Cyclodestructive Procedures in Treatment of Glaucoma
Introduction[edit | edit source]
Destruction of the ciliary body has been used to treat glaucoma since the 1930s1. In cyclodestructive procedures, the secretory epithelium of the ciliary epithelium is damaged, which leads to reduced aqueous humor secretion and lower IOP. Because the ciliary epithelium can regenerate, multiple treatments are necessary in some patients to achieve the desired long term IOP lowering effect.
The different modalities to achieve cyclodestruction are: diathermy1, surgical excision, cryotherapy2, ultrasound3, and laser light4,5. Cyclophotocoagulation (CPC) is the most common procedure to perform cyclodestruction. It can be performed using different laser wavelengths. CPC was first performed by Beckman et al.4 using a ruby laser (693 nm wavelength). Neodymium:yttrium-aluminum-garnet (Nd:YAG) laser (1064 nm wavelength)6-8 has been used either with non-contact or contact methods to achieve cyclodestruction. Presently, diode laser (810 nm wavelength) either transsceral or with an endoscopic probe is used to perform CPC. The diode laser is preferred over other wavelengths since the melanin in the ciliary epithelium better absorbs this wavelength than others and therefore causes more targeted destruction with less inflammation9.
Indications[edit | edit source]
Transscleral CPC (TS-CPC) and endocylcophotocoagulation (ECP) are performed for similar glaucoma conditions (Table-1 and Table-2 respectively). In general, TS-CPC and ECP are indicated for refractory glaucoma, or eyes with poor visual acuity or poor visual potential.
|Elevated IOP with poor vision or poor visual potential|
|Pain relief due to elevated IOP in a blind painful eye10|
Uncontrolled glaucoma in the presence of conjunctival scarring from previous surgery
|Patient's medical condition preclude going to operating room|
|Patient refuses surgery in operating room|
|Primary surgical treatment of glaucoma11|
|Primary open-angle glaucoma12|
|Glaucoma after penetrating keratoplasty17|
|Silicone oil induced glaucoma19|
|Patients who are poor candidates for glaucoma filtration surgery or glaucoma drainage implant20|
|Primary open-angle glaucoma21|
|Glaucoma after penetrating keratoplasty22|
|Glaucoma associated with retinal surgery22|
Surgical Technique[edit | edit source]
Diode TS-CPC:[edit | edit source]
A semi-conductor solid state diode laser system (Oculight SLx, Iridex Corporation, Mountain View, CA) with a wavelength of 810 nm is used to perform TS-CPC9. A handpiece (G probe, Iridex, Mountain View, CA) is used to deliver the laser energy. Diode TS-CPC can be performed in a minor procedure room or in an operating suite. Retrobulbar or peribulbar anesthesia is needed, as the procedure is painful. A block consisting of either a 50:50 mixture of lidocaine 2% without epinephrine and bupivacaine 0.75% or straight lidocaine can be given. A lid speculum helps to provide better exposure to the peri-limbal area. This author uses the following laser parameters: Initial power of 1250 mW and duration of 4 seconds. The power is increased in 150 mW increments until an audible “pop” is heard. The audible “pop” signifies tissue explosion of the ciliary process, the iris root, or the retina9. When a “pop” is heard the power is decreased by 150 mW until there is no audible “pop”. The maximum power used is 2250 mW. Others will start at 2000 mW and 2 seconds and titrate the energy down. Generally 6 spots are used per quadrant for a total of 18 spots. Some surgeons recommend treating only 3 quadrants to avoid anterior segment necrosis, and many recommend sparing the 3:00 and 9:00 positions where the ciliary nerves lie. After completion of the procedure a topical antibiotic, steroid, and cycloplegic agents are placed on the eye. The eye should be patched after a block is used to protect the cornea. The patient is seen the next day for follow-up.
Endocyclophotocoagulation (ECP):[edit | edit source]
The ECP laser unit (Endo Optiks, Little Silver, NJ) has 4 different components, the diode laser (pulsed continuous-wave energy at 810 nm), a xenon light source, a helium-neon laser aiming beam, and video monitor and recorder. The probe is 20 gauge with a full view of 110 degrees and depth of focus of 1-30mm. The equipment console consists of the video camera, light source, video monitor, and the video recorder. Initially the laser probe is placed into the anterior chamber by looking through the surgical microscope. Then the surgeon looks through the video monitor to locate the ciliary processes and perform the laser photocoagulation. The goal of each laser application is to whiten and shrink the ciliary process. The entire ciliary process should be treated. Generally 270-360 degrees of the ciliary processes are treated. Gas bubble formation, pigmentary dispersion, audible “pops”, photocoagulation of non-ciliary process tissue should be avoided20. The laser settings are as follows: Power 0.2 W, continuous-wave mode. The power is titrated to achieve whitening and shrinkage of the ciliary process by positioning the probe either closer or further from the processes. Ideally, 3 processes should be within view during treatment.
ECP can be performed in phakic, pseudophakic, or aphakic eye with the endolaser probe through the limbus or pars plana. In the limbal approach, a 1.5-2.0 mm incision is made in the clear cornea or sclera. A cohesive viscoelastic is injected posterior to the iris and anterior to the lens capsule to deepen the ciliary sulcus space. Next the probe is placed in the anterior chamber. The ciliary processes are visualized and treated. At the end of the procedure, the viscoelastic is removed. In phakic patients great care should be taken not to nick the anterior lens capsule. In pseudophakic/aphakic eyes, the pars plana approach is advantageous since the ciliary processes are better visualized. The incision is made 3.5-4.0mm posterior to the limbus. Anterior vitrectomy is performed, then cyclophotocoagulation with the endolaser probe is performed. ECP can be combined with phacoemulsification to treat cataract and glaucoma at the same time23. In combined cases ECP can be performed before or after inserting the intraocular lens in the lens bag. Endoscopic Cylcophotocoagulation (ECP)
Management[edit | edit source]
Post-operatively the patient is started on cycloplegics (atropine 1% twice a day for 2 weeks) and topical corticosteroids (prednisolone acetate 1% 4 times a day). If there is extensive anterior chamber inflammation the steroid drops can be applied more frequently. Additionally subtenon’s steroid injection and/or oral steroids can be used. After ECP topical antibiotics are necessary since it is an intraocular procedure. The pre-laser glaucoma medications are continued post-operatively and can be tapered based on the intraocular pressure (IOP) lowering effect of the laser. Miotics should be stopped because they can enhance the inflammatory response and cause posterior synechiae. Consideration should also be given to stopping the prostaglandin analogs if the IOP is well controlled since they can cause anterior chamber inflammation.
Complications[edit | edit source]
TS-CPC:[edit | edit source]
Pain is usually transient and controlled with over-the-counter analgesics, although some patients may require prescription strength analgesics. Hyphema occurs more frequently in neovascular glaucoma patients. Iridocyclitis occurs commonly after TS-CPC. Few patients can develop a chronic low-grade anterior chamber inflammation due to a breakdown in the blood-aqueous barrier. Conjunctival burns are rare, but they can occur if the conjunctival surface becomes dry during laser applications, with high energy settings in cases of darkly pigmented conjunctiva, and due to the use of defective, damaged, or soiled laser probes. Hypotony has been reported after CPC. In one study24 5 out of 20 patients with neovascular glaucoma undergoing CPC developed hypotony. In this study, patients who had 2 or more previous pars plana vitrectomies also developed hypotony. Vision loss can occur after TS-CPC11,12,25 (incidence ranging from 13%-50% depending on the study population). Phthisis bulbi is a rare complication of TS-CPC26. Malignant glaucoma27, necrotizing scleritis28, and sympathetic ophthalmia29,30 have been reported after TS-CPC.
ECP:[edit | edit source]
Chen et. al.31 performed a retrospective study on 68 eyes that underwent ECP for refractory glaucoma. They reported the following complications: fibrin exudates (24%), hyphema (12%), cystoids edema (10%), vision loss of 2 lines or more (6%). They did not have any cases of phthisis bulbi, endophthalmitis, or sympathetic ophthalmia, which are possible. Traumatic injury to the iris has been reported with ECP32. This complication is due to laser being improperly applied to the iris or through mechanical trauma. Therefore the surgeon must be aware of the location of the endolaser probe at all times and the laser should only be applied to the ciliary processes.
Clinical outcomes[edit | edit source]
TS-CPC:[edit | edit source]
TS-CPC has been used in different types of intractable glaucoma (see Table-1). Rivier et al.33 reported that TS-CPC can be used before or after keratoprosthesis surgery to control the IOP. In their study, the mean IOP was significantly lowered at 6, 12, 24, 36, and 48 months. At the last follow-up visit (mean follow-up: 26.6 months) the mean best-corrected visual acuity and the number of glaucoma medications was stable. Since CME is a complication of TS-CPC, this laser is usually performed in eyes with poor vision and/or poor visual potential. However, recent studies have shown that TS-CPC can be performed in eyes with good vision12,34. Rotchford et al.34 analyzed TS-CPC in patients with pre-laser visual acuity of 20/60 or better. The median visual acuity before the laser was 20/30 (Range; 20/16-20/60) and the median follow-up was 5 years. 31% of eyes lost 2 or more lines of vision. 67% of eyes retained visual acuity of 20/60 or better and 16% of eyes had a visual acuity less than 20/200. In eyes that lost 2 or more lines of vision, the main cause was glaucoma progression (50%). Other causes were: macular edema, retinal detachment, cataract formation, and macular degeneration. In another study12, in a subset of 23 POAG eyes with good vision only 3 eyes had decreased visual acuity at the final visit. In two of these eyes, the decreased vision was due to cataract formation and in one eye reduced vision was due to chronic anterior uveitis and glaucoma progression. TS-CPC has been used has primary surgical treatment for POAG with good results11. In this study, the IOP decreased by 20% in 47% of eyes and the IOP was 22 mmHg or less in 48% of eyes. There were no serious complications such as hypotony, phthisis bulbi, or sympathetic ophthalmia. In 77% of eyes the vision remained the same or was better after the laser.
ECP:[edit | edit source]
In a study of 68 eyes with refractory glaucoma that underwent ECP, the mean IOP reduced from 27.7mmHg ro 17.0mmHg (34% mean reduction) 31. The number of glaucoma medications decreased from 3 to 2. The mean follow-up period was 12.9 months. Ninety percent of eyes had IOP less than 22mmHg at the last follow-up period. ECP was found to be as effective as trabeculectomy in IOP lowering when combined with cataract surgery35. In a prospective study, ECP has shown to be effective as Ahmed valve in lowering IOP in eyes with refractory glaucoma. The frequency of complications was higher in the Ahmed valve group22. ECP has been used in eyes that have had a prior drainage device implant and uncontrolled IOP36. In this study 25 eyes with prior history of a glaucoma drainage implant and uncontrolled IOP underwent ECP. At 12 months, the mean IOP dropped from 24mmHg to 15.4mmHg, and mean number of glaucoma medications decreased from 3.2 to 1.5. There were no serious complications. ECP has moderate success rates in aphakic and pseudophakic glaucoma in children37. ECP reduce d the IOP from a mean of 32.6mmHg to 22.9mmHg at last follow-up. The average number of procedures was 1.5. There were 2 cases of retinal detachment. Hypotony was not observed in this study.
Conclusion[edit | edit source]
Both TS-CPC and ECP are safe and effective procedures to control IOP in refractory glaucomas. Recently TS-CPC has been performed in patients with good vision with good results. ECP can be combined with cataract surgery to with good success rates.
References[edit | edit source]
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