There were 16 patients in the ranibizumab-only group and 19 in the combined group with data available through 24 months. Out of the potential visits (492 in the ranibizumab-only group and 517 in the combined group), an average 10% were missed in each group. On OCT, both groups showed a typical anti-VEGF response with a reduction in edema; these differences were not statistically significant.
“Likewise, on average, patients gained 10 letters in both groups,” Dr. Kim said. “When we analyzed 15-letter gainers, 40% in monotherapy versus 30% in the combination arms gained 15 or more letters, but again this was not statistically significant.”
The group now has 80% of original subjects who have completed Year 3, Dr. Kim said.
But the “big” question was whether the targeted laser treatment made a difference in decreasing the number of injections needed to achieve those gains.
“The bottom line is, no!” Dr. Kim pointed out. “The combination arm actually had a slightly higher percentage of PRN injections than the monotherapy, demonstrating that adding laser treatment did not reduce the injection burden for DME.”
Patients in the monotherapy group received an average of 18.3 injections compared to an average of 19.7 injections in the combination group. In Year 3, the combination group had a 73% rate of re-injection (down from 80% in Year 2) compared to 64% in the ranibizumab-only group in Year 3 (down from 73% in Year 2).
There are some theories about why adding PRP did not reduce the burden, Dr. Kim said. For one, there is an average of 92 million photoreceptors in the human retina, a majority of which are located posteriorly.
“Since we don’t treat the posterior pole, we’re preserving about a half of photoreceptors,” Dr. Kim explained. “Even if you obliterate a significant amount of peripheral retina, about half the photoreceptors are unaffected. Perhaps to decrease the VEGF load, we would have to destroy valuable retina, which we’re not willing to sacrifice.”
However, the combined treatment was safe over the study timeframe, and did provide similar anatomic and visual acuity benefits. What that means for the role of PRP moving forward remains unanswered, she said.