Seventy-four eyes of 54 patients with diabetic macular edema were enrolled in the study. Nine patients failed to complete the study: Three patients died (one of cardiovascular disease, two of cancer), five patients withdrew their consent for reasons unrelated to the study, and one patient suffered an adverse event (skin rash) and was discontinued. Five eyes in three patients were excluded because of potential interference with the measurement of blood–retinal barrier permeability due to posterior vitreous liquefaction. The vitreous was evaluated from 30-minute vitreous fluorometry scans, a horizontal vitreous concentration curve being considered evidence of vitreous degeneration.
8 9 10 Photocoagulation treatment for fovea-threatening diabetic macular edema was given during the study in two eyes with vitreous degeneration and in two eyes of two other patients. All four eyes were excluded from analysis. Thus, 55 (74%) eyes in 41 (76%) patients were included in the data analysis (placebo: 13 eyes; 4 mg/d: 17 eyes; 16 mg/d: 11 eyes; 32 mg/d: 14 eyes). At baseline, mean age was 51.9 (median, 54; range, 24–69) years; mean duration of diabetes in patients with type I diabetes, 22.9 (median, 20; range, 16–32) years; and mean duration in patients with type II diabetes 12.9 (median, 13; range, 2–26) years. The study population comprised 11 women and 30 men, of whom 12 had type I diabetes, and 29 had type II diabetes
(Table 1) .
The present study was designed as an exploratory substudy using vitreous fluorometry to elucidate the effect of RBX on blood–retinal barrier permeability, as part of a larger double-masked, placebo-controlled, dose-ranging, parallel, randomized, multicenter, multinational clinical trial. The study adhered to the tenets of the Declaration of Helsinki, and informed consent was obtained from all patients before they were enrolled in the study, which was conducted according to the ICH-Guidelines for Good Clinical Practice (ICH GCP). The main study was approved by the FDA and EMEA and locally by The Danish Medicines Agency and the medical ethics committee of Copenhagen County. The substudy was approved locally.
Ocular eligibility was defined as the presence of one sixth or more of disc area (DA) of definite retinal thickening within two disc diameters (DD) of the center of the macula and ETDRS severity of retinopathy level ≤47A, as determined by stereoscopic fundus photograph grading.
11 Ocular ineligibility was defined as the presence of clinically significant macular edema,
except that retinal thickening or hard exudates adjacent to retinal thickening at/or within 500 μm but no closer than 300 μm from the fovea was allowed if visual acuity was ≥77 ETDRS letters.
12 The patients were randomly assigned to one of four study arms (RBX 4, 16, or 32 mg/d or placebo) and examined at baseline and 3, 12, and 18 months. All patients were being observed closely and were monitored continuously for progression of macular edema and retinopathy.
The primary end point of the study was defined as a change in permeability of the blood–retinal barrier as determined by vitreous fluorometry. The method is an extension of fundus fluorescein angiography whereby retinal vascular leakage of fluorescein into the vitreous is quantitatively assessed by an optical instrument and used to calculate a summary measure of blood–retinal barrier permeability. In healthy subjects, the permeability is 2.0 ± 0.48 nm/s (mean ± SD).
13 14 15 16 17 Secondary end points included change in best corrected ETDRS visual acuity at 4 m, HbA
1c level, and resting arterial blood pressure. The level of diabetic retinopathy was graded with seven standard field stereoscopic color fundus photographs evaluated by the Wisconsin Fundus Photographic Reading Center (University of Wisconsin, Madison, WI). The study included ETDRS grading levels 35, 43, 47, 53, and higher than 53. Deterioration of retinopathy was defined as an increase of one or more levels and improvement or stable retinopathy as a decrease or no change.
The effect of RBX treatment at any dosage was compared statistically with that of a placebo, incorporating data from repeated measurements at all visits and analyzed using a mixed linear model, including repeated measures and random effects. The latter accounts for random effects and interaction between patients and eyes, when more than one eye was included per patient, which happened in 14 patients. The dependent variable was blood–retinal barrier permeability. Independent variables included HbA1c, systolic and diastolic blood pressure, plasma lipids, retinopathy level, baseline blood–retinal barrier permeability, duration of treatment, and interactions between these variables and treatment. As independent variables, the final model included time, HbA1c level, and baseline blood–retinal barrier permeability on the basis of the descriptive factors found to be of statistical significance after a successive removal of all interactions and main effects with P > 0.05. Square-root transformation was applied to the permeabilities to obtain a regular distribution of residuals. A post hoc analysis was also performed comparing placebo and the three different RBX doses. The relation between baseline permeability and the level of retinopathy was tested with a generalized linear model. The effect of treatment on the change in retinopathy during the study was analyzed with the Fisher exact test (comparing improved and stable retinopathy versus increasing levels of retinopathy). Student’s t-test was used for comparison of quantitative variables between the placebo- and the RBX-treated groups. The level of statistical significance was set at 5%. Data were analyzed on computer (SAS software package, ver. 8e; SAS Institute, Cary, NC).
A post hoc evaluation of baseline stereo fundus photographs by the central Reading Center at University of Wisconsin stated that 62% of the 55 eyes were defined as non–clinically significant macular edema, and 38% were CSME level 4 and 5 by a new macular edema grading scale with a total of 11 levels from questionable edema (level 1) to central involvement (level 11, Wisconsin DME Severity Scale; Davis R, personal communication, April 2005; recorded by Girach A, Sander B). Inclusion of data evaluated by this unpublished macular edema grading scale did not influence the conclusion of the study.