Pathophysiology of laser trabeculoplasty

Five-Year Long-Term Follow-Up of Selective Laser Trabeculoplasty in Open-Angle Glaucoma

PURPOSE

Selective laser trabeculoplasty (SLT) is known as a safe laser therapy for an effective reduction in intraocular pressure (IOP). The aim of this study was to examine the therapeutic success of SLT in open-angle glaucoma (OAG) patients with a long-term follow-up of 5 years.

METHODS

Forty-six eyes of forty OAG patients, some with previous intraocular surgery, underwent SLT (24 males, 16 females). Therapeutic success was categorized as: category (I) - IOP reduction ≤ 21 mmHg and > 20% compared to baseline IOP with additional glaucoma medication; category (II) - IOP reduction ≤ 18 mmHg and > 30% compared to baseline IOP with additional glaucoma medication; category (III) - IOP reduction ≤ 18 mmHg without any additional glaucoma medication at all follow-ups. Therapeutic failure was defined as the necessity of any further glaucoma surgery (IV).

RESULTS

(1) SLT was well tolerated in all eyes, and no severe side effects or complications were recorded. (2) After 1-year follow-up, therapeutic success was 27% (I), 30% (II), and 3% (III). The therapeutic failure rate was 40% (IV). (3) After 2 years follow-up, therapeutic success was 7% (I), 10% (II), and 0% (III). The therapeutic failure rate was 83% (IV). (4) After 3 years follow-up, the therapeutic failure rate increased up to 100% (IV).

CONCLUSION

SLT seemed to be effective in lowering IOP in the first year in the present cohort, however, the long-term effect is low and additional local therapy or surgical interventions are necessary.

Low-energy Selective Laser Trabeculoplasty Repeated Annually: Rationale for the COAST Trial

The recent Laser in Glaucoma and Ocular Hypertension Trial provided the evidentiary basis for a paradigm shift away from the historical medication-first approach to glaucoma--which has numerous limitations, the most important of which is poor adherence to therapy --and toward a laser-first approach. Now 20 years after its commercialization, selective laser trabeculoplasty (SLT) is routinely performed consistently with its initial description, with energy titrated to the appearance of fine, champagne-like cavitation bubbles. A recent data set suggested that lower energy SLT, applied as primary therapy and repeated annually irrespective of intraocular pressure--rather than pro re nata when its effect wanes and irrespective of intraocular pressure rises --yields longer medication-free survival than standard energy SLT repeated pro re nata. A new study--Clarifying the Optimal Application of SLT Therapy --has been initiated to explore this preliminary finding in a pair of consecutive randomized trials. Herein, we provide an evidence-based rationale for the use of low-energy SLT repeated annually as primary therapy for mild to moderate primary open-angle glaucoma or high-risk ocular hypertension.

[Diode and argon trabeculoplasty in primary open-angle glaucoma treatment]

Laser trabeculoplasty is one of the methods used to decrease intraocular pressure (IOP) as part of comprehensive glaucoma treatment. Argon laser trabeculoplasty (ALT) and diode laser trabeculoplasty (DLT) are two of the most widely used laser trabeculoplasty techniques. The mechanism of its hypotensive action is based on the effect that laser emission photocoagulate has on trabecular meshwork and subsequent outflow facilitation, but the difference in wavelength and emission energy determine the difference in direct laser action and the features of postoperative clinical appearance. The efficacy of both methods has been verified in many studies; however, relatively few of them have made comparative analysis of the two techniques. The article reviews publications dedicated to comparing the efficacy of ALT and DLT, including their hypotensive effect, safety, as well as data on laser surgery tolerance and complications.

Mechanism of Action of Selective Laser Trabeculoplasty and Predictors of Response

Purpose

This study was designed to evaluate the changes in aqueous humor dynamics (AHD) produced by selective laser trabeculoplasty (SLT) and to explore if baseline AHD parameters are predictive of IOP response to SLT.

Methods

Thirty-one consecutive subjects diagnosed with ocular hypertension or primary open-angle glaucoma scheduled to undergo SLT as their primary IOP-lowering therapy were enrolled in this prospective observational study. Subjects underwent baseline assessment of AHD in both eyes. Variables assessed were IOPs at 9 AM and noon, aqueous humor flow rate (fluorophotometry), episcleral venous pressure (EVP, venomanometry), outflow facility (pneumatonography and fluorophotometry) and uveoscleral outflow (calculated using modified Goldmann equation). All subjects underwent 360 degrees SLT and AHD measurements were repeated 3 months later.

Results

Compared with baseline, IOPs after SLT were significantly lower at 9 AM (22.9 ± 5.1 vs. 19.7 ± 3.0 mm Hg; P = 0.001) and noon (23.4 ± 4.6 vs. 20.0 ± 3.5 mm Hg; P < 0.001). Outflow facility by fluorophotometry was significantly increased from 0.17 ± 0.11 μL/min/mm Hg at baseline to 0.24 ± 0.14 μL/min/mm Hg at 3 months (P = 0.008). Outflow facility by tonography (baseline: 0.16 ± 0.07 μL/min/mm Hg vs. 3 months: 0.22 ± 0.16 μL/min/mm Hg; P = 0.046) was similarly increased. No change in aqueous flow or EVP was observed. There were no changes in IOP or AHD in the contralateral untreated eye. Using multiple linear regression models, higher baseline aqueous flow, lower baseline outflow facility, and possibly lower uvescleral outflow were associated with more IOP lowering with SLT.

Conclusions

The IOP-lowering effect of SLT is mediated through an increase in outflow facility. There is no contralateral effect. Higher aqueous flow and lower outflow facility may be predictive of better response to SLT.

Feasibility of laser trabeculoplasty in angle closure glaucoma: a review of favourable histopathological findings in narrow angles

Selective laser trabeculoplasty (SLT) has been indicated as a safe and efficient treatment for primary open-angle glaucoma; however, recent studies have also shown positive results with the use of SLT in some clinical conditions related to primary angle-closure glaucoma (PACG). Despite the potential benefits of SLT in selected cases of PACG, the mechanisms underlying the modifications in the trabecular meshwork tissue of patients with PACG are poorly understood. This narrative review approached both the current, limited knowledge about the histological changes observed in different forms of PACG and the clinical results of SLT treatment for PACG. Favourable outcomes of SLT in patients with PACG, specifically in areas of non-occluded angle, need further substantiation through large controlled clinical trials. A deeper understanding of the biomolecular changes of those areas is essential to improve both laser technical details and the clinical efficacy of SLT therapy.

Transplantation of iPSC-derived TM cells rescues glaucoma phenotypes in vivo

Glaucoma is a common cause of vision loss or blindness and reduction of intraocular pressure (IOP) has been proven beneficial in a large fraction of glaucoma patients. The IOP is maintained by the trabecular meshwork (TM) and the elevation of IOP in open-angle glaucoma is associated with dysfunction and loss of the postmitotic cells residing within this tissue. To determine if IOP control can be maintained by replacing lost TM cells, we transplanted TM-like cells derived from induced pluripotent stem cells into the anterior chamber of a transgenic mouse model of glaucoma. Transplantation led to significantly reduced IOP and improved aqueous humor outflow facility, which was sustained for at least 9 wk. The ability to maintain normal IOP engendered survival of retinal ganglion cells, whose loss is ultimately the cause for reduced vision in glaucoma. In vivo and in vitro analyses demonstrated higher TM cellularity in treated mice compared with littermate controls and indicated that this increase is primarily because of a proliferative response of endogenous TM cells. Thus, our study provides in vivo demonstration that regeneration of the glaucomatous TM is possible and points toward novel approaches in the treatment of this disease.

Effect of intraoperative factors on IOP reduction after phacoemulsification

The purpose of the study was to determine the independent predictors of long-term intraocular pressure (IOP) reduction after cataract surgery with phacoemulsification. This is a retrospective review of uncomplicated cataract surgeries from 2006 to 2008 at the Baltimore VA Medical Center with longitudinal follow-up. Demographic, clinical, biometric, and intraoperative variables including phacoemulsification parameters were recorded. Univariate and multivariate linear regression were used to analyze the relationship between these variables and postoperative IOP, which was the outcome variable. Analysis was performed in 115 eyes of 115 patients who underwent uncomplicated phacoemulsification during the study period. There was an average postoperative IOP reduction through 12, 24, and 36 months of -1.7 ± 3.1, -1.5 ± 3.8, and -1.3 ± 2.6 mmHg, respectively. Higher preoperative IOP (P < 0.001), a more anterior relative lens position (P < 0.05), and longer phaco time (P < 0.05) were significantly associated with greater postoperative decrease in IOP using univariate analysis. Using multivariate analysis, preoperative IOP (P < 0.001), and phaco time (P = 0.038) were associated with greater postoperative IOP reduction through 24 months. Phaco time is independently associated with IOP reduction after adjusting for age and preoperative IOP. Higher preoperative IOP is associated with a greater IOP-lowering effect after phacoemulsification.

Intraocular pressure variations: causes and clinical significance

Reduction of intraocular pressure (IOP) is the only known effective treatment for glaucoma. However, IOP is a highly variable and dynamic parameter, undergoing virtually constant changes from numerous factors, including body position and circadian rhythms. Despite this variability, evidence for the efficacy of IOP reduction in glaucoma is based on studies designed to assess mean IOP and not IOP variations. Post hoc analysis of data from major clinical trials has suggested that IOP variations may be an independent risk factor for the development of glaucoma or glaucomatous progression, at least in some patients, but the evidence is incomplete and further studies are required. In the interim, judicious selection of existing therapies can help to minimize IOP variations. In general, therapies that improve outflow instead of suppressing aqueous humor production result in more stable IOP. However, new technology to allow better monitoring of IOP, ideally in a continuous 24-hour manner, is required to fully understand the role of IOP variations in glaucoma.

Repeat selective laser trabeculoplasty can be effective in eyes with initial modest response

PURPOSE

To evaluate the effectiveness of repeat selective laser trabeculoplasty (SLT) in eyes exhibiting only a modest response upon initial treatment.

MATERIALS AND METHODS

Retrospective chart review was conducted of 51 eyes that received initial 360 degree SLT (SLT1) and subsequent SLT (SLT2) from 2003-2011 at a large academic ophthalmology practice. Successful response (S) was a post-treatment 12 month mean IOP reduction ≥ 20% from baseline, while modest response (M) was <20% reduction over the same time. Chi-squared and log rank analyses were used to determine if success after SLT2 depended on having successful (S1) or modest (M1) response after SLT1.

RESULTS

IOP was significantly reduced from baseline in both SLT1 and SLT2. The proportion of eyes with S2 was not significantly different between those with initial M1 or S1 (36.67% vs. 52.38%, respectively; P = 0.26). Log rank analysis revealed no differences between M1 and S1 in determining SLT2 success (P = 0.41). This outcome was similar when the analyses were performed for the right and left eye independently.

CONCLUSION

The proportion of eyes that successfully responded to repeat SLT did not differ based upon whether the response to initial SLT was successful or modest. This raises the possibility that repeat SLT should not be excluded as an option for those eyes that have only a modest initial response.

Mechanisms of selective laser trabeculoplasty: a review

Selective laser trabeculoplasty is a safe and effective treatment for glaucoma, with greater cost effectiveness than its pharmacological and surgical alternatives. Nevertheless, although the basic science literature on selective laser trabeculoplasty continues to grow, there remains uncertainty over the mechanism by which laser trabeculoplasty reduces intraocular pressure. To address this uncertainty, the evidence behind several potential biological and mechanical mechanisms of selective laser trabeculoplasty were reviewed. In particular, cytokine secretion, matrix metalloproteinase induction, increased cell division, repopulation of burn sites and macrophage recruitment were discussed. Refining our understanding of these mechanisms is essential both to understanding the pathophysiology of ocular hypertension and developing improved therapies to treat the condition.

Effect of topical loteprednol on intraocular pressure after selective laser trabeculoplasty for open-angle glaucoma

Introduction

To determine whether there is a statistically significant difference in the decrease in intraocular pressure (IOP) after selective laser trabeculoplasty (SLT) between patients receiving a 5–7 days co-administration of loteprednol versus no loteprednol over the course of 1 year.

Methods

We conducted a retrospective chart review to evaluate use of loteprednol in patients aged 30–85 years undergoing SLT for open-angle glaucoma at our center over a 3-year period.

Results

Three hundred and eighteen eyes from 313 patients who underwent a 360° SLT treatment between January 2008 and August 2011 were included in the analysis. Patients who received loteprednol showed a mean reduction of 2.5 (±SE 0.3) mmHg or 11.8% (±1.5%) in IOP versus a mean reduction of 3.2 (±0.6) mmHg or 14.9% (±2.5%) in those not treated with loteprednol. This difference showed a trend toward lower IOP without loteprednol, but this was not statistically significant (p = 0.29).

Conclusion

Postoperative use of loteprednol does not appear to significantly affect IOP in patients undergoing SLT. A randomized double-blinded study in a larger group of patients would be required to clarify this issue. Until such information is available, we recommend that individual clinical judgment be used regarding whether to use topical steroids in patients undergoing SLT.

Selective Laser Trabeculoplasty: An Overview

Given the obvious quality of life concerns with medical and surgical lowering of intraocular pressure (IOP), lasers have received considerable attention as a therapeutic modality for glaucoma. Selective laser trabeculoplasty (SLT) is increasingly being used in clinical practice as both the primary procedure and as an adjunct to medical and surgical therapy. Preliminary published evidence suggests that SLT is an effective, compliance-free, repeatable and safe therapeutic modality having only minor, transient, self-limiting or easily controlled side effects with no sequelae. This review attempts a broad overview of the current knowledge of its mechanism, efficacy, indications and limitations, point out the knowledge lacunae that still exist with respect to this highly promising technology which has captured the attention of glaucoma surgeons all over the world.

HOW TO CITE THIS ARTICLE

Jha B, Bhartiya S, Sharma R, Arora T, Dada T. Selective Laser Trabeculoplasty: An Overview. J Current Glau Prac 2012;6(2):79-90.

Changes in the intraocular pressure of fellow untreated eyes following uncomplicated trabeculectomy

BACKGROUND AND OBJECTIVE

Previous studies have reported changes in the intraocular pressure (IOP) of fellow eyes following unilateral trabeculectomy or selective laser trabeculoplasty. This study evaluates changes in the IOP of fellow eyes following unilateral trabeculectomy and examines correlations of findings with clinical information.

PATIENTS AND METHODS

Sixty-one patients who underwent unilateral uncomplicated trabeculectomy were included. The IOP of both eyes was recorded on postoperative days 2, 3, 4, 15, 30, 60, and 90. Differences between preoperative and postoperative IOP in both eyes and correlations with clinical parameters were examined.

RESULTS

The IOP of the fellow eyes was significantly reduced on the fourth postoperative day. This reduction was significantly correlated (inversely) with central corneal thickness of fellow eyes and with the level of IOP reduction to the operated eyes.

CONCLUSION

The IOP of the fellow eyes remains largely unchanged during the first 3 months following trabeculectomy. However, a significant short-term reduction is noted on the fourth day, implying that unknown (possibly neurocrine) mechanisms may participate in the regulation of the IOP of fellow eyes.

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.

Intraocular pressure reduction in the untreated fellow eye after selective laser trabeculoplasty

OBJECTIVE

To investigate the effect of selective laser trabeculoplasty (SLT) on the intraocular pressure (IOP) of untreated fellow eyes in patients with open-angle glaucoma.

STUDY DESIGN

Retrospective chart review.

PATIENTS AND METHODS

Charts of all patients who underwent SLT at the University of Texas Southwestern Medical Center at Dallas between September 2003 and May 2006 were reviewed. Each patient had IOP measurements by Goldmann applanation tonometry in both eyes preoperatively, and at 1 hour, 2 weeks, 3 months, and 6 months postoperatively. Patient age, gender, diagnosis, central corneal thickness (CCT), previous intraocular surgeries, and degrees of laser treatment were tabulated for each patient. Patients with a history of previous glaucoma surgery in either eye were excluded as were those who underwent any change in glaucoma medications or further laser or surgical intervention in either eye within 6 months of SLT. Data were analyzed using a paired two-tailed t-test, an unpaired two-tailed t-test, ANOVA, and linear regression.

RESULTS

A total of 43 patients were included through 6 months of follow-up. Mean reduction in IOP in the treated eye was 3.9 +/- 0.6 mmHg or 18.8% (p < 0.001) at final exam. Mean IOP reduction in the fellow untreated eye was 2.1 +/- 0.5 mmHg or 11.2% (p < 0.01). Patients with higher preoperative IOPs had a greater reduction in IOP in both eyes (p < 0.001 for treated eyes, and p = 0.02 for untreated eyes). Patients who were on a larger number of glaucoma medications preoperatively had a greater response in both eyes (treated eye p = 0.002, untreated eye p = 0.008). There was no significant difference in IOP response in either eye based on age, gender, CCT, degrees of treatment, or phakic status.

CONCLUSIONS

SLT produces a sustained and statistically significant IOP reduction in the fellow untreated eyes of patients with open-angle glaucoma. The results of our study support a biological mechanism of action for SLT. Limitations of this study include its retrospective design, relatively small sample size, a possible effect of increased compliance with medical therapy following SLT, and an inherent bias of excluding patients who underwent a change in medications or further laser or surgical therapy during the period under review.

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.

Effect of previous argon laser trabeculoplasty on the ocular hypotensive action of latanoprost

PURPOSE

To study the effect of previous argon laser trabeculoplasty (ALT) on the hypotensive activity of latanoprost in primary open-angle glaucoma (POAG).

METHODS

This was a prospective, observer-masked study. We measured the intraocular pressure (IOP) before and after 3 months of monotherapy with latanoprost in 43 eyes that had undergone a previous ALT, and in a control group (not treated with ALT) of 43 IOP-matched eyes with POAG.

RESULTS

Latanoprost induced a 17.4+/-16.6% IOP decrease in the study group (ALT-treated eyes) and a 25.8+/-17.2% IOP reduction in the control eyes (P=0.02, unpaired Student's t-test).

CONCLUSIONS

Latanoprost is less effective in ALT-treated eyes than in eyes with POAG not treated with ALT.

A new insight into the cellular regulation of aqueous outflow: how trabecular meshwork endothelial cells drive a mechanism that regulates the permeability of Schlemm's canal endothelial cells

AIM

To test the hypothesis that trabecular meshwork endothelial cells (TMEs) increase the permeability of Schlemm's canal endothelial cells (SCEs) by actively releasing ligands that modulate the barrier properties of SCEs.

METHODS

The TMEs were first irradiated with a laser light and allowed to condition the medium, which is then added to SCEs. The treatment response is determined by both measuring SCE permeability (flow meters) and the differential expression of genes (Affymetrix chips and quantitative polymerase chain reaction (PCR)). The cytokines secreted by the treated cells were identified using ELISA and the ability of these cytokines to increase permeability is tested directly after their addition to SCEs in perfusion experiments.

RESULTS

SCEs exposed to medium conditioned by the light activated TMEs (TME-cm) respond by undergoing a differential expression (DE) of 1,120 genes relative to controls. This response is intense relative to a DE of only 12 genes in lasered SCEs. The TME-cm treatment of SCEs increased the SCE permeability fourfold. The role of cytokines in these responses is supported by two findings: adding specific cytokines established to be secreted by lasered TMEs to SCEs increases permeability; and inactivating the TME-cm by boiling or diluting, abrogates these conditioned media permeability effects.

CONCLUSION

These experiments show that TMEs can regulate SCE permeability and that it is likely that TMEs have a major role in the regulation of aqueous outflow. This novel TME driven cellular mechanism has important implications for the pathogenesis of glaucoma and the mechanism of action of laser trabeculoplasty. Ligands identified as regulating SCE permeability have potential use for glaucoma therapy.

Ultrasound activates the TM ELAM-1/IL-1/NF-kappaB response: a potential mechanism for intraocular pressure reduction after phacoemulsification

PURPOSE

Elevated intraocular pressure (IOP), the major causal risk factor for glaucoma, often decreases after cataract removal by phacoemulsification ultrasound. In this study, the hypothesis that ultrasound energy propagated through a fluid medium induces a stress response with the potential to lower IOP was investigated.

METHODS

Normal and glaucomatous trabecular meshwork (TM) cell culture lines were initiated from tissue isolated from human cadaveric eyes or trabeculectomy specimens. Cultured cells were treated for 60 seconds with a phacoemulsification ultrasound probe set to a power of 70%. Activation of the TM cell-specific stress response was assayed by enzyme-linked immunosorbent assay (ELISA) and immunolocalization.

RESULTS

Normal TM cell cultures did not release detectable levels of the stress response protein, IL-1alpha, into their culture medium. In contrast, IL-1alpha was easily detected after treatment with ultrasound energy. Consistent with earlier findings, glaucomatous TM cells produced IL-1alpha constitutively, and the level of expression was increased after treatment with phacoemulsification ultrasound. As was previously demonstrated, the stress-regulated transcription factor NF-kappaB was present in the cytoplasm of normal cells, but in the nucleus of glaucomatous cells. After treatment with ultrasound energy, NF-kappaB translocated to the nucleus in the normal cells. Endothelial leukocyte-adhesion molecule (ELAM)-1 was not detected in normal TM cells, but was constitutively present on glaucomatous TM cells, consistent with findings in previous work. ELAM-1 expression was induced in normal cells by ultrasound treatment.

CONCLUSIONS

A potentially IOP-lowering stress response is induced in TM cells by ultrasound. The findings suggest that this response may be induced clinically during cataract removal by phacoemulsification, and may be one mechanism responsible for the reduction in IOP that often follows this procedure.

Comparison of the morphologic changes after selective laser trabeculoplasty and argon laser trabeculoplasty in human eye bank eyes

OBJECTIVE

To compare the histopathologic changes in the human trabecular meshwork (TM) after argon laser trabeculoplasty (ALT) and selective laser trabeculoplasty (SLT) with a Q-switched, frequency-doubled, neodymium:yttrium-aluminum-garnet laser.

DESIGN

Human "in vitro" experimental study. TISSUE AND CONTROLS: Eight human autopsy eyes were obtained within 18 hours of death from persons aged 71 to 78 years.

METHODS

The anterior segment of autopsy eyes was isolated, and one half of each trabecular meshwork underwent SLT and the other half ALT. Specimens were evaluated with scanning and transmission electron microscopy.

MAIN OUTCOME MEASURES

Structural changes in the TM were detected by scanning electron microscopy, and cellular or intracellular changes were seen with transmission electron microscopy.

RESULTS

Evaluation of the TM after ALT revealed crater formation in the uveal meshwork at the junction of the pigmented and nonpigmented TM. Coagulative damage was evident at the base and along the edge of craters, with disruption of the collagen beams, fibrinous exudate, lysis of endothelial cells, and nuclear and cytoplasmic debris. Evaluation of the TM after SLT revealed no evidence of coagulative damage or disruption of the corneoscleral or uveal trabecular beam structure. Minimal evidence of mechanical damage was present after SLT, and the only ultrastructural evidence of laser tissue interaction was cracking of intracytoplasmic pigment granules and disruption of trabecular endothelial cells.

CONCLUSIONS

SLT applied "in vitro" to the TM of human eye bank eyes seemed to cause no coagulative damage and less structural damage to the human TM when compared with ALT and, therefore, may be a safer and more repeatable procedure.

How does nonpenetrating glaucoma surgery work? Aqueous outflow resistance and glaucoma surgery

Histologic, experimental, and theoretical studies of the aqueous outflow pathways point toward the juxtacanalicular region and inner wall of Schlemm's canal as the likely site of aqueous outflow resistance in the normal eye. At least 50% of the aqueous outflow resistance in the normal eye and the bulk of the pathologically increased resistance in the glaucomatous eye resides in the trabecular meshwork and the inner wall of Schlemm's canal. The uveoscleral, or uveovortex, pathway, which accounts for perhaps 10% of the aqueous drainage in the healthy aged human eye, can become a major accessory route for aqueous drainage after pharmacologic treatment. Surgeries designed to incise or remove the abnormal trabecular meshwork of glaucoma address the pathologic problem of the disease. Surgeries that unroof Schlemm's canal or expand the canal, such as viscocanalostomy, probably cause inadvertent ruptures of the inner wall and juxtacanalicular tissue, thus relieving the abnormal outflow resistance of glaucoma. This review is a summary of current thought on the pathophysiology of aqueous outflow resistance in glaucoma and, in light of this, provides an interpretation of the mechanism of pressure reduction created by these new surgeries.

Optical properties of human trabecular meshwork in the visible and near-infrared region

BACKGROUND AND OBJECTIVES

Despite disparate treatment parameters, similar success in laser trabeculoplasty (LT) is attained using the argon (514.5 nm) and diode (810 nm) laser. However, the mechanism of this success remains unresolved. To further understand LT, this study characterizes the optical properties of trabecular meshwork (TM).

STUDY DESIGN/MATERIALS AND METHODS

Reflectance was measured from 10 TM samples over wavelengths of 400-820 nm, using an integrating sphere/spectrophotometer. Corrections were made for reflections at boundaries of refractive index mismatch. Kubelka-Munk coefficients were calculated and converted to linear transport coefficients.

RESULTS

Scattering greatly dominated absorption. The scattering and absorption coefficients were, respectively, 141.20 +/- 15.80 cm(-1) and 4.89 +/- 1.95 cm(-1) at 514.5 nm, and 94.44 +/- 15.03 cm(-1) and 0.0874 +/- 0.111 cm(-1) at 810 nm (estimated anisotropy of 0.90). The corresponding penetration depths (1/e) were 69 microm (514.5 nm) and 106 microm (810 nm).

CONCLUSION

The absorption coefficient of 514 nm energy is two orders of magnitude greater than 810 nm energy, while scattering coefficients are much closer. The fluence used at 514.5 nm is higher at the surface than that at 810 nm, but falls below it deep within the TM due to the differential absorption. Therefore, similar initial therapeutic effects are obtained with 810 nm using less total absorbed energy. Thermal damage resultant from excess energy deposited at 514.5 nm may be related to the lack of success in repeat argon LT, pointing out the need for studies of repeat diode LT.

Immediate intraocular pressure response to selective laser trabeculoplasty

BACKGROUND/AIMS

Selective laser trabeculoplasty targets the pigmented trabecular meshwork cells without damage to the trabecular meshwork architecture in vitro. A study was conducted in vivo of eight eyes with uncontrolled open angle glaucoma to ascertain the immediate intraocular response to selective laser trabeculoplasty.

METHODS

The trabecular meshwork of each eye was treated 360 degrees with a frequency doubled Q-switched Nd:YAG laser. Intraocular pressure was measured 1, 2, 24 hours and 1, 4, 6 weeks after treatment.

RESULTS

The average preoperative intraocular pressure was 26.6 (SD 7) mm Hg (range 18-37). Two hours and 6 weeks respectively after selective trabeculoplasty intraocular pressure was reduced in all the eyes treated with an average fall of 10.6 (5.2) mm Hg or 39.9%. A pressure spike of 10 mm Hg verified in one eye 1 hour after treatment.

CONCLUSIONS

Selective laser trabeculoplasty decreased intraocular pressure by an amount similar to that achieved with standard trabeculoplasty. Additional study is needed to determine whether the beneficial effect is sustained over a longer period of follow up.

Five-year results of a randomized, prospective, clinical trial of diode vs argon laser trabeculoplasty for open-angle glaucoma

PURPOSE

To evaluate the safety and efficacy of laser trabeculoplasty (LTP) with a semiconductor diode laser (810 nm, [DLT]) vs an argon blue-green laser (488 to 514 nm, [ALT]).

METHODS

In a prospective, randomized clinical trial, 50 eyes of 46 patients with uncontrolled open-angle glaucoma on maximally tolerated medical therapy were treated and followed at regular intervals for 5 years. Fifty laser spots were applied over 180 degrees using either maximal laser power or sufficient power to produce blanching or a small bubble (570 to 850 mW, DLT; 400 to 1,100 mW, ALT). We performed DLT using a 100-microm spot size, a 0.5-second exposure, and a Ritch lens; we conducted ALT with a 50-microm spot, a 0.1-second exposure, and a Goldmann lens. Patients in the study were followed until trabeculectomy was required.

RESULTS

The mean follow-up times +/- SD for all eyes were 38.6 +/- 5.4 months, DLT (n = 22; range, 1 to 68 months) and 35.5 +/- 4.8 months, ALT (n = 28; range, 1 to 66 months). Those in the diode laser group (n = 16) who had more than 1 year of follow-up were tracked for 49.4 months, and those in the argon laser group (n = 21) were tracked for 45.8 months. There were no significant differences in the mean pretreatment intraocular pressures (IOPs): 21.2 mm Hg, DLT (n = 22) and 21.5, ALT 21.5 mm Hg (n = 28); P = .81] or in mean final IOPs (15.7 mm Hg, DLT and 17.1 mm Hg, ALT; P = .19). Time to surgical failure showed no significant differences, with 50% of the DLT eyes and 58% of the ALT eyes surviving at 5 years (P = .59).

CONCLUSION

In eyes with open-angle glaucoma and unsatisfactory IOP control on maximally tolerated medical therapy, DLT and ALT are equally effective in lowering IOP over a 5-year period.

Laser trabeculoplasty for primary open-angle glaucoma

The purpose of the Committee on Ophthalmic Procedure Assessments is to evaluate on a scientific basis new and existing ophthalmic tests, devices, and procedures for their safety, efficacy, clinical effectiveness, and appropriate uses. Evaluations include examination of available literature, epidemiological analyses when appropriate, and compilation of opinions from recognized experts and other interested parties. After appropriate review by all contributors, including legal counsel, assessments are submitted to the Academy's Board of Trustees for consideration as official Academy policy.

Effect of topical anti-inflammatory treatment on the outcome of laser trabeculoplasty. The Fluorometholone-Laser Trabeculoplasty Study Group

PURPOSE

We investigated the effect of anti-inflammatory treatment on the outcome of argon laser trabeculoplasty.

METHODS

In this multicenter, double-masked, randomized, placebo-controlled, parallel comparison study, 140 chronic open-angle glaucoma patients received either 0.25% fluorometholone or vehicle four times a day unilaterally, beginning 24 hours before and continuing one week after argon laser trabeculoplasty. The laser surgeon placed 50 to 60 burns over the inferior 180 degrees of the trabecular meshwork. The patients were followed up frequently for five weeks after the procedure.

RESULTS

Following argon laser trabeculoplasty, signs of anterior chamber inflammation were significantly lower in the fluorometholone group. However, there was no significant difference between the fluorometholone and the vehicle groups in the incidence of increased intraocular pressure in the immediate post-argon laser trabeculoplasty period. Intraocular pressure decreased significantly in both groups from day 1 throughout the follow-up period. A significant between-group difference in intraocular pressure decrease was found only at week 5 (7.83 +/- 6.27 [S.D.] mm Hg for the fluorometholone group vs 6.63 +/- 5.79 mm Hg for the vehicle group, P = .046). No drug-related clinically significant adverse events were observed.

CONCLUSIONS

Use of fluorometholone is effective in attenuating inflammation and has no clinically significant impact on the outcome of argon laser trabeculoplasty or on the incidence of intraocular pressure spikes during the immediate post-argon laser trabeculoplasty period.

The effect of argon laser trabeculoplasty on the blood-aqueous barrier and intraocular pressure in human glaucomatous eyes treated with diclofenac 0.1%

BACKGROUND

We studied the effect of argon laser trabeculoplasty (ALT) on the blood-aqueous barrier (BAB) in 41 eyes of 41 patients with primary open-angle glaucoma, pseudoexfoliation glaucoma, or pigment dispersion glaucoma using the Fluorotron Master II.

METHODS

Fluorophotometry was performed the day before ALT and on the 3rd day after surgery at 30 and 60 min after intravenous injection of 7 mg/kg body weight sodium fluorescein 10%. Intraocular pressure (IOP) was measured using Goldmann applanation tonometry on the day before surgery and at 3rd days and 1 year (mean) after ALT. Patients were treated with argon laser by one surgeon (180 degrees, 0.1 s, 50 microns 0.6-1.0 W, 56 laser burns). Eyes were randomly assigned to either diclofenac-sodium 0.1% eye drops or vehicle. Eye drops were applied six times 1 h before ALT into the operated eyes and five times daily for 3 days postoperatively.

RESULTS

On the 3rd day after ALT there was significant disruption of the BAB in the placebo-treated eyes compared to the diclofenac 0.1%-treated eyes. In the placebo-treated eyes as well as in diclofenac-sodium 0.1%-treated eyes there was a significant decrease of IOP postoperatively for up to 1 year. There was no significant difference concerning the IOP reduction after 1 year. Diclofenac-sodium 0.1% eye drops significantly stabilized the BAB on the 3rd day after ALT, compared to placebo, in this model.

CONCLUSION

Diclofenac-sodium 0.1% significantly stabilized the disruption of the blood-aqueous barrier on the 3rd day after ALT. Concerning the IOP-lowering effect of ALT, the postoperative application of steroids should be avoided.

Early changes in matrix metalloproteinases and inhibitors after in vitro laser treatment to the trabecular meshwork

Extracellular matrix turnover in the trabecular meshwork may play a role in regulating aqueous humor outflow. Laser trabeculoplasty is a common treatment for open-angle glaucoma. The mechanism of this treatment is not understood. We investigated changes in the levels and expression of the matrix metalloproteinases and their tissue inhibitors (TIMPs) in this tissue using cultured human anterior segment explants and standard clinical-parameter laser treatment. Medium gelatinase A activity levels are relatively high for sham-treated controls and are not changed dramatically following laser treatment. Medium gelatinase B and stromelysin activity levels are low in sham-treated explants and increase significantly by 24 h after treatment. TIMP1 levels, as assessed by immunoblots of Western transfers, are initially low. However, by 24 h TIMP1 levels have increased significantly. Using semi-quantitative reverse transcription and the polymerase chain reaction, mRNA levels of stromelysin, gelatinase B and TIMP1 are shown to increase after laser treatment, while gelatinase A and TIMP2 remain relatively constant. The increases in trabecular stromelysin and gelatinase B in response to laser trabeculoplasty may have important implications for the mechanism of action of this treatment for open-angle glaucoma.

Efficacy and safety of indomethacin 0.1% versus flurbiprofen 0.03% eyedrops in inflammation after argon laser trabeculoplasty. The Belgian Study Group on Glaucoma

After Argon Laser Trabeculoplasty (ALT), non steroidal anti-inflammatory drugs (Indomethacin 1% suspension and Flurbiprofen 0.03% solution) were shown to be efficient in the management of post laser inflammation. To evaluate the efficacy and safety of Indomethacin 0.1% solution versus Flurbiprofen 0.03% eyedrops in that purpose. 64 patients suffering from glaucoma were recruited in a multicenter randomized double masked study. The results demonstrate that Indomethacin 0.1% eyedrops is as efficient as Flurbiprofen 0.03% in terms of control of post ALT inflammation, with a good tolerance.

Factors influencing in vivo trabecular cell replication as determined by 3H-thymidine labelling; an autoradiographic study in cats

Because trabecular cell loss is thought to play a role in the pathogenesis of some forms of glaucoma, identification of factors which influence trabecular cell division may provide some insight into the mechanisms and potential treatment of this disease. We studied several commonly encountered clinical situations which may affect the trabecular meshwork: phagocytosis of debris, hyphema, and argon laser trabeculoplasty. The effect of these factors on trabecular cell division was determined using 3H-thymidine autoradiography. Laser trabeculoplasty induced a 307% increase in 3H-thymidine labelling of trabecular cells while phagocytosis and hyphema had no effect on cell labelling. In addition, subgroups of eyes with a loss of trabecular cells or with inflammation did not have increased labelling. Thus laser trabeculoplasty, known to increase outflow facility, was associated with increased trabecular cell labelling while factors often associated with decreased outflow facility and glaucoma were not.

Diode laser compared with argon laser for trabeculoplasty

A randomized prospective study on two groups of ten patients compared the efficacy of diode laser and argon laser trabeculoplasty. In the diode laser group the intraocular pressure was 23.0 +/- 3.97 mm Hg before the treatment, 20.2 +/- 4.49 mm Hg at two hours, 16.3 +/- 3.13 at six months, and 16.9 +/- 2.80 mm Hg at one year. The differences from baseline were statistically significant at six months (P = .0001) and at one year (P = .0001) but not at two hours. In the argon laser group the intraocular pressure was 23.4 +/- 3.6 mm Hg before the treatment, 22.7 +/- 4.35 mm Hg at two hours, and 17.6 +/- 4.53 mm Hg at six months. One patient had uncontrolled mean high intraocular pressure and underwent surgery. In the nine patients who completed the study the intraocular pressure at one year was 16.7 +/- 3.00 mm Hg. The differences from baseline were significant at six months (N = 10; P = .0001) and 12 months (N = 9; P = .0001) but not at two hours. Differences between the two groups were not significant at two hours, six months, and one year. Laser trabeculoplasty may be effectively with a diode laser.

Laser trabeculoplasty

Over a decade, laser trabeculoplasty has evolved from being a novel new treatment to one that is a commonly accepted intervention in the management of open-angle glaucoma. Despite its widespread use, however, there are still many unanswered questions about laser trabeculoplasty, including its mechanism of action and the ideal treatment parameters. In this review, we will discuss the history of the technique, the clinical experience, and some of the experimental studies that have been conducted to answer the questions regarding its mechanism of action.