Korean J Ophthalmol.  2012 Jun;26(3):182-188. 10.3341/kjo.2012.26.3.182.

Low Limit for Effective Signal Strength in the Stratus OCT in Imperative Low Signal Strength Cases

• Ha MM
• Kim JM
• Kim HJ
• Park KH
• Kim M
• Choi CY

• KMID: 1376123
• DOI: http://doi.org/10.3341/kjo.2012.26.3.182

Abstract

PURPOSE
To determine the lowest limit of signal strength that is still effective for accurate analysis of optic coherence tomography (OCT) values, we investigated the reproducibility of OCT scans by signal strength (SS).
METHODS
A total of 668 subjects were scanned for measurements of retinal nerve fiber layer (RNFL) thickness using the Stratus OCT twice on the same day. The variability of overall RNFL thickness parameters obtained at different SS was analyzed and compared by repeated-measures of ANOVA and Spearman's correlation coefficient. Values of the intraclass correlation coefficient (ICC) and variability (standard deviation) of RNFL thickness were obtained. The false positive ratio was analyzed.
RESULTS
When SS was 3, the variability of RNFL thickness was significantly different (low ICC, high variability) in comparison to when SS was 4 or greater. Significant negative correlations were observed between variability in RNFL thickness and signal strength. The difference of variability of average RNFL thickness between SS 4 (4.94 microm) and SS 6 (4.41 microm) was 0.53 microm.
CONCLUSIONS
Clinically, the difference of variability of average RNFL thickness between SS 4 and SS 6 was quite small. High SS is important, however, when signal strength is low due to uncorrectable factors in patients in need of OCT for glaucoma and retinal disease. Our results suggest that SS 4 is the lowest acceptable limit of signal strength for obtaining reproducible scanning images.

Keyword

Glaucoma; Optic coherence tomography; Retinal nerve fiber layer; Signal strength; Variability

MeSH Terms

Adolescent
Cross-Sectional Studies
Diagnosis, Differential
Disease Progression
False Positive Reactions
Female
Glaucoma/complications/*diagnosis
Humans
Male
Prospective Studies
Reproducibility of Results
Retinal Diseases/*diagnosis/etiology
Retinal Ganglion Cells/*pathology

Figure

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  Fig. 1 The variability of retinal nerve fiber layer (RNFL) thickness by signal strength (SS). When SS was 3, the variability of RNFL thickness increased significantly, as opposed to when signal strength was 4 or greater.

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  Fig. 2 The box-plot diagram of correlations between the coefficient of variation (CV) in average retinal nerve fiber layer (RNFL) thickness, the RNFL thickness of four quadrants, the 12 o'clock hour (×) RNFL thickness, and signal strength. Significant negative correlations were observed between CV in RNFL thickness and signal strength (SS), indicating that decreased SS is associated with increased variability in RNFL thickness.

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