Techniques and outcomes of minimally invasive trabecular ablation and bypass surgery

Minimally invasive glaucoma surgeries (MIGS) can improve the conventional, pressure-dependent outflow by bypassing or ablating the trabecular meshwork (TM), or creating alternative drainage routes into the suprachoroidal or subconjunctival space. They have a highly favourable risk profile compared to penetrating surgeries, and lower intraocular pressure with variable efficacy that may depend on the extent of outflow segments accessed. Since they are highly standardised procedures that use clear corneal incisions, they can elegantly be combined with cataract and refractive procedures to improve vision in the same session. There is a growing need for surgeons to become proficient in MIGS to address the increasing prevalence of glaucoma and cataracts in a well-informed, aging population. Techniques of visualisation and instrumentation in an anatomically highly confined space with semitransparent tissues are fundamentally different from other anterior segment surgeries, and present even experienced surgeons with a substantial learning curve. Here, we provide practical tips, and review techniques and outcomes of TM bypass and ablation MIGS.

CO2, excimer and erbium:YAG laser in deep sclerectomy

PURPOSE

Deep sclerectomy is a non-penetrating filtering procedure that is not generally accepted, as tissue dissection is difficult and varying success rates have been reported. The purpose of the present study was to compare the use of CO2, excimer and erbium:YAG lasers in dissection of the deep corneoscleral lamella.

METHODS

In enucleated porcine eyes a superficial lamellar scleral flap of 5 x 5 mm was surgically dissected. The deep lamella was removed using a pulsed erbium:YAG, a CO2 or an excimer laser (10 eyes/group). All eyes were analysed histologically and 3 in each group by scanning electron microscopy (SEM).

RESULTS

It is feasible to ablate the deep corneoscleral lamella with the CO2, excimer and erbium:YAG lasers without perforating the anterior chamber. The following histology and SEM showed a smoother surface after dissection with the CO2 and excimer lasers compared to the erbium:YAG laser. There was no thermal damage after excimer laser treatment, compared to a damage zone of 10-30 mum using the erbium laser and one of 70-100 microm with the CO2 laser.

CONCLUSIONS

Excimer,erbium:YAG and CO2 lasers allow the microsurgical dissection of the deep lamella. The excimer and CO2 lasers achieve a more regular and smoother tissue surface. The excimer laser has the advantage to dissect without thermal tissue damage.

Efficacy and safety of ab interno excimer laser trabeculotomy in primary open-angle glaucoma: two years of follow-up

Ab interno trabeculotomy was performed using the recently developed XeCl excimer laser in 21 eyes of 21 patients with primary open-angle glaucoma refractory to medical therapy. The patients were followed at the Eye Department of S. Antonio Hospital in Padova, for an average of 25.3 +/- 1.3 months. Intraocular pressure (IOP), visual acuity and ocular complications were evaluated. The laser procedure was quick and relatively easy, with minimal manipulation of tissues; complications were clinically insignificant. At the last follow-up, a marked IOP-lowering effect compared to baseline was observed (from 24.8 +/- 2.0 to 16.9 +/- 2.1 mm Hg; -31.8%, p < 0.0001). Nineteen patients (90.5%) had an IOP lowering of 20% or more; however, 8 of these eyes (38.1%) required additional IOP-lowering medical therapy. The procedure failed in 2 cases (9.5%) despite additional therapy. In conclusion ab interno excimer laser trabeculotomy seems effective to decrease IOP, serves to reduce the number of antiglaucoma medications and is relatively safe, proving to be a promising therapeutic option in glaucoma surgery.

Femtosecond laser photodisruption of human trabecular meshwork: an in vitro study

The goal of this in vitro study was to test the feasibility of using femtosecond (fsec) laser pulses to fistulize the human trabecular meshwork (TM), and to determine the minimum exposure time and energy dosage needed to create an ablation channel. Corneo-scleral rims were obtained from tissue used for penetrating keratoplasty. Four millimeter tissue strips hydrated in Optisol-GS were used to create partial thickness fistulas in the human TM by focusing a Ti:Sapphire laser beam (45 fsec, 1 kHz, 800 nm) with various pulse energies (7.2 and 14.4 microJ) and exposure times (0.25, 0.5, 1, and 2 sec) on the inner surface of the TM. Two-photon images of the lesions were obtained with a multiphoton microscope, using an ultrafast Ti:Sapphire light source. In addition, sections of fixed tissue were examined by light microscopy. Diameters and lengths of the lesions were determined from the hematoxylin and eosin (H&E) stained sections, and the collagen structure surrounding the lesion was evaluated from the two-photon images. All selected time points (except for 0.25 sec) and energies achieved the desired photodisruption of the TM. Incisions created with 0.5 sec/14.4 microJ irradiation appeared to be the most suitable because they were able to achieve consistent full thickness trabecular ablation. Incisions created at 1 sec /14.4 microJ/pulse and 2 sec/14.4 microJ/pulse were deeper than those at shorter time points with the same pulse energy. Longer exposure times and higher pulse energies were usually more variable and associated with deeper and larger incisions and slight collateral damage. Our results indicate that, with appropriate exposure time and pulse energy, fsec photodisruption can be employed to create lesions in the human TM without damaging the surrounding tissues. This study demonstrates that fsec laser treatments may have future potential for the surgical treatment of glaucoma.

Combined cataract and glaucoma surgery: endoscope-controlled erbium:YAG-laser goniotomy versus trabeculectomy

BACKGROUND

To compare endoscopic infrared laser trabecular ablation and trabeculectomy (both combined with cataract surgery) regarding intraocular pressure (IOP), visual acuity, anti-glaucomatous drugs and complications.

METHODS

Seventeen eyes of 14 patients [age 74.7+/-11.7 years (arithmetic mean +/- standard deviation)]-13 with primary open-angle glaucoma (POAG) and four with pseudoexfoliation glaucoma (PEXG)-underwent standard cataract surgery. After lens implantation, a probe (1.1 mm external diameter) with optic and laser fibres and an irrigation tube was introduced through the cataract incision. To perforate Schlemm's canal, 15-17 single pulses (16 mJ, 160 micros) were applied using a photo-ablative infrared laser (Er:YAG, lambda=2.94 microm). All eyes except one received antiglaucoma treatment. The control group treated with cataract surgery and trabeculectomy consisted of 17 eyes (13 POAG, four PEXG) of 15 patients (age 75.0+/-5.6 years), each eye received antiglaucoma treatment.

RESULTS

Mean follow-up was 3 years. The eyes treated with the endoscopic laser showed a mean preoperative IOP of 23.3+/-4.3 mmHg, which was reduced to 15.0+/-2.1 mmHg (mean IOP lowering 33.7%) after 3 years. Five eyes needed no medication for IOP-control after the procedure. Two eyes needed further surgery for IOP-control. In the control group, mean IOP was 24.5+/-2.6 mmHg in the beginning and 17.3+/-6.2 mmHg after 3 years, corresponding to a 33.3% lowering of IOP. Six eyes needed no medication, four eyes needed further surgery to lower IOP.

CONCLUSIONS

After 3 years follow-up of a small pilot group, combined endoscopic infrared laser surgery with cataract surgery seems to be a safe and effective way to lower IOP. It shows the same ability to lower IOP as combined cataract surgery with trabeculectomy. In addition, there are markedly less complications with the endoscope-controlled photo-ablative laser procedure.

Erbium: yttrium-aluminum-garnet laser induced vapor bubbles as a function of the quartz fiber tip geometry

BACKGROUND

The use of modern erbium: yttrium-aluminum-garnet (YAG) laser systems in opthalmic microsurgery requires a precise knowledge of the size and dynamics of the laser induced vapor bubbles. The aim of this work was to clarify the possibilities of controlling the vapor bubble shape and size by using an optimized fiber tip geometry for various ophthalmic applications with the erbium: YAG laser.

METHODS

The mid-infrared radiation of free-running erbium: YAG laser was coupled optically into means of different low OH(-) quartz fiber tips to investigate the vapor bubble formation in water by high-speed photography. The core diameter of four fiber tips ranged from 200 up to 940 microm. Fourteen fiber tips were polished at an angle graduated from 10 degrees to 70 degrees over the full core diameter (seven fiber tips) and over the half core diameter (seven fiber tips). Three fiber tips were produced to have a curvature at the distal end with curvature radii of 160, 230, and 420 microm.

RESULTS

The shape as well as the size of erbium: YAG laser induced vapor bubbles can be controlled systematically by using adequate fiber tip geometries. In detail, the used different angles and curvatures demonstrate that the propagation direction of the vapor bubbles can be estimated by optical modeling considering Snell's law and the Fresnel laws at a quartz-air boundary. Beside this, the size of a vapor bubble can be predetermined by choosing ideal fiber tip geometries to reduce or increase the radiant exposure at the distal end of the quartz fiber tip.

CONCLUSIONS

The good possibility of controlling the shape and size of vapor bubbles offers a wider range of new applications, especially in ophthalmic microsurgery such as erbium YAG laser vitrectomy.

Erbium: YAG laser trabecular ablation (LTA) in the surgical treatment of glaucoma

BACKGROUND AND OBJECTIVE

Laser trabecular ablation (LTA) aims to remove trabecular tissue and to open Schlemm's canal in order to improve outflow facility in glaucomatous eyes. The purpose of our study was to investigate the pressure-reducing effect of LTA in chronic open-angle glaucoma 1 year following laser surgery.

STUDY DESIGN/MATERIALS AND METHODS

Eleven eyes of 11 patients with chronic open-angle glaucoma were treated by circumscribed laser ablation of the trabecular meshwork. We used an Erbium:YAG laser (2.94 microm) with a quartz fiber contact endoprobe (320 microm core-diameter, 385 microm coating-diameter) applying 11-30 single neighbouring laser pulses (5-7 mJ) to the trabecular meshwork by an ab-interno approach. Laser procedure was gonioscopically visualized.

RESULTS

Mean maximum intraocular pressure (IOP) of all 11 patients before LTA was 36 mmHg and dropped down to 22 mmHg after a mean follow-up of 12 months following LTA; this represents an IOP decrease of 38% (P=0.008). The average number of medications per eye dropped from 2.8 to 1.5 per eye (P=0.021).

CONCLUSION

Although IOP lowering effect of Erbium:YAG laser trabecular ablation did not prove as effective as in filtering procedures, LTA might be a valuable alternative in glaucoma surgery especially in order to avoid conjunctival scarring and postoperative hypotony.

Ab interno infrared laser trabecular ablation: preliminary short-term results in patients with open-angle glaucoma

BACKGROUND

Outflow obstruction of trabecular drainage structures results in elevation of intraocular pressure (IOP) in various forms of chronic open-angle glaucoma. In vitro studies have shown that laser trabecular ablation (LTA) with opening of Schlemm's canal can be reproducibly performed by use of infrared lasers with minimal damage to collateral tissue structures.

METHODS

In order to investigate the clinical applicability and efficacy of ab interno contact laser photoablation of trabecular meshwork in the surgical treatment of human glaucoma, we conducted a pilot study using an erbium: YAG laser (2.94 microns) with a quartz fiber endoprobe (320 microns core diameter) applying 10-20 single laser pulses (5-7 mJ) to the trabecular meshwork.

RESULTS

Under goniocopic visualization trabecular tissue was photovaporized in eight patients with primary or secondary chronic open-angle glaucoma. Intraoperatively, moderate reflux bleeding occurred from laser-induced craters. No major intra- or postoperative complications occurred. Preoperative and postoperative gonioscopy of the treated area demonstrated successful removal of trabecular tissue. Mean IOP was reduced from 36.1 mmHg ot 21.3 mmHg at a limited follow-up of 3 months.

CONCLUSION

With modifications this technique may have clinical potential in the surgical management of glaucoma. Prospective long-term studies with more patients are warranted to evaluate the outcome of LTA.