Quantification of error in optical coherence tomography central macular thickness measurement in wet age-related macular degeneration

Abstract

Purpose To assess error indicators encountered during optical coherence tomography (OCT) automated retinal thickness measurement (RTM) in neovascular age-related macular degeneration (NVAMD) before and after bevacizumab (Avastin; Genentech Inc, South San Francisco, California, USA) treatment.

Design Retrospective observational cross-sectional study.

Methods Each of the 6 radial lines of a single Stratus fast macular OCT study before and 3 months following initiation of treatment in 46 eyes with NVAMD, for a total of 552 scans, was evaluated. Error frequency was analyzed relative to the presence of intraretinal, subretinal (SR), and subretinal pigment epithelial (SRPE) fluid. In scans with edge detection kernel (EDK) misplacement, manual caliper measurement of the central macular (CMT) and central foveal (CFT) thicknesses was performed and compared to the software-generated values. The frequency of the various types of error indicators, the risk factors for error, and the magnitude of automated RTM error were analyzed.

Results Error indicators were found in 91.3% and 71.7% of eyes before and after treatment, respectively (P = .013). Suboptimal signal strength was the most common error indicator. EDK misplacement was the second most common type of error prior to treatment and the least common after treatment (P = .005). Eyes with SR or SRPE fluid were at the highest risk for error, particularly EDK misplacement (P = .039). There was a strong association between the software-generated and caliper-generated CMT and CFT measurements. The software overestimated measurements by up to 32% and underestimated them by up to 15% in the presence of SR and SRPE fluid, respectively.

Conclusions OCT errors are very frequent in NVAMD. SRF is associated with the highest risk and magnitude of error in automated CMT and CFT measurements. Manually adjusted measurements may be more reliable in such eyes.