Logarithmic Transformation of Spectral-Domain Optical Coherence Tomography Data in Uveitis-Associated Macular Edema

Abstract

To determine the utility of logarithmic transformation of spectral-domain optical coherence tomography (logSD-OCT) retinal thickness data for assessment of clinically meaningful changes in uveitis-associated macular edema. Patients with noninfectious uveitis-associated macular edema at our institution between August 2010 and March 2011 were identified. Only those with SD-OCT imaging were included. The clinical diagnoses, visual acuities, and central subfield thickness (CST) measurements were recorded. Logarithmic transformation of the retinal thickness was performed and frequency histograms plotted. A linear mixed-effects model of the logarithm minimum angle of resolution (logMAR) visual acuity on logSD-OCT was created to account for within-patient correlation among visits and between eyes. A total of 98 SD-OCT images from 34 patients were analyzed. The mean age at examination was 40 years (range, 11-69 years). Anatomic diagnoses included anterior/intermediate uveitis (23%), intermediate uveitis (21%), posterior uveitis (12%), and panuveitis (44%). LogSD-OCT data provided a more normal distribution than standard CST. Skewness and kurtosis of CST data were 1.04 and 0.37, respectively, and skewness and kurtosis of logSD-OCT data were 0.40 and -0.48, respectively. There was a positive correlation between logSD-OCT and logMAR visual acuity. Specifically, for each 0.1-unit increase in logSD-OCT, the logMAR visual acuities increased (worsened) by 0.082 units (95% CI: 0.057-0.107, P < 0.001). Logarithmic transformation of SD-OCT measurements provided a more normal distribution and positively correlated with logMAR visual acuity. This transformation of retinal thickness may be valuable for assessing clinically significant changes in SD-OCT measurements in future uveitis studies.