In diabetic retinopathy, foveal thickness of 300 mum seems to correlate with functionally significant loss of vision.

Purpose: To study the relationship between foveal thickness assessed by optical coherence tomography (OCT) and foveal function measured with multi focal electroretinography (mfERG) in patients with non-proliferative diabetic retinopathy, and with no previous laser treatment.

Methods: Twenty-six eyes from 18 diabetic patients (13 men), aged 59 years, (range 28-79 years), diabetes duration 15 years, (range 2-27 years), with a macular thickness between 200 and 600 microm were evaluated by mfERG, visual acuity (ETDRS score) and OCT. Mean amplitudes and implicit times of the mfERG responses were analyzed within the four innermost (14 degrees) of the six concentric rings. For comparison with the results from the OCT (diameter of measured area = 6 mm) we analyzed the summed response from the first and second ring (central zone), corresponding to the central area of the OCT. The third(zone 2) and fourth (zone 3)of the four innermost of the six concentric rings measured by the mfERG corresponding to the second and third area of OCT.

Results: An increased macular thickness in the central area of the OCT correlated to reduced amplitudes (r = -0.541; P = 0.004) and prolonged implicit times (r = 0.548; P = 0.004) in the central zone of the mfERG, and inversely correlated with visual acuity, -0.49; P = 0.045. Retinal thickness in the second area was correlated to prolonged implicit times in the second mfERG zone (r = -0.416; P = 0.034). No correlations were found for the third area of the OCT. When macular thickness exceeded 300 mum the decrease of amplitudes and prolonged implicit times, measured by mfERG, seemed to be more pronounced.

Conclusion: In conclusion increased macular thickness is correlated with reduced amplitudes and prolonged implicit times on the mf ERG and worse visual acuity.