Standardizing Retinal Nerve Fiber Layer (RNFL) Thickness Measurements Across Time Domain and Spectral Domain Optical Coherence Tomography (TD- and SD-OCT) Devices While Accounting for Scan Location

Abstract

 

Purpose:

 

To standardize the RNFL thickness measurements among TD- and various SD-OCT devices by establishing calibration equations while accounting for variable TD-OCT scan location using a scan location matching (SLM) algorithm.

 

Methods:

 

Eighteen eyes (11 healthy and 7 glaucoma) had nine circumpapillary TD-OCT (Stratus OCT; Carl Zeiss Meditec, Inc., Dublin, CA (CZMI)) scans (one centered and 8 intentionally off-centered). In addition, one 3D cube scan centered at the optic nerve head was obtained for each eye using 3 SD-OCT devices: Cirrus HD-OCT (CZMI), RTVue (Optovue, Fremont, CA), and Spectralis (Heidelberg Engineering, Heidelberg, Germany). Matched scan location for each TD-OCT scan (centered and off-centered) was detected on each of the 3 corresponding SD-OCT cube data using the SLM algorithm. RNFL thickness measurement calibration equations from TD- to SD-OCTs were computed separately.

 

Results:

 

Before calibration, the global mean RNFL thickness measurements of Cirrus, RTVue, and Spectralis were significantly higher than TD-OCT circle scan (16.6, 30.7, and 16.4% increase, respectively; p0.06) (Figure).

 

Conclusions:

 

Calibration equations standardized RNFL thickness measurements so that they are directly comparable among TD- and various SD-OCT devices. This may allow us to longitudinally study populations across the OCT technology generations.  

 

Keywords: imaging/image analysis: clinical • nerve fiber layer • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound)