Ophthalmologists in Sydney have been treated to an update on minimally invasive glaucoma surgeries (MIGS) hosted by Glaukos. While there was discussion about several innovative MIGS devices, the focus for the evening was on the company’s new iStent inject W and Preserflo, two devices indicated for mild-to- moderate glaucoma as a stand-alone procedure or in combination with cataract surgery.
Providing an overview of the latest MIGS devices, Dr Aparna Raniga (Concord Eye Specialists, Sydney), emphasised the opportunity to individualise surgical care because one glaucoma treatment strategy does not meet the needs of all. She highlighted the important place glaucoma surgery holds in the treatment paradigm for mild-to-moderate glaucoma due to the inadequate control that can be achieved via drops alone – primarily due to two thirds of patients being unable to administer their eye drops correctly, and more than 50% struggling to remember to use them at all. Fortunately, there are now many glaucoma surgical devices to choose from. She said, “We’re lucky in the sense that we now have extensive published data on randomised controlled trials and longitudinal data” to guide treatment strategies for individual patients.
ISTENT INJECT W
This trans-trabecular device is inserted through the trabecular meshwork to create direct communication between the anterior chamber and the Schlemm’s canal. One of the smallest medical devices known to be implanted in the human body, the iStent inject is backed by robust, diverse, and long-term clinical evidence, some of which was presented at the dinner event.
Acknowledging the support of industry, including Glaukos, Dr Colin Clement described Australian ophthalmology as being at the forefront of glaucoma research and education.
With a wealth of data available, he chose to focus on studies from the Fight Glaucoma Blindness! Registry (FGB!), a prospective collection of point-of-care data that can be used for research and personal audit.
The first study Dr Clement focused on was a large cohort study reviewing outcomes of patients implanted with the iStent inject combined with cataract surgery.1
Data was extracted for 2,051 eyes over 36 months, 50% of whom had primary open angle glaucoma.
The study found reduction in intraocular pressure (IOP) after treatment at six months was 16.7%, tapering to 7.7% at the 36-month mark. Medications approximately halved and were maintained at 36 months.
When those with a baseline IOP higher than 21 prior to surgery were examined, the researchers found that IOP reduction was even more impressive: at the six-month mark, a 36% reduction in IOP had been achieved, tapering to 27.6% at 36 months. Medication reduction of around 50% had been maintained.
With the iStent inject being indicated for mildto- moderate glaucoma, Dr Clement pointed out that, for treatment to be defined as ‘successful’, a large reduction in IOP is not required – indeed, sometimes there is no need to reduce IOP at all. Instead, the aim is to get patients off medications.
With this in mind, the researchers came up with a new measure of success based on achieving any reduction in IOP; any reduction in medication; and any reduction in medication and IOP.
When assessing the success of iStent inject combined with cataract surgery at 12 months they found:
‘Any IOP reduction’ was achieved in 74% of eyes,
‘Any medication reduction’ was achieved in 51%, and
‘Any reduction in medication and IOP’ was achieved in 46%.
Dr Clement said this information is useful when consulting with patients in a clinic.
Adverse reactions were minimal with a 1–2% increase in IOP, some macular oedemas, and about 2% after six months, increasing to 11% at 36 months, requiring a subsequent procedure.
Dr Clements went on to discuss a second study drawing on data from the FGB! Registry. This one was published this year in Clinical Experimental Ophthalmology,2 and compared real world two-year outcomes for 120 eyes undergoing Hydrus vs 224 eyes undergoing iStent inject or iStent inject W microinvasive glaucoma surgery implants with cataract surgery.
Analysis of patients revealed different devices were selected for different demographic populations, with those selected for Hydrus tending to have, at baseline, worse visual acuity, higher IOP, and more reliance on medications.
Dr Clement said this bias could be because glaucoma specialists tend to use the Hydrus whereas the iStent inject is more likely to be used by both glaucoma specialists and general ophthalmologists. Alternatively, it could be because there is a perception that the Hydrus has more IOP lowering capabilities, making it the preferred option for more advanced glaucoma.
Because of the two different population demographics, with multiple important variables to be considered, for this study the researchers used propensity matching to extract 75 eyes from each group that were similar across the majority of baseline metrics.
Outcomes for the entire cohort showed an absolute reduction in IOP that was not statistically different between the groups. Although there was a larger reduction in medications in the iStent group compared to the Hydrus group across the whole cohort, there was no difference when comparing the propensity matched cohort. Dr Clement reports a trend towards greater medication in the iStent group up to 24 months, but no statistical difference. Similarly, there was no statistical difference in adverse events.
PRESERFLO
Dr Hamish Dunn explored the features and surgical techniques required to implant the Preserflo Microshunt (Glaukos), an innovative device made from biocompatible, degradation-resistant SIBS Poly(styrene-block-isobutylene-block-styrene). Glaukos claims that this material minimises inflammation, scarring, and encapsulation.3
Prospective studies and real-world data, together, provide reasonably big numbers, which is valuable in helping determine how to treat glaucoma patients. Dr Dunn said we now have early reassuring data in support of Preserflo, which shows a reduction in IOP out to five years. This data includes randomised and non-randomised studies comparing the Preserflo head-to-head against the gold standard trabeculectomy procedure.
A randomised two-year trial found that at one year, patients who had undergone trabeculectomy had lower IOP than those treated with Preserflo. However, a pivotal non-randomised prospective interventional cohort study, comparing outcomes of both normal tissue glaucoma and POAG patients who needed trabeculectomy and were offered Preserflo at that time, produced different results. Age, medication, and duration of disease was matched across groups receiving trabeculectomy vs Preserflo. Six-month outcomes for the 52 patients showed that neither IOP nor diurnal fluctuations were statistically different between groups at 12 months.
Common across randomised and non-randomised studies comparing Preserflo with trabeculectomy were less interventions required in the Preserflo group (five of 26 Preserflo patients required six intervention vs 16 of 26 trabeculectomy patients requiring an intervention). Dr Dunn noted that this was probably a higher proportion of patients than he sees in his clinic. There were no adverse events in either group.
References
- Clement CI, Nguyen V, Howes F, Danks J, Lee V, Gillies M and Lawlor M. Phaco-emulsification with trabecular bypass stents (iStent inject): longitudinal outcomes from the Fight Glaucoma Blindness Registry. Ophthalmology 2022 Submitted
- Holmes DP, Clement CI, Nguyen V, Healey PR, Lim R, White A, Yuen J, Lawlor M. Comparative study of 2-year outcomes for Hydrus or iStent inject microinvasive glaucoma surgery implants with cataract surgery. Clin Exp Ophthalmol. 2022 Apr;50(3):303-311. doi: 10.1111/ceo.14048. Epub 2022 Feb 4. PMID: 35077009.
- Pinchuk L, Riss I, Batlle JF, et al. The development of a micro-shunt made from poly(styrene-block-isobutyleneblock- styrene) to treat glaucoma. J Biomed Mater Res Part B. 2017;105B:211-221. doi:10.1002/jbm.b.33525.
