Edematous retinal thickening does not correlate with clinically visible fundus pathologies in diabetic patients
Purpose. The availability of a sensitive method to measure the retinal thickness allowed us to investigate the relationship between thickening and the underlying vascular pathology observed clinically. Methods- The measurements were performed on a non-scanning version of the Retinal Thickness Analyzer (RTA). A green laser slit, 2mm in length, was focused on the retina through a flat contact lens and its intersection with the retina was recorded on film. Optical cross sections were obtained at ten locations in the macula. The images were digitized and analyzed by an operator-free algorithm to yield quantitative retinal thickness measurements. An experienced masked grader identified and marked the area of hard exudates, soft exudates, hemorrhages and microaneurysms, on fundus photographs. The pathology within 1 mm of the measurement location was compared to the thickness. For each of 60 diabetic patients the worse eye was included. Results. No correlation was found between hard exudates, soft exudates, hemorrhages and microaneurysms and the retinal thickness. The prevalence of retinal thickening considered significantly above normal (97.5% confidence) was not higher at locations with pathology compared to locations without any pathology. In eyes without any hard exudate or microaneurysm in the whole macula the prevalence of thickening was 31% and it was 44% when either were present. Conclusion. Retinal thickening due to diabetic macular edema is not associated with the presence of clinically visible fundus pathology. The finding provides the first quantitative confirmation of the conclusion reached by the ETDRS that the presence of macular edema needs to be based on the assessment of thickening. The results indicate that the accumulation of fluid is related to subtle changes in the vasculature.
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