Comparing total macular volume changes measured by Optical Coherence Tomography with retinal lesion volume estimated by active contours.

Abstract

Abstract: : Purpose:To evaluate a practical approach for quantitative assessment of total macular volume changes on Optical Coherence Tomography (OCT) images of patients with retinal lesions associated with neovascular age–related macular degeneration. This study was intended to determine whether quantifying retinal lesions is meaningful in correlating changes in retinal morphology with changes in visual acuity as a function of treatment. Methods:We analyzed OCT images of twenty–one patients enrolled in a study of the VEGF–binding antibody fragment, rhuFAB V2. Patients were monitored for safety and visual acuity for a total period of 16 weeks and followed through 20 weeks. An active contour model was used to outline the fluid–filled regions, allowing to quantify them independently from the retinal tissue. For quantitative interpretation, the retinal volume c hanges were assessed at the foveal and peripheral regions over time and compared with the lesion volume before treatment. Visual acuity was defined as change from baseline in total number of letters read correctly (gained or lost) on the Early Diabetic Retinopathy Study [ETDRS] chart. Stable vision was defined as losing or gaining less than 15 letters on the ETDRS chart. Results:The detection method used proved effective in capturing the complexity of fluid–filled regions in OCT images. By using the active contour model it is possible to outline the fluid–filled regions in order to quantify their changes as a function of treatment and to correlate these morphological changes with changes in visual acuity over time. Results demonstrate a trend of decreasing macular volume with improving visual acuity. At week 20 (Day 140), 19 of the 21 patients (90%) had stable (± 4 letters) or improved (> 5 letters) vision with 11 patients (52%) gaining at least 3 lines (15 letters). Stable and improved visual acuity correlated well with decreased fluorescein angiographic leakage and decreased retinal thickness measured by OCT. Conclusions:Our study suggests that the ability of OCT to correlate changes in retinal morphology with changes in visual acuity after therapy could be improved by comparing total macular volume changes over time measured by OCT with lesion volume estimated by active contours. The resulting evaluation of this method would ultimately lead to a more rational and effective approach to therapy of macular disorders and improved diagnosis.

Keywords: age–related macular degeneration • retina • visual acuity