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P. J. Patel, G. Abedi, M. Subramanian; Stratus versus Cirrus Optical Coherence Tomography Scans in Healthy Eyes. Invest. Ophthalmol. Vis. Sci. 2009;50(13):3779.
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Optical Coherence Tomography (OCT) is an optical signal acquisition and processing measure allowing high quality, potentially three dimensional images of biologic tissue, such as the neuroretina. The purpose of this study is to compare the third generation Stratus OCT (Carl Zeiss, Inc) and the high definition, newer generation, spectral domain Cirrus OCT (Carl Zeiss, Inc) on their respective measures of central macular thickness (CMT) in healthy human eyes.
In this study, both Stratus and Cirrus machines were used to take pictures of 46 healthy subjects’ eyes, without diabetes or other medical conditions. The average visual acuity was 20/19.3. Of the 92 eyes, 63 were myopic, 20 were emmetropic, and 9 were hyperopic. Of the 63 myopic eyes, 37 presented with mild myopia (-0.25 to -3.00), 18 presented with moderate myopia (-3.25 to -5.75), and 8 eyes were highly myopic (>6.00).
A two-tailed t-test revealed a highly significant difference (p= 1.1x10-33) between the two machines based on the CMT measurement. The average CMTs obtained using the Stratus and Cirrus OCT machines were 193.91 microns and 252.83 microns, respectively. Differences in the patients’ refractive error did not appear to alter the measurements of central foveal thickness.
The statistical analysis confirms a significant difference in central foveal thickness between the Stratus and Cirrus OCT. The differences in CMT may be due to the inclusion of the photoreceptor segments and RPE by the Cirrus OCT, resulting in increased apparent thickness. It is important to note that the level of refractive error is independent of their respective CMT measures and therefore, did not influence the variation in measurement between the two tools. Though differences in signal strength between the machines do suggest that the newer generation Cirrus OCT is more accurate, it is yet to be determined if this will translate into improvement in the care of macular diseases.
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