Data were analyzed from 80 patients with persistent macular edema refractory to medical or laser treatment who had been randomly assigned to observation or one of two doses of dexamethasone in a biodegradable drug delivery system. The results showed both a baseline correlation between greater retinal thickness and worse visual acuity and, following treatment, a significant correlation between improvement in visual acuity and decreases in macular edema among patients who had received the higher dose of the corticosteroid.
The study involved 315 patients with persistent macular edema who were assigned to either observation or treatment with 350 μg or 700 μg of dexamethasone. Macular edema was assessed using optical coherence tomography (OCT) in one eye of 80 of these patients at baseline and at day 90. This analysis was a spinoff of a larger study conducted to assess the effectiveness of the dexamethasone implant and was intended to mine the dataset for more information that would help with clinical care and research, Dr. Haller said. She is the Katharine Graham Professor of Ophthalmology, Wilmer Eye Institute, Johns Hopkins University School of Medicine, Baltimore.
Best-corrected visual acuity (BCVA) was measured using the standard ETDRS protocol. Pearson correlation coefficients were calculated to estimate the correlation between macular thickness and BCVA.
The 80 patients who had OCT readings at baseline and day 90 included 44 with diabetic macular edema, 25 with macular edema associated with retinal vein occlusion, and 11 who had macular edema associated with uveitis or Irvine-Gass syndrome.
At baseline, greater retinal thickness was associated with worse visual acuity for all 80 eyes (r = 0.406, p <0.001). The correlation was also present in 44 eyes in patients with diabetic macular edema (r = 0.369, p = 0.014).
Results at day 90 showed a correlation between a decrease in macular thickness and improvement in visual acuity from baseline among eyes treated with 700 μg of dexamethasone in the drug delivery system (r = 0.350, p = 0.009). The change was not significant for the observation group or eyes treated with 350 μg of dexamethasone.
The correlations at baseline and at 90 days were consistent with earlier findings, Dr. Haller said. Contributing factors other than macular thickening can influence visual function in eyes with macular edema, however, and these factors need to be identified and quantified, she added.
"It comes as no surprise to people who have been working with OCT for some time now that, for any given level of visual acuity, there are going to be a wide range of retinal thicknesses, and for any one retinal thickness, there could be a wide range of visual acuities, so there is more to it than just the thickness itself. But the thickness is an important component of visual acuity," she said.
Other factors that may warrant additional study include the duration of macular edema, retinal perfusion, type of thickening (subretinal fluid versus cystic changes versus diffuse thickening), total retinal volume, and vitreomacular interface abnormalities such as epiretinal membranes and traction.
Although the findings of correlations between visual acuity and macular thickness found in the analysis were not novel, they are important to the search for objective measures that can help make evaluations and assist with drug development, clinical trials, and patient care, Dr. Haller added.
"This study and studies like this have relevance for clinical care, definitely, but very importantly they are significant in terms of evaluating new treatments," she said.