Benha Medical Journal

REVIEW ARTICLE
Year
: 2017  |  Volume : 34  |  Issue : 1  |  Page : 1--4

Microinvasive glaucoma surgeries


Tarek T Aboulnasr1, Hazem M Elfiky1, Yasser A Mohamed2,  
1 Department of Ophthalmology, Benha University, Benha, Egypt
2 Dar El Oyoun Hospital, Giza, Egypt

Correspondence Address:
Yasser A Mohamed
40 Ansar Street, Dokki, Giza 11123
Egypt

Abstract

Because of the complications of current penetrating glaucoma surgeries as in trabeculectomy or glaucoma drainage devices, there is now an increased interest in newly introduced microinvasive glaucoma surgeries, which provide a safer and not a less-efficient alternative for such procedures, along with a decrease in dependence of glaucoma medications postoperatively. The microscopic implants can be implanted by following either an ab-interno approach (e.g. iStent, CyPass, Trabectome, and Xen Gel microshunt) or an ab-externo approach (e.g. Ex-Press minishunt and canaloplasty). The procedures aim to utilize the trabecular pathway, suprachoroidal space, or the subconjunctival space to increase aqueous drainage. These procedures can be performed in conjunction with phacoemulsification to augment the intraocular pressure-lowering effect, and the devices can be implanted during the same session without or with minimal additional risk.



How to cite this article:
Aboulnasr TT, Elfiky HM, Mohamed YA. Microinvasive glaucoma surgeries.Benha Med J 2017;34:1-4


How to cite this URL:
Aboulnasr TT, Elfiky HM, Mohamed YA. Microinvasive glaucoma surgeries. Benha Med J [serial online] 2017 [cited 2017 Oct 22 ];34:1-4
Available from: http://www.bmfj.eg.net/text.asp?2017/34/1/1/206898


Full Text



 Introduction



Glaucoma is the first cause of irreversible blindness in the developing world, and a major health problem in the developed world. There are 12.3 million blind people because of glaucoma alone. There is a published estimate of 60 million people suffering from glaucoma worldwide in 2010, increasing to 79.6 million by 2020 [1]. The modern goal of glaucoma management is to avoid glaucomatous nerve damage and preserve the visual field and total quality of life in patients, with minimal side effects [2]. Newly developed surgeries, microinvasive glaucoma surgeries (MIGSs), offer reduction in intraocular pressure (IOP), decrease in dependence on glaucoma medications, and an excellent safety profile. Their role within glaucoma treatment continues to be clarified and differs from the role of more invasive glaucoma surgeries such as trabeculectomy or glaucoma draining devices [3].

 Indications



Patient candidates for MIGS are those with mild–moderate glaucoma, primary open-angle glaucoma, pseudoexfoliation glaucoma, pigmentary dispersion glaucoma, glaucoma that is uncontrolled with maximum pharmacologic treatment or when there are barriers preventing adequate medication dosing, patients older than 18 years, and patients with clinically significant cataract, as surgery may be performed simultaneously [4].

 Contraindications



Relative contraindications for this procedure may include angle-closure glaucoma, secondary glaucoma, moderate to advanced glaucoma, previous glaucoma surgery, or severely uncontrolled IOP. Other considerations include patients with previous refractive procedures as well as monocular patients [5].

 Classification



MIGS can be classified as ab-externo and ab-interno. Ab-externo surgeries include Ex-Press glaucoma filtration device (Alcon, Texas, US), canaloplasty, and Gold microshunt (GMS) (SOLX, US). Ab-interno surgeries include iStent (Glaukos corp., California, US) trabecular microbypass, CyPass (Alcon, Texas, US), Aquesys Xen Glaucoma Implant (Aquesys, California, US), the Hydrus (Ivantis, California, US) microstent, and Trabectome (NeoMedix Corporation, California, US) [6].

 Devices



Ab-externo devices

Ex-Press glaucoma filtration device

The Ex-Press glaucoma implant ([Figure 1]) is a nonvalved implant made of medical-grade implantable stainless steel. The material is Food and Drug administration (FDA) approved for ophthalmic applications and is MRI compatible [7]. A large randomized prospective multicenter trial by Netland et al. [8] included 59 eyes treated with the Ex-Press implant and 61 eyes treated with trabeculectomy. The mean IOP was similar in both groups during postoperative follow-up, with a mean IOP of 14.7±4.6 mmHg in the Ex-Press group and 14.6±7.1 mmHg in the trabeculectomy group at 2 years after surgery. With success defined as IOP 5–18 mmHg with or without medications, and without further glaucoma surgery, success rates were 90 and 87% at 1 year and 83 and 79% at 2 years in the Ex-Press and trabeculectomy groups, respectively [8].{Figure 1}

Canaloplasty

Canaloplasty is a technique in which Schlemm’s canal is circumferentially catheterized and dilated, using a flexible microcatheter, to improve the trabecular outflow [9]. Bull et al. [10] conducted a prospective uncontrolled study to examine the long-term effect of canaloplasty. Canalization was successful in all patients (109), and the placement of tension sutures was possible in 90% of patients. A small subgroup of 16 patients underwent canaloplasty combined with phacoemulsification and were analyzed separately. The preoperative IOP of this group was 24.3±6.0 mmHg and an IOP decrease of 10.5 mmHg (43.2%) was achieved after 3 years. The IOP decrease in the combined group was greater than that in the group of patients who underwent canaloplasty alone, although not significantly (P=0.22). The percentage of patients with medication need changed from 81.2% preoperatively to 38.5% 3 years postoperatively [11].

The Gold microshunt

The GMS ([Figure 2]) is a flat 24-karat gold plate that is ∼5.2 mm long and 3.2 mm wide with a thickness of 44 µm. The GMS is made of 99.95% pure gold, a biocompatible material that is hoped will minimize tissue ingrowth or protein adherence that could cause blockage of aqueous flow [12]. In a prospective randomized clinical trial by Skaat et al. [12], two models of the gold shunt were tested, one of 24 µm microchannel diameter and one of 48 µm. The mean IOP for the 24 gold shunt was 20.0±1.9 mmHg (compared with 25.7±0.7 mmHg preoperatively) and the mean number of medications reduced from 2.9±0.6 to 1.7±0.8. In the 48 model, the mean IOP was 17.9±2.3 mmHg (compared with 35.6±2.2 mmHg preoperatively) and the mean number of medications reduced from 3.2±0.5 to 1.8±0.4. The success rate, defined as an IOP between 5 and 22 mmHg and a decrease of 20% or more, was achieved in 77.8% in the 24 µm gold shunt group and 72.7% in the 48-µm model [13].{Figure 2}

Ab-interno devices

iStent trabecular microbypass

The Glaukos iStent ([Figure 3]) device received FDA approval in June 2012. It is one of the smallest medical implants with a 1 mm body and an angular pointed tip and retention ridges that are arch-shaped and continue onto a tubular inlet device known affectionately as the ‘snorkel’ [15]. Neuhann published a case series of 62 eyes that included those with moderate to advanced glaucoma, and also patients who had undergone previous glaucoma surgery in that eye. The outcomes in the previous surgery group were good, although the lower target pressure needed for their more advanced glaucoma resulted in a higher medication burden than that in the group that had undergone no previous surgery. At month 36, the mean IOP in the group with prior glaucoma surgery was 14.2±2.3 mmHg, with 44% of eyes on medications. In the group with no prior glaucoma surgery, the mean IOP at month 36 was 15.4±2.2 mmHg, with only 13% of eyes receiving medications [16].{Figure 3}

CyPass

CyPass ([Figure 4]) is a biocompatible but nonresorbable polyimide tube 6.3 mm long with a 510-μm external diameter that is implanted ab-interno through a 1.5-mm corneal incision into the supraciliary space. The Duette trial evaluated the safety and effectiveness of CyPass microstent implantation for reducing IOP and medication use in primary open-angle glaucoma patients who had failed ≥1 class of topical medical therapy. Of 65 eyes, all achieved successful implantation. More than 80% of patients were controlled with the CyPass procedure. At the 12-month visit, 47 eyes were available for efficacy evaluation. In a paired analysis, IOP was reduced by a mean of 32% as compared with baseline to a mean value of 16.7±5.5 mmHg, and the mean number of IOP-lowering medications was 1.5±1.3, with an average reduction of 0.5 medication per patient [18].{Figure 4}

Aquesys Xen Glaucoma Implant

The Xen Implant is a hydrophilic tube composed of a porcine gelatin and cross-linked with glutaraldehyde. It decreases IOP by creating an outflow pathway from the anterior chamber to the subconjunctival space through which the aqueous humor can flow [19]. A pilot study published in 2015 on cataract surgery combined with a Xen 63 (63 nm lumen) or Xen 140 (140 nm lumen) showed a reduction of IOP from 22.4±4.2 to 15.4±3.0 mmHg at 12 months postoperatively (P=0.0001). The number of medication classes reduced from 2.5±1.4 to 0.9±1.0 [20].

The Hydrus microstent

Hydrus ([Figure 5]) is a new Schlemm’s canal scaffold with three posterior windows. It can be inserted through a small corneal incision and can be used in combination with phacoemulsification. Clinical results were published by Pfeiffer et al. [18] where 100 eyes were randomized to cataract surgery alone or cataract surgery plus Hydrus. At 24 months the proportion of patients using no hypotensive medications was significantly higher in the Hydrus plus cataract surgery group (73 vs. 38%). The primary endpoint of a 20% reduction in washed-out diurnal IOP compared with baseline was achieved in a significantly higher proportion of Hydrus patients than with cataract surgery alone (80 vs. 46). The washed-out diurnal IOP at 24 months was also significantly lower in the Hydrus patients (16.9±3.3 vs. 19.2±4.7 mmHg) [21].{Figure 5}

Trabectome

The Trabectome device is FDA cleared in the USA, and has regulatory approval in many countries worldwide for the treatment of adult and juvenile glaucoma. The device is a microelectro handpiece with irrigation and aspiration components, designed to ablate the trabecular meshwork and inner wall of Schlemm’s canal [17]. Francis published a prospective, nonrandomized, controlled trial, comparing combined phacotrabectome with phacoemulsification alone. The mean preoperative IOP in the combined group was 22.2±5.9 mmHg, and an IOP decrease of 6.9 mmHg (28%) was achieved after 2 years. In the phacoemulsification group, the preoperative IOP was lower (16.2±4.2 mmHg) because no glaucoma patients were included. Not surprisingly, the IOP decrease was limited to 1.9 mmHg (11.7%) after 2 years. The difference in population is an important bias in this study and makes the comparison not meaningful [22].

 Conclusion



In conclusion, MIGS can provide a safer, easier, and an efficient alternative for penetrating glaucoma surgery in mild to moderate glaucoma cases and is even beneficial in more advanced cases in terms of reducing the number of needed medications. With continuous innovation and development more benefits are expected.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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