Slow-Coagulation Continuous-Wave Transscleral Cyclophotocoagulation Laser for Treatment of Glaucoma

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Article initiated by:

Abdelrahman M. Elhusseiny, MD, MSc, Abdulla Shaheen

All contributors:

Abdelrahman M. Elhusseiny, MD, MSc, Abdulla Shaheen, Ahmad A. Aref, MD, MBA, Mohamed M Khodeiry, Mohamed.Sayed, Richard.Lee, Ahmad A. Aref, MD, MBA, Daniel B. Moore, MD, Leonard K. Seibold, MD, Abdelrahman M. Elhusseiny, MD, MSc

Assigned editor:

Leonard K. Seibold, MD

Review:

Assigned status Up to Date

 by Ahmad A. Aref, MD, MBA on October 4, 2024.

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Contributing Editors:	add

Background

Glaucoma management traditionally involves reducing intraocular pressure (IOP) with medications, laser procedures, and surgeries. Cyclodestructive laser procedures lower IOP by decreasing aqueous production. Cyclodestructive procedures evolved from initial techniques like cyclodiathermy and cyclocryotherapy to cyclophotocoagulation and micropulse laser treatment. Laser types in cyclophotocoagulation transitioned from Ruby to Neodymium-doped Yttrium Aluminum Garnet (Nd:YAG), and recently, to diode lasers. During transscleral diode laser cyclophotocoagulation (TSCPC), laser energy applied to the sclera is absorbed by the melanin pigment in the ciliary processes, resulting in coagulative necrosis of the ciliary body. The advances in the TSCPC techniques have broadened its application beyond end-stage glaucoma patients with poor visual acuity or limited visual potential. It is now considered a relatively safe and efficient option for patients with good vision, pediatric patients, and as an adjunct to other surgeries such as cataract extraction.

Slow coagulation cyclophotocoagulation surgical technique

In continuous wave-TSCPC, two primary methods of diode laser energy delivery have been widely used: the traditional 'pop' technique and the more recent slow-coagulation continuous wave technique. The conventional 'pop' technique starts with a laser energy power of around 1750-2000 milliwatts (mW) applied for 2 seconds. The energy is incrementally increased until an audible 'pop' is heard. Once the 'pop' sound is detected, the laser power is then reduced until the 'pop' sounds cease. On the other hand, the slow-coagulation transscleral cyclophotocoagulation (SC-TSCPC) technique delivers a fixed, lower amount of diode laser energy over an extended period, typically at a power of 1250 mW over 4 seconds. This method has been proposed to minimize the collateral tissue damage and inflammation outside the ciliary body, leading to more controlled coagulative ciliary body ablation and, consequently, fewer intra- and post-operative adverse events. Studies have suggested that the SC-TSCPC technique is as effective as the conventional 'pop' approach and associated with lower complication rates. Managing postoperative intraocular inflammation and controlling the amount of delivered laser energy are the two key elements determining the IOP reduction success rates and the safety of SC-TSCPC. Accurate placement of the probe is crucial for effective energy delivery; it must be positioned perpendicular to the sclera to fully target the ciliary body. Any deviation greater than 10 degrees from the perpendicular can lead to energy delivery variation by 20% or more. The number of laser shots typically administered is based on the extent of IOP elevation, the number of glaucoma medications, patient’s race and gender, and any previous glaucoma surgeries. Thorough control of inflammation is paramount to minimize sight-impacting iridocyclitis, cystoid macular edema (CME), and other laser-associated complications. Unless the patient is known to be a steroid responder, we generally administer sub-tenon triamcinolone, sub-conjunctival dexamethasone, in addition to topical prednisolone and ketorolac. In certain cases, oral prednisone can be used to control intraocular inflammation, especially in patients with a known history of auto-immune or uveitic diseases. Topical steroid eye drops should be tapered slowly, one drop less every 2-3 weeks, accompanied by ketorolac.

Potential advantages over traditional surgeries

SC-TSCPC technique presents substantial benefits over traditional filtration and tube surgeries:

1. TSCPC is a relatively noninvasive procedure that can be adjusted and repeated as necessary.
2. It serves as a viable alternative for types of glaucoma that have a high risk of failure of trabeculectomy and glaucoma drainage devices. Additionally, it does not limit future surgical interventions as it minimally affects the conjunctiva and does not occupy any conjunctival or trabecular 'real estate' that might be needed for device implantation in the future.
3. It is considered a cost-effective surgical treatment option for glaucoma.
4. It can be performed quickly in an office or operating room setting, and patients typically have a short postoperative recovery period.

Outcomes

Several studies have evaluated the effectiveness and safety of the SC-TSCPC in various glaucoma subtypes including neovascular glaucoma (NVG), uveitic glaucoma, and glaucoma associated with aphakia and pseudophakia. It is also a viable choice for patients with refractory and recalcitrant glaucoma, in post-keratoplasty chronic angle-closure glaucoma, and glaucoma secondary to pars-plana vitrectomy and silicone oil injection (SOI).

A) Glaucoma Patients Without Prior Incisional Surgery

Sheheitli et al. assessed the effectiveness of SC-TSCPC as a primary surgical treatment in 48 glaucomatous eyes with no previous incisional surgery. Patients were divided into high (mean (standard deviation [SD]) baseline IOP 30.6 [6.3] mmHg) and low (mean 16.2 [2.8] mmHg) baseline IOP groups. At one year, success rate (defined as IOP between 6-21 mmHg and ≥20% IOP decrease from baseline, with no need for further glaucoma intervention or development of vision-threatening complications) was 58.3% in the high group versus 28.1% in the low group (P=0.052). The high baseline IOP group had a significant IOP reduction at all postoperative visits (1-, 3-, 6-, 12-, and 18-month; P<0.05) and reduced medication usage through one year (P< 0.05).7 For the low baseline IOP group, no significant change was observed in the IOP at follow-up visits after the first month. However, similar to the high baseline IOP group, the low baseline IOP group also experienced a decrease in glaucoma medication usage at the 1-, 3-, 6-, and 12-month postoperative visits (P<0.05).7 The slow-coagulation technique was associated with generally mild complications. Cataract progression occurred in 18.8% of phakic eyes, but most regained baseline acuity after phacoemulsification. No cases of persistent hypotony, maculopathy, or phthisis were seen. However, four eyes (8.3%) declined to light perception and two (4.2%) to no light perception; all had baseline acuity of counting fingers or worse. Ongoing anterior chamber inflammation affected 16.7% (8/48) at one month. Three patients (6.3%) had rebound iritis after discontinuing steroids. Clinically significant CME occurred in 4 eyes (8.3%). Iris neovascularization developed postoperatively in 2 eyes (4.2%), likely from poor steroid compliance. One eye (2.1%) had transient hyphema attributed to iritis. No cases occurred of conjunctival burns, persistent pain, corneal edema, choroidal effusion, or phthisis.

B) Treatment Outcomes of Slow-coagulation TSCPC in Pseudophakic Glaucoma Patients

Khodeiry et al. evaluated outcomes of SC-TSCPC in 74 pseudophakic glaucoma patients. The 1- and 2-year cumulative success rates (defined as IOP of 6-21 mmHg with ≥20% IOP reduction from baseline at 2 consecutive follow-up visits, no additional glaucoma surgery with the exception of additional TSCPC if needed, and no loss of light perception) were 60.6% and 58.5%, respectively. They further divided the cohort into a low pretreatment IOP group (IOP < 21 mmHg) and a high IOP group (IOP > 21 mmHg). The 1- and 2-year cumulative success rates for the low IOP group were 52.0% and 45.5%, respectively, and for the high IOP group were a 64.9% at both time points. Notice that the high IOP group had similar demographic and clinical characteristics except for being slightly older with a worse baseline visual acuity. Among the entire cohort, the mean (SD) IOP decreased from 27.5 (9.8) mmHg pretreatment to 15.8 (6.4) mmHg at 12 months (P<0.001), and to 15.2 (4.2) mmHg at 24 months (P<0.001). Likewise, the mean (SD) number of required medications also showed a drop from 4.1 (0.9) at baseline, to 3.1 (1.3) at the 12-month point (P<0.001), and to 3.4 (1.1) at the 24-month point (P<0.001). A similar IOP and medication reduction trend was demonstrated in the subgroup analyses of the high and low IOP groups. The high IOP group experienced an IOP reduction from 32.9 (1.0) mmHg at baseline to 16.7 (1.0) mmHg at 12 months and 16.2 (1.0) mmHg at 24 months (P < .001 at both intervals). The low IOP group had a decrease from 17.1 (0.6) mmHg to 14.4 (1.0) mmHg at 12 months and to 13.2 (1.1) mmHg at 24 months. As for medication reduction, the high IOP group had a baseline mean of 4.3 (0.9) medications, which decreased to 3.4 (1.3) at the 12-month follow-up and remained at 3.4 (0.9) at the 24-month follow-up (P < 0.001 at both time points). In the low IOP group, the mean number of medications reduced from a baseline of 3.6 (0.8) to 3.0 (1.3) at the 12-month visit and further to 3.1 (1.1) at the 18-month visit (P = .013 and p = 0.008, respectively).

Postoperative complications were generally uncommon. One patient (1.4%) with an initial vision of hand movement experienced vision loss. Nine patients (12.2%) developed iridocyclitis at the one-month postoperative mark, with the condition persisting in two of these patients (2.7%) at the final follow-up. Cystoid macular edema was noted in two patients (2.7%), remaining in one of them (1.4%) at their last visit. Spontaneous resolution of postoperative hyphema occurred in one patient (1.4%) within four weeks. No instances of hypotony maculopathy, choroidal effusion, corneal decompensation, pupillary abnormalities, conjunctival scarring, sympathetic ophthalmia, or phthisis bulbi were observed.

C) Recalcitrant Glaucoma Secondary to Pars Plana Vitrectomy (PPV) and Silicone Oil Injection

Khodeiry et al. retrospectively evaluated the effectiveness of SC-TSCPC for managing glaucoma after pars- plana vitrectomy and silicone oil injection. The study included 18 patients with a mean (SD) age of 51.94 (14.5) years. Mean (SD) IOP decreased significantly from 29.7 (9.6) mmHg at baseline to 14.6 (6.5) mmHg at 12 months post SC-TSCPC (P<0.001). Mean (SD) number of glaucoma medications was significantly reduced, from 4.2 (0.9) at baseline to 1.9 (1.3) at 12 months (P<0.001).

The success rate (defined as IOP of 6-21 mmHg with ≥20% IOP reduction from baseline at 2 consecutive follow-up visits, no additional glaucoma surgery) at 12 months was 72.2%. Postoperative inflammation occurred in 2 patients (11.1%) at 1 week and was managed with topical steroids. Cystoid macular edema occurred in 1 patient (5.6%). Transient hyphema and hypotony each occurred in 1 patient (5.6%). No cases occurred of loss of light perception, conjunctival burns, choroidal effusion, sympathetic ophthalmia, pupillary abnormalities, persistent pain, or phthisis. These results demonstrate the safety and effectiveness of SC-TSCPC for glaucoma after pars-plana vitrectomy and SOI.

D) Neovascular Glaucoma

Neovascular glaucoma management necessitates a dual-pronged approach of addressing ischemic factors causing neovascularization and IOP control. SC-TSCPC offers an effective solution for managing IOP in medically unmanageable NVG.11 A retrospective study by Khodeiry et al. involving 53 NVG patients (mean age 69.6 (16.6) years). The SC-TSCPC treatment showed significant IOP reductions from a mean (SD) of 40.7 (8.6) mmHg preoperatively to 18.4 (12.2) mmHg postoperatively (P <0.001). Glaucoma medications usage also decreased from a mean (SD) of 3.3 (1.1) at baseline to 2.0 (1.5) post-treatment (P<0.001). The success rate (defined as IOP of 6-21 mmHg with ≥20% IOP reduction from baseline at 2 consecutive follow-up visits,, no additional glaucoma surgery) at 24 months was 64.2%. Visual acuity decline was experienced by 13.2% of patients, largely attributed to glaucoma progression and diabetic retinopathy exacerbation.11 Other transient complications included anterior chamber inflammation (9.4%) and postoperative hypotony and CME (each 3.8%).

E) Post-Keratoplasty Glaucoma

Khodeiry et al. assessed SC-TSCPC as the primary intervention for managing post-keratoplasty glaucoma. Success (defined as IOP between 6-21 mmHg with ≥20% reduction from baseline on 2 consecutive follow-up visits and no requirement for additional glaucoma surgeries during the 2 year follow up period) were 68.1% and 66.0% at 1- and 2-year postoperatively, respectively.

The type of keratoplasty procedure—penetrating keratoplasty (PKP) or Descemet's stripping endothelial keratoplasty (DSAEK)—did not significantly affect the success rates (P=0.836), suggesting that SC-TSCPC's efficacy was consistent irrespective of the corneal transplant surgery type. Post-SC-TSCPC, there were no statistically significant changes in central corneal thickness, indicating minimal impact on corneal thickness from the treatment. One instance of graft rejection was reported a year post-treatment, which was unlikely to be directly linked to the cyclophotocoagulation procedure.15 While the procedure was mostly free from serious complications such as persistent hypotony, phthisis, loss of light perception, or choroidal detachment or hemorrhage, a few mild postoperative complications were noted. Five patients (10.6%) developed iridocyclitis in the first month, which was managed with topical steroids. Tube shunt glaucoma surgeries were required in three patients (6.4%) to lower uncontrolled IOP. Spontaneous resolution occurred in two cases (4.2%) of hyphema, and one instance (2.1%) of transient hypotony was recorded at the 1 month follow-up visit, which resolved with the use of topical steroids and cycloplegics without accompanying visual acuity decline. No reports of CME, loss of light perception vision, choroidal effusion, phthisis bulbi, sympathetic ophthalmia, prolonged pain, or pupillary abnormalities were observed. This information further underscores SC-TSCPC's safety and efficacy as a surgical treatment option for medically uncontrolled post-keratoplasty glaucoma.

F) Aphakic glaucoma

Elhusseiny et al. evaluated the effectiveness of SC-TSCPC as a primary surgical intervention for secondary aphakic adult glaucoma following complicated cataract surgery. The application of SC-TSCPC as the first line of treatment yielded a success rate (defined as a postoperative IOP between 6-21 mmHg with a reduction of at least 20% from baseline and no additional glaucoma surgeries or vision-threatening complications) of 63.4% at the one-year follow-up visit.13 The study showed a statistically significant decrease in the mean (SD) IOP from 29.6 (5.8) mmHg at baseline to 19.0 (6.4) mmHg after one year (P<0.001). Concurrently, the mean number of glaucoma medications used by the patients was reduced from 3.9 (1.0) at baseline to 2.5 (1.2) at the one-year follow-up visit. During the follow-up period, retreatment with SC-TSCPC was necessary for 4 eyes, while 2 required incisional glaucoma surgeries. Postoperative complications included visual acuity decline by ≥2 lines in 7 eyes, iritis in 6 eyes, hyphema in 5 eyes, CME in 2 eyes, and transient hypotony in one eye. These findings support the use of SC-TSCPC as a viable non-incisional primary surgical approach for managing medically uncontrolled secondary aphakic adult glaucoma.

Conclusions

SC-TSCPC represents a significant advancement in the surgical management of glaucoma. By delivering laser energy in a fixed, lower amount over a longer duration, this technique offers a more controlled and selective approach to ciliary body ablation, thereby effectively controlling IOP and theoretically minimizing adjacent tissue damage. The procedure has shown promising results in treating various scenarios of glaucomatous patients, including medically refractory cases, and offers an efficient and relatively safer alternative to traditional treatments.