Influence of OCT Signal Strength on Macular, Optic Nerve Head, and Retinal Nerve Fiber Layer Parameters

Abstract

To examine the influence of different signal strengths on measurements made with optical coherence tomography (OCT) of macular, optic nerve head, and retinal nerve fiber layer (RNFL) parameters. From 2003 to 2005, 2092 children, mostly aged 12 years, were examined, and macular, optic nerve head, and RNFL parameters were measured by OCT. Multiple fast scans were acquired, and only right eyes were included in the analyses. Signal strength category was determined after averaging individual signal strengths from each scan and classifying scans as providing moderate (average signal strength, 5-7.49), good (average signal strength, 7.5-9.49), and excellent (average signal strength, >or=9.5) image quality. General linear models were used after adjustment for covariates. Significant differences were observed between measurements obtained at excellent signal strengths compared with those obtained at moderate and good signal strengths for both macular and optic nerve parameters. However, although statistically significant, the magnitude of the differences in macular parameters was very small (approximately 5 microm, or a 2% difference). Differences in optic nerve head parameters were much greater (up to a 32% difference), with larger measurements recorded for most parameters with increasing signal strength category. Significant differences in RNFL parameters with increasing signal strength were not demonstrated. Significantly larger macular and optic nerve head OCT measurements were obtained with increasing signal strength measurements, although absolute differences in macular measurements were small and are of questionable clinical importance. The results support the robustness of OCT in providing precise macular imaging.