Pearls for Effective Laser Cyclophotocoagulation of the Glaucomatous Eye

Transscleral cyclophotocoagulation (TSCPC) is a laser procedure used to reduce aqueous humor production through ciliary body destruction and thereby lower IOP. With diode laser TSCPC, an 810-nm laser system transmits energy through the sclera to the ciliary body via a handpiece placed along the perilimbal conjunctiva, typically with the patient under retrobulbar or peribulbar anesthesia. Two types of TSCPC are currently in use: continuous and micropulse. This article reviews the use of continuous-wave TSCPC, which we currently find to be more reliable and effective than micropulse CPC.^1,2

Traditionally, TSCPC has been used in eyes with low visual potential and elevated IOP refractory to hypotensive agents and in poor candidates for invasive glaucoma surgery. With refinement of the technique, a paradigm shift in glaucoma management has occurred: TSCPC is now performed earlier in treatment algorithms, even as primary therapy,³ and for many types of recalcitrant and advanced glaucoma. We have had excellent results with significant safety and consistency in the treatment of glaucoma that is pseudophakic, aphakic, neovascular, associated with silicone oil after vitrectomy, associated with corneal transplantation, and more.^4-8 We believe that TSCPC likely represents the most minimally invasive and versatile surgical glaucoma treatment presently available.

TSCPC offers several advantages. The procedure can be performed in the clinic or OR, and treatments are titratable and repeatable. The risk of infection is minimal (no incisions, sutures, etc.) when performed properly to avoid neurotrophic keratitis (see the article section on treatment areas). A fast and comfortable postoperative recovery is also possible. As with any procedure, there are nuances to performing TSCPC to increase effectiveness and minimize complications. This article reviews the technique we use for TSCPC, with discussion of its indications in clinical practice with different types of glaucoma and stages of glaucoma management.

SETTINGS

The TSCPC technique can be modified in several ways, mainly by adjusting the power and duration of laser energy delivered. To keep outcomes more predictable and reliable, we start with a power of 1,250 mW and a duration of 4,000 ms (slow coagulation).⁹ These settings are rarely modified. Power will be titrated down only if excessive “pops” are heard. Power is almost never increased, in contrast to conventional pop-titrated CPC technique teaching, which recommends increasing the power until an audible “pop” occurs.¹⁰

Anecdotally, two types of pops can be heard during TSCPC: anterior and posterior to the sclera. The anterior pop is higher pitched, resulting from cavitation bubbles within an air or fluid pocket interface between the probe, conjunctiva, Tenon capsule, and/or sclera. The posterior pop is deeper and duller in pitch. This dull pop occurs when excessive energy is applied to the ciliary body, causing an implosion of the ciliary body. This can be highly inflammatory and painful in the postoperative period. It is crucial to listen that the laser energy is applied for the entire 4-second duration and take care not to lift the probe from the eye or foot from the pedal too early. The probe delivers only 4 seconds of energy as dictated by the settings, so we recommend leaving the probe on the eye and foot on the pedal for an additional 0.5 seconds for each application to ensure complete treatment.

PROBE PLACEMENT

Uniform positioning of the handpiece, or G-probe (Iridex), on the eye helps to maintain consistent energy delivery. The handpiece should be placed perpendicular to the sclera (not vertical or perpendicular to the ground) unless the eye is rotated. The handpiece should be placed with all four corners of the footplate against the globe. The shorter edge of the wedge-shaped handpiece should be anterior, facing the limbus.

It is essential to have a wet interface between the handpiece and globe with either balanced salt solution or hydroxypropyl methylcellulose as a coupling agent. This interface may need to be reapplied several times during the procedure. The handpiece should be coupled to the surface of the eye so any pockets of fluid or air between the handpiece and sclera (eg, chemosis from the anesthetic block) are squeegeed out before treatment. The Randolph cannula, which is blunt and flat and typically found on the assistant’s balanced salt solution bottle, is a useful stiff tool to squeegee out any subconjunctival fluid to ensure proper coupling of the handpiece and sclera (Figure).

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Figure. Positioning of the eye for CPC probe placement. A Randolph cannula with a flat tip is used to wet the eye and to infero-duct the globe to improve visualization to the limbal region of the globe. The CPC probe is then placed perpendicular to the sclera with all four corners of the footplate flush against the perilimbal sclera. There should be no significant fluid or air interface between the sclera, conjunctiva, or CPC probe.

TREATMENT AREAS

We currently apply treatment circumferentially around the limbus while avoiding several key areas. The first areas to avoid generously are the 3 and 9 clock positions. The long ciliary nerves, which are critical to corneal sensation, tear production, the blink reflex, and corneal epithelium structure and function, are located within these clock hours. Damage to them can lead to neurotrophic keratitis and ulceration, especially in patients who are predisposed (medicamentosa, dry eye, a history of corneal transplantation, etc.).^11,12 It is also advisable to avoid areas of scleral thinning and areas of prior glaucoma surgery (eg, trabeculectomy and tube shunt surgery). TSCPC energy applied in these areas can lead to excess energy delivery, conjunctival and scleral perforation, and complications related to prior surgeries.

The handpiece should be placed approximately 0.5 mm posterior to the limbus; transillumination of the globe can reveal the location of the ciliary body in abnormally short, long, or pediatric glaucomatous eyes. A handpiece placed too anteriorly can result in complications, including anterior chamber cavitation bubbles, hyphema (especially in neovascular glaucoma), segmental mydriasis observed during the laser treatment, and severe inflammation with fibrin membrane formation, which will require prolonged treatment with antiinflammatory medications. After each application of energy, the handpiece should move the distance of approximately one footplate for adjacent, subsequent applications. Consecutive applications placed too close together can result in increased inflammation. After 360º treatment, random quadrants can be re-treated so that an adequate number of appropriately spaced applications are applied. We typically perform 22 to 26 applications per TSCPC procedure; however, the number of applications is multifactorial, based on the level of IOP elevation, number of glaucoma medications, race, sex, age, and prior glaucoma surgeries.

POSTOPERATIVE MANAGEMENT

As with any surgical procedure, TSCPC results in postoperative inflammation, and many of its complications result from excessive or untreated inflammation. We therefore recommend aggressive and prolonged antiinflammatory management following TSCPC.

Intraoperatively, a subconjunctival injection of dexamethasone 4 mg/mL is performed. Occasionally, a sub-Tenon injection of triamcinolone is performed in patients prone to severe inflammation. On postoperative day 1, prednisolone acetate 1% is started, with one drop instilled every 2 hours while awake in the operative eye. This is continued for 3 to 4 weeks and then tapered slowly every 2 weeks until cessation. If the probe was placed too anteriorly to the limbus with the aforementioned complications (ie, hyphema, cavitation bubbles, etc.), then steroids can be administered every hour.

In addition, a topical NSAID (eg, ketorolac, diclofenac, or nepafenac) is started, with one drop instilled four times per day in the operative eye to minimize postoperative cystoid macular edema. This regimen is continued for 3 to 4 weeks and then tapered slowly every 2 weeks with the topical steroid.

Patients who are prone to inflammation (eg, those who are phakic, are younger, have increased pigmentation, are Black, or have uveitis) may require a longer duration of steroid treatment (ie, a drop tapered every 3 weeks). Those who are phakic should be counseled on the possibility of cataract progression after TSCPC.

INDICATIONS

Given its safety, efficacy, and reliability, TSCPC should be considered earlier in the glaucoma treatment algorithm, including as primary therapy.³ TSCPC is a conjunctiva-sparing procedure, allowing it to be used before or after more invasive glaucoma surgeries when viable conjunctiva is lacking. It is also versatile and can be performed in eyes with different types of advanced and refractory glaucomas and in conjunction with cataract surgery.^4-8

TSCPC is a relatively efficient procedure with a fast postoperative recovery time; it can therefore be performed in nearly any patient population, including those who may be more difficult to manage, such as pediatric and elderly patients and patients with disabilities, cognitive impairment, or a history of poor compliance. TSCPC is titratable, allowing repeat treatments to lower IOP as needed. Additionally, it is a cost-effective procedure, owing to its quick duration and ability to be performed in the clinic and OR, the minimal follow-up visits, and a reduction in costly glaucoma medications.¹³ With these benefits in mind, we believe that TSCPC likely represents the most minimally invasive and versatile surgical glaucoma treatment available.