Morphological studies about the efficiency of laser beams upon the structures of the angle of the anterior chamber. Facts and concepts related to the treatment of the chronic simple glaucoma

Laser Management of Glaucoma in Exfoliation Syndrome

Argon laser trabeculoplasty as well as selective laser trabeculoplasty can be used in patients with exfoliation syndrome with similar safety and efficacy. However, treatment effect may abruptly reverse and patients need to be followed regularly to monitor intraocular pressure control. Newer laser treatment modalities including micropulse laser trabeculoplasty, titanium sapphire laser trabeculoplasty and pattern scanning trabeculoplasty show promising results but need to be studied in exfoliation patients. For exfoliation patients with angle closure, peripheral iridectomy, iridoplasty or cataract extraction can be very helpful. For refractory exfoliation glaucoma, transscleral diode laser cyclophotocoagulation offers a reasonable option to lower intraocular pressure. Other approaches to cyclophotocoagulation such as micropulse transcleral diode laser need to be studied further in exfoliation patients.

Impact of laser trabeculoplasty on Trabectome® outcomes

BACKGROUND AND OBJECTIVE

To report the impact of prior laser trabeculoplasty on clinical outcomes of Trabectome (NeoMedix Corporation, Tustin, CA) surgery.

PATIENTS AND METHODS

This is a retrospective, non-comparative study of consecutive cases of Trabectome surgery with 36 months of follow-up. Main outcome measures were intraocular pressure (IOP), number of glaucoma medications, and the occurrence of secondary procedures.

RESULTS

In the trabeculoplasty group, mean IOP measured 16.5 +/- 4.0 mm Hg with an average decrease of 24% from preoperative IOP at 12 months. In eyes without previous trabeculoplasty, IOP measured 15.7 +/- 3.0 mm Hg with an average decrease of 30% at 12 months. Adjunctive medications decreased to 2.1 and 1.5 glaucoma medications, respectively. Secondary procedures were performed in 12% and 10% of eyes in each group.

CONCLUSION

Previous laser trabeculoplasty does not appear to significantly impact IOP, but may increase the need for glaucoma medication in patients undergoing Trabectome surgery.

Argon laser trabeculoplasty versus selective laser trabeculoplasty

The clinical role of laser trabeculoplasty remains a controversial topic with many different opinions. In the following three viewpoints the authors have taken contrasting positions on whether argon laser trabeculoplasty remains the "gold standard" or has been supplanted by selective laser trabeculoplasty. Questions are raised regarding the position of laser trabeculoplasty within the stepping of the treatment paradigm for open-angle glaucoma. The appropriate use of laser trabeculoplasty at different stages of disease severity is analyzed. A broader perspective with new insights on laser trabeculoplasty from these articles will hopefully lead to a better understanding of its clinical role in practice.

Microendoscopic trabecular surgery in glaucoma management

OBJECTIVE

To evaluate the safety and efficacy of trabecular surgery under microendoscopic control in the management of advanced chronic open-angle glaucoma when the presence of corneal opacification obscures adequate visualization of the anterior segment.

STUDY DESIGN

Comparative interventional case series.

PARTICIPANTS AND INTERVENTION

Fifteen eyes of 15 patients with medically uncontrolled open-angle glaucoma and moderate-to-severe corneal opacification underwent trabecular surgery under microendoscopic control. Seven eyes were treated by photoablative laser goniopuncture and eight eyes by goniocurettage.

MAIN OUTCOME MEASURES

The intraocular pressure (IOP) and number of medications before and after surgery were measured. Intraoperative and postoperative complications were analyzed.

RESULTS

The ophthalmic microendoscope was successfully used in visualizing and identifying the anterior chamber angle structures and in controlling the trabecular surgical procedures in all eyes. The IOP dropped from 34.5 +/- 6.9 millimeters of mercury (mmHg) (range, 27-46 mmHg) under maximal-tolerated medical therapy before surgery to 18.5 +/- 3.0 mmHg (range, 15-23 mmHg) at 21 months after surgery. Medication averaged 2.3 +/- 0.6 before surgery and dropped to 1.0 +/- 0.7 at last follow-up. No difference was observed in the surgical outcome between the laser-treated eyes and those receiving goniocurettage. No severe intraoperative or postoperative complications relating to either the trabecular surgery or to the use of the microendoscope were observed.

CONCLUSION

The ophthalmic microendoscope appears to be safe and effective in simultaneously providing illumination, video recording, and clear endoscopic view of the fine details of the anterior chamber angle structures. Microendoscopy enables various trabecular surgical procedures, such as goniocurettage or photoablative laser goniopuncture, which can be performed in the presence of corneal opacification that might otherwise preclude adequate visualization and treatment. It thus appears that microendoscopic trabecular surgery may in the future be considered as an alternative choice of surgical treatment in some cases of open-angle glaucoma.

Experimental microendoscopic photoablative laser goniotomy as a surgical model for the treatment of dysgenetic glaucoma

PURPOSE

The aim of this study was to investigate the feasibility of photoablative Er:YAG laser goniotomy under microendoscopic control in a surgical cloudy corneal model of primary infantile glaucoma.

METHODS

Pectinate ligaments of 12 freshly enucleated cadaver porcine eyes were treated by ab interno single-pulse (5 mJ, 200 microseconds) Er:YAG laser (2.94 microns) photoablation. Through a clear corneal incision near the limbus an ophthalmic microendoscope (18 and 20 gauge) was inserted into the anterior chamber. Internal structures were observed and photoablative laser goniotomy was conducted under video guidance. Following treatment all eyes were prepared for light and scanning electron microscopy.

RESULTS

Anterior chamber angle structures and tissue photoablation were clearly visualized on the videoscreen using ophthalmic microendoscopy. Energy settings of 5 mJ per pulse proved to be sufficient for reproducible photoablation of pectinate ligaments, accompanied by the root of the iris falling back and exposing trabecular meshwork. This was confirmed histopathologically. Scatter thermal damage was less than 30 microns.

CONCLUSION

This new therapeutic modality, which combines endoscopic visualization of the internal structures with photoablative laser goniotomy, can be effective in the management of dysgenetic glaucoma in the presence of a cloudy cornea. High reproducibility of contact laser photoablation enabled sufficient control of incision depth and was not accompanied by inadvertent tissue damage to adjacent intraocular structures.

Pulsed neodymium-YAG laser trabeculotomy: energy requirements and replicability

Short pulsed laser trabeculotomy has been shown to reduce intraocular pressure in patients with primary open angle glaucoma. This study seeks to determine the energy levels required to produce a fistula into the canal of Schlemm for four different Q-switched neodymium-YAG lasers. The laser was fired at fixed human trabecular meshwork specimens at a range of energy settings for each laser and the characteristics and replicability of the lesions produced were analysed. Energy levels between 3 and 5 mJ were sufficient to produce fistulae into the canal of Schlemm with an approximately 50% success rate for each instrument.

Picosecond optical breakdown: tissue effects and reduction of collateral damage

The effects of picosecond laser-induced optical breakdown on tissue were investigated using high-intensity 40 ps Nd:YAG laser pulses at 1.06 microns. Tissue damage was evaluated using the corneal endothelium in vitro as a model system. Systematic studies were performed to determine the scaling of the tissue damage and damage range with pulse energy. For suprathreshold lesions, the radius of the damage zone varies as the cube root of the pulse energy, in agreement with simple physical scaling laws. A minimum damage range of less than 100 microns was observed for pulse energies of 8 muJ. Damage morphology was investigated by scanning electron microscopy. Three different damage patterns were observed; cell damage, cell removal, and rupture of Descemet's membrane. Different irradiation geometries were used to study damage mediated by either the shock wave or the cavitation bubble. Comparative studies using 10 ns pulses demonstrated that picosecond pulses yielded a significant reduction in collateral tissue damage.

Long-term follow-up of neodymium: YAG laser angle surgery for open-angle glaucoma

Seventy-nine eyes (61 patients) with open-angle glaucoma and uncontrolled intraocular pressure (IOP) of 23 mmHg or more despite maximal tolerated medical therapy and prior argon laser trabeculoplasty (75 eyes) were treated with neodymium: YAG (Nd: YAG) laser angle surgery and followed for at least 1 year. Ten pulses of 10 mJ were applied to the midtrabecular meshwork over 40 degrees in the most visible portion of the angle. The IOP was controlled successfully (less than or equal to 22 mmHg) in 60 eyes (76%) 1 month after treatment and in 36 of 78 eyes (46%) 1 year after treatment. Long-term complications included two eyes with advanced glaucoma that lost central fixation despite good IOP control after treatment.

Parameters for neodymium-YAG laser trabeculotomy: an in-vitro study

A Biophysic Médical Nanolas Q-Switched pulsed neodymium-YAG laser has been used to produce lesions in human trabecular meshwork in vitro. Sectors of corneoscleral tissue containing trabecular meshwork were suspended in a waterbath which had had a Trokel gonioscopic contact lens mounted into one side by means of a watertight seal. The laser was used to produce lesions in the trabecular meshwork on either side of each specimen. The energy levels delivered ranged from 0.5 to 7.0 mJ, and convergence angles of 10 degrees and 18 degrees were employed. The energy levels required to produce discrete lesions into the canal of Schlemm without perforating the underlying sclera were 3.0-5.0 mJ at the 10 degrees convergence angle and 4.0-6.0 mJ at the 18 degrees convergence angle setting. It is recommended that such data be determined for each type of laser prior to attempting short-pulsed laser internal trabeculotomy in patients with glaucoma.

Long-term results of Nd:YAG laser posterior capsulotomy with the Swiss laser

The Microruptor II (MR-II) Nd:YAG laser developed by Fankhauser was evaluated in a national multicenter prospective study of posterior capsulotomy. Results are reported on 3,711 patients who underwent Nd:YAG laser photodiscission. Ninety-two percent of patients experienced an improvement in vision at some point following photodiscission and the postoperative complications of persistent cystoid macular edema and glaucoma occurred at rates of 2.5% and 0.2%, respectively, indicating the safety and efficacy of the MR-II for posterior capsulotomy.

Neodymium: YAG laser trabeculopuncture in open-angle glaucoma

Ten eyes of eight patients with open-angle glaucoma (OAG) had neodymium (Nd):YAG trabeculopuncture performed in an investigational protocol as an alternative to surgical intervention. In each, at four to six sites in the mid-trabecular meshwork, three to six superimposed applications were made (2 to 6 mJ). In four of six patients with adult OAG, a small decrease in intraocular pressure (IOP) was noted (from a mean of 25.5 to 20.0 mmHg after 3-4 weeks in the treated eyes, compared to no change at 21 mmHg in the fellow eyes). There appeared to be further attenuation of this IOP effect over the subsequent 2 to 11 months, and all patients demonstrated gonioscopic closure of all the puncture sites with time. One patient demonstrated an acute IOP elevation to 58 mmHg after the procedure, necessitating emergency filtration surgery. In contrast, in four eyes of two patients with juvenile open angle glaucoma, a dramatic lowering of IOP and improvement in tonographic outflow facility was demonstrated, although the effects were only temporary in one patient. YAG laser treatment to the trabecular meshwork may have its greatest potential usefulness when abnormalities in the uveal meshwork are involved, such as in certain cases of juvenile or congenital glaucoma, and may help identify the need for a surgical goniotomy. With more usual forms of OAG, however, widespread use of this technique should be avoided until greater efficacy can be achieved.

In vitro studies with a pulsed neodymium/YAG laser

The relationships between the destructive effects of Q-switched Nd/YAG laser pulses and a number of experimental parameters were studied for various target materials including in particular excised, fixed samples of human trabecular meshwork. The laser parameters altered were the pulse energy, the convergence angle of the focused beam, and the position of the focus of the beam relative to the target's axial position. The main finding was that it was possible to make deep holes, of a diameter less than 100 micron, in virtually transparent samples of trabecular meshwork with a laser delivery system of 6 degrees convergence and pulse energies of 14 mJ or more. The relevance of this and the other experimental results to the development of a reliable system for performing internal trabeculotomies for the treatment of open-angle glaucoma is presented.

Transpupillary CW YAG laser coagulation. A comparison with argon green and krypton red lasers

The authors have developed a CW YAG laser for transpupillary coagulation. The effects of CW YAG coagulation on the retina, retinal vessels, and fovea were compared with those produced by the krypton red and argon green lasers. To produce threshold coagulative lesions in monkeys and rabbits, we needed five to ten times more energy with the CW YAG than with the krypton red or argon green lasers. Nerve fiber damage was observed only when coagulating retinal vessels with the argon green laser. At the parameters used, none of the lasers damaged the sensory retina of the fovea. The CW YAG may be used as a new mode of laser coagulation in the treatment of retinal diseases.

Threshold for retinal damage associated with the use of high-power neodymium-YAG lasers in the vitreous

Ultrashort, Q-switched or mode-locked, neodymium-YAG laser pulses focused within 2 mm of the retina caused reproducible retinal damage in four eyes of two monkeys and in four eyes of three rabbits. The distance of the laser focus from the retina for clinically observed threshold retinal damage was characterized for pulse energies up to 9 mJ. For the 2- to 6-mJ pulse energies necessary to rupture vitreal membranes in clear media in rabbits, the high-power laser pulses could not be focused within 2 mm of the retina without substantial risk of damaging the underlying retina. These laser pulses did not rupture vitreal membranes in hazy ocular media that prevented precise focusing. The retinal damage was somewhat greater than expected for retinal absorption of 1.06-micron laser energy, suggesting that secondary effects such as self-focusing and shock waves emanating from the focus may be important.

Argon laser lesions of the rabbit iris: quantitative aspects

The destructive effect of nonperforating argon laser coagulations in the brown irides of rabbits was studied with quantitative histological methods. Power, spot size, and exposure time were systematically varied. The lateral and axial extensions of the crater and the denaturation of the adjacent tissue were studied. The main conclusions are: (1) the extent of tissue damage is significantly correlated with power and spot size, though the correlation is not proportional; (2) the lateral extension of the tissue reaction is far more pronounced than the axial extension; (3) increase in exposure time is effective up to 0.2 s, though a further increase up to 0.5 s does not enhance the tissue reaction. It is discussed that for conventionally switched lasers the main determinant for the final extension of the lesion is the density and distribution of the pigment granules within the iris. The radial distribution of the protrusions of the melanocytes in brown irides of the rabbits used in this study favors the lateralization of the tissue reaction. The nonlinearity of the tissue reaction and exposure time might be due to the fact that after initial damage in early phases of irradiation (e.g., up to 50 or 100 ms, the absorbed laser energy is dissipated in already destroyed tissue. Some practical aspects for iridectomy are discussed.

Electron microscopy of argon laser therapy in phakic open-angle glaucoma

In 22 subjects with phakic open-angle glaucoma, trabeculectomies were performed at intervals of three hours to one year after argon laser treatment (ALT). In ten patients the ALT was done with informed consent anticipating that trabeculectomy would be performed at a scheduled time (three hours to two weeks following laser therapy). In 12 other patients, trabeculectomies were required for failure of ALT (one month to one year later). Scanning and transmission electron microscopy of the specimens examined at earlier intervals after laser therapy revealed evidence of heat effects with disruption of trabecular beams, fibrinous material, and necrosis of occasional cells, including melanin-containing endothelial cells, followed by shrinkage of the collagenous components of the trabecular meshwork. The specimens excised at longer intervals after laser treatment showed partial or total occlusion of intertrabecular spaces by a cellular layer of abnormal corneal and/or trabecular endothelial cells with widened cellular interdigitations and numerous prominent filopodial processes typical of migrating cells.

Clinical studies on the efficiency of high power laser radiation upon some structures of the anterior segment of the eye. First experiences of the treatment of some pathological conditions of the anterior segment of the human eye by means of a Q-switched laser system

A series of pathological conditions such as pupillary block glaucoma, angle block glaucoma, acoria, pupillary membranes and goniosynechias of various origins have been treated successfully by means of pulses emitted from a Nd:YAG Q-switched laser above optical breakdown threshold. Since linear absorption is not required, non-pigmented or entirely transparent structures are easily dissected by this method. We have also opened the supraciliary and suprachoroidal space in a series of cases of wide angle glaucomas. In all cases however, the clefts closed by secondary wound reactions. This method may be applied to extracapsular cataract surgery for opening the anterior capsule before lens extraction and to the hydrophthalmic eye.