Target Placement of iStent Combined with Phacoemulsification
A patient’s surgical candidacy for microinvasive glaucoma surgery (MIGS) should have been assessed preoperatively by evaluating the angle anatomy with slit lamp-based gonioscopy to ensure adequate visualization to safely perform surgery (University of Iowa Health Care Ophthalmology and Visual Sciences, www.gonioscopy.org). The scleral spur serves as a surgical landmark separating the pigmented trabecular meshwork (TM) anteriorly from the ciliary body band posteriorly. The Schlemm’s Canal (SC) located deep to the pigmented TM is the final resting place for the micro-stent. The rate-limiting step in performing angle surgery is visualization of the angle with intraoperative gonioscopy (Exp Rev Ophthalmol 9(6):515–527, 2014; University of Rochester School of Medicine and Dentistry). Target placement of the iStent (Glaukos Corp.) includes areas of greater TM pigmentation (Invest Ophthalmol Vis Sci 50(4):1692–1697, 2009) believed to be in close proximity to collector channels (CC) for optimal aqueous outflow via the aqueous veins (AV) to the episcleral veins (EV) (Surgical innovations in glaucoma, New York, 2014). The authors propose that following induction of relative ocular hypotony, areas of initial focal blood reflux into SC adjoin CC and serve as intraoperative surgical targeting for iStent implantation in optimizing aqueous outflow. One can anticipate a reduction in IOP and/or reduction in medication burden post-op (J Cataract Refract Surg 41(12):2664–2671, 2015). Should the desired pressure reduction not be achieved or there is evidence of glaucoma progression, the patient may need to be restarted on glaucoma medical therapy. Additionally, angle surgery does not preclude traditional ab externo filtration or tube shunt surgery and forms part of a continuum in glaucoma surgical management. Risks, benefits and alternatives, and appropriate educational material should have been provided to the patient regarding angle surgery and need for cataract surgery based upon visual impairment as outlined in chapters addressing cataract extraction in this textbook.
Shareef S, Sharma S. Target placement of iStent® combined with phacoemulsification. In: Rosenberg ED, Nattis A, Nattis RJ, editors. Operative dictations in ophthalmology. Cham, Switzerland: Springer International Publishing; 2017. pp. 215-24.