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E. White, F. Ikeji, C. Bunce, P. Hykin; The Effect of Visual Acuity in Patients With Diabetic Macular Oedema on the Agreement Between Fast and Slow Macula Scan Protocols for the Stratus OCT . Invest. Ophthalmol. Vis. Sci. 2006;47(13):4029.
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© ARVO (1962-2015); The Authors (2016-present)
To establish if poor visual acuity (VA) in patients with diabetic macular oedema effects the method agreement of the fast and slow macula scanning protocols of the Stratus OCT (OCT).
50 eyes of 50 patients with diabetic macular oedema were randomised and imaged using both the fast and slow macula scans by one of two experienced OCT operators; the order in which the scans were performed was also randomised. All patients underwent a full clinical examination and refraction prior to imaging. VA was recorded and patients divided into two groups representing good to moderate vision (≤6/18) and moderate to poor (≥6/24). Statistical analysis was carried out using Bland Altman. A difference between method measurements of 20% or more was deemed clinically relevant.
Of the 50 patients imaged, 8 were excluded due to poor image quality and the inability of the software to correctly map the layers of the retina. 24 patients had a VA of ≤6/18 with 18 patients recording a VA of ≥6/24. Analysis of the foveal minimum thickness of the ≤6/18 group (95% limits of agreement) showed a spread of –31.8 to 39.0 microns with a mean of 3.6, compared to a spread of –42.8 to 47.3 microns with a mean of 2.3 for the ≥6/24 group. The results of the foveal thickness for the ≤6/18 group showed a spread of –26.3 to 24.1 microns and a mean of –1.1, with the ≥6/24 group achieving a spread of –29.9 to 33.9 and a mean of 2.0.
The Bland Altman did show there was slightly better method agreement with better VA’s, however, the difference was small and of little clinical significance. It is reasonable to assume that poor visual acuity should in turn lead to poor fixation, but the OCT appears to be able to eliminate the majority of artefacts that poor fixation introduces. The fixation target is a central one, therefore being slightly easier to find for the patient, and the ability of the OCT operator to position the scan over the macula ensures that poor VA need not be a barrier to good images.
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