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Amun Sachdev, Magdalena Sinczak, Rupal Morjaria, Victor Chong; Comparing the Microperimetric to Structural Findings in Patients with Branch Retinal Vein Occlusion and Diabetic Macular Edema. Invest. Ophthalmol. Vis. Sci. 2013;54(15):2419.
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Microperimetry is useful in assessing retinal sensitivity. Previous work has suggested that there is a correlation between microperimetry findings and structural changes in patients with diabetic macular edema (DME). In this study, we have compared the microperimetric findings in patients with DME and in patients with branch retinal vein occlusion (BRVO).
Patients who had focal DME and BRVO were included in the study. Microperimetry and Spectral Domain Optical Coherent Topography (SD-OCT) were carried out in Optos OTI OCT. In each eye, the parafoveal ring of 16 microperimetry points was analysed. The thickness of the retina at each microperimetry point was manually measured. The area was defined as abnormal when there was significant edema with clearly defined cystic spaces. The average retinal sensitivity and thickness of the abnormal areas were compared with that of the normal areas in the same eye. The data was analysed by paired Student t-test.
There were 20 eyes with focal DME and 9 eyes with BRVO included in this pilot study. The average retinal thickness was 400.3 microns, and 302.7 microns in the abnormal and normal areas respectively in DME (p<0.0001). The average retinal thickness was 480.2 microns and 322.3 microns in the abnormal and normal areas respectively in BRVO (p=0.0001). The average retinal sensitivity was 10.05 dB and 12.09 dB in the abnormal and normal areas respectively in DME (p=0.0029). The average retinal sensitivity was 6.78 dB and 12.95 dB in the abnormal and normal areas respectively in BRVO (p=0.0006). In DME, 47.7 microns increase in thickness is correlated with 1 dB reduction of retinal sensitivity. In BRVO, 25.6 microns increase in thickness is correlated with 1 dB reduction of retinal sensitivity.
The advantage of using the Optos OTI OCT is that the microperimetry and the SD-OCT are carried out on the same machine with the same optics, allowing point to point correlation. In this pilot study, we found that there was a difference in the amount of retinal thickness per dB loss in retinal sensitivity between DME and BRVO. Further studies to investigate why this is the case are required. It is possible that in DME the majority of edema is in the inner retina, which causes less reduction in retinal function, whilst in BRVO, the entire retina is equally involved.
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