Commentary on: Micropulse transscleral cyclophotocoagulation: Redefining the role of cyclodestruction in glaucoma management

Micropulse transscleral cyclophotocoagulation (MP TSCPC) has emerged as a significant innovation in the surgical management of glaucoma, challenging the traditional perception of cyclodestructive procedures as interventions of last resort. By delivering diode laser energy in a micropulsed, duty-cycled manner, MP TSCPC aims to achieve intraocular pressure (IOP) reduction while minimizing collateral thermal damage to the ciliary body and adjacent tissues.

This technological refinement has broadened the potential indications of cyclophotocoagulation and prompted reconsideration of its place in contemporary glaucoma care. It employs infrared diode laser radiation of 810 nm targeting the melanin present in pigmented ciliary epithelium. The key feature differentiating it from continuous wave trans-scleral diode cyclophotocoagulation (CW TSCPC) is the energy, which is delivered in short pulses in an on-and-off cycle fashion. The longer “off phase” allows energy dissipation and minimizes collateral tissue damage by allowing them to thaw which has been proven histologically. In MP TSCPC, the probe is directed to pars plicata unlike the CW TSCPC, where laser is delivered at the level of pars plana.

The possible mechanisms of action include: (i) targeted action in the form of subthreshold cellular damage on the pigmented epithelium and indirect effect on nonpigmentary epithelium of ciliary body causing reduced aqueous production, (ii) improving uveoscleral outflow by mediating extracellular matrix remodeling, and (iii) a possible pilocarpine-like effect where micropulse causes the longitudinal fibers of the ciliary muscles to contract, thereby displacing the scleral spur posteriorly, which results in improving the conventional outflow pathway by opening the trabecular beams.

Although both continuous-wave and micropulse CPC use infrared radiation to target aqueous humor production, their outcomes differ, largely due to the on–off laser delivery cycles employed in micropulse TSCPC. A randomized trial demonstrated that IOP reduction was better in MP TSCPC group at 6-month and 1-year follow-up, but it was similar at 18 months in both the groups.[1] However, the IOP lowering effect was found to have more predictable pattern and there was a significant decrease in incidence of post-op inflammation in MP TSCPC as compared to CW TSCPC.[1] The major advantage was in the incidence of post-laser complications like prolonged hypotony, phthisis bulbi, and persistent anterior chamber inflammation, which was found to be significantly higher in CW TSCPC group as compared to MP TSCPC. The drop in visual acuity which is attributed to the mydriasis was also found to be higher in the CW TSCPC group.

Another prospective interventional study analyzing the applicability of MP TSCPC as primary versus additional mode of intervention found that there was no statistical difference in complications and additional interventions between the two groups.[2] This indicates that MP TSCPC can be an effective tool for IOP control in eyes having high risk of vision-threatening complications with invasive surgery.

When it comes to energy parameters, no definitive settings have been defined. The duty-on cycle which defines the duration for which the laser is actively emitted is kept at 31.3% for glaucoma treatment. The energy settings range from 62 to 225 J, and there are varied published data on outcomes of low, mid, and high energy settings. The current role of MP TSCPC in the management of various types of glaucoma based on the available evidence is highlighted in Table 1.[1,2,3,4,5,6,7,8]

Table 1.

Role of micropulse transscleral cyclophotocoagulation in various types of glaucoma

Type of Glaucoma	Role of MPTSCPC	Comments
Refractory/Postsurgical glaucoma	Preferred cyclodestructive procedure after failed trabeculectomy or tube surgery	Consistent IOP reduction (~30–45%) with better safety than CW-TSCPC; repeatable and conjunctiva-sparing
Neovascular Glaucoma	Adjunctive or temporizing measure for IOP and pain control	Useful alongside PRP and anti-Vascular Endothelial Growth Factors; lower risk of hypotony than CW-TSCPC; long-term durability variable
Uveitic glaucoma	Alternative to incisional surgery in selected cases	Moderate IOP reduction with lower risk of inflammation flare when perioperative steroids used
Primary open-angle glaucoma (POAG)	Intermediate option between maximal medical therapy and incisional surgery	Increasing use in eyes with good visual potential; predictable IOP reduction but less than filtering surgery
Pseudoexfoliation glaucoma (PXG)	Similar role to POAG, especially in surgically high-risk eyes	Effective IOP lowering; outcomes comparable to POAG in small series
Primary angle-closure glaucoma (PACG)	Adjunctive therapy after iridotomy±lens extraction	Useful when residual IOP elevation persists with extensive PAS or in eyes where incisional surgery carries high risk
Acute angle-closure glaucoma	Adjunctive only	Not definitive; angle-opening procedures remain primary

In management of refractory glaucoma in the pediatric age group, MP TSCPC has reported good safety but mixed results in terms of efficacy.[7,8] In comparison with CW TSCPC, the IOP lowering effect was comparable; the rate of complications, pain, and inflammation seemed to be lower in the first group, but this difference was not statistically significant. When it comes to applicability of MP TSCPC, race has to be kept in mind and use of shorter treatment times in heavily pigmented eyes (African-Americans) reduces the incidence of severe postprocedure inflammation.

In conclusion, MP TSCPC has transformed the conceptual framework of cyclophotocoagulation in glaucoma management. While it does not replace trabeculectomy, tube shunt surgery, or minimally invasive glaucoma surgery, it fills an important therapeutic gap between maximal medical therapy and incisional surgery with a favorable balance of efficacy, safety, and flexibility. As clinical experience grows and treatment protocols become more refined, MP TSCPC is likely to secure a well-defined and enduring role in the modern glaucoma treatment algorithm. However, there is still a need to fully understand its mechanism of action, long term outcomes, and ideal treatment dose with duration. Furthermore, concrete evidence on its repeatability needs to be explored.