|Year : 2021 | Volume
| Issue : 2 | Page : 292-296
Micropulse transscleral cyclophotocoagulation Cyclo G6 laser at low energy levels: Initial results in Indian eyes with advanced glaucoma treated in a single session
Department of Glaucoma, Centre for Sight, Banjara Hills, Hyderabad, Telangana, India
|Date of Submission||22-Jul-2020|
|Date of Acceptance||30-Oct-2020|
|Date of Web Publication||01-Apr-2021|
Dr. Vanita Pathak-Ray
Glaucoma Fellowship, University of Toronto, Canada, Centre for Sight, Road No 2 Banjara Hills, Hyderabad - 500 034, Telangana
Source of Support: None, Conflict of Interest: None
Micropulse–transscleral–cyclophotocoagulation [MPTSCPC] delivered with the G6 laser system is one of the newer laser systems which purports greater safety without compromising efficiency in the reduction of intraocular pressure. This is due to the pulsed nature of the delivery of the laser in on and off cycles. We report the initial results of the laser used at low energy levels in consecutive Indian eyes [n = 8] with advanced or end-stage glaucoma, in one session. Three representative cases are described in this case series.
Keywords: Advanced glaucoma, Cyclo G6 laser, Micropulse Transscleral diode photocoagulation, MP3 probe, MPTSCPC, Transscleral diode cyclophotocoagulation, TSCPC
|How to cite this article:|
Pathak-Ray V. Micropulse transscleral cyclophotocoagulation Cyclo G6 laser at low energy levels: Initial results in Indian eyes with advanced glaucoma treated in a single session. Indian J Ophthalmol Case Rep 2021;1:292-6
|How to cite this URL:|
Pathak-Ray V. Micropulse transscleral cyclophotocoagulation Cyclo G6 laser at low energy levels: Initial results in Indian eyes with advanced glaucoma treated in a single session. Indian J Ophthalmol Case Rep [serial online] 2021 [cited 2022 Dec 5];1:292-6. Available from: https://www.ijoreports.in/text.asp?2021/1/2/292/312375
Diode laser cyclophotocoagulation is being increasingly used in all etiologies of glaucoma as the angle status does not play a role in the delivery of the laser. Micro-pulsed laser [MPTSCPC] has been a recent addition which helps minimise thermal damage as it has on and off cycles, as opposed to a continuous wave one. It is a non-invasive procedure delivered via a single-use special Micropulse MP3 probe attached to the laser system, Iridex Cyclo G6 [IRIDEX Laser Systems, Iris Medical Instruments, Mountain View, CA, USA].
| Case Reports|| |
Three representative cases are described below.
A-20-year-old aphakic male patient, with only one seeing eye and nystagmus, presented with uncontrolled IOP following failed Trabeculectomy with Mitomycin C [Trab + MMC] and Ahmed Glaucoma Valve [AGV] surgery. The best corrected visual acuity [BCVA] was 20/100 and the patient complained of deteriorating vision at an IOP level of 20 mmHg on 3 anti-glaucoma medications [AGM]. The cup-to-disc ratio was 0.95. and only a 10-2 Humphrey Visual Field [HVF] was possible; Mean Deviation had deteriorated to -16.98 dB from -13.26 dB a year ago, though Pattern Standard Deviation was relatively stable. The eye received 130 seconds of MPTSCPC [detailed later]* and 1-year later had an IOP of 12 mmHg and slightly improved BCVA [20/80] on 1 AGM. HVF was also stable at 1-year.
A 68-year-old aphakic gentleman, with previous high myopia and pseudo-buphthalmos [axial length > 30 mm] presented with a BCVA of CF 0.5 m and an IOP of 21 mmHg on 5 AGM. The fellow eye was pseudophakic with a BCVA of 20/60 and an IOP of 13 mmHg without AGM post Trab + MMC. Both the eyes had extensive myopic chorio-retinal atrophy involving the posterior pole and demonstrated advanced cupping. The eye received 150 seconds of MPTSCPC; he developed moderate inferior superficial punctate keratitis, even though there was no lagophthalmos and Bell's was moderate. This settled on conservative management and at 1-year his BCVA was unchanged with an IOP of 15 mmHg on 2 AGM.
A-33-year-old male patient pseudophakic with steroid induced glaucoma and a BCVA of 20/200 with a past history of trab + MMC, needling + MMC, non-valved glaucoma drainage device and tube-extender surgery for retracted-impacted tube, found his vision deteriorating further due to decompensating cornea. He underwent a penetrating keratoplasty, but soon IOP became uncontrolled [21 mmHg] on 4-AGM and vision deteriorated further. The fellow left eye had a failed AGV surgery elsewhere and an opaque cornea. Prior to MPTSCPC, his BCVA in the only seeing eye was CF at 0.5 m and had an improvement of vision to CF at 1.5 m. Whilst this may seem extremely modest, it provided him the ability to be more independent for vision-related tasks. His IOP at last follow-up was 15 mmHg on 2 AGM.
All procedures were performed in the operating room; each eye received three applications of topical anesthesia proparacaine HCl 0.5% and betadine 5% eye drops. Peri-ocular painting with betadine was done prior to peribulbar anesthesia [1:1 mixture of bupivacaine 0.5% and lidocaine 2%].
The OR was specially laid out with side-by-side tables to minimise loss of time in-between patients.
A single-use fiber-optic handheld delivery device [MP3 handpiece] with the Iridex Cyclo G6, at a standardized preset power of 2000 mW and a duty cycle of 31.33% [micropulse “on”0.5 ms, micropulse “off”1.1 ms] for an exposure of 130-180 seconds[s], was used. The tip fits 3 mm posterior to the limbus, the curved surface facing the limbus [[Figure 1]. Top & Bottom] Approximately 4 to 6 passes of the probe were done superiorly and inferiorly, avoiding the 3&9o'clock position, as well as the site of failed filtration bleb, if present. [Video Clip 1] The probe was thoroughly cleaned with a 70% alcohol swab in between eyes. All the procedures [n = 8] were completed within one-hour of connection. Subconjunctival dexamethasone [4 mg/ml] was given after the application of the laser.
|Figure 1: Top photograph shows tip of Micropulse P3 probe with fiber optic tip protruding (white arrow), one curved (curved double-sided black arrow) and one flat surface (straight double-sided black arrow) Bottom photograph shows placement of this probe over the eye with the curved surface facing the limbus for ‘painting’ motion for delivery of laser. [Details in Video clip 1.]|
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The eye was patched for 24 hours; thereafter, topical moxifloxacin [1 week], prednisolone acetate 1% 6-8 times [tapered in 4-6 weeks] and homatropine HCl for 1 week [if required] was advised. Topical anti-glaucoma medication [AGM] was adjusted for each patient at every visit and reduced in a stepwise approach.
Baseline characteristics, laser parameters and post-laser outcomes of 8 eyes of 7 patients who received MPTSCPC in the same sitting are listed in [Table 1]. Before reviewing the data, success was defined as an IOP ≥5 and ≤18 mm Hg, achieved with or without IOP-lowering agents. Failure was defined as loss of light perception and/or need for further glaucoma procedures to control IOP.
|Table 1: Baseline characteristics, laser parameters and 1-year post-laser outcomes of 8 eyes of 7 patients who received Micropulse Transscleral Cyclophotocoagulation (MPTSCPC) at fixed power of 2000 milli Watts, in the same sitting|
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All completed 1-year follow-up. Mean duration of laser exposure was 156.25 ± 14.1 s at a fixed power of 2000 mW and mean total energy was 97.8 ± 8.8 Joules[J]. IOP reduced from 24.5 ± 11.1 mm Hg to 15.4 ± 1.7 [p = 0.048], a decrease of 36.8%. IOP was lowest at week-1 and stabilised by month-3. [Figure 2] Use of AGM reduced from 4.0 ± 0.75 to 1.5 ± 1.1 at 1 year, a 62.5% decrease [p = 0.001]. None of the eyes required re-treatment, nor was there need for oral acetazolamide; none of the eyes lost vision and no serious sight-threatening complications occurred.
|Figure 2: Graph showing Intraocular pressure (IOP) and anti-glaucoma medications (AGM) at various intervals in Micropulse transscleral cyclophotocoagulation|
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| Discussion|| |
MPTSCPC is a relatively new pulsed laser which is used as a non-invasive treatment option, believed to minimise collateral thermal tissue damage, unlike its predecessor, continuous wave-TSCPC [CWTSCPC], which does so by delivering continuous high intensity energy to the ciliary body. When MPTSCPC was compared to CWTSCPC by Aquino and colleagues, ocular complication rate was lower in the former, as MP3 probe applies pulsed laser in a continuous painting fashion to pars plana, rather than individual spot burn applications of CWTSCPC to the pars plicata, via the G-probe. Five patients developed hypotony in the CWTSCPC group, none in the micropulse group.
More than its photocoagulative effect, MPTSCPC is hypothesised to increase uveoscleral outflow by an ill-understood mechanism and, so far, it is unclear what role is played by ocular pigmentation, impacting on the total energy used. As it is a relatively new technique, there is still no clarity on the guidelines for the ideal laser parameters that balances efficacy with side effects.
Encouraged by its short-term efficacy,, several other authors have now reported outcomes with somewhat longer follow-up,,, with use of diverse treatment parameters.
Sanchez et al. hypothesized that a range between 112-150 J of total energy [=power in Watts[W] X treatment duration in seconds[s] X ON cycle (31.3%)] allows a moderate IOP lowering effect of around 30% with few/no complications. Zaarour et al., using a standardized protocol [energy 108 J], achieved a 73.3% success rate at 1-year in their cohort of 75 eyes. Though seven eyes [9%] needed additional glaucoma surgery, no serious complications occurred. Tan et al. and Aquino et al. applied much shorter treatment regimens, but achieved the same effect as that reported by Zaarour et al.
On the other hand, Williams et al. and Emmanuel et al., using a non-standardized treatment protocol, achieved greater reduction in IOP [67% vs. 41.2% success respectively] but with a higher complication rate [8.3% hypotony and 2.5% phthisis in the former study and 6% hypotony and loss of VA by ≥2 lines in 26% in the latter study]. Both these studies also reported prolonged inflammation; Emmanuel and colleagues have recommended shorter treatment time in pigmented eyes.
In relatively larger cohorts, Sarrafpour and colleagues and Kaba and colleagues, also noted that there was a greater reduction in IOP at higher power when compared to lower, even though the magnitude of reduction was different in the two studies.
All these studies have been summarised in [Table 2].
|Table 2: Summary of various studies published in Micropulse Transscleral Cyclophotocoagulation (MPTSCPC)|
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Guided by the hypothesis proposed by Sanchez et al., as well as the recommendations of Emmanuel et al. and thereby remaining conservative, we did not exceed total energy of 100 J, except in 1 eye. Total energy equalling 100 J was used in 4 eyes; 93.9 J in 2 eyes, and only 81.4 J in an only seeing eye with aphakic glaucoma which failed after trabeculectomy and AGV surgery. Only one eye [case 8, [Table 2]] with Light Perception (LP) vision received laser energy greater than 100 J [total 112.7 J]. This eye was painful and also had thyroid-related severe exposure keratopathy and a previous history of perforation and management with tissue adhesive and bandage contact lens, with a very high digital IOP pre-laser [GAT was not possible]. IOP was recordable by GAT only 4 months post laser – and was 17 mmHg without use of AGM and unchanged BCVA [LP] post laser; however complete resolution of pain occurred within a few weeks of the procedure.
There were 3 eyes with pre-laser IOP of less than 20 mmHg – effect of laser was the least in 2 out of these 3 eyes and they also demonstrated a very modest benefit in terms of reduction of AGM, and a dose-response relationship has been reported by Sarrafpour et al. Other than a relatively minor complication of superficial punctate keratitis in a pseudo-buphthalmos eye, none of the other complications attributed to this laser – inflammation, cystoid macular edema, hypotony, phthsis - occurred. Several authors, have describe prolonged inflammation with the laser; hence, to prevent long-term inflammation in these eyes, a tapering dose of topical prednisolone 1% was used for 4-6 weeks. Most notably none of the eyes lost vision even though the cohort consisted of refractory or end-stage glaucoma.
Based on our pre-defined criteria for success, all eyes achieved it, with or without medication. However, this non-invasive procedure, which can also be delivered in the outpatients setting, comes at a substantial cost to the patient [cost of single-use probe is approximately 400 USD]. Therefore, the relative advantages of the laser may become obscure in low-to-middle income countries, where cost is a major concern. However, a probe remains 'activated' for approximately 90 minutes once attached to the laser system. We leveraged this knowledge and administered laser to consecutive eyes in a single sitting via a single probe with adequate precautions.
| Conclusion|| |
Currently MPTSCPC is not widely used in India; however, use of low-energy MPTSCPC in Indian eyes, as reported here, appears to be promising. Aiming for reduction of AGM with achievement of target IOP without adverse events, was better accomplished with cumulative low dose energy < 120 J. Use of a single activated MP3 probe in multiple eyes in a single session, with adequate precautions, drives down the expense, making it accessible to indigent populations in low-to-middle income countries. As it a very useful adjunct in the management of glaucoma, hitherto unreported in Indian eyes, larger studies with longer-term evaluations are recommended.
Dr Anil Kumar Bura and Dr. Raghuvarathan, Department of Anesthesia, Centre for Sight, Banjara Hills, Hyderabad, India 500034.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2]
[Table 1], [Table 2]