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Wing Cheung Ho, Chea-Su Kee, Henry Ho-lung Chan; Characteristics Of Multifocal Electroretinogram (mfERG) In Chicks Exposed To Optical Defocuses. Invest. Ophthalmol. Vis. Sci. 2011;52(14):6311.
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To (1) characterize mfERG response and, (2) determine the effect of optical defocus on mfERG response in chicks.
Exp.1: MfERG using global flash paradigm was recorded from White Leghorn chicks aged from two to three weeks (n=13) under fully corrected optical condition. The stimulus pattern consisted of 103 non-scaled hexagons subtending a total of 45 degree horizontal and 39 degree vertical visual field. The mfERG response was analyzed by using the system software (VERIS). Exp.2: The same group of chicks was exposed to myopic (+4D, +8D) and hyperopic defocused (-4D, -8D) conditions while mfERG was recorded with the same paradigm. Retinal region with top 5 percentile of the response amplitude was identified by the system software. The amplitudes and implicit times for both direct (DC) and induced (IC) components were calculated and compared across different defocused conditions using Kruskal-Wallis test.
Exp.1: MfERG waveforms with distinct DC and IC responses can be identified from all chicks. For all chicks, the response amplitude topographical maps identified a highly responsive, elongated zone located at the nasal field, outside this zone there were obvious drop in response amplitude across the whole examined area. Exp.2: Optical defocus produced significant change in DC amplitude (p < 0.05) but not in IC amplitude, DC and IC implicit times (p > 0.05). Post-hoc test revealed that the DC amplitude under 8D of hyperopic defocus was significantly smaller than those under 8D of myopic defocus (p < 0.05).
Chicks demonstrated characteristic mfERG responses with a highly sensitive area responsive to optical defocus. In agreement with previous findings in chicks, our results provide further evidence that optical defocus can be decoded as early as at the retinal level.
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