effectively brought under control with the use of a topical medication. In most cases, IOP-reducing therapy can be gradually withdrawn after 3 weeks post surgery. The moderate tissue swelling round the thalamus observed in vitro could be the reason for transient postoperative IOP peaks. Preliminary histological investigations of two post mortem human eyes following sclerothalamotomy ab interno did not indicate signs of indirect necrosis in cell layers adjacent to the thalamus formed by high-frequency diathermy. It is as yet not clear if the inner surface of the thalamus will be covered by endothelial cells of corneal or trabecular origin, and whether the thalamus and its function will remain intact on a much longer timescale.

Advantages of sclerothalamotomy ab interno include the comparative simplicity and quickness of the surgical procedure itself. The technique also avoids stimulation of episcleral and conjunctival tissues as in trabeculectomy and conventional nonpenetrating surgery. In the example presented in this section, diathermy was used to create four thalami and this corresponds to a resorption surface area of 2.4mm2. The number of thalami chosen was arbitrary and seemed to provide a sufÞcient long-term decrease of IOP as a low rate of postoperative complications. There is potential for a further IOP drop if six applications are made. Further investigations will be performed to support this hypothesis. Further studies will be conducted to compare sclerothalamotomy ab interno, trabeculectomy, and deep sclerectomy for the surgical treatment of primary open-angle glaucoma.

References

1.Burian HM (1960) A case of MarfanÕs syndrome with bilateral glaucoma. With a description of new type of operation for developmental glaucoma (trabeculotomy ab externo). Am J Ophthalmol 50:1187Ð1192

2.Fronimopoulos J, Lambrou N, Pelekis N et al (1970) ElliotÕs trepanation with scleral cover (procedure for protecting the Þstula in ElliotÕs trepanation with a lamellar scleral cover). Klein Monatsbl Augenheilkd 156:1Ð8

3.Starita RJ, Fellmann RL, Spaeth GL et al (1985) Shortund long-term effects of postoperative corticosteroids on trabeculectomy. Ophthalmology 92:938Ð946

4.Schwartz AL, Anderson DR (1974) Trabecular surgery. Arch Ophthalmol 92:134Ð138

5.Grant WM (1963) Experimental aqueous perfusion in enucleated human eyes. Arch Ophthalmol 69:738Ð801

6.Johnson DH, Johnson M (2001) How does nonpenetrating glaucoma surgery work? Aqueous outßow resistance and glaucoma surgery. J Glaucoma 10:55Ð67

7.Schuman JS, Chang W, Wang N et al (1999) Excimer laser effects on outßow facility and outßow pathway morphology. Invest Ophthalmol Vis Sci 40:1676Ð1680

8.Fjodorov SN, Loffe DI, Ronkina TI (1984) Deep sclerotomy: technique and mechanism of new glaucomatous procedure. Glaucoma 6:281Ð283

9.Stegmann R, Pienaar A, Miller D (1999) Viscocanalostomy for open-angle glaucoma in black African patients. J Cataract Refract Surg 25:316Ð322

10.Benedikt O, Hiti H (1976) Die Ziliarkšrperfreilegung. Eine neue Operationsmethode zur Behandlung des irreversiblen Winkelblockglaukoms und des Aphakieglaukoms. Klein Monatsbl Augenheilkd 169:711Ð716

11.Pallas G, Pajic B (2000) Die Sklerothalamektomie (STE): stabile postoperative Augendruckregulierung beim Offenwinkelund KapselhŠutchenglaukom. Klein Monatsbl Augenheilkd 216:256Ð260

12.Spiegel D, Kobuch K (2002) Trabecular meshwork bypass tube shunt: initial case series. Br J Ophthalmol 86:1228Ð1231

13.Schwenn O, Dick B, Pfeiffer N (1998) Trabekulotomie, tiefe Sklerektomie und Viskokanalostomie. Ophthalmologe 95: 835Ð843

14.Akafo SK, Goulstine DB (1990) Long-term post trabeculectomy intraocular pressure. Acta Ophthalmologica 70: 312Ð316

15.Cairns JE (1968) Trabeculectomy. Preliminary report of a new method. Am J Ophthalmol 66:673Ð679

16.Mermoud A, Salmon JF, Barron A et al (1993) Surgical management of posttraumatic angle recession glaucoma. Ophthalmology 100:634Ð642

17.Mills KB (1981) Trabeculectomy: a retrospective long-term follow-up of 444 cases. Br J Ophthalmol 65:790Ð795

18.Molteno ACB, Bosma NJ et al (1999) Otago glaucoma surgery outcome study. Ophthalmology 106:1742Ð1750

19.Morell AJ, Searle AET, OÕNeill EC (1992) Trabeculectomy as an introduction to intraocular surgery in an ophthalmic training program. Ophthalmic Surg 23:38Ð39

20.Popovic V, Sjšstrand J (1991) Long-term outcome following trabeculectomy: visual Þeld survival. Acta Ophthalmologica 69:305Ð309

21.Roth SM, Spaeth G, Starita RJ et al (1991) The effects of postoperative corticosteroids on trabeculotomy and the clinical course of glaucoma: Þve-year follow-up study. Ophthalmic Surg 22:724Ð729

22.Saiz A, Alcuaz A, Maquet JA et al (1990) Pressure-curve variations after trabeculectomy for chronic primary openangle glaucoma. Ophthalmic Surg 21:799Ð801

23.Tanihara H (1993) Surgical effects of trabeculectomy ab externo on adult eyes with primary open angle glaucoma and pseudoexfoliation syndrome. Arch Ophthalmol 111: 1653Ð1661

24.Vernon SA, Spencer AF (1995) Intraocular pressure control following microtrabeculectomy. Eye 9:299Ð303

25.Watson PG, Barnett F (1975) Effectiveness of trabeculectomy in glaucoma. Am J Ophthalmol 74:831Ð845

26.Watson PG (1987) When to operate an open angle glaucoma. Eye 1:51Ð54

27.Demailly P, Lavat P, Kretz G et al (1997) Non-penetrating deep sclerectomy with or without collagen device in primary open-angle glaucoma: middle-term retrospective study. Int Ophthalmol 20:131Ð140

28.Mermoud A, Schnyder CC, Sickenberg M et al (1999) Comparison of deep sclerotomy with collagen implanta and trabeculectomy in open-angle glaucoma. J Cataract Refract Surg 25:323Ð331

29.Sanchez E, Schnyder CC, Sickenberg M et al (1997) Deep sclerectomy: results with and without collagen implant. Int Ophthalmol 20:157Ð162

30.Pajic B, Pallas G, Gerding H et al (2006) A novel technique of ab interno glaucoma surgery: follow-up results after 24 months. Graefes Arch Clin Exp Ophthalmol 244:22Ð27

31.Edmunds B, Thompson JR, Salmon JF et al (2002) The national survey of trabeculectomy. III. Early and late complications. Eye 16:297Ð303

32.El Sayyad F, Helal M, El-Kholify H et al (2000) Nonpenetrating deep sclerectomy versus trabeculectomy in bilateral primary open-angel glaucoma. Ophthalmology 107: 1671Ð1674

33.Konstans AGP, Jay JL, Marshall GE et al (1993) Prevalence, diagnostic feature, and response to trabeculectomy in exfoliation glaucoma. Ophthalmology 100: 619Ð627

8.4Glaukos® iStent® Trabecular Micro-Bypass Implant

8.4.1Introduction to Glaucoma Surgery with a Micro-Bypass Implant

In any Þeld of medicine, the ideal surgery combines high effectiveness with a low rate of intraoperative and postoperative complications. In glaucoma, as in other subspecialties of ophthalmology, the search for new surgical techniques is never-ending. Given the impossibility of treating the optic nerve directly, the most commonly used surgical options try to establish communication between the anterior chamber and the subconjunctival space, either by removing part of the trabecular meshwork and thus decreasing resistance to the passage of the aqueous humor, or by means of drainage tubes that conduct the aqueous humor toward extraocular subconjunctival reservoirs. Although they achieve a high level of hypotensive effectiveness, these forms of surgery are not exempt from potential complications and are highly dependent on the inßammatory and healing response of the patient [1]. The use of antimetabolites to regulate this healing response is also linked to a higher rate of complications [2Ð7].

The Glaukos trabecular stent attempts to restore the physiology of the conventional drainage path of the aqueous humor through the trabecular meshwork and the SchlemmÕs canal, toward the collecting channels and the episcleral veins [1]. Grant demonstrated that the greatest resistance to drainage of the aqueous humor in glaucoma patients is located at the level of the trabecular meshwork and, more speciÞcally, at the inner wall of the SchlemmÕs canal [1]. Once implanted, the trabecular stent allows direct communication between the anterior chamber and the SchlemmÕs canal, thus decreasing the resistance of the juxtacanalicular tissue to drainage of the aqueous humor. Bahler et al. demonstrated in cadaver eyes that the implantation of a trabecular stent increased the aqueous humor outßow facility by 84%, producing a decrease in IOP of 9 mmHg (21.4

± 3.8 to 12.4 ± 4.2 mmHg) [8].

The Glaukos¨ iStent¨ trabecular micro-bypass is made of titanium and coated with a layer of heparin (Duraßo¨ powder). It is L-shaped and measures 1 × 0.4 mm, with an external diameter of 180 mm designed to Þt in the lumen of the SchlemmÕs canal (Fig. 8.49). The distal portion of the stent is bevelled and sharpened

28.Mermoud A, Schnyder CC, Sickenberg M et al (1999) Comparison of deep sclerotomy with collagen implanta and trabeculectomy in open-angle glaucoma. J Cataract Refract Surg 25:323Ð331

29.Sanchez E, Schnyder CC, Sickenberg M et al (1997) Deep sclerectomy: results with and without collagen implant. Int Ophthalmol 20:157Ð162

30.Pajic B, Pallas G, Gerding H et al (2006) A novel technique of ab interno glaucoma surgery: follow-up results after 24 months. Graefes Arch Clin Exp Ophthalmol 244:22Ð27

31.Edmunds B, Thompson JR, Salmon JF et al (2002) The national survey of trabeculectomy. III. Early and late complications. Eye 16:297Ð303

32.El Sayyad F, Helal M, El-Kholify H et al (2000) Nonpenetrating deep sclerectomy versus trabeculectomy in bilateral primary open-angel glaucoma. Ophthalmology 107: 1671Ð1674

33.Konstans AGP, Jay JL, Marshall GE et al (1993) Prevalence, diagnostic feature, and response to trabeculectomy in exfoliation glaucoma. Ophthalmology 100: 619Ð627

8.4Glaukos® iStent® Trabecular Micro-Bypass Implant

8.4.1Introduction to Glaucoma Surgery with a Micro-Bypass Implant

In any Þeld of medicine, the ideal surgery combines high effectiveness with a low rate of intraoperative and postoperative complications. In glaucoma, as in other subspecialties of ophthalmology, the search for new surgical techniques is never-ending. Given the impossibility of treating the optic nerve directly, the most commonly used surgical options try to establish communication between the anterior chamber and the subconjunctival space, either by removing part of the trabecular meshwork and thus decreasing resistance to the passage of the aqueous humor, or by means of drainage tubes that conduct the aqueous humor toward extraocular subconjunctival reservoirs. Although they achieve a high level of hypotensive effectiveness, these forms of surgery are not exempt from potential complications and are highly dependent on the inßammatory and healing response of the patient [1]. The use of antimetabolites to regulate this healing response is also linked to a higher rate of complications [2Ð7].

The Glaukos trabecular stent attempts to restore the physiology of the conventional drainage path of the aqueous humor through the trabecular meshwork and the SchlemmÕs canal, toward the collecting channels and the episcleral veins [1]. Grant demonstrated that the greatest resistance to drainage of the aqueous humor in glaucoma patients is located at the level of the trabecular meshwork and, more speciÞcally, at the inner wall of the SchlemmÕs canal [1]. Once implanted, the trabecular stent allows direct communication between the anterior chamber and the SchlemmÕs canal, thus decreasing the resistance of the juxtacanalicular tissue to drainage of the aqueous humor. Bahler et al. demonstrated in cadaver eyes that the implantation of a trabecular stent increased the aqueous humor outßow facility by 84%, producing a decrease in IOP of 9 mmHg (21.4

± 3.8 to 12.4 ± 4.2 mmHg) [8].

The Glaukos¨ iStent¨ trabecular micro-bypass is made of titanium and coated with a layer of heparin (Duraßo¨ powder). It is L-shaped and measures 1 × 0.4 mm, with an external diameter of 180 mm designed to Þt in the lumen of the SchlemmÕs canal (Fig. 8.49). The distal portion of the stent is bevelled and sharpened

to facilitate penetration into the tissue of the trabecular meshwork. The external surface features three retention barbs that impede the movement of the stent once it has been implanted. The implant weighs approximately 0.1 mg. It is delivered preloaded on an insertion device and it is implanted at the level of the trabecular meshwork with the aid of a SwanÐJacob-type goniolens (Fig. 8.50) [9, 10].

8.4.1.1Indications for Implantation of Glaukos® iStent® Micro-Bypass Implant

Type of Glaucoma

The indications for the trabecular stent are reduced to cases with primary open-angle, pigmentary, or pseudoexfoliative glaucoma. In secondary open-angle glaucoma, this type of surgery may be indicated as long as the SchlemmÕs canal and collecting channels are found to be undamaged. In cases of glaucoma due to elevation of the episcleral venous pressure, the implantation of the trabecular stent is contraindicated.

The extraction of the lens in combination surgery can widen the angle and enable the surgery to be performed in cases with angles that are not very open, in which the trabecular meshwork was not initially accessible.

Stage of Glaucoma

The ideal candidate for this type of surgery is a patient with early or moderate stage glaucoma. Patients with advanced glaucoma or those who require very low target pressures to obtain stabilization of their disease are not suitable candidates for this type of surgery, given that the episcleral venous pressure restricts the pressure decrease obtained with the trabecular stent.

Combined Surgery

The coexistence of a surgical stage cataract means that combined surgery can be performed [11Ð13]. The implantation of the trabecular stent does not increase the surgery time excessively, nor does it modify the