| ObjectiveThis study was to observe and analyze whether wearing a scleral search coil has an impact on the magnitude of microsaccades.Methods1. The first step was to measure the system precision of the video eye tracker and evaluate the effect of the related factors on the result. The EyeLink2000high speed video eye tracker and a pair of artificial eyes were used in this study. Firstly the artificial eyes were firmly fixed to the corresponding position as the real human eyes, and then related parameters were set before recording. Each session of recording was undertaken under different combined conditions of infrared illumination (100%,75%and50%) and indoor illumination (llux,301ux,3001ux and22001ux). The sampling frequency of binocular recording is1000Hz. Each session of recording lasted for60seconds. The system precision was calculated as the root mean square (RMS) of angular distances between successive data points. SPSS17.0statistical software was used to perform the one-way ANOVA to analyse the difference among system precisions under the same infrared illumination or that under the same indoor illumination. The S-N-K test was chosen to perform the post hoc multiple comparisons.2. We used customized scleral search coils as the experimental material. The microsaccade eye movements of the healthy volunteers without ametropia under different conditions with the optimal system precision of the video eye tracker were recorded. The volunteers’eyes were topically anesthetized before wearing the scleral search coils. The volunteers fixated at the target on the screen in front of them, and the recording lasted for1min.We used a Matlab program to detect and analyze the microsaccade events, The SPSS17.0statistical software was adopted to perform the paired-samples t test to analyze the difference of the two eyes in each group.Results1.The highest system precision came out to be0.00501°±0.00020°under the 100%infrared illumination and llux indoor illumination. Under the indoor illumination of llux,301ux,3001ux and22001ux respectively, the system precisions showed statistically significant difference when the infrared illumination changed (F11ux=3791.447,P<0.01;F301ux=3716.024,P<0.01; F30o1ux=3120.527,P<0.01; F22001ux=::3325.239,P<0.01). The difference was also significant (P<0.05) as to the post hoc multiple comparisons. Under the infrared illumination of100%,75%and50%respectively, the system precisions showed significant difference when the indoor illumination changed (F100%=65.355, P<0.01; F75%/=16.936, P<0.01; F50%=33.757, P<0.01). As for the comparison between each two groups, when the infrared illumination was100%, significant difference (P<0.05) was observed between each two groups. For the75%infrared illumination groups, no significant difference was observed between3001ux and22001ux groups (P=0.197), while the difference was statistically significant between each two of the rest groups(P<0.05). For the50%infrared illumination groups, no significant difference was found between301ux and3001ux groups(P=0.383), while the difference was statistically significant (P<0.05) between each two of the rest groups in contrast.2.For the group of naked eyes without anesthesia, there showed no significant difference for the binocular microsaccade magnitudes between the left eye and right eye (P=0.203). For the anesthesia only group, there came the same result, the binocular microsaccade magnitudes between the anesthesia eye(left eye) and the eye without anesthesia (right eye) showed no difference (P=0.651). While with the SSC in the left eye, significant difference was found for the binocular microsaccade magnitudes between the left eye and right eye, P=0.002). The microsaccades of the eye with the SSC (left eye) were smaller than the other eye (right eye). When the SSC was inserted in both eyes, the difference of the binocular microsaccade magnitudes was not significant between the two eyes,P=0.881). As to the monocular microsaccade magnitudes, no difference was observed between the two eyes in all of the four groups.Conclusion1.The Eyelink2000video eye tracker has high system precision, which is even superior to that of the SSC under the optimal experiment condition (0.00501°±0.00020°)2. Both the infrared illumination of the video eye tracker and the indoor illumination for examination have an effect on the system precision. The system precision becomes better with higher infrared illumination and lower indoor illumination for examination.3. Wearing the SSC has a significant impact on the binocular microsaccade magnitude. When inserted the SSC in single eye, the binocular microsaccades of the eye with the SSC is smaller than that of the contralteral eye. While the SSC has no significant influence on the monocular microsaccades.4. The impact of wearing SSC on the binocular microsaccades should be attributed to the change of the oculomotor command signals, rather than that of the mechanical factors. |
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