Surgeon shares experience with Preserflo microshunt
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In the last 50 years, trabeculectomy with antimetabolites has been the gold standard of glaucoma surgical treatment, with valved or non-valved glaucoma drainage devices also in use.
Both techniques have significant complications and are burdensome for the patient, so the surgical approach to glaucoma is often delayed to advanced stages and after prolonged multi-drug topical therapy even in clearly progressing patients.
Consequently, in recent years, there has been growing interest in techniques that minimize the risks of trabeculectomy and tubes, allowing an earlier and safer surgical approach. These techniques are collectively defined as minimally invasive glaucoma surgery (MIGS).
Different outflow routes have been tried, but my experience and many published data show that the most effective and reproducible route is subconjunctival filtration.
The Preserflo microshunt (Santen) is a small tubular drainage device composed of a biocompatible synthetic polymer known as SIBS. The device has an overall length of 8.5 mm with a 1-mm fin positioned 4.5 mm from the beveled tip; it has an outer diameter of 350 µm and a lumen size of 70 µm. These features allow the device to self-regulate flow based on the Hagen-Poiseuille equation: In experimental settings (both in vitro and in vivo), the device proved to yield an internal resistance about 6.5 mm Hg at a flow rate of 2.5 µL/min (the normal aqueous rate of production), thus preventing dangerous early hypotony.
About 2 years ago, the Preserflo became available in Italy, and I immediately introduced this new device in my surgical practice. Since then, I have implanted more than 70 Preserflo microshunts, and it is now my first choice in pseudophakic patients both as a primary glaucoma procedure and in cases of failed previous surgery (provided that there is a quadrant of mobile conjunctiva), but I am confident to implant it in phakic patients and to combine the implant with phacoemulsification.
The surgical technique is standardized: a superotemporal or superonasal conjunctival flap with careful Tenon’s capsule dissection on a wide posterior area, minimal hemostasis, mitomycin C application at 0.4 mg/mL concentration, and sclerocorneal tunnel starting 3 mm to 3.5 mm from the limbus and performed with a 1-mm blade and a 25-gauge needle on a plane parallel to and as close as possible to the iris plane. The Preserflo is inserted in the tunnel and pushed forward until the lateral fins are well buried in the tunnel to stabilize the implant and to prevent peritubular filtration. It is advisable to ascertain the filtration by direct observation before carefully placing the distal part under Tenon’s capsule flat to the sclera and closing Tenon’s and conjunctiva with a watertight suture. Intraoperative complications are uncommon, but sometimes it is necessary to perform a second tunnel if the Preserflo appears to be too close to the endothelium.
Source: Enrico Martini, MD
The anterior chamber is always well preserved, and the surgery may be safely scheduled as an outpatient procedure. The postoperative course is almost uneventful with “single-digit” IOP on day 1 but usually with a deep anterior chamber and diffuse posterior bleb. There are few postop complications — sometimes first-day hypotony and shallow anterior chamber and choroidal detachment. To avoid more serious complications such as malignant glaucoma or hemorrhagic choroidal detachment, it is advisable to instill atropine drops at the end of the surgery.
The postop therapy is simple: antibiotic/steroid fixed combination six to eight times per day during the first 2 weeks and then dexamethasone eye drops with a slow tapering over 4 to 6 months. The impact of the surgery on visual acuity and refraction is limited with a good recovery within 3 to 5 days. There is also a reduced need for postoperative bleb management compared with other filtering surgeries, notably less need for needling, which in these cases is more difficult to perform at the slit lamp.
This favorable postoperative course and management proved to be most valuable in the last 12 months during the COVID-19 pandemic because it allowed us to minimize the access of operated patients to hospital facilities, which were operating with reduced capacity and severe restrictions.
The surgical learning curve proved to be easy and fast. After the first 10 to 12 cases, there is a remarkable reproducibility of results.
Let us talk about results. Thirty-six cases have at least 12 months of follow-up; 30 eyes were pseudophakic and six were phakic (four stand-alone procedures and two combined procedures). The mean preoperative IOP was 24.7 mm Hg, and the mean IOP at month 12 was 12.4 mm Hg. With a success cut-off at 18 mm Hg, the success rate at month 12 was 83.3%, with 58.3% of eyes not receiving any IOP-lowering therapy (complete success). Six eyes were classified as failures due to IOP higher than 18 mm Hg (16.7%). Two cases underwent revision and thereafter performed well with IOPs of 12 mm Hg and 13 mm Hg at 12 months. The four other cases underwent further surgery.
In conclusion, Preserflo microshunt in my experience has been an effective and useful tool to offer each patient a better solution to maintain good visual function. The technique can be well managed by experienced glaucoma surgeons, has a favorable postoperative course, and has a good and prolonged IOP-lowering effect. I think it allows surgeons to propose surgery earlier and safely in patients with worsening damage.
- References:
- Acosta AC, et al. Arch Ophthalmol. 2006;doi:10.1001/archopht.124.12.1742.
- Arrieta EA, et al. Ophthalmic Surg Lasers Imaging. 2011;doi:10.3928/15428877-20110603-01.
- Durr GM. Glaucoma Today. Sept-Oct 2020:34-35.
- Fantes F, et al. Invest Ophthalmol Vis Sci. 2006;47:3547.
- Sadruddin O, et al. Eye Vis (Lond). 2019;doi:10.1186/s40662-019-0162-1.
- For more information:
- Enrico Martini, MD, can be reached at Sassuolo Hospital, Via Francesco Ruini 2 Sassuolo, 41049 Italy; email: enricomartini@inwind.it.
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