|Year : 2016 | Volume
| Issue : 2 | Page : 80-84
Micropulse laser trabeculoplasty for open-angle glaucoma
Mahmoud A Abouhussein FRCO, Glasgow, MD
Department of Ophthalmology, Faculty of Medicine, Alexandria University, Alexandria, Egypt
|Date of Submission||06-Apr-2016|
|Date of Acceptance||25-May-2016|
|Date of Web Publication||30-Aug-2016|
Mahmoud A Abouhussein
9 Hassan Allam Street, Kasr Elmoltazem, Smouha, Alexandria 1103
Source of Support: None, Conflict of Interest: None
The aim of this study was to evaluate the pressure-lowering effect of 577 nm micropulse laser trabeculoplasty in eyes treated for primary open-angle glaucoma.
Patients and methods
This prospective interventional case series included 30 eyes of 30 patients treated for primary open-angle glaucoma (one eye of each patient).
was delivered using the IQ 577 nm laser system with fixed treatment parameters: 577-nm (yellow) wavelength, 300-µm spot size, 300-ms envelope duration using 1000 mW of power at a 15% duty cycle, and delivering confluent applications for 360°.
The mean intraocular pressure at baseline was 18.07±1.91 mmHg. There was a prompt and significant decrease in intraocular pressure that was maintained during the 6-month follow-up, reaching 14.17±1.56 mmHg (P<0.0001).
Five-hundred and seventy-seven nanometer micropulse laser trabeculoplasty offers a safe, effective adjuvant treatment to pharmacotherapy in treating primary open-angle glaucoma.
Keywords: laser trabeculoplasty, micropulse, primary open-angle glaucoma
|How to cite this article:|
Abouhussein MA. Micropulse laser trabeculoplasty for open-angle glaucoma. Delta J Ophthalmol 2016;17:80-4
| Introduction|| |
Argon laser trabeculoplasty (ALT) is a common form of treatment for primary open-angle glaucoma (POAG), exfoliation syndrome glaucoma, pigmentary glaucoma, and normal-tension glaucoma .
ALT was shown to have a good pressure-lowering effect comparable to medical treatment in treating newly diagnosed POAG . However, ALT has not become the primary treatment of choice; it has mainly been used as an adjunctive therapy, reserved for patients with poorly controlled intraocular pressure (IOP) under maximum tolerated medical therapy. Despite the fact that ALT is effective in reducing IOP, side effects are commonly encountered, including IOP spikes in the early post-ALT period, local scarring of the trabecular meshwork, appearance of peripheral anterior synechiae, and decreased effect after repeated ALT ,,.
Selective laser trabeculoplasty (SLT) utilizes a single 3 ns duration pulse of a 532 nm laser with large 400 µm spot to selectively destroy pigmented trabecular meshwork cells with no damage to adjacent nonabsorbing cells . SLT has been documented to cause a decrease in IOP comparable to the effect of ALT with a less incidence of postoperative inflammation, less occurrence of pressure spikes, and peripheral anterior synechiae ,,,,.
Trabeculoplasty with subvisible applications (subthreshold) of repetitive short diode laser pulses is called micropulse diode laser trabeculoplasty (MDLT) to differentiate it from the conventional continuous wave (CW) diode laser trabeculoplasty. Both MDLT and conventional CW trabeculoplasty produce statistically significant IOP reduction; however, with MDLT, intraoperative pain, postoperative inflammation, and cell/flare reaction are negligible and significantly lower than that with conventional CW trabeculoplasty ,,.
Micropulse technology finely controls thermal elevation by ‘chopping’ a CW beam into a train of repetitive microsecond pulses separated by brief rest periods that prevent the buildup of thermal energy. Studies showed that it is as clinically effective as conventional CW laser for the treatment of diabetic macular edema without any visible laser-induced damage during and at any time after treatment ,,.
The use of micropulse for the treatment of glaucoma has been compared with SLT. However, they do differ in their theoretical mechanisms of action. SLT targets intracellular melanin and activates macrophages and selectively damages pigmented cells in the trabecular meshwork, which may induce postoperative inflammation and IOP spikes . Micropulse laser trabeculoplasty (MLT) thermally affects trabecular cells without destroying them by allowing a cooling period between pulses, thereby preventing tissue destruction. The goal of MLT is to stimulate a biological response within the trabecular meshwork while reducing tissue damage ,,.
The purpose of this study was to evaluate the pressure-lowering effect of 577 nm yellow MLT in cases of POAG.
| Patients and methods|| |
This prospective interventional case series included 30 eyes of 30 consecutive patients treated for POAG. One eye of each patient, the eye with higher IOP, was chosen to perform MLT in addition to the already administered topical treatment, whereas the fellow eye was kept on its same topical treatment.
The research protocol was approved by the Alexandria University Institutional Review Board and Ethics Committee. Informed consent was taken from the patients.
Patients with POAG on topical antiglaucoma medications (pretreatment IOP<21 mmHg), with glaucomatous field changes on Humphrey Visual Field Analyzer (Dublin, California, USA), open angle on gonioscopy (Shaffer grading 3 or 4), a minimum 6 months of follow-up after MLT, and no antiglaucoma medication changes during follow-up were included in the study.
Exclusion criteria were as follows: having an angle closure or secondary glaucoma, having received prior laser trabeculoplasty, any corneal abnormalities, any intraocular surgery within the previous 6 months before micropulse trabeculoplasty, having advanced field changes, and having other retinal or optic nerve diseases.
Baseline data for each patient included full ocular and medical history, best-corrected visual acuity, slit lamp biomicroscopy with gonioscopy, IOP measurement using Goldmann applanation tonometer (Haag Streit, Switzerland), fundus examination, and visual field assessment (Humphrey Visual Field Analyzer 24-2).
The number of medications used before micropulse trabeculoplasty was recorded. Fixed combination medications were counted as two types of antiglaucoma medication.
Treatment was delivered with the IQ 577 nm laser system (IRIDEX, Mountain View, California, USA) with fixed treatment parameters: 577-nm (yellow) wavelength, 300-µm spot size, 300-ms duration using 1000 mW of power at a 15% duty cycle, and delivering confluent applications for 360°.
After topical anesthesia, the patient was seated at the slit lamp and a laser antireflective-coated Goldmann three-mirror lens (Ocular Instruments, Bellevue, Washington, USA) was placed on the eye to be treated. The laser was carefully focused on the pigmented trabecular meshwork and confluent applications were administered for 360°. As no visible laser-induced tissue change endpoint was produced, the placement of invisible confluent applications relied on the surgeon’s judgment, resulting in a variable number of confluent spots. The total number of laser applications delivered to each eye was recorded after each treatment.
No postlaser treatment was given apart from the patient’s pre-existing antiglaucoma medications.
Patients were evaluated at 1 day, 1 week, 1 month, 3 months, and 6 months after treatment. At each visit, anterior segment examination, best-corrected visual acuity, and IOP measurement were recorded, and gonioscopy was performed to look for peripheral anterior synechiae. Visual field was repeated at the end of 6 months of follow-up.
Patients were kept on the same antiglaucoma treatment for the 6 months of follow-up after micropulse trabeculoplasty.
The data were collected and entered into a personal computer. Statistical analysis was carried out using statistical package for the social sciences (SPSS, version 20; SPSS Inc., Chicago, Illinois, USA) software.
For comparison between baseline IOP and follow-up IOP measurements, t-test was used. The level of significance was 0.05.
| Results|| |
Thirty eyes of 30 patients were included in this study. The mean±SD age of the patients was 62.12±5.48 years (range: 53–72 years). Eighteen patients were female and 12 were male. [Table 1] summarizes the patients’ baseline data.
The total number of laser applications delivered to treated eyes ranged from 115 to 126 applications, with a mean of 121.07±2.64.
The mean IOP at baseline of 18.07±1.91 mmHg had a prompt and significant decrease that was maintained during the 6-month follow-up, as shown in [Table 2].
|Table 2 Changes in intraocular pressure following micropulse laser trabeculoplasty|
Click here to view
The highest percentage of IOP reduction was recorded at 1 month after MLT and the lowest percentage of IOP reduction was recorded at day 1 after MLT.
There were no significant complications after MLT. No post-treatment inflammatory cells or flare was noticed in the anterior chamber during follow-up visits. During the 6-month follow-up, no eyes developed peripheral anterior synechiae.
Visual field parameters were statistically similar before and after MLT.
| Discussion|| |
The micropulse laser technology uses subvisible repetitive short laser pulses to the trabecular meshwork. Each pulse is spaced with a long relaxation time. Micropulse trabeculoplasty uses 15% duty cycle instead of a continuous 100% duty cycle laser wave, so that targeted tissue reaches sublethal temperature and remains viable. Using micropulse technology in trabeculoplasty does not cause coagulative damage to the trabecular meshwork and laser-related complications such as IOP spikes and pigment dispersion and serious inflammatory response are minimal. ALT was shown to cause shrinkage with adjacent stretching and scarring of the trabecular meshwork, whereas SLT caused selective destruction of the pigmented trabecular meshwork cells without producing any adjacent collateral damage .
The objective of this prospective case series study was to evaluate the pressure-lowering potential of MLT in eyes treated for POAG. This study results indicate that the IOP reduction response is generally well maintained.
The mechanism of action of laser trabeculoplasty is not well known, but the most recent theory suggests a responsive cellular biochemical reaction. The threshold of laser-induced cellular effect to produce that reaction is not known . This can be the reason why 577 nm yellow MLT has a pressure-lowering effect, even with subvisible laser applications. These applications produce gentle photothermal effects that might initiate the therapeutic cellular cascade without causing a clinically visible damage in the trabecular meshwork.
In a study by Fea et al. , the pressure-lowering potential of subthreshold MDLT was evaluated. The study included 20 eyes of 20 consecutive patients with uncontrolled POAG followed up for 12 months. The laser was applied using confluent subthreshold laser applications over the inferior 180° of the anterior Trabecular Meshwork (TM) using an 810 nm diode laser in a micropulse operating mode. The results were that four (20%) eyes did not respond to treatment during the first week. One additional eye failed at the 6-month visit. The treatment was successful in 15 (75%) eyes 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%. In the present study, 577 nm micropulse laser was used instead of 810 nm diode and we used 360° protocol instead of 180°.
Detry-Morel et al. , in their randomized prospective trial, aimed at assessing the safety and the IOP-lowering effect of MDLT and ALT in patients with open-angle glaucoma. The 26 POAG patients were randomized to receive either MLT using a diode laser (810 nm) versus ALT. At 3 months, MDLT induced significantly less IOP reduction compared with ALT. The percentage of eyes with an IOP drop more than 20% was also significantly lower with diode laser than with ALT. MDLT induced minimal anterior segment inflammation and seemed to exhibit a good safety profile. The decreased effect of MDLT may be due to the fact that 810 nm wavelength diode laser is not specifically targeting the pigment in the trabecular meshwork. The 577 nm wavelength is probably better in affecting the pigmented trabecular meshwork.
Recently, Ahmed et al.  reported their experience in using MLT with 532 nm wavelength in patients with open-angle glaucoma. They used the same treatment parameters: 300-µm spot size, 300-ms duration, and 15% duty cycle. However, they compared the effect of using different power settings: 300 mW (13 eyes of 13 patients), 700 mW (14 eyes of 14 patients), and 1000 mW (18 eyes of 18 patients). The results showed that a power setting of 1000 mW generated the greatest reduction in IOP at 1 and 4 months. They suggested that the higher power will provide a longer-lasting effect. In the current study, 577 nm wavelength with the same treatment parameters and 1000 mW power was used.
In contrast to ALT and SLT in which champagne bubble formation is visible on the trabecular meshwork during treatment, MLT does not result in any visible tissue reaction or endpoint during treatment, making the procedure more difficult.
A bigger study on a larger number of patients is needed to confirm the benefit of micropulse 577 nm trabeculoplasty. We need to test the response in virgin eyes in a randomized trial against current treatment options such as ALT, SLT, or other antiglaucoma medications.
| Conclusion|| |
MLT offers a safe, effective treatment for lowering the IOP in patients treated from POAG.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2]
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