PSTI, focal laser deemed safe for diabetic macular edema

March 15, 2005

New Orleans—Posterior subtenon triamcinolone injection (PSTI) combined with focal laser improves the clinical outcome in diabetic macular edema (DME), according to results of a small, single-center, randomized prospective study, said Murat Tunc, MD, during the American Academy of Ophthalmology annual meeting.

"In combined usage of posterior subtenon triamcinolone and focal laser, the level of improvement in ETDRS scores is greater than with conventional macular laser photocoagulation alone. This indicates an adjunctive role of posterior subtenon triamcinolone injection to macular laser therapy," said Dr. Tunc, a Fulbright scholar and research fellow, Doheny Retina Institute, University of Southern California, Los Angeles. He is also associate professor of ophthalmology, Duzce Medical School, Abant Izzet Baysal University, Bolu, Turkey.

Dr. Tunc noted that diffuse macular edema has a particularly poor prognosis despite laser therapy and that while intravitreal triamcinolone is effective in the treatment of refractory DME, it carries the risk of significant vision-threatening complications.

After giving informed consent, 60 patients with type 2 diabetes who had diffuse macular edema were randomly assigned to two groups of 30 each. The study group received combined treatment of PSTI and focal laser. The control group received conventional grid and focal laser photocoagulation. Patients who had prior treatment for macular edema and other ocular diseases were excluded.

Macular edema was graded during stereoscopic slit lamp fundus examinations. Investigators performed fluorescein angiography and took color fundus photographs before and after the treatment. They also noted patients' demographic characteristics and diabetic control by hemoglobin A1c levels. There was no significant difference in age and gender distribution, duration of diabetes, or hemoglobin A1c levels between the treatment groups.

Investigators used a yellow-green, 532-nm laser (Prima Laser, Nidek Inc.) for laser photocoagulation. In the combined therapy group, PSTI was administered following laser treatment on the same day. They injected 0.5 ml of 40 mg posterior subtenon triamcinolone from the superiotemporal quadrant. The injection was repeated 8 weeks later.

Outcome measures were the change in Early Treatment Diabetic Retinopathy Study (ETDRS) scores and improvement in clinical and angiographic macular edema.

The mean baseline ETDRS score was 44.5 ± 12.6 (range 22 to 66) in the combined treatment group and 45.9 ±12.7 (range 22 to 66) in the laser-only treatment group. At 18 weeks, the mean ETDRS score was 52.5 in the combined treatment group and 46.4 in the laser treatment group. At the final examination, ETDRS scores were rising in most cases in the combined treatment group.

"The improvement in ETDRS scores was not statistically significant in the laser photocoagulation group," Dr. Tunc said. "In our analysis comparing the baseline and final ETDRS scores, there was a significant improvement in patients who received combined treatment. Twelve of 30 eyes in the photocoagulation group and 20 of 30 eyes in the combined treatment group had an improvement greater than or equal to 5 letters in ETDRS scores at 18 weeks."

The mean number of letters improvement was 7.8 in the macular photocoagulation group and 12.4 in the combined treatment group, which was statistically significant.

Nine patients in each treatment group had unchanged scores from the baseline ETDRS level, while one patient in the combined treatment group and nine patients in the macular photocoagulation group lost 5 or more letters at 18 weeks, a difference that was also statistically significant.

In a subgroup of patients who had a baseline ETDRS score over 40, 42% of the cases in the laser photocoagulation group and 88% of the cases in the combined treatment group showed an increase of more than 5 letters at 18 weeks, Dr. Tunc said.

Clinically, the lesions showed an improvement in DME in 40% of the cases in the macular photocoagulation group and 80% of the cases in the combined treatment group. This was statistically significant.