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L. Guerrero Altares, G. Rebolleda Fernandez, F. J. Munoz Negrete; Comparison of Retinal Nerve Fiber Layer Measurements Using Time Domain and Spectral Domain Optical Coherence Tomography in Optic Nerve Head Drusen. Invest. Ophthalmol. Vis. Sci. 2010;51(13):660.
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There are currently no prospective studies comparing the Stratus and Cirrus OCT RNFL thickness measurements in patients with optic nerve head drusen (ONHD).We compared RNFL thickness values obtained with each device in normal eyes and eyes with ONHD.
Among the 20 participants, 14 were women and 6 were men. Among the 40 eyes, 38 had ONHD and 28 were healthy eyes All study subjects were recruited prospectively and examined between April 2008 and April 2009. They underwent a complete ophthalmologic examination including a Humphrey field analyzer and Stratus OCT and Cirrus OCT.Intraclass correlation coefficient (ICC) was used to compare the Cirrus and Stratus RNFL measurements. A Bland-Altman plot was graphed to asses the agreement between the 2 instruments. The same analysis was used for the mean, quadrant and clock hour RNFL thickness values.
The RNFL thickness measured by Stratus OCT and Cirrus OCT were correlated in all sectors. The Spearman’s rho for mean RNFL thickness between the 2 instruments was 0.96 for ONHD eyes and 0.92 for control eyes. These correlations were weaker in the nasal quadrant (r= 0.6; P<0.001) and in the clock hour 9.Bland- Altman plots showed that for thinner RNFL thickness (Grade III discs) Stratus measurements tend to be thinner than Cirrus, whereas for thicker RNFL thickness, Stratus measurements tend to be thicker than Cirrus.
To our knowledge, no previous studies have been published comparing RNFL thickness in normal subjects and subjects with ONHD scanned with Stratus OCT and Cirrus OCT.The results of the current study demonstrate that Cirrus RNFL thickness measurements correlate well with those from Stratus OCT in normal subjects and patients with ONHD. However, there is a systematic difference in measurements values between the 2 instruments.Stratus measurements of RNFL thickness are greater than Cirrus in patients with ONHD. Nevertheless in cases involving a severe thinning of RNFL thickness (grade III discs) an opposite behaviour is measured.Correlation does not mean that the measurements are the same. Clinicians need to be aware that there are systematic differences between measurements made by the 2 instruments, and measurements should not be considered interchangeable. Further studies with longer follow-up are needed in order to better evaluate the differences between both.
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