Expanding Utilization of Slow-Coagulation TSCPC

Over the years, various cyclodestructive procedures have been developed for the treatment of glaucoma, including cyclodiathermy, cyclocryotherapy, beta irradiation, microwave therapy, ultrasonography, Nd:YAG laser therapy, semiconductor laser therapy, and surgical ciliary body resection. These techniques have not, however, gained substantial popularity because of the severe complications associated with their use.

Cyclodestruction was consequently reserved primarily for eyes with end-stage glaucoma, for eyes with elevated IOP and poor visual acuity potential, or for pain relief in eyes with poor or no vision. The introduction of the cyclodiode laser represents a significant advance, as it offers safer and more efficacious ciliary body ablation to control IOP. With this approach, the diode laser energy is absorbed by the ciliary body melanin pigments, and treatment can be applied to the ciliary body via an extraocular transscleral or direct intraocular approach.

With traditional continuous wave-transscleral cyclophotocoagulation (CW-TSCPC), 1,750 to 2,000 mW of laser energy is applied for 2 seconds. Power is increased until an audible “pop” occurs and subsequently reduced to subthreshold levels. Although this technique is effective for IOP reduction, its use is limited to eyes with refractory glaucoma or low vision potential owing to severe inflammation and the high risk of complications. A recent systematic review by Souissi and colleagues summarized vision-threatening complications associated with traditional CW-TSCPC, including the loss of at least 2 lines of visual acuity (11%–55%), hypotony (3%–39%), phthisis (1.2%–9.9%), corneal decompensation (1%–10%), inflammation (1.9%–20%), and choroidal detachment (1%–20%).¹

A report by the AAO reviewed literature evaluating the effectiveness and safety of traditional TSCPC that was published between the years 1968 and 2000.² The investigators concluded that TSCPC was indicated for patients with refractory glaucoma in whom filtering surgeries had failed and for individuals with low vision potential. The report was published a quarter of a century ago—before significant advances in TSCPC, the introduction of slow-coagulation (SC) parameters, and the development of micropulse transscleral laser treatment.

SC-TSCPC

In 2009, Gaasterland proposed using “popless” and SC laser parameters (1,250 mW for 4 seconds) instead of the aforementioned traditional CW-TSCPC parameters.³ We view SC-TSCPC as the least invasive of currently available MIGS procedures. The SC parameters have rendered the TSCPC procedure safe and well tolerated, cost-efficient, reliable, and effective in reducing IOP. The low amount of energy delivered is unlikely to cause implosive “pop” ciliary body damage, suggesting a modified mechanism for IOP reduction. One hypothesis is that SC-TSCPC shrinks the ciliary processes, causes posterior movement of the peripheral iris, and improves aqueous drainage through the trabecular meshwork.⁴

Our retrospective case series compared the outcomes of conventional pop-titrated CW-TSCPC (n = 26 eyes) versus SC-TSCPC (n = 52 eyes) for any type or stage of glaucoma.⁵ The procedures were similar in terms of IOP reduction and visual acuity outcomes. The mean number of complications, however, was significantly higher in the CW-TSCPC than the SC-TSCPC group (1.46 ±1.24 vs 0.62 ±0.75).

Sheheitli and colleagues⁶ evaluated the effectiveness of SC-TSCPC as a primary surgical intervention for medically uncontrolled glaucoma. Forty-eight eyes were divided into two groups based on preoperative IOP: (1) low IOP (≤ 21 mm Hg) and (2) high IOP (> 21 mm Hg). At the 12-month follow-up visit, the surgical success rates were 58.1% in the high IOP group and 28.1% in the low IOP group, with 41.3% of all patients achieving a reduction in their medication burden. The strict success criteria may explain the low success rate observed in the low IOP group because these eyes were less likely to experience a reduction from baseline IOP that was greater than 20%. Most complications were transient, with no patient developing serious vision-threatening complications. The most common complication was cataract progression with reversible vision loss, which has been reported after other glaucoma surgical procedures.^7,8

Since the publication of studies by Duerr et al⁵ and Sheheitli et al,⁶ SC-TSCPC has become our preferred surgical approach to many types of glaucoma, especially disease that is not controlled by medical therapy and eyes without much conjunctival “real estate” for invasive surgical approaches. SC-TSCPC balances safety and effectiveness, making it an excellent primary surgical modality for treating different types of glaucoma.

TSCPC is also effective for refractory and complex glaucomas. Khodeiry and colleagues⁹ investigated the effectiveness of SC-TSCPC in 53 eyes of 53 patients with neovascular glaucoma and no history of glaucoma surgery. Over a mean of 12.7 months, mean IOP decreased from 40.7 ±8.6 mm Hg on 3.3 ±1.1 glaucoma medications preoperatively to 18.4 ±12.2 mm Hg on 2.0 ±1.5 glaucoma medications at the last follow-up visit. Seven eyes experienced a decline in vision postoperatively, mainly owing to glaucomatous progression and worsening diabetic retinopathy rather than a surgical complication.

Elhusseiny and colleagues¹⁰ evaluated 41 adult patients with aphakic glaucoma. At 1 year postoperatively, mean IOP had decreased from 29.6 ±5.8 mm Hg on 3.9 ±1.0 glaucoma medications preoperatively to 19.0 ±6.4 mm Hg on 2.5 ±1.2 glaucoma medications. Another study reviewed SC-TSCPC outcomes in 74 patients with pseudophakic glaucoma.¹¹ Mean IOP decreased from 27.5 ±9.8 mm Hg on 4.1 ±0.9 glaucoma medications preoperatively to 16.1 ±6.3 mm Hg on 3.1 ±1.3 glaucoma medications postoperatively. The investigators reported a success rate of approximately 61% at 1 year postoperatively,¹¹ which is similar to the success rates of invasive procedures such as glaucoma drainage implant surgery and trabeculectomy.^12-14

SC-TSCPC has also been shown to be effective for the treatment of chronic angle-closure glaucoma associated with corneal transplantation (penetrating keratoplasty or Descemet stripping endothelial keratoplasty). One study reported a reduction in mean IOP after SC-TSCPC from 31.8 ±8.0 mm Hg on 4.0 ±1.0 glaucoma medications preoperatively to 16.9 ±9.0 mm Hg on 2.7 ±1.4 glaucoma medications at the final follow-up visit. Success rates were comparable between eyes that had undergone penetrating keratoplasty (68.1%) and those that received Descemet stripping endothelial keratoplasty (66%).¹⁵ Another study on silicone oil–associated glaucoma showed a 72.2% success rate for SC-TSCPC at 12 months postoperatively.¹⁶

SPECIAL CONSIDERATIONS

Neurotrophic keratopathy is a rare complication of CW-TSCPC and SC-TSCPC. Possible mechanisms include damage to the long ciliary nerves and collateral damage to the perilimbal nerve plexus.^17-19 In our retrospective chart review, the incidence of neurotrophic keratopathy was less than 1%. Caution should be exercised when performing TSCPC in patients with low corneal sensitivity or severe ocular surface disease.

The literature on TSCPC for the treatment of uveitic glaucoma is sparse, as inflammation reactivation is a concern in this population. In a prospective study of 22 eyes with inflammatory glaucoma, TSCPC had a 77% success rate. No vision-threatening adverse events such as prolonged hypotony, phthisis, or inflammation reactivation were observed.²⁰

CONCLUSION

SC-TSCPC is a relatively noninvasive, safe, effective, and conjunctiva-sparing surgical glaucoma procedure. This approach is repeatable and titratable, and it does not limit future invasive glaucoma surgeries.

Authors’ note: The Bascom Palmer Eye Institute is supported by NIH Center Core Grant P30EY014801 and a Research to Prevent Blindness Unrestricted Grant. R.K.L. is partly supported by the Walter G. Ross Foundation. This work was partly supported by the Camiener Foundation Glaucoma Research Fund and the Gutierrez Family Research Fund.