Positional independence of optic nerve head and retinal nerve fiber layer thickness measurements with spectral-domain optical coherence tomography

To evaluate repeatability and positional independence of optic nerve head (ONH) and retinal nerve fiber layer (RNFL) thickness measurements in sitting and supine body positions using portable spectral-domain optical coherence tomography (iVue SD-OCT; Optovue Inc).

Evaluation of diagnostic technology.

Sixty eyes of 30 subjects (10 healthy younger adults aged 20-27 years, 10 healthy older adults aged 50-66 years, and 10 glaucoma patients aged 38-82 years) were included prospectively. For each participant, all measurements were taken in a single session. After 5 minutes in the supine position, 5 scans were obtained from both eyes. Following a 5-minute sitting adaptation, 5 scans were then obtained in the sitting position. The same instrument was used for all measurements. Repeatability and correlation between supine and sitting measurements of 4 ONH and 3 RNFL parameters were assessed using intraclass correlation coefficients (ICC), concordance correlation coefficients (ρ), and Bland-Altman plots.

Measurements were highly repeatable within individual eyes, both for ONH (ICC range, 73%-99%) and RNFL (ICC range, 72%-99%) parameters. The correlation between supine and sitting ONH measurements was strong and ranged from ρ = 97%-99% (younger healthy) to ρ = 98%-99% (older healthy) and ρ = 84%-99% (glaucoma). Bland-Altman plots indicated good agreement between sitting and supine readings of ONH and RNFL parameters.

Repeatability of measurements of ONH and RNFL is high and measurements between sitting and supine are highly correlated. The ability of the iVue SD-OCT to evaluate ONH and RNFL parameters is good to excellent in both body positions.