Glaucoma surgery can be classified as either cyclodestructive (reducing inflow) or filtering (increasing outflow). Filtration has traditionally been the procedure of first resort because of its efficacy and relative predictability, whereas ciliary destruction has been reserved for more refractory cases of glaucoma and in eyes which have little or no visual potential. Refractory glaucomas include neovascular glaucoma, post-traumatic glaucoma, glaucoma associated with aphakia, severe congenital/developmental glaucoma, post-retinal surgery glaucoma, glaucoma associated with penetrating keratoplasties, and glaucoma in eyes with scarred conjunctiva from surgery or disease processes.
In the past, cyclodestruction has been carried out by various methods including surgical excision, (1,2) diathermy, (3-6) cryotherapy, (7-11) and laser. (12-25) Laser cyclophotocoagulation has now become the principal method for "turning down the tap." Beckman and Sugar popularised the use of trans-scleral cyclophotocoagulation (TCP) in the early 1970s. (12,13) Initially, they used the ruby laser (12) but soon discovered that the neodymium:yttrium-aluminium-garnet (Nd:YAG) laser was more effective in penetrating the sclera and optimising energy absorption by the diary epithelium. (13) The delivery of laser energy through the sclera may be performed by either the non-contact or contact method. (Thanspupillary cyclophotocoagulation with the argon laser has also been utilised; however, it is only applicable in certain aphakic eyes.) In the non-contact approach, a slit lamp is employed to apply laser energy through the conjunctival/scleral surface. (12-19) A contact lens may be used to keep the eyelids open and b lanch the conjunctiva. The focus of energy delivery is 1-1.5 mm behind the limbus and is offset from the aiming beam so that maximal therapeutic effect is at the level of the ciliary body. The total number of laser applications is usually about 32 (eight per quadrant), avoiding the 3 and 9 o'clock positions in order to preserve the long posterior ciliary arteries.
More recently, contact cyclophotocoagulation has gained favour as a preferred method for treating refractory cases of glaucoma. (20-22) Using the Nd:YAG laser (Surgical Laser Technologies (SLT), Inc, Malvern, PA, USA), a hand held sapphire tipped probe is placed on the conjunctiva and sclera, centred 1-2 mm behind the limbus, for the transmission of laser energy. Sixteen to 28 spots are applied, also avoiding the 3 and 9 o'clock positions. Energy levels are titrated to avoid an audible "pop" which indicates overtreatment and explosion of the ciliary body tissue.
The development of compact, portable diode lasers for ophthalmic use has made it more convenient to perform contact TCP. (23-25) The semiconductor diode laser (Iris Oculight SLx, Iris Medical Inc. Mountain View, CA, USA) emits at 810 nm wavelength and is better absorbed by melanin than the ND:YAG, although scleral transmission is reduced at this wavelength. (23-25) The flat tip of the hand piece (known as the "G-Probe") protrudes 0.7 mm deeper than the contact surface, indenting the conjunctiva and sclera to allow better laser penetration. Principles of treatment are similar to the Nd:YAG laser.
Both contact and non-contact TCP have been shown to be effective surgeries for treating end stage and/or severe glaucoma in which other surgeries have failed or potential vision is very limited. (12-25) Although definitions of success vary among reports, success rates for intraocular pressure (IOP) control have been between 34% and 81%, with mean follow ups of up to 30 months. (12-25) Even though TCP has been used effectively for managing refractory and severe glaucoma, it is a procedure that has a significant incidence of (12-29) and postoperative discomfort, and should be reserved for eyes with very limited visual potential.
A new method to directly photocoagulate the ciliary body under endoscopic guidance--known as endoscopic cyclophotocoagulation (ECP)--has become an increasingly important weapon in the glaucoma surgeon's armamentarium for the treatment of refractory glaucomas (30-34) and may have distinct advantages over the trans-scleral approach in eyes with visual potential. Furthermore, ECP may have advantages in the management of glaucoma associated with penetrating keratoplasty. (32 35)
DESCRIPTION OF DEVICE
The laser unit for ECP (Endo Optiks, Little Silver, NJ, USA) incorporates a diode laser that emits pulsed continuous wave energy at 810 nm, a 175 W xenon light source, a helium-neon laser aiming beam, and video camera imaging which can …