Purchase this article with an account.
Lisa Ostrin, Christine Wildsoet; Pattern ERG in chicks. Invest. Ophthalmol. Vis. Sci. 2013;54(15):1915.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
The pattern (p)ERG is believed to arise from the inner retinal. The aim of this study was to characterize the chick pERG and effects of optical defocus, diffusing blur, and optic nerve section (ONS).
Monocular pERG was recorded in 18 normal White Leghorn chickens (ages 2-3 wks) using a checkerboard pattern stimulus at 50 cm. Chicks were anesthetized, eyelids held open with a speculum, and DTL fiber electrodes positioned along the lower cornea. Parameters included 8 spatial frequencies (SFs: 0.1 to 4.4 c/d, 100% contrast), 13 contrast levels (1-100%, 0.2c/d checkerboard), and 8 temporal reversal frequencies (0.5 to 20 Hz). Effects of optical defocus (-10, -5, +5 & +10 D lenses) and diffusing blur (0.6, 0.2, <0.1 & LP Bangerter filters) were also examined. For 4 additional chicks that underwent monocular ONS, binocular flash and pERG responses were measured 1 and 3 weeks post surgery, complemented with SD-OCT imaging to evaluate nerve fiber loss.
The response to 1Hz, 100% contrast stimuli showed characteristic positive and negative going waveforms at 43 ms (P50) and 75 ms (N95), respectively, for SFs between 0.1 to 4.4 c/d, with a maximum P50 amplitude of 21.9±2.5µV (0.13 c/d), and minimum of 6.9±5.2µV (4.4 c/d), which elicited a response in half of the chicks tested. Amplitudes decreased across all SFs with both optical defocus and diffusing blur. Contrast levels of 5-10% and higher yielded measureable P50 responses, with amplitudes plateauing at 50% contrast. Responses were transient and monophasic for temporal frequencies from 0.5 to 5 Hz, with higher frequencies (10 & 20 Hz) yielding steady state responses. While thinning of the nerve fiber layer was evident by SD-OCT one week after ONS, both flash ERG and pERG response amplitudes remained near normal three weeks after the surgery.
Maximum pERG responses in the chick are obtained with a SF of 0.13 c/d, 50% or great contrast and 1-5 Hz reversal. The SF curve had a low pass filter shape, with a cut-off ~4.4 c/d. P50 amplitude increased linearly with contrast over the 5-50% range. Irrespective of its sign, defocus decreased the P50 amplitude, as did decreases in spatial contrast, with the responses to higher spatial frequencies being most sensitive. In further ONS experiments, the possibility that low contrast settings are more sensitive to subtle changes in retinal integrity will be evaluated and experiments extended beyond three weeks to look for late changes in function.
This PDF is available to Subscribers Only