Continuous-wave (CW) transscleral cyclophotocoagulation (TSCPC) is a method of treating glaucoma that involves cycloablation of the ciliary body epithelium to decrease the production of aqueous humour by the ciliary body, thereby lowering IOP.1
TSCPC is a safe and effective treatment modality we can utilise at all disease stages of glaucoma, whether as a standalone procedure or in conjunction with standard treatment therapies including minimally invasive glaucoma surgery (MIGS) or trabeculectomy.
The technique micropulse TSCPC utilises a different delivery modality than its predecessor, CW laser cycloablation, to produce a biological reaction without the lethal effects caused by thermal buildup. Despite a gentler laser application, the treatment remains efficacious at lowering IOP.
The micropulse laser works by chopping the laser beam into a train of repetitive short pulses, allowing the tissue to cool between pulses and preventing thermal elevation.
I recently participated in a study evaluating the safety and efficacy of this laser in patients with mild to moderate glaucoma. The retrospective cohort study reviewed the charts of 95 consecutive glaucoma patients who received micropulse TSCPC.
Patients were administered with a retro-bulbar block and treated with the MicroPulse P3 glaucoma device (IRIDEX IQ810 Laser Systems) at 2–2.5 watts with a duration of 90 seconds per hemisphere at a 31.3% duty cycle. In cases requiring re-treatment, the same treatment parameters were used with an increase in power up to 3 watts.
Patients were prescribed topical corticosteroids in the operative eye post-procedurally with a 1-month taper and IOP-lowering medications were withdrawn as appropriate. Patients were seen postoperatively on day 1, week 1, and months 1, 3, 6 and 12.
All patients received follow-up care for at least 1 year. Outcome measures included postoperative IOP and number of postoperative IOP medications required.
The glaucoma subtypes treated included primary open-angle glaucoma (n = 51); exfoliation glaucoma (n = 24); chronic angle closure glaucoma (n = 15); and congenital/juvenile glaucoma (n = 5). The results were as follows.
The mean preoperative IOP was 25.1 ± 5.3 mm Hg, and the mean postoperative IOP at 12 months was 17.5 ± 5.1 mm Hg (P = 0.004).
The mean number of IOP-lowering medications used preoperatively was 3.0 ± 1.1; the mean number of medications used at the 12 month postoperative visit was 1.4 ± 1.0 (P = 0.03).
Twenty-two patients received at least one re-treatment with an increase in energy; eight patients had three rounds of treatment, four patients had four rounds of treatment and one patient had five rounds.
The mean preoperative IOP in this study was lower and more analogous to what I see in my daily practice in comparison to that of a previous investigation using micropulse TSCPC,2 which was conducted on a more mature and severely diseased population.
This study suggests the device does not need to be reserved as a treatment of last resort; it can be utilised as an effective therapy earlier than where traditional algorithms may place it.
Many of us were conditioned during our residency or fellowship to reserve traditional laser therapy as a last resort due to its commonly associated adverse events including tissue destruction, vision loss and inflammation.1,3 However, it is time to put old notions aside so that we can bring our patients sight-preserving therapy.
Benefits and considerations
Micropulse technology, unlike CW laser application, does not induce fatal architectural damage to the cellular structure. It is a repeatable procedure and is proving to be an effective option to fill the gaps between topical medical therapy, MIGS and traditional glaucoma-filtering surgery.
Notwithstanding the progressive nature of glaucoma, any time we can preserve vision and postpone a more aggressive treatment plan, the patient benefits.
Patients like the idea of a non-incisional procedure because it means less pain, little to no downtime, and minimal risk of infection or leaking, which could potentially lead to low IOP or hypotony. Although the procedure is essentially pain free, patients usually prefer a full block for comfort.
Using a block insures a quick, usually three-minute procedure. Side effects include inflammation and blurred vision immediately following the procedure; however, these tend to be transient and resolve quickly.
Micropulse therapy is generally safe on the whole spectrum of patients. I may use it as a first-line therapy on patients with drop intolerance or extreme fear of injections. Patients requiring immediate or aggressive IOP-lowering effects benefit most when the laser is used in combination with MIGS, tube or trabeculectomy.
The technology offers a viable option for patients who are opposed to or who are not incise candidates, such as post-corneal transplant or severe dry eye patients. In these patients, healing tends to be poor, but with micropulse TSCPC, we do not have to worry about how the surface of the eye heals.
Furthermore, patients who have failed another type of surgery, such as trabeculectomy, can benefit from attacking the inflow side of the algorithm in addition to the outflow issues.
A majority of glaucoma patients are using topical medications and as a result have dry eye or an otherwise compromised ocular surface. In some cases, the technology produces minor insult to the peripheral corneal nerves, which can also be potentially exacerbated by postsurgical drops.
Typically a transient side effect, we simply treat it like other ocular surface disease by increasing lubrication or administering anti-inflammatories. As with all glaucoma patients, those with a severely damaged ocular surface are not ideal candidates.
Safety and efficacy
Micropulse TSCPC offers a kinder, gentler mechanism of action. Histopathologic studies demonstrate that its application does not coagulate or scar the treated region.4 We avoid this level of injury because we are not wiping out ciliary tissue, but rather inducing a change to the ciliary muscle in that region to lower IOP.
No cases of long-term hypotony were noted in treated eyes, a result that is shared by other investigators using the device.3,5 Since the tissue remains intact, even if the barrier breaks down more than intended, the effect is transient rather than a permanent structural change.
In addition to attacking the disease on the inflow front, there is evidence that IOP lowering is causal to a dual mechanism of decreased aqueous production and increased porosity producing uveoscleral outflow action.
With few disadvantages, micropulse TSCPC is an effective tool for improving our standard of care to glaucoma patients. Every patient is different, and we may not always achieve the desired result the first attempt, but the device affords the ability to repeat and customise treatment algorithms. While one technology does not help all, we can keep fighting.
1. Guptha N, Weinreb RN. Diode laser transscleral cyclo-photocoagulation. J Glaucoma. 1997;6:426-429.
2. Tan AM, et al. Micropulse transscleral diode laser cyclophotocoagulation in the treatment of refractory glaucoma. Clin Experiment Ophthalmol. 2010;38:266-272.
3. Kosoko O, et al. Long-term outcome of initial ciliary ablation with contact diode laser transscleral cyclophotocoagulation for severe glaucoma. The Diode Laser Ciliary Ablation Study Group. Ophthalmology. 1996;103:1294-1302.
4. Pantcheva MB, et al. Comparison of acute structural and histopathological changes of the porcine ciliary processes after endoscopic cyclophotocoagulation and transscleral cyclophotocoagulation. Clin Experiment Ophthalmol. 2007;35:270-274.
5. Kuchar S, et al. Treatment outcomes of micropulse transscleral cyclophotocoagulation in advanced glaucoma. Lasers Med Sci. 2016;31:393-396.