Multifocal electroretinogram findings of different types of diabetic macular edema

Background It is very important for us to understand retinal function change in the patient with diabetic mellitus in clinic. At present,the study about diabetic mellitus associated with macular edema includes fundus fluorescense angiography ( FFA) and multifocal electroretinogram ( mfERG) etc.. However, seldom research is performed in the mfERG findings for different types of diabetic macular edema. Objective This study aimed to investigate the mfERG change in different types of diabetic macular edema compared with normal population. Methods Fifty-seven eyes with diabetic macular edema from 40 patients and 35 eyes from age-and gender-matched normal subjects were enrolled in this study. The eyes with diabetic macular edema were assigned to local macular edema group (n=16) ,diffuse macular edema group (n = 22) and cystoid macular edema ( n = 17 ) based on the manifestation of FFA. MfERG was recorded in all the individuals. The informed consent was obtained from each subject prior to any the medical examination. Results In focal diabetic macular edema group,the response density of P1 wave was significantly attenuated in ring 1 , showing a statistical difference in comparison with controls (t =2. 170,P = 0.038) ,and the latencies of P1 and N1 waves showed obvious prolong in ring 4 and 5 (t = 2.519,P = 0. 017 ;t = 2. 451 ,P = 0. 020). In diffuse diabetic macular edema group,the response densities of P1 and N1 waves were declined in ring 1,3,5 and ring 1,3,4,5 respectively,and the latencies of P, in ring 3,4 were significantly delayed respectively in comparison with controls (all P < 0. 05 ). In cystoid diabetic macular edema group, the response densities of P1 and N1 waves were lowed from ring 1 through 5 respectively, and the latencies of P1 and N1 waves were significantly longer from ring 3 through 5 and ring 4 respectively with the statistically significant difference from controls (all P<0. 05). The visual function of fovea was badly damaged. Conclusion These studies indicate that the most serious damage of visual function is in foveal area in cystoid diabetic macular edema group, and is then parafoveal area of diffuse diabetic macular edema group and perifoveal area in focal diabetic macular edema group. The outcome of mfERG presents a good consistency with FFA findings in the patients with diabetic macular edema. Key words: Diabetes;  Macular edema;  Multifocal electroretinogram;  Fundus fluorescein angiography