Ординатура / Офтальмология / Английские материалы / Step by Step Minimally Invasive Glaucoma Surgery_Garg, Melamed, Bovet, Pajic, Carassa, Dada_2006

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Laser parameters: Energy of 40-100 mJ, Frequency of 1-10 Hz, spot size 500 microm and 1 mm (divergent beam).

Technique

After creating a superficial scleral flap (4.0 × 4.0 mm); a deep scleral ablation (3.0 × 3.0 mm) is performed with the pulsed Er:YAG laser to remove 220±40 microns thick deep scleral tissue. Schlemm’s canal is removed, and the cornea is dissected to Descemet’s membrane until aqueous humor percolates. This is followed by a water tight closure of scleral flap and conjunctiva.

Study by Verges C et al showed a decrease in mean IOP from 28.3± 6.1 mmHg preoperatively to 16.3±4.2 mm Hg at 3 months, and 15.3±2.7 mm Hg at 15 months post-operatively. There were no significant complications. The success rate (IOP < or =18 mm Hg without medication) was 93.47 percent at 1 month and 84.78 percent at 15 months.

Deep sclerectomy using the Er:YAG laser may be considered as a safe and effective in eyes with POAG, with significantly lower complications compared to trabeculectomy. Studies with a larger sample size and longer follow-up are needed to establish its efficacy.

ANTERIOR HYALOIDOTOMY

In eyes with aphakic and pseudophakic malignant glaucoma, Nd:YAG laser rupture of the anterior hyaloid phase directly, brings a dramatic cure due to release of the trapped aqueous. This procedure results in immediate deepening of the anterior chamber and relieves acute pain and provides sudden symptomatic relief to the patient.

This procedure requires careful handling and should be done by experience laser surgeons only. The trick is to go deep and try and break the vitreous phase from behind

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forward using 1-2mj of energy since chamber is very shallow therefore, chances of corneal damage are very high. However, even if the endothelium gets damaged at one place, we should try it at other place since this is much more convenient then going in for a vitrectomy which is a more difficult affair.

LYSIS OF VITREOUS STRAND IN THE CATARACT WOUND

It is well known that any strand of vitreous incarcerated in the wound can result in complications. The strand forms a route from where infection can travel into the eye. Also when a person goes from bright light to dim light the pupil size changes and this causes a pull on the strand. This can result in a retinal detachment.

Lysis of such a strand can easily be carried out using the energy of 1-1.5 mJ of Nd:YAG spot focused directly on the strand to lyse it (Fig. 6.3).

Fig. 6.3: Vitreous strand going to the wound site which can be cut with YAG laser

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BIBLIOGRAPHY

Neodymium YAG Laser Iridolenticular Synechiolysis

1.Fankhauser F, Kwasniewska S, et al. Neodymium Q-Switched YAG laser lysis of irisens synechiae. Ophthalmology 1985;92:790-92.

2.James WA Jr, Roeth Jr, et al. Argon Laser Photomydriasis. Am J Ophthalmol 1976;81:6270.

3.Kumar H, Sony P. A new technique for Nd:YAG iridolenticular synechiolysis (In press) Ophthalmic Surgery Lasers and imaging.

4.L’Esperance FA Jr, James WA Jr. Argon Laser Photocoagulation of iris abnormalities. Trans Am Acad Ophthalmol Otolaryngol 1975;79:321-39.

5.Obstbaum SA, Barasch KR, Galin MA, et al. Laser Photomydriasis in pseudophakic pupillary block. Am Intraocul Implant Soc J 1981;7:28-30.

Laser Suturolysis

1.Akova YA, Dursun D, Aydin P, Akbatur H, Duman S. Management of hypotony maculopathy and a large filtering bleb after trabeculectomy with mitomycin C: Success with argon laser therapy. Ophthalmic Surg Lasers 2000;31:491-94.

2.Day S, Uveal Tract, Taylor D (Eds): Paediatric Ophthalmology, Boston, Blackwell Scientific Publications. 1990; 276-98.

3.Hara T, Hara T. Deep sclerectomy with Nd:YAG laser trabeculotomy ab-interno: Two-stage procedure. Ophthalmic Surg 1988;19:101-06.

4.Liebmann MF. Doide laser suturolysis following trabeculectomy with mitomycin C. Arch Ophthalmol 1996;114:364.

5.Liu Y, Yang W, Li S. Neodymium: YAG laser therapy in aphakic pupillary block glaucoma and aphakic malignant

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INTRODUCTION

Open-angle glaucoma is the second leading cause of blindness in the world.1,2 Glaucomatous optic neuropathy (GON) is characterized by a loss of retinal ganglion cells and their axons, associated by a tissue remodeling both of the optic nerve head (ONH) and the retina leading to the characteristic ONH cupping. Many glaucoma patients present with elevated intraocular pressure (IOP), most often caused by reduced outflow capacity of aqueous humor. The outflow resistance is localized at the level of the trabecular meshwork, or, more precisely, at the juxtacanalicular meshwork and the inner wall of Schlemm’s canal.

Data from several major studies available on this topic, such as the OHTS,3 EGPS,4 CIGTS,5 EMGT6 and the AGIS7 suggest that both development and progression of glaucomatous damage can be mitigated by lowering IOP. Moreover, the NTGS has clearly demonstrated that lowering of the IOP can slow down the progression of the disease even in patients with normal-tension glaucoma (NTG).8

Topical IOP-lowering medication is often the first-line therapy for glaucoma, even though it harbors potential disadvantages such as local and systemic side effects, tachyphylaxis, and, probably most important, compliance problems. Friedman and co-workers recently examined a cohort of 1712 glaucoma suspects and 3623 diagnosed glaucoma patients and found that a large proportion of individuals requiring treatment are falling out of care and are being monitored at rates lower than expected from recommendations of published guidelines because they do not come for follow-up visits and do not ask for a refill of their prescribed glaucoma medication.9 Apart from this disappointing information, it has to be added that local

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medication is also not always sufficient if a very low individual target IOP is required. The CNTGS has shown that a 30 percent reduction in IOP is often only reached by surgical intervention. Another point is that the costs of medical control over a lifetime might also be prohibitive for some glaucoma patients.

Glaucoma surgery includes nowadays a number of potential therapies all aiming either to increase the outflow of aqueous humor or to decrease its production. Argon laser trabeculoplasty (ALT), for example, increases the conventional outflow through the trabecular meshwork and is easy to perform. The procedure has, however, a limited efficacy and duration of effect, as ALT produces thermal effects with coagulation of the trabecular meshwork. A successfully performed trabeculectomy shows a much better efficacy, however, a number of potential complications such as hypotony, suprachoroidal hemorrhage, and bleb failure exist. Patients often find the conjunctival bleb uncomfortable, moreover it can become thin and avascular, thus increasing the risk of bleb leaks, blebitis and endophthalmitis. In case of surgery failure, repeated operations can become necessary, however, the chances for success decrease as both sclera and conjunctiva are subjected to repeated surgical insults. Glaucoma drainage devices (tube shunts) have a relatively high success rate in experienced hands, however the patients are at greater risk for complications.

In 1996, Vogel and co-workers reported a new IOPlowering operation technique: Using an excimer laser, they managed to ablate trabecular meshwork tissue with minimal thermal effects and necrosis, thus resulting in only minimal scar formation. The authors assumed that it should be possible to create an open connection between the anterior chamber and Schlemm’s canal. The group treated

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6 patients with open-angle glaucoma. In 4 cases intraocular pressure was reduced by 11 mmHg over a follow-up time of 5 months. In 2 cases IOP rose by 2 mmHg in spite of medication.10

ERBIUM-YAG GONIOTOMY

Also in 1996, an endoscopic erbium-YAG laser system allowing effects on trabecular tissue comparable to those produced by a 308 nm excimer laser became available. In the following years we could demonstrate a reduction in IOP with this laser system that was comparable to the excimer laser.11 We performed combined cataract surgery and erbium-YAG goniotomy in 24 eyes and compared the IOP results to a control group that underwent cataract surgery. In the combined surgery group, mean IOP dropped from 21.8 to 15.5 mmHg. IOP regulation was successful in 88 percent of these cases. In eyes that underwent only cataract surgery, the IOP reduction was less pronounced (mean IOP preoperative 20.0, postoperative 17.4, success rate 35%). The follow-up in this preliminary study was 4 months (mean 6.5 months, max. 12 months).12

In another non-randominized clinical trial with a 3 years follow-up, we treated 20 eyes of 20 patients suffering from both glaucoma and cataract with combined phacoemulsification and erbium-YAG goniotomy and compared them to a control group that underwent cataract surgery. Main outcome variables were IOP, visual acuity, and number of antiglaucomatous drugs 1 year after surgery. The mean IOP dropped by 30 percent (23.5 to 16.3 mmHg) after 12 months in the laser-treated group and by 9 percent (19.8 to 18.1 mmHg) in the control group. After 3 years, the mean IOP in the laser group was 15.0 mmHg. The mean

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number of antiglaucomatous drugs needed decreased significantly from 1.6 to 0.5 in the laser group and from 1.0 to 0.8 in the control group. Anterior chamber hemorrhage occurred in 12 eyes after laser treatment and resolved within 72 hours in all but 1 patient who was on warfarin sodium therapy. There were no cases of hypotony in either group.13

We also aimed to compare the efficacy of erbium:YAG goniotomy to trabeculectomy, with both methods as adjuncts to cataract surgery. Fifty-nine eyes of 59 glaucoma patients with coexistent cataract underwent combined phacoemulsification and erbium:YAG goniotomy. We compared this prospective treatment arm to a retrospective inclusion-matched control group treated by trabeculectomy and cataract surgery in a single procedure. Primary endpoints were IOP, number of antiglaucomatous drugs, postoperative complications, hospitalization time and visual acuity 1 year after surgery. In the laser-treated group, the mean IOP dropped by 30 percent from 23.4 to 16.3 mmHg after 12 months. Without reoperation, treatment was successful in 71 percent of these eyes. In the control group, the IOP decreased by 33.5 percent from 22.7 to 15.1 mmHg. The success rate without reoperation was 46 percent. The number of antiglaucomatous drugs needed decreased from 1.48 to 0.48 in the laser-treated group and from 2.0 to 0.39 in the controls. Postoperative complications were more frequent in the control group, and postoperative visual acuity was as well. Hospitalization time was shorter in the laser group. It can be concluded from these data that the IOP-lowering effect of combined erbium:YAG goniotomy and cataract surgery is comparable to that of combined trabeculectomy and cataract surgery. Moreover, due to fewer postoperative complications, erbium:YAG goniotomy seems to be superior to standard fistulation