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Oliver Comyn, Rishma Gohil, Praveen J Patel, James W B Bainbridge, Philip G Hykin, Sobha Sivaprasad; Correlation of retinal sensitivity with retinal thickness and morphological features of diabetic macular oedema. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):1733. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
The relationship between retinal structure and function in diabetic macular oedema is not well understood. The aim of this study was to investigate the correlation between retinal sensitivity and both quantitative and qualitative changes seen on optical coherence tomography (OCT) scans in a cohort of patients receiving ranibizumab or laser as part of a prospective, randomised clinical trial (The LUCIDATE Study).
At baseline and 48 weeks subjects underwent Nidek MP1 microperimetry and Spectralis OCT scans. The 12°, 45-point microperimetry grid was overlaid on the macular thickness map derived from the fast volume scan protocol and retinal thickness at each test locus was obtained from the automated measurement in the Heidelberg Eye Explorer software. At each locus, a grader masked to treatment allocation recorded the presence of morphological features and disruptions in the lines representative of outer retinal structures. Correlation between retinal sensitivity and thickness is reported, and the effect of morphological features on sensitivity is estimated.
Thirty-three subjects completed 48 weeks follow-up in the trial. In the central 5 ETDRS subfields, point retinal sensitivity increased with decreasing retinal thickness by 1 dB per 45 µm reduction (Pearson r = -0.52, P<0.0001). At 48 weeks in the ranibizumab group, but not in the laser group, there was a significant correlation between changes in point retinal sensitivity and in retinal thickness, with each 1 dB gain associated with a 74 µm thickness reduction (r = -0.31, P<0.0001). At baseline, 1530 loci were graded. Mean sensitivity at loci with no morphological abnormalities present (n=682) was 16.7 (SD 2.42) dB. When isolated external limiting membrane disruption was present, sensitivity was 11.5 (1.74) dB (n=22, P<0.0001), without an associated change in retinal thickness.
Retinal thickness correlates well with point sensitivity from microperimetry in subjects with diabetic macular oedema. Treatment with ranibizumab leads to measurable improvements in retinal thickness, which may be associated with improved retinal sensitivity in a predictable manner. Outer retinal disruption had the greatest effect on measured sensitivity, but was not associated with increased thickness, suggesting quantitative analysis alone is insufficient for accurate structure-function correlation in this condition.
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