The steroid injections were not superior to laser with respect to increasing the chance of improved vision and decreasing the chance of vision loss, the primary objective of a study reported in 2008. "However, there was evidence that steroids can affect the pathways that lead to the development of new blood vessels on the surface of the retina in diabetes, a secondary objective of the study" says Bressler. "Controlling blood glucose levels can help prevent the development of retinopathy and laser treatments can reduce the risk of vision loss, but the identification of other treatments remains important."

Bressler and colleagues, in the Diabetic Retinopathy Clinical Research (DRCR) Network, discovered that after two years, retinopathy had progressed in 31 percent of 330 eyes treated with laser treatment, 29 percent of 256 eyes treated with 1-milligram doses of triamcinolone acetonide, and 21 percent of 254 eyes treated with 4-milligram doses. The differences appeared to be sustained at three years, even though most eyes in the triamcinolone groups did not receive injections every four months during the second year and less than half received any injections in the third year because there no longer was macular edema, or less commonly, because side effects from the injections precluded applying additional steroids when following the study's treatment protocol.

Bressler says the study suggests that corticosteroids interfere with the creation of new blood vessels by reducing the production of compounds that spur their growth and cautions that steroids are also associated with other eye diseases. "Researchers now need to find ways of using the steroid effect on these blood vessels for treatment, but, not at the expense of causing glaucoma and the side effects of cataract formation or worsening of cataracts which could lead to the need for a patient to undergo cataract surgery."

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