Transpupillary thermotherapy effectively treats CNV secondary to AMD

The Iridex 810-nm diode laser was shown to cause only a minimal reduction in vision.

ByBob Kronemyer

Color fundus photograph and fluorescein angiogram of a choroidal neovascular membrane encroaching under the fovea.

LONDON — Transpupillary thermotherapy is promising treatment for classic and occult choroidal neovascularization secondary to age-related macular degeneration, according to the results of a retrospective study of 44 eyes (42 patients).

“Although this a relatively small pilot series, we were pleasantly surprised by the minimal reduction in vision caused by transpupillary thermotherapy (TTT),” said co-author J. Dominic A. McHugh, MD, FRCS, FRCOphth, a consultant ophthalmic surgeon at King’s College Hospital here. “Our results compare favorably with the Macular Photocoagulation Study that treated subfoveal membranes.”

The current study, which recently appeared in the British Journal of Ophthalmology, consisted of 12 membranes with predominantly classic choroidal neovascularization (CNV) and 32 predominantly occult membranes. Mean follow-up was 6.1 months (range 2 to 19 months).

“The mean change in vision for classic membranes was –0.75 (SD 1.75) and for occult membranes it was –0.66 (SD 2.1) Snellen lines,” Dr. McHugh said.

Predominantly classic membranes were also closed in 75% of eyes, and remained persistent in 25%. “There were no cases of recurrence in these eyes,” Dr. McHugh told Ocular Surgery News. Occult membranes were closed in 78% of eyes and remained persistent in 12.5%. Among predominantly occult membranes, the recurrence rate was 5.1%.

Treatment protocol

TTT was performed with an 810-nm diode laser from Iridex Corporation. The IRIS Medical OcuLight SLx laser system has a dedicated slit lamp-mounted delivery system. “Laser settings were adjusted to give faint retinal graying following 1 minute of treatment,” Dr. McHugh said. Beam diameters varied between 800 µm and 3000 µm.

The average number of treatment sessions was 1.8, spread over 1 to 6 months. “We used an average power of 486 mW and a beam diameter of 1.69 nm,” he said. Eyes received 4.25 laser spots per treatment. In patients with large lesions, confluent overlapping treatments were standard.

“The treatment itself is not difficult,” Dr. McHugh said. “Apart from the laser, I use a fundus contact lens.” By using low power settings, “complications are rare and patient tolerance is good.” Only two patients experienced significant post-treatment hemorrhage, but no patients complained of pain, although some sensation was common. No anterior segment damage was noted or reported by any patient.

Following TTT the membrane has closed, with minimal laser-related atrophic or fibrotic changes. The patient’s vision remained stable.

Interstitial hyperthermia

Dr. McHugh’s interest in TTT was first sparked by the experience of ocular oncologists in the treatment of tumors. “They applied the concept of ‘interstitial hyperthermia,’ in which relatively modest radiant energies were applied to the lesion, using an infrared laser with an emission wavelength of 810 nm. The temperature elevations that were induced heated the tumor, but did not cause a ‘burn’.”

This beneficial effect “appears to be related to the release of cytotoxic free radicals and perhaps the inhibition of DNA repair mechanisms. The potential advantage of this method is that the target lesion can be treated, while non-therapeutic damage to adjacent normal tissue can be minimized,” he said.

A CNV membrane can be likened to a vascular tumor. “It seems justifiable that similar beneficial mechanisms of action may apply when using TTT to treat subfoveal lesions.” Although conventional laser photocoagulation with an argon laser can be effective in treating a CNV membrane, “its use for subfoveal membranes is often associated with an immediate and significant reduction and vision. For this reason, one is reluctant to recommend this modality for the patient,” Dr. McHugh said.

Cost-effective treatment

Dr. McHugh, who has been performing TTT in the treatment of CNV membrane for more than 3 years, said the novel therapy is “considerably cheaper” than photodynamic therapy (PDT) because it “does not require a pharmacologic agent. The laser itself also has multimodality applications.” There is also early evidence that TTT closed a much higher proportion of predominately classic membranes (75%) compared to PDT (19%).

Study results compare favorably with the natural history of occult CNV, where 63% of patients suffered 3 or more lines of visual loss in the first 6 months. The study also compares well to the Macular Photocoagulation Study of classic membranes, which had a reported recurrence rate of 59%.

For Your Information:

J. Dominic A. McHugh, MD, FRCS, FRCOphth, can be reached at 73 Harley St., London W1G 8QJ, United Kingdom; (44) 207 935 5874; fax: (44) 207 224 5210; e-mail: dommch@msn.com. Dr. McHugh has no direct financial interest in the products mentioned in this article, nor is he a paid consultant for any companies mentioned.

Iridex Corporation can be reached at 1212 Terra Bella Ave., Mountain View, CA 94943; +(1) 650-962-8100; fax: (650) 962-0468.

Reference:

Newsom RSB, McAlister JC, et al. Transpupillary thermotherapy (TTT) for the treatment of choroidal neovascularisation. Br J Ophthalmol. 2001:85;173-178.