The spatial resolution of the porcine multifocal electroretinogram for detection of laser-induced retinal lesions

Purpose: This study aimed to investigate the spatial resolution of a porcine multifocal electroretinogram (mfERG) protocol by testing its ability to detect laser-induced retinal lesions. Furthermore, we wanted to describe time-dependent changes in implicit time and amplitude of the different mfERG peaks after laser-induced retinal damage. Methods: Three pigs underwent a three-port pars plana vitrectomy, followed by laser photocoagulation of different lesion sizes within the visual streak. In an additional six non-vitrectomized pigs, we studied changes in mfERG signals with time after a uniform laser photocoagulation within the visual streak. The animals were evaluated with mfERG 1 and 6 weeks after treatment. After the last mfERG examination, selected eyes were processed for histological examination. Results: The size of the smallest lesion detected was approximately 1/4 of the longest diameter of the optic disc (LDOD) measured in pixels. When analysing the uniform lesions we found that signals deriving from the centre of the laser lesions were characterized by a significant reduction in the amplitude of all three peaks after 1 week of observation. After 6 weeks, the amplitudes of P1 and N2 were still significantly reduced. The implicit times were unaffected by laser treatment in the acute phase. After 6 weeks only P1 was significantly delayed. Conclusion: We have determined the spatial resolution of the mfERG in the porcine retina to be smaller than or equal to the area of two adjacent hexagons, corresponding to a width of approximately 288 pixels or 1.2 mm. Laser lesions of uniform size resulted in a significant reduction of the amplitudes 1 and 6 weeks after treatment.