RESUMEN
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.
RESUMEN
Background Sweep pattern visual evoked potential (SVEP) is an objective method of visual test.There is a clear correlation between SVEP acuity and subjective vision,but they are not identical.Recent studies showed that new regression method can improve the accuracy of SVEP acuity. Objective This trial was to investigate and compare the outcome between amplitude-spatial frequency (A-SP) regression method and amplitudelogVA (A-logVA) regression method in extrapolating the SVEP acuity.Methods SVEP was recorded in 113 eyes of 64 subjects using GT-2000 ( Guo Te,China) with the gratings of 10 different spatial frequency from 0.99 to 12.89 cpd as stimulus.The 1 13 eyes included cataract,glaucoma,corneal disease,optical neuropathy,retinal disease,ocular trauma,refractive error and normal eyes.The correlation were analyzed of SVEP acuity,decimal visual acuity and LogMAR visual acuity.The response were averaged and DFT on the monitor display.SVEP acuity was calculated by extrapolating 0 response amplitude.Results The correlation indices of decimal visual acuity curves obtained by the A-logVA function was 0.663,and that obtained by the A-SP function was 0.705.The positive correlation was seen between subjective decimal visual acuity and A-logVA decimal visual acuity (r =0.540,P＜ 0.01 ) and between subjective decimal acuity and decimal acuity calculated by the A-SP regression method (r=0.620,P＜0.01 ).SVEP decimal acuity calculated by the A-SP function regression method was significantly different from the that calculated by the A-logVA function regression method (Z =-8.688,P＜0.01 ).And the correlation indices of LogMAR visual acuity curves obtained by the A-logVA function was 0.733 and that obtained by the A-SP function was 0.715.The positive correlation was found between the subjective LogMAR acuity and that calculated by the A-SP regression method (r=0.700,P＜ 0.01 ) and between the subjective LogMAR acuity and LogMAR acuity calculated by the A-logVA regression method (r=0.710,P＜0.01 ).SVEP LogMAR acuity from A-SP function regression method was significantly different from the LogMAR acuity from A-logVA function regression method (Z=-8.748,P＜0.01 ).No significant differences of VA LogMAR were found in gender,eyes,type of disease and age(x2 =2.171,P=0.338;x2 =0.976,P=0.614;x2 =6.032,P=0.420;x2 =14.720,P=0.257 ).Conclusions SVEP can obtain the visual outcome in human.The amplitude-logVA function regression method is more accurate in extrapolating SVEP acuity.