Case study: iStent Inject G2 (Glaukos)

June 25, 2019 Dr Dean Corbett

It’s been more than two and half years since I implanted the first Glaukos iStent Inject. So, what have we learned from our experience with this revolutionary new device?

 

Background: MIGS 

 

Trabecular bypass minimally invasive glaucoma surgery (TB MIGS) is an area of surgery that has started to become mainstream. Frustratingly the delays in adoption are related not to efficacy but more to funding barriers. Thankfully, now almost all district health boards are on board with funding the procedure, though major barriers continue in the private healthcare area. Whilst some private insurance companies have made case-by-case dispensations to fund the devices, the largest funder is sticking firm to refusing to contribute to any costs associated with this effective procedure.

 

The MIGS area is full of misconceptions and confusion, perhaps because it is new and also because the indications for these novel surgical devices are still evolving. TB MIGS is somewhat unique in having more than 100 peer-reviewed publications supporting its efficacy and safety. The ability to implant a device that provides good efficacy with almost no risk to the patient – and, coincidently, removes the burden of lifelong medication issues, including compliance and side effects - is nothing short of disruptive from a clinical point of view. 

 

Why then has this approach not been disruptive at the clinical coalface of glaucoma care?

 

Perhaps it is for the same reason that Pharmac is beginning to receive attention (not of the positive variety) for its approach to medicating the people of New Zealand. Ethically, it is a dilemma that is only too familiar for politicians worldwide who serve an ageing population, particularly in countries with a ‘baby boom’ bulge such as Australia and New Zealand.

 

Trabecular bypass stents (Glaukos iStent, iStent Inject and Ivantis Hydrus) are a group of very low risk devices that bypass the trabecular meshwork and thus have the potential to reduce intraocular pressures (IOPs) to a level close or equal to episcleral venous pressure - around 14mmHg. Efficacy data supports this is a long-term effect in most cases as there is a minimal healing response. This differs from other aqueous/conjunctival shunts which are hampered by healing, just as we experience in trabeculectomy.

 

Multiple studies (see references below) have shown efficacy both in terms of IOP reduction but also with a decrease in medication load. This later aspect of care should not be underestimated. Not only do we miss opportunity for adequate treatment of IOP lowering due to poor compliance and adherence, but by reducing medication load we can also have a tangible influence on patient wellbeing, reducing the possibility for falls (beta blockers) but also limiting the devastating effect of prostaglandin-related orbitopathy. The unwanted adnexal effects of prostaglandin analogues not only cause an unsightly appearance but may also permanently alter lid and ocular function leading to potentially sight-threatening complications and should not be underestimated. 

 

I have, in more than one patient, seen alterations in eyelid tightening and fibrosis, such that it has become impossible to measure the IOP with applanation; quite an ironic result for a medication that’s meant to improve the outcomes of the patients it serves. Thus, any alternatives that are minimally invasive, such as TB MIGS devices, must be seen as a great addition to the range of tools we have at our disposal to prevent glaucomatous blindness.

 

 

 

Procedure and results: iStent Inject 

 

The procedure itself is exquisite with respect to doctor and patient. For an experienced surgeon, placement of the two stents takes minimal additional surgical time and is well tolerated by patients. I routinely use topical anaesthesia for cataract surgery and the stent placement is not challenging with this mode of eye preparation.

 

I have followed my small cohort of patients for three years and there have been no complications. My first New Zealand patient to receive the iStent Inject was reviewed 20 months after surgery. The preoperative IOP was 22 on one medication and currently this patient is drops free and running an IOP of 16. 

 

This outcome is in-line with the averages and must suggest a potentially revolutionary approach to glaucoma care is either very near or already surrounding us. I am hopeful we will have easier access to the technology as better funding and greater cooperation with private funders allows patients to have more choice in their surgical care in the future.

 

References

 

  • Berdahl, Voskanyan, Myers et al. Implantation of two second‐generation trabecular micro‐bypass stents and topical travoprost in open‐angle glaucoma . Clin Exp Ophthalmol. 2017 Nov; 45(8): 797–802.
  • Malvankar-Mehta MS, Iordanous Y et al. (2015) iStent with Phacoemulsification versus Phacoemulsification Alone for Patients with Glaucoma and Cataract: A Meta-Analysis. PLoS ONE 10(7):  0131770. doi:10.1371/journal. pone.0131770
  • Tham YC, Li X, Wong TY, et al. Global prevalence of glaucoma and projections of glaucoma burden through 2040: a systematic review and meta-analysis. Ophthalmology. 2014;121:2081e2090.
  • Berdahl, Voskanyan, Myers et al. Implantation of two second‐generation trabecular micro‐bypass stents and topical travoprost in open‐angle glaucoma. Clin Exp Ophthalmol. 2017 Nov; 45(8): 797–802.
  • Park J, Cho HK, Moon JI, Changes to upper eyelid orbital fat from use of topical bimatoprost, travoprost, and latanoprost. Jpn. J Ophthalmol. 2011; 55(1):22-27

 

Dr Dean Corbett is a specialist cataract and refractive surgeon with a special interest in glaucoma working at Auckland Eye. He has introduced a number of new and innovative products and techniques to New Zealand and has worked in the public sector for over 20 years.