Rates of visual field change and functional progression in glaucoma following trabecular microbypass implantation of iStent technologies: a meta-analysis

Abstract

Background/aim: While intraocular pressure (IOP) remains the only modifiable risk factor for glaucoma progression, the ultimate goal of glaucoma management is to preserve patients' functional vision and quality of life. To this end, minimally invasive glaucoma surgeries (MIGSs) aim to reduce IOP with minimal eye trauma. Commonly used MIGS devices include iStent technologies, which have well-documented IOP-reducing potential and favourable safety profiles. However, no study concluded on their effect on the rates of visual field (VF) changes. The aim of this meta-analysis is to determine the long-term effect of iStent technology implantation on glaucoma functional progression.

Methods: Electronic medical literature databases were searched to identify studies reporting on iStent technologies. Reports with follow-up durations <12 months, retention rates <75% and missing VF data were excluded. Fifteen studies reporting on 1115 eyes were identified. The overall weighted mean VF mean deviation (MD) progression, IOP reduction and follow-up duration were calculated.

Results: Weighted mean IOP at baseline was 19.0±3.1 mm Hg. At the end of a 37.9-month mean follow-up (range 12-96 months), a weighted mean 26.6% IOP reduction was achieved (range 15.2%-42.3%). Over the same duration, the weighted mean VF MD progression rate was -0.02±0.34 dBs/year, from a mean baseline of -5.76±5.68 dBs.

Conclusion: In this review, which examines functional stability of 1115 eyes, iStent technologies achieved a mean rate of progression of -0.024 dBs/year with serial standard automated perimetry, which is similar to that reported in non-glaucomatous eyes and slower than that reported in medically treated glaucoma.

Keywords: Field of vision; Glaucoma; Treatment Surgery.

Figure 1

Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) flow chart showing the systematic review and screening process.

Figure 2

Summary table of the key design (A, top) and clinical characteristics (B, bottom) of all included study. Quality assessment includes whether the study was prospective, randomised, with masked intraocular pressure (IOP) measurements, whether any blinding method was used, or if any incomplete reporting was observed. The retention rate, type of visual field strategy used, type of device studies (original iStent microbypass or iStent inject), the number of devices implanted, whether the procedure was stand-alone or combined with cataract surgery, the type of glaucoma studied (open-angle glaucoma (OAG), primary open-angle glaucoma (POAG), primary angle-closure (PAC), ocular hypertension (OHT) or normal-tension glaucoma (NTG)), the main country in which the studies were conducted, the mean baseline visual field mean deviation (MD) and its SD, the number of eyes involved at baseline, the follow-up duration, and the mean rate of visual field MD progression were also reported for each study.

Figure 3

Observed visual field mean deviation (MD) progression following stand-alone and combined iStent technologies implantation (pink lines) compared with the rates of progression reported in the literature for ocular hypertension (OHT; blue lines) and treated glaucoma (yellow lines). BL, baseline.