The Ahmed ClearPath (New World Medical, Rancho Cucamonga, California), a valveless glaucoma drainage device, arrived on the market in late 2019. In ordinary times, ophthalmologists would have used the intervening months to familiarize themselves with this device, but such opportunities have been severely limited during COVID-19.
As clinics slowly return to normal, Dr Shuchi Patel reached out to her colleague Dr Thomas Patrianakos, who is well acquainted with the Ahmed ClearPath, to discuss its unique design and potential benefits. Dr Patrianakos is a board-certified ophthalmologist with subspecialty fellowship training in glaucoma. In 2007, Dr Patrianakos completed a glaucoma fellowship at Massachusetts Eye and Ear, Harvard Medical School, Boston. He currently serves as the chair of ophthalmology at the Cook County Health and Hospitals System in Chicago and as a member of the glaucoma planning committee for the American Society of Cataract and Refractive Surgery.
How ClearPath Compares With Current Options
Shuchi B. Patel, MD: How is the Ahmed ClearPath different from the Ahmed glaucoma valve, model FP7, that most of us have been using?
Thomas D. Patrianakos, DO: The biggest difference is that this is a valveless tube shunt. Unlike the FP7, the ClearPath tube has no valve mechanism that opens and closes according to the intraocular pressure (IOP). Instead, it relies on the formation of a capsule around the implant, which takes approximately 6-8 weeks to form, in order to control the final IOP.
Patel: How does ClearPath's design compare with current valveless implants, such as the Baerveldt glaucoma implant?
Patrianakos: There are some features that make it easier to implant. Most notably, the suture arms are approximately 2 mm more anterior, making it easier to suture to the sclera. You don't have to twist the suture needle as much to tie through the eyelets. It's easier to reach in that aspect. This also means that you're not suturing over the thinnest part of the sclera. With the Baerveldt, the eyelets for suturing the implant onto the sclera sit right around where the muscles insert, which tends to be the thinnest part of the sclera. Because this is 2 mm anterior, you're actually farther anterior on the sclera, where it tends to be a little bit thicker and there is less chance of perforation.
The shunt plate is a little softer than the Baerveldt, so it is easier to get between the muscles. The tube itself is also less rigid than the Baerveldt, so it might be a little bit harder to get it into the ostium and into the needle track that you make with a 23-gauge needle. There is a 4-0 Prolene ripcord in the lumen, which is preplaced into the tube; I have found it beneficial to keep in the ripcord because you can use it as a stylus to help insert the tube into the needle track. Then, once you get it in, you can pull the ripcord from the actual plate if you don't want it or keep it in if you do.
Patel: Is there a learning curve to adopting the Ahmed ClearPath? Do we still have to hook muscles? Also, do we have to be more careful to avoid diplopia like with the Baerveldt, as opposed to the traditional Ahmed?
Patrianakos: If you can put an Ahmed valve in the eye, you should have no problem inserting this one.
With the ClearPath Model 350, and to some extent the ClearPath Model 250, it is important to place the plate behind the recti muscles and to isolate the recti muscles. The plastic that comprises the plate tends to be more malleable than the Baerveldt and easier to fold. You can insert it in a smaller incision than you would a Baerveldt or an Ahmed FP7. You also can fold the plate into two and then insert it underneath the muscles and let it fold out. It tends to work well.
The Ahmed ClearPath has a unique contour that allows it to follow the contour of the globe itself, so it tends to have a lower profile than the Ahmed FP7. Cosmetically, it doesn't leave as large of a bleb or bubble over the plate as a traditional Ahmed.
Initial Outcomes and Hurdles
Patel: Overall, what have your IOP-lowering outcomes been after implanting the Ahmed ClearPath compared with the Ahmed FP7 and the Baerveldt?
Patrianakos: Several studies, most notably the Ahmed Baerveldt Comparison Study, indicate that tubes without a valve mechanism generally end up resulting in a lower long-term IOP than tubes with a valve mechanism. In this relatively short period of time, my experience has shown this to be true with the Ahmed ClearPath compared with the Ahmed FP7, and the IOP has been compatible with the Baerveldt 350 and 250. I think the end, IOP will be a little lower than with the Ahmed FP7.
Patel: Have you had any complications that you think are unique to this device?
Patrianakos: I don't know if I would call it a complication, but initially I noticed that it was more difficult to insert the actual tube into the 23-gauge needle track that goes into the anterior chamber. I tend to make my needle track in the sclera a little bit longer, because I feel that it keeps the tube from eroding. For the first couple of tries, when I removed the ripcord and inserted the tube without it, it was difficult for me to get that tube through the long needle track. I was pushing it, which probably made the track a little larger on the periphery. Because of that, I think there was leakage around the tube, which caused the pressure to be low the first week or so after the surgery. As I mentioned earlier, by keeping that Prolene ripcord in place and using it as a stylus to guide that tube into the needle track, it is a lot easier. I'm not struggling to get the tube in there.
The Right Device for the Right Patient
Patel: Now that we have even more devices to choose from, how do you decide which one to use in patients who are good candidates for a glaucoma drainage implant?
Patrianakos: It has to do with the type and severity of the glaucoma.
Generally, in patients with uveitic glaucoma, I prefer to do a valve type of tube shunt. The reason is that if they have ciliary body shutdown, the valve should in theory close and there should be no flow of aqueous and hypotony should be prevented. I also tend to use a valve mechanism in patients whom I believe may not have the luxury of waiting 6-8 weeks for the valveless device to fully function. In those cases, if I am worried that I might snuff out the nerve and the patient has end-stage glaucoma, I might end up putting a valved tube in the eye in the hope that their pressures will lower immediately and stay low — although the problem is that they may not get as low as you need them to be with the valve-type surgeries.
For everything else, I tend to go toward more of the valveless tube shunts because I feel that they are lower-profile and provide better IOP results for patients with glaucoma.
Patel: That is also the approach for my patients in whom we are particularly concerned about hypotony in the future, for whatever reason. It is nice to be prepared for what to do if the pressures get low.
How would you decide between using the Baerveldt vs the new Ahmed ClearPath?
Patrianakos: I am starting to use the ClearPath more than the Baerveldt. This is because of its ease of use, the unique contour and profile of the tube itself, and the similar results between the two. I like the fact that you can use a smaller incision, and it is also easier to tie down the plate to the sclera.
Patel: I know that you did do a large proportion of Baerveldt implantations in your practice, so to hear that you would consider converting a lot of your patients to this option is an enthusiastic response.
Is there anything you would like to add?
Patrianakos: The only thing is that, obviously, the ClearPath has not been around that long. It would be nice to have longer follow-up on some of my patients.
Nonetheless, I have had very good results with patients in whom I have used this tube shunt. Again, the results have been like those of the Baerveldt during the short follow-up period.
Patel: We have yet to find the one answer for every patient with glaucoma, so having multiple options gives us a chance to really tailor the treatment depending on a variety of factors, such as disease type, the need to lower IOP more quickly, and cosmetic factors. Also, with COVID-19, we may be increasingly seeking out options that require less frequent in-person visits.
I look forward to seeing what the long-term results are with this device, as well as trying to further incorporate it into my own practice.
Shuchi B. Patel, MD, is director of glaucoma services in the Department of Ophthalmology at West Palm Beach VA Medical Center in Florida. She explores the ever-changing glaucoma space for Medscape, including advances in diagnostics and treatments.
Medscape Ophthalmology © 2021 WebMD, LLC
Any views expressed above are the author's own and do not necessarily reflect the views of WebMD or Medscape.
Cite this: Shuchi B. Patel. The New Valveless Glaucoma Drainage Device: An Expert's Take - Medscape - Apr 28, 2021.