Micropulse diode laser trabeculoplasty – 180-degree treatment


Elina Rantala
Department of Ophthalmology
Päijät-Häme Central Hospital
Keskussairaalankatu 7
FIN-15180 Lahti
Tel: + 358 3 819 4811
Fax: + 358 3 819 4803
Email: elina.rantala@helsinki.fi


Purpose:  To evaluate the outcome of 180° micropulse diode laser trabeculoplasty (MDLT) in patients with open-angle glaucoma.

Methods:  A retrospective review of 40 eyes of 29 MDLT-treated patients with a minimum follow-up time of 6 months. Successful outcome was defined as follows: (i) a ≥20% or (ii) a ≥3-mmHg decrease of intraocular pressure (IOP), no further need for laser- or incisional surgery and the number of glaucoma medication was the same or less than preoperative. These definitions will from now on be referred to as definition one and definition two.

Results:  Life-table analysis showed an overall success rate of 2.5% (1/40) and 7.5% (3/40) (according to definitions one and two, respectively) after up to 19 months of follow-up. The average time for failure was by definition one 2.9 months (standard deviation, SD ± 3.5, range 1–12 months) and by definition two 3.3 months (SD ± 3.9, range 1–16 months). There were no intra- or postoperative complications caused by MDLT. Postoperative inflammatory reaction, cells and flare, was scanty.

Conclusion:  Our results suggest that 180° MDLT is a safe but ineffective treatment in patients with open-angle glaucoma.


Argon laser trabeculoplasty (ALT) became a commonly performed procedure in eyes with open-angle glaucoma after the Wise & Witter report 1979. Micropulse diode laser trabeculoplasty (MDLT) was first described by Ingvoldstad at the ARVO annual meeting in 2005 (Fort Lauderdale, FL, USA). Micropulse is a laser delivery modality that adds subvisible applications (subthreshold) of repetitive short diode laser pulses. This differentiates it from the conventional continuous wave diode laser. The typical or the most common laser complications of ALT, such as peripheral anterior synechiae formation, intraocular pressure (IOP) spikes and inflammation, are due to the burning effect on trabecular meshwork (Thomas et al. 1982; Tuulonen & Airaksinen 1983; Damji et al. 1999). MDLT is claimed to minimise damage to the trabecular meshwork (Ingvoldstad et al. 2005).

To date, only one report has been published that considers the IOP lowering effect of 180° MDLT in patients with open-angle glaucoma (Detry-Morel et al. 2008). MDLT has been found to reduce IOP less than ALT at the end of a 3-month follow-up (Detry-Morel et al. 2008). The purpose of our study is to evaluate the pressure-lowering potential of 180° MDLT treatment with a minimum follow-up time of 6 months in patients with open-angle glaucoma.

Materials and Methods

Between May 2007 and July 2008, a series of 49 consecutive patients (64 eyes) treated with MDLT at the Department of Ophthalmology, Päijät-Häme Central Hospital, were reviewed. The eligibility criteria for this retrospective study were open-angle glaucoma, first-time 180° MDLT, a minimum 6-month follow-up and no antiglaucoma medication changes simultaneously with MDLT (Fig. 1).

Figure 1.

 The flow chart of the study population throughout the entire study. The chart (A) describes the reasons for the failure by definition 1 i.e. no intraocular pressure (IOP) reduction of ≥20% and the chart (B) by definition 2 i.e. no IOP reduction of ≥3 mmHg.

Twenty-four eyes of 21 patients did not fit those eligibility criteria and were not accepted into the study. For six eyes, the glaucoma medication was changed simultaneously at the day of the MDLT treatment. In 6 eyes, 360° was treated. Five eyes treated with MDLT had other glaucoma diagnosis than open-angle glaucoma (three eyes had ocular hypertension, one eye had post-traumatic glaucoma, one eye had IOP elevation because of a central retinal vein occlusion without rubeosis, one eye had congestive glaucoma). Four eyes had a shorter than 6-month follow-up. Two eyes had the second-time MDLT. For one eye, the IOP was not recorded (the transcriptionist did not hear the number dictated into the tape).

Follow-up time of the 40 eyes (29 patients) was defined as starting from the date of the MDLT procedure and ending on the date of the last follow-up. The first follow-up was 1 month after the treatment according to the normal schedule of our clinic. Because of the retrospective nature of this study, the second follow-up was an average 3 months postoperatively and the third follow-up an average 6 months postoperatively. Patients underwent MDLT procedure when their respective physician felt their IOP was above their target pressure.

MDLT was performed with the Iris Medical OcuLight SLx 810-nm diode laser system (Iridex Corporation, Mountain view, CA, USA). MDLT treatments were performed by eight different surgeons who used the same laser settings. All physicians used a Goldman 2-mirror goniolens with methylcellulose and the same micropulse laser settings with every study patient: 300 μm spot size diameter, 2 W power, 200-ms duration with 15% duty cycle (Ingvoldstad et al. 2005; Detry-Morel et al. 2008). With these settings, a train of 60–66 laser pulses was evenly distributed around 180° in the trabecular band. Every patient was administered a brimodine 2 mg/ml drop (Alphagan®; Allergan Inc., Irvine, CA, USA) immediately after treatment. At each postoperative visit, IOP and anterior chamber inflammation reaction were examined and data from the glaucoma medication and further surgical procedures collected. Also intra- and postoperative complications were observed.

Statistical analyses were performed using spss version 17.0 for Windows (SPSS Inc., Chicago, IL, USA). Continuous variables were analysed using two-tailed t-tests. The Kaplan–Meier life-table was used to determine the surgical outcome.

The eye was regarded as being successfully treated with MDLT when the following conditions were met: the IOP was reduced by definition one ≥20% or by definition two ≥3 mmHg, there was no need for further laser trabeculoplasty or glaucoma surgery and the number of glaucoma medication was the same or less than preoperative. The number of preoperative pharmaceuticals was maintained unchanged or less throughout the course of the study. If the number of pharmaceuticals was increased, the case met the criteria for failure. Preoperative IOP and the total number of glaucoma medication were calculated on the day of MDLT treatment.


Table 1 gives the characteristics of the study population. MDLT was the primary surgical treatment for 26 of the 40 eyes (65%). The mean ± standard deviation (SD) preoperative IOP was 21.8 ± 4.9 mmHg (range 14–34 mmHg) with the mean number of glaucoma medication 2.0 ± 1.3 (range 0–4). The mean follow-up time was 12.2 ± 3.3 months (range 8–19 months).

Table 1.   Demographic data of 40 eyes treated with micropulse diode laser trabeculoplasty.
  1. * More than 1 procedure may be present in one eye. ALT = argon laser trabeculoplasty.

Age, years, mean ± standard deviation71 ± 7.6 (range 54–84)
 Male6 (15%)
 Female34 (85%)
No. of antiglaucoma medication
 04 (10%)
 113 (33%)
 29 (23%)
 37 (18%)
 47 (18%)
Type of antiglaucoma medications
 Beta-blocker19 (48%)
 Carbonic anhydrase inhibitor (topical)12 (30%)
 Carbonic anhydrase inhibitor (p.o.)2 (5%)
 Prostaglandin agonists32 (80%)
 Alpha agonist13 (33%)
Glaucoma types
 Primary open angle17 (42.5%)
 Exfoliative23 (57.5%)
Prior surgery*
 Cataract extraction8 (20%)
 ALT5 (13%)
 Iridotomy + ALT2 (5%)
 Trabeculectomy1 (2.5%)
Lens status
 Phakic32 (80%)
 Pseudophakic8 (20%)

During the follow-up time, additional surgery was performed: two eyes had further MDLT, five eyes ALT, three eyes trabeculectomy, three eyes shunt, two eyes selective laser trabeculoplasty (SLT) and five eyes cataract surgery. More than one procedure may be present in one eye, and all these eyes were defined as failures during the follow-up time. The IOP during the follow-up was ≤6 mmHg in two eyes. Both of these eyes had a trabeculectomy.

There was no significant difference between the mean preoperative IOP and the mean IOP at the time of the failure by definition one 22.6 ± 5.9 mmHg (range 15–35 mmHg, p = 0.311, paired t-test) and by definition two 23.0 ± 5.9 mmHg (range 15–35 mmHg, p = 0.157, paired t-test). The IOP change during the follow-up time is presented in Fig. 2.

Figure 2.

 The mean intraocular pressure (IOP) of the eyes before and after the 180-degree micropulse diode laser trabeculoplasty with the failure criteria 2 i.e. no IOP reduction ≥3 mmHg (Curve A) and with the failure criteria 1 i.e. no IOP reduction ≥ 20% (Curve B). Analysis is made without failed eyes using the last observation carried forward method (LOCF).

A Kaplan–Meier life-table analysis of the study patients is presented in Fig. 3. According to definition one, life-table analysis showed an overall success rate of 2.5% (one eye) after 19 months of follow-up. According to definition two, the overall success rate was 7.5% (three eyes) after 19 months of follow-up. The average time for failure was by definition one 2.9 ± 3.5 months (range 1–12 months) and by definition two 3.3 ± 3.9 months (range 1–16 months).

Figure 3.

 Survival curves (Kaplan–Meier) for 40 eyes of 29 patients after 180° micropulse diode laser trabeculoplasty with the failure criteria 2 i.e. no intraocular pressure (IOP) reduction ≥3 mmHg (Curve A) and with the failure criteria 1 i.e. no IOP reduction ≥20% (Curve B).

We compared the eyes that were on ≥3 glaucoma medication preoperatively with the eyes that were on lower number of medications. No significant difference was demonstrated in the IOP at the end of the follow-up between these two groups (p = 0.142, paired t-test). There were no intra- or postoperative complications due MDLT. None of the study eyes had flare/cells either at the beginning or at the first month follow-up visit.


Since the 1970s, various laser therapies have been used to reduce IOP in patients with glaucoma. SLT was first introduced in 1995 by Latina and Park (Latina & Park 1995). SLT delivers less than 1% of the energy of ALT by using a nanosecond pulse duration and selectively targeting the cells. This minimises coagulation and collateral damage to the nonpigmented cells or adjacent structures (Kramer & Noecker 2001). ALT has been assumed to cause more structural damage to human eyes in comparison with newer laser techniques, such as SLT or MDLT (Kramer & Noecker 2001; Detry-Morel et al. 2008).

The interpulse separation of the MDLT is long enough to allow the temperature to return to baseline prior to the arrival of the next pulse. As a consequence, in theory MDLT cannot produce micro-explosions, pigment dispersion, IOP spikes or a risk of IOP increases in eyes with heavily pigmented trabecular meshwork (Ingvoldstad et al. 2005). Both ALT and SLT might cause postoperative IOP spikes (Thomas et al. 1982; Tuulonen & Airaksinen 1983; Latina et al. 1998).

MDLT is a relatively new technology. This study is based on our initial experience with this new procedure. The failure rate for MDLT in our series was higher than the prior MDLT study by Detry-Morel et al. (2008): 97.5% versus 35.7%. Detry-Morel et al. followed the patients for 3 months, and their success criterion was ≥20% IOP reduction. All study patients were treated with the same treatment parameters in both studies. Our retrospective clinical study shows that no statistically significant IOP reduction can be achieved with 180° MDLT. The lower failure rate in the study by Detry-Morel et al. may be explained by the shorter follow-up time in their study. According to this study, it seems that 180° treatment might be inadequate or that the treatment parameters that were used suboptimal. Prasad et al. (2009) described increased efficacy with 360° compared with 180° procedure in patients treated with SLT.

Only 35% of study eyes had ≥3 medication for treatment of glaucoma preoperatively, and the rest 65% of eyes were on lower number of medications. Rouhiainen et al. (1995) reported statistically better IOP responses with ALT in patients with lower numbers of glaucoma medication preoperatively. In our study, eyes with lower number of medications did not have a better success rate than eyes with ≥3 medication.

The mean preoperative IOP in our study patients was 21.8 mmHg, which is about the same level as in the Detry-Morel et al. study (2008) (20.7 mmHg). Prior studies describe that the amount in pressure drop is directly related to the height of the pretreatment pressure: the higher the preoperative IOP, the greater the postoperative reduction (Pollack & Robin 1982; Thomas et al. 1982). In our study, only ten out of 39 failure eyes (26%) needed further incisional surgery during the follow-up time. More than one procedures may be present in one eye. This indicates that MDLT was not the last treatment option among study patients before filtration surgery.

We did not find any intra- or postoperative MDLT complications. Inflammatory reaction, cells and flare, with MDLT was scanty, indicating minimal thermal effect on trabecular meshwork. However, one study has reported that MDLT induced minimal anterior segment inflammation (Detry-Morel et al. 2008).

The major weakness of our study is that it is a retrospective study. One might argue that the outcome of the study might have been influenced by the fact that eight different surgeons performed the treatment. However, each physician used the same laser settings for every study eye and treated each study eye with almost the same number of laser pulses (ranged from 60 to 66). The severity of the glaucoma was not evaluated in this study. This might be a potential confounding variable because patients with advanced glaucoma tend to get a high failure rate.

Our results suggest that 180° MDLT is a safe but ineffective treatment in patients with open-angle glaucoma. In our study, MDLT had an overall high life-table failure rate. According to our results, we have to stop using 180° MDLT and continue using 180° SLT as a treatment for open-angle glaucoma until further optimal treatment parameters for MDLT are reported. Further studies of a prospective nature are needed to clarify the efficacy of MDLT.


The authors have no financial or proprietary interest in the materials described in the article.