Chapter 237 – Cyclodestructive Procedures in Glaucoma
MARLENE R. MOSTER
TAREK M. EID
The goal of glaucoma surgery is to lower the intraocular pressure (IOP) predictably, either by maximizing outflow (as in filtration and tube-shunt surgery) or by decreasing inflow (as with cyclodestructive procedures). The destruction of the ciliary body carries a considerable complication rate, which includes phthisis bulbi, visual loss, and an unpredictable degree of IOP reduction. Usually these procedures are reserved for eyes that have glaucoma refractory to medical, laser, and surgical treatment.
Selective destruction of the ciliary body with electrocautery was first applied by Weve in 1933 (nonpenetrating diathermy) and Vogt in 1936 (penetrating diathermy). However, the high complication rate, the less than satisfactory results, and the introduction of cyclocryotherapy by Biette in 1950 reduced the use of cyclodiathermy.  Cyclocryotherapy was the cyclodestructive procedure of choice for more than three decades.
However, the IOP reduction was inconsistent and the complication rate was still high. The use of xenon arc photocoagulation in 1961 and the ruby laser in 1971 led to the application of laser energy as a method of cycloablation. In 1981, Fankhauser and associates incorporated a thermal mode into a neodymium:yttrium-aluminum-garnet (Nd:YAG) laser system to perform trans-scleral cyclophotocoagulation (CPC). The availability of the instrument facilitated wide clinical application.
More recently, semiconductor diode laser technology has been used successfully for cyclodestructive surgery.           Currently, 810?nm (diode) and 1064?nm (Nd:YAG) are the two most popular wavelengths for trans-scleral cyclodestructive surgery.
PREOPERATIVE EVALUATION AND DIAGNOSTIC APPROACH
Cyclodestructive procedures are generally reserved for eyes that have poor visual potential [visual acuity less than 20/400 (6/120)], eyes in which other glaucoma procedures failed or are not applicable (e.g., extensive conjunctival scarring), eyes in which filtering surgery has a high failure rate (e.g., neovascular glaucoma, aphakic and pseudophakic glaucoma, and glaucoma associated with silicone oil), and eyes of patients who, for medical reasons, are unable to undergo filtration surgery.
MECHANISM OF ACTION
Cyclocryotherapy damages the epithelial, vascular, and stromal components of the ciliary body. Maximum cell death seems to require a rapid freeze followed by a slow thaw. Cell necrosis has been shown to occur at temperatures of -10°C and below. In vivo, -60 to -80°C at the sclera produces a temperature of -10°C in the ciliary processes after 20–30 seconds of application.
Figure 237-1 Transmission of laser light through the sclera. The laser beam is focused on the ciliary processes.
The Nd:YAG laser allows effective scleral penetration ( Fig. 237-1 ) with less backscatter than with lasers of shorter wavelength. Higher energies are created in the free-running mode as contrasted with the single-pulse mode. Laser CPC is more effectively absorbed by pigmented tissue in the ciliary body compared with cryotherapy, which is diffusely absorbed. The contact methods produce less scatter and thus require less energy than the noncontact methods.
The semiconductor diode laser with a wavelength of 810?nm has lower scleral transmission than the Nd:YAG laser (1064?nm) but greater absorption by melanin. This allows the use of 50% less energy than used with the Nd:YAG laser.
Histologically, most likely both lasers produce fragmentation and detachment of the epithelium of the ciliary processes with simultaneous destruction of the ciliary body vasculature. At least three mechanisms are thought to be important in lowering IOP: (1) inflammation, which is prominent in the first week or so after treatment; (2) decreased aqueous production through ablation of the pars plicata, through either a direct or indirect effect on the vasculature; and (3) increased uveoscleral outflow resulting from laser delivery to the region of the pars plana.
ALTERNATIVES TO A CYCLODESTRUCTIVE PROCEDURE
The alternatives to a cyclodestructive procedure include trabeculectomy surgery along with an adjunctive antimetabolite (see Chapters 239 and 240 ) and drainage implant surgery (see Chapter 242 ). The cyclodestructive procedure has the advantage of being faster and an office procedure but is generally reserved
for eyes that have poorer visual potential because of the risk of later diminished visual acuity.
The ciliary processes are highly innervated and painful to treat without adequate anesthesia. Trans-scleral procedures require local (retrobulbar or peribulbar) anesthesia and can usually be performed in an office setting. Endoscopic CPC requires local (retrobulbar or peribulbar) or general anesthesia and is performed in an outpatient surgical or hospital setting. Glaucoma medications, except miotics, may be continued before and after cyclodestructive procedures.
The anterior edge of the cryoprobe is placed 1.0–1.5?mm posterior to the limbus in the superior quadrant and 1.0?mm from the limbus for the remaining 270°. Various sizes of cryoprobe with diameters in the range 1.5–4.0?mm have been used. Moderate compression of the sclera with the cryoprobe may reduce the distance between the cryoprobe and the targeted tissues.  A temperature of -80°C at the probe tip is delivered for 60 seconds. To reduce the complication rate (particularly phthisis bulbi), the treatment is usually limited to one application at each clock hour (six in total) over 180°. The ice ball is allowed to thaw slowly, rather than using irrigation, to allow the maximal effect. Subconjunctival dexamethasone is injected, and atropine and an antibiotic-corticosteroid combination are prescribed. All glaucoma medications (except for miotics) are continued postoperatively. The full effect of treatment may take 2–4 weeks to become manifest, so a second treatment is not considered until 1 month has elapsed. The same area may be retreated, or another quadrant may be included. One quadrant must be left untouched to avoid anterior segment necrosis.
Cyclocryotherapy has been used extensively in the past; however, its unpredictable results and complication rate have encouraged pursuit of other forms of cyclodestruction.
Trans-scleral Cyclophotocoagulation ( Table 237-1 )
NONCONTACT ND:YAG LASER CYCLOPHOTOCOAGULATION.
A noncontact Nd:YAG laser unit transmits the laser energy through air from a slit-lamp delivery system. The typical laser settings for noncontact trans-scleral Nd:YAG CPC are 4–8?J/pulse, 20?ms duration, and a maximum offset at position 9. The number of applications is 30–40, with 8–9 spots per quadrant; the 3 and 9 o’clock positions are spared to avoid long posterior ciliary arteries ( Fig. 237-2 ). The laser spot is placed 1.0–1.5?mm posterior to the limbus. This distance is measured using calipers or the aiming beam in the center of a 3?mm slit beam. The Shields contact lens may be used during the procedure. Its central opaque disc helps to prevent the entrance of stray laser light into the eye, and its limbal portion compresses the conjunctiva and blanches blood vessels to improve the
Figure 237-2 Markings on the sclera after noncontact ND:YAG laser cyclophotocoagulation.
focus. Atropine 1% is administered twice a day and prednisolone acetate 1% four times a day; these are tapered as inflammation subsides ( Fig. 237-4 ). All preoperative glaucoma medications except for miotics are continued and IOP is checked 1 hour, 1 day, and 1 week after treatment.
Transmission of Laser Light through the Sclera
CONTACT ND:YAG LASER CYCLOPHOTOCOAGULATION.
Contact trans-scleral photocoagulation is achieved by using the Nd:YAG laser in the continuous mode via a fiberoptic system in direct contact with the conjunctiva. Effective reduction of IOP is provided using less power than required with the noncontact Nd:YAG laser.
The fiberoptic laser probe is positioned perpendicularly on the conjunctiva with the anterior edge 0.5–1.0?mm posterior to the surgical limbus ( Fig. 237-3 ). Laser settings include a power level of 4–9?W and duration of 0.5–0.7 seconds. The number of applications varies in the range 16–40 over the entire area of the ciliary body with the 3 and 9 o’clock positions spared. Efficient energy transfer is facilitated by pushing the probe against the sclera, which increases light transmission through the sclera.
SEMICONDUCTOR DIODE LASER TRANS-SCLERAL CYCLOPHOTOCOAGULATION.
Diode laser trans-scleral cyclophotocoagulation (DCPC) is one of the most widely used methods of ciliary ablation with reported success rates ranging from 40 to 80%. The technique used with the semiconductor diode laser (wavelength 810?nm) is similar to that used for the contact Nd:YAG laser. The anterior edge of the probe approximates the surgical limbus and the laser beam is directed 1–1.5?mm posteriorly so that the ciliary processes are ablated. Settings are 1500–2500?mW of power for 1.0–2.0 seconds and a total of 16–18 spots. The 3 and 9 o’clock positions are spared. The results are similar to those achieved using Nd:YAG CPC   despite the lower energy used with the diode laser (55% of that used with the Nd:YAG laser). In addition, because semiconductor diode lasers have a solid-state construction, they have the advantages of portability, durability, and smaller size compared with the Nd:YAG laser. 
TABLE 237-1 — TECHNIQUES OF TRANS-SCLERAL LASER CYCLOPHOTOCOAGULATION
Noncontact Nd: YAG
Contact Nd: YAG
Distance from limbus
Figure 237-3 Application of the laser probe in contact trans-scleral Nd:YAG cyclophotocoagulation. The probe is placed on the conjunctiva with the anterior edge 0.5–1?mm posterior to the surgical limbus.
OTHER TECHNIQUES OF LASER CYCLOPHOTOCOAGULATION
Other techniques are being investigated, including transpupillary CPC, transvitreal endocyclophotocoagulation, and endoscopic CPC. Direct transpupillary treatment of the ciliary processes with the argon laser (488?nm) is rarely used because a clear visual axis and a well-dilated pupil are required to enable photocoagulation of the entire length of the ciliary processes. Transpupillary CPC of the ciliary processes, exposed through peripheral iridectomy or a widely dilated pupil, can be effective in the treatment of ciliary block glaucoma.  The mechanism may be related to a laser-induced retraction of the ciliary body. Endocyclophotocoagulation, an intraocular procedure in which a laser probe is used to treat the ciliary processes at the time of pars plana vitrectomy, offers the possibility of selectively treating the ciliary body epithelium with relatively sparing of underlying tissues.  It requires clear media and aphakia or pseudophakia to visualize directly and treat the ciliary processes, which are scleral depressed into the view of the operating microscope. The argon laser parameters used were continuous duration at 300 to 600?mW of energy. The diode uses up to 1 second duration at 300 to 800?mW of energy.     Endoscopic CPC through a cataract incision at the time of cataract surgery with trabeculectomy and cataract surgery appears to be a reasonably safe and effective procedure for managing glaucoma and cataract.   Endoscopic CPC may prove to have more predictable results and lower complication rates than trans-scleral procedures; however, this is a more invasive technique, which is not currently in wide use.
It has also been shown that red 647?nm krypton laser CPC is an effective and reasonably well-tolerated procedure for lowering IOP in post-traumatic glaucoma. Although transmission through the sclera is lower with the red 647?nm krypton laser than with the infrared 810?nm diode and Nd:YAG lasers, this is compensated for by using contact application and compressing the sclera with the probe.
TABLE 237-2 — COMPLICATIONS OF CYCLOCRYOTHERAPY AND LASER TRANS-SCLERAL CYCLOPHOTOCOAGULATION
Pain (mild to severe)
Iritis, usually mild, but may be severe
Loss of more than one line of visual acuity
Persistent hypotony and phthisis bulbi
Transient flat anterior chamber with hypotony, and choroidal detachment
Scleral thinning (with laser)
Corneal epithelial defects and corneal graft failure
Hyphema and vitreous hemorrhage
Sympathetic ophthalmia (with laser)
Figure 237-4 Fibrin clot after Nd:YAG cyclophotocoagulation.
Complications are summarized in Table 237-2 . All forms of cyclodestructive procedures may damage ciliary muscle as well as ciliary epithelium, adjacent iris, and retina. Complications include reduced visual acuity, uveitis, pain, hemorrhage, and phthisis bulbi (see Table 237-2 ). All these complications, especially pain and inflammation, seem less severe after laser CPC than after cyclocryotherapy. For trans-scleral procedures, the occurrence of audible tissue disruptions does not correlate with success rate. Audible pops correlate with intraocular tissue disruption but not necessarily at the target tissue of the ciliary body. These are considered unwanted side effects, as is intraocular hemorrhage or exposure to uveal antigen.  Decreased visual acuity is not uncommon   ; possible causes of loss of vision include a spike in IOP in the perioperative period,   postoperative cystoid macula edema, backward scatter from the laser, and progression of glaucomatous optic neuropathy in spite of the cyclodestructive treatment. The occasional gain in vision is presumably due to a decrease in corneal edema. Potential complications of trans-scleral diode CPC include conjunctival surface burns that may occur when tissue debris becomes coagulated on the tip and chars. In addition, increased perilimbal conjunctival pigmentation has been correlated with conjunctival burns, which heal quickly. A higher incidence of persistent hypotony and visual loss has been reported in neovascular glaucoma.  Graft failure is a major problem after cycloablation for refractory glaucoma. It has been reported to occur in 11–44% of patients.  Hyphema and vitreous hemorrhage are rare. Phthisis, hypotony, and loss of visual acuity may become chronic complaints.
The potential complications of endoscopic CPC include all risks listed except for conjunctival surface burns. In addition, endoscopic CPC carries the risk of damage to the crystalline lens, zonular rupture, and the inherent risks of an intraocular procedure, which include retinal detachment and endophthalmitis. There have been no reported cases of these potential complications in the literature. 
Cyclocryotherapy is more effective in some forms of glaucoma than others. Glaucoma in aphakic eyes and in eyes after penetrating keratoplasty responds well to cyclocryotherapy. In neovascular glaucoma, pain is reduced effectively but the incidence of visual loss and phthisis is high.  Contact or noncontact methods of Nd:YAG or diode laser CPC are fast, easy to perform, and repeatable and have a lower complication rate than cyclotherapy and cyclodiathermy.         The results of both noncontact and contact Nd:YAG CPC are comparable, with a satisfactory IOP reduction in 45–72% of cases. Between 29 and 48% of Nd:YAG CPC cases require one or more repeated treatments.
Trans-scleral diode CPC produces results equivalent to those of the same operation performed with the Nd:YAG laser (IOP < 22?mmHg in 60–84% and retreatment rate of 28–45%)      while offering certain technological advantages. Postoperative complications, including pain, inflammation, hyphema, and phthisis, were less common than in other cyclodestructive procedures. Three different kinds of lasers (diode laser, free-running Nd:YAG, and continuous wave mode Nd:YAG laser) were compared in neovascular glaucoma patients. Diode CPC had the best success lowering IOP in 55.9% of patients after 3 years with the fewest complications.
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