Diode laser compared with argon laser for trabeculoplasty

Laser trabeculoplasty for open-angle glaucoma and ocular hypertension

BACKGROUND

Open-angle glaucoma (OAG) is an important cause of blindness worldwide. Laser trabeculoplasty, a treatment modality, still does not have a clear position in the treatment sequence.

OBJECTIVES

To assess the effects of laser trabeculoplasty for treating OAG and ocular hypertension (OHT) when compared to medication, glaucoma surgery or no intervention. We also wished to compare the effectiveness of different laser trabeculoplasty technologies for treating OAG and OHT.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (which contains the Cochrane Eyes and Vision Trials Register) (2021, Issue 10); Ovid MEDLINE; Ovid Embase; the ISRCTN registry; LILACS, ClinicalTrials.gov and the WHO ICTRP. The date of the search was 28 October 2021. We also contacted researchers in the field.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) comparing laser trabeculoplasty with no intervention, with medical treatment, or with surgery in people with OAG or OHT. We also included trials comparing different types of laser trabeculoplasty technologies.

DATA COLLECTION AND ANALYSIS

We used standard methods expected by Cochrane. Two authors screened search results and extracted data independently. We considered the following outcomes at 24 months: failure to control intraocular pressure (IOP), failure to stabilise visual field progression, failure to stabilise optic neuropathy progression, adverse effects, quality of life, and costs. We graded the 'certainty' of the evidence using GRADE.

MAIN RESULTS

We included 40 studies (5613 eyes of 4028 people) in this review. The majority of the studies were conducted in Europe and in the USA. Most of the studies were at risk of performance and/or detection bias as they were unmasked. None of the studies were judged as having low risk of bias for all domains. We did not identify any studies of laser trabeculoplasty alone versus no intervention. Laser trabeculoplasty versus medication Fourteen studies compared laser trabeculoplasty with medication in either people with primary OAG (7 studies) or primary or secondary OAG (7 studies); five of the 14 studies also included participants with OHT. Six studies used argon laser trabeculoplasty and eight studies used selective laser trabeculoplasty. There was considerable clinical and methodological diversity in these studies leading to statistical heterogeneity in results for the primary outcome "failure to control IOP" at 24 months.  Risk ratios (RRs) ranged from 0.43 in favour of laser trabeculoplasty to 1.87 in favour of medication (5 studies, I2 = 89%). Studies of argon laser compared with medication were more likely to show a beneficial effect compared with studies of selective laser (test for interaction P = 0.0001) but the argon laser studies were older and the medication comparator group in those studies may have been less effective. We considered this to be low-certainty evidence because the trials were at risk of bias (they were not masked) and there was unexplained heterogeneity. There was evidence from two studies (624 eyes) that argon laser treatment was associated with less failure to stabilise visual field progression compared with medication (7% versus 11%, RR 0.70, 95% CI 0.42 to 1.16) at 24 months and one further large recent study of selective laser also reported a reduced risk of failure at 48 months (17% versus 26%) RR 0.65, 95% CI 0.52 to 0.81, 1178 eyes). We judged this outcome as moderate-certainty evidence, downgrading for risk of bias. There was only very low-certainty evidence on optic neuropathy progression. Adverse effects were more commonly seen in the laser trabeculoplasty group including peripheral anterior synechiae (PAS) associated with argon laser (32% versus 26%, RR 11.74, 95% CI 5.94 to 23.22; 624 eyes; 2 RCTs; low-certainty evidence); 5% of participants treated with laser in three studies of selective laser group had early IOP spikes (moderate-certainty evidence). One UK-based study provided moderate-certainty evidence that laser trabeculoplasty was more cost-effective.  Laser trabeculoplasty versus trabeculectomy Three studies compared laser trabeculoplasty with trabeculectomy. All three studies enrolled participants with OAG (primary or secondary) and used argon laser. People receiving laser trabeculoplasty may have a higher risk of uncontrolled IOP at 24 months compared with people receiving trabeculectomy (16% versus 8%, RR 2.12, 95% CI 1.44 to 3.11; 901 eyes; 2 RCTs). We judged this to be low-certainty evidence because of risk of bias (trials were not masked) and there was inconsistency between the two trials (I2 = 68%). There was limited evidence on visual field progression suggesting a higher risk of failure with laser trabeculoplasty. There was no information on optic neuropathy progression, quality of life or costs. PAS formation and IOP spikes were not reported but in one study trabeculectomy was associated with an increased risk of cataract (RR 1.78, 95% CI 1.46 to 2.16) (very low-certainty evidence).

AUTHORS' CONCLUSIONS

Laser trabeculoplasty may work better than topical medication in slowing down the progression of open-angle glaucoma (rate of visual field loss) and may be similar to modern eye drops in controlling eye pressure at a lower cost. It is not associated with serious unwanted effects, particularly for the newer types of trabeculoplasty, such as selective laser trabeculoplasty.

[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.

The cost-effectiveness of medication, laser trabeculoplasty, and trabeculectomy for treatment of open-angle glaucoma in South Korea

OBJECTIVES

Open-angle glaucoma (OAG) imposes high disease burden in South Korea. Although various effective interventions are available to manage the progression of OAG, there is limited data on the cost-effectiveness of these treatment strategies in South Korea.

METHODS

Using a Markov cohort model, we evaluated the cost-effectiveness of 3 major treatment strategies (medication, laser trabeculoplasty, and trabeculectomy) for South Korean patients with OAG. We projected a 25-year time horizon to study a hypothetical cohort of 10,000 patients of age 40 with mild OAG. The outcome measures were quality-adjusted life-years (QALYs) gained, cost from the societal perspective, and the incremental cost-effectiveness ratio (ICER) of medication, laser trabeculoplasty, and trabeculectomy. Interventions were evaluated at a willingness-to-pay (WTP) threshold of 30,000,000 KRW ($29,152) per QALY gained. Deterministic and probabilistic sensitivity analyses were conducted to address the model uncertainty.

RESULTS

The mean costs for medication, laser trabeculoplasty, and trabeculectomy were 29,661,740 KRW, 17,34,1342 KRW, and 22,275,438 KRW, respectively. The mean QALYs gained were 15.7, 15.3, and 14.8 for medication, laser trabeculoplasty, and trabeculectomy, respectively. Surgery was strongly dominated because it generated fewer expected QALYs but incurred greater expected cost than laser. The ICER was 30,885,179 KRW per QALY for medication versus laser trabeculoplasty. Laser was cost-effective, however, at a lower WTP threshold of 21,000,000 KRW per QALY gained or below. The results were most sensitive to the progression rates from mild to moderate glaucoma under laser treatment.

CONCLUSION

Under the WTP threshold of 30,000,000 KRW per QALY, medication was cost-effective compared with laser trabeculoplasty and trabeculectomy for treating mild OAG in South Korean population. Laser, however, can be a cost-effective alternative in more resource-limited settings.

Lasers in glaucoma

While lasers have been used for many years for the treatment of glaucoma, proper indications and use of the procedures need to be considered before their application. This review summarizes the important laser procedures in Glaucoma.

Different strategies and cost-effectiveness in the treatment of primary open angle glaucoma

Glaucoma is the second highest cause of blindness worldwide with an estimated half of the glaucoma population unaware of their disease. To date, intraocular pressure is the most important modifiable risk factor and lowering it has been proven to reduce progression of visual field loss associated with glaucoma. Different strategies are available to lower intraocular pressure and include medical, laser, or surgical treatment in the form of topical or systemic medications, argon or selective laser trabeculoplasty, and glaucoma drainage surgery such as trabeculectomy, deep sclerectomy, or other drainage devices. The effectiveness of these treatments has been well documented however their cost-effectiveness between the developed world and third world remains unclear.

Clinical options for the reduction of elevated intraocular pressure

Elevated IOP in clinical practice is usually seen in glaucoma or ocular hypertension. Glaucoma affects 60 million people worldwide and 8.4 million are bilaterally blind from this chronic disease.1 Options for reducing IOP rely on pharmacological agents, laser treatments and surgery which may be penetrating or non-penetrating. The last twenty years has seen significant changes in all of these strategies. This review aims to cover these clinical options and introduce some of the new technologies currently in development for the clinical lowering of IOP.

Micropulse diode laser trabeculoplasty (MDLT): A phase II clinical study with 12 months follow-up

Objective

This pilot study evaluates the pressure lowering potential of subthreshold micropulse diode laser trabeculoplasty (MDLT) for a clinically meaningful duration in patients with medically uncontrolled open angle glaucoma (OAG).

Design

prospective interventional case series.

Participants

Thirty-two eyes of 20 consecutive patients with uncontrolled OAG (12 bilateral and 8 unilateral).

Methods

Confluent subthreshold laser applications over the inferior 180° of the anterior TM using an 810 nm diode laser in a micropulse operating mode. The intraocular pressure (IOP) was measured at baseline and at 1 hour, 1 day, 1 week, 3, 6, 9, and 12 months post-treatment. Flare was measured with a Kowa FM 500 flare-meter at baseline and at 3 hours, 1 day, 1 week, and 12 months post-treatment. After treatment, the patients were maintained on their pre-treatment drug regimen.

Main outcome measures

Criteria for treatment response were IOP reduction ≥3 mm Hg and IOP ≤21 mm Hg within the first week after MDLT. Eyes not complying to the above criteria during the follow-up were considered treatment failure. Mean IOP change and percentage of IOP reduction during the follow-up were calculated.

Results

One eye was analyzed for bilateral patients. A total of 20 eyes were thus included. Four eyes (20%) did not respond to treatment during the first week. One additional eye failed at the 6 month visit. The treatment was successful in 15 eyes (75%) at 12 months. The IOP was significantly lower throughout follow-up (p < 0.01). At 12 months, the mean percentage of IOP reduction in the 15 respondent eyes was 22.1% and 12 eyes (60%) had IOP reduction higher than 20%. During the first two postoperative days, one eye with pigmentary glaucoma experienced a significant increase of flare associated with an IOP spike (34 mm Hg) that was controlled with systemic drugs; afterwards it qualified as a respondent and completed the study. No increase of flare was found in any other patient. No peripheral anterior synechiae formed.

Conclusions

In this case series, MDLT was effective in reducing IOP in 75% of medically insufficiently controlled OAG eyes without significant complications. This justifies randomized clinical studies to compare MDLT with current IOP lowering strategies.

Laser trabeculoplasty for open angle glaucoma

BACKGROUND

Open angle glaucoma (OAG) is an important cause of blindness worldwide. Laser trabeculoplasty, a treatment modality, still does not have a clear position in the treatment sequence.

OBJECTIVES

The objective of this review was to study the effects of laser trabeculoplasty for OAG.

SEARCH STRATEGY

We identified trials from CENTRAL in The Cochrane Library, MEDLINE, EMBASE, LILACS and manual searching. We also contacted researchers in the field.

SELECTION CRITERIA

We included randomised controlled trials comparing laser trabeculoplasty with no intervention, with medical treatment, or with surgery. We also included trials comparing different technical modalities of laser trabeculoplasty.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed trial quality and extracted the data. We contacted trial investigators for missing information.

MAIN RESULTS

This review included 19 trials involving 2137 participants. Only five trials fulfilled the criteria of good methodological quality. One trial compared laser trabeculoplasty with topical beta-blocker to no intervention in early glaucoma. The risk of glaucoma progression was higher in the control group at six years of follow up (risk ratio (RR) 0.71 95% confidence interval (CI) 0.53 to 0.95). No difference in health-related quality of life was observed between the two groups. Three trials compared laser trabeculoplasty to medication (regimens used before the 1990s) in people with newly diagnosed OAG. The risk of uncontrolled intraocular pressure (IOP) was higher in the medication group compared to the trabeculoplasty group at six months and two years of follow up. Three trials compared laser trabeculoplasty with trabeculectomy. The risk of uncontrolled IOP was significantly higher in the trabeculoplasty group at six months but significant heterogeneity was observed at two years. Diode and selective laser are compared to argon laser trabeculoplasty in three trials and there is some evidence showing a comparable effect in controlling IOP at six months and one year of follow up.

AUTHORS' CONCLUSIONS

Evidence suggests that, in people with newly diagnosed OAG, the risk of uncontrolled IOP is higher in people treated with medication used before the 1990s when compared to laser trabeculoplasty at two years follow up. Trabeculoplasty is less effective than trabeculectomy in controlling IOP at six months and two years follow up. Different laser technology and protocol modalities were compared to the traditional laser trabeculoplasty and more evidence is necessary to determine if they are equivalent or not. There is no evidence to determine the effectiveness of laser trabeculoplasty compared to contemporary medication (prostaglandin analogues, topical anhydrase inhibitors and alpha2-agonists) and also with contemporary surgical techniques. Also there should be further investigation in to the effectiveness of laser trabeculoplasty in specific racial groups, specific diagnostic groups, such as pseudoexfoliation and pigmentary glaucoma and different stages of OAG. More research is also required determining cost-effectiveness of laser trabeculoplasty in the management of glaucoma.

Effect of low fluence diode laser irradiation on the hydraulic conductivity of perfused trabecular meshwork endothelial cell monolayers

OBJECTIVE

To determine the effect of low-fluence diode laser irradiation upon the fluid perfusion characteristics of cultured human trabecular meshwork cell monolayers when placed in a specially designed testing apparatus and subjected to fluid flow driven by a hydrostatic pressure gradient.

METHODS

Two experimental series were conducted. In the first series, six low-fluence diode laser irradiation experiments were conducted using cultured human trabecular meshwork cell monolayers grown on filter supports. Upon reaching a steady state perfusion condition at approximately 5.0 mmHg, monolayers were irradiated at fluencies ranging from 0.2619 to 0.8571 J/cm2 using a diode laser (lambda=810 nm). Perfusion and data collection continued for 45 minutes post-irradiation, after which the monolayers were tested to determine post-experimental viability. Hydraulic conductivity values were analyzed for post-irradiation response in 2.5-minute intervals, grouped by viability. In the second series, a total of six irradiated experiments and six simultaneous nonirradiated control experiments were conducted. Fluence values of 0.3571 J/cm2 (n=3) and 0.4286 J/cm2 (n=3) were used. Hydraulic conductivity values were analyzed for post-irradiation response in 2.5-minute intervals, grouped by irradiated vs. nonirradiated control groups.

RESULTS

In the first series, analysis showed that the viable monolayers exhibited a statistically significant increase in hydraulic conductivity (p<0.001) from 10 minutes post-irradiation onward. The non-viable monolayers exhibited a statistically significant decrease in hydraulic conductivity. In the second series, irradiated groups showed a significant difference (p<0.001) from nonirradiated controls from 10 minutes post-irradiation onward.

CONCLUSION

Low-fluence diode laser irradiation increases hydraulic conductivity in viable perfused TM cell monolayers when compared to baseline values or simultaneous nonirradiated controls while decreasing hydraulic conductivity in nonviable monolayers.

Comparative evaluation of diode laser trabeculoplasty vs frequency doubled Nd : YAG laser trabeculoplasty in primary open angle glaucoma

AIMS

To evaluate the efficacy of diode laser trabeculoplasty (DLT) and frequency doubled Nd : YAG laser trabeculoplasty (YLT) in primary open angle glaucoma (POAG).

METHODS

A total of 52 eyes of 35 patients with POAG were included. In all, 25 eyes underwent DLT (Group I) and 27 eyes underwent YLT (Group II). IOP, gonioscopy and visual fields were evaluated before and 3, 6, and 9 months and 1 year after the laser. An IOP<21 mmHg without medications or a decrease in the number of glaucoma medications with no progression of disc and field changes was considered a success.

RESULTS

The mean age of patients in Group I was 57.72+/-8.1 years and the patients in Group II had a mean age of 59.85+/-7.76 years. The mean prelaser IOP was 24.93+/-1.49 mmHg and 25.36+/-1.57 mmHg. The mean IOP after DLT at 12 months follow-up was 18.0+/-0.93 mmHg and after YLT was 18.6+/-1.52 mmHg. The reduction of IOP was statistically significant in both the groups at 3, 6, 9, and 12 months (P<0.001), however there was no significant difference between the two groups. Success rates in both groups were similar, 92% in Group I and 92.6% in Group II.

CONCLUSIONS

DLT and Fd YLT are equally effective in controlling IOP in eyes with POAG.

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.

Q-switched 532-nm Nd:YAG laser trabeculoplasty (selective laser trabeculoplasty): a multicenter, pilot, clinical study

OBJECTIVE

To investigate the safety and efficacy of a new laser procedure using a q-switched 532-nm neodymium (Nd):YAG laser, also called "selective laser trabeculoplasty," to lower intraocular pressure (IOP) in patients with open-angle glaucoma (OAG). The laser parameters were set to selectively target pigmented trabecular meshwork (TM) cells without coagulative damage to the TM structure or nonpigmented cells.

DESIGN

Nonrandomized, prospective, clinical trial.

PARTICIPANTS

Thirty eyes of 30 patients with uncontrolled OAG (OAG group) and 23 eyes of 23 patients with uncontrolled OAG treated previously with argon laser trabeculoplasty (ALT group) were observed for 4 to 26 weeks. Forty-four of the 53 eyes were observed for 26 weeks.

INTERVENTION

Patients were treated with the Coherent Selecta 7000 (Coherent, Inc, Palo Alto, CA) frequency-doubled q-switched Nd:YAG laser (532 nm). A total of approximately 50 nonoverlapping spots were placed over 180 degrees of the TM at energy levels ranging from 0.6 to 1.2 mJ per pulse. After surgery, patients were maintained with the identical drug regimen as that before treatment.

RESULTS

Both the OAG and ALT groups showed similar IOP reductions over time. Seventy percent of patients in each group responded to treatment with an IOP reduction of least 3 mmHg. At 26 weeks of follow-up, mean IOP reduction was 5.8 mmHg (23.5%, P < 0.001) for the OAG group and 6.0 mmHg (24.2%, P < 0.001) for the ALT group. The untreated eye showed a 9.7% (P < 0.001) reduction of IOP at 26 weeks. However, the IOP difference between the treated and untreated eyes was statistically significant at P < 0.003. Transient IOP elevation of 5 mmHg or greater was seen in 24% of patients.

CONCLUSION

The selective laser trabeculoplasty appears to be a safe and effective method to lower IOP in patients with OAG and patients treated previously with ALT. A reduction of IOP can be achieved without coagulation of the TM.

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.

High-power diode laser in neurosurgery: clinical experience in 30 cases

BACKGROUND

High-power semiconductor diode lasers were recently introduced and have been tested in ophthalmology and general surgery. These lasers are attractive from the practical and economical standpoint, and have enough power to perform most surgical procedures. They could replace other surgical lasers such as CO2, argon, 1.06 microm, and 1.32 microm Nd-YAG lasers for many applications in neurosurgery. We report our initial experience with the first available 0.805-microm surgical diode laser, the Diomed 25 (Diomed, Ltd, Cambridge, U.K.) in a series of 30 patients.

METHODS

The diode laser was evaluated during surgical resection of various types of central nervous system tumors in 30 patients. It was used free-hand in 27 patients in contact and non-contact, continuous wave (cw) and pulsed modes, and during ventricular endoscopy in three patients. Average time of laser use during a procedure was 248 seconds. Output power ranged from 1 to 25 watts, with an average power per patient of 2.64 to 15.5 watts (mean, 8.78 watts). Total energy delivered ranged from 65 to 11,051 joules per patient.

RESULTS

Using 600- or 400-microm non-contact optic fiber, well pigmented tumor tissue hemostasis was obtained at cw 3 to 10 watts with a defocused beam, whereas vaporization required 10-25 cw or pulsed watts with a focused beam. Soft and tough tissue section could be obtained using a sculpted cone-shaped (600-300 microm tip) contact fiber at 7-10 cw watts after fiber tip charring. Because of the deeper penetration of 0.805-microm light in non-pigmented tissues, non-contact mode is not recommended for white matter or poorly vascularized tumors. The contact mode was not efficient on very soft tissues such as edematous brain parenchyma. The contact fibers proved to be very fragile because of heat generation.

CONCLUSIONS

The high power diode laser proved to be efficient for hemostasis, section and vaporization, using contact and non-contact modes, at different output powers. Economical and ergonomical advantages of this new generation of surgical lasers may cause them to replace other surgical lasers such as argon, CO2, and Nd-YAG lasers, mostly for tumor surgery.

Argon vs diode laser trabeculoplasty

PURPOSE

To compare the efficacy of diode laser and argon laser trabeculoplasty in a randomized prospective study of 11 paired fellow eyes.

METHODS

Fellow eyes of 11 patients, having had no prior laser trabeculoplasty and requiring laser trabeculoplasty to lower intraocular pressure, were randomly assigned prospectively to diode laser trabeculoplasty in one eye and argon laser trabeculoplasty in the other eye.

RESULTS

In the diode laser group, the average baseline intraocular pressure was 21.6 +/- 2.0 mm Hg before trabeculoplasty and 19.6 +/- 2.1 mm Hg (or a 7.7% +/- 11.5% mean pressure reduction) at 1 month, 19.3 +/- 2.6 mm Hg (or a 6.9% +/- 13.5% mean reduction) at 2 months, and 19.0 +/- 3.3 mm Hg (or a 2.4% +/- 16.9% mean reduction) at 3 months postoperatively. In the argon laser group, the average intraocular pressure was 24.4 +/- 3.5 mm Hg before treatment and 17.6 +/- 1.7 mm Hg (or a 24.7% +/- 11.4% mean pressure reduction) at 1 month, 16.8 +/- 2.5 mm Hg (or a 26.7% +/- 15.3% mean reduction) at 2 months, and 15.5 +/- 1.2 mm Hg (or a 30.0% +/- 16.5% mean reduction) at 3 months after laser trabeculoplasty. The difference between argon and diode laser intraocular pressure reduction was statistically significant at 1 month (P < .01), 2 months (P < .01), and 3 months (P < .05) after treatment.

CONCLUSION

Argon laser trabeculoplasty appears to be more effective than diode laser therapy in lowering intraocular pressure during the first 3 months after treatment.

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.

Argon and low energy, pulsed Nd:YAG laser trabeculoplasty. A prospective, comparative clinical and morphological study

Argon laser trabeculoplasty (ALT; 1.0 W, 0.1 sec, 50 microns) was performed in right eyes, and low energy, Q-switched Nd:YAG laser trabeculoplasty (Nd:YAGLT; 1.1-4.8 mJ/pulse) in left eyes of 14 patients with primary open-angle glaucoma and in one patient with juvenile glaucoma. The pre-laser intraocular pressure (IOP) was medically uncontrollable (IOP > 21 mmHg). The interocular pressure difference varied between 0 and 3 mmHg. In 9 patients IOP decreased to less than 22 mmHg (success) in both eyes. No statistically significant difference has been revealed with paired t-test in the degree of IOP decrease between ALT and Nd:YAGLT treated eyes during the 1-18 months' follow-up. Treatment variables of Nd:YAGLT had no statistically significant effect on the duration of the post-laser success with Cox-regression. In 4 patients both treatments were ineffective (IOP > 21 mmHg). In 2 patients ALT was successful but Nd:YAGLT was ineffective. In three cases of early bilateral laser failure (IOP > 21 mmHg at the first month visit) trabeculectomy was performed on both eyes in the third post-laser month. Following ALT the uveoscleral meshwork was severely destroyed in the area of the laser spots, and the surrounding collagen fibres were heat-damaged. The meshwork between the laser spots was covered by a membrane formed by migrating endothelial cells. In the uveoscleral meshwork Nd:YAGLT induced severe focal damage surrounded by circumscript shrinkage and scarring. The juxtacanalicular tissue remained free of laser induced damage. No endothelial membrane was present. The results suggest that low energy, Q-switched Nd:YAGLT may represent an alternative method of glaucoma laser surgery.

Lasers in ophthalmology

This article reviews the principle uses of ophthalmic lasers, providing historical background with an emphasis on new applications and areas of investigation. Ophthalmic photocoagulation was the first medical laser application and has restored or maintained vision in millions of people. More recently, photodisruption and, increasingly, ablation have gained prominence for treating a wide range of ocular pathology. The unique properties of lasers have also been harnessed for diagnostic purposes, with optical coherence tomography representing a significant improvement over existing imaging methods. Many ophthalmic applications of lasers have been developed, but the field is a dynamic one which continues to evolve along with laser technology itself.

Diode lasers in ophthalmology

Compact laser emitting diodes of gallium-aluminium-arsenide are now available for incorporation into clinical lasers in ophthalmology. These lasers are cheap and have low running costs. They are portable and their wavelength of emission (810 nm) may be advantageous in certain clinical situations. Clinical trials in retinal vascular disease, trabeculoplasty, and cyclophotocoagulation, have been encouraging. Recent advances allow laser delivery through binocular indirect ophthalmoscopes, endolaser and contact transscleral probes in addition to slit lamp mounted versions. Laser delivery in situations which were previously impossible has immense implication for prevention of blindness due to glaucoma and retinal vascular disease throughout the world.

Diode laser surgery. Ab interno and ab externo versus conventional surgery in rabbits

BACKGROUND

Fibroblastic proliferation of subconjunctival tissues remains a primary mechanism of failure in filtration surgery. Minimizing the surgical manipulation of episcleral tissues may reduce scarring. Laser sclerostomy surgery involves minimal tissue dissection, and is gaining attention as a method of potentially improving filter duration in high-risk cases.

METHODS

Twenty-five New Zealand rabbits underwent filtration surgery in one eye, and the fellow eye remained as the unoperated control. Ten rabbits underwent ab externo diode laser sclerostomy surgery, ten underwent ab interno diode sclerostomy surgery, and five had posterior sclerostomy procedures. Filtration failure was defined as a less-than-4-mmHg intraocular pressure (IOP) difference between the operative and control eyes.

RESULTS

The mean time to failure for the ab externo, ab interno, and conventional posterior sclerostomy techniques measured 17.4 +/- 11.5, 13.1 +/- 6.7, and 6.0 +/- 3.1 days, respectively. In a comparison of the laser-treated groups with the conventional procedure, the time to failure was significantly longer (P = 0.02) for the ab externo filter. The mean ab interno sclerostomy duration was longer than the posterior lip procedure, but this difference was not statistically significant (P = 0.15). The overall level of IOP reduction was similar in the three groups.

CONCLUSIONS

These data suggest that diode laser sclerostomy is a feasible technique in rabbits, and the ab externo approach resulted in longer filter duration than the conventional posterior lip procedure in this model.

Diode versus argon-green laser panretinal photocoagulation in proliferative diabetic retinopathy: a randomized study in 44 eyes with a long follow-up time

A clinical randomized study using argon-green (532 nm) and diode (810 nm) lasers was carried out on 44 eyes (34 patients) affected by proliferative diabetic retinopathy (PDR), with the aim of evaluating the long-term effects of diode panretinal photocoagulation. Of the total 44 eyes, 22 were randomized to argon laser treatment (ALT) and 22 to diode laser treatment (DLT). The mean follow-up time was 25 +/- 5 months in the ALT group versus 24 +/- 4 months in the DLT group. In the ALT group 20 eyes (91%) showed regression of PDR whereas 2 eyes (9%) deteriorated. In the DLT group regression of neovascularization was observed in 22 eyes (100%). These results show that the long-term efficacy of diode laser PRP in the treatment of PDR is similar to that of argon-green laser PRP.

Laser advances in urology

This paper reviews the current use of lasers in urology--CO 2, Nd:YAG, KTP/532, Diode, pulsed dye--and describes the most common procedures performed with them. It discusses surgical techniques of lasers that are expected to be useful to urologists in the future and concludes that lasers are important tools for this specialty.

Comparison of the anterior chamber inflammatory response to diode and argon laser trabeculoplasty using a laser flare meter

BACKGROUND

Diode laser trabeculoplasty (DLT) has a similar hypotensive action to argon laser trabeculoplasty (ALT). However, anterior chamber inflammatory response and laser-induced discomfort are less pronounced with DLT. The authors compared the breakdown of the blood-aqueous barrier after DLT and ALT over the time course of 1 week and the hypotensive action over 8 weeks.

METHODS

Twenty-five patients with uncontrolled intraocular pressure (IOP) were randomized to either DLT or ALT. If two eyes required treatment, then the second eye would be treated with the alternative laser to the first. Flare values were measured at 1, 3, 24, 48, 72, 96, and 168 hours using a laser flare and cell meter. Intraocular pressures were measured at similar intervals and at 8 weeks.

RESULTS

Of 38 eyes treated, 21 underwent ALT and 17 DLT. Both forms of treatment induced a similar hypotensive effect with a significant reduction in IOP at 8 weeks compared with initial IOP (P < 0.01) (paired Student's t test). However, there was a significantly greater disruption of the blood-aqueous barrier with ALT when compared with DLT at 1, 3, and 24 hours (P < 0.001) and at 48, 72, and 96 hours (P < 0.01) (unpaired Student's t test). By 1 week, however, there was no significant difference in flare values between the two groups. Postlaser pain occurred in seven eyes treated with ALT but in no eyes treated with DLT. In addition, peripheral anterior synechiae occurred in four eyes after ALT by 8 weeks but none occurred in the DLT group.

CONCLUSION

Argon laser trabeculoplasty produces a greater disruption of the blood-aqueous barrier than DLT. This may be associated with the development of complications in the anterior segment.

Diode laser iridotomy in rabbit and human eyes

We investigated the use of an infrared diode laser to perform iridotomies in 20 eyes of ten rabbits and 40 eyes of 24 patients with primary angle-closure glaucoma. We used a two-stage method with initial circular stretch burns and subsequent penetrating multiple burns. The iris was perforated in one session and remained patent through ten months in rabbits, and seven to nine months in humans. Transitory clinical complications included intraocular pressure increase of more than 10 mm Hg (20%, eight of 40 eyes), corneal endothelial changes (5%, two of 40 eyes), clouding of lens surface (60%, 24 of 40 eyes), localized cataract (5%, two of 40 eyes), and pupillary distortion (70%, 28 of 40 eyes). No retinal damage was observed. Diode laser can be used for peripheral iridotomy.