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

2 Step by Step Minimally Invasive Glaucoma Surgery

INTRODUCTION

Glaucoma is a complex disorder to treat. Increased intraocular pressure (IOP) accompanied with optic nerve damage requires a life long mandatory treatment to maintain IOP level at acceptable level with visual acuity preservance. Medical management of glaucoma is usually first line of defence which has its own side effects and complications on prolonged use. Second line of treatment is conventional glaucoma surgery – Trabeculectomy which has its own postoperative complications specially bleb leakage.

In last one decade intensive research work has been done in glaucoma surgery. When conventional methods fail patients can be well served by innovative new surgical techniques specially non-penetrating glaucoma surgery also known as minimally invasive glaucoma surgery. These new techniques clear the way for restored fluid passage through the eye. These infrastructure improvements are essentially extraocular techniques which has improved visual success rate with minimum postoperative complications.

CLASSIFICATION

Minimally invasive glaucoma surgery (MIGS) are broadly classified in following groups :

a.Surgical-based MIGS or NPGS.

b.Laser-based MIGS or NPGS.

c.Scleral expansion bands.

Here, I am giving broad outlines as the details are

described in different chapters of this book.

Minimally Invasive Glaucoma Surgery — A New Approach 3

Surgical Based MIGS

Surgical based MIGS have made tremendous strides in last one decade. It includes viscocanalostomy, deep sclerectomy, milling trabeculoplasty, sclerothalamotomy ab interno and deep sclero-canalostomy (DSC).

Viscocanalostomy

Viscocanalostomy introduced by Dr. Robert Stegmann (South Africa) in early nineties increases the aqueous outflow through different mechanism of action. It creates a bypass by which aqueous humor can reach Schlemm’s canal skipping the trabecular meshwork which is the site of the increased outflow resistance in OAG. Viscocanalostomy has several potential advantages over conventional trabeculectomy the major being the absence of external filtration thus independent of conjunctival and episcleral scarring. Postoperative management is comparatively easy with minimal complications. However, this technique is technically strong and requires a long learning curve.

Deep Sclerectomy

Deep sclerectomy is another non-penetrating glaucoma surgery which has offered excellent results. This techniques has been advocated with the implantation of a collagen drainage device. Dr. Andre Mermoud (Switzerland) has shown the excellent results of deep sclerectomy alone and very deep sclerectomy with collagen implant (VDSCI) which is relatively a new technique. It has been clinically documented that deep sclerectomy significantly lowers the complication rates of glaucoma surgery.

4 Step by Step Minimally Invasive Glaucoma Surgery

Milling Trabeculoplasty

Milling trabeculoplasty developed by Dr. Jorge L. Alio (Spain) is considered a variation of deep sclerectomy with more refining. This technique provides the opportunity to perform a non-penetrating glaucoma surgery with greater attention for the dissection of the deep scleral flap or the deroofing of the Schlemm’s canal with the additional advantage that is being much faster. Certainly milling trabeculoplasty is an evolving technique for sclapel free NPGS. It is a promising technique specially for surgical management of POAG.

Sclerothalamotomy (STT)

Sclerothalamotomy ab interno is a new NPGS technique developed by Dr. Bojan Pajic (Switzerland). STT ab interno circumvents the trabecular meshwork resistance by creating a drainage canal in the sclera but the site of perforation is reached from inside and four sclerectomy sites are created using a special high frequency diathermy probe. STT is certainly a promising technique which ensures an efficacy and longevity of filtration.

Deep Sclerocanalostomy (DSC)

Deep sclerocanalostomy technique has been shown by Dr. Jerome Bovet (Switzerland). This combined new technique of NPGS is all connected with dissection or injection of the Schlemm canal. DSC allows a synthesis of the three main surgical techniques for non-penetrative Filter surgery. This reduces the risks of each while increasing the long-term chances of such in term of IOP control.

Minimally Invasive Glaucoma Surgery — A New Approach 5

Laser-Based MIGS

Besides the conventional laser techniques in glaucoma management, a number of new techniques are on the horizon with better IOP control and visual acuity management. Research ophthalmologists have shown new techniques with the use of Excimer Laser, Infrared Laser, CO2, Laser and Selective Laser Trabeculoplasty (SLT).

Excimer Laser Trabeculotomy

Excimer laser trabeculotomy ab interno (ELT) developed by Jens Funk (Germany) is a minimally invasive procedure that uses an excimer laser to ablate pores in the trabecular meshwork of patients with open angle glaucoma. As this procedure uses photoablation, no thermal effect is generated thus helps in thermal necrosis and scar formation potentially allowing a persistent effect over the years. ELT is certainly effective as monotherapy. Prof. Khristo Takhchidi (Russia) has designed a special excimer laser unit with 193 nm wavelength for glaucoma surgery. This new technique of NPGS that uses the excimer laser can reduce the risk of perforating the trabeculodescemetic membrane. With this technique the ablation is precise and homogenous.

Titanium Sapphire Laser Trabeculoplasty

Dr. Gabriel Simon (Spain) has evolved a new technique of titanium Sapphire Laser Trabeculoplasty (TiSaLT) using infra red laser. In this techniques laser energy targets and is absorbed by pigment inciting shock waves through the tissue ablating the tissue and unclogging blocked passage ways. This procedure causes minimal thermal damage and can be repeated.

6 Step by Step Minimally Invasive Glaucoma Surgery

Non-penetrating Glaucoma Surgery with the CO2 Laser

Dr. Ehud Assia (Israel) has shown a new technique of nonpenetrating glaucoma surgery with the CO2 laser. The clinical studies have shown that CO2 laser can effectively ablate the dry tissue without tissue perforation. In this procedure deep ablation down to the trabecular meshwork and Descemet’s membrane leaving a microthin wall 30u-50u thick with no perforation. This promising procedure enables accurate dissection of the scleral wall and unroofing of the Schlemm’s canal without penetration into the anterior chamber.

Selective Laser Trabeculoplasty

Selective laser trabeculoplasty (SLT) is another promising MIGS technique Dr. Mark. A Latina (USA) has pioneered this technique. In this procedure we can selectively treat the trabecular meshwork. With an Nd : YAG laser without creating a thermal burn. This procedure has been developed as an alternative to argon laser trabeculoplasty (ALT). In SLT ophthalmic surgeon selectively target pigmented trabecular meshwork cells instead of complete photocoagulation of the trabecular meshwork which is not necessary. SLT is certainly a better procedure with minimal side effects with good efficacy at lowering of IOP over a longer period.

Scleral Expansion Bridge (SEB)

Scleral expansion bridge (SEB) best known for their use in presbyopia has been recently shown to be useful in glaucoma management. The cornerstone behind use of SEBs is the Schachar theory of accommodation. This procedure is in early stages of development with essential

Minimally Invasive Glaucoma Surgery — A New Approach 7

principle of increasing the effective working distance of the lens by expanding the sclera which shall reverse presbyopia and increase the tension of the longitudinal muscle improve aqueous outflow and thus reduces intraocular tension. The scleral expansion band offers a new potentially reversible, safe surgical alternative to the management of ocular hypertension and primary open angle glaucoma.

By these state of Art MIGS techniques, in near future we can indeed personalize an operation for every given glaucoma patient with maximal visual acuity preservance, effective IOP control and minimum complications. Certainly glaucoma customization holds great future.

10 Step by Step Minimally Invasive Glaucoma Surgery

INTRODUCTION

Meyer Schwickerath reported for the first time the use of Xenon arc photocoagulator in cracking a hole in the iris.1 But the heat produced by xenon led to corneal and lenticular damage.1,2 Ruby laser was tried for some time without much success.3 The first successful laser iridotomy by argon laser was reported in 1970s.4-7 In 1980 the laser iridotomy replaced the surgical iridotomy. Later Nd:YAG laser was found more successful for this procedure.8-10 It is now most commonly applied laser for iridotomy.

INDICATIONS

•Acute/subacute angle closure glaucoma with symptoms

•Chronic congestive glaucoma with anterior synechiae

•Occludable angles with positive provocative tests

•Occludable angle with signs of previous attack/ critically narrrow angle

•Fellow eye

•Iris bombe

•Subluxated or luxated lens with intact vitreous face

•Phacomorphic glaucoma with pupillary block mechanism

•Aphakic/pseudophakic pupillary block

•Nanophthalmos

•Incomplete surgical iridectomy

•Mixed mechanism glaucoma if filtering surgery is not required

•Aqueous miss direction syndrome

•Phakic IOLs

•Plateau iris syndrome

•Pigmentary glaucoma

•To deepen narrow angle before laser trabeculoplasty

YAG Laser Iridotomy 11

CONTRAINDICATIONS

•Opaque or cloudy cornea

•Widely dilated pupil

•Flat anterior chamber with iridocorneal touch

•Active inflammation

•Rubeosis irides

ABRAHAM CONTACT LENS

Abraham contact lens is most commonly used lens for performing this procedure.11 It has a 66 planoconvex button bounded in the front surface of the lens. When laser beam falls on this lens its size is reduced to half of the original size on the iris and doubles the original size on cornea. This increases the power density on the iris and decreases power density to one-fourth on cornea. This helps immensely during the argon laser iridotomy. Same lens is very useful for YAG laser iridotomy also. A high magnification up to 40X should be used on slit-lamp for performing this procedure (Fig. 2.1).

Contact lens helps in the following ways:

1.The lids remain separated.

2.Chances of corneal epithelial burns are reduced as the lens absorbs heat energy by acting as a heat sink.

3.The eye movements can be controlled by the lens.

PREOPERATIVE PREPARATION

Pilocarpine eye drops are instilled preoperatively. It stretches the iris, which thins the iris stroma and also facilitates in the penetration of laser beam because cutting a well-stretched thin paper is easier than cutting a loose paper.