If all other therapies fail or are contraindicated, it is possible to reduce aqueous production and lower intraocular pressure (IOP) by destroying elements of the ciliary body. Cyclophotocoagulation procedures destroy the ciliary epithelium, stroma, and vascular supply ( Fig. 32-1 ). They have been found to be effective, but complications are significant. In successful cases, inflammation, postoperative IOP increases, iritis, pain, and perhaps some loss of visual acuity are common. Thus laser cyclophotocoagulation procedures have historically been considered a last resort, with indications similar to those for cyclocryodestruction. Laser therapies tend to have fewer complications than does cyclocryodestruction, but most glaucoma specialists do not attempt cyclophotocoagulation until other attempts at IOP reduction have failed. Age, preoperative IOP, and gender do not appear to affect the success of these procedures.
Destruction of the ciliary processes to reduce aqueous production can be accomplished by direct visualization with a variety of lasers, or trans-sclerally, with a 1064-nm neodymium:yttrium-aluminum-garnet (Nd:YAG) laser in the thermal continuous wave (cw) mode or an 810-nm diode laser. Direct (transpupillary or intracamerally with endoscopic control) cyclophotocoagulation has the advantage of ensuring that laser light is targeted accurately on the ciliary epithelium, which may be missed in trans-sclerallaser cyclophotocoagulation. Because most glaucoma patients do not possess the large pupils and clear media necessary for the transpupillary approach, however, trans-scleral cyclophotocoagulation with the Nd:YAG or 810-nm diode laser is used more frequently. Recently, endocyclophotocoagulation (see below) has been increasingly popular.
In laser trans-scleral destruction of ciliary processes, 30–40 applications of energy are directed at the limbus at an angle that will strike the secretory portion of the ciliary processes. The laser energy may be delivered with a slit-lamp (non-contact) delivery system or with a fiber-optic probe placed directly on the conjunctiva (contact) ( Fig. 32-2 ). Retrobulbar anesthesia is usually required for the patient’s comfort during and after the procedure. The patient’s eyelids may be separated manually or, more conveniently, with a speculum. A specialized contact lens may be useful to help control eye movement, compress the conjunctiva, and assist in placing laser applications with the non-contact variety. With non-contact treatment, the angle of laser incidence of the beam should roughly parallel the visual axis and strike the globe approximately 1–2 mm posterior to the limbus. Generally the 3 and 9 o’clock meridians are avoided to prevent damage to the long posterior ciliary arteries. Preoperative vasoconstriction with an α agonist (iopidine, alphagan P) may reduce energy absorption by conjunctival vessels and decrease the likelihood of subconjunctival hemorrhage.
Laser energy parameters are variable, because the energy output of various instruments is also variable. One technique uses energy levels of 0.5–2.75 J for 32 applications distributed over 360° of the ciliary body. Treating 270° with 16–18 applications may decrease the incidence of complications and is recommended. Exposure times range from 10 to 20 ms. Some surgeons use up to 8 J. Because of the varying amounts of energy delivered by each type of laser instrument, it is advisable to obtain recommendations from a surgeon experienced with the particular instrument being used.
Although repeat treatments often are needed, 60–70% of cases can be controlled, maintaining IOPs of 22 mmHg or lower. Complications include reduced visual acuity, uveitis, pain, hemorrhage, and phthisis bulbi. All of these complications, especially pain and inflammation, seem less severe than those experienced after cyclocryotherapy.
Contact trans-scleral cyclophotocoagulation (TCP) ( Fig. 32-3 ) has been accomplished using the same laser energy levels but delivered with a fiber-optic probe lightly pressed onto the conjunctiva ( Tables 32-1 and 32-2 ). Slightly lower energy levels than those used for non-contact procedures are advisable because the contact pressure increases the transparency of the sclera. Retrobulbar anesthesia is necessary, as is a speculum to separate the eyelids. The probe should be placed 0.5–1.0 mm from the limbus and held as perpendicular to the sclera as possible. Probes made especially for cyclophotocoagulation such as the G-Probe™ of Gaasterland make placement easier and more uniform.
|1064-nm Nd:YAG||810-nm Diode|
|Power||5–6 J||1.5–2.5 W, 1–2 sec|
|Distance from limbus||0.5–1 mm||1.2 mm|
|Spot size||0.9 mm||100–400 μm|
|1064-nm Nd:YAG||810-nm Diode|
|Power||4–8 J||1200–1500 mW, 1 sec|
|Distance from limbus||1–2 mm||0.5–1.0 mm|
|Spot size||0.9 mm||100–400 μm|
|Depth of focus||3.6 mm beyond surface||3.6 mm beyond surface|
All forms of trans-scleral laser cyclophotocoagulation may damage ciliary muscle as well as ciliary epithelium, adjacent iris, and retina. Extreme care must also be taken to avoid excessive destruction of the ciliary body, which could lead to hypotony and possibly phthisis. To target the ciliary epithelium more accurately, some physicians favor the use of an endoscopic probe and laser delivery fiber introduced via a limbal incision. This allows the surgeon to directly visualize and destroy the ciliary processes. This is an invasive technique, however, that requires sterile technique but is gaining in popularity.
Endocyclophotocoagulation procedures are currently under clinical and laboratory investigation. Endocyclophotocoagulation may be most useful for aphakic and pseudophakic eyes or in combination with phacoemulsification procedures. Following endocyclophotocoagulation, some surgeons inject sub-Tenon’s dexamethasone over the perilimbal area treated by the laser; others use topical steroids and atropine drops alone.
Since immediate postoperative pressure spikes are common with all types of cyclophotocoagulation, often an oral carbonic anhydrase inhibitor (acetazolamide 500 mg, methazolamide 50–100 mg) is administered immediately pre- or postoperatively. It is important to monitor patients closely in the short-term postoperative period.
The operated eye is usually patched postoperatively overnight or until the anesthetic wears off. Long-acting anesthetics such as bupivacaine help with immediate postoperative pain control. The patient should be sent home with an adequate supply of major analgesic medication as the eye may be quite painful after the anesthetic wears off. Topical regimens typically include prednisolone acetate 1% four times daily and atropine sulfate 1% twice daily. Medications are tapered gradually until inflammation has disappeared. Preoperative glaucoma medications may be continued as needed, except for miotics. Repeat cyclodestructive procedures are often necessary, although fewer spots should be treated to avoid hypotony and phthisis.
These procedures are alternatives to cyclocryotherapy. All cyclodestructive procedures may cause side effects of pain, phthisis, and reduced vision, although laser techniques may cause less pain and allow for more precise control of energy delivery.
OTHER LASER PROCEDURES
Lasers have also achieved widespread use in conjunction with surgical procedures such as trabeculectomy. Laser suture lysis, for example, can safely sever trabeculectomy flap sutures to increase filtration. Laser bleb reopening and remodeling may reduce the need for further invasive filtration surgery. Finally, lasers provide a safe and often effective approach to closing cyclodialysis clefts, removing peripheral anterior synechiae from the angle or cornea, and enlarging miotic pupils. Laser procedures are safer than surgical alternatives in all of these capacities.
SEVERING OF SUTURES
Subconjunctival trabeculectomy flap sutures can be lysed with the laser postoperatively if there is inadequate filtration. Dark nylon or proline sutures can usually be severed with the argon laser using settings of 200–1000 mW for 0.02–0.15 second with a 50–100-μmspot size. This allows the surgeon to suture the wound more securely at the time of surgery. Tighter suturing maintains the integrity of the eye better and reduces the incidence of flat chambers and hypotony in the early postoperative period. The procedure is feasible from about 3–15 days after surgery or up to at least 2 months or more after mitomycin-C use.
Laser suture lysis (LSL) is accomplished by first anesthetizing the eye with an appropriate topical agent and then compressing the conjunctiva overlying the suture with the flat corner of a four-mirror gonioprism or specially designed laser suture lens such as that described by Hoskins. Phenylephrine 2.5% or apraclonidine 0.5% (Iopidine®) is useful to blanch the superficial vessels of the conjunctiva. Gentle but constant pressure with the lens will displace fluid from the most edematous conjunctiva and provide a clear view of the underlying suture, which usually can be lysed with one or two laser applications. If possible, sutures should be lysed close to their tissue penetration site to prevent the loose ends from springing up and potentially disrupting the conjunctiva. Very edematous flaps may require 1–2 minutes of sustained gentle pressure over the suture before the suture is clearly visible ( Figs 32-4 and 32-5 ). Dense hemorrhage in the tissues overlying the suture will absorb the energy, prevent treatment, and possibly cause conjunctival perforation. Similarly, fluorescein-stained conjunctiva limits argon laser energy transmission to the sutures and may cause conjunctival perforation. Therefore eyes with conjunctival hemorrhage obscuring the suture cannot be treated with this technique.