Background: To investigate the outer and inner retinal function in patients with multiple evanescent white dot syndrome (MEWDS).
Methods: The retinal function of three subjects with MEWDS was investigated using one or a combination of full-field electroretinography (ERG), multifocal electroretinography (mfERG) or recording of multifocal oscillatory potentials (mfOP).
Results: In case 1, the scotopic, maximal, photopic and flicker ERG responses of the two eyes were similar but the amplitudes of the dark- and light-adapted OPs were markedly reduced in the affected eye. In cases 2 and 3, the ERG responses were grossly reduced in amplitude and as expected the OPs were also diminished. However, using the mfERG a residual area of 'normal' retinal function in the affected eye was identified. The local OP, assessed by the mfOP, within the residual 'normal' retinal area was reduced as compared with the corresponding retinal area of the fellow unaffected eye. Subsequently, the mfERG responses of the 'normal' retinal area were also reduced.
Conclusion: The OPs were reduced throughout the retina in patients with MEWDS, even in the area with a normal mfERG. The electrophysiological findings suggest that functional abnormality in MEWDS may occur initially in the inner retina and subsequently involves the outer retina.