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Time domain OCT measures of retinal nerve fiber layer may not correlate with spectral domain OCT
Ophthalmology. 2009;116(7):1271-1277.
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Time domain optical coherence tomography generally measures a thicker retinal nerve fiber layer than spectral domain optical coherence tomography, but the measurement may be skewed by thin nerve fiber layers, as may be present in glaucoma patients.
In a side-by-side comparison of thickness measurements of a time domain OCT device (Stratus, Carl Zeiss Meditec) and a spectral domain OCT device (Cirrus, Carl Zeiss Meditec) in healthy subjects and glaucoma patients measured on the same day, researchers noted that average retinal nerve fiber layer thickness was measured as thicker in 29 patients without glaucoma by time domain OCT (99.4 µm) compared with spectral domain OCT (92 µm)
However, in patients with either suspect or diagnosed glaucoma, the two scan modalities varied in average retinal fiber layer thickness. Spectral domain OCT measured average retinal fiber layer thickness as 88.1 µm (glaucoma suspect), 73.3 µm (mild glaucoma), 60.9 µm (moderate glaucoma) and 55.3 µm (severe glaucoma). By comparison, time domain OCT measured average retinal fiber layer thickness as 94.5 µm (glaucoma suspect), 79 µm (mild glaucoma), 62.7 µm (moderate glaucoma) and 51 µm (severe glaucoma).
The only difference between the two scan modalities that was not statistically significant was in patients with moderate glaucoma, according to the study.