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Wissam Charafeddin, Srinivas Sadda, Muneeswar Nittala, Mark Humayun, Aldo Oregon-Miranda; Relationship between reflectivity and volume of subretinal tissue in choroidal neovascular membranes associated with age-related macular degeneration. Invest. Ophthalmol. Vis. Sci. 2013;54(15):4158.
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To evaluate the relationship between subretinal tissue (SRT) volume and reflectivity using spectral-domain optical coherence tomography (SD-OCT) in subjects treated with anti-VEGF therapy for choroidal neovascular membranes (CNVM) in eyes with exudative age-related macular degeneration (AMD).
Eight eyes of 8 patients diagnosed with Type 2 or mixed Type 1/ Type 2 CNV from AMD were included in this analysis. Volume SD-OCT image cubes were obtained from each patient at baseline, 1 month, 3 months, 6 months, 9 months and 12 months after the first injection. Detailed manual segmentation and delineation of SRT and other components of the CNV lesion and the adjacent neurosensory retina were performed on every B-scan at every visit using the customized grading software (OCTOR). A total of 6144 B-scans were analyzed. Retinal thickness, SRT volume and SRT reflectivity were calculated for each visit for all cases. Because reflectivity can vary due to various factors including media opacity, nerve fiber layer reflectivity was used to normalize the signal across cases.
The mean baseline best-corrected visual acuity (VA) was 20/130 (Log MAR = 0.82) and improved to 20/75 (Log MAR=0.58), though it was not statistically significant. Similar to the large clinical trials, OCT response paralleled VA, with a reduction in retinal volume from 10.1 microL at baseline to 9.1 microL at month 12 after starting anti-VEGF treatment. SRT volume demonstrated a similar decline from 0.48 microL to 0.19 microL whereas reflectivity showed a significant increase from 0.83 to 1.09 units (p=0.012). SRT reflectivity was positively correlated with visual acuity (r= 0.69, P = 0.06). Although a negative correlation was observed between SRT reflectivity and SRT volume (r = - 0.786, P = 0.021), volume change could only account for 61% of the variability in reflectivity. Indeed, SRT reflectivity remained an independent predictor of VA in multi-variable models.
Reflectivity of the subretinal tissue, while partially correlated with tissue volume, appears to carry independent information regarding disease activity. Normalization approaches allow tissue reflectivity levels to be compared between cases and over time. SRT reflectivity may be useful parameter for monitoring disease activity and response to therapy in future studies.
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