Retinal thickness measurement and evaluation of natural history of the diabetic macular edema through optical coherence tomography.

PURPOSE 1) Diagnose, through optical coherence tomography (OCT) exam, the occurrence of diabetic macular edema in patients with diabetic retinopathy and visual acuity of 20/40 or better, by measuring the foveal center point thickness, during one year. 2) Evaluate the edema natural history, during this period, associating the center point thickness with hemoglobin A1c and changes in visual acuity. 3) Correlate the obtained results with the control group. METHODS A prospective study was done, of a sample of 30 patients with diabetic macular edema and visual acuity of 20/40 or better. Measurements of the best corrected visual acuity, hemoglobin A1c level, biomicroscopy with 78-diopter lens, fluorescein angiogram and optical coherence tomography were made. The retinal thickness was selected as the main variable. Besides descriptive statistics, additional tests were applied to analyze the results and determine the correlation between these variables, such as t-Student, Chi-Square, Tukey and ANOVA. The relation of optical coherence tomography with visual acuity and hemoglobin A1c was studied through linear regression. RESULTS It was found that there is no significant difference between patients and normal individuals, for the variables age and gender. The values of center point thickness found for men were greater than those for women, showing the influence of gender on that thickness. As many as 83.33% of the diabetic patients with clinically significant macular edema presented moderate non-proliferative diabetic retinopathy (NPDR), 10% presented mild NPDR and 6.66% severe non-proliferative diabetic retinopathy. Patients under combined treatment of insulin and oral hypoglycemiant presented influence on the results of center point thickness (through OCT) and visual acuity. The mean duration of diabetes was 9.63 years. Values of center point thickness were always found greater for patients than those for normal eyes. Levels of hemoglobin A1c did not have influence on the center point thickness data, whereas values of visual acuity were significantly correlated with it. CONCLUSION This study presents the optical coherence tomography applicability in the detection and semiologic evaluation of diabetic macular edema in patients with visual acuity 20/40 or greater, during one year, showing the retinal thickening in the early stages of diabetic retinopathy. Further, it evidenced the correlation between the increase in foveal thickness and the reduction in visual acuity. Levels of hemoglobin A1c did not influence the center point thickness data. An early detection of clinically significant macular edema leads us to a redefinition of the real meaning of incipient retinopathy and can prevent further significant reduction of vision.