Using multifocal electroretinography hard exudates affect macular function in eyes with diabetic retinopathy

To evaluate the influence of hard exudates on macular function in patients with diabetic retinopathy.

Thirty seven eyes from 27 diabetic patients, aged 57 ± 14 years, diabetes duration 12.5 ± 9 years, not previously treated with photocoagulation, underwent fundus photography, multifocal electroretinography (mfERG) and optical coherence tomography (OCT). Hard exudates were graded from fundus photography with superimposed OCT and a superimposed hexagonal pattern (mfERG) by one retinal specialist, unaware of mfERG and OCT results. We defined three groups; A = eyes with exudates in the analyzed zone, B = eyes with no exudates in the analyzed zone but elsewhere, and C = eyes with no exudates. The mfERG responses and OCT values from five defined areas in the macula were compared.

MfERG showed that the implicit time was significantly prolonged in group A compared to group C in the central, middle and outer areas and in the nasal and temporal area (p = 0.045, 0.019, 0.017 and 0.035 and 0.016 respectively), in group B compared to group C in the central area (p = 0.016), and in group A compared to group B in the outer area (p = 0.035). Amplitude differed between group A and C in the middle area and outer area (14.2 ± 5.2 nV/deg² vs 21.1 ± 8.7 nV/deg², p = 0.037 and 14.1 ± 3.9 nV/deg² vs 17.7 ± 7.1 nV/deg² , p = 0.02 respectively), and between group B and C in the temporal area 14.5 ± 2.2 nV/deg² vs 20.0 ± 8.7 nV/deg², p = 0.017). Macular thickness assessed with OCT was similar between the groups.

In eyes with diabetic retinopathy, hard exudates prolong the implicit time assessed with mfERG, compared to eyes without hard exudates, and independently of macular thickness. These results indicate that the hard exudates in the macular region, even at a distance from the fovea centre, have a deleterious effect on macular function.