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John Hetling, Hadi Tajalli, Yelena Krakova, Zahra Derafshi; Spatial differences in corneal potentials in healthy rat eyes evaluated with multi-electrode electroretinography (meERG). Invest. Ophthalmol. Vis. Sci. 2013;54(15):6133.
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© ARVO (1962-2015); The Authors (2016-present)
It is known that ERG potentials exhibit spatial variation across the cornea, and that this variation is affected by spatial differences in retinal activation (e.g. local laser damage), suggesting that knowledge of the spatial variation could have diagnostic value. However, no technology is currently available to adequately measure local ERG potentials on the corneal surface. Here we demonstrate efficacy of a novel Contact Lens Electrode Array (CLEAr Lens) designed to record ERG potentials from 25 locations simultaneously.
The CLEAr Lens consists of a plano-concave PMMA base lens and parylene thin-film electrode array. The 25 recording electrodes are arranged in concentric rings with the 12 electrodes of the peripheral ring near the corneal margin. Long Evans rats (n=8) were prepared as for conventional electroretinography (dark adapted, general anesthesia, pupil dilation, corneal anesthetic). Full-field flash stimuli were presented at two luminance values. Each stimulus/response resulted in a 25-channel meERG data set, which was evaluated for a-wave amplitudes.
To evaluate spatial asymmetry in a-wave amplitudes, a normalized ratio, expressed as a percentage of the amplitude recorded at the center of the cornea, was calculated for each of the 12 peripheral electrodes (peripheral / central x 100). For each of the 12 electrodes, these ratios were averaged across eight experiments; mean ratios had an average value of 102.3+0.7% for the five superior electrodes, and 97.6+1.4% for the five inferior electrodes (p = 0.004). Spatial differences in a-wave amplitudes were similar for sub-saturated and saturated a-waves (flash strength 3.4 and 1842 sc cd s m-2, respectively).
The CLEAr Lens provides a means to simultaneously record distinct potentials at 25 locations across the cornea. There are significant spatial differences in ERG potentials recorded from healthy rat eyes, with the superior cornea being approximately 5% higher than the inferior cornea. Multi-electrode ERG may provide an objective means of detecting asymmetries in retinal function, analogous to the psychophysical glaucoma hemifield test, but extending to the entire anatomical retina.
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