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Advanced Glaucoma Surgery with a Focus on Schlemm’s Canal
Trabecular Micro-bypass (iStent) suggest that these procedures are safe, whether performed ab
The concept behind iStent is to bypass the trabecular meshwork and externo or ab interno. They are designed to obviate the need for a
to re-route aqueous from the anterior chamber into the Schlemm’s filtering bleb and all the problems inherent with transscleral filtration.
canal without disrupting the scleral surface. The iStent is a titanium Moreover, hypotony is virtually eliminated due to the intrinsic
L-shaped implant coated with heparin (see Figure 4). It is guided into resistance of the episcleral venous system.
Schlemm’s canal by means of a Swan-Jacobs lens and a special
inserter. The procedure is suitable for combined surgery as the same However, this is the other side of the same coin. Schlemm’s canal
temporal corneal incision is used as for cataract surgery. surgery is limited in its ability to lower IOP below 12mmHg and may
not be suitable for eyes in which a very low IOP goal is deemed
A multicentre study reported on 58 patients who underwent combined necessary. Canaloplasty and Trabectome may be more promising
iStenting and cataract surgery.
40
The IOP and the number of medications than the micro-bypass iStent, simply for the fact that they target a
was reduced from 21.7±3.9 to 17.4±2.9mmHg (p<0.001) and from larger area of diseased trabecular meshwork. Comparative,
1.6±0.8 to 0.4±0.6, respectively. In some smaller case studies, IOPs in randomised studies and long-term results are awaited to draw final
the mid-teens in iStent-alone procedures were achieved.
39
conclusions as all procedures remain subject to biological changes
and repair mechanisms over the years.
Potential complications of the iStent may include chronic
inflammation, clogging of the device’s lumen and poor function in In the near future, the significance of surgery in glaucoma therapy
the case of malposition in the canal. will be redefined and the time of intervention scrutinised owing to
the good safety profiles of the newer techniques. There will be a
Conclusions and Future Directions trend towards earlier intervention with Schlemm’s canal surgery. This
In open-angle glaucoma, the bulk of the pathologically increased is because many surgeons are concerned that eyes treated for years
resistance to aqueous outflow is located in the juxtacanalicular with topical antiglaucomatous drugs
41
may have a poorer surgical
tissue and inner wall. For this reason, bypassing or selective removal outcome, particularly if success depends largely on the integrity of
of the site of maximal outflow resistance without harming other the physiological outflow system, as in Schlemm’s canal surgery. n
structures of the eye has been the declared goal of glaucoma
surgery for many years. Trabeculectomy was originally designed to
Matthias C Grieshaber is a Consultant in the Glaucoma
restore the natural physiological system, but for more than 40 years
Service in the Department of Ophthalmology at the
the key to success in the standard glaucoma procedure has been
University Hospital of Basel. He is a fellowship-trained
subconjunctival filtration.
glaucoma, cataract and anterior segment surgeon
practising in Schaffhausen. He is a Fellow of the European
Board of Ophthalmology (FEBO) and a member of the
However, the ongoing struggle with complications has forced
American Academy of Ophthalmology (AAO), the
surgeons to search for safer alternatives. Owing to recent technical
American Society of Cataract and Refractive Surgery
(ASCRS) and the European Society of Cataract and
advances, the concept of re-establishing the physiological pathway
Refractive Surgeons (ESCRS), among others. Dr Grieshaber’s main research interest is the
has moved again into the centre of attention. Surgeries involving
development and implementation of new surgical techniques for glaucoma surgery. He
Schlemm’s canal correct the pathological defect in the system and
has authored more than 30 scientific papers and written or edited over 20 book chapters.
force aqueous into the collector channel system. Current data
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2005;16:107–13. 17. Khairy HA, Green FD, Nassar MK, et al., Eye, augenarztliche Fortbildung, 1953;122:665–82.
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4. Krasnov MM, Br J Ophthalmol, 1968;52:157–61. 19. Kobayashi H, Kobayashi K, Okinami S, Graefes Arch Clin Exp 2006;12(1).
5. Kozlov V, Bagrov SN, Anisimova SY, Eye Microsurgery, Ophthalmol, 2003;241:359–66. 33. Lewis RA, von Wolff K, Tetz M, et al. J Cataract Refract Surg,
1990;3:157–62. 20. Goldsmith JA, Ahmed IK, Crandall AS, Ophthalmol Clin North 2007;33:1217–26.
6. Fyodorov SID, Ronkina TI, Vestn Oftalmol, 1982;6–10. Am, 2005;18:443–60, vii. 34. Lewis RA, von Wolff K, Tetz M, et al. J Cateract Refract Surg,
7. Stegmann R, An Inst Barraquer, Spain, 1995;25:229–32. 21. Mielke C, Dawda VK, Anand N, Br J Ophthalmol, 2009;35:814–24.
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Glaucoma, 2002;11:287–93. 22. Smit BA, Johnstone M, Invest Ophthalmol Vis Sci, 2000;S578. 2005;112:962–7.
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EUROPEAN OPHTHALMIC REVIEW 43
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