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Signal Strength is an Important Determinant of Accuracy of Nerve Fiber Layer Thickness Measurement by Optical Coherence Tomography

Wu, Ziqiang MD*; Huang, Jingjing MD; Dustin, Laurie MS; Sadda, Srinivas R. MD*

doi: 10.1097/IJG.0b013e31817eee20
Original Studies

Purpose To investigate the effect of signal strength on the measurement of the retinal nerve fiber layer (RNFL) using optical coherence tomography (OCT).

Methods Eyes with known or suspected glaucoma or nonglaucomatous optic atrophy were scanned twice within the same visit using Stratus OCT's Fast Nerve Fiber Layer Thickness protocol. Only those eyes with 2 high-quality scans (signal strengths of at least 5 and different from each other, no error messages, and no obvious segmentation errors) were included in the study. The RNFL thickness measurements from the initial and the repeat scans were compared and then correlated with the differences in signal strength. Subgroup analyses were performed similarly among patients with average RNFL thickness less than 90 μm and those with at least 90 μm.

Results Scans with higher signal strengths are associated with greater RNFL thickness measurements if the signal strength is less than 7. Scans with signal strength of at least 7 have higher reproducibility. This is true among all patients and subgroups divided on the basis of average RNFL thickness. Additionally, we found that the greater the variability between the initial and repeat scans, the greater the variability in the RNFL thickness measurements. Scans with higher signal strengths have less variability, especially when the optic nerve is relatively healthy.

Conclusions When measuring the RNFL thickness with the Stratus OCT, it is important to aim for a signal strength of at least 7. Visual field testing may be more reliable in some patients, especially when the optic nerve is significantly compromised.

*Doheny Eye Institute, Department of Ophthalmology

The State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, China

Department of Preventive Medicine, Keck School of Medicine, University of Southern California, Los Angeles, CA

Supported in part by: Grants EY 11753 and EY 03040 from the National Eye Institute and the National Center on Minority Health and Health Disparities, National Institutes of Health, Bethesda, MD, and an unrestricted grant from the Research to Prevent Blindness, New York, NY.

Reprints: Srinivas R. Sadda, MD, Doheny Eye Institute, DEI 3623, 1450 San Pablo Street, Los Angeles, CA 90033 (e-mail:

Received for publication January 26, 2008; accepted May 3, 2008

Conflict of Interest: The authors have no proprietary interest in any of the topics discussed in this manuscript.

© 2009 Lippincott Williams & Wilkins, Inc.