Cyclodestructive Procedures in Treatment of Glaucoma
Destruction of the ciliary body has been used to treat glaucoma since the 1930s. In cyclodestructive procedures, the secretory epithelium of the ciliary epithelium is damaged, which leads to reduced aqueous humor secretion and lower intraocular pressure (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: diathermy, surgical excision, cryotherapy, ultrasound, and laser light . 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. using a ruby laser (693 nm wavelength). Neodymium:yttrium-aluminum-garnet (Nd:YAG) laser (1064 nm wavelength)   has been used either with non-contact or contact methods to achieve cyclodestruction. Currently, a diode laser (810 nm wavelength), either transscleral 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 inflammation.
Over the past years, Micropulse Transscleral Cyclophotocoagulation was introduced in the management of glaucoma. Furthermore, new parameters have been proposed for CPC using lower energy over an extended period of time (known as Slow-Coagulation Continuous-Wave Transscleral Cyclophotocoagulation Laser for Treatment of Glaucoma) compared to the traditional continuous wave trans-scleral CPC. Another recently introduced intervention is Ultrasound Cycloplasty in Glaucoma, which is a non-incisional procedure based on high-intensity focused ultrasound.
These techniques are discussed in separate sections. The current article discusses only the traditional continuous-wave trans-scleral cyclophotocoagulation (TS-CPC) and endoscopic cyclophotocoagulation (ECP).
TS-CPC and 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 eye|
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 glaucoma|
|Primary open-angle glaucoma|
|Glaucoma after penetrating keratoplasty|
|Silicone oil induced glaucoma|
|Patients who are poor candidates for glaucoma filtration surgery or glaucoma drainage implant|
|Primary open-angle glaucoma|
|Glaucoma after penetrating keratoplasty|
|Glaucoma associated with retinal surgery|
The use of CPC and ECP in childhood glaucoma is discussed in a separate section (Cyclophotocoagulation in Pediatric Glaucoma).
A semiconductor 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. There is no consensus about the optimal parameters; however, some surgeons will start at 1750-2000 mW and 2 seconds and increase the energy gradually until a "pop" sound is heard, and the titrate the energy down gradually. 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.
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 a depth of focus of 1-30mm. The equipment console comprises a video camera, light source, video monitor, and 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”, and 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 the 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, and then cyclophotocoagulation with the endolaser probe is performed. ECP can be combined with phacoemulsification to treat cataract and glaucoma simultaneously. In combined cases, ECP can be performed before or after inserting the intraocular lens in the lens bag.
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.
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 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 study, 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-CPC (incidence ranging from 13%-50% depending on the study population). Phthisis bulbi is a rare complication of TS-CPC. Malignant glaucoma, necrotizing scleritis, and sympathetic ophthalmia  have been reported after TS-CPC.
Chen et al. performed a retrospective study on 68 eyes that underwent ECP for refractory glaucoma. They reported the following complications: fibrin exudates (24%), hyphema (12%), cystoid macular edema (10%), and 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 ECP. This complication is due to the 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.
TS-CPC has been used in different types of intractable glaucoma (see Table-1). Rivier et al. 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 vision. Rotchford et al. 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 study, 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 as primary surgical treatment for POAG with good results. 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.
In a study of 68 eyes with refractory glaucoma that underwent ECP, the mean IOP reduced from 27.7mmHg to 17.0mmHg (34% mean reduction) . 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 surgery. In a prospective study, ECP has been shown to be effective as Ahmed glaucoma valve in lowering IOP in eyes with refractory glaucoma. The frequency of complications was higher in the Ahmed valve group. ECP has been used in eyes that have had a prior drainage device implant and uncontrolled IOP. 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 the mean number of glaucoma medications decreased from 3.2 to 1.5. There were no serious complications.
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.
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