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Eyes treated with TTT lost on average two lines of visual acuity, while sham-treated eyes lost four lines.
Fort Lauderdale, FL-A longitudinal analysis of a subgroup from the Transpupillary Thermotherapy of Occult Subfoveal Choroidal Neovascular Membranes in Patients with Age-Related Macular Degeneration (TTT4CNV) study showed an increasingly beneficial effect of TTT over time in eyes with best-corrected visual acuity (BCVA) of 20/100 or less, said Elias Reichel, MD, study chairman.
In this subgroup, 24% of treated eyes demonstrated improvement of vision by one or more lines compared with none of the eyes in the sham-treated control group. At 24 months, there was a near two-line benefit in preserving vision in the TTT-treated group, compared with the control group.
Eyes treated with TTT lost on average two lines of visual acuity, while sham-treated eyes lost four lines. Both of these findings were statistically significant (p = 0.03). About 42% of patients enrolled had baseline vision of 20/100 or worse and were included in the subgroup analysis. "These subgroup findings indicate that TTT is beneficial compared with natural history in eyes with subfoveal occult CNV and best-corrected visual acuity of 20/100 or worse," Dr. Reichel said.
The TTT4CNV study enrolled 305 patients with subfoveal occult CNV with a maximum diameter of 3 mm and visual acuity between 20/50 and 20/400. Patients were randomly assigned 2:1 to TTT (800 mW for 60 seconds with a 3-mm spot size) or sham treatment. One re-treatment was allowed at 3 months at investigator discretion. The multicenter, prospective, double-masked, placebo-controlled trial was conducted at 22 sites in the United States.
In October 2004, investigators reported that in the entire intent-to-treat group, 47% of patients treated with TTT avoided modest or severe vision loss after 2 years, compared with 43% of those who received sham treatment. These results were not statistically significant. It was subsequently determined that not only was a three-line improvement statistically significant, but so was a one-line improvement in the entire cohort at 1 year, Dr. Reichel said.
Subgroup analyses However, a trend favoring TTT prompted investigators to perform various subgroup analyses of the data collected during the 2-year trial, Dr. Reichel said.
"When you look at mean loss of vision in the entire group, there is a four-letter difference favoring TTT. That was one reason that prompted us to take a closer look."
Similar results from various case series of TTT, which primarily included patients with BCVA of 20/100 or worse, also were a factor in the decision to analyze the data further.
In addition, outcomes from studies of other treatments for CNV indicated that patients whose vision was 20/100 or worse benefited more from therapy. These treatments included photodynamic therapy and subretinal surgery for histoplasmosis and idiopathic membranes.
"There may be something about patients with poorer vision or worse vision that for some reason they benefit more from these treatments relative to patients with better vision," Dr. Reichel said. "It is unclear why, but it may be that patients with poorer vision have active disease whereas patients with better vision have inactive disease and therefore are less likely to show a benefit to any treatment."
TTT is a large-spot-size, low-irradiance, long-exposure, infrared (810 nm) laser photocoagulation protocol that uses the IRIS Medical OcuLight SLx laser and Large Spot Slit Lamp Adapter from Iridex.