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C. Wolsley, K.J. Saunders, G. Silvestri, R.S. Anderson; How Does Contact Lens Induced Refractive Blur Affect the Multifocal ERG . Invest. Ophthalmol. Vis. Sci. 2005;46(13):3433.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Controversy exists regarding the effect of optical defocus on the multifocal electroretinogram (mfERG). It has been suggested that small retinal lesions may be less well defined in the mfERG response if the stimulus is blurred and as a result, corrected vision is recommended for testing. Most previous studies have used spectacle lens correction, which necessitates moving the stimulus toward or away from the subject to compensate for the changing spectacle magnification and retinal image size. However, it is not clear if a simple linear change is required and this also may result in different levels of stimulus luminance for each subject. To avoid significant spectacle magnification and the need to move the stimulus, this study uses contact lenses to investigate the effect of induced refractive blur on the mfERG response amplitude and implicit time. Methods: Six normal subjects had repeated mfERGs recorded with the VERIS 4 system using DTL corneal contact electrodes. In each case the right eye was fully dilated (>7mm) and fitted with soft contact lenses to give optical defocus of 0, +1.50 and +3.00 diopters at the stimulus distance (33 cm) without accommodation. The left eye was occluded during testing. The stimulus array was composed of 103 hexagonal elements covering a field of view of at least 45°. Under each condition, recording occurred for 7mins 17secs split into segments of 28secs. Results: There was no significant effect of optical blur on waveform implicit timings. The amplitude of the average response in the central retinal area (±4.5° of visual angle around fixation) was reduced by 8% and 15% for +1.50D and +3.00D blur respectively. This was significant at +3.00D blur level (p<0.05). Peripheral retinal responses were unaffected by dioptric blur (p>0.05). Conclusions: Mild optical blur causes decreased central retinal mfERG amplitudes but peripheral retinal responses are preserved. This may be because the mfERG uses a scaled stimulus pattern designed to compensate for differences in signal density across the retina. A mild degree of optical blur may be sufficient to reduce image contrast in the smaller, central hexagonal elements such that signal response is reduced but this blur may impact less on the larger peripheral elements, preserving their response amplitude. The choice of stimulus array size, and hence the required level of spatial resolution, is a factor that will determine the need for optical correction for mfERG testing.
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