Micropulse laser trabeculoplasty may be therapy for central serous retinopathy

February 1, 2010

In the future, clinicians may be able to offer patients with central serous retinopathy effective and safe treatment with micropulse laser trabeculoplasty.

San Francisco-In the future, clinicians may be able to offer patients with central serous retinopathy (CSR) effective and safe treatment with micropulse laser trabeculoplasty (MLT) (MicroPulse, Iridex Corp.), according to André Maia, MD.

This approach is of particular importance because current treatment approaches to CSR, which include laser photocoagulation and photodynamic therapy (PDT), are associated with unwanted side effects and suboptimal outcomes, said Dr. Maia at the annual meeting of the American Academy of Ophthalmology.

Typically observed as a self-limiting disease, CSR will undergo spontaneous resolution-in most cases-within 3 months. Although the disease can return in about 50% of all cases, patients have a similarly good outlook without therapy.

"Chronic cases of CSR need to be treated actively, [because] irreversible damage to the retina may occur," said Dr. Maia, of the department of ophthalmology, Federal University of São Paulo (UNIFESP), São Paulo, Brazil. "Using its tissue-sparing technology, [MLT] appears to address this condition very effectively and safely."

Advantages

The leakage point in CSR may be found right at or very close to (200 to 300 µm) the center of the fovea. Because of the close proximity to the fovea, conventional approaches such as photocoagulation with a thermal laser (diode green laser) are considered risky because of potential damage to the retina that may result in scarring and lead to irreversible impaired vision.

According to Dr. Maia, MLT technology can avoid damaging the fovea best because of the nature by which the laser energy is delivered.

Conventional continuous-wave photocoagulators produce laser pulses of uniform power. With MLT technology, laser pulses are emitted repetitively in pulse ''envelopes'' that contain a series or "pulse train" of very brief micropulses. Each micropulse in the envelope has the same duration and power. The pulse train of micropulses has a characteristic frequency (repetition rate in Hz) and duty factor (the percentage of time that the laser is ''on'' during the pulse envelope).

"The subvisible photocoagulation achieved in [MLT] therapy potentially localizes and decreases chorioretinal thermal injury, [which] is desirable because of the proximity to the fovea," he said. "The power in subvisible retinal procedures is often selected as a fraction of that needed to produce visible lesions at peripheral retinal sites."

Treatment protocol

The standard treatment protocol in patients with CSR is to observe them for up to 3 months in the hope of a spontaneous resolution of their symptoms. The minority of patients with persistent disease can be treated with a thermal laser, if the leakage is outside the central fovea. If the leakage is not outside the central fovea, however, Dr. Maia said that PDT also can be used.

Originally used for the treatment of macular degeneration, PDT with verteporfin for injection (Visudyne, Novartis) recently has been employed in the treatment of CSR, resulting in beneficial visual outcomes in most patients.

The mechanism of action of PDT for treating CSR is thought to be short-term choriocapillaris hypoperfusion and long-term choroidal vascular remodeling, leading to reduction in choroidal congestion, vascular hyperpermeability, and extravascular leakage.

The application of conventional PDT in CSR, however, can result in potential complications such as retinal pigment epithelial atrophy, choroidal ischemia, and secondary choroidal neovascularization.

"[MLT] is a new technology that has been effectively and safely used in the treatment of diabetic macular edema (DME), resulting in fewer side effects compared [with] other treatment modalities," Dr. Maia said. "I am confident [MLT] may be the future treatment of many . . . macular diseases, including CSR and DME."

Reporting real results

To date, Dr. Maia has used MLT therapy successfully in 15 patients with CSR with disease duration of at least 4 months, in whom leakage occurred at the center of the macula. This characteristic excluded conventional laser treatment as an option in these patients.

For all patients, the MLT yellow-diode laser was set from 80 to 120 mW, a spot size of 200 µm, a laser duration of 300 ms, and a micropulse of 15% (meaning that the laser fired 15% of the time and was off 85% of the time). None of the patients demonstrated any complications following the therapy, with the longest follow-up out to 18 months.

Treatment was deemed successful if there was a reduction or complete resolution of the subretinal fluid that could be verified on optical coherence tomography, angiograms, and autofluorescence examination, as well as improvement of the visual acuity at 2 to 3 weeks postoperatively.

"Though the results with [MLT] therapy for CSR are promising, its use for this indication still is in its fledgling stages," Dr. Maia said. "For now, we should concentrate on understanding its therapeutic potential and only treat patients who really require treatment, such as patients who have symptoms of CSR for 4 months or longer until long-term safety studies have been done."

The more the leakage of fluid, the greater the chance of increased retinal detachment, he said. Sometimes, the visual acuity cannot be improved significantly. This is related directly to the severity and duration of disease, however, he added.

Future trials with MLT should be aimed at addressing CSR as soon as possible, should spontaneous resolution not occur within the first few months after disease presentation, according to Dr. Maia.