The objective visual acuity in normal adult C57BL/6J mice:assessment with sweep visually evoked potential / 眼科新进展

ABSTRACT

Objective To evaluate the reliability of sweep visual evoked potential (SVEP) for assessing the normal objective visual acuity in adult wild-type C57BL/6J mice.Methods A total of 6 wild C57BL/6J mice of either gender at 32-33 days of age were collected.After the mice were anesthetized,the recording electrode (a 2-mm diameter tungsten electrode) was placed at 3 mm lateral to lambda over the left cortex (contralateral to the stimulated right eyes) and advanced to 400 μm within the cortex,and the needle electrodes which placed in the forehead and tail served as the reference and the ground,accordingly.Left eyes (unstimulated eyes) were covered during the recording.The screen (mean luminance 25 cd · m-2) was placed 20 cm in front of the mice,thereby covering 100° (horizontal) × 82° (vertical) of the visual field.The mice were stimulated by vertically sinusoidal grating,which consisted of 11 spatial frequencies,stimulus contrast was 100％,and time frequency was 1 Hz;the entire sweep took 12 seconds (11 spatial frequencies + 1s pre-adaptation),and the values were averaged until the error bars for the data were stable.The VEP waveforms of visual cortex corresponding to the left and right eyes were recorded separately.At least 3-4 trials consisting of 20 events for different frequencies were averaged.Left and right eye were tested alternately.Then the coordinate system was established by using the spatial frequency logarithm as x-axis and the amplitude of the response obtained by the discrete Fourier analysis as y-axis,the objective visual acuity was obtained by extrapolation to zero amplitude of the linear regression through the 4 effective data points adjacent to noise.Results SVEP showed that the amplitude of N100 wave was maximal at a spatial frequency of 0.05 c · deg-1.With the increase of the stimulus spatial frequency progressively,SVEP decreased in amplitude and increased in latency.The cortical electrical signal could not be distinguished from noise at a spatial frequency of 0.65 c · deg-1.The average acuity of 6 mice was (0.56 ± 0.04) c · deg-1 for right eyes and (0.50 ± 0.04)c · deg-1 for left eyes respectively.There was no significant difference between the two eyes(P＞0.05);The visual evoked potential acuity of 12 eyes was (0.53 ±0.03)c ·deg-1.Conclusion SVEP could be used to estimate the mouse VEP acuity,which was closed to the behavioral visual acuity.However,the VEP acuity was more objective and accurate as well as time-saving.