1. At 24 months, frequency doubling perimetry (FDP) foveal sensitivity was significantly decreased in the placebo group (-1.9 dB) and increased in the group treated with Doxycycline (+1.8 dB, p=0.02). This difference was consistently observed beginning at 6 months.
2. There were no other significant differences between the placebo and Doxycycline arms among functional and anatomic metrics.
Evidence Rating Level: 2 (Good)
Study Rundown: This study aimed to identify whether the anti-inflammatory component of doxycycline could impede progression of nonproliferative diabetic retinopathy. Thirty patients were divided into placebo and treatment arms, with the latter receiving daily doxycycline for 24 months. While multiple functional and anatomic markers were used as metrics to identify any changes, only frequency doubling perimetry (FDP) foveal sensitivity was significantly elevated among the treatment arm, but decreased among the control group beginning at the 6-month mark and persisting through 24 months (p=0.02-0.04). None of the other markers were significantly different between the groups. This may have been due to the small sample size or short length of study, both which were limitations. It is also possible that given the subtle nature of nonproliferative diabetic retinopathy, these tests were not sufficiently sensitive to detect change. Another limitation is that not all measurements could be completed at 24 months, significantly reducing the statistical power at this time point. Ultimately, this study encourages further investigation into the role of inflammation in diabetic retinopathy.
In-Depth [randomized control trial]: In this study, the authors attempted to study whether a daily low-dose of doxycycline can impair the progression of diabetic retinopathy or perhaps improve vision. Patients were randomized to either receive placebo or low-dose doxycycline for 24 months. Multiple functional and anatomic metrics were utilized as outcome measures, including frequency doubling perimetry (FDP), contrast sensitivity, visual acuity, quality of life, retinal thickening, macular thickness, and retinal vessel diameters. FDP is thought to be a sensitive measure of inner retinal function, which is often affected in diabetes and mild diabetic retinopathy. At 12 months, FDP foveal sensitivity was significantly decreased in the placebo (-1.60 dB) and increased in the treatment group (+1.66 dB, p=0.04). This change persisted through the end of the study at 24 months, at which time FDP foveal sensitivity was significantly decreased in the placebo group (-1.9 dB) and increased in the doxycycline group (+1.8 dB, p=0.02). However, changes among other functional and anatomic markers were insignificant. These data appear to suggest that there may be an inflammatory component in the pathogenesis of diabetic retinopathy that can be impaired with doxycycline.
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