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R. D. Vincent, F. N. Sabates, N. R. Sabates, G. Gallimore, A. J. Bonham, V. A. Shah; Comparison of Manual Versus Automated Placement of Scan Circle Location for Mean Retinal Nerve Fiber Layer Thickness Measurement by Optical Coherence Tomography. Invest. Ophthalmol. Vis. Sci. 2009;50(13):3336.
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To evaluate and compare the reproducibility/variability (short term) of mean peripapillary retinal nerve fiber layer thickness measurements obtained by manual placement of the scan circle on the optic nerve head versus automated placement using the retest feature by spectral domain optical coherence tomography (OCT) (OPKO Inc, Canada).
This is an IRB approved prospective consecutive study of 24 healthy individuals with normal ophthalmology examination and best corrected visual acuities ≥ 20/25. Eyes were scanned with the Spectral Domain OCT (OPKO Inc, Canada SLO/OCT) after informed consent. The circular scan utilized by the OCT was centered on the optic nerve head with a diameter of 3.4 mm. 42 eyes of these 24 individuals were scanned 3 times in a single session. The first scan was used as a baseline measurement for comparison. The second and third scans were obtained by using the retest feature on the OCT and manual replacement of the circular scan on the optic nerve head, respectively. This instrument provides the benefit of a retest function that allows for precise placement of the circular scan over a previously measured area. This is done by superimposing optic nerve head images from a prior scan and the current one in an automated fashion to retest nerve fiber layer thickness along the same circle. Mean thickness for each quadrant was recorded and the absolute difference from the initial control measurement determined. Paired sample t-tests were used to compare the automated retest values to the manual values on absolute difference from the control measurement in each of the 4 quadrants.
There was no statistically significant difference between the 2 measurement types at the inferior (p= 0.184), nasal (p=0.228), or temporal (p=0.465) quadrants. The superior quadrant, however, did show a significantly larger difference with manual placement of the scan circle compared with automated placement (p=0.016).
In this data set, only the superior quadrant was found to have statistically significantly better reproducibility with automated placement of the scan circle. In two other quadrants there was a suggestion that automated retest may have less variability. This is an ongoing project and a larger study population will be presented.
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