Clinical Relevance of Foveal Location on Retinal Nerve Fiber Layer Thickness Using the New FoDi Software in Spectralis Optical Coherence Tomography

Abstract

To evaluate the effect of improper foveal location on retinal nerve fiber layer (RNFL) thickness measurements by using the new FoDi software in spectral-domain optical coherence tomography (Spectralis SDOCT). Cross-sectional study with 126 subjects: 66 healthy, 30 early, and 30 moderate glaucomatous eyes. Fast RNFL scans were performed by using the new FoDi technology. The position of the fovea was manually displaced inferiorly after acquisition (producing clockwise torsion of scan circle) and then superiorly (counterclockwise) to generate study sets of images. Differences in RNFL thickness between foveal-guided and alternative scans were analyzed and color changes in sector charts were evaluated. In healthy eyes, placing the fovea inferiorly led to significant RNFL thickness changes in all sectors. Locating the fovea superiorly seemed to have less impact. Early glaucomatous eyes were more susceptible to quantitative changes, but moderate glaucomatous eyes were more susceptible to qualitative changes. Improper fovea disc alignment when using the FoDi software in Spectralis OCT significantly affected sectoral RNFL thickness measurements and color chart representation. As final report of FoDi analysis does not show the foveal position used, careful acquisition is encouraged, so that results are reliable. Otherwise, this technique can easily be misinterpreted and patients could be misdiagnosed.