published in Ophthalmology in 2015, showed that patients who were treated with cataract surgery plus the Hydrus Microstent versus those treated with cataract surgery alone were more likely to be medication-free over a 2-year span. Three-quarters of patients treated with the Hydrus and cataract surgery were medication-free, whereas only about one-half of those treated with cataract surgery alone were medication-free. Comparing the 12-month data with the 2-year data, there was a 74% increase in response rate, indicating a significant improvement in effect over 2 years.
The Compare study is a head-to-head trial comparing the placement of two iStents (Glaukos) versus one Hydrus Microstent for mild and moderate glaucoma. The surgeons implanting these devices are not novice users; each has already placed a number of the devices. That is now collecting 2-year results, which should be out soon.
In April 2017, the FDA granted Ivantis clearance to initiate a second IDE trial of the Hydrus Microstent. The Summit trial will investigate the Hydrus in more challenging cases and will include 60 patients with advanced glaucoma for whom conventional therapies have proven unsuccessful. Patients in this trial will undergo standalone glaucoma surgery without combined cataract surgery.
The Spectrum registry includes real-world data collected by surgeons outside the United States who are implanting the Hydrus Microstent. Outcomes show that even patients with more advanced disease gain a significant benefit from the Hydrus Microstent. In this group of patients, almost one-third are undergoing standalone surgery.
In my experience using the Hydrus Microstent and looking at the data collected so far, this device can be placed in patients with mild to moderate glaucoma. As we know, many glaucoma patients, despite intervention, progress to a more advanced stage of disease. Implanting the Hydrus Microstent at an earlier stage could potentially serve to preserve the health of the patient’s collector channel and provide benefit from the beginning to the end of the disease.
The Hydrus Microstent is safe and effective, as indicated by level-one multicenter randomized trial data. Its effect has proven to be sustained up to 2 years. It was designed to be used in combination with cataract surgery, but standalone benefits are being proven by real-world results and study data. It is an exciting time for MIGS devices.