Glaucoma is one of the most common causes of blindness worldwide, and its prevalence is increasing. The aim of the present review is to describe the current medical and surgical treatment trends in the management of open-angle glaucoma. There has been an increase in the availability of glaucoma medications and the use of laser trabeculoplasty over the past decade, with a subsequent decrease in invasive incisional surgery. In addition, a new class of glaucoma procedures, termed microinvasive glaucoma surgery, has emerged, which aims to fill the gap between conservative medical management and more invasive surgery.

Glaucoma treatment trends: a review.

Aqueous outflow - A continuum from trabecular meshwork to episcleral veins.

A Randomized Trial of a Schlemm's Canal Microstent with Phacoemulsification for Reducing Intraocular Pressure in Open-Angle Glaucoma

A Schlemm Canal Microstent for Intraocular Pressure Reduction in Primary Open-Angle Glaucoma and Cataract: The HORIZON Study.

Traditional glaucoma surgery has been challenged by the advent of innovative techniques and new implants in the past few years. There is an increasing demand for safer glaucoma surgery offering patients a timely surgical solution in reducing intraocular pressure (IOP) and improving their quality of life. The new procedures and devices aim to lower IOP with a higher safety profile than fistulating surgery (trabeculectomy/drainage tubes) and are collectively termed “minimally invasive glaucoma surgery (MIGS).” The main advantage of MIGS is that they are nonpenetrating and/or bleb-independent procedures, thus avoiding the major complications of fistulating surgery related to blebs and hypotony. In this review, the clinical results of the latest techniques and devices are presented by their approach, ab interno (trabeculotomy, excimer laser trabeculotomy, trabecular microbypass, suprachoroidal shunt, and intracanalicular scaffold) and ab externo (canaloplasty, Stegmann Canal Expander, suprachoroidal Gold microshunt). The drawback of MIGS is that some of these procedures produce a limited IOP reduction compared to trabeculectomy. Currently, MIGS is performed in glaucoma patients with early to moderate disease and preferably in combination with cataract surgery.

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Update on Minimally Invasive Glaucoma Surgery (MIGS) and New Implants

PURPOSE. An intracanalicular scaffold (Hydrus microstent) designed to reduce intraocular pressure as a glaucoma treatment was tested in human anterior segments to determine changes in outflow facility (C). METHODS. Human eyes with no history of ocular disease or surgeries were perfused within 49 hours of death. The anterior segments were isolated and connected to a perfusion system. Flow rates were measured at pressures of 10, 20, 30, and 40 mm Hg. The scaffold was inserted into Schlemm’s canal of the experimental eye, while a control eye underwent a sham procedure. Flow rate measurements were repeated at the four pressure levels. Individual C values were computed by dividing the flow rate by its corresponding pressure, and by averaging the four individual C measurements. The change in C between control and experimental eyes was assessed by the ratio of the baseline and second C measurement. In two eyes, the placement of the scaffold was evaluated histologically. RESULTS. After scaffold implantation in the experimental eyes, the average C increased significantly from baseline (n ¼ 9, P < 0.05). Ratios of C at all pressure levels, except for 10 mm Hg, were significantly higher in experimental eyes (n ¼ 9) than control eyes (P < 0.05, n ¼ 7). Histologically, the scaffold dilated Schlemm’s canal with no visible damage to the trabecular meshwork. CONCLUSIONS. The Hydrus Microstent provided an effective way to increase outflow facility in human eyes ex vivo. (Invest Ophthalmol Vis Sci. 2012;53:6115‐6121) DOI:10.1167/ iovs.12-9570

A novel Schlemm's Canal scaffold increases outflow facility in a human anterior segment perfusion model.

PURPOSE To mathematically model the conventional aqueous humor outflow system with trabecular meshwork (TM) bypass and Schlemm canal (SC) dilation. METHODS The SC was modeled as a rectangular channel with the TM modeled as a permeable membrane. The collector channels (CCs) were modeled as fluid sinks distributed along the outer wall of SC. Two different implants were investigated in this study. The Hydrus Microstent (scaffold) was modeled with a TM bypass and a dilated region in SC that was 7 or 15 mm long and approximately 5-fold larger than the normal height of SC (h0). The iStent trabecular microbypass was modeled with a similar structure except that the dilated region in SC was 1 mm long and 25% larger than h0. RESULTS Creation of a TM bypass structure would increase the pressure in the surrounding regions inside the SC and make it close to the intraocular pressure. SC dilation would increase the pressure more uniformly in the dilated region. The pressure increase led to higher flow rates in SC and CCs, and subsequently increased outflow facility (C). If CCs were uniformly distributed, the increase in C was the smallest after implantation of 1 microbypass, compared with that after implantation of 2 microbypasses or 1 scaffold. If CCs were nonuniformly distributed, the magnitude of increase in C was sensitive to the location of implant, and the sensitivity was higher for the microbypass than the scaffold. CONCLUSION The study showed that creation of TM bypass and SC dilation significantly increased outflow facility, and the amount of increase correlated with the length of dilated regions in SC.

Mathematical Modeling of Outflow Facility Increase With Trabecular Meshwork Bypass and Schlemm Canal Dilation.

Purpose To assess the biocompatibility of a novel implant made of Nitinol (nickel-titanium alloy), designed to improve aqueous humor outflow. Materials and methods In the first arm of biocompatibility testing, microstents were surgically inserted into Schlemm's canal (SC) of 2 non-human primates (NHPs), and a third NHP served as a surgical sham control. After 13 weeks the animals were killed, and the eyes were examined by light and scanning electron microscopy. Two masked investigators evaluated the histology sections. The second arm utilized 8 New Zealand white rabbits; each rabbit received a microstent inserted into the sclera and subconjunctival space by means of passage across the anterior chamber thus providing contact with several representative ocular tissues. The fellow eye of each rabbit underwent a sham procedure without microstent insertion. The rabbits were killed after 26 weeks, and a trained ocular pathologist examined the specimens using light microscopy. Results Histologic and scanning electron microscopy analysis of the NHPs demonstrated that the microstents were located in SC. There was no evidence of an acute or chronic inflammatory response, granulation response, or fibrosis in the outflow system or in adjacent tissues. Rabbit eyes showed minimal mononuclear cell infiltration and minimal fibrotic responses at the site of the implants when compared with sham-treated control eyes. Conclusions The Hydrus Microstent was associated with minimal inflammation in both NHP and rabbit eyes with extended follow-up. These preclinical studies demonstrate that the Hydrus Microstent appears to have excellent long-term biocompatibility.

A Novel Schlemm's Canal Scaffold: Histologic Observations.

Effects of a Schlemm canal scaffold on collector channel ostia in human anterior segments.

Modular IOL systems including a base and a lens, wherein the lens includes fixed and actuatable tabs for connection to the base. The modular IOL allows for the lens to be adjusted or exchanged while leaving the base in place, either intra-operatively or post-operatively. Drug delivery capabilities and/or sensing capabilities may be incorporated into the base. Injector devices may be used to facilitate placement of the base and the lens sequentially or simultaneously into the eye.

Andrew T. Schieber

Papers

A novel Schlemm's Canal scaffold increases outflow facility in a human anterior segment perfusion model.

Mathematical Modeling of Outflow Facility Increase With Trabecular Meshwork Bypass and Schlemm Canal Dilation.

A Novel Schlemm's Canal Scaffold: Histologic Observations.

Effects of a Schlemm canal scaffold on collector channel ostia in human anterior segments.

Modular intraocular lens designs, tools and methods