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F. Forooghian, P. F. Stetson, S. A. Meyer, E. Y. Chew, W. T. Wong, C. Cukras, C. B. Meyerle, F. L. Ferris, III; Relationship Between Photoreceptor Outer Segment Length and Visual Acuity in Diabetic Macular Edema. Invest. Ophthalmol. Vis. Sci. 2009;50(13):1388.
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To quantify photoreceptor outer segment (PROS) length in patients with diabetic macular edema (DME) using spectral-domain optical coherence tomography (SD-OCT) and to correlate PROS length to visual acuity in DME.
Thirty eyes of 27 patients with DME received 3 repeated SD-OCT scans in a single session using CirrusTM HD-OCT. Macular PROS length was measured using a prototype algorithm. Overall retinal thickness and PROS length were calculated for 3 retinal loci: macular grid, central subfield, and center foveal point. Intrasession repeatability was assessed using coefficient of variation (CVW) and intraclass correlation coefficient (ICC). Association between retinal and PROS measures with visual acuity was assessed using linear regression and Pearson correlation analyses.
Mean retinal thicknesses and PROS lengths were 298-381 µm and 30-32 µm, respectively, for macular parameters assessed in this study. CVW values were 0.75-4.13% for retinal thickness, and 1.97-14.01% for PROS length. ICC values were 0.96-0.99 and 0.73-0.98 for retinal thickness and PROS length, respectively. Linear regression analyses assessing the association of retinal thickness and visual acuity were not significantly different from zero (p>0.20), whereas the associations of PROS length and visual acuity were statistically significant (p<0.0005). Correlation coefficients for macular thickness and visual acuity ranged from 0.13 to 0.22, while coefficients for PROS length and visual acuity ranged from -0.61 to -0.81.
PROS length can be quantitatively assessed using CirrusTM HD-OCT. Although the intrasession repeatability of PROS measurements was less than that of macular thickness measurements, the stronger correlation of PROS length with visual acuity suggests that PROS measures may be more directly related to visual function. PROS length may be a useful physiologic anatomic outcome measure for future clinical trials.
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