Transscleral diode laser Cyclophotocoagulation (CPC)

Abstract

Traditionally cyclodestructive procedures, achieved either by freezing (cryotherapy) or laser CPC, have been used to treat refractory glaucoma with poor visual potential, presence of extensive scarring from prior surgery, immobile conjunctiva precluding an ab externo approach, or in those at high risk for intraoperative complications (Alward, Chapter 18: Cyclodestructive procedures. In: Krachmer J (ed) Glaucoma: the requisites in ophthalmology. Mosby Inc., St. Louis, 2000). Even in eyes with no light perception, the procedure can provide relief from chronic pain, conjunctival injection, and corneal decompensation from elevated IOP. Cyclodestruction is associated with several potential complications including visual loss that may result not necessarily from the procedure itself but from the underlying disease process including hypotony, macular edema, cataract formation, proliferative diabetic retinopathy, central retinal vein occlusion, neovascular glaucoma, and glaucoma progression (Ishida Curr Opin Ophthalmol 24:102-110, 2013). The transscleral diode laser delivers a continuous 810 nm beam of energy via a customized delivery tip called the G-Probe (Iridex Corp, CA) (Alward, Chapter 18: Cyclodestructive procedures. In: Krachmer J (ed) Glaucoma: the requisites in ophthalmology. Mosby Inc., St. Louis, 2000). The presence of a fiber-optic tip protrusion at the base of the probe is designed to optimally deliver energy to the ciliary body by indenting the sclera 1.2 mm posterior to the limbus. The laser is absorbed by pigment within the ciliary body and coagulates proteins within pigmented epithelial cells reducing aqueous production (Gaasterland, Reconsidering transscleral cyclophotocoagulation. Insert to Glaucoma Today. 2012). A clinical judgment needs to be made regarding how much one needs to laser. If the IOP is exceedingly high and needs to be decreased substantially, then more laser applications should be administered. Conversely, if a modest drop in IOP is the goal, then one needs to taper the number of delivered laser applications. In patients with altered limbal anatomy from prior surgery, pannus formation, megalocornea, or congenital glaucoma, accurate localization of the ciliary body is paramount with transillumination to guide proper placement of the G-Probe (Morales et al J Ophthalmol 2013:1-16, 2013). Otherwise, there may be no apparent benefit in IOP lowering with laser being delivered to the peripheral cornea. Scleral thinning following standard transscleral diode laser CPC has been reported in a series of patients all under 30 years of age using recommended manufacturer settings (Morales et al Ophthalmic Surg Lasers Imaging 38:301-306, 2007). This may in part be due to an enhanced heat-induced thinning of juvenile collagen vs. adults (Morales et al Ophthalmic Surg Lasers Imaging 38:301-306, 2007). Conjunctival and scleral burns can occur on the surface either due to accumulation of debris on the fiber-optic tip or the presence of perilimbal conjunctival pigment absorbing the laser energy (Shareef and Wax, Peri-limbal burns in areas of conjunctival melanosis during cyclophotocoagulation. Presented as Poster at American Glaucoma Society (AGS), San Francisco, 28 Feb 2013). The company has introduced MicroPulse Technology using the Cyclo G6 Glaucoma Laser System (iridex. com/Products/Lasers/CYCLOG6174MicroPulseP3. aspx) with a novel contact probe continuous-wave laser beam that can be delivered either in a continuous or a pulsatile manner, the latter with interspersed brief rest periods allowing heat to dissipate. This approach is more tissue sparing and potentially enables glaucoma intervention in earlier phases of the disease with functional vision and not just refractory cases. The operative template below outlines only the use of the continuous-wave laser beam transscleral diode laser in the treatment of eyes with refractory glaucoma and poor visual potential or blind hypertensive eyes with associated eye pain. The procedure can be performed either in the office or operating room setting. For those interested in MicroPulse technology, they are advised to contact the manufacturer or publications for recommended optimal laser parameters to ensure safety and efficacy in eyes with functional vision (Zaarour et al, J Glaucoma 28(3): 270-275, 2019).