C. Nucci et al. (Eds.) Progress in Brain Research, Vol. 173 ISSN 0079-6123 Copyright r 2008 Elsevier B.V. All rights reserved
Laser therapies for glaucoma: new frontiers G.L. Scuderi and N. Pasquale University of Rome, ‘‘La Sapienza’’ 2nd Faculty of Medicine, Rome, Italy
Abstract: Glaucoma is a long-term ocular neuropathy deﬁned by optic disc or retinal nerve ﬁber structural abnormalities and visual-ﬁeld defects. Treatment for glaucoma consists of reducing intraocular pressure (IOP) to an acceptable target range to prevent further optic-nerve damage. Currently available treatments include topical drug (single then multidrug combinations) followed, for those patients on maximal tolerated medical therapy who still need additional IOP reduction, by laser treatments. These included laser iridotomy, laser trabeculoplasty, laser iridoplasty, laser cyclophotocoagulation. Although the various types of laser enjoyed great success as glaucoma therapy for many years, recently the excimer laser trabeculotomy is a promising IOP-lowering technique. Keywords: glaucoma; iridectomy; iridotomy; pupillary block; trabecular ring; ciliary body
of acute attacks. Meyer-Schwickerath (1956) demonstrated the efﬁcacy in this setting of xenon-arc laser iridectomy, but this technique was later abandoned because of its high rate of complications. By the 1980s, incisional iridectomy for angleclosure glaucoma associated with pupillary block had been largely replaced by laser iridotomy using argon and later Nd:YAG lasers. Iridotomy has become the procedure of choice for preventing acute attacks of glaucoma, and its use has reduced the total number of these pathologic events (Scuderi et al., 1995).
Background For more than half a century, many types of lasers (xenon, krypton, argon, neodymium:YAG (Nd: YAG, diode, excimer) have been used to treat glaucoma in its different forms. The aims and outcomes of these treatments have varied. Some have been abandoned, along with the lasers used to perform them; others continue to play roles of primary importance in the parasurgical treatment of glaucoma.
Von Graefe (1857) proposed surgical iridectomy for the treatment of glaucomatous disease. This approach was widely used for over a century, especially in cases of angle-closure glaucoma and in the treatment
The indications proposed by the European Glaucoma Society include all clinically relevant cases of pupillary block, regardless of degree. More speciﬁcally, the following conditions are considered:
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Acute angle-closure glaucoma: Treatment must be administered during the initial phases
of the attack or after drug therapy aimed at reducing the intraocular pressure (IOP) and attenuating inﬂammation of the iris and corneal edema. Narrow-angle glaucoma with positive results in provocative tests: treatment is indicated in young, high-risk patients with positive family histories. Pigment dispersion syndrome and the initial phases of pigmentary glaucoma: the aim here is to eliminate iris concavity and iris-zonular contact. The long-term efﬁcacy of laser therapy in this syndrome has not been demonstrated although its use is supported by the results of numerous studies (Gandolﬁ et al., 1996; Lagreze et al., 1996; Scuderi et al., 1997; Carassa et al., 1998). Preparation for argon laser trabeculoplasty (ALT).
Contraindications The main contraindications are corneal opacity, neovascularization of the iris, and athalamia. Patient preparation After the patient’s informed consent has been obtained, miotic drops (e.g., dapiprazole 0.5% or pilocarpine 2% or 4%) are usually administered to constrict the pupil and reduce the thickness of the iris so that it can be perforated more easily. Pilocarpine is a more effective miotic than dapiprazole, but it also causes greater congestion of the iris vessels, which increases the risk of bleeding. Systemic administration of acetazolamide or topical application of 1% apraclonidine 1 h before and immediately after the treatment prevents IOP increases and reduces the bleeding of the iris. Laser treatment is performed under topical anesthesia with 4% benoxinate or 4% oxybuprocaine. Technique Peripheral iridectomy must be performed in the upper quadrants, approximately 2/3 of the distance between the margin of the pupil and the limbus. The iridotomy is then covered by the upper
eyelid to prevent monocular diplopia. This is particularly important for the large iridotomies created with an argon laser; the location is less important for small YAG iridotomies. The thinner areas of the iris, such as the crypts, are the preferred treatment sites. Visible blood vessels should be avoided. Peripheral laser iridectomies can be done with an argon laser or with an Nd:YAG laser, with the aid of an Abraham or Wise contact lens. Both lasers are effective, but they have different features. The predominant effect of the argon laser is photocoagulation with energy absorption by the iris pigment; the YAG laser produces photodestruction through a chromophoreindependent mechanism. Many authors prefer the Nd:YAG treatment because it is simpler to perform, uses less energy, and is associated with a lower rate of iridotomy closure than argon laser treatment. However, in eyes with visible iris vessels and for patients on anticoagulants, the iridotomy site should ideally be pretreated with argon. Nd:YAG laser iridectomy The Nd:YAG laser is the laser of choice for iridectomies. Power consumption ranges from 1 to 6 mJ. One or more impacts are needed to perforate the iris. Depending on the model, applications consisting of pulse trains or a single pulse may be used; the spot diameter ranges from 50 to 70 mm. Use of a converging contact lens equipped with a magniﬁcation area improves laser-spot focusing and reduces energy consumption. Perforation of the iris is generally accompanied by movement of the aqueous humor, together with particles of iris pigment, from the posterior to the anterior chamber (Fig. 1). Perforation can be veriﬁed by the use of transillumination, which allows visualization of the choroidal reﬂex through the gap in the stroma of the iris. Mild, posttraumatic hemorrhage is a common ﬁnding. It can be controlled by exerting light pressure on the cornea for 10–20 s with the contact lens. If this is not sufﬁcient, argon treatment with long-duration pulses can be used to coagulate the edges of the treatment area.
The most common complications are less severe. They include:
Fig. 1. Iridotomy.
Argon laser iridectomy Laser parameters vary depending on the type of treatment being administered and the color of the iris. For lightly pigmented irides, energy levels of 800–1000 mW are used with a spot size of 50 mm and an exposure time of 0.2 s. For thick, darkbrown irides, 1500–2500 mW of power is used with an exposure time of 0.02–0.05 s and a spot diameter of 50 mm. Complications When the iridotomy is done correctly, both intraoperative and long-term complications are very rare. There are reports in the literature of isolated cases with complications, including some that are serious: retinal detachment, cataract, lens luxation, and rupture of Descemet’s membrane (Mastropasqua et al., 1984; Zadok and Chayet, 1999; Liu et al., 2002).
Transient increases in pressure, which occur in approximately one third of treated eyes. They are caused by treatment debris, which impedes outﬂow of the aqueous humor (Hsiao and Hsu, 2003). This problem can be prevented by the administration of topical timolol and oral acetazolamide (Fleck and Wright, 1997). Temporary ‘‘fogging.’’ Laser-induced iritis; posterior synechiae (rare); the risk of these events can be reduced with the use of topical steroids. Diplopia — this occurs when the iridotomy is positioned on the horizontal meridians and not covered by the upper eyelid. Bleeding. Damage to the corneal endothelium (Wu and Jeng, 2000). Incomplete (partial-thickness) iridotomy.
Efficacy Laser iridotomy is now a valid, effective alternative to surgical procedures for the treatment of narrow-angle glaucoma (Rivera et al., 1985; Fleck and Wright, 1997). It is easy to perform, relatively safe, and rarely associated with complications. The efﬁcacy of this approach has been widely demonstrated over the past 20 years. In 70–85% of the patients treated (Playfair and Watson, 1979; Jiang, 1991; Fleck and Wright, 1997) signiﬁcant reductions in IOP have been achieved without IOPreducing drug therapy in follow-ups ranging from 1 to 3 years. The iridocorneal angle remains open in 70–80% of treated patients, and only a small percentage require retreatment (Thomas and Arun, 1999; Ritch et al., 2004).
LASER trabeculoplasty The ﬁrst experimental laser treatments of the iridocorneal angle were the ‘‘goniopuncture’’
procedures performed by Krasnov (1973) to improve aqueous-humor outﬂow. The method known as ALT was developed laterby Wise and Witter (1979). In the 23 years that have passed since its introduction, ALT has not undergone any substantial modiﬁcations. It involves a series of photocoagulations that produce nonperforating thermal lesions uniformly distributed over the trabecular ring.
Treatment technique Laser trabeculoplasty is frequently used to treat glaucoma, and it produces good long-term results. It is usually done with an argon laser (use of diode lasers is less common) and a gonioscopic contact lens. The most widely used gonioscopy lenses are the Goldmann three-mirror lens and the Ritch gonioprism, which allows better visualization of the trabecular mesh and uses less energy. The standard settings proposed by Wise and Witter include a spot diameter of 50 mm and an exposure time of 0.1 s. The power varies depending on the response of the tissue and the type of lens (600–1200 mW with the Goldmann lens, 600–800 mW with the Ritch). The spots (20–25 per quadrant) must be uniformly distributed along the entire circumference of the trabecular meshwork. The recommended site of application is the junction of the pigmented and nonpigmented trabecular meshworks. This approach spares part of the ﬁltering trabecula and the posterior trabecular meshwork, thus reducing the incidence of pressure spikes and posttreatment peripheral anterior synechiae (PAS). ALT can be performed in one or two 50-to-60-spot sessions to reduce the risk of laser-induced pressure spikes. The laser produces whitening of the treated zone or the formation of a small bleb in the burst zones. When an argon laser is used, green light is just as effective as blue-green, and it reduces the risk of damage to the photoreceptors of the operator (Berringer et al., 1989). The operator can also use a contact lens with a metal halide coating to reduce the risk of macular damage caused by reﬂected light.
Mechanism of action Various mechanisms of action have been hypothesized; according to the theory proposed by Wise, the thermal effect produced by the laser spots stretches and widens the trabecular meshes and/or the Schlemm’s canal (Wise and Witter, 1979). Other authors maintain that the laser triggers physiological changes in the activities of the endothelial cells with increased phagocytotic activity (Bylsma et al., 1988) or increased cell replication within the trabeculate that promote the outﬂow of aqueous humor (Wilensky and Weinreb, 1983). Indications for treatment The European Glaucoma Society’s guidelines recommend trabeculoplasty in the following cases:
Primary open-angle glaucoma that is refractory to medical therapy. Patients who are noncompliant or unable to tolerate medical therapy. Pseudoexfoliation glaucoma. Pigmentary glaucoma.
Contraindications to treatment Treatment is contraindicated in patients whose angular structures cannot be explored and/or those with uveal inﬂammation or congenital malformations involving the trabecular structures, as in the following cases:
Narrow or closed angle. Corneal opacity that precludes gonioscopy. Absence of trabecular pigmentation. Inﬂammatory or postuveitic glaucoma. Juvenile glaucoma. Absence of effects in the contralateral eye.
Patient preparation and postoperative follow-up Written consent should be obtained from the patient after the objectives of the treatment and its potential risks have been presented and discussed.
Before and after the laser treatment apraclonidine 0.5% or brimonidine 0.2% should be added to the patient’s normal antiglaucoma regimen to prevent or attenuate iop spikes (Chen and Ang, 2001). Topical anesthesia with 4% benoxinate or 4% oxybuprocaine is generally sufﬁcient. During the immediate postoperative period (4–7 days), local steroid treatment or topical nonsteroidal anti-inﬂammatory drugs (NSAIDs) should be applied 3–4 times a day. NSAIDs can also be administered 24 h before the treatment to reduce the release of prostaglandins that are responsible for the inﬂammatory response (Hotchkiss et al., 1984). The patient should be reexamined 24 h after treatment and at 4–6 weeks to evaluate the effects of the treatment and make sure there are no complications. The European Glaucoma Society recommends closer follow-up (1 and 3 h after treatment) for patients with serious visual-ﬁeld defects, markedly elevated pretreatment IOPs, exfoliation syndrome, one-eyed patients, and those who have had previous laser trabeculoplasties. Complications of the treatment The most common complication of laser trabeculoplasty is the acute, transient elevation of IOP, which is evident immediately after treatment. Thirty to ﬁfty percent of all patients experience IOP increases of 10 mmHg or more 1–7 h after treatment (Krupin et al., 1987; Tuulonen et al., 1989). The incidence and the magnitude of these pressure spikes seem to be reduced when ALT is performed in two 50-spot sessions. The literature contains rare reports of ocular hypertension with onset several weeks after trabeculoplasty, including some that were associated with posttreatment uveitis. PAS are found in 12–47% of treated eyes, depending on the various statistics; the mean frequency reported in the Glaucoma Laser Trial was 33% (Glaucoma Laser Trial Research Group, 1995). According to this study, synechiae formation is associated with intense pigmentation of the trabecular meshwork; other studies suggest that this complication is dependent on the site of treatment (posterior versus the root of the iris). Iritis, hemorrhages, transient reductions in visual acuity caused by the gonioscopy ﬂuid (used
to enhance contact), and corneal lesions are rare complications. Efficacy The effects of the laser treatment are not immediate; 4–6 weeks must pass before the results can be properly evaluated. In 84% of all patients who undergo trabeculoplasty, signiﬁcant reductions in IOP are observed within 12 months of treatment. However, the rate decreases as the duration of follow-up increases, reaching 55% 5 years after treatment (Fellman et al., 1984; Lunde, 1993). In two other long-term studies, the effect of ALT persisted for 1 year in 67–80% of treated eyes, for 5 years in 35–50%, and for 10 years in 5–30%, with an annual loss of efﬁcacy in the range of 6–10% (Shingleton and Richter, 1987; Spaeth and Baez, 1992). Patients who have had ALT thus have to be followed constantly, with ongoing monitoring of clinical examinations. It is difﬁcult to predict if or when increases in IOP will occur: they may appear after months or even years of follow-up. Retreatment carries a considerably reduced likelihood of success compared with the initial ALT. In these cases, surgical treatment should probably be considered.
Selective laser trabeculoplasty Selective laser trabeculoplasty (SLT) is a recently introduced technique that was developed by Latina and Park (1995). In March of 2001, it was approved by the Food and Drug Administration for treatment of open-angle glaucoma. In terms of both efﬁcacy and safety, SLT has been judged to be clinically equivalent to ALT, which was previously used for patients with open-angle glaucoma. It is based on the use of a Q-switched frequency-doubled 532 nm Nd:YAG laser with a spot diameter of 400 mm, a power range of 0.2–2.0 mJ, and a pulse duration of 3–10 ns; it can be used to treat 1801 of the trabecular meshwork (50 spots) or the full circumference (100 spots). Latina and Park showed that a Q-switched laser emitting at 532 nm with a pulse duration in the nanosecond range can selectively lyse the
pigmented cells of the trabecular meshwork without provoking thermal damage to adjacent nonpigmented cells. The absence of these unwanted thermal effects is the result of the afﬁnity of the 532 nm wavelength for the chromophore/target represented by melanin, but also by the pulse duration of a few nanoseconds, which is shorter than the time required — around 1 ms — for the conversion of radiant electromagnetic energy into heat by the chromophore melanin in pigmented cells. When radiant energy is released rapidly, as it is with a nanosecond-range pulse, only a minimal part is converted into heat. This limits the thermal dissipation and coagulative damage, not only in the treatment zone but also in the surrounding tissues. The success of SLT depends on a precise, highly sensitive mechanism that involves the destruction of certain cells and the sparing of others, thus preserving the structural integrity of the trabecular meshwork. The injured cells release cytokines that recruit macrophages and provoke other changes. The result is increased outﬂow, a reduction of IOP that occurs within a few hours, the birth of new cells, and lasting increases in the outﬂow capacity.
Results The efﬁcacy and safety of SLT have been clearly demonstrated. Thirty months after treatment, success was observed in 77% of the patients with chronic open-angle glaucoma and in 74% of those with exfoliation glaucoma (Latina, 1998). Maximum pressure-reducing effects were observed 7–14 days after treatment, with an IOP of approximately 10 mmHg during the ﬁrst postoperative hours. However, the presence of an inﬂammatory reaction was documented, and the IOP during the ﬁrst few hours was higher than that observed after ALT. Six months after treatment, the pressure-reducing effect of SLT is comparable to that of laser trabeculoplasty. In a population-based study, response rates treatment were slightly different from those associated with treatment of 3601 to 1801 (Nagar et al., 2005) 901 SLT is generally not effective. 1801 and 3601 SLT appears to be an effective treatment
with approximately 60% of eyes achieving an IOP reduction of 30% or more. In conclusion, SLT is an interesting method and an excellent alternative to ALT, and it should be considered a ﬁrst-line treatment for patients with chronic open-angle glaucoma (Latina et al., 2002; Martinez-de-la-Casa, 2004). SLT can be repeated, even after laser trabeculoplasty. It seems to produce better results than ALT in eyes with nonpigmented angles and is also associated with a lower risk of for trabecular damage.
LASER iridoplasty Peripheral iridoplasty, also known as gonioplasty, involves photocoagulative treatment of the peripheral iris based on the induction of thermal contraction of the stroma of the iris, which widens the angular recess. Indications The European Glaucoma Society guidelines recommend the use of iridoplasty in the following conditions:
Plateau iris syndrome. Preparation for laser trabeculoplasty when the iridocorneal angle is narrow and difﬁcult to see. Angle closure in nanophthalmus.
Contraindications Treatment is not advisable if the following conditions are present:
Severe edema or corneal opacity that impairs visualization of the peripheral iris. Marked gerontoxon. Athalamia. Angle closure secondary to synechiae.
Treatment technique Laser iridoplasty is done under topical anesthesia after instillation of a miotic to distend the
peripheral iris. An argon or diode laser is used with an Abraham contact lens or gonioscopy lens and the following laser parameters: spot diameter 200–500 mm, power 200–400 mW, and a duration of 0.2–0.5 s. For 3601 treatment, the ideal number of applications per quadrant is 5–6 (total: 20–30 distributed along the circumference); each should be separated by a distance equal to twice the spot diameter, and visible vessels should be avoided. Conﬂuence of the photocoagulative lesions produces ischemic zones in the iris, secondary atrophy, and widening of the angle. Topical steroids are administered for the ﬁrst 4–7 postoperative days. The patient is reexamined 24 h, 1 week and 3–4 weeks after treatment to evaluate efﬁcacy and check for complications. Complications The most common complications are mild, transient iritis associated with an increase in the IOP; endothelial lesions (especially in patients with nanophthalmus); anterior angle and posterior iridolenticular synechiae; and permanent mydriasis (rare). Efficacy Peripheral iridoplasty is an effective and relatively safe treatment provided that is not performed with high-energy levels. A single treatment is sufﬁcient to open the angular recess in 85–90% of patients with the plateau iris syndrome followed for 10 years (Ritch et al., 2004). A recent randomized controlled trial demonstrated the efﬁcacy of this approach in cases of acute angle-closure glaucoma compared with conventional systemic pressurereducing drug therapy (Lam et al., 2002).
diathermy and penetrating diathermy, respectively, for the electrocoagulative destruction of the ciliary body in patients with glaucoma. Cyclodiathermy, which was associated with a high complication rate and poor results, was eventually abandoned in favor of cyclocryotherapy. The latter technique was introduced by Bietti (1950) and it was regarded as the cyclodestructive procedure of choice for over 30 years. The mechanism by which cyclocryotherapy destroys the ciliary process involves the formation of intracellular calcium crystals, which is associated with ischemic necrosis of the epithelium and stromal components of the ciliary body (Wilkes and Fraunfelder, 1979). The standard method calls for application of the cryoprobe to the conjunctiva with the anterior border approximately 22 mm from the limbus. The temperature is reduced (between 701C and 901C), and four to eight applications are made per quadrant (depending on operator preferences). Because of the high rate of complications associated with this approach (pressure spikes, hypotonia, marked inﬂammatory reactions, intense pain, hemophthalmus, cataract, phthisis bulbi), cyclocryotherapy has also be gradually abandoned. Beckman et al. (1972) proposed the use of a ruby laser (694 nm) for transscleral cyclophotocoagulation of the ciliary bodies, but in the past decade, cyclocryocoagulation has gradually been abandoned in favor of cyclophotocoagulation performed with an Nd:YAG (1064 nm) laser, which guarantees good results with moderate complications. The most widely used techniques are transscleral contact and noncontact photocoagulation and transpupillary photocoagulation. Indications and contraindications
LASER cyclophotocoagulation Introduction The use of methods aimed at diminishing IOP by destroying the ciliary body and thus reducing aqueous-humor production dates back to the 1930s. Weve (1933) and Vogt (1936) proposed
Cyclophotocoagulation procedures have traditionally been reserved for patients whose glaucoma is refractory to medical and surgical treatment, those with neovascular glaucoma, blindness and eye pain due to increased IOP, and cases of advanced or end-stage glaucoma (Pastor et al., 2001). In effect, this approach has been considered the treatment of last resort. In recent years, however, some
ophthalmologists with more extensive experience with cyclophotocoagulation have extended its indications, noting that the complication rates are lower than once believed (Scuderi et al., 1993; Gayton et al., 1999; Pastor et al., 2001). Cycloablation is still contraindicated, however, when safer options are available and in patients whose visual capacity is high.
seen as crater-shaped whitening of the ciliary process. Transpupillary photocoagulation is not associated with an excessively high rate of complications; however, since its use is limited to rare cases, the transscleral approach is usually preferred.
Endoscopic cyclophotocoagulation Patient preparation As with all parasurgical procedures, the patient must provide informed consent after the objectives and potential risks of the procedure have been presented and discussed. Cyclophotocoagulation procedures can be performed in an outpatient setting; local anesthesia can be achieved with a peri- or retrobulbar injection of 2% lidocaine+0.75% bupivacaine with hyaluronidase (50:50). During the preparation phase, systemically administered acetazolamide and/or mannitol can be prescribed to decompress the eye and reduce the risk of choroidal hemorrhage. During the preoperative phase, topical apraclonidine can be given to decongest the conjunctiva and reduce the risk of posttreatment increases in IOP (Chen and Ang, 2001).
Treatments involving the ciliary processes have been further improved in recent years thanks to the introduction of small endoscopes (21-gauge) that use ﬁber optics for illumination, observation, and laser treatment. This approach, known as endoscopic cyclophotocoagulation (ecp) is considered a surgical method (Shields et al., 1985) because it requires that an instrument be introduced into the ocular bulb through the pars plana or the limbus. Its advantages include more precise visualization of the anatomic structure being treated, lower energy consumption (normally around 0.3 W per 1 s with around 60 applications) and reduced involvement of contiguous structures. ECP can be performed in association with phacoemulsiﬁcation procedures (Uram, 1995).
Introduced by Lee (1971), transpupillary photocoagulation allows destruction of the ciliary processes through the pupil or a wide surgical iridectomy. The laser spot can be focused on the ciliary processes directly or indirectly with the aid of a gonioscopy lens. This treatment is obviously reserved for eyes in which at least one third of the circumference of the ciliary processes can be clearly visualized, i.e., patients with maximum mydriasis, aniridia, wide surgical iridectomy, or retraction of the iris, which may be present in advanced forms of neovascular glaucoma. Transpupillary cyclophotocoagulation is usually done with an argon laser; less frequently, diode laser is used. Argon lasers are used with a spot diameter of 100–200 mm, exposure time of 0.1–0.2 s, and 700–1000 mW of power; the effect is
Transscleral cyclophotocoagulation was introduced by Vucicevic et al. (1961). It involves the transmission of energy across the conjunctiva and the sclera without direct visualization of the ciliary bodies. It can be carried out with or without contact using either an Nd:YAG (continuousemission or pulsed) or diode laser. Pulsed lasers (Microrupter series) deliver short, high-energy pulses that provoke considerable tissue destruction; continuous-emission lasers (Surgical Laser Technologies, Oaks, PA, Lasag Microruptor III) require longer exposure times and produce coagulative effects. Diode units (Oculigt SLX and DC-3000) are contact-delivery systems; they requires longer exposure times than pulsed highenergy Nd:YAG units and produce tissue effects that are mainly coagulative.
Transscleral noncontact cyclophotocoagulation Transscleral noncontact photocoagulation is done with an Nd:YAG laser and a slit-lamp; air serves as the energy transmission medium. The laser spot is positioned 1.0–1.5 mm posterior to the sclerocorneal limbus; the distance is calculated with a compass or by positioning the sight at the center of a luminous slit 3 mm in length. The laser can be used in the free-running mode with pulses of 4–8 J, 20-s duration, and the defocus set to 9. With these parameters, one can treat 3601 (total: 30–40 spots, 8–9 per quadrant); the 3 and 9 o’clock positions are excluded from treatment to avoid damage to the long posterior ciliary arteries. Treatment is facilitated by the use of the Shields transscleral lens, which improves focusing and facilitates the passage of the laser energy, thus reducing the risk of conjunctival burns. Postoperative treatment is based on the administration of antibiotics and steroids for approximately 2 weeks; pressure-reducing therapy is continued (with possible withdrawal of miotics), and the patient is checked 1 h, 1 day, and 1 week after treatment.
Transscleral contact cyclophotocoagulation Transscleral contact cyclophotocoagulation is the most widely used cyclophotocoagulation technique. Contact treatment offers the advantage of energy transmission through the conjunctiva and sclera by means of an optic ﬁber probe placed directly on the bulb. Compared with the noncontact approach, this technique uses less energy. It can be carried out with a Nd:YAG laser (1064 nm) in the continuous-emission mode by means of an optical ﬁber or with a diode laser (810 nm). In the Nd:YAG procedure, the probe is positioned at a right angle to the conjunctiva, 0.5–1 mm behind the sclerocorneal junction; the full circumference (3601) is treated (total: 16–40 spots, 4–6 J) with the exception of the 3 and 9 o’clock positions. The exposure time is 0.5–0.7 s, and scleral indentation facilitates energy transmission. Better results are obtained with a relatively
light initial treatment followed by one or more additional treatments as needed. With diode systems, the energy is delivered by means of the G-probe, a bundle of optical ﬁbers whose contour adapts to the curvature of the sclerocorneal junction. The application site is 0.5–2.0 mm behind the limbus; transillumination is used to visualize the ciliary processes; 8–15 spots (1500–2500 mW lasting 1–2 s) are made from 901 to 2701. The upper temporal zone is generally spared so that trabeculectomy or other surgical procedures can be performed if necessary. The diode laser (DLCP) is a semiconductor laser with a wavelength of 810 nm. Its advantages include good penetration and selective absorption by the pigmented tissue of the ciliary body; transscleral DLCP is thus a selective cycloablative technique that is more conservative than the others. Complications In all cases subjected to cyclophotocoagulation treatment, mild reactive iritis develops after treatment. Conjunctival edema and pain during the treatment are common, especially when contact application is used. The most severe complications are seen is eyes treated with noncontact methods, which use high-energy levels and are often associated with arbitrary focusing of the laser beam. In the literature, phthisis bulbi is reported in 10% of all cases, permanent hypotonus in 26%, and anterior-chamber hemorrhage in 10–30%; less frequent complications include detachment of the choroid, hemovitreous, and sympathetic ophthalmia. Complications are rare in eyes treated with a diode laser: phthisis bulbi 1.6% (Kramp et al., 2002) pain during treatment 25% Pupil ovalization due to the use of high-energy lasers (2000 mW) (very rare) (Pucci and Tappainer, 2003). Recent studies have assessed the efﬁcacy and complication rates of diode laser treatment with spots of different energy levels in patients with refractory glaucoma: there were no signiﬁcant differences in the reductions in IOP. However,
high-energy spots were associated with a higher rate of postlaser complications (hypotonus, transient hyphema, and anterior-chamber exudates) (Murphy and Burnett, 2003; Chang et al., 2004). Efficacy The results of contact and noncontact YAG laser cyclophotocoagulation are similar. Pressure reductions (p24 mmHg) are observed in 45–80% of cases during the ﬁrst year of follow-up; additional medical treatment is necessary in 28–70% of treated eyes and retreatment in 30–50% (Dickens and Nguyen, 1995; Lin et al., 2004). The success of the treatment varies with the energy used: high energy increases the efﬁcacy but also the rate of complications. Transscleral contact diode laser photocoagulation reduces the IOP by 35–43% from pretreatment levels with a single treatment; the need for pressure-reducing drugs is reduced by approximately 50%, with improvements in the quality of life and compliance with medical therapy.
Retreatment is necessary in 45% of all cases (Pucci and Tappainer, 2003). The efﬁcacy of the treatment seems to be positively correlated with the age of the patient, inversely correlated with previous surgical procedures and the type of glaucoma: higher rates of success are reported in cases of open-angle, inﬂammatory, or neovascular glaucoma (Schlote and Derse, 2001). Excimer laser trabeculotomy Excimer laser trabeculotomy (ELT) is a new minimally invasive method for treatment of open-angle glaucoma that can easily be combined with cataract surgery. Laser spots are applied on to trabecular meshwork via an endoscopic ﬁber and a gonio lens (Fig. 2). In contrast to ALT, shunts between the anterior chamber and Schlemm’s canal are prepared by a photoablative laser, thus increase the outﬂow of aqueous humor (Herdener and Pache, 2007).
Fig. 2. ELT endoscopic ﬁber.
ELT is a promising IOP-lowering technique both as a stand-alone procedure and in combination with cataract surgery. It is especially suitable for patients with high preoperative IOP levels (Pache et al., 2006).
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