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T. M. Harding, D. Myers, A. Domalpally, Q. Peng, L. Hubbard, R. P. Danis; Evaluation of Hard Exudate Plaques in Diabetic Macular Edema (DME). Invest. Ophthalmol. Vis. Sci. 2009;50(13):1313.
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DME may include deposition of hard exudates (HE); lipoprotein material settling in the outer retina. When large amounts of HE aggregate under the center of the macula, this material may become very dense, even fibrotic-- the resulting lesions are called HE plaques. Their presence has been associated with increased visual impairment (ETDRS Report #22 ., Arch Ophth 1997). We sought to compare color fundus photo (color photo) findings with morphology assessment and retinal thickness measurements on optical coherence tomography (OCT) images.
Color photos with HE plaques in the macula were compared with OCT images from multiple multicenter clinical trials in diabetes. From color photo, severity of retinal thickening at the centerpoint was evaluated as described in ETDRS Report #10 (Ophthalmology, 1991). In OCT images, the presence and location of changes corresponding to HE plaques were evaluated. The thickness of the retina at the centerpoint was measured, both including and excluding the hyper-reflective appearance of the plaque, and compared with color photo grading of retinal thickening
Evaluaton and comparison of color photos and OCT was performed on 101 eyes. In OCT images, very dense hyper-reflectivity in the outer retina in the central subfield was definitely seen in 58 (57%) images. Median centerpoint retinal thickness exclusive of the HE plaque was 61 µm (25th ,75th percentile 30, 98) and median centerpoint retinal thickness including the HE plaque was 271 µm (25th ,75th percentile 208,345). When severity of retinal thickening at the macular center was graded with concurrent reference to OCT, the original grade from CP alone was changed in 54 (53%) eyes, usually to a lesser grade.
OCT images help distinguish retinal thickening from HE plaques per se and retinal thickening from intra-retinal fluid. Grading of color photographs tends to overestimate the severity of retinal thickening compared to measurements by OCT. Retinal tissue overlying HE plaques is frequently abnormally thin and atrophic. The question as to whether the best measurement of center point thickness on OCT is inclusive or exclusive of the HE plaque material remains debatable but is important in clinical trials of DME.
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